HK1246065B - Method and apparatus for control flow enhancements for lte-unlicensed - Google Patents

Description

Method and apparatus for control flow enhancement for unlicensed LTE

Cross-references

This patent application claims priority to U.S. patent application No. 15/149,752, filed by Yerramalli et al. on May 9, 2016, entitled “Control Flow Enhancements for LTE-Unlicensed,” and U.S. provisional patent application No. 62/165,814, filed by Yerramalli et al. on May 22, 2015, entitled “Control Flow Enhancements for LTE-Unlicensed,” each of which is assigned to the assignee of this application.

background

The following relates generally to wireless communications, and more particularly to control flow enhancements for unlicensed LTE.

Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, etc. These systems can support communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems (e.g., LTE systems). A wireless multiple-access communication system may include several base stations, each of which simultaneously supports communication for multiple communication devices, which may also be referred to as user equipment (UE).

In an LTE or LTE-Advanced (LTE-A) network, a base station and a UE can communicate over a dedicated spectrum licensed to a network operator. A licensed operator network (e.g., a cellular network, etc.) may be referred to as a public land mobile network (PLMN). As data traffic in cellular networks using dedicated (e.g., licensed) radio frequency bands continues to increase, offloading at least some of the data traffic to unlicensed or shared radio frequency spectrum may enhance data transmission capacity and efficient resource usage. Unlicensed and shared radio frequency spectrum may also provide services in areas where access to dedicated radio frequency spectrum is not available. Unlicensed spectrum generally refers to spectrum that is available for use without a license and is typically subject to technical regulations regarding transmit power for access. Shared spectrum generally refers to spectrum that is available for devices associated with one of multiple operators.

Listen-before-talk (LBT) procedures can be used for contention resolution when accessing shared frequency resources in licensed or unlicensed spectrum without pre-coordinated resource allocation. The LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a shared channel is available. When a shared channel is determined to be available, a device may transmit a signal to reserve the channel before transmitting data. Other devices may monitor the reservation signal to detect transmissions and may also monitor the shared channel using energy detection to determine whether the shared channel is busy or idle.

Operation using an LTE signal waveform on a shared radio frequency spectrum may be referred to as unlicensed LTE (LTE-U) operation, and an LTE device that supports LTE-U operation may be referred to as an LTE-U device. Operation using an LTE/LTE-A carrier in an unlicensed or shared spectrum may be used in a standalone mode of operation, where the LTE/LTE-A carrier may be used as the primary cell for the UE. The LTE/LTE-A carrier may also be used in a licensed assisted access (LAA) mode, where the UE is configured with a primary cell and an LTE/LTE-A carrier in an unlicensed or shared spectrum is configured as a secondary cell in carrier aggregation mode.

Because unlicensed cells (e.g., standalone or LAA) operating in unlicensed or shared spectrum may be subject to LBT procedures, control flow management procedures designed around predetermined timing for dedicated spectrum may be subject to unpredictable timing variations. Additionally, unlicensed or shared spectrum may have additional constraints that impose limits on transmission power or duration, which may affect control flow management for unlicensed cells.

Overview

Systems, methods, and apparatus for control flow enhancements for LTE-U operation. Aspects include enhancements to control flow handling for floating transmission time interval (TTI) operation in unlicensed cells, including enhanced physical downlink control channel (ePDCCH) handling, aperiodic channel state information (CSI) reporting, discontinuous reception (DRX) operation, and extended TTI at the end of a transmission burst. The described aspects also include enhancements to reference signal configuration for unlicensed cells, handling of joint grants for multiple unlicensed cells, ePDCCH handling for partial subframes, and multi-channel DRS operation.

A method of wireless communication is described. The method may include identifying a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identifying a transmission from the secondary cell comprising at least one subframe; and determining a reference signal configuration for the transmission based at least in part on a cross-subframe indicator for the at least one subframe.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; means for identifying a transmission from the secondary cell comprising at least one subframe; and means for determining a reference signal configuration for the transmission based at least in part on a cross-subframe indicator for the at least one subframe.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identify a transmission from the secondary cell comprising at least one subframe; and determine a reference signal configuration for the transmission based at least in part on a cross-subframe indicator for the at least one subframe.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identify an LBT transmission from the secondary cell comprising at least one subframe; and determine a reference signal configuration for the transmission based at least in part on a cross-subframe indicator for the at least one subframe.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the determining includes identifying an initial transmission subframe set associated with at least one reference signal configuration.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the reference signal subframe indicator is received by a licensed cell operating in a dedicated spectrum band.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the reference signal subframe indicator comprises a field of a downlink control information (DCI) format received via a downlink control channel of the licensed cell. Additionally or alternatively, in some examples, the reference signal subframe indicator is received by the secondary cell in an indicator channel or on a field of a downlink control information (DCI) format received via a downlink control channel of the secondary cell.

Some examples of the methods, apparatus, or non-transitory computer-readable media described herein may further include processes, features, apparatus, or instructions for identifying at least one subframe having asynchronous symbol timing relative to a licensed cellular cell operating in a dedicated spectrum band; and determining one or more symbol positions for at least one reference signal within the at least one subframe based at least in part on a detected symbol preamble associated with the transmission.

A method of wireless communication is described. The method may include identifying a plurality of cells in a transmission from a base station on a shared spectrum band, wherein the transmission is subject to a listen-before-talk (LBT) procedure for the shared frequency channel; identifying a first scheduling configuration for a first set of subframes for an initial transmission of the transmission, the first scheduling configuration including one or more search spaces for a first group of cells configured to carry individual grants for respective cells of the plurality of cells; and identifying a second scheduling configuration for a second set of subframes in the transmission subsequent to the first set of subframes, the second scheduling configuration including at least one search space for at least one cell associated with a joint grant for the plurality of cells.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a plurality of cells in a transmission from a base station on a shared spectrum band, wherein the transmission is subject to a listen-before-talk (LBT) procedure for the shared frequency channel; means for identifying a first scheduling configuration for a first set of subframes for initial transmission of the transmission, the first scheduling configuration including one or more search spaces for a first group of cells configured to carry individual grants for respective cells in the plurality of cells; and means for identifying a second scheduling configuration for a second set of subframes in the transmission following the first set of subframes, the second scheduling configuration including at least one search space for at least one cell associated with a joint grant for the plurality of cells.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a plurality of cells in a transmission from a base station on a shared spectrum band, wherein the transmission is subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identify a first scheduling configuration for a first set of subframes for an initial transmission of the transmission, the first scheduling configuration including one or more search spaces for a first group of cells configured to carry individual grants for respective cells in the plurality of cells; and identify a second scheduling configuration for a second set of subframes in the transmission subsequent to the first set of subframes, the second scheduling configuration including at least one search space for at least one cell associated with a joint grant for the plurality of cells.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a plurality of cells in a shared frequency spectrum band, wherein a transmission is subject to a listen-before-talk (LBT) procedure for the shared frequency channel; identify a first scheduling configuration for a first set of subframes for an initial transmission of the transmission, the first scheduling configuration including one or more search spaces for a first group of cells configured to carry individual grants for respective cells in the plurality of cells; and identify a second scheduling configuration for a second set of subframes in the transmission subsequent to the first set of subframes, the second scheduling configuration including at least one search space for at least one cell associated with a joint grant for the plurality of cells.

Some examples of the methods, apparatus, or non-transitory computer-readable media described herein may further include processes, features, means, or instructions for determining a subset of cells from the plurality of cells having associated frequency channels successfully reserved for the transmission. Additionally or alternatively, some examples may include processes, features, means, or instructions for determining the at least one cell from the subset of the plurality of cells based at least in part on a UE-specific identifier.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the at least one cell comprises a licensed cell operating in a dedicated spectrum band.

A method of wireless communication is described. The method may include identifying a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identifying a transmission from the secondary cell comprising at least one subframe; and receiving an indicator specifying a format of a partial subframe contained within the transmission.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for the shared frequency channel; means for identifying a transmission from the secondary cell comprising at least one subframe; and means for receiving an indicator specifying a format of a partial subframe contained within the transmission.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identify a transmission from the secondary cell comprising at least one subframe; and receive an indicator specifying a format of a partial subframe contained within the transmission.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel; identify a transmission from the secondary cell comprising at least one subframe; and receive an indicator specifying a format of a partial subframe contained within the transmission.

A method of wireless communication is described. The method may include estimating channel demodulation information from a finite set of antenna ports associated with a control channel for one or more cells of a shared spectrum band, determining a control channel search space comprising partial subframes for the one or more cells, and demodulating control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of antenna ports.

An apparatus for wireless communication is described. The apparatus may include: means for estimating channel demodulation information from a finite set of antenna ports associated with a control channel for one or more cells of a shared spectrum band; means for determining a control channel search space comprising partial subframes for the one or more cells; and means for demodulating control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of antenna ports.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: estimate channel demodulation information from a finite set of antenna ports associated with a control channel for one or more cells of a shared spectrum band; determine a control channel search space comprising partial subframes for the one or more cells; and demodulate control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of antenna ports.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: estimate channel demodulation information from a finite set of antenna ports associated with a control channel for one or more cells of a shared spectrum band; determine a control channel search space comprising partial subframes for the one or more cells; and demodulate control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of antenna ports.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the control channel includes an EPDCCH.

A method of wireless communication is described. The method may include identifying a configuration for communications using synchronized cells, the synchronized cells operating in a shared spectrum band and having static subframe positions; identifying a LBT transmission for the synchronized cell; determining a dynamic TTI for a shared data channel of the synchronized cell based at least in part on a channel reservation signal of the LBT transmission; and determining a search space for a control channel within a shared data region including the shared data channel based at least in part on an offset between the dynamic TTI and a boundary of the static subframe position.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a configuration for communications using synchronized cells, the synchronized cells operating in a shared spectrum band and having static subframe positions; means for identifying a LBT transmission for the synchronized cell; means for determining a dynamic TTI for a shared data channel of the synchronized cell based at least in part on a channel reservation signal of the LBT transmission; and means for determining a search space for a control channel within a shared data region including the shared data channel based at least in part on an offset between the dynamic TTI and a boundary of the static subframe position.

Another apparatus for wireless communication is described. The apparatus may include a processor, a memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a configuration for communications using a synchronized cell, the synchronized cell operating in a shared spectrum band and having static subframe positions; identify a LBT transmission for the synchronized cell; determine a dynamic TTI for a shared data channel of the synchronized cell based at least in part on a channel reservation signal of the LBT transmission; and determine a search space for a control channel within a shared data region that includes the shared data channel based at least in part on an offset between the dynamic TTI and a boundary of the static subframe position.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a configuration for communications using a synchronized cell, the synchronized cell operating in a shared spectrum band and having static subframe positions; identify a LBT transmission for the synchronized cell; determine a dynamic TTI for a shared data channel of the synchronized cell based at least in part on a channel reservation signal of the LBT transmission; and determine a search space for a control channel within a shared data region including the shared data channel based at least in part on an offset between the dynamic TTI and a boundary of the static subframe position.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the search space includes the same set of symbols as the dynamic TTI. Additionally or alternatively, in some examples, the search space includes a subset of symbols of the dynamic TTI, and wherein the subset of symbols of the dynamic TTI is determined at least in part based on an offset between the dynamic TTI and a boundary of the static subframe position.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the control channel includes an enhanced physical downlink control channel (ePDCCH). Additionally or alternatively, some examples may include a process, feature, apparatus, or instruction for determining a number of symbol periods of a last TTI of the LBT transmission based at least in part on a field included in at least one of a physical frame format indicator channel (PFFICH) or a grant received in the control channel.

Some examples of the methods, apparatus, or non-transitory computer-readable media described herein may further include processes, features, apparatus, or instructions for determining a search space for a control channel for the last TTI based at least in part on at least one of a static number of symbol periods or a determined number of symbol periods.

A method of wireless communication is described. The method may include identifying a configuration for communication using at least a first cell and a second cell, the second cell operating in a shared spectrum band; identifying a LBT transmission from the second cell; receiving a request for an aperiodic CSI report in a control channel of the second cell; and determining a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a configuration for communication using at least a first cell and a second cell, the second cell operating in a shared spectrum band; means for identifying a LBT transmission from the second cell; means for receiving a request for an aperiodic CSI report in a control channel of the second cell; and means for determining a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a configuration for communications using at least a first cell and a second cell, the second cell operating in a shared spectrum band; identify a LBT transmission from the second cell; receive a request for an aperiodic CSI report in a control channel of the second cell; and determine a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a configuration for communications using at least a first cell and a second cell, the second cell operating in a shared spectrum band; identify a LBT transmission from the second cell; receive a request for an aperiodic CSI report in a control channel of the second cell; and determine a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the timing parameter comprises a first symbol of the control channel or a last symbol of the control channel. Additionally or alternatively, in some examples, the control channel comprises a physical downlink control channel (PDCCH) or an ePDCCH.

A method of wireless communication is described. The method may include identifying a configuration for communications using a cell operating in a shared spectrum band; enabling reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a discontinuous reception (DRX) configuration associated with the cell; receiving a CRS on a first symbol of the paging occasion; and identifying a symbol offset for a control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion.

An apparatus for wireless communication is described. The apparatus may include: means for identifying a configuration for communications using a cell operating in a shared spectrum band; means for enabling reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a DRX configuration associated with the cell; means for receiving a CRS on a first symbol of the paging occasion; and means for identifying a symbol offset for a control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: identify a configuration for communications using a cell operating in a shared spectrum band; enable reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a DRX configuration associated with the cell; receive a CRS on a first symbol of the paging occasion; and identify a symbol offset for a control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: identify a configuration for communications using a cell operating in a shared spectrum band; enable reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a DRX configuration associated with the cell; receive a CRS on a first symbol of the paging occasion; and identify a symbol offset for a control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion.

In some examples of the methods, apparatus, or non-transitory computer-readable media described herein, the control channel includes an ePDCCH.

A wireless communication method is described. The method may include receiving a discovery signal measurement timing configuration (DMTC) associated with one or more cells of a shared spectrum band, determining a subframe associated with a discovery reference signal (DRS) for the one or more cells, and determining a starting symbol for the DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell.

An apparatus for wireless communication is described. The apparatus may include: means for receiving a discovery signal measurement timing configuration (DMTC) associated with one or more cells of a shared spectrum band; means for determining a subframe associated with a discovery signal measurement timing configuration (DRS) for the one or more cells; and means for determining a starting symbol for the DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: receive a discovery signal measurement timing configuration (DMTC) associated with one or more cells of a shared spectrum band; determine a subframe associated with a discovery signal measurement timing configuration (DRS) for the one or more cells; and determine a starting symbol for the DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: receive a discovery signal measurement timing configuration (DMTC) associated with one or more cells of a shared spectrum band; determine a subframe associated with a discovery signal measurement timing configuration (DRS) for the one or more cells; and determine a starting symbol for the DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell.

In some examples of methods, apparatus, or non-transitory computer-readable media described herein, a DMTC is associated with multiple cells of the one or more cells. Additionally or alternatively, in some examples, the multiple cells include at least two cells in two different frequency bands, the two different frequency bands having independent aggregate transmit power limits.

A method of wireless communication is described. The method may include operating multiple cells on a shared spectrum band, wherein DRSs for the multiple cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the multiple cells transmits with a different starting symbol offset; and transmitting the DRS for each of the multiple cells at a DRS power level that is independent of a transmit power level of a shared data channel for each of the multiple cells.

An apparatus for wireless communication is described. The apparatus may include: means for operating a plurality of cells on a shared spectrum band, wherein DRSs for the plurality of cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the plurality of cells transmits with a different starting symbol offset; and means for transmitting the DRS for each of the plurality of cells at a DRS power level that is independent of a transmit power level of a shared data channel for each of the plurality of cells.

Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory that, when executed by the processor, are operable to cause the apparatus to: operate a plurality of cells on a shared spectrum band, wherein DRSs for the plurality of cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the plurality of cells transmits with a different starting symbol offset; and transmit a DRS for each of the plurality of cells at a DRS power level that is independent of a transmit power level of a shared data channel for each of the plurality of cells.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to: operate a plurality of cells on a shared spectrum band, wherein DRSs for the plurality of cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the plurality of cells transmits with a different starting symbol offset; and transmit a DRS for each of the plurality of cells at a DRS power level that is independent of a transmit power level of a shared data channel for each of the plurality of cells.

