HK1242887B - Apparatus configured to report aperiodic channel state information for dual connectivity - Google Patents

Description

Apparatus configured to report aperiodic channel state information of dual connectivity

Priority Declaration

This patent application claims the benefit of priority to U.S. Patent Application No. 14/741,233, filed on June 16, 2015, which claims the benefit of priority to U.S. Provisional Patent Application No. 62/084,997, filed on November 26, 2014, and U.S. Provisional Patent Application No. 62/081,281, filed on November 18, 2014, each of which is incorporated herein by reference in its entirety.

Technical Field

Embodiments relate to wireless access networks.Some embodiments relate to aperiodic channel state information (CSI) processing and reporting in cellular networks such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks.

Background Art

Current problems in transmitting data over wireless networks may include low throughput, frequent handoffs, handoff failures, inefficient offloading, and service interruptions.

Dual connectivity in LTE networks can significantly improve per-user throughput, reduce handovers, and mitigate handover failures by allowing users to simultaneously connect to a primary cell group and a secondary cell group via a macro evolved Node B (eNB) and a small cell eNB.

Regarding low throughput, dual connectivity can increase per-user throughput by aggregating radio resources from at least two eNBs. Furthermore, throughput can be increased by sending or receiving multiple streams and dynamically adapting to the best radio conditions across multiple cells. Furthermore, small cell eNBs can provide additional capacity to user equipment (UE) with multiple radio connections.

Furthermore, mobile UEs experience frequent handover failures, inefficient offloading, and service interruptions. The consequences are more severe if the UE's speed is high and the cell coverage is limited. Dual connectivity can reduce handover failure rates by maintaining a macro eNB (e.g., primary cell) connection as a coverage layer. Dual connectivity also facilitates load balancing between the macro eNB and small cell eNBs (e.g., secondary cells).

Furthermore, dual connectivity can reduce the signaling overhead to the core network caused by frequent handovers. For example, signaling overhead can be reduced by not issuing a handover operation as long as the UE is within macro coverage.

However, dual connectivity can pose several technical challenges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a functional diagram of a Third Generation Partnership Project (3GPP) network according to some embodiments;

FIG2 is a functional diagram of a user equipment (UE) according to some embodiments;

FIG3 is a functional diagram of an evolved Node B (eNB) according to some embodiments;

FIG4 illustrates an example of a heterogeneous network for dual connectivity implementation according to some embodiments;

FIG5 illustrates an example scenario of dual connectivity implementation according to some embodiments;

FIG6 illustrates an example of channel state information (CSI) attributes for prioritizing CSI processing calculations according to some embodiments;

FIG7 illustrates method operations performed by a UE for calculating prioritized CSI processing for CSI reporting based on two CSI aperiodic requests received in the same subframe; and

8 illustrates method operations performed by an eNB for selecting a transmission mode based on CSI reports received from a UE, in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and accompanying drawings sufficiently illustrate the specific embodiments to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in other embodiments or may be replaced by those of other embodiments. The embodiments recited in the claims encompass all available equivalents of those claims.

In this disclosure, embodiments are often discussed with reference to macro eNBs and small cell eNBs. A small cell eNB may be a pico eNB. Furthermore, various embodiments disclosed herein may be applicable to other settings with other terminology. For example, a macro eNB may be referred to as an "anchor eNB," "primary eNB," or "master eNB," while a small cell eNB may be referred to as an "assisting eNB," "secondary eNB," or "slave eNB."

Figure 1 is a functional diagram of a 3GPP network according to some embodiments. The network includes a radio access network (RAN) (e.g., as depicted, E-UTRAN or Evolved Universal Terrestrial Radio Access Network) 100 and a core network 120 (e.g., shown as an Evolved Packet Core (EPC)), which are coupled together via an S1 interface 115. For convenience and brevity, only a portion of the core network 120 and the RAN 100 are shown.

The core network 120 includes a mobility management entity (MME) 122, a serving gateway (serving GW) 124, and a packet data network gateway (PDN GW) 126. The RAN 100 includes an evolved Node B (eNB) 104 (which may operate as a base station) for communicating with a user equipment (UE) 102. The eNB 104 may include a macro eNB and a low power (LP) eNB, e.g., a micro eNB.

The MME 122 is functionally similar to the control plane of the legacy Serving GPRS Support Node (SGSN). The MME 122 manages mobility aspects of the access, such as gateway selection and tracking area list management. The Serving GW 124 terminates the interface to the RAN 100 and routes data packets between the RAN 100 and the core network 120. In addition, the Serving GW 124 can be the local mobility anchor point for inter-eNB handovers and can also provide an anchor point for inter-3GPP mobility. Other responsibilities may include lawful interception, charging, and some policy enforcement. The Serving GW 124 and the MME 122 can be implemented in the same physical node or in different physical nodes. The PDN GW 126 terminates the SGi interface to the packet data network (PDN). The PDN GW 126 routes data packets between the EPC 120 and external PDNs and can be a key node for policy enforcement and charging data collection. The PDN GW 126 can also provide an anchor point for mobility for non-LTE accesses. The external PDN may be an IP Multimedia Subsystem (IMS) domain as well as any type of IP network. The PDN GW 126 and the Serving GW 124 may be implemented in one physical node or in different physical nodes.

The eNB 104 (macro and micro eNBs) terminates the air interface protocol and can be the first point of contact for the UE 102. In some embodiments, the eNB 104 can implement various logical functions of the RAN 100, including but not limited to RNC (radio network controller) functions, such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management. According to an embodiment, the UE 102 can be configured to transmit orthogonal frequency division multiplexing (OFDM) communication signals with the eNB 104 over a multi-carrier communication channel in accordance with orthogonal frequency division multiple access (OFDMA) communication technology. OFDM signals can include multiple orthogonal subcarriers.

