HK1223223B - User equipment and evolved node-b and methods for operation in a coverage enhancement mode - Google Patents

Description

User equipment, evolved Node B, and method for operating in coverage enhancement mode

Priority claim

This application claims priority to U.S. Provisional Patent Application Serial No. 61/898,425, filed October 31, 2013, which is hereby incorporated by reference in its entirety.

Technical Field

Embodiments relate to wireless communications. Some embodiments relate to wireless networks including LTE networks. Some embodiments relate to operation in coverage enhancement mode. Some embodiments relate to machine type communications (MTC).

Background Art

Mobile devices operating in a cellular network may experience performance degradation in some situations, which may affect the device's ability to connect or reconnect to the network. As an example, as a mobile device moves toward or away from the edge of a sector or cell of the network, the mobile device may lose coverage. As another example, a mobile device may be expected to operate in an environment with low link quality. Devices supporting, for example, machine type communications (MTC) may exchange small amounts of data at infrequent rates in such low link conditions.

In any case, connecting or reconnecting to a network in these and other scenarios can be challenging.Therefore, methods and techniques for connecting or reconnecting to a network are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a functional diagram of a 3GPP network according to some embodiments;

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

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

FIG4 is an example of a scenario in which a UE operating in a network may experience degraded coverage from an eNB according to some embodiments;

FIG5 illustrates operations of a method of communicating on a random access channel (RACH) in accordance with some embodiments;

FIG6 illustrates operations of another method of communicating on a RACH in accordance with some embodiments;

FIG7 illustrates an example of a MAC Random Access Response (RAR) according to some embodiments;

FIG8 illustrates a method for connecting or reconnecting according to some embodiments; and

FIG. 9 illustrates an example of a table of repetition levels, according to 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 variations, logical variations, process variations, and other variations. Portions and features of some embodiments may be included in other embodiments, or portions and features of some embodiments may be substituted for portions and features of other embodiments. The embodiments set forth in the claims encompass all available equivalents of those claims.

FIG1 illustrates a portion of an end-to-end network architecture of an LTE network and various components of the network, according to some embodiments. The network 100 includes a radio access network (RAN) (e.g., as described, E-UTRAN or Evolved Universal Terrestrial Radio Access Network) 100 and a core network 120 (e.g., shown as an Evolved Packet Core (EPC)) coupled together via an S1 interface 115. For convenience and brevity, only the core network 120 and a portion of 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 function as a base station) to communicate with user equipment (UE) 102. The eNB 104 may include a macro eNB and a low power (LP) eNB.

The MME is functionally similar to the control plane of the legacy Serving GPRS Support Node (SGSN). The MME manages mobility aspects of access, such as gateway selection and tracking area list management. The Serving GW 124 terminates the interface toward the RAN 100 and routes data packets between the RAN 100 and the core network 120. Additionally, it may be the local mobility anchor point for inter-eNB handovers and may also provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful interception, charging, and some policy enforcement. The Serving GW 124 and MME 122 may be implemented on the same physical node or on separate physical nodes. The PDN GW 126 terminates the SGi interface toward the Packet Data Network (PDN). The PDN GW 126 routes data packets between the EPC 120 and external PDNs and may be a key node for policy enforcement and charging data collection. It may also provide an anchor point for mobility with non-LTE access. External PDNs can be any type of IP network, as well as IP Multimedia Subsystem (IMS) domains. The PDN GW 126 and the Serving GW 124 may be implemented on one physical node or separate 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 for 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 communicate OFDM communication signals with the eNB 104 over a multi-carrier communication channel in accordance with OFDMA communication technology. OFDM signals may include multiple orthogonal subcarriers.

According to some embodiments, UE 102 may transmit a physical random access channel (PRACH) preamble based on the uplink access repetition number to be received at eNB 104. UE 102 may also receive a random access response (RAR) message based on the downlink repetition number from eNB 104. These embodiments are described in more detail below.