Some examples of the methods, apparatus, or non-transitory computer-readable media described herein may further include processes, features, apparatus, or instructions for adjusting the transmit power level of the shared data channel for each of the plurality of cells based at least in part on the DRS power level and the predefined transmit power level.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are described with reference to the following drawings:

1 illustrates an example of a wireless communication system supporting control flow enhancements for unlicensed LTE in accordance with various aspects of the present disclosure;

2 illustrates a wireless communication system in which LTE/LTE-A may be deployed in different scenarios using shared spectrum bands according to various aspects of the present disclosure;

FIG3A illustrates a timeline of communications in an uplink according to various aspects of the present disclosure;

FIG3B illustrates a timeline of communications in an uplink according to various aspects of the present disclosure;

3C illustrates a timeline of communications in an uplink of a shared radio frequency spectrum band, and execution of an LBT procedure followed by transmission of a channel reservation signal, in accordance with various aspects of the present disclosure;

4A illustrates a wireless communication system in which LTE/LTE-A may be deployed in a carrier aggregation mode in accordance with various aspects of the present disclosure;

4B illustrates a wireless communication system in which LTE/LTE-A may be deployed in multiple connectivity scenarios (e.g., coordinated multi-point (CoMP) scenarios) according to various aspects of the present disclosure;

FIG5A illustrates an example of cross-subframe indication of a CSI reference signal configuration according to various aspects of the present disclosure;

FIG5B illustrates an example of a cross-subframe indication of a CSI reference signal configuration according to various aspects of the present disclosure;

FIG6 illustrates an example of joint and individual grant transmission and processing according to various aspects of the present disclosure;

7 illustrates a diagram of a limited set of antenna ports for partial control channel monitoring in accordance with various aspects of the present disclosure;

FIG8A illustrates an example of dynamic TTI usage according to various aspects of the present disclosure;

FIG8B illustrates an example of dynamic TTI usage according to various aspects of the present disclosure;

FIG9 illustrates an example of dynamic TTI usage according to various aspects of the present disclosure;

FIG10 illustrates an example of discovery window allocation within a DMTC period according to various aspects of the present disclosure;

FIG11 illustrates an example discovery window in which a DRS may be transmitted in each of a plurality of cells in accordance with various aspects of the present disclosure;

12-19 illustrate block diagrams of wireless devices and components supporting control flow enhancements for unlicensed LTE according to various aspects of the present disclosure;

20 illustrates a block diagram of a system including user equipment (UE) supporting control flow enhancements for unlicensed LTE in accordance with various aspects of the present disclosure;

FIG21 illustrates a block diagram of a wireless device supporting control flow enhancements for unlicensed LTE in accordance with various aspects of the present disclosure;

22 illustrates a block diagram of a system including a base station supporting control flow enhancements for unlicensed LTE in accordance with various aspects of the present disclosure; and

23-32 illustrate methods for control flow enhancement for unlicensed LTE according to various aspects of the present disclosure.

Detailed description

The described features generally relate to improved systems, methods, or apparatus for control flow enhancements for LTE-U operation. These techniques include enhancements to control flow handling for floating TTI operation in unlicensed cells, including ePDCCH handling, aperiodic channel state information (CSI) reporting, DRX operation, and extended TTI at the end of a transmission burst. The described techniques also include enhancements to reference signal configuration for unlicensed cells, handling of joint grants for multiple unlicensed cells, ePDCCH handling for partial subframes, and multi-channel DRS operation.

Aspects of the present disclosure are initially described in the context of wireless communication systems. Specific examples of control flow enhancements for LTE-U operation are subsequently described. These and other aspects of the present disclosure are further illustrated and described by and with reference to apparatus diagrams, system diagrams, and flow diagrams related to control flow enhancements for unlicensed Long Term Evolution (LTE).

1 illustrates an example of a wireless communication system 100 that supports RRM measurements and reporting for LAA according to various aspects of the present disclosure. The wireless communication system 100 includes a base station 105, at least one user equipment (UE) 115, and a core network 130. The core network 130 can provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The base station 105 interfaces with the core network 130 via a backhaul link 132 (e.g., S1, etc.). The base station 105 can perform radio configuration and scheduling for communication with the UE 115, or can operate under the control of a base station controller (not shown). In various examples, the base stations 105 can communicate with each other directly or indirectly (e.g., through the core network 130) on a backhaul link 134 (e.g., X1, etc.), which can be a wired or wireless communication link.

Base stations 105 can communicate wirelessly with UEs 115 via one or more base station antennas. Each base station 105 can provide communication coverage for a respective geographic coverage area 110. The wireless communication system 100 can include base stations 105 of different types (e.g., macro base stations or small cell base stations). There can be overlapping geographic coverage areas 110 of different technologies. The communication links 125 shown in the wireless communication system 100 can include uplink (UL) transmissions from a UE 115 to a base station 105, or downlink (DL) transmissions from a base station 105 to a UE 115.

In some examples of the wireless communication system 100, the base station 105 or the UE 115 may include multiple antennas to employ an antenna diversity scheme to improve the quality and reliability of communication between the base station 105 and the UE 115. Additionally or alternatively, the base station 105 or the UE 115 may employ multiple-input multiple-output (MIMO) technology, which may utilize a multipath environment to transmit multiple spatial layers carrying the same or different coded data.

The wireless communication system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timing, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timing, and transmissions from different base stations 105 may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operation.

A communication network that can accommodate some of the various disclosed examples can be a packet-based network operating according to a layered protocol stack, and the data in the user plane can be IP-based. The radio link control (RLC) layer can perform packet segmentation and reassembly to communicate on logical channels. The medium access control (MAC) layer can perform priority handling and multiplex logical channels into transport channels. The MAC layer can also use hybrid automatic repeat request (HARQ) to provide retransmissions at the MAC layer, thereby improving link efficiency. In the control plane, the radio resource control (RRC) protocol layer can provide establishment, configuration, and maintenance of the RRC connection between the UE 115 and the base station 105. The RRC protocol layer can also be used for the core network 130 to support radio bearers for user plane data. In the physical (PHY) layer, transport channels can be mapped to physical channels.

In some examples, wireless communication system 100 is an LTE/LTE-Advanced (LTE-A) network. In an LTE/LTE-A network, the term evolved Node B (eNB) may be used generally to describe base station 105, while the term UE may be used generally to describe UE 115. UE 115 may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. UEs may be capable of communicating with various types of base stations and network equipment, including macro eNBs, small cell eNBs, relay base stations, and the like. Wireless communication system 100 may be a heterogeneous LTE/LTE-A network, in which different types of eNBs provide coverage for various geographic regions. For example, each eNB or base station 105 may provide communication coverage for a macro cell, a small cell, or other types of cells. Depending on the context, the term "cell" may be used to describe a base station, a carrier or component carrier associated with a base station, or a coverage area (e.g., a sector, etc.) of a carrier or base station.

A UE 115 attempting to access a wireless network may perform an initial cell search by detecting a primary synchronization signal (PSS) from a base station 105. The PSS enables synchronization of slot timing and may indicate a physical layer identity value. The UE 115 may then receive a secondary synchronization signal (SSS). The SSS enables radio frame synchronization and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The SSS may also enable detection of duplex mode and cyclic prefix length. Both the PSS and SSS may be located in the center 62 and 72 subcarriers of a carrier, respectively. In some cases, the PSS, SSS, and other signals (such as a cell-specific reference signal (CRS) used for channel estimation) may be configured according to a transmission schedule with reduced periodicity to save energy or reduce inter-cell interference. Such a configuration may be referred to as a discovery reference signal (DRS) configuration.

UE 115 may enter idle mode and use discontinuous reception (DRX) in idle mode to reduce power consumption. In DRX operation, the UE is configured to periodically wake up to receive paging messages according to a DRX cycle, which may be a default DRX cycle for the cell or a UE-specific DRX cycle. The UE determines the paging frame in which it will wake up to check for paging messages based on the DRX cycle and a UE-specific identifier determined from the unique International Mobile Subscriber Identity (IMSI) assigned to the UE 115. The UE 115 checks for a specific paging occasion, which is a subframe within a paging frame determined based on the DRX cycle and the UE-specific identifier. If a serving gateway (S-GW) receives data for the UE 115, the S-GW may notify the mobility management entity (MME), which may send a paging message to each base station 105 within an area known as a tracking area. Each base station 105 within the tracking area may send a paging message to the UE 115 during the paging occasion. Therefore, the UE may remain idle without updating the MME until it leaves the tracking area.

In some cases, UE 115 may be configured to be in connected mode DRX. In connected mode DRX, the DRX cycle includes an "On duration" during which UE 115 may monitor control information (e.g., on a physical downlink control channel (PDCCH)) and a "DRX period" during which UE 115 may power down the radio components. In some cases, UE 115 may be configured with a short DRX cycle and a long DRX cycle. In some cases, UE 115 may enter a long DRX cycle if it is inactive for one or more short DRX cycles. The transition between short DRX cycle, long DRX cycle, and continuous reception may be controlled by an internal timer or by messaging from base station 105. UE 115 may receive a scheduling message on PDCCH during the On duration. When monitoring the scheduling message on PDCCH, UE 115 may initiate a "DRX inactivity timer." If the scheduling message is successfully received, UE 115 may be ready to receive data and the DRX inactivity timer may be reset. When the DRX inactivity timer expires without receiving a scheduling message, the UE 115 may move to a short DRX cycle and may start a “DRX short cycle timer.” When the DRX short cycle timer expires, the UE 115 may resume a long DRX cycle.

The base station 105 may insert periodic pilot symbols, such as cell-specific reference signals (CRS), to assist the UE 115 in channel estimation and coherent demodulation. Based on the physical cell identity of the transmitting cell (which may be one of 504 different cell identities), CRSs from different cells may have different sequences and/or be transmitted on different transmission resources. CRSs may be modulated using quadrature phase shift keying (QPSK) and power-boosted (e.g., transmitted at 6 dB higher power than the sounding data elements) to make them more robust to noise and interference. CRSs may be embedded in 4 to 16 resource elements per resource block based on the number of antenna ports or layers of the receiving UE 115 (up to 4). In addition to the CRS, which can be utilized by all UEs 115 in the coverage area 110 of the base station 105, a demodulation reference signal (DMRS), also known as a UE-specific reference signal (UE-RS), can be directed to specific UEs 115 and can be transmitted only on resource blocks assigned to those UEs 115. The DMRS may include signals on six resource elements in each resource block in which a signal is transmitted. The DM-RS for different antenna ports may each utilize the same six resource elements and may use different orthogonal cover codes to distinguish them (e.g., masking each signal with a different combination of 1 or -1 in different resource elements). In some cases, two DMRS sets may be transmitted in contiguous resource elements. In some cases, an additional reference signal, known as a CSI reference signal (CSI-RS), may be included to help determine the CSI parameters to be reported. On the UL, the UE 115 may transmit a combination of a periodic sounding reference signal (SRS) and UL DMRS for link adaptation and demodulation, respectively.

The base station 105 can collect channel condition information from the UE 115 to efficiently configure and schedule the channel. This information can be sent from the UE 115 in the form of a CSI report. The CSI report can include a rank indicator (RI) requesting the number of layers to be used for DL transmission (e.g., based on the antenna port of the UE 115), a precoding matrix indicator (PMI) indicating a preference for which precoder matrix should be used (based on the number of layers), or a channel quality indicator (CQI) indicating the highest modulation and coding scheme (MCS) that can be used. The CQI can be calculated by the UE 115 after receiving predetermined pilot symbols (such as CRS or CSI-RS). If the UE 115 does not support spatial multiplexing (or is not in a mode that supports spatial multiplexing), the RI and PMI can be excluded. The type of information included in the report determines the report type. CSI reports can be periodic or aperiodic. That is, the base station 105 can configure the UE 115 to send periodic reports at regular intervals and can also request additional reports as needed. Aperiodic reports may include wideband reports indicating channel quality across the entire cell bandwidth, reports indicating UE selection of the best subband subset, or configured reports where the reported subbands are selected by the base station 105 .

In some cases, the wireless communication network 100 may include small cells whose coverage areas 110 may overlap with the coverage areas 110 of one or more macro base stations 105. In some cases, small cells may be added in areas with high user demand or in areas not adequately covered by macro base stations 105. For example, small cells may be located in shopping malls or in areas where signal transmission is blocked by terrain or buildings. In some cases, small cells may improve network performance by allowing macro base stations 105 to offload traffic when the load is high. A network that includes both large cells and small cells may be referred to as a heterogeneous network. A heterogeneous network may also include a Home Evolved Node B (HeNB), which may provide service to a restricted group called a Closed Subscriber Group (CSG). For example, an office building may contain small cells that are only used by the building's occupants. In some cases, heterogeneous networks may involve more complex network planning and interference mitigation techniques than homogeneous networks.

The wireless communication system 100 may support operation across multiple cells or carriers, a feature that may be referred to as carrier aggregation (CA) or multi-carrier operation. A carrier may also be referred to as a component carrier (CC), layer, channel, etc. The term "component carrier" may refer to each of the multiple carriers utilized by a UE in CA operation and may be distinct from other portions of the system bandwidth. For example, a component carrier may be a relatively narrow bandwidth carrier that is readily utilized independently or in combination with other component carriers. Each component carrier may provide the same capabilities as a single carrier based on Release 8 or Release 9 of the Long Term Evolution (LTE) standard. Multiple component carriers may be aggregated or utilized concurrently to provide greater bandwidth and higher data rates to some UEs 115. Thus, individual component carriers may be backward compatible with legacy UEs 115 (e.g., UEs 115 implementing LTE Release 8 or Release 9), while other UEs 115 (e.g., UEs 115 implementing LTE versions post-Release 8/9) may be configured with multiple component carriers in multi-carrier mode. A carrier used for downlink (DL) may be referred to as a DL CC, while a carrier used for uplink (UL) may be referred to as a UL CC. UE 115 may be configured with multiple DL CCs and one or more UL CCs for carrier aggregation. Each carrier may be used to transmit control information (e.g., reference signals, control channels, etc.), overhead information, data, etc. UE 115 may utilize multiple carriers to communicate with a single base station 105, and may also communicate with multiple base stations simultaneously on different carriers. UE 115 may be configured with multiple downlink CCs and one or more uplink CCs for carrier aggregation. Carrier aggregation may be used with both FDD and TDD component carriers.

Each cell of base station 105 includes a CC that can be a DL CC or a TDD CC. The cell can include a UL CC in FDD operation. The coverage area 110 of each serving cell of base station 105 can be different (e.g., CCs on different frequency bands can experience different path losses). In some examples, one carrier is designated as the primary carrier or primary component carrier (PCC) for UE 115, which can be served by a primary cell (PCell). The primary cell can be semi-statically configured on a per-UE basis by higher layers (e.g., radio resource control (RRC), etc.). Certain uplink control information (UCI) (e.g., acknowledgment (ACK)/NACK, channel quality indicator (CQI), and scheduling information) transmitted on a physical uplink control channel (PUCCH) is carried by the primary cell. Additional carriers can be designated as secondary carriers or secondary component carriers (SCCs), which can be served by a secondary cell (SCell). The secondary cell can also be semi-statically configured on a per-UE basis. In some cases, the secondary cell may not include or be configured to transmit the same control information as the primary cell. In other cases, one or more secondary cells (Scells) may be designated to carry the Physical Uplink Control Channel (PUCCH), and the SCells may be organized into PUCCH groups based on which CC is used to carry the associated UL control information. Some wireless networks may utilize enhanced Carrier Access Control (CA) operation based on a large number of carriers (e.g., between 5 and 32 carriers), operation in unlicensed spectrum, or the use of enhanced CCs.

In some cases, a configured SCell is activated and deactivated for an individual UE 115 by a configured cellular cell (e.g., a PCell, etc.) using a primary carrier. For example, activation and deactivation commands for a configured SCell may be carried in MAC signaling. When an SCell is deactivated, the UE 115 does not need to monitor control information for the SCell. The UE 115 also does not need to receive the corresponding downlink CC, cannot transmit in the corresponding uplink CC, and is not required to perform channel quality information (CQI) measurements. When the SCell is deactivated, the UE may also clear all HARQ buffers associated with the SCell. In contrast, when the SCell is active, the UE 115 receives control information and/or data transmission for the SCell and is expected to be able to perform CQI measurements. The activation/deactivation mechanism is based on a combination of a MAC control element and a deactivation timer. The MAC control element carries a bitmap for individual activation and deactivation of the SCell so that each SCell can be activated and deactivated individually, and a single activation/deactivation command can activate/deactivate a subset of the SCells. A deactivation timer is maintained per SCell, but a common value is configured per UE by RRC.