The S1 interface 115 separates the RAN 100 and the EPC 120. The S1 interface 115 is divided into two parts: S1-U, which carries traffic data between the eNB 104 and the Serving GW 124, and S1-MME, which is the signaling interface between the eNB 104 and the MME 122. The X2 interface is an interface between eNBs 104. The X2 interface consists of two parts: X2-C and X2-U. X2-C is the control plane interface between eNBs 104, while X2-U is the user plane interface between eNBs 104.

For cellular networks, LP cells are typically used to extend coverage to indoor areas where outdoor signals don't reach well, or to increase network capacity in areas with high phone usage (e.g., train stations). As used herein, the term "low-power (LP) eNB" refers to any suitable, relatively low-power eNB used to implement narrower cells (narrower than macrocells), such as femtocells, picocells, or microcells. Femtocell eNBs are typically provided by mobile network operators to their residential or enterprise users. Femtocells are typically the size of a residential gateway or smaller and are typically connected to a user's broadband line. Once powered on, femtocells connect to the mobile operator's mobile network and provide additional coverage to residential femtocells, typically with a range of 30 to 50 meters. Therefore, an LP eNB can be a femtocell eNB because it is coupled through PDN GW 126. Similarly, picocells are wireless communication systems that typically cover a small area, such as within a building (office, shopping mall, train station, etc.) or, more recently, on an airplane. A picocell eNB can typically connect to another eNB (e.g., a macro eNB) via its base station controller (BSC) functionality via an X2 link. Thus, a low-performance (LP) eNB can be implemented as a picocell eNB, as it is coupled to the macro eNB via the X2 interface. A picocell eNB or other low-performance (LP) eNB can incorporate some or all of the functionality of a macro eNB. In some cases, a low-performance (LP) eNB may be referred to as an "access point base station" or "enterprise femtocell."

In some embodiments, a downlink resource grid can be used for downlink transmissions from eNB 104 to UE 102, while uplink transmissions from UE 102 to eNB 104 can use similar techniques. The grid can be a time-frequency grid (referred to as a "resource grid" or "time-frequency resource grid"), which represents the physical resources for the downlink in each time slot. This time-frequency representation is common in OFDM systems and makes radio resource allocation more intuitive. Each column and row of the resource grid corresponds to an OFDM symbol and an OFDM subcarrier, respectively. The duration of the resource grid in the time domain can correspond to a time slot in a radio frame. The smallest time-frequency unit in the resource grid is represented as a "resource element." Each resource grid includes multiple resource blocks, which describe the mapping of specific physical channels to resource elements. Each resource block includes a collection of resource elements, and in the frequency domain, each resource block represents the minimum amount of resources currently available for allocation. There are several different physical downlink channels that are communicated using these resource blocks. Two of these physical downlink channels that are particularly relevant to the present disclosure are the physical downlink shared channel and the physical downlink control channel.

The physical downlink shared channel (PDSCH) carries user data and higher layer signaling to the UE 102. The physical downlink control channel (PDCCH) or enhanced downlink control channel (EPDCCH) carries information related to the PDSCH channel, such as resource allocation and transport format. The PDCCH or EPDCCH also informs the UE 102 about the transport format, resource allocation, and hybrid automatic repeat request (H-ARQ) of the uplink shared channel. Typically, downlink scheduling (allocation of control and shared channel resource blocks to UEs 102 within a cell) is performed at the eNB 104 based on channel quality information fed back to the eNB 104 from the UE 102. The downlink resource allocation information is then sent to the UE 102 on the control channel (PDCCH) intended for (allocated to) the UE 102.

PDCCH uses control channel elements (CCE) to convey control information. Before being mapped to resource elements, PDCCH complex symbols are first grouped into quadruplets, which are then arranged using a sub-block interleaver for rate matching. Each PDCCH is transmitted using one or more of these CCEs, where each CCE corresponds to 9 groups of physical resource elements (called resource element groups (REGs)), with each group having 4 physical resource elements. 4 quadrature phase shift keying (QPSK) symbols are mapped to each REG. Depending on the size of the downlink control information (DCI) and the channel conditions, one or more CCEs can be used to transmit the PDCCH. Four or more different PDCCH formats may be defined in LTE, with different numbers of CCEs (e.g., aggregation levels, L=1, 2, 4, or 8).

Figure 2 is a functional diagram of a user equipment (UE) 200 according to some embodiments. Figure 3 is a functional diagram of an evolved Node B (eNB) 300 according to some embodiments. It should be noted that in some embodiments, the eNB 300 may be a stationary, non-mobile device. The UE 200 may be the UE 102 shown in Figure 1 , and the eNB 300 may be the eNB 104 shown in Figure 1 . The UE 200 may include physical layer circuitry (PHY) 202 for transmitting and receiving signals to and from the eNB 300, other eNBs, other UEs, or other devices using one or more antennas 201. The eNB 300 may include physical layer circuitry (PHY) 302 for transmitting and receiving signals to and from the UE 200, other eNBs, other UEs, or other devices using one or more antennas 301.

The UE 200 may further include a medium access control layer (MAC) circuit 204 for controlling access to the wireless medium, and the eNB 300 may further include a medium access control layer (MAC) circuit 304 for controlling access to the wireless medium.

The UE 200 may further include processing circuitry 206 and memory 208 arranged to perform the operations described herein, and the eNB 300 may further include processing circuitry 306 and memory 308 arranged to perform the operations described herein.