The S1 interface 115 separates the RAN 100 from the EPC 120. It 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 very dense phone usage, such as train stations. As used herein, the term low-power (LP) eNB refers to any suitable relatively low-power eNB for implementing narrow cells (narrower than macro cells), such as femtocells, picocells, or microcells. Femtocell eNBs are typically provided by mobile network operators to their residential or enterprise customers. Femtocells are typically the size of a residential gateway or smaller and are typically connected to the user's broadband line. Once inserted, the femtocell connects to the mobile operator's mobile network and provides additional coverage for the residential femtocell, typically within a range of 30 to 50 meters. Therefore, an LP eNB may be a femtocell eNB because it is coupled via a PDN GW 126. Similarly, a picocell is a wireless communication system that typically covers a small area, such as in a building (office, shopping mall, train station, etc.) or, more recently, in an airplane. A picocell eNB is typically connected to another eNB via an X2 link, such as a macro eNB through its base station controller (BSC) functionality. Therefore, a low-end (LP) eNB can be implemented using a picocell eNB, as the picocell eNB is coupled to the macro eNB via the X2 interface. A picocell eNB or other low-end (LP) eNB can include some or all of the functionality of a macro eNB. In some cases, this 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 similar techniques can be used for uplink transmissions from UE 102 to eNB 104. The grid is a time-frequency grid, referred to as a resource grid or time-frequency resource grid, which represents the physical resources in the downlink during each time slot. This time-frequency representation is a convention in OFDM systems and makes radio resource allocation intuitive. Each row and column of the resource grid corresponds to an OFDM symbol and an OFDM subcarrier, respectively. The duration of the resource grid in the time domain corresponds to a time slot in a radio frame. The smallest time-frequency unit in the resource grid represents a resource element. Each resource grid includes multiple resource blocks, which describe the mapping of certain physical channels to resource elements. Each resource block includes a collection of resource elements, and in the frequency domain, this represents the minimum amount of resources that can currently be allocated. There are several different physical downlink channels represented using such resource blocks. Of particular relevance to the present disclosure, two of these physical downlink channels 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 UE 102 ( FIG. 1 ). The physical downlink control channel (PDCCH) carries, among other things, information about resource allocations and transport formats associated with the PDSCH channel. It also informs UE 102 about H-ARQ information, transport formats, and resource allocations associated with uplink shared channels. Typically, downlink scheduling (allocation of control and shared channel resource blocks to UEs within a cell) is performed at the eNB based on channel quality information fed back from UE 102 to eNB 104, and downlink resource allocation information is then sent to UE 102 on a control channel (PDCCH) intended for (and allocated to) UE 102.

PDCCH uses CCE (control channel element) to transmit control information. Before being mapped to resource elements, PDCCH complex-valued symbols are first organized into quadruplets, which are then premuted for rate matching using a sub-block interleaver. Each PDCCH is sent using one or more of these control channel elements (CCE), where each CCE corresponds to nine groups of four physical resource elements called resource element groups (REGs). Four QPSK symbols are mapped to each REG. Depending on the size of the DCI and the channel conditions, the PDCCH can be sent using one or more CCEs. Four or more different PDCCH formats with different numbers of CCEs (e.g., aggregation levels, L=1, 2, 4, or 8) are defined in LTE.

FIG2 shows a block diagram of a UE 200 according to some embodiments, while FIG3 shows a block diagram of an 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 FIG1 , while the eNB 300 may be the eNB 104 shown in FIG1 . The UE 200 may include physical layer circuitry 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 also include physical layer circuitry 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 also include a medium access control layer (MAC) circuit 204 to control access to the wireless medium, while the eNB 300 may also include a medium access control layer (MAC) circuit 304 to control access to the wireless medium. The UE 200 may also include a processing circuit 206 and a memory 208 arranged to perform the various operations described herein, while the eNB 300 may also include a processing circuit 306 and a memory 308 arranged to perform the various operations described herein.