In some cases, the UE 115 or base station 105 may operate in a shared spectrum band. As used herein, the term "shared spectrum band" means one or more frequency bands of an unlicensed or shared spectrum that are subject to contention resolution procedures to access the shared frequency resources of the band. A cellular cell operating in a shared spectrum band may be configured to be used in a standalone operation mode (e.g., as a primary carrier for one or more UEs) or in a license-assisted access (LAA) mode. Other devices may also operate in an unlicensed or shared spectrum. As an example, FIG1 shows a network including a Wi-Fi access point (AP) 150 in communication with a Wi-Fi station (STA) 155 via a communication link 165 in an unlicensed spectrum. When communicating via an unlicensed cellular cell, the device uses a listen-before-talk (LBT) procedure (e.g., clear channel assessment (CCA) or the like) to determine whether the channel is available before communicating. CCA may include an energy detection procedure to determine whether there are any other active transmissions. For example, a device may infer that a detected energy (e.g., RSSI) exceeding a certain level indicates that the channel is occupied. Specifically, signal power concentrated in a certain bandwidth and exceeding a predetermined noise floor can indicate that another wireless transmitter is currently transmitting on the channel. LBT procedures can also include detecting a specific sequence that indicates channel usage. For example, another device can transmit a specific preamble before transmitting a data sequence.

In some examples, UE 115 can be configured to use a PCell in a dedicated spectrum and one or more SCells in a shared spectrum band for CA. A UE 115 or eNB 105 using an LAA cell can utilize LBT procedures for transmissions in the shared spectrum band. These devices can perform LBT procedures to determine whether a channel is available before communicating. LBT procedures can include energy detection and preamble detection procedures to determine whether there are any other active transmissions.

FIG2 shows a wireless communication system 200 in which LTE/LTE-A can be deployed in different scenarios using shared spectrum bands according to various aspects of the present disclosure. More specifically, FIG2 illustrates an example in which a supplemental downlink mode (e.g., LAA), a carrier aggregation (CA) mode, and a standalone (SA) mode of LTE/LTE-A are deployed using shared spectrum bands. The wireless communication system 200 may be an example of portions of the wireless communication system 100 described with reference to FIG1 . In addition, the first eNB 105-a and the second eNB 105-b may be examples of aspects of one or more of the eNBs 105 described with reference to FIG1 , and the first UE 115-a, the second UE 115-b, the third UE 115-c, and the fourth UE 115-d may be examples of aspects of one or more of the UEs 115 described with reference to FIG1 .

In an example of a supplemental downlink mode (e.g., LAA) in the wireless communication system 200, the first eNB 105-a can use a downlink channel 220 to transmit an OFDMA waveform to the first UE 115-a. The downlink channel 220 can be associated with frequency F1 in a shared spectrum band. The first eNB 105-a can use a first bidirectional link 225 to transmit an OFDMA waveform to the first UE 115-a and can use the first bidirectional link 225 to receive an SC-FDMA waveform from the first UE 115-a. The first bidirectional link 225 can be associated with frequency F4 (or multiple frequencies) in a dedicated spectrum band. The downlink channel 220 in the shared spectrum band and the first bidirectional link 225 in the dedicated spectrum band can operate concurrently. The downlink channel 220 can provide downlink capacity offload for the first eNB 105-a. In some examples, the downlink channel 220 can be used for unicast services (e.g., addressed to one UE) or for multicast services (e.g., addressed to multiple UEs). This scenario is possible for any service provider (eg, mobile network operator (MNO) etc.) that has deployed capacity in dedicated spectrum and has the capability to offload to a shared spectrum band.

In one example of a carrier aggregation mode in the wireless communication system 200, the first eNB 105-a may transmit an OFDMA waveform to the second UE 115-b using a second bidirectional link 230 and may receive an OFDMA waveform, an SC-FDMA waveform, or a resource block interleaved FDMA waveform from the second UE 115-b using the second bidirectional link 230. The second bidirectional link 230 may be associated with frequency F1 in the shared spectrum band. The first eNB 105-a may also transmit an OFDMA waveform to the second UE 115-b using a third bidirectional link 235 and may receive an SC-FDMA waveform from the second UE 115-b using the third bidirectional link 235. The third bidirectional link 235 may be associated with frequency F2 in the dedicated spectrum band. The second bidirectional link 230 may provide downlink and uplink capacity offloading for the first eNB 105-a. Similar to the supplemental downlink mode described above, this scenario is possible for any service provider (e.g., an MNO) that has deployed capacity in the dedicated spectrum and has the ability to offload to the shared spectrum band.

In another example of a carrier aggregation mode in the wireless communication system 200, the first eNB 105-a may transmit an OFDMA waveform to a third UE 115-c using a fourth bidirectional link 240 and may receive an OFDMA waveform, an SC-FDMA waveform, or a resource block interleaved waveform from the third UE 115-c using the fourth bidirectional link 240. The fourth bidirectional link 240 may be associated with frequency F3 in the shared spectrum band. The first eNB 105-a may also transmit an OFDMA waveform to the third UE 115-c using a fifth bidirectional link 245 and may receive an SC-FDMA waveform from the third UE 115-c using the fifth bidirectional link 245. The fifth bidirectional link 245 may be associated with frequency F2 in the dedicated spectrum band. The fourth bidirectional link 240 may provide downlink and uplink capacity offloading for the first eNB 105-a. This example, as well as those provided above, is provided for illustrative purposes, and other similar operating modes or deployment scenarios may exist that combine LTE/LTE-A in the dedicated spectrum band and use the shared spectrum band for capacity offloading.

As described above, one type of service provider that can benefit from the capacity offload provided by using LTE/LTE-A in shared spectrum bands is a traditional MNO with access to LTE/LTE-A dedicated spectrum bands. For these service providers, operational examples may include a bootstrapping mode (e.g., supplemental downlink, carrier aggregation) using an LTE/LTE-A primary component carrier (PCC) on the dedicated spectrum band and at least one secondary component carrier (SCC) on the shared spectrum band.

In carrier aggregation mode, data and control may be communicated, for example, in a dedicated spectrum band (e.g., via first bidirectional link 225, third bidirectional link 235, and fifth bidirectional link 245), while data may be communicated, for example, in a shared spectrum band (e.g., via second bidirectional link 230 and fourth bidirectional link 240). The carrier aggregation mechanisms supported when using a shared spectrum band may be classified as hybrid frequency division duplex-time division duplex (FDD-TDD) carrier aggregation or TDD-TDD carrier aggregation with different symmetries across component carriers.

In one example of a standalone mode in the wireless communication system 200, the second eNB 105-b can transmit an OFDMA waveform to the fourth UE 115-d using a bidirectional link 250 and can receive an OFDMA waveform, an SC-FDMA waveform, or a resource block interleaved FDMA waveform from the fourth UE 115-d using the bidirectional link 250. The bidirectional link 250 can be associated with frequency F3 in a shared spectrum band. The standalone mode can be used in non-traditional wireless access scenarios, such as in-stadium access (e.g., unicast, multicast). Examples of service provider types for this mode of operation can be stadium owners, cable companies, event organizers, hotels, enterprises, or large corporations that do not have access to dedicated spectrum bands.

In some examples, a transmitting device (such as one of the eNBs 105 described with reference to FIG. 1 or 2 or one of the UEs 115 described with reference to FIG. 1 or 2 ) may use a gating interval to gain access to a channel of a shared spectrum band (e.g., a physical channel of a shared spectrum band). In some examples, the gating interval may be periodic. For example, the periodic gating interval may be synchronized with at least one boundary of an LTE/LTE-A radio interval. The gating interval may define the application of a contention-based protocol (such as an LBT protocol based on the LBT protocol specified in the European Telecommunications Standards Institute (ETSI) (EN 301 893)). When a gating interval defining the application of an LBT protocol is used, the gating interval may indicate when the transmitting device needs to perform a contention procedure (e.g., an LBT procedure), such as a CCA procedure. The result of the CCA procedure may indicate to the transmitting device whether the channel of the shared spectrum band is available for use or in use during the gating interval (also referred to as an LBT radio frame). When the CCA procedure indicates that the channel is available for the corresponding LBT radio frame (e.g., "cleared" for use), the transmitting device may reserve or use the channel of the shared spectrum band during part or all of the LBT radio frame. When the CCA procedure indicates that the channel is unavailable (e.g., the channel is used or reserved by another transmitting device), the transmitting device may be prevented from using the channel during the LBT radio frame.

3A illustrates a timeline 300 for communications in the uplink according to various aspects of the present disclosure. Timeline 300 illustrates a transmission opportunity 305 that includes a downlink transmission (Tx) period 310 followed by an uplink transmission (Tx) period 315. In some examples, the downlink transmission period 310 may be subdivided into multiple downlink TTIs (e.g., downlink (D) subframes), and the uplink transmission period 315 may be subdivided into multiple uplink TTIs (e.g., uplink (U) subframes).

In some examples, one or more downlink TTIs in downlink transmission period 310 may carry uplink grants for one or more uplink TTIs in uplink transmission period 315 (e.g., for same-carrier scheduling or self-scheduling of uplink transmissions). In other examples, one or more uplink grants for one or more uplink TTIs in uplink transmission period 315 may be transmitted on a different CC than the CC shown in FIG. 3A (e.g., for cross-carrier scheduling).

When multiple TTIs are scheduled for an uplink transmission period 315, the DCI for the multiple TTIs (e.g., DCI format 0) may include parameters such as resource block (RB) allocation, modulation and coding scheme (MCS) and redundancy value (RV), new data indicator (NDI), transmit power control (TPC) command, cell-specific demodulation reference signal (CS-DMRS), uplink (UL) index, downlink assignment index (DAI), channel state information (CSI) request, sounding reference signal (SRS) request, resource allocation type, or a combination thereof. In LTE/LTE-A networks, TDD format 0 allows two separate uplink grants to be carried to a single UE in a downlink TTI in a dedicated radio frequency spectrum band. The application of each uplink grant may be determined by the UL index associated with the uplink grant and may affect power control, non-periodic CSI reporting, and PUSCH transmission. Similar functionality may be provided for uplink grants applied to uplink transmissions in a shared radio frequency spectrum band.

Assuming there is no cross-transmission opportunity scheduling or cross-carrier scheduling, multiple uplink grants for multi-TTI uplink transmissions in a shared radio frequency spectrum band during an uplink transmission period 315 (which may be carried within a single downlink TTI of a downlink transmission period 310) may each include DCI fields such as: a UL index field, a HARQ index field, a reference signal and PUSCH multiplexing indicator field (e.g., an SRS/PUSCH multiplexing indicator field), a resource reuse indicator field (e.g., a PUCCH/PRACH resource reuse indicator field), LBT parameters, or a combination thereof. The UL index may indicate to the UE which uplink TTI (e.g., uplink subframe) in a transmission opportunity 305 (also referred to as a current transmission burst) carries the PUSCH transmission. The UL index may reference the end of the downlink TTI that carries the uplink grant including the UL index. The LBT parameters may indicate to the UE whether to puncture the first codeword of the uplink TTI to perform a shortened LBT procedure (e.g., a 25μs LBT procedure) or whether to perform a full-length LBT procedure (e.g., a Category (CAT) 4 LBT procedure). When indicating that a CAT 4 LBT procedure is to be performed, the LBT parameters may indicate one or more of an LBT priority class or a contention window size. In some examples, a failure of contention (e.g., for a UE performing a CAT 4 LBT procedure) to access a shared radio frequency spectrum band during a TTI of a multi-TTI uplink transmission may cause the UE to transfer the CAT 4 LBT procedure parameters to the next TTI of the multi-TTI uplink transmission.

FIG3B illustrates a timeline 320 of communications in the uplink according to various aspects of the present disclosure. Timeline 320 illustrates a first transmission opportunity 325 followed by a second transmission opportunity 340. The first transmission opportunity 325 may include a first downlink transmission period 330 followed by a first uplink transmission period 335. The second transmission opportunity 340 may include a second downlink transmission (Tx) period 345 followed by a second uplink transmission period 350. In some examples, one or both of these downlink transmission periods (e.g., the first downlink transmission period 330 or the second downlink transmission period 345) may be subdivided into multiple downlink TTIs (e.g., D subframes), and one or both of these uplink transmission periods (e.g., the first uplink transmission period 335 or the second uplink transmission period 350) may be subdivided into multiple uplink TTIs (e.g., U subframes).

In some examples, one or more downlink TTIs in the first downlink transmission period 330 may carry uplink grants for one or more uplink TTIs in the second uplink transmission period 350 (e.g., cross-transmission opportunity scheduling of uplink transmissions).

Assuming that cross-transmission opportunity scheduling is used to schedule uplink transmissions in the second uplink transmission period 350, and assuming that the second downlink transmission period 345 precedes the second uplink transmission period 350, multiple uplink grants for multi-TTI uplink transmissions in the shared radio frequency spectrum band during the second uplink transmission period 350 (which may be carried within a downlink TTI of the first downlink transmission period 330) may each include DCI fields such as the following: UL index field, HARQ index field, reference signal and PUSCH multiplexing indicator field (e.g., SRS/PUSCH multiplexing indicator field), resource reuse indicator field (e.g., PUCCH/PRACH resource reuse indicator field), LBT parameters, or a combination thereof. In addition, each uplink grant may include DCI fields such as the following: current transmission burst index field, target transmission burst index field, or PUSCH transmission skip policy field. The current transmission burst index may indicate to the UE the first transmission burst in which the uplink grant is received (e.g., the first transmission opportunity 325), and the target transmission burst index may indicate to the UE the second transmission burst to which the uplink grant applies (e.g., the second transmission opportunity 340). In some examples, the base station may broadcast the current transmission burst index to multiple UEs in a DCI on a common PDCCH. The UL index may identify the uplink TTI in which the PUSCH transmission in the second transmission burst (e.g., the second transmission opportunity 340) begins. The PUSCH transmission skip policy may indicate to the UE whether to skip at least the first PUSCH transmission in time or at least the last PUSCH transmission in time when the LBT procedure for at least the first TTI of a multi-TTI transmission is unsuccessful.

In some examples, a UE that receives at least one uplink grant for at least one TTI of a multi-TTI uplink transmission in a shared radio frequency spectrum band may execute an LBT procedure to contend for access to the shared radio frequency spectrum band for a TTI of the multi-TTI uplink transmission. Once the contention for accessing the shared radio frequency spectrum band for the TTI fails, the UE may trigger an uplink transmission forwarding strategy. The uplink transmission forwarding strategy may indicate to the UE whether to forward or not forward parameters associated with the TTI for which the contention for accessing the shared radio frequency spectrum band failed to the next TTI of the multi-TTI uplink transmission. In some examples, the parameters may include CSI transmission parameters, or SRS transmission parameters, or TPC commands, or a combination thereof. In some examples, the forwarded TPC commands may be applied cumulatively to the TTIs.

In some examples, a UE that receives at least one uplink grant for at least one TTI of a multi-TTI uplink transmission in a shared radio frequency spectrum band may perform an LBT procedure to contend for access to the shared radio frequency spectrum band for one TTI of the multi-TTI uplink transmission. Upon winning contention for access to the shared radio frequency spectrum band for the TTI, the UE may transmit data associated with the LBT priority class (e.g., best-effort data, video data, etc.) indicated in the uplink grant for the TTI. Upon exhausting the data associated with the LBT priority class, the UE may or may not transmit junk data for the remainder of the TTI.

In some examples, a UE that receives at least one uplink grant for at least one TTI of a multi-TTI uplink transmission in a shared radio frequency spectrum band can be triggered to transmit SRS without PUSCH transmission during the TTI by disabling all transport blocks (TBs) within the TTI.

3C illustrates a timeline 360 for communications in an uplink of a shared radio frequency spectrum band, and execution of an LBT procedure 380 followed by transmission of a channel reservation signal 385, in accordance with various aspects of the present disclosure. The timeline 360 illustrates one TTI 365 (e.g., one uplink (U) subframe) of an uplink transmission period (e.g., one TTI of the uplink transmission period 315 described with reference to FIG. 3A or the first uplink transmission period 335 or the second uplink transmission period 350 described with reference to FIG. 3B ). The TTI 365 includes a plurality of symbol periods (e.g., 14 symbol periods numbered 0-13) spanning two time slots (e.g., time slot 0 370 and time slot 1 375).

The UE may perform an LBT procedure 380 for a TTI 365. In some examples, the LBT procedure 380 may be performed during a first symbol period in time (e.g., symbol period 0) of the TTI 365. In some examples (not shown), the LBT procedure 380 may be synchronized to the end of the first symbol period, and upon winning contention for access to the shared radio frequency spectrum band, the UE may immediately begin uplink transmission (e.g., PUSCH transmission, or PUCCH transmission, or PRACH transmission, or SRS transmission, or a combination thereof) in a second symbol period in time (e.g., symbol period 1) of the TTI 365. In other examples (not shown), the LBT procedure 380 may be synchronized to the beginning of the first symbol period and performed during a first portion of the first symbol period, and upon winning contention for access to the shared radio frequency spectrum band, the UE may transmit a channel reservation signal (RES 385) during a second portion of the first symbol period. A channel reservation signal may be transmitted to reserve the shared radio frequency spectrum band between the time contention for access to the shared radio frequency spectrum band is won and the time the uplink transmission is scheduled to begin.