The eNB 300 may also include one or more interfaces 310 that may enable communication with other components, including other eNBs 104 ( FIG. 1 ), components in the core network 120 ( FIG. 1 ), or other network components. Furthermore, the interfaces 310 may enable communication with other components not shown in FIG. 1 , including components external to the network. The interfaces 310 may be wired interfaces, wireless interfaces, or a combination of both.

Antennas 201, 301 may include one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas, or other types of antennas suitable for transmitting radio frequency (RF) signals. In some multiple-input multiple-output (MIMO) embodiments, antennas 201, 301 may be effectively separated to take advantage of different channel characteristics and spatial diversity that may occur.

In some embodiments, the mobile device or other device described herein may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capabilities, a web tablet, a wireless phone, a smart phone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other devices including wearable devices that can wirelessly receive and/or send information. In some embodiments, the mobile device or other device may be a UE or eNB configured to operate according to a 3GPP standard. In some embodiments, the mobile device or other device may be configured to operate according to other protocols or standards (including IEEE 802.11 or other IEEE standards). In some embodiments, the mobile device or other device may include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, a speaker, and other mobile device elements. The display may be an LCD screen including a touch screen.

Although the UE 200 and the eNB 300 are shown as each having several separate functional elements, one or more of these functional elements may be combined and may be implemented by a combination of software-configured elements (e.g., a processing element including a digital signal processor (DSP)) and/or other hardware elements. For example, some elements may include one or more microprocessors, DSPs, field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), radio frequency integrated circuits (RFICs), and various combinations of hardware and logic circuits for performing at least the functions described herein. In some embodiments, a functional element may refer to one or more processes running on one or more processing elements.

Embodiments may be implemented in one or a combination of hardware, firmware, and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and run by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transient mechanism for storing information in a machine (e.g., computer) readable form. For example, a computer-readable storage device may include a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, and other storage devices and media. Some embodiments may include one or more processors that may be configured with instructions stored in a computer-readable storage device.

In some embodiments, UE 200 may be configured to receive OFDM communication signals over a multi-carrier communication channel in accordance with OFDMA communication techniques. OFDM signals may include multiple orthogonal subcarriers. In some broadband multi-carrier embodiments, eNB 300 may be part of a broadband wireless access (BWA) communication network, such as a Worldwide Interoperability for Microwave Access (WiMAX) communication network, a Third Generation Partnership Project (3GPP) Universal Terrestrial Radio Access Network (UTRAN) Long Term Evolution (LTE), or a Long Term Evolution (LTE) communication network, although the scope of the present invention is not limited in this respect. In these broadband multi-carrier embodiments, UE 200 and eNB 300 may be configured to communicate in accordance with OFDMA techniques.

FIG4 illustrates an example of a heterogeneous network 400 for a dual connectivity implementation according to some embodiments. FIG4 illustrates examples of different deployments of large cells, including a macro cell 410. The heterogeneous network 400 may further include small cells 420 (e.g., micro cells) in the same frequency as the macro layer (which includes the macro cell 410). In addition, the heterogeneous network 400 may include small cells 430 deployed in clusters and small cells deployed in non-clusters (e.g., scattered throughout a city) in different frequency layers than the macro cell 410. Furthermore, the heterogeneous network 400 may include beamformed small cells 440 (deployed with beamforming capabilities) that employ different radio access technologies (RATs).

Accordingly, in such a heterogeneous network 400 , dual connectivity may allow the UE 102 to be simultaneously connected to the macro cell 410 and the small cell 430 that is on a different frequency layer than the macro cell 410 .

As previously described, dual connectivity in LTE networks can significantly improve per-user throughput, reduce handovers, and reduce handover failures by allowing users to be simultaneously connected to macro cell 410 and small cells (e.g., small cell 420, small cell 430, and/or small cell 440).

FIG5 illustrates an example scenario 500 for dual connectivity implementation according to some embodiments. In dual connectivity, serving cells are operated in different eNBs. For example, a primary cell is served by a macro cell 510, and a secondary cell is served by a small cell (e.g., a first small cell 520 and/or a second small cell 530). In some instances, the small cells may be pico cells or femto cells. For example, the first small cell 520 is a first pico cell, and the second small cell 530 is a second pico cell.

As previously mentioned, one motivation for dual connectivity is to avoid frequent handovers in heterogeneous deployments, as illustrated in FIG4 . As shown in scenario 500 , UE 102 can move within the coverage area 560 of macro cell 510 . Since the coverage area of each small cell (not shown) (e.g., the coverage area of first small cell 520 and second small cell 530 ) is smaller than the coverage area of macro cell 510 , if UE 102 is connected only to small cells, the UE may need to be handed over to macro cell 510 or another small cell. On the other hand, if the UE is connected to macro cell 510 , no handover is required, but offloading to the small cell is not provided either. To achieve offloading and avoid frequent handovers, carrier aggregation can be performed.

Through carrier aggregation, a UE can be served by both a macro cell 510 operating at a first frequency 540 and a small cell (e.g., a first small cell 520 and/or a second small cell 530) operating at a second frequency 550. For example, the primary cell may be the macro cell 510, and the secondary cells may be small cells (e.g., the first small cell 520, the second small cell 530).