In some embodiments, the mobile device or other device described herein may be a portion 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 smartphone, 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 device that can wirelessly receive and/or transmit information. In some embodiments, the mobile device or other device may be a UE 200 or an eNB 300 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 components. The display may be an LCD screen including a touch screen.

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 RF signals. In some multiple-input multiple-output (MIMO) embodiments, antennas 201, 301 may be effectively separated to exploit spatial diversity and potentially different channel characteristics.

Although the UE 200 and the eNB 300 are each shown as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by a combination of software-configured elements (such as 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 a combination of various 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 operating 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 executed by at least one processor to implement the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). 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 and may be configured with instructions stored on a computer-readable storage device.

According to an embodiment, UE 102 may determine a coverage enhancement (CE) category for UE 102 based at least in part on downlink channel statistics related to reception of one or more downlink signals from eNB 104. The CE category may reflect one of a system resource level and an additional link margin level that enables performance to reach or exceed a performance threshold. UE 102 may also transmit a physical random access channel (PRACH) preamble in a PRACH frequency resource according to an uplink access repetition number. The PRACH frequency resource and the uplink access repetition number may be based at least in part on the CE category of UE 102. These embodiments are described in more detail below.

In some scenarios, a UE 102 operating in a cellular communication network (e.g., 100) may lose connectivity to the network or may have difficulty remaining connected to the network for various reasons. As an example, the UE 102 may move toward an area with reduced coverage (e.g., the edge of a cell or sector). As another example, the UE 102 may be operating in an area substantially outside the normal coverage of the network (e.g., the basement of a building). As another example, the UE 102 or other device may support machine type communication (MTC). An MTC device or a device operating in MTC mode may be expected to operate in highly challenging link budget scenarios while exchanging small amounts of data at infrequent rates.

Referring to FIG4 , an example connection scenario 400 is shown in which a tower eNB 405 (which may be eNB 104) and three UEs 410, 415, and 420 (which may be UE 102) located at various distances from eNB 405 are operating or attempting to operate as part of a 3GPP or other network. It should be noted that eNB 405 is not limited to a tower configuration and the scenario described herein is not limited to the number or distribution of eNBs 405 or UEs 410, 415, and 420 shown in FIG4 . A first UE 410 is in communication with eNB 405 via link 430 and is well within the coverage area 450 of eNB 405. As such, it is not expected that the first UE 410 will be involved in a reconnection process. A second UE 415 is located in a demarcated area 460 outside of coverage area 450 and may attempt a reconnection process via link 435 (note that the link may not actually have been established or is not yet stable). Similarly, the third UE 420 is also located in another defined area 470 outside the coverage area 450, which is farther away from the eNB 405 than the first defined area 460. The third UE 420 may also attempt a reconnection procedure via the link 440 (which may not actually be established or is not stable yet).

Second UE 415 and third UE 420 may be described as requiring "coverage enhancement," or operating in "coverage enhancement mode," because they are outside coverage area 450. Furthermore, while both UEs 415 and 420 are outside coverage area 450, third UE 420 may experience more difficulty or challenges reconnecting than second UE 415 because it is further away from eNB 405. Therefore, different categories of coverage enhancement may be specified depending on how far out of coverage the UE is, or other factors. In some embodiments, a description of the categories may be used. For example, third UE 420 may be considered to be in a "high" category of coverage enhancement mode, while second UE 415 may be considered to be in a "low" category of coverage enhancement mode. In some embodiments, the categories may be quantified, such as 5 dB, 10 dB, and 15 dB, which may represent the additional link budget that may be added to UEs 415 and 420 to achieve "normal operation." Normal operation may be characterized by any suitable criteria (e.g., target packet error rate, acquisition time, data throughput, etc.).