In some examples, the UE may select one of multiple different channel reservation signals to transmit during the second portion of the first symbol period (e.g., as RES 385). When the UE is scheduled to transmit SRS prior to PUSCH during TTI 365, the selected channel reservation signal may include an SRS waveform. When the UE is scheduled to transmit PUSCH but not SRS during TTI 365, and a junk SRS interface is active during the first symbol period of the TTI, the selected channel reservation signal may include a junk SRS waveform. When the network access device transmitting the uplink grant for TTI 365 does not indicate a selection methodology for selecting the channel reservation signal, the selected channel reservation signal may include a Wi-Fi channel reservation signal (e.g., Clear to Send to Self (CTS2S)). Alternatively, when the network access device transmitting the uplink grant for TTI 365 does not indicate a selection methodology for selecting the channel reservation signal, the UE may select any form of channel reservation signal.

FIG4A illustrates a wireless communication system 400 in which LTE/LTE-A may be deployed in a carrier aggregation mode according to various aspects of the present disclosure. The wireless communication system 400 may be an example of portions of the wireless communication system 100 or 200 described with reference to FIG1 or 2. Furthermore, the eNB 105-c may be an example of aspects of one or more of the eNBs 105 described with reference to FIG1 or 2, and the UE 115-e may be an example of aspects of one or more of the UEs 115 described with reference to FIG1 or 2.

When communicating in carrier aggregation mode using LTE/LTE-A communication, UE 115-e can use multiple CCs to communicate with eNB 105-c. One of these CCs can be designated as a primary CC, and the remaining CCs can be designated as secondary CCs. Each CC can be used as a DL CC and/or an UL CC. As an example, FIG4A illustrates communication between UE 115-e and eNB 105-c on five CCs, including a first CC 420, a second CC 425, a third CC 430, a fourth CC 435, and a fifth CC 440. Each of first CC 420, second CC 425, third CC 430, fourth CC 435, and fifth CC 440 can operate in a dedicated spectrum band or a shared spectrum band, depending on how the CCs are allocated or configured.

When UE 115-e is configured to operate in a supplemental downlink operation mode using a shared spectrum band (as described with reference to FIG2 ), and when UE 115 operates in a carrier aggregation mode, one or more of the first CC 420, the second CC 425, the third CC 430, the fourth CC 435, or the fifth CC 440 may operate as a UL CC or DL CC in a dedicated spectrum band, and one or more of the first CC 420, the second CC 425, the third CC 430, the fourth CC 435, or the fifth CC 440 may operate as a DL CC in a shared spectrum band.

When UE 115-e is configured to operate in a carrier aggregation mode of operation using a shared spectrum band (as described with reference to FIG. 2 ), one or more of first CC 420, second CC 425, third CC 430, fourth CC 435, or fifth CC 440 may operate as a UL CC or DL CC in a dedicated spectrum band, and one or more of first CC 420, second CC 425, third CC 430, fourth CC 435, or fifth CC 440 may operate as a DL CC or UL CC in a shared spectrum band. In some examples, all DL CCs may operate in a dedicated spectrum band, or all UL CCs may operate in a shared spectrum band, but not all DL CCs and all UL CCs may operate in a shared spectrum band (e.g., at least one DL CC or at least one UL CC operates in a dedicated spectrum band).

When UE 115-e is configured to operate in a standalone operation mode using a shared spectrum band (as described with reference to FIG2 ), and when UE 115 is operating in a carrier aggregation mode, each of the first CC 420, the second CC 425, the third CC 430, the fourth CC 435, and the fifth CC 440 can operate in the shared spectrum band.

FIG4B illustrates a wireless communication system 450 in which LTE/LTE-A may be deployed in a multiple connectivity scenario (e.g., a coordinated multipoint (CoMP) scenario) according to various aspects of the present disclosure. The wireless communication system 450 may be an example of portions of the wireless communication system 100 or 200 described with reference to FIG1 or 2. In addition, the first eNB 105-d and the second eNB 105-e may be examples of aspects of one or more of the eNBs 105 described with reference to FIG1, 2, or 4A, and the UE 115-f may be an example of aspects of one or more of the UEs 115 described with reference to FIG1, 2, or 4A.

When communicating in multiple connectivity mode using LTE/LTE-A communication, UE 115-f may use multiple CCs to communicate with multiple eNBs (such as a first eNB 105-d and a second eNB 105-e). One of these CCs may be designated as a primary CC, and the remaining CCs may be designated as secondary CCs. Each CC may be configured as a DL CC, a UL CC, or a cell (e.g., a CC that may be configured to function as a DL CC and/or a UL CC). As an example, FIG4B illustrates communication between UE 115-f and eNBs 105-d and 105-e on three CCs, including a first CC 455, a second CC 460, and a third CC 465. In some examples, the first CC 455 and the second CC 460 (in communication with the first eNB 105-d) can be configured as a primary CC group 470 in multiple connectivity operation, while the third CC 465 (in communication with the second eNB 105-e) can be configured as a secondary CC group 475 (e.g., a group of one CC in this example) in multiple connectivity operation. The first CC 455, the second CC 460, and the third CC 465 can be configured for various operating modes using dedicated spectrum bands or shared spectrum bands, similar to how component carriers can be used in a carrier aggregation operating mode, as described, for example, with reference to FIG.

For LTE/LTE-A operation, the UE performs channel measurements based on the CSI reference signal configuration, which specifies the location of the reference signal in each subframe. This CSI reference signal configuration can be used for purposes such as rate matching or channel measurement. When a CSI reference signal is transmitted on a cell in a dedicated spectrum band, the transmission of the CSI reference signal is periodic, and the periodicity of the transmission is based on the configuration. When a CSI reference signal (e.g., eCRS, CSI-RS, ZPCSI-RS, IMR signal, PSS, or SSS) is transmitted on a cell in a shared spectrum band, the transmission of the CSI reference signal can be periodic or aperiodic. In addition, since the transmission may be subject to LBT procedures, the transmission of CSI reference signals on cells in a shared spectrum band may be opportunistic. Thus, a CSI reference signal configuration may indicate that the CSI reference signal will be transmitted, but the eNB may not transmit the CSI reference signal because it did not win contention for access to the shared spectrum band (i.e., the CSI reference signal configuration may indicate that the CSI reference signal will be transmitted in a DL subframe, but that DL subframe may not be a valid DL subframe). Therefore, there is ambiguity regarding the configuration of CSI reference signals (eg, the presence and location of CSI reference signals) in DL subframes transmitted on cells in a shared spectrum band.

According to some aspects, ambiguity regarding the configuration of CSI reference signals (e.g., in DL subframes transmitted on a cellular cell in a shared spectrum band) is resolved by designating the first N subframes of a DL burst as subframes carrying CSI reference signals. The configuration of the specified N subframes and the CSI reference signal configuration(s) may be provided to the UE on a static or semi-static basis. In some examples, the configuration may indicate a set of CSI reference signals, ports, etc. that are common to each of the N subframes. In other examples, the configuration may indicate a set of CSI reference signals, ports, etc. for each of the N subframes (e.g., the set of CSI reference signals, ports, etc. may vary from subframe to subframe). In some cases, the UE may identify the start of a DL burst by detecting the transmission of a channel reservation signal (e.g., CUBS) and may then apply the CSI reference signal configuration to the next N subframes.

According to other aspects, ambiguity regarding the configuration of a CSI reference signal (e.g., in a DL subframe transmitted on a cell in a shared spectrum band) is resolved by explicitly indicating the configuration of the first subframe in the second subframe. This option may be referred to as cross-subframe indication of the CSI reference signal configuration and is described in more detail with reference to Figures 5A and 5B.

FIG5A illustrates an example 500 of a cross-subframe indication of a CSI reference signal configuration according to various aspects of the present disclosure. In example 500, an eNB may communicate with a UE across multiple cells, including a first cell 505 in a dedicated spectrum band and a second cell 510 in a shared spectrum band (and, in some cases, additional cells in either the dedicated spectrum band or the shared spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , FIG2 , FIG4A , and FIG4B .

As shown in FIG5A , the presence of a CSI reference signal in a set of one or more DL subframes 520 transmitted in a transmission opportunity on the second cell 510 may be indicated in a DL subframe 515 transmitted on the first cell 505 (e.g., by a reference signal subframe indicator) (e.g., the cross-subframe indication may be a cross-carrier indication). When the timing of the subframes transmitted on the first cell 505 and the second cell 510 is synchronized (e.g., when the subframes are aligned), the cross-subframe indication may include a relative indicator of the set of one or more DL subframes 520 (e.g., the DL subframe 515 may have a subframe index n, the set of one or more DL subframes 520 may begin at the DL subframe 525 having a subframe index n+m, and the cross-subframe indication may indicate a value m). In some examples, m may be any integer such that m may be equal to or less than 0. When m may be a negative integer, a UE receiving a DL subframe on the first cell 505 and the second cell 510 will buffer data for at least m subframes.

In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate the presence (or absence) of a CSI reference signal in a single DL subframe (e.g., a single DL subframe of the second cell 510 that is aligned with a DL subframe of the first cell 505). In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate the presence (or absence) of a CSI reference signal in N DL subframes, where N ≥ 1. However, when the cross-subframe indication is used to indicate the presence of a CSI reference signal in a DL subframe, the UE may still have to verify that the DL subframe is a valid DL subframe (e.g., the UE may have to verify that the eNB has won contention for access to the shared spectrum band).

In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate a selection from a set of possible CSI reference signal configurations. The cross-subframe indication may be indicated using a field of a DCI format included in a downlink control channel of the first cell 505 (e.g., similar to how an eIMTA configuration is indicated). The cross-subframe indication of the CSI reference signal configuration may also be indicated using different RNTIs known to a subset of UEs (or all UEs) associated with the eNB. In some cases, the timing reference used for the cross-subframe indication may be derived from the subframe in which the grant including the cross-subframe indication is decoded.

When the set of one or more DL subframes 520 is transmitted as part of an LBT transmission synchronized to one or more dynamic TTIs (rather than a periodic radio frame structure), a UE receiving the LBT transmission may identify that at least one dynamic TTI has asynchronous symbol timing relative to the first cell 505 and may determine a location (e.g., symbol position) of a CSI reference signal configuration based on a detected symbol preamble associated with the LBT transmission. In some variations of example 500, both the first cell 505 and the second cell 510 may be provided in a shared spectrum band.

FIG5B illustrates an example 550 of a cross-subframe indication of a CSI reference signal configuration according to various aspects of the present disclosure. In example 550, an eNB may communicate with a UE on a cell 555 in a shared spectrum band (and, in some cases, on additional cells in the shared spectrum band or one or more cells in a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , FIG2 , FIG4A , and FIG4B .

As shown in FIG5B , the presence of a CSI reference signal in a set of one or more DL subframes 560 transmitted in a transmission opportunity on a cell 555 may be indicated (e.g., by a reference signal subframe indicator therein) in another DL subframe 565 transmitted on the cell 555 (e.g., the cross-subframe indication may be self-scheduled). In some examples, the cross-subframe indication may include a relative indicator of the set of one or more DL subframes 560 (e.g., the DL subframe 565 may have a subframe index n, the set of one or more DL subframes 560 may begin at a DL subframe 570 having a subframe index n+m, and the cross-subframe indication may indicate a value of m).

In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate the presence (or absence) of a CSI reference signal in a single DL subframe (e.g., a single DL subframe aligned with the DL subframe of cell 555). In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate the presence (or absence) of a CSI reference signal in N DL subframes, where N ≥ 1. However, when the cross-subframe indication is used to indicate the presence of a CSI reference signal in a DL subframe, the UE may still have to verify that the DL subframe is a valid DL subframe (e.g., the UE may have to verify that the eNB has won contention for access to the shared spectrum band).

In some examples, the cross-subframe indicator of the CSI reference signal configuration may be provided in a UE-specific grant. In some examples, the cross-subframe indicator of the CSI reference signal configuration may be provided in a common grant (e.g., a PDSCH grant) or a physical layer channel transmission (e.g., similar to a physical frame format indicator channel (PFFICH)). In some examples, the cross-subframe indication of the CSI reference signal configuration may indicate a selection from a set of possible CSI reference signal configurations. The cross-subframe indicator may be indicated using a field of a DCI format included in a downlink control channel of the cell 555 (e.g., similar to how an eIMTA configuration is indicated).

When the eNB uses fixed DL subframes with dynamic TTIs (e.g., a TTI that may include portions of multiple DL subframes) to communicate with the UE, the cross-subframe indication of the CSI reference signal configuration may be used as described with reference to Figures 5A and 5B. When dynamic TTIs are used for transmission, the time reference used for the cross-subframe indication may be the time reference of the subframe in which the channel reservation signal (e.g., CUBS) is detected.

When communicating with a UE in a shared spectrum band, communication overhead can sometimes be reduced by transmitting a joint grant (e.g., a grant for resources in multiple cells, where these cells may be used in carrier aggregation or multi-connectivity operations). However, the joint grant may need to be prepared or transmitted before the eNB knows how many cells are available in the shared spectrum band (e.g., 1-2 milliseconds before the CCA procedure or ECCA procedure completes). As a result, the transmission of the joint grant may lead to ambiguity. This ambiguity may cause HARQ buffer corruption.

According to some aspects, ambiguity in the joint grant is resolved by preparing and transmitting individual grants (e.g., individual resource grants per cell) for N (N≥1) DL subframes transmitted at the beginning of a DL burst, and switching to transmitting the joint grant for DL subframes transmitted after these N DL subframes. Thus, individual grants can be transmitted for a set of cells that the eNB expects to use when transmitting a DL burst, and the joint grant can be transmitted for cells that are actually available and will be used. In this way, the unavailability of a cell for which a grant is sent only results in ambiguity regarding the portion of the transmission scheduled for the unavailable cell, and not regarding the portion of the transmission scheduled for other cells. However, if the individual grants are self-scheduled, the eNB's failure to win contention for access to the unavailable cell can result in the individual grant for the unavailable cell not being transmitted, completely removing the ambiguity.

FIG6 illustrates an example 600 of joint and individual grant transmission and processing according to various aspects of the present disclosure. In example 600, an eNB 105-f may communicate with a UE 115-g over a set of cells, including at least one cell in a shared spectrum band (and, in some cases, at least one cell in a shared spectrum band and at least one cell in a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , 2 , 4A , and 4B .

The eNB 105-f may prepare a number of individual grants for a first set of cells identified for use in LBT transmissions (eg, DL bursts in a transmission opportunity) at 605. The first set of cells may include at least one cell in a shared spectrum band.

The eNB 105-f may contend for access to the at least one cell in the shared spectrum band at 610. Upon winning or losing contention for access to each of the at least one cell in the shared spectrum band, the eNB 105-f may identify a second set of cells for use in the LBT transmission and may transmit a channel reservation signal (e.g., CUBS) on each cell in the second set of cells at 615. The second set of cells may include all cells in the first set of cells or, if contention for access to one or more cells in the shared spectrum band is not won, a subset of the cells in the first set of cells.

At 620, the eNB 105-f may transmit a first set of subframes for LBT transmission to the UE 115-g. The first set of subframes may be transmitted in the second set of cells and may include a first scheduling configuration for the first set of subframes. The first scheduling configuration may include one or more search spaces for the second set of cells, wherein the one or more search spaces carry at least individual grants intended for the second set of cells (the individual grants prepared at 605).

The UE 115-g may identify a first scheduling configuration for a first set of subframes for LBT transmission at 625. The UE 115-g may also process the first set of subframes according to the first scheduling configuration.

At 630, the eNB 105-f may prepare several joint grants for the second set of cells, and at 635, the eNB 105-f may transmit a second set of subframes for LBT transmission to the UE 115-g. The second set of subframes may be transmitted in the second set of cells and may include a second scheduling configuration for the second set of subframes. The second scheduling configuration may be conveyed via at least one search space of the second set of cells, wherein the at least one search space carries the joint grant(s) prepared at 630. The joint grant may be self-scheduled (i.e., the joint grant may be transmitted on the cell to which the joint grant corresponds), cross-scheduled (i.e., the joint grant may be transmitted on a cell other than the cell to which the joint grant corresponds), or carried within a joint search space of the second set of cells. In the cross-scheduling scenario, the cell to which the joint grant for the UE 115-g is transmitted may be determined at least in part based on a UE-specific identifier (e.g., an RNTI assigned to the UE 115-g). Joint grants for other UEs may be transmitted in the same cell or in different cells.Self-scheduling or cross-carrier scheduling of joint grants may be independent of the cell's configuration regarding individual scheduling.