For example, at _T1 , UE 102 is within the coverage area of macro cell 510 (e.g., coverage area 560) and can be served by macro cell 510 as a primary cell. Then, at _T2 , when UE 102 is within the coverage area of macro cell 510 and a first small cell 520, the first small cell 520 can be added as a secondary cell while the macro cell 510 is maintained as the primary cell. Furthermore, at _T3 , when UE 102 is within the coverage area of macro cell 510 but moves out of the coverage area of the first small cell 520, the first small cell 520 can be removed from serving as a secondary cell while the macro cell 510 is maintained as the primary cell. Later, at _T4 , when UE 102 is within the coverage area of macro cell 510 and a second small cell 530, the second small cell 530 can be added as a secondary cell while the macro cell 510 is maintained as the primary cell. Finally, at _T5 , when UE 102 is within the coverage area of macro cell 510 but moves out of the coverage area of second small cell 530, second small cell 530 may be removed from serving as a secondary cell while maintaining macro cell 510 as a primary cell.

In the example of FIG5 , the primary cell (e.g., macro cell 510) can be responsible for mobility management, so that the UE 102 does not need to perform handover as long as it moves within the coverage area of the macro cell 510. In addition, the secondary cells (e.g., first small cell 520, second small cell 530) can be used for data transmission, and the UE can take advantage of offloading to the secondary cells. Changing from the first small cell 520 to the second small cell 530 can be supported by adding or removing secondary cells instead of handover.

The scenario shown in Figure 5 illustrates an example of the difference between dual connectivity and LTE Rel-10 carrier aggregation. For example, in dual connectivity, a macro cell (e.g., macro cell 510) and a small cell (e.g., first small cell 520, second small cell 530) are served by different eNBs 104, and the two cells are connected via an X2 interface. In LTE Rel-10 carrier aggregation, it can be assumed that all serving cells are served by the same eNB 104.

Considering that a macro cell (e.g., macro cell 510) and small cells (e.g., first small cell 520, second small cell 530) are served by different eNBs 104, UE 102 may receive more than one aperiodic CSI request from both the macro cell and the small cell in the same subframe. Figures 6-8 illustrate techniques for prioritizing and calculating CSI processing when multiple aperiodic CSI requests are received in the same subframe.

Furthermore, in some embodiments, in addition to dual connectivity, LTE carrier aggregation may also be deployed. For example, macro and/or pico eNBs 104 may aggregate multiple component carriers (or cells) in downlink and/or uplink channels.

Channel State Information (CSI) reporting

LTE-Advanced (LTE-A) can support two types of CSI reporting: periodic reporting and aperiodic reporting. Periodic CSI reporting can primarily be used to indicate the channel quality of the downlink channel at UE 102 on a long-term basis. Periodic CSI can be provided by UE 102 according to a predefined reporting schedule configured by the serving cell using higher-layer signaling (e.g., Radio Resource Control (RRC)), and is generally low-overhead.

In contrast, aperiodic CSI reporting can be used to provide larger and more detailed reports in a single reporting instance based on dynamic CSI requests triggered by the serving cell using the CSI request field in the downlink control information (DCI). The DCI can include the Physical Downlink Control Channel (PDCCH) or the Enhanced Physical Downlink Control Channel (EPDCCH).

In transmission mode 10, multiple CSI reports corresponding to multiple CSI processes on the same serving frequency may be requested by the eNB 104 according to Table 7.2.1-1B defined in TS 36.213 Rel-11 (reproduced below). A set of CSI processes for reporting corresponding to CSI request fields "01," "10," and "11" may be configured using RRC signaling.

Table 7.2.1-1B: CSI request field in UE-specific search space for PDCCH/EPDCCH in uplink DCI format

In carrier aggregation mode, multiple CSI reports corresponding to multiple downlink cells may be requested by the eNB 104 according to Table 7.2.1-1A defined in TS 36.213 Rel-10 (reproduced below). The set of serving cells for reports corresponding to CSI request fields "10" and "11" is configured using RRC signaling.

Table 7.2.1-1A: CSI request field in UE-specific search space for PDCCH/EPDCCH in uplink DCI format

Considering that UE 102 does not expect to receive more than one CSI request in one downlink subframe, as defined in Section 7.2.1 of TS 36.211, the maximum number of CSI reports generated by UE 102 in one subframe may be limited to 5.

In the case of carrier aggregation, due to the ideal backhaul link and the limitation of one CSI request per downlink subframe, the maximum number of CSI requests is 5. As mentioned above, in LTE Rel-10 carrier aggregation, it can be assumed that all serving cells are served by the same eNB 104.

However, in a dual connectivity scenario, the macro cell (e.g., macro cell 510) and the small cells (e.g., first small cell 520, second small cell 530) are served by different eNBs 104, and the two cells are connected via an X2 interface. Therefore, it is not possible to send more than one CSI request in one downlink subframe. Furthermore, with dual connectivity, which may have a non-ideal backhaul link with high variable latency, ensuring that only one CSI request is sent in each downlink subframe may be difficult.

Furthermore, due to the complexity of CSI calculations, it is desirable to keep CSI calculations at a reasonable level at UE 102. Therefore, in some instances, a predetermined number of CSI reports to be calculated by UE 102 may be set. For example, the predetermined number of CSI reports may be set to 5, which is now a constraint on the maximum number of CSI reports. In this disclosure, several embodiments are described that limit the number of CSI processes calculated and reported in any subframe to 5. For example, CSI processes are prioritized, and the first 5 CSI processes are calculated by UE 102.

According to some embodiments, the various aperiodic CSI reporting processes disclosed herein enable reducing CSI computation complexity at the UE 102 when dual connectivity is used.

FIG6 illustrates an example of a CSI attribute 600 according to some embodiments. For example, when more than five CSI processes are requested during the same subframe, the CSI attribute 600 may be used to select (e.g., prioritize) the first five CSI processes for calculation by the UE 102. The CSI attributes may include, but are not limited to, a cell group index 610, a CSI process index 620, a component carrier (CC) index 630, and a CSI subframe index 640. The cell group index 610 may include an index value corresponding to a macro cell 612 and an index value corresponding to a small cell 614.