It should be noted that for illustrative purposes, the above discussion focuses on path loss due to distance, but this is not limiting. It is known in the art that path loss, signal loss, coverage holes, and the like can result from effects other than distance, such as obstructions or indoor locations. For example, a device located in the basement of a building close to eNB 405 may actually require coverage enhancement, while another device located further away but outdoors may have a stronger connection to eNB 405 and require less or no coverage enhancement.

Referring to FIG5 , a method 500 operating in accordance with a coverage enhancement mode is illustrated. It is important to note that embodiments of the method 500 may include more or even fewer operations or processes than those illustrated in FIG5 . Furthermore, embodiments of the method 500 are not necessarily limited to the chronological order illustrated in FIG5 . In describing the method 500, reference may be made to FIG1-4 and FIG6-9 , although it should be understood that the method 500 may be implemented using any other suitable system, interface, or component. For example, reference may be made to the scenario 400 in FIG4 , previously illustrated for illustrative purposes, although the techniques and operations of the method 500 are not limited thereto.

Furthermore, while method 500 and other methods described herein may refer to an eNB 104 or UE 102 operating in accordance with 3GPP or other standards, embodiments of those methods are not limited to those eNBs 104 or UEs 102 and may also be implemented on other mobile devices such as Wi-Fi access points (APs) or user stations (STAs). Furthermore, method 500 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 (e.g., IEEE 802.11). Furthermore, method 500 and other methods described herein may be implemented by a UE or other device that supports or is configured to support machine type communication (MTC) operations.

At operation 505 of method 500, a coverage enhancement (CE) category may be determined for UE 102. The CE category of UE 102 may reflect one of an additional link margin level and a system resource level that brings performance to or above a performance threshold associated with a normal operating mode of UE 102. In some embodiments, the CE category may be determined from a group of candidate CE categories. As examples, candidate CE categories may include 5, 10, or 15 dB, which may refer to a link budget increase that enables a performance level for UE 102 in terms of error rate, throughput, or other performance metrics. Other CE categories may include "no CE" or the like, which may reflect that UE 102 is not operating in CE mode. In addition, the examples previously described with respect to CE categories, such as "high" and "low," may also be used.

The determination of the CE category may be based at least in part on downlink channel statistics related to the reception of one or more downlink signals from an evolved Node B (eNB) at the UE. In some embodiments, the downlink channel statistics may include reference signal received power (RSRP) or other path loss metrics at the UE. As an example, the path loss determined at the UE 102 may be compared to a predetermined link budget path loss to determine the CE category of the UE 102. The predetermined link budget path loss may indicate a maximum path loss for "normal" operation in terms of packet error rate or other metrics. Statistics may be based on or collected during any suitable time period, which may be on the order of symbol periods, subframes, seconds, minutes, or longer. Measurements may include averages, moving averages, weighted averages, or other suitable statistics, and may refer to scalar or logarithmic (dB) quantities.

At operation 510, a PRACH preamble may be transmitted in a PRACH frequency resource based on the uplink access repetition number. The PRACH frequency resource may be based at least in part on the CE category of the UE 102. In some embodiments, the group of candidate CE categories may include a first and a second candidate CE category, wherein the PRACH frequency resources for the first CE category and the PRACH frequency resources for the second CE category are mutually exclusive. In addition, the group of candidate CE categories may include more than the first and second candidate CE categories, and some or all of the candidate CE categories may be associated with different PRACH frequency resources, which may be mutually exclusive. Thus, the frequency resources used for transmission of the PRACH preamble may indicate or reflect the CE category determined for the UE 102. The mapping or allocation of PRACH frequency resources to candidate CE categories may be predetermined, may be part of a 3GPP or other standard, or may be determined by the network. In addition, the PRACH frequency resources used by the UE 102 when operating in CE mode may be separate from the PRACH frequency resources used by the UE 102 when not operating in CE mode.