At 640, the UE 115-g may identify a second scheduling configuration for a second set of subframes for LBT transmission. The UE 115-g may also process the second set of subframes according to the second scheduling configuration.

When communicating with a UE in a shared spectrum band, the timing of winning or losing contention for access to the shared spectrum band is not always predetermined and may vary (e.g., in situations where ECCA is performed). In some situations, contention for access to the shared spectrum band may be won close to the next subframe boundary, thereby reserving the shared spectrum band until the next subframe boundary and commencing transmission at the next subframe boundary, enabling subframe synchronization between licensed and unlicensed cells to be maintained at a relatively low cost. In other situations, contention for access to the shared spectrum band may be won well in advance of the next subframe boundary, such that reserving the shared spectrum band until the next subframe boundary and commencing transmission at the next subframe boundary represents a significant waste of resources. Such waste of resources may be exacerbated, for example, when the number of possible subframes (or TTIs) available for transmission is already small. For example, in some jurisdictions, the TTI for LTE/LTE-A transmissions is limited to 4 milliseconds (e.g., 4 subframes).

Partial subframe transmissions (e.g., transmissions that use less than the maximum transmission duration of a subframe or TTI) can be used to mitigate resource waste. However, the multiple potential start times and durations of partial subframes can be burdensome for the UE in terms of increased processing, power usage, etc. One way to reduce the burden that partial subframes place on the UE is to reduce the number of antenna ports that the UE has to monitor for control channel monitoring, as described in FIG7 .

7 shows a diagram 700 of a limited set of antenna ports for partial control channel monitoring according to various aspects of the present disclosure. The antenna port set of antenna ports 710-a, 710-b, 710-c, and 710-d can be mapped to a reference signal (e.g., UE-RS) of a downlink channel 705.

Before transmitting a DL subframe in a cell in the shared spectrum band, the eNB 105-g may contend for access to one or more cells in the shared spectrum band (e.g., by performing CCA or ECCA). Upon winning or losing contention for access to a cell in the shared spectrum band, the eNB 105 may transmit the DL subframe to the UE 115. Depending on when the eNB 105 wins or loses contention for access to a cell in the shared spectrum band, the DL subframe may be a full subframe or a partial subframe and may have the same or a different start time than other DL subframes. In some examples, the DL subframe may be transmitted using each antenna port in a first set of antenna ports including antenna ports 710-a, 710-b, 710-c, and 710-d. A control channel for the DL subframe (e.g., a PDCCH or EPDCCH for one or more cells of the shared spectrum band) may be modulated according to one of the antenna ports 710 and transmitted to the UE 115. Thus, the UE 115 may receive the control channel and decode the control channel by performing channel and interference estimation for the antenna ports and using the channel and interference estimates to demodulate the control channel candidates (eg, blindly decode the candidates).

Because a DL subframe can be a full subframe or a partial subframe and can have one of several different start times, the UE 115 may require a significant number of control channel search spaces for the control channel, including search spaces that occur in (or span) different time periods. Monitoring a large number of control channel search spaces can impose processing, power usage, and other burdens on the UE 115. However, these burdens can be alleviated by limiting the set of antenna ports 710 used to transmit the control channel. As shown in Figure 7, a limited set of antenna ports 720 is used, which includes antenna ports 710-a and 710-b. In LTE/LTE-A, antenna ports 107/108/109/110 can be defined for demodulating ePDCCH, and in some examples, the limited set of antenna ports 720 can correspond to antenna ports 107/108.

While monitoring a finite set of second antenna port sets (e.g., antenna ports 710-a and 710-b), UE 115 may estimate channel demodulation information (e.g., SNR or interference estimate) from the finite set of second antenna port sets, determine a control channel search space, and demodulate control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of second antenna port sets.

As previously discussed, the timing of winning or losing contention for access to the shared spectrum band is not always predetermined and may vary (e.g., in situations where ECCA is performed). This may result in situations where partial subframes are available for communication between eNBs or UEs. In some cases, partial subframes may be transmitted at the beginning of an LBT transmission. In other cases, and as described in more detail with reference to Figures 8A and 8B, partial subframes may be included in a dynamic (e.g., floating) TTI that is synchronized with the beginning of the LBT transmission, and in some of these cases, an extended TTI may be provided at the end of the LBT transmission, as described in more detail with reference to Figure 9. When using dynamic TTIs, components of the transmission (such as reference signals (CRS and UE-RS), PDCCH, and PCFICH) may be synchronized to subframe boundaries, but the PDSCH may be synchronized to a dynamic TTI, which may have a start time that depends on when the eNB wins or loses contention for access to the shared spectrum band. For example, when a subframe has a length or duration of 14 code period and contention for access to a shared spectrum band used to transmit the subframe is won in code period 8, the PDSCH of the subframe may be mapped to a dynamic TTI that starts in code period 8 and extends to code period 7 of the next subframe.

FIG8A illustrates an example 800 of dynamic TTI usage according to various aspects of the present disclosure. In example 800, an eNB may communicate with a UE on a cell 810 operating in a shared spectrum band (and, in some cases, on additional cells in a shared spectrum band or a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , 2, 3, 6, and 7.

As shown in FIG8A , communications in a cell 810 operating in a shared spectrum band may be synchronized to a periodic radio frame structure 805 and have static subframe positions (e.g., subframe positions with static boundaries such as boundaries 815 - a and 815 - b ). In some examples, the periodic radio frame structure 805 may be an LTE/LTE-A radio frame structure used by an LTE/LTE-A cell in a dedicated spectrum band.

Upon winning contention for access to cell 810 for an LBT transmission, the eNB may transmit a channel reservation signal 820 (e.g., CUBS) to reserve cell 810 for the LBT transmission. The channel reservation signal 820 may establish the timing of a dynamic TTI 830 corresponding to the LBT transmission (e.g., the timing of a leading boundary 825-a or a trailing boundary 825-b), as well as the leading boundary or trailing boundary of a shared data channel (e.g., a PDSCH) for the LBT transmission. The dynamic TTI 830 may include a shared data region, which may include a shared data channel and a search space 835 for a control channel (e.g., an EPDCCH). The leading and/or trailing boundaries of the search space 835 may be based, at least in part, on an offset 840 (e.g., a symbol offset) between the dynamic TTI 830 (e.g., the leading boundary 825-a of the dynamic TTI 830) and a boundary of a static subframe position (e.g., boundary 815-a). As shown and as an example, the offset 840 may indicate to the UE that the search space 835 for the control channel includes the same set of code element periods as the dynamic TTI 830 (e.g., the leading and trailing boundaries of the search space 835 for the control channel coincide with the leading and trailing boundaries 825-a and 825-b of the dynamic TTI 830).

While some transmissions during the dynamic TTI 830 may have timing synchronized to the dynamic TTI 830, other transmissions (e.g., reference signals (e.g., CRS and UE-RS) or PCFICH) may be transmitted at times synchronized (or fixed) with respect to static boundaries of the periodic radio frame structure 805.

Because dynamic TTI 830 is not aligned with the boundaries of static subframe structure 805, there may be ambiguity as to the CSI reference subframe (or reference timing) to be used for aperiodic CSI reporting. For example, when a control channel transmitted in search space 835 requests an aperiodic CSI report from a UE, there may be ambiguity at the UE as to whether subframe 845-a before boundary 815-a or subframe 845-b after boundary 815-a is to be used as the CSI reference subframe for the aperiodic CSI report. In some examples, this ambiguity may be resolved based on a timing parameter of the control channel relative to the subframe index of cell 810. For example, the timing parameter may be the last symbol period of the control channel transmitted in search space 835, and the CSI reference subframe may be the subframe in which the last symbol period of the control channel was transmitted, which in FIG8A is subframe 845-b.

When a UE receiving the LBT transmission shown in FIG8A is configured to operate in DRX mode, the UE may enter a disabled reception state (e.g., a dormant state) periodically or upon the occurrence of certain events or conditions. The UE may periodically awaken from the disabled reception state and enter an enabled reception state based on a paging occasion associated with the DRX configuration associated with cell 810. The beginning of the paging occasion may be synchronized to the beginning of a subframe of the periodic radio frame structure 805. When an LBT transmission is transmitted according to a dynamic TTI that is not synchronized to the periodic radio frame structure 805, and when the search space for control channels (e.g., search space 835) is synchronized to a dynamic TTI (e.g., dynamic TTI 830), the UE may awaken in the middle of an LBT transmission, be unaware of the start of the LBT transmission, and be unable to locate the search space for the control channel. To mitigate this, the eNB may transmit a CRS in the first symbol period of the UE's paging occasion (e.g., in the first symbol period of a subframe synchronized to the periodic radio frame structure 805). The eNB may also transmit an indication of the offset 840 in a static location of the UE's paging occasions. In some examples, the indication of the offset 840 may be transmitted in an indicator channel, in the same symbol period in which the CRS is transmitted, but using a tone not used to transmit the CRS.

FIG8B illustrates an example 850 of dynamic TTI usage according to various aspects of the present disclosure. In example 850, an eNB may communicate with a UE on a cell 860 operating in a shared spectrum band (and, in some cases, on additional cells in a shared spectrum band or a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , 2, 3, 6, and 7.

As shown in FIG8B , communications in a cell 860 operating in a shared spectrum band may be synchronized to a periodic radio frame structure 855 and have static subframe positions (e.g., subframe positions with static boundaries such as boundaries 865-a and 865-b). In some examples, the periodic radio frame structure 855 may be an LTE/LTE-A radio frame structure used by an LTE/LTE-A cell in a dedicated spectrum band.

Upon winning contention for access to cell 860 for an LBT transmission, the eNB may transmit a channel reservation signal 870 (e.g., CUBS) to reserve cell 860 for the LBT transmission. The channel reservation signal 870 may establish the timing of a dynamic TTI 880 corresponding to the LBT transmission (e.g., the timing of a leading boundary 875-a or a trailing boundary 875-b), as well as the leading boundary or trailing boundary of a shared data channel (e.g., a PDSCH) for the LBT transmission. The dynamic TTI 880 may include a shared data region, which may include a shared data channel and a search space 885 for a control channel (e.g., an EPDCCH). The leading and/or trailing boundaries of the search space 885 may be based, at least in part, on an offset 890 (e.g., a symbol offset) between the dynamic TTI 880 (e.g., the leading boundary 875-a of the dynamic TTI 880) and a boundary of a static subframe position (e.g., boundary 865-a). As shown and as an example, offset 890 can indicate to the UE that the search space 885 for the control channel includes a subset of symbol periods of the dynamic TTI 880. In some examples, the subset of symbol periods included in the search space 885 can be fixed with respect to a boundary of a static subframe location (e.g., boundaries 865-a and 865-b) (e.g., the location of the search space 885 can be fixed regardless of the timing of the dynamic TTI 880 relative to the static subframe location). As an example, FIG8B shows that the search space 885 includes 4 symbol periods before a static subframe boundary (e.g., boundary 865-a or 865-b).

In some examples, the number of symbol periods included in search space 885 for control channels or the location of search space 885 may be based on the presence of offset 890 and may include the same number of symbol periods regardless of the length of offset 890. In other examples, the number of symbol periods included in search space 885 for control channels or the location of search space 885 may vary based on the length of offset 890.

While some transmissions during the dynamic TTI 880 may have timing synchronized to the dynamic TTI 880, other transmissions (e.g., reference signals (e.g., CRS and UE-RS) or PCFICH) may be transmitted at times synchronized (or fixed) with respect to static boundaries of the periodic radio frame structure 855.

Because dynamic TTI 880 is not aligned with the boundaries of static subframe structure 855, there may be ambiguity as to the CSI reference subframe (or reference timing) to be used for aperiodic CSI reporting. For example, when a control channel transmitted in search space 885 requests an aperiodic CSI report from a UE, there may be ambiguity at the UE as to whether subframe 895-a before boundary 865-a or subframe 895-b after boundary 865-a is to be used as the CSI reference subframe for the aperiodic CSI report. In some examples, this ambiguity may be resolved based on a timing parameter of the control channel relative to the subframe index of cell 810. For example, the timing parameter may be the last symbol period of the control channel transmitted in search space 885, and the CSI reference subframe may be the subframe of the last symbol period in which the control channel is transmitted, which in FIG8B is subframe 895-a.

When a UE receiving the LBT transmission shown in FIG8B is configured to operate in DRX mode, the UE may enter a disabled reception state (e.g., a dormant state) periodically or upon the occurrence of certain events or conditions. The UE may periodically awaken from the disabled reception state and enter an enabled reception state based on a paging occasion associated with the DRX configuration associated with cell 860. The beginning of the paging occasion may be synchronized to the beginning of a subframe of the periodic radio frame structure 855. When an LBT transmission is transmitted according to a dynamic TTI that is not synchronized to the periodic radio frame structure 855, and when the search space for control channels (e.g., search space 885) is synchronized to a dynamic TTI (e.g., dynamic TTI 880), the UE may awaken in the middle of an LBT transmission, be unaware of the start of the LBT transmission, and be unable to locate the search space for the control channel. To mitigate this, the eNB may transmit a CRS in the first symbol period of the UE's paging occasion (e.g., in the first symbol period of a subframe synchronized to the periodic radio frame structure 855). The eNB may also transmit an indication of the offset 890 in a static location of the UE's paging occasion. In some examples, the indication of the offset 890 may be transmitted in an indicator channel, in the same symbol period in which the CRS is transmitted, but using a tone not used to transmit the CRS.

FIG9 illustrates an example 900 of dynamic TTI usage according to various aspects of the present disclosure. In example 900, an eNB may communicate with a UE on a cell 910 operating in a shared spectrum band (and, in some cases, on additional cells in a shared spectrum band or a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , 2, 3, 6, and 7.

As shown in FIG9 , communications in a cell 910 operating in a shared spectrum band may be synchronized to a periodic radio frame structure 905 and have static subframe positions (e.g., subframe positions with static boundaries such as boundaries 915 - a , 915 - b , and 915 - c ). In some examples, the periodic radio frame structure 905 may be an LTE/LTE-A radio frame structure used by an LTE/LTE-A cell in a dedicated spectrum band.

Upon winning contention for access to cell 910 for an LBT transmission, the eNB may transmit a channel reservation signal 920 (e.g., CUBS) to reserve cell 910 for the LBT transmission. The channel reservation signal 920 may establish the timing of a dynamic TTI 930 corresponding to the LBT transmission (e.g., the timing of a leading boundary 925-a or a trailing boundary 925-b), as well as the leading boundary or trailing boundary of a shared data channel (e.g., a PDSCH) for the LBT transmission. The dynamic TTI 930 may include a shared data region, which may include a shared data channel and a search space 935 for a control channel (e.g., a PDCCH or EPDCCH). The leading and/or trailing boundaries of the search space 935 may be based, at least in part, on an offset 940 (e.g., a symbol offset) between the dynamic TTI 930 (e.g., the leading boundary 925-a of the dynamic TTI 930) and a boundary of a static subframe position (e.g., boundary 915-a). As shown and as an example, the offset 940 may indicate to the UE that the search space 935 for the control channel includes the same set of code element periods as the dynamic TTI 930 (e.g., the leading and trailing boundaries of the search space 935 for the control channel coincide with the leading and trailing boundaries 925-a and 925-b of the dynamic TTI 930).

As also shown in FIG. 9 , in some cases, LBT transmission may terminate at a static boundary (e.g., boundary 915-c) at one of the subframe positions in periodic radio frame structure 905 (rather than at the end of a dynamic TTI). Sometimes, the length of a partial subframe resulting from terminating an LBT transmission at a static boundary (e.g., boundary 915-b) at one of the subframe positions may cause partial subframe 945 to have a length shorter than the minimum partial subframe length. In such cases, partial subframe 945 may be included in an extended TTI (e.g., extended TTI 950) that includes the partial subframe 945. If the minimum partial subframe length is 4 symbol periods, the length of the extended TTI may be 14, 15, 16, or 17 symbol periods. As an example, the length of extended TTI 950 is 16 symbol periods.

In some examples, a field included in at least one of the PFFICH or grant received in the control channel may signal the number of symbol periods of the extended (or last) TTI 950 for LBT transmission. In some examples, the extended TTI 950 may include a shared data region, where the shared data region may include a shared data channel and a search space 955 for a control channel (e.g., a PDCCH or EPDCCH). The leading and/or trailing boundaries of the search space 955 for the control channel may be based at least in part on the number of symbol periods in a non-extended TTI (or the number of symbol periods in a static subframe of the periodic radio frame structure 905). Alternatively, the leading and/or trailing boundaries of the search space 955 for the control channel may be based at least in part on the number of symbol periods included in the extended TTI 950. In the latter case, the symbol periods to which the search space 955 for the control channel is not mapped may, in some cases, carry only PDSCH data and CRS (e.g., no CSI-RS, etc.). The configuration of the search space 955 may be indicated to the UE and/or determined by the UE for rate matching purposes.