In a first set of embodiments, when aperiodic CSI requests from both the primary eNB and the secondary eNB are received by the UE 102 , a CSI (eg, CSI processing) calculation priority may be defined based on predetermined rules.

For example, in the case where a total of N CSI processes are requested in a given subframe, where N>5, UE 102 may update a predetermined number (e.g., 5) of high-priority CSI processes. Furthermore, the remaining (e.g., N-5 when the predetermined number is 5) lower-priority CSI processes may not be updated. In some instances, default values may be used for the remaining (e.g., non-updated) CSI processes. Alternatively, previously calculated values may be used for the remaining CSI processes.

A priority list of CSI processes may be defined based on CSI attributes 600 , which may be, for example, a cell group index 610 (eg, type of eNB), a CSI process index 620 , a CC index 630 , and a CSI subframe index 640 .

An example of a possible priority order (starting with higher priority) can be defined as follows:

Cell group index 610 > CSI process index 620 > CC index 630 > CSI subframe index 640;

CSI process index 620 > cell group index 610 > CC index 630 > CSI subframe index 640;

CSI process index 620 > CC index 630 > cell group index 610 > CSI subframe index 640;

CSI process index 620 > CC index 630 > CSI subframe index 640 > cell group index 610 .

In one example, a lower cell group index 610 value (e.g., an index value corresponding to a small cell 614) may have a higher priority for CSI calculation relative to a higher cell group index 610 value (e.g., an index value corresponding to a macro cell 612). Alternatively, in another example, a lower cell group index 610 value may have a lower priority for CSI calculation relative to a higher cell group index 610 value. In some embodiments, the macro cell 612 may be included in a macro cell cluster operating in a different frequency band than the small cell 614 or another macro cell.

In some instances, all CSI requests for CSI processing may be reported, but not all CSI requests may be updated. The CSI reports that are not updated may be CSI reports that were previously reported based on previously received aperiodic CSI data or a default value. For example, the default value may be a channel quality indicator (CQI) with an index value of "0," which may correspond to an indication that the UE 102 is out of range. Additionally, a CQI with an index value of "0" may indicate that the UE 102 has not received any usable LTE signal. Furthermore, aperiodic CSI configurations (i.e., configurations of CSI request fields for different UEs 102) may be exchanged between the master and secondary eNBs over the X2 interface.

In a second set of embodiments, the sum of the maximum number of CSI processes configured by the master eNB and the secondary eNB for each CSI request field may not exceed a predetermined number of CSI processes (eg, 5).

In a third set of embodiments, the primary and secondary eNBs may use different CSI subframes for aperiodic CSI triggering. The subframes used by the primary eNB for triggering may not be used for aperiodic CSI triggering by the secondary eNB. Bitmap signaling may be used to coordinate subframes between the primary and secondary eNBs. For frequency division duplexing (FDD), the bitmap may be 40 bits long.

FIG7 illustrates operations of a method 700 for calculating CSI for selected CSI processes in accordance with some embodiments. As shown in FIG5 and FIG6, multiple CSI requests may be received in the same subframe, which may result in more than five requested CSI processes needing to be calculated by UE 102. In such a case, a selected subset of the requested CSI processes is calculated based on CSI attributes 600. However, embodiments are not limited to these configurations, and some or all of the techniques and operations described herein may be applicable to systems or networks that exclusively utilize macro cells or micro cells.

It is worth noting that embodiments of method 700 may include additional or even fewer operations or processes than those illustrated in FIG7 . Furthermore, embodiments of method 700 are not necessarily limited to the chronological order illustrated in FIG7 . In describing method 700, reference may be made to FIG7 , but it should be understood that method 700 may be implemented using any other suitable systems, interfaces, and components. For example, for illustration, reference may be made to scenario 500 in FIG5 (described previously), but the techniques and operations of method 700 are not limited thereto.

Furthermore, while the method 700 and other methods described herein may involve an eNB 104 or UE 102 operating in accordance with 3GPP or other standards, embodiments of these methods are not limited to those eNBs 104 or UEs 102 and may also be implemented by other mobile devices such as Wi-Fi access points (APs) or subscriber stations (STAs). Furthermore, the method 700 and other methods described herein may be implemented by wireless devices configured to operate in other suitable types of wireless communication systems, including systems configured to operate in accordance with various IEEE standards such as IEEE 802.11.

At operation 710 of method 700, UE 102 receives a first aperiodic CSI request from a first cell group in a first subframe. Physical layer circuitry 202 (in FIG. 2 ) may receive the first aperiodic CSI request from an eNB (e.g., eNB 104). The first cell group may be served by a primary eNB. The first cell group may include macro cell 510.

As described in Table 7.2.1-1B above, in transmission mode 10, the request field value for the first aperiodic CSI request may be "01", "10", or "11".

As described in Table 7.2.1-1A above, in the carrier aggregation mode, the request field value for the first aperiodic CSI request may be "10" or "11".

Dual connectivity in an LTE network allows a UE 102 to simultaneously connect to a primary cell group and a secondary cell group via a primary eNB and a secondary eNB. Therefore, in some instances, the UE 102 may receive more than one aperiodic CSI request in the same subframe. For example, the UE 102 may receive a CSI request from the primary eNB at operation 710 and another CSI request from the secondary eNB in the same subframe at operation 720.

At operation 720, UE 102 receives a second aperiodic CSI request from a second cell group in a first subframe. Physical layer circuitry 202 may receive the second aperiodic CSI request from another eNB 104. The second cell group may be served by a secondary eNB. The second cell group may include the first small cell 520 or the second small cell 530. Furthermore, the second cell group may operate at a different frequency than the first cell group.