In some embodiments, the random access radio network temporary identifier (RA-RNTI) calculated for the PRACH preamble transmission may depend on whether the UE 102 is in CE mode. As an example, the RA-RNTI may be calculated as (1+t_id+10*f_id+c*MTC_id), where t_id is the index of the first subframe of the specified PRACH preamble, f_id is the index of the specified PRACH preamble within the subframe, the value of "c" may be 60, and MTC_id is 0 or 1 when the UE 102 is not in CE mode or is in CE mode.

The uplink access repetition number may be based at least in part on the CE category of the UE 102. In some embodiments, the group of candidate CE categories may include a first and a second candidate CE category, wherein the uplink access repetition number for the first CE category is different from the uplink access repetition number for the second CE category. The uplink access repetition number may refer to the number of repetitions of the PRACH preamble to be sent by the UE 102. In addition, the group of candidate CE categories may include more than the first and second candidate CE categories, and some or all of the candidate CE categories may be associated with different uplink access repetition numbers. In some embodiments, the uplink access repetition number (or other repetition numbers or levels described herein) considered "high" for a CE category may be greater than the uplink access repetition number considered "low" for a CE category. For example, the UE 102 may repeat the PRACH preamble 100 times when operating in a 15 dB CE category, and may only repeat the PRACH preamble 20 times when operating in a 5 dB CE category. Thus, when UE 102 operates in a higher CE category, a larger number of repetitions may provide it with additional diversity or energy gain. The number of repetitions for a candidate CE category may be predetermined by simulation or analysis or other techniques. In some embodiments, repetitions of the PRACH preamble may be transmitted during different time periods.

At operation 515 of method 500, a random access response (RAR) may be received from eNB 104 based on the downlink repetition number. As previously described, the PRACH resource used by UE 102 may indicate the CE category determined for UE 102, which may be determined by eNB 104 using knowledge of the mapping and allocation between PRACH frequency resources and CE categories described previously. The downlink repetition number may refer to the number of repetitions of the RAR to be sent by eNB 104, and the repetition number may be different for some or all of the candidate CE categories. Therefore, the downlink repetition number may be based at least in part on the CE category of UE 102 and may be predetermined through simulation or analysis or other techniques.

In some embodiments, the downlink repetition number may be included in the PDCCH. A new downlink control information (DCI) format or an existing DCI format in the 3GPP standard (e.g., "1A" or other) may include a downlink repetition number or an indicator thereof. As an example, the downlink repetition number may include a two-bit bit field corresponding to "no repetition" and a repetition level of 0, 1, or 2, wherein the number of repetitions associated with each repetition level may be predefined or signaled in other messages. As another example, the downlink repetition number may be a single bit corresponding to "no repetition" or a repetition according to a predefined or pre-signaled number of repetitions. As another example, the downlink repetition number may be a bit field that explicitly states the number of repetitions to be used. However, the embodiments are not limited to the levels or the number of bits described in the above examples, because the downlink repetition number may describe or specify the number of repetitions in any suitable manner. In some embodiments, the downlink repetition number may refer to a "PDSCH repetition level" to be described below.

In some embodiments, RAR may be received on PDSCH frequency resources that are based at least in part on the CE category of UE 102. In addition, the PDSCH frequency resources used for RAR may be separated from the PDSCH frequency resources used for RAR messages or other messages for UEs not operating in CE mode. In some embodiments, a predefined frequency allocation for PDSCH may be determined. Thus, PDCCH may not need to be decoded at UE 102, which may be beneficial given that UE 102 may have to use a large number of repetitions of PDCCH when operating in CE mode. That is, UE 102 may avoid decoding PDCCH as part of receiving RAR. Such an arrangement may be considered "PDCCH-less" operation.

In some embodiments, dedicated PDSCH frequency resources may be appropriately predefined and configured for coverage-limited MTC UEs. Furthermore, knowledge of a fixed timing relationship between PRACH transmissions and RAR receptions may be utilized at UE 102. Knowledge of the transport format of PDSCH transmissions may also be utilized at UE 102. In some embodiments, control messages such as SIB-2 or other system information block (SIB) messages may include information such as the timing relationship or transport format just described. A control message (either a dedicated message or a broadcast message) may be sent by eNB 104 to UE 102. Furthermore, in some embodiments, information such as the timing relationship or transport format just described may also be predetermined.