The eNB may periodically transmit a DRS on each of one or more cells. The DRS may be transmitted at a fixed location within the discovery window (e.g., at a fixed location based at least in part on the cell ID), or at one or more configurable locations within the discovery window. When the eNB transmits on multiple cells simultaneously, the eNB may also transmit a DRS simultaneously for each cell. However, when transmitting multiple DRSs in a shared spectrum band, the eNB may be required to implement an aggregate transmit power limit for the shared spectrum band, which requires the eNB to limit the power of simultaneous transmissions in the shared spectrum band. Thus, instead of transmitting each DRS in a cell of the shared spectrum band at maximum transmit power, each DRS may be limited to 25% or less of the maximum transmit power to meet the aggregate transmit power limit. Reducing the transmit power of each DRS may reduce the size of the coverage area in which the eNB can be found.

FIG10 illustrates an example 1000 of discovery window allocation within a DMTC period according to various aspects of the present disclosure. In example 1000, an eNB may communicate with a UE on a set of one or more cells (e.g., cells 1005, 1010, and 1015) in a shared spectrum band (and, in some cases, additional cells in a shared spectrum band or a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , FIG2 , FIG3 , FIG6 , and FIG7 .

As shown in FIG10 , a DMTC period 1020 may be associated with the set of cells 1005, 1010, and 1015. The DMTC period 1020 may be associated with all cells of all eNBs operating within the eNB network or cluster. Within the DMTC period 1020, a discovery window 1025 may be configured for eNBs communicating via the set of cells 1005, 1010, and 1015. In some examples, the discovery window 1025 may be a subframe. In some examples, the DMTC period 1020 may have a duration on the order of 40-80 milliseconds, and the discovery window 1025 may have a duration on the order of 5-10 milliseconds. Other non-overlapping or overlapping discovery windows may be configured for other eNBs.

In some examples, the eNBs communicating via the set of cells 1005, 1010, and 1015 may transmit DRS on each of these cells simultaneously, at a fixed location within the discovery window 1025, or at one or more configurable locations within the discovery window 1025. However, simultaneous DRS transmissions may be power limited by an aggregate transmit power limit. One way to mitigate the effects of the aggregate transmit power limit is to define a set of staggered DMTC periods for the cells 1005, 1010, and 1015. The staggered DMTC periods and the discovery windows therein may cause DRS transmitted in different cells to be transmitted at different times, thereby avoiding the need for the eNB to enforce aggregate transmit power limits for the shared spectrum band. Another way to mitigate the effects of the aggregate transmit power limit is described with reference to FIG.

FIG11 illustrates an example discovery window 1100 in which a DRS may be transmitted in each of a plurality of cells according to various aspects of the present disclosure. In discovery window 1100, an eNB may communicate with a UE on a set of one or more cells in a shared spectrum band (e.g., cells 1105, 1110, and 1115) (and, in some cases, additional cells in a shared spectrum band or a dedicated spectrum band). The eNB and UE may be examples of aspects of the eNB 105 or UE 115 described with reference to FIG1 , 2, 3, 6, and 7.

The discovery window 1100 may be an example of the discovery window 1000 described with reference to FIG10 and may be allocated within a DMTC period. A first DRS 1120 may be transmitted in a first cell 1105, a second DRS 1125 may be transmitted in a second cell 1110, and a third DRS 1130 may be transmitted in a third cell 1115. The starting symbol periods (or starting symbol offsets) of the first DRS 1120, the second DRS 1125, and the third DRS 1130 may be staggered so that the first DRS 1120, the second DRS 1125, and the third DRS 1130 do not overlap, thereby allowing each of the first DRS 1120, the second DRS 1125, and the third DRS 1130 to be transmitted at a maximum transmit power allowed by the aggregate transmit power limit of the shared spectrum band. In some examples, the position of the starting symbol of the DRS may be a function of the cell ID of the cell in which the DRS is transmitted. In some examples, the location of the starting symbols may be reused in different spectrum bands, where the different spectrum bands are associated with independent aggregate transmit power limits.

When transmission of DRS is multiplexed with transmission of a shared data channel (e.g., PDSCH) on one or more of cellular cells 1105, 1110 and 1115, the transmit power level of DRS can be set independently of the transmit power level of PDSCH, and when the transmit power level of DRS is too high to enable simultaneous transmission of PDSCH within the aggregate transmit power limit, the transmit power level of PDSCH can be reduced (or PSDSCH may not be transmitted).

FIG12 shows a block diagram of a wireless device 1200 configured for control flow enhancement for unlicensed LTE according to various aspects of the present disclosure. The wireless device 1200 may be an example of aspects of the UE 115 described with reference to FIG1-11. The wireless device 1200 may include a receiver 1205, an unlicensed cell control flow manager 1210, and a transmitter 1215. The wireless device 1200 may also include a processor. Each of these components may be in communication with each other.

The receiver 1205 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to control flow enhancements for unlicensed LTE). The information may be passed to the unlicensed cell control flow manager 1210 and to other components of the wireless device 1200.

The unlicensed cell control flow manager 1210 may perform the enhanced techniques described above for control flow processing for floating TTI operation in unlicensed cells, including ePDCCH processing, aperiodic CSI reporting, DRX operation, and extended TTI at the end of a transmission burst. The unlicensed cell control flow manager 1210 may also perform the enhanced techniques described above for reference signal configuration for unlicensed cells, processing of joint grants for multiple unlicensed cells, ePDCCH processing for partial subframes, and multi-channel DRS operation.

The transmitter 1215 may transmit signals received from other components of the wireless device 1200. In some examples, the transmitter 1215 may be co-located in a transceiver with the receiver 1205. The transmitter 1215 may include a single antenna, or it may include multiple antennas.

FIG13 shows a block diagram 1300 of an unlicensed cell control flow manager 1210-a, which may be a component of the wireless device 1200 for enhanced control flow for unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-a may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12. The unlicensed cell control flow manager 1210-a may include an unlicensed cell configuration identifier 1310, a transmission detector 1320, a reference signal receiver 1330, a reference signal processor 1340, a subframe detector 1350, and a CSI processor 1360. Each of these components may be in communication with one another.

The unlicensed cell configuration identifier 1310 may identify a configuration for communications using a secondary cell in a shared spectrum band, as described with reference to FIGs. 2-11.

The transmission detector 1320 may identify a transmission from the secondary cell that includes multiple subframes, as described with reference to FIGURES 2-11. The transmission may be the secondary cell data block 1315.

The reference signal receiver 1330 may receive a reference signal subframe indicator, as described with reference to FIG. 2-11 . The indicator may be an indicator data block 1325 . In some examples, the reference signal subframe indicator may be a cross-subframe indicator. In some examples, the cross-subframe indicator may be received on different secondary cells in a shared spectrum band. In some examples, the cross-subframe indicator may be received by a licensed cell operating in a dedicated spectrum band. In some examples, the cross-subframe indicator includes a field of a downlink control information (DCI) format received via a downlink control channel of the licensed cell. In some examples, the cross-subframe indicator may be received by the secondary cell in an indicator channel or on a field of a downlink control information (DCI) format received via a downlink control channel of the secondary cell.

The reference signal processor 1340 may determine a reference signal configuration for at least one subframe of the transmission based at least in part on a cross-subframe indicator, as described with reference to FIG. 2-11 . The indicator may be a reference signal subframe data block 1335 . In some examples, the determination includes identifying a set of subframes for initial transmission associated with the at least one reference signal configuration. The reference signal processor 1340 may also determine one or more symbol positions for at least one reference signal within the at least one subframe based at least in part on a detected preamble associated with the transmission.

The subframe detector 1350 may identify at least one subframe having asynchronous symbol timing relative to a licensed cell operating in a dedicated spectrum band, as described with reference to FIGs.

The CSI processor 1360 can measure the characteristics of the channel used by the UE for communication and then determine the CSI parameters for reporting. These parameters can be sent from the UE in the form of a CSI report. The CSI report can include a rank indicator (RI) requesting the number of layers to be used for DL transmission (e.g., based on the antenna ports of the UE 115), a precoding matrix indicator (PMI) indicating a preference for which precoder matrix should be used (based on the number of layers), or a channel quality indicator (CQI) indicating the highest modulation and coding scheme (MCS) that can be used. The CQI can be calculated by the UE 115 after receiving predetermined pilot symbols (such as CRS or CSI-RS). If the UE 115 does not support spatial multiplexing (or is not in a mode that supports spatial multiplexing), the RI and PMI can be excluded. The type of information included in the report determines the report type. CSI reports can be periodic or aperiodic.

FIG14 shows a block diagram 1400 of an unlicensed cell control flow manager 1210-b, which may be a component of the wireless device 1200 for enhanced control flow for unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-b may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-13. The unlicensed cell control flow manager 1210-b may include a transmission detector 1320-a, an LBT DCI processor 1410, an LBT joint grant processor 1420, and an LBT individual grant processor 1430. Each of these components may be in communication with one another.

The transmission detector 1320-a may identify a plurality of cells in a transmission from a base station on a shared spectrum band, wherein the transmission is subject to a listen-before-talk (LBT) procedure for a shared frequency channel, as described with reference to FIGURES 2-11. The transmission detector 1320-a may also determine a subset of cells in the plurality of cells that have associated frequency channels successfully reserved for the LBT transmission.

The LBT DCI processor 1410 may identify a first scheduling configuration 1415-a for a first set of subframes for an initial transmission of the transmission, the first scheduling configuration 1415-a including one or more search spaces for a first group of cells configured to carry individual grants for corresponding cells in the plurality of cells, as described with reference to FIGURES 2-11. The LBT DCI processor 1410 may also identify a second scheduling configuration 1415-b for a second set of subframes in the transmission that follows the first set of subframes, the second scheduling configuration 1415-b including at least one search space for at least one cell associated with a joint grant for the plurality of cells.

The LBT joint grant processor 1430 may process individual grants associated with the first scheduling configuration 1415-a.The LBT joint grant processor 1430 may output first resource allocation information 1425-a associated with a first set of subframes for the plurality of cells.

The LBT joint grant processor 1420 may process a joint grant associated with the second scheduling configuration 1415-b. In the case of cross scheduling, the LBT joint grant processor 1420 may also determine the at least one cell from the subset of the multiple cells based at least in part on a UE-specific identifier, as described with reference to FIG2-11. The UE-specific identifier may be an RNTI assigned to the UE. In some examples, the at least one cell includes a licensed cell operating in a dedicated spectrum band. The LBT joint grant processor 1430 may output second resource allocation information 1425-b associated with a second subframe set of the multiple cells. The first and second resource allocation information 1425-a, 1425-b may be used to receive and process data transmissions via the multiple cells.

FIG15 shows a block diagram 1500 of an unlicensed cell control flow manager 1210-c, which may be a component of a wireless device 1200 for control flow enhancement of unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-c may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-14. The unlicensed cell control flow manager 1210-c may include a channel demodulation estimator 1510 and an LBT DCI processor 1410-a. Each of these components may be in communication with one another.

The channel demodulation estimator 1510 may estimate channel demodulation information from a finite set of antenna ports associated with a control channel for one or more cells of a shared spectrum band, as described with reference to FIGs. 2-12.

The LBT DCI processor 1410-a may determine a control channel search space comprising partial subframes for the one or more cells, as described with reference to FIG. 2-11. The LBT DCI processor 1410-a may also use estimated channel demodulation information from the finite set of antenna ports to demodulate control channel candidates in the control channel search space. The estimated channel demodulation information may be a channel demodulation data block 1515. In some examples, the control channel comprises an enhanced physical downlink control channel (ePDCCH).

FIG16 shows a block diagram 1600 of an unlicensed cell control flow manager 1210-d, which may be a component of a wireless device 1200 for control flow enhancement of unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-d may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-15. The unlicensed cell control flow manager 1210-c may include an unlicensed cell configuration identifier 1310-a, a transmission detector 1320-b, an LBT dynamic TTI detector 1350-a, and an LBTDCI processor 1410-b.

The unlicensed cell configuration identifier 1310 - a may identify a configuration for communications using synchronized cells operating in a shared spectrum band and having static subframe positions, as described with reference to FIGs. 2-11 .

The transmission detector 1320 - b may identify listen-before-talk (LBT) transmissions for the synchronized cell, as described with reference to FIGURES 2-11.

The LBT dynamic TTI detector 1350 - a may determine the dynamic TTI of the shared data channel of the synchronized cell based at least in part on the channel reservation signal of the LBT transmission, as described with reference to FIGURES 2-11. The channel reservation signal of the LBT transmission may be a channel reservation signal block 1605.

The LBT DCI processor 1410-b may determine a search space for a control channel within a shared data region including a shared data channel based at least in part on an offset between the dynamic TTI and a boundary of a static subframe position, as described with reference to Figures 2-11. The determination may be based on a characteristic of the LBT transmission, which may be a transmission characteristic data block 1610. In some examples, the search space includes the same set of codewords as the dynamic TTI. In some examples, the search space includes a subset of codewords for the dynamic TTI, and wherein the subset of codewords for the dynamic TTI may be determined at least in part based on an offset between the dynamic TTI and a boundary of a static subframe position. In some examples, the control channel includes an ePDCCH. The LBT DCI processor 1410-b may also determine the number of codeword periods of the last TTI of the LBT transmission based at least in part on a field included in at least one of a physical frame format indicator channel (PFFICH) or a grant received in the control channel. The LBT DCI processor 1410-b may also determine a search space for a control channel for the last TTI based at least in part on at least one of a static number of symbol periods or a determined number of symbol periods.

FIG17 shows a block diagram 1700 of an unlicensed cell control flow manager 1210-e, which may be a component of the wireless device 1200 for control flow enhancement of unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-e may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-16. The unlicensed cell control flow manager 1210-e may include an unlicensed cell configuration identifier 1310-b, a transmission detector 1320-c, an LBT DCI processor 1410-c, and an LBT aperiodic CSI reference timing processor 1710.

The unlicensed cell configuration identifier 1310 - b may identify a configuration for communications using at least a first cell and a second cell, the second cell operating in a shared spectrum band, as described with reference to FIGs. 2-11 .

The transmission detector 1320 - c may identify transmissions for the second cell, as described with reference to FIGs. 2-11 .

The LBT DCI processor 1410 - c may receive a request for an aperiodic CSI report in a control channel of the second cell, as described with reference to FIGURES 2- 11. The request for an aperiodic CSI report may be a request block 1705.

LBT aperiodic CSI reference timing processor 1710 may determine a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell, as described with reference to FIG. 2-11 . In some examples, the timing parameter comprises the first symbol of the control channel or the last symbol of the control channel. In some examples, the control channel comprises a PDCCH or an ePDCCH. The timing parameter may be a timing parameter data block 1715.

FIG18 shows a block diagram 1800 of an unlicensed cell control flow manager 1210-f, which can be a component of a wireless device 1200 for control flow enhancement of unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-f can be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-17. The unlicensed cell control flow manager 1210-e can include an unlicensed cell configuration identifier 1310-c, a DRX paging controller 1810, and an LBT paging occasion offset identifier 1820.

The unlicensed cell configuration identifier 1310 - c may identify a configuration for communications using a cell operating in a shared spectrum band, as described with reference to FIGs. 2-11 .

The DRX paging controller 1810 may enable reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a DRX configuration associated with the cell, as described with reference to FIG. 2-11 . The DRX paging controller 1810 may also receive a CRS on a first symbol of the paging occasion. The paging occasion may be the paging occasion data block 1805.

LBT paging occasion offset identifier 1820 can identify a symbol offset for a control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion, as described with reference to FIG. 2-11 . In some examples, the control channel includes an ePDCCH. The symbol offset can be derived from channel characteristics block 1815 .

FIG19 shows a block diagram 1900 of an unlicensed cell control flow manager 1210-g, which may be a component of a wireless device 1200 for control flow enhancement of unlicensed LTE according to various aspects of the present disclosure. The unlicensed cell control flow manager 1210-g may be an example of aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12-18. The unlicensed cell control flow manager 1210-g may include an LBT DMTC processor 1910 and an LBT DRS timing processor 1920.

LBT DMTC processor 1910 may receive a discovery signal measurement timing configuration (DMTC) associated with one or more cells in a shared spectrum band, as described with reference to FIG. 2-11 . In some examples, the DMTC may be associated with multiple cells in the one or more cells. In some examples, the multiple cells include at least two cells in two different frequency bands, the two different frequency bands having independent aggregate transmit power limits. The DMTC may be DMTC data block 1905 .