As described in the above Table 7.2.1-1B, in transmission mode 10, the request field value for the second aperiodic CSI request may be "01", "10", or "11".

As described in Table 7.2.1-1A above, in carrier aggregation mode, the request field value for the second aperiodic CSI request may be "10" or "11".

In some examples, when the first aperiodic CSI request is received within 33 microseconds of the second aperiodic CSI request, the first aperiodic CSI request and the second aperiodic CSI request are received in a first subframe.

In one example, the first cell group includes macro eNBs, and the second cell group includes small cell eNBs. In another example, the first cell group includes small cell eNBs, and the second cell group includes macro eNBs. In yet another example, the first cell group and the second cell group may include different macro eNBs operating at different frequencies. In yet another example, the first cell group and the second cell group may include different small cell eNBs operating at different frequencies.

At operation 730, the UE 102 determines the number of requested CSI processes corresponding to the first aperiodic CSI request and the second aperiodic CSI request. In some examples, the processing circuit 206 (in FIG. 2 ) determines the number of requested CSI processes. The number of requested CSI processes may be determined by adding the number of CSI processes associated with the first aperiodic CSI request to the number of CSI processes associated with the second aperiodic CSI request. As previously described, due to the computational complexity of CSI, the number of CSI processes to be calculated and reported in any subframe may be limited to a predetermined number of CSI processes (e.g., 5).

At operation 740, when the determined number of requested CSI processes is greater than a predetermined number (e.g., 5), UE 102 selects a subset of the requested CSI processes. For example, when there are more than 5 requested CSI processes, UE 102 may select a subset of the requested CSI processes. In some examples, processing circuitry 206 selects a subset of CSI processes for updating (e.g., calculation). The number of requested CSI processes is determined at operation 730.

In some examples, the selected CSI processes include a total of five CSI processes. For example, the CSI processes are prioritized and the first five CSI processes are selected by the UE 102.

In some examples, the selected CSI processes include at least one less CSI process than the requested CSI processes, for example, when the number of requested CSI processes is 7, the number of selected CSI processes is 6 or less.

In some instances, the processing circuit 206 is further configured to generate a priority list of requested CSI processes based on the CSI attributes. Furthermore, selecting the subset of requested CSI processes at operation 740 may be based on the priority list. The CSI attributes may include the CSI attributes 600 of FIG. 6 . The CSI attributes 600 may include a cell group index 610, a CSI process index 620, a CC index 630, and a CSI subframe index 640.

The priority list may be preset by a UE (e.g., UE 102) or an eNB (e.g., eNB 104). In some instances, the CSI process index 620 may have a higher priority in the priority list than the CC index 630. In some instances, the CC index 630 may have a higher priority in the priority list than the CSI subframe index 640.

In some instances, a lower cell group index 610 may have a higher priority in the priority list than a higher cell group index 610. Alternatively, a lower cell group index 610 may have a lower priority in the priority list than a higher cell group index 610. A lower cell group index 610 may correspond to a small cell eNB or a secondary eNB. A higher cell group index 610 may correspond to a macro eNB or a master eNB.

At operation 750, the UE 102 calculates CSI for the CSI process selected according to operation 740. The processing circuit 206 may calculate CSI for each selected CSI process. As previously described, a total of five CSI processes may be selected at operation 740, and thus CSI for the five processes may be calculated at operation 750.

The calculated CSI may include a precoding matrix indicator value. As described in method 800, the transmission parameters set or sent by the eNB 104 may include precoding weights for the eNB's transmit antennas, the precoding weights being based on the precoding matrix indicator value.

Additionally, the calculated CSI may include a rank index (RI) value. The number of layers determined by the eNB 104 in method 800 is based on the RI value.

Furthermore, the calculated CSI may include a channel quality indicator (CQI) value.The modulation and coding scheme (MCS) determined by the eNB 104 in method 800 may be based on the CQI value.

In some instances, method 700 may further include generating a first CSI report and a second CSI report. For example, the CSI reports may be generated using processing circuit 206. The first CSI report may include CSI corresponding to the first aperiodic CSI request calculated according to operation 750. The second CSI report may include CSI corresponding to the second aperiodic CSI request calculated according to operation 750.

In addition, method 700 may further include sending a first CSI report to the first cell group and sending a second CSI report to the second cell group. As previously described, the first cell group sends a first aperiodic CSI request at operation 710, and the second cell group sends a second aperiodic CSI request at operation 720. For example, the physical layer circuit 202 may send the first CSI report to the first cell group and send the second CSI report to the second cell group.

Furthermore, all requested CSI processes from the first aperiodic request and the second aperiodic request are included in the first CSI report or the second CSI report, but CSI is calculated only for the CSI process selected at operation 740 .

In some examples, the processing circuit 206 is further configured to access previously stored CSI for a remaining process that is different from the CSI process selected at operation 740. Furthermore, the first CSI report or the second CSI report may include the CSI accessed for the remaining process. For example, the remaining CSI process is a CSI process that is not updated (e.g., calculated) at operation 750. The processing circuit 206 may access a value for the remaining CSI process stored in the memory 208. The value may correspond to the previously calculated CSI associated with the remaining CSI process.

In some instances, the processing circuit 206 is further configured to generate general CSI for the remaining processes. As previously described, the remaining processes are different from the CSI process selected at operation 740. In addition, the general CSI indicates that the remaining processes have not yet been calculated. Moreover, the first CSI report or the second CSI report may include the general CSI for the remaining processes. For example, the portion of the first CSI report associated with the remaining processes includes a channel quality indicator (CQI) set to zero to indicate that the CQI has not yet been calculated.