The LBT DRS timing processor 1920 may determine a subframe associated with the DRS for the one or more cells, as described with reference to FIG. 2-11. The LBT DRS timing processor 1920 may also determine a starting symbol for the DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell. The cell identifier may be the cell identifier data block 1915.

FIG20 illustrates a diagram of a system 2000 including a UE 115 configured for control flow enhancement for unlicensed LTE, according to various aspects of the present disclosure. System 2000 may include a UE 115-i, which may be an example of a wireless device 1200 or a UE 115 as described with reference to FIG1 , FIG2 , and FIG12 - 19 . UE 115-i may include an unlicensed cell control flow manager 1210, which may include aspects of the unlicensed cell control flow manager 1210 described with reference to FIG12 - 19 . UE 115-i may also include components for two-way voice and data communication, including components for transmitting communications and components for receiving communications. For example, UE 115-i may engage in two-way communication with base station 105-h or UE 115-j.

UE 115-i may also include a processor 2005, as well as a memory 2015 (including software (SW) 2020), a transceiver 2035, and one or more antennas 2040, each of which may communicate with each other directly or indirectly (e.g., via a bus 2045). The transceiver 2035 may communicate bidirectionally with one or more networks via the antennas 2040 or a wired or wireless link, as described above. For example, the transceiver 2035 may communicate bidirectionally with a base station 105 or another UE 115. The transceiver 2035 may include a modem to modulate packets and provide the modulated packets to the antennas 2040 for transmission, and to demodulate packets received from the antennas 2040. Although the UE 115-i may include a single antenna 2040, the UE 115-i may also have multiple antennas 2040 capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 2015 may include random access memory (RAM) and read-only memory (ROM). The memory 2015 may store computer-readable, computer-executable software/firmware code 2020 including instructions that, when executed, cause the processor 2005 to perform the various functions described herein (e.g., control flow enhancements for unlicensed LTE, etc.). Alternatively, the software/firmware code 2020 may not be directly executable by the processor 2005, but (e.g., when compiled and executed) causes the computer to perform the functions described herein. The processor 2005 may include an intelligent hardware device (e.g., a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), etc.).

FIG21 shows a block diagram of a wireless device 2100 for control flow enhancement for unlicensed LTE according to various aspects of the present disclosure. The wireless device 2100 may be an example of aspects of the wireless device 2000 or base station 105 described with reference to FIG1-20. The wireless device 2100 may include a receiver 2105, an unlicensed cell control flow manager 2110, and a transmitter 2115. The wireless device 2100 may also include a processor. Each of these components may be in communication with one another. The unlicensed cell control flow manager 2110 may include an unlicensed cell DRS operator 2120, an unlicensed cell DRS transmitter 2130, and an unlicensed cell transmit power regulator 2140.

The receiver 2105 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to control flow enhancements for unlicensed LTE). The information may be passed to the unlicensed cell control flow manager 2110 and to other components of the wireless device 2100.

The unlicensed cell DRS operator 2120 may operate multiple cells on a shared spectrum band, wherein DRSs of the multiple cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the multiple cells is transmitted with a different start symbol offset, as described with reference to FIG. 2-19 .

The unlicensed cell DRS transmitter 2130 may transmit the DRS for each of the plurality of cells at a DRS power level that is independent of the transmit power level of the shared data channel for each of the plurality of cells, as described with reference to FIGs. 2-19.

The unlicensed cell transmit power adjuster 2140 may adjust the transmit power level of the shared data channel for each of the plurality of cells based at least in part on the DRS power level and the predefined transmit power level, as described with reference to FIGs. 2-19.

The transmitter 2115 may transmit signals received from other components of the wireless device 2100. In some examples, the transmitter 2115 may be co-located in a transceiver with the receiver 2105. The transmitter 2115 may include a single antenna, or it may include multiple antennas.

FIG22 illustrates a diagram of a system 2200 including a base station 105 configured for control flow enhancement for unlicensed LTE, in accordance with various aspects of the present disclosure. System 2200 may include base station 105-i, which may be an example of wireless device 1600, wireless device 1700, or base station 105 as described with reference to FIG1 , FIG2 , and FIG1 6 - 18. Base station 105-i may include an unlicensed cell control flow manager 2110-a, which may be an example of unlicensed cell control flow manager 2110-a as described with reference to FIG21. Base station 105-i may also include components for bidirectional voice and data communication, including components for transmitting communications and components for receiving communications. For example, base station 105-i may communicate bidirectionally with UE 115-k or UE 115-1.

In some cases, base station 105-i may have one or more wired backhaul links. Base station 105-i may have a wired backhaul link (e.g., an S1 interface, etc.) to core network 130-a. Base station 105-i may also communicate with other base stations 105 (such as base station 105-m and base station 105-n) via an inter-base station backhaul link (e.g., an X2 interface). Each base station 105 may communicate with UE 115 using the same or different wireless communication technologies. In some cases, base station 105-i may utilize base station communication manager 2225 to communicate with other base stations (such as 105-m or 105-n). In some examples, base station communication manager 2225 may provide an X2 interface within the LTE/LTE-A wireless communication network technology to provide communication between some base stations 105. In some examples, base station 105-i may communicate with other base stations via core network 130. In some cases, base station 105-i may communicate with core network 130 via network communication manager 2230.

The base station 105-i may include a processor 2205, a memory 2215 (including software (SW) 1920), a transceiver 2235, and an antenna 2240, each of which may communicate directly or indirectly with one another (e.g., via a bus system 2245). The transceiver 2235 may be configured to communicate bidirectionally with the UE 115 (which may be a multi-mode device) via the antenna 2240. The transceiver 2235 (or other components of the base station 105-i) may also be configured to communicate bidirectionally with one or more other base stations (not shown) via the antenna 2240. The transceiver 2235 may include a modem configured to modulate packets and provide the modulated packets to the antenna 2240 for transmission, and to demodulate packets received from the antenna 2240. The base station 105-i may include multiple transceivers 2235, each having one or more associated antennas 2240.

The memory 2215 may include RAM and ROM. The memory 2215 may also store computer-readable, computer-executable software code 2220 containing instructions that, when executed, are configured to cause the processor 2205 to perform the various functions described herein (e.g., control flow enhancement for unlicensed LTE, selection of coverage enhancement technology, call processing, database management, message routing, etc.). Alternatively, the software 2220 may not be directly executable by the processor 2205, but is configured to cause the computer to perform the functions described herein (e.g., when compiled and executed). The processor 2205 may include an intelligent hardware device, such as a CPU, a microcontroller, an ASIC, etc. The processor 1105 may include various specialized processors, such as an encoder, a queue processing module, a baseband processor, a radio head controller, a digital signal processor (DSP), etc.

The base station communication manager 2225 may manage communications with other base stations 105. In some cases, the base station communication manager may include a controller or scheduler for controlling communications with the UE 115 in coordination with the other base stations 105. For example, the base station communication manager 2225 may coordinate the scheduling of transmissions to the UE 115 for various interference mitigation techniques, such as beamforming or joint transmission.

The components of the wireless device 2100 and the unlicensed cell control flow manager 2110 may be implemented individually or collectively using at least one ASIC adapted to perform some or all applicable functions in hardware. Alternatively, these functions may be performed by one or more other processing units (or cores) on at least one IC. In other examples, other types of integrated circuits (e.g., structured/platform ASICs, field programmable gate arrays (FPGAs), or other semi-custom ICs) that can be programmed in any manner known in the art may be used. The functionality of each unit may also be implemented in whole or in part using instructions stored in memory and formatted to be executed by one or more general-purpose or application-specific processors.

FIG23 shows a flow chart illustrating a method 2300 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2300 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2300 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below.

At block 2305, the UE 115 may identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for a shared frequency channel, as described with reference to Figures 2-20. In some examples, the operations of block 2305 may be performed by the unlicensed cell configuration identifier 1310, as described with reference to Figure 13.

At block 2310, the UE 115 may identify a transmission comprising a plurality of subframes from the secondary cell, as described with reference to FIGs. 2-20. In some examples, the operations of block 2310 may be performed by the transmission detector 1320 as described with reference to FIG.

At block 2315, UE 115 may determine a reference signal configuration for at least one subframe of the transmission based at least in part on the cross-subframe indicator, as described with reference to FIGs. 2-20. In some examples, the operations of block 2315 may be performed by reference signal receiver 1330 as described with reference to FIG.

FIG24 shows a flow chart illustrating a method 2400 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2400 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2400 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 2400 may also incorporate aspects of method 2300 of FIG23.

At block 2405, the UE 115 may identify a configuration for communications using a secondary cell in a shared spectrum band, wherein transmissions via the secondary cell are subject to a listen-before-talk (LBT) procedure for the shared frequency channel, as described with reference to Figures 2-20. In some examples, the operations of block 2405 may be performed by the unlicensed cell configuration identifier 1310, as described with reference to Figure 13.

At block 2410, UE 115 may identify a transmission including at least one subframe from the secondary cell, as described with reference to Figures 2-20. In some examples, the operations of block 2410 may be performed by transmission detector 1320, as described with reference to Figure 13.

At block 2415, UE 115 may determine a reference signal configuration for the transmission based at least in part on the cross-subframe indicator of at least one subframe, as described with reference to FIGs. 2-18. In some examples, the operations of block 2415 may be performed by reference signal receiver 1330 as described with reference to FIG.

At block 2420, UE 115 may identify at least one subframe having asynchronous symbol timing relative to a licensed cell operating in a dedicated spectrum band, as described with reference to FIGs. 2-18. In some examples, the operations of block 2420 may be performed by subframe detector 1350 as described with reference to FIG.

At block 2425, UE 115 may determine one or more symbol positions for at least one reference signal within the at least one subframe based at least in part on the detected symbol preamble associated with the transmission, as described with reference to FIGs. 2-20. In some examples, the operations of block 2425 may be performed by reference signal receiver 1330 as described with reference to FIG.

FIG25 shows a flow chart illustrating a method 2500 for enhanced control flow for unlicensed LTE according to various aspects of the present disclosure. The operations of the method 1600 may be implemented by the UE 115 or its components as described with reference to FIG1-15. For example, the operations of the method 1600 may be performed by the unlicensed cell control flow manager 1210 as described with reference to FIG12-19. In some examples, the UE 115 may execute a set of codes for controlling the functional elements of the UE 115 to perform the functions described below. Additionally or alternatively, the UE 115 may use dedicated hardware to perform aspects of the functions described below.

At block 2505, the UE 115 may identify a plurality of cells in a transmission from a base station on a shared spectrum band, wherein the transmission is subject to a listen-before-talk (LBT) procedure for a shared frequency channel, as described with reference to FIG. 2-11. In some examples, the operations of block 2505 may be performed by a transmission detector 1320-a, as described with reference to FIG. 14.

At block 2510, the UE 115 may identify a first scheduling configuration for a first set of subframes for an initial transmission of the transmission, the first scheduling configuration including one or more search spaces configured to carry individual grants for a first set of cells in the plurality of cells, as described with reference to FIG. 2-11. In some examples, the operations of block 2510 may be performed by the LBT DCI processor 1410 as described with reference to FIG. 14.

At block 2515, the UE 115 may identify a second scheduling configuration for a second set of subframes subsequent to the first set of subframes in the transmission, the second scheduling configuration including at least one search space for at least one cell associated with the joint grant for the plurality of cells, as described with reference to FIG. 2-11. In some examples, the operations of block 2515 may be performed by the LBT DCI processor 1410 as described with reference to FIG. 13.

FIG26 shows a flow chart illustrating a method 2600 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2600 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2600 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 2600 may also incorporate aspects of methods 2300, 2400, and 2500 of FIGs. 23-25.

At block 2605, UE 115 may identify a configuration for communications using a secondary cell in a shared spectrum band, as described with reference to Figures 2-20. In some examples, the operations of block 2605 may be performed by unlicensed cell configuration identifier 1310 as described with reference to Figure 13.

At block 2610, the UE 115 may identify an LBT transmission from the secondary cell comprising at least one TTI, as described with reference to FIGs. 2-20. In some examples, the operations of block 2610 may be performed by the transmission detector 1320 as described with reference to FIG.

At block 2625, UE 115 may estimate channel demodulation information from a finite set of antenna ports associated with control channels for one or more cells of a shared spectrum band, as described with reference to Figures 2-20. In some examples, the operations of block 2625 may be performed by channel demodulation estimator 1510, as described with reference to Figure 15.

At block 2630, the UE 115 may determine a control channel search space comprising partial subframes for the one or more cells, as described with reference to FIG. 2-18. In some examples, the operations of block 2630 may be performed by the LBT DCI processor 1410-a as described with reference to FIG.

At block 2635, the UE 115 may demodulate the control channel candidates in the control channel search space using the channel demodulation information estimated from the finite set of antenna ports, as described with reference to FIGURES 2-18. In some examples, the operations of block 2635 may be performed by the LBT DCI processor 1410-a as described with reference to FIGURE 15.

FIG27 shows a flow chart illustrating a method 2700 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2700 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2700 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 2700 may also incorporate aspects of methods 2300, 2400, 2500, and 2600 of FIGs. 23-26.

At block 2705, UE 115 may identify a configuration for communications using a secondary cell in a shared spectrum band, as described with reference to FIGs. 2-18. In some examples, the operations of block 2705 may be performed by unlicensed cell configuration identifier 1310 as described with reference to FIG.

At block 2710, the UE 115 may identify an LBT transmission from the secondary cell comprising at least one TTI, as described with reference to FIGs. 2-18. In some examples, the operations of block 2710 may be performed by the transmission detector 1320 as described with reference to FIG.

At block 2715, the UE 115 may determine a plurality of reference signal configurations for the LBT transmission, as described with reference to FIGs. 2-18. In some examples, the operations of block 2715 may be performed by the LBT TTI RS mapper 1330-a as described with reference to FIG.

At block 2720, UE 115 may determine a subset of cells in the plurality of cells that have associated frequency channels successfully reserved for the LBT transmission, as described with reference to FIGs. 2-18. In some examples, the operations of block 2720 may be performed by transmission detector 1320 as described with reference to FIG.

At block 2725, the UE 115 may identify a configuration for communications using synchronized cells operating in a shared spectrum band and having static subframe positions, as described with reference to FIGURES 2-18. In some examples, the operations of block 2725 may be performed by the unlicensed cell configuration identifier 1310, as described with reference to FIGURE 13.

At block 2730, the UE 115 may identify LBT transmissions for the synchronized cell, as described with reference to FIGs. 2-18. In some examples, the operations of block 2730 may be performed by the transmission detector 1320, as described with reference to FIG.

At block 2735, the UE 115 may determine a dynamic TTI for the shared data channel of the synchronized cell based at least in part on the channel reservation signal transmitted by the LBT, as described with reference to FIG. 2-18. In some examples, the operations of block 2735 may be performed by the LBT dynamic TTI detector 1350-a as described with reference to FIG.

At block 2740, UE 115 may determine a search space for a control channel within a shared data region including a shared data channel based at least in part on an offset between the dynamic TTI and a boundary of a static subframe position, as described with reference to FIGURES 2-18. In some examples, the operations of block 2740 may be performed by LBT DCI processor 1410-b as described with reference to FIGURE 16.

FIG28 shows a flow chart illustrating a method 2800 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2800 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2800 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 2800 may also incorporate aspects of methods 2300, 2400, 2500, 2600, and 2700 of FIGs. 23-27.

At block 2805, the UE 115 may identify a configuration for communications using synchronized cells operating in a shared spectrum band and having static subframe positions, as described with reference to Figures 2-20. In some examples, the operations of block 2805 may be performed by the unlicensed cell configuration identifier 1310-a, as described with reference to Figure 16.

At block 2810, the UE 115 may identify LBT transmissions for the synchronized cell, as described with reference to FIGs. 2-20. In some examples, the operations of block 2810 may be performed by a transmission detector 1320-b as described with reference to FIG.

At block 2815, the UE 115 may determine a dynamic TTI for the shared data channel of the synchronized cell based at least in part on the channel reservation signal transmitted by the LBT, as described with reference to FIG. 2-20 . In some examples, the operations of block 2815 may be performed by the LBT dynamic TTI detector 1350 - a as described with reference to FIG. 16 .

At block 2820, UE 115 may determine a search space for a control channel within a shared data region including a shared data channel based at least in part on an offset between the dynamic TTI and a boundary of a static subframe position, as described with reference to FIGURES 2-20. In some examples, the operations of block 2820 may be performed by LBT DCI processor 1410-b as described with reference to FIGURE 16.

At block 2825, the UE 115 may determine the number of symbol periods of the last TTI of the LBT transmission based at least in part on a field included in at least one of a physical frame format indicator channel (PFFICH) or a grant received in the control channel, as described with reference to FIG. 2-20 . In some examples, the operations of block 2825 may be performed by the LBT dynamic TTI detector 1350 - a as described with reference to FIG. 16 .

FIG29 shows a flow diagram illustrating a method 2900 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 2900 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 2900 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 2900 may also incorporate aspects of methods 2300, 2400, 2500, 2600, 2700, and 2800 of FIGs. 23-28.

At block 2905, the UE 115 may identify a configuration for communications using at least a first cell and a second cell, the second cell operating in a shared spectrum band, as described with reference to FIG. 2-18 . In some examples, the operations of block 2905 may be performed by the unlicensed cell configuration identifier 1310 - b as described with reference to FIG. 17 .

At block 2910, the UE 115 may identify an LBT transmission from the second cell, as described with reference to FIGs. 2-20. In some examples, the operations of block 2910 may be performed by a transmission detector 1320-c, as described with reference to FIG.

At block 2915, the UE 115 may receive a request for an aperiodic CSI report in a control channel of the second cell, as described with reference to FIGs. 2-20. In some examples, the operations of block 2915 may be performed by the LBTDCI processor 1410-c as described with reference to FIG.

At block 2920, the UE 115 may determine a reference timing for the aperiodic CSI report based at least in part on a timing parameter of the control channel relative to a subframe index of the first cell, as described with reference to FIGs. 2-20. In some examples, the operations of block 2920 may be performed by the LBT aperiodic CSI reference timing processor 1710, as described with reference to FIG. 17.

FIG30 shows a flow chart illustrating a method 3000 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of method 3000 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-22. For example, the operations of method 3000 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 3000 may also incorporate aspects of methods 2300, 2400, 2500, 2600, 2700, 2800, and 2900 of FIGs. 23-29.

At block 3005, the UE 115 may identify a configuration for communications using a cell operating in a shared spectrum band, as described with reference to Figures 2-18. In some examples, the operations of block 3005 may be performed by an unlicensed cell configuration identifier 1310-c as described with reference to Figure 18.

At block 3010, the UE 115 may enable reception for the cell from a disabled reception state based at least in part on a paging occasion associated with a DRX configuration associated with the cell, as described with reference to Figures 2-18. In some examples, the operations of block 3010 may be performed by the DRX paging controller 1810 as described with reference to Figure 18.

At block 3015, the UE 115 may receive the CRS on the first symbol of the paging occasion, as described with reference to FIGURES 2-18. In some examples, the operations of block 3015 may be performed by the LBT TTI RS mapper 1330-a as described with reference to FIGURE 18.

At block 3020, the UE 115 may identify a symbol offset for the control channel of the cell based at least in part on an indicator channel having a static position within the paging occasion, as described with reference to FIGs. 2-18. In some examples, the operations of block 3020 may be performed by the LBT paging occasion offset identifier 1820 as described with reference to FIG.

FIG31 shows a flow chart illustrating a method 3100 for control flow enhancement for unlicensed LTE according to various aspects of the present disclosure. The operations of method 3100 may be implemented by UE 115 or components thereof as described with reference to FIGs. 1-19. For example, the operations of method 3100 may be performed by unlicensed cell control flow manager 1210 as described with reference to FIGs. 12-19. In some examples, UE 115 may execute code sets for controlling functional elements of UE 115 to perform the functions described below. Additionally or alternatively, UE 115 may use dedicated hardware to perform aspects of the functions described below. Method 3100 may also incorporate aspects of methods 2300, 2400, 2500, 2600, 2700, 2800, 2900, and 3000 of FIGs. 23-30.

At block 3105, the UE 115 may receive a discovery signal measurement timing configuration (DMTC) associated with one or more cells of the shared spectrum band, as described with reference to Figures 2-11. In some examples, the operations of block 3105 may be performed by the unlicensed cell configuration identifier 1310-d, as described with reference to Figure 19.

At block 3110, the UE 115 may determine subframes associated with the DRS for the one or more cells, as described with reference to Figures 2-11. In some examples, the operations of block 3110 may be performed by the LBT DMTC processor 1910, as described with reference to Figure 19.

At block 3115, UE 115 may determine a starting symbol for a DRS for at least one of the one or more cells within the subframe based at least in part on a cell identifier associated with the at least one cell, as described with reference to FIGs. 2-11. In some examples, the operations of block 3115 may be performed by LBTDRS timing processor 1920, as described with reference to FIG.

FIG32 shows a flow chart illustrating a method 3200 for control flow enhancements for unlicensed LTE according to various aspects of the present disclosure. The operations of the method 3200 may be implemented by the UE 115 or its components as described with reference to FIGs. 1-19. For example, the operations of the method 3200 may be performed by the unlicensed cell control flow manager 2110 as described with reference to FIGs. 21-22. In some examples, the UE 115 may execute a set of codes for controlling the functional elements of the UE 115 to perform the functions described below. Additionally or alternatively, the UE 115 may use dedicated hardware to perform aspects of the functions described below.

At block 3205, the UE 115 may operate multiple cells on a shared spectrum band, wherein DRSs for the multiple cells are transmitted according to a shared discovery signal measurement timing configuration (DMTC), and wherein each of the multiple cells is transmitted with a different starting symbol offset, as described with reference to FIG. 2-11. In some examples, the operations of block 3205 may be performed by the unlicensed cell DRS operator 2120 as described with reference to FIG. 21.

At block 3210, the UE 115 may transmit a DRS for each of the multiple cells at a DRS power level that is independent of a transmit power level of a shared data channel for each of the multiple cells, as described with reference to Figures 2-11. In some examples, the operations of block 3210 may be performed by the unlicensed cell DRS transmitter 2130 as described with reference to Figure 21.

At block 3215, the UE 115 may adjust the transmit power level of the shared data channel for each of the plurality of cells based at least in part on the DRS power level and the predefined transmit power level, as described with reference to FIGs. 2-11. In some examples, the operations of block 3215 may be performed by the unlicensed cell transmit power adjuster 2140, as described with reference to FIG.

Thus, methods 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, and 3200 may provide control flow enhancements for unlicensed LTE. It should be noted that methods 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, and 3200 describe possible implementations, and that these operations and steps may be rearranged or otherwise modified to enable other implementations. In some examples, aspects of two or more of methods 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, and 3200 may be combined.

The description herein provides examples and does not limit the scope, applicability, or examples set forth in the claims. The functions and arrangements of the elements discussed may be changed without departing from the scope of this disclosure. Various examples may appropriately omit, substitute, or add various procedures or components. In addition, features described with reference to some examples may be combined in other examples.

The techniques described herein can be used in various wireless communication systems, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and other systems. The terms "system" and "network" are often used interchangeably. A code division multiple access (CDMA) system can implement radio technologies such as CDMA2000 and Universal Terrestrial Radio Access (UTRA). CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 versions 0 and A are often referred to as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is often referred to as CDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other CDMA variants. A time division multiple access (TDMA) system can implement radio technologies such as Global System for Mobile Communications (GSM). Orthogonal Frequency Division Multiple Access (OFDMA) systems can implement radio technologies such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, and the like. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-a) are new versions of the Universal Mobile Telecommunications System (UMTS) that use E-UTRA. UTRA, E-UTRA, the Universal Mobile Telecommunications System (UMTS), LTE, LTE-a, and Global System for Mobile Communications (GSM) are described in documents from an organization called the 3rd Generation Partnership Project (3GPP). CDMA2000 and UMB are described in documents from an organization called the 3rd Generation Partnership Project 2 (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned above as well as for other systems and radio technologies. However, the description herein describes an LTE system for example purposes, and LTE terminology is used in much of the description above, but the techniques may also be applicable to applications other than LTE applications.

In LTE/LTE-a networks (including such networks described herein), the term evolved Node B (eNB) may be generally used to describe a base station. One or more wireless communication systems described herein may include heterogeneous LTE/LTE-A networks in which different types of eNBs provide coverage for various geographic regions. For example, each eNB or base station may provide communication coverage for a macro cell, a small cell, or other types of cells. Depending on the context, the term "cell" is a 3GPP term that may be used to describe a base station, a carrier or component carrier associated with a base station, or a coverage area (e.g., a sector, etc.) of a carrier or base station.

A base station may include or may be referred to by those skilled in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a Node B, an evolved Node B (eNB), a Home Node B, a Home evolved Node B, or some other suitable term. The geographic coverage area of a base station may be divided into sectors that constitute only a portion of the coverage area. One or more wireless communication systems described herein may include different types of base stations (e.g., macro or small cell base stations). The UEs described herein may be able to communicate with various types of base stations and network equipment (including macro eNBs, small cell eNBs, relay base stations, etc.). There may be overlapping geographic coverage areas of different technologies.

A macro cell generally covers a relatively large geographic area (e.g., an area with a radius of several kilometers) and may allow unrestricted access by UEs with service subscriptions with a network provider. In contrast to a macro cell, a small cell is a low-power base station that may operate in the same or different frequency bands (e.g., licensed, unlicensed, etc.) as the macro cell. According to various examples, small cells may include pico cells, femto cells, and micro cells. A pico cell, for example, may cover a smaller geographic area and may allow unrestricted access by UEs with service subscriptions with a network provider. A femto cell may also cover a smaller geographic area (e.g., a residence) and may provide restricted access by UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs of users in the residence, etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or more (e.g., two, three, four, etc.) cells (e.g., component carriers). A UE may be able to communicate with various types of base stations and network equipment, including macro eNBs, small cell eNBs, relay base stations, etc.

One or more wireless communication systems described herein may support synchronous or asynchronous operation. For synchronous operation, each base station may have similar frame timing, and transmissions from different base stations may be approximately aligned in time. For asynchronous operation, each base station may have different frame timing, and transmissions from different base stations may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operation.

The downlink transmission described herein may also be referred to as forward link transmission, and the uplink transmission may also be referred to as reverse link transmission. Each communication link described herein, such as the wireless communication systems 100 and 200 of Figures 1 and 2, may include one or more carriers, where each carrier may be a signal composed of multiple subcarriers (e.g., a waveform signal of a different frequency). Each modulated signal may be sent on a different subcarrier and may carry control information (e.g., a reference signal, a control channel, etc.), overhead information, user data, etc. The communication links described herein (e.g., the communication link 125 of Figure 1) may use frequency division duplex (FDD) operation (e.g., using paired spectrum resources) or time division duplex (TDD) operation (e.g., using unpaired spectrum resources) to transmit bidirectional communications. A frame structure for frequency division duplex (FDD) (e.g., frame structure type 1) and a frame structure for TDD (e.g., frame structure type 2) may be defined.

The description set forth herein in conjunction with the accompanying drawings describes example configurations and does not represent all examples that can be implemented or fall within the scope of the claims. The term "exemplary" as used herein means "serving as an example, instance, or illustration" and does not mean "better than" or "better than other examples." This detailed description includes specific details to provide an understanding of the described techniques. However, these techniques can be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form to avoid obscuring the concepts of the described examples.

In the accompanying drawings, similar components or features may have the same reference number. In addition, components of the same type may be distinguished by following the reference number with a dash and a second reference number that distinguishes between the similar components. If only the first reference number is used in the specification, the description applies to any of the similar components having the same first reference number, regardless of the second reference number.

The information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in conjunction with the disclosure herein may be implemented or executed with a general purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, each function may be stored on or transmitted by a computer-readable medium as one or more instructions or codes. Other examples and implementations fall within the scope of this disclosure and the appended claims. For example, due to the nature of software, the functions described above may be implemented using software executed by a processor, hardware, firmware, hardwiring, or any combination thereof. Features that implement the functions may also be physically located in various locations, including being distributed so that parts of the functions are implemented at different physical locations. In addition, as used herein (including in the claims), "or" used in an enumeration of items (e.g., an enumeration of items with a phrase such as "at least one of" or "one or more of") indicates an inclusive enumeration, such that, for example, an enumeration of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

Computer-readable media include both non-transient computer storage media and communication media, which include any media that facilitates a computer program to be transferred from one place to another. Non-transient storage media can be any available medium that can be accessed by a general or special-purpose computer. As an example and not limitation, non-transient computer-readable media may include RAM, ROM, electrically erasable programmable read-only memory (EEPROM), compact disc (CD) ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other non-transient medium that can be used to carry or store the desired program code means of an instruction or data structure form and can be accessed by a general or special-purpose computer or a general or special-purpose processor. Any connection is also properly referred to as a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves, then the coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves are included in the definition of medium. Disk and disc, as used herein, include CDs, laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

The description herein is provided to enable those skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be apparent to those skilled in the art, and the universal principles defined herein may be applied to other variations without departing from the scope of the present disclosure. Thus, the present disclosure is not limited to the examples and designs described herein, but should be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims (14)

1. A method for conducting wireless communication at a user equipment (UE), comprising: The configuration identifies the use of secondary cells in a shared spectrum band for communication, wherein transmissions via said secondary cells are subject to the Listen-Before-Talk (LBT) protocol of the shared frequency channel; Receive transmissions comprising multiple subframes from the subcell; and The reference signal configuration of at least one subframe of the transmission is determined at least in part based on a cross-subframe indicator received in the subframe, the cross-subframe indicator indicating the value of the subframe offset between the subframe in which the cross-subframe indicator is received and the at least one subframe. 2. The method as described in claim 1, wherein the cross-subframe indicator is received on different sub-cells of the shared spectrum band. 3. The method as claimed in claim 1, wherein the cross-subframe indicator is received on a licensed cell operating in a dedicated spectrum band. 4. The method of claim 3, wherein the cross-subframe indicator includes a field in the format of downlink control information (DCI) received via the downlink control channel of the licensed cell. 5. The method as claimed in claim 1, wherein the cross-subframe indicator is received by the subcell in the indicator channel or in a field of downlink control information (DCI) format received via the downlink control channel of the subcell. 6. The method of claim 1, further comprising: The at least one subframe is identified as having asynchronous symbol timing relative to a licensed cell operating in a dedicated spectrum band; and The positions of one or more symbols for at least one reference signal within the at least one subframe are determined based on the detected symbol preamble associated with the transmission. 7. An apparatus for performing wireless communication at a user equipment (UE), comprising: A means for identifying the configuration of communications using secondary cells in a shared spectrum band, wherein transmissions via said secondary cells are subject to the Listen-Before-Talk (LBT) protocol of the shared frequency channel. A means for receiving a transmission comprising multiple subframes from the subcell; and A means for determining a reference signal configuration of at least one subframe of the transmission based at least in part on a cross-subframe indicator received in a subframe, the cross-subframe indicator indicating a value of a subframe offset between the subframe in which the cross-subframe indicator is received and the at least one subframe. 8. The apparatus of claim 7, wherein the device identifier for determination is associated with the initial transmission of a set of subframes for at least one reference signal configuration. 9. The equipment as claimed in claim 7, wherein the cross-subframe indicator is received on different subcells of the shared spectrum band. 10. The equipment as claimed in claim 7, further comprising: Means for identifying that the at least one subframe has asynchronous symbol timing relative to a licensed cell operating in a dedicated spectrum band; and A means for determining, at least in part, the positions of one or more symbols for at least one reference signal within the at least one subframe based on a detected symbol preamble associated with the transmission. 11. A user equipment (UE), comprising: processor; A memory in electronic communication with the processor; and A program stored in the memory, which, when executed by the processor, is operable to enable the user equipment (UE) to: The configuration identifies the use of secondary cells in a shared spectrum band for communication, wherein transmissions via said secondary cells are subject to the Listen-Before-Talk (LBT) protocol of the shared frequency channel; Receive transmissions comprising multiple subframes from the subcell; and The reference signal configuration of at least one subframe of the transmission is determined at least in part based on a cross-subframe indicator received in the subframe, the cross-subframe indicator indicating the value of the subframe offset between the subframe in which the cross-subframe indicator is received and the at least one subframe. 12. The User Equipment (UE) as claimed in claim 11, wherein the cross-subframe indicator is received on different subcells of the shared spectrum band. 13. The user equipment (UE) as claimed in claim 11, wherein the program, when executed by the processor, is operable to cause the user equipment (UE) to: The at least one subframe is identified as having asynchronous symbol timing relative to a licensed cell operating in a dedicated spectrum band; and The positions of one or more symbols for at least one reference signal within the at least one subframe are determined at least in part based on the detected symbol preamble associated with the transmission. 14. A computer-readable storage medium having a computer program stored thereon, the computer program performing the following steps when executed by a processor: The configuration identifies the use of secondary cells in a shared spectrum band for communication, wherein transmissions via said secondary cells are subject to the Listen-Before-Talk (LBT) protocol of the shared frequency channel; Receive transmissions comprising multiple subframes from the subcell; and The reference signal configuration of at least one subframe of the transmission is determined at least in part based on a cross-subframe indicator received in the subframe, the cross-subframe indicator indicating the value of the subframe offset between the subframe in which the cross-subframe indicator is received and the at least one subframe.