In some examples, the processing circuit 206 is further configured to generate a CSI report based on the CSI calculated for the selected processing.In addition, the physical layer circuit 202 is further configured to send the CSI report to the first cell group and the second cell group.

FIG8 illustrates operations of a method 800 for selecting a transmission mode based on calculated CSI, according to some embodiments. It is noted that embodiments of method 800 may include additional or even fewer operations or processes than those illustrated in FIG8 . Furthermore, embodiments of method 800 are not necessarily limited to the chronological order illustrated in FIG8 . While describing method 800, reference may be made to FIG8 , but it should be understood that method 800 may be implemented using any other suitable systems, interfaces, and components.

Furthermore, while the method 800 and other methods described herein may involve an eNB 104 or UE 102 operating in accordance with 3GPP or other standards, embodiments of these methods are not limited to those eNBs 104 or UEs 102 and may also be implemented by other mobile devices such as Wi-Fi access points (APs) or subscriber stations (STAs). Furthermore, the method 800 and other methods described herein may be implemented by wireless devices configured to operate in other suitable types of wireless communication systems, including systems configured to operate in accordance with various IEEE standards such as IEEE 802.11.

Methodology 800 may be performed by eNB 104 to select a transmission mode for a UE (eg, UE 102) having dual connectivity in a heterogeneous network.

At operation 810, the eNB 104 may send an aperiodic CSI request to the UE 102. In some examples, the physical layer circuitry 302 may send the CSI request.

In some instances, different CSI subframes may be used by the primary and secondary eNBs for aperiodic CSI triggering. Subframes used by the primary eNB for aperiodic CSI triggering may not be used by the secondary eNB for aperiodic CSI triggering. Bitmap signaling may be used to coordinate subframes between the primary and secondary eNBs. For frequency division duplexing (FDD), the bitmap may have a length of 40 bits. Furthermore, each bit may correspond to a downlink subframe, where a "1" indicates that the trigger can be used, while a "0" indicates that the trigger cannot be used.

At operation 820, PHY 302 of eNB 104 may receive a CSI report based on the aperiodic request sent at operation 810. The CSI report may be generated and sent by UE 102 using method 700 of Figure 7. In some examples, physical layer circuitry 302 of eNB 300 may receive the CSI report.

The CSI report may include the CSI for the selected CSI process calculated at operation 750. Furthermore, the CSI process may be selected by UE 102 at operation 740. Furthermore, the CSI report may include general CSI for the remaining processes. The remaining processes may be CSI processes that were not selected at operation 740 but were requested in the aperiodic CSI request sent at operation 810.

At operation 830, the eNB 104 may determine, based on the general CSI, that the remaining CSI processing has not yet been calculated. In some examples, operation 830 may be performed by the processing circuitry 306 of the eNB 300.

At operation 840, processing circuitry 306 of eNB 104 may select transmission parameters based on the CSI calculated for the selected CSI process in the CSI report. In some examples, operation 840 may be performed by processing circuitry 306 of eNB 300.

The transmission parameter(s) may be received at the UE 102. The transmission parameters may be set or sent by one of the eNBs 104 (e.g., the eNB 104 of the serving cell). Accordingly, the decision by the eNB 104 to indicate the transmission mode may be based at least in part on the information included in the CSI report described previously.

In some examples, the transmission parameters include precoding weights for transmit antennas of the eNB, the precoding weights being based on precoding matrix indicator values in the CSI calculated for a selected CSI process.

In some examples, the transmission parameters include a number of layers based on a rank indicator (RI) value in the CSI calculated for a selected CSI process.

In some examples, the transmission parameters include a modulation and coding scheme (MCS) based on a channel quality indicator (CQI) value in the CSI calculated for a selected CSI process.

Disclosed herein is a non-transitory computer-readable storage medium storing instructions, wherein the instructions are executed by one or more processors to perform operations for reporting channel state information (CSI) in a cellular network. These operations can configure a UE to: receive a first aperiodic CSI request from a first cell group in a first subframe; receive a second aperiodic CSI request from a second cell group in the first subframe; determine the number of requested CSI processes corresponding to the first aperiodic CSI request and the second aperiodic CSI request; when the determined number of requested CSI processes is greater than 5, select a subset of the requested processes; calculate CSI for the selected CSI processes; generate a CSI report based on the CSI calculated for the selected CSI processes; and send the CSI report to the first cell group and the second cell group.

The Abstract is provided to comply with 37 C.F.R. § 1.72(b) to allow the reader to ascertain the nature and gist of the present disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. The appended claims are incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims (25)

1. A means for reporting channel state information (CSI) of a user equipment (UE), the means comprising: Physical layer circuitry (PHY) is used for: Receive a first aperiodic CSI request from the first cell group in the first subframe; and Receive a second aperiodic CSI request from the second cell group in the first subframe; and Processing circuitry, used for: Determine the number of requested CSI processes corresponding to the first aperiodic CSI request and the second aperiodic CSI request. When the number of requested CSI processes is greater than the predetermined number, a subset of the requested CSI processes is selected. Compute CSI for a selected subset of the requested CSI processing; A first CSI report is generated using one or more calculated CSIs corresponding to the first aperiodic CSI request; and A second CSI report is generated using one or more calculated CSIs corresponding to the second aperiodic CSI request; and The PHY is also used for: Send the first CSI report to the first cell group; and The second CSI report is sent to the second cell group. 2. The apparatus of claim 1, wherein the predetermined number is 5, and wherein the selected subset of the requested CSI processes comprises a total of 5 CSI processes. 3. The apparatus of claim 1, wherein the UE is configured to receive the first aperiodic CSI request and the second aperiodic CSI request in the first subframe for dual connectivity operation, and wherein the UE is configured to receive a single CSI request in the first subframe for non-dual connectivity operation. 4. The apparatus of claim 1, wherein the UE has dual connectivity with the first cell group and the second cell group, and wherein the first cell group is served by a first eNB and the second cell group is served by a second eNB. 5. The apparatus of claim 1, wherein the UE has dual connectivity with the first cell group and the second cell group, and wherein the first cell group and the second cell group are served by similar eNBs. 6. The apparatus of claim 1, wherein when the first aperiodic CSI request is received within 33 microseconds of the second aperiodic CSI request, the first aperiodic CSI request and the second aperiodic CSI request are received in the first subframe. 7. The apparatus of claim 1, wherein the processing circuitry suppresses the calculation of CSI processes not included in the selected subset of the requested CSI processes. 8. The apparatus of claim 1, wherein the processing circuit is further configured to: Access the CSI previously stored for the remaining CSI processes, which are different from the subset of the selected requested CSI processes; and wherein, The first CSI report includes the CSIs accessed for the remaining CSI processing. 9. The apparatus of claim 1, wherein the processing circuit is further configured to: Generate a general CSI for the remaining CSI processes, which differ from the selected subset of requested CSI processes; and wherein, The general CSI indicates that the remaining CSI processes have not yet been calculated, and the first CSI report includes the general CSI for the remaining CSI processes. 10. The apparatus of claim 9, wherein the general CSI included in the first CSI report in connection with the remaining CSI processing includes a Channel Quality Indicator (CQI) value, which is set to zero to indicate that the CQI has not yet been calculated. 11. The apparatus of claim 1, wherein the request field value for the first aperiodic CSI request is “01”, “10”, or “11”. 12. The apparatus of claim 1, wherein the first cell group is a macro-evolved node B (eNB) and the second cell group is a small cell eNB. 13. The apparatus of claim 1, wherein the processing circuit is further configured to: Generate a priority list for the requested CSI processing based on CSI attributes; and among them, The step of selecting a subset of the requested CSI processing is performed based on the priority list. 14. The apparatus of claim 13, wherein the CSI attribute includes a cell group index, a CSI processing index, a member carrier (CC) index, or a CSI subframe index. 15. The apparatus of claim 14, wherein the CSI processing index has a higher priority than the CC index in the priority list. 16. The apparatus of claim 14, wherein the CC index has a higher priority than the CSI subframe index in the priority list. 17. The apparatus of claim 14, wherein the lower cell group index has a higher priority than the higher cell group index in the priority list, and wherein the lower cell group index corresponds to a small cell eNB and the higher cell group index corresponds to a macro eNB. 18. The apparatus of claim 14, wherein the lower cell group index has a lower priority than the higher cell group index in the priority list, and wherein the lower cell group index corresponds to a small cell eNB and the higher cell group index corresponds to a macro eNB. 19. A method for reporting Channel State Information (CSI) in a cellular network, the method comprising: Receive the first aperiodic CSI request from the first cell group in the first subframe; Receive a second aperiodic CSI request from the second cell group in the first subframe; Determine the number of requested CSI processes corresponding to the first aperiodic CSI request and the second aperiodic CSI request. When the number of requested CSI processes is greater than 5, a subset of the requested processes is selected. Calculate CSI for the selected CSI process; A first CSI report is generated based on the CSI calculated for the selected CSI process; A second CSI report is generated based on the CSI calculated for the selected CSI processing. Send the first CSI report to the first cell group; and The second CSI report is sent to the second cell group. 20. A computer-readable medium storing code that, when executed by a machine, causes the machine to perform the method of claim 19. 21. An evolved Node B (eNB) configured to perform handover decisions in a cellular network, the eNB comprising: Physical layer circuitry (PHY) is used for: Send non-periodic CSI requests; and Receive a CSI report based on the aperiodic CSI request from the user equipment (UE), the CSI report having a CSI calculated for the selected CSI process and a general CSI for the remaining CSI processes; and Processing circuitry, used for: Based on the general CSI, it is determined that the remaining CSI processes have not yet been calculated; and The transmission parameters are selected based on the CSI calculated for the selected CSI process in the CSI report. 22. The eNB of claim 21, wherein the transmission parameters include precoding weights for the transmit antennas of the eNB, the precoding weights being based on precoding matrix index values in the CSI calculated for one of the selected CSI processes. 23. The eNB of claim 21, wherein the transmission parameters include a number of layers, the number of layers being based on a rank index value in the CSI calculated for one of the selected CSI processes, and wherein the aperiodic CSI request is transmitted at a predetermined subframe based on bitmap signaling. 24. The eNB of claim 21, wherein the transmission parameters include a modulation and coding scheme based on a Channel Quality Index (CQI) value in a CSI calculated for one of the selected CSI processes. 25. An apparatus for reporting channel state information (CSI) in a cellular network, the apparatus comprising: A means for receiving a first aperiodic CSI request from a first cell group in a first subframe; A means for receiving a second aperiodic CSI request from a second cell group in the first subframe; A means for determining the number of requested CSI processes corresponding to the first aperiodic CSI request and the second aperiodic CSI request. A means for selecting a subset of the requested CSI processes when the determined number of requested CSI processes is greater than 5; A device for calculating CSI for a selected CSI process; A means for generating a first CSI report based on the CSI calculated for the selected CSI process; A means for generating a second CSI report based on the CSI calculated for the selected CSI process; A means for sending the first CSI report to the first cell group; and A means for sending the second CSI report to the second cell group.