At operation 520, an uplink control message may be sent on the PUSCH resources according to the uplink control repetition number. The transmission may be in response to reception of the RAR at the UE 102. In some embodiments, the uplink control message may be an "L2/L3" message, or may include one or more L2/L3 messages, or be included in one or more L2/L3 messages.

The uplink control repetition number may refer to the number of repetitions of the uplink control message to be sent by UE 102, and the repetition number may be different for some or all CE categories in the candidate CE categories. In some embodiments, the uplink control repetition number may be based at least in part on the CE category of UE 102 and may be predetermined by simulation or analysis or other techniques. In some embodiments, the uplink control repetition number may be included in the RAR message received at UE 102 in operation 515. In some embodiments, the uplink control repetition number may be included in the RAR content of the RAR message or may be included in the uplink grant included in the RAR message (as will be described in more detail with respect to method 600 and FIG. 7 ). In addition, the uplink control repetition number may be a "PUSCH repetition level" that refers to the number of repetitions to be used for PUSCH transmission.

Uplink control messages may be sent on PUSCH frequency resources based at least in part on the CE category of UE 102. Furthermore, PUSCH frequency resources used for uplink control messages may be separate from PUSCH frequency resources used for uplink control messages or other messages for UEs not operating in CE mode.

In some embodiments, the uplink control message may include a second CE category for the UE 102, which may be determined at the UE 102 at least in part based on the reception of the RAR at operation 515. For example, based on the received signal quality, signal level, or other metric of the RAR, the UE 102 may select the second CE category for the UE 102. The second category may be selected from a second group of candidate CE categories, which may be different from or the same as the group of candidate CE categories used in other operations such as 505-520. For example, the second group of candidate CE categories may cover a larger range or provide finer granularity. Thus, the second CE category may be a new or refined value that may provide the eNB 104 with more information about the coverage enhancement for the UE 102.

At operation 525, a contention resolution message may be received from the eNB based on a downlink repetition number. In some embodiments, the downlink repetition numbers of operations 515 and 525 may be the same. However, this arrangement is not limiting, and in some embodiments, the two numbers may be different. As previously described, the downlink repetition number used at operation 525 may refer to the number of repetitions of the contention resolution message sent by the eNB 104, and the repetition numbers may be different for some or all of the candidate CE categories. In some embodiments, the downlink repetition number used at operation 525 may be based at least in part on the CE category of the UE 102 and may be predetermined through simulation or analysis or other techniques.

Referring to FIG6 , a method 600 for operating in coverage enhancement mode is shown. As previously mentioned with respect to method 500, embodiments of method 600 may include more or even fewer operations or processes than those shown in FIG6 , and embodiments of method 600 are not necessarily limited to the time sequence shown in FIG6 . In describing method 600, reference may be made to FIG1-5 and FIG7-9 , although it should be understood that method 600 may be implemented using any other suitable systems, interfaces, or components. For example, reference may be made to scenario 400 in FIG4 , previously shown for illustrative purposes, although the techniques and operations of method 600 are not limited thereto. Furthermore, embodiments of method 600 may be referred to as eNB 104, UE 102, AP, STA, or other wireless or mobile device.

It should be noted that method 600 may be implemented at eNB 104 and may include an exchange of signals or messages with UE 102. Similarly, method 500 may be implemented at UE 102 and may include an exchange of signals or messages with eNB 104. In some cases, the operations and techniques described as part of method 500 may be related to method 600. For example, the operations of method 500 may include the transmission of a message by UE 102, while the operations of method 600 may include the reception of the same message at eNB 104.

At operation 605 of method 600, a PRACH preamble may be received at eNB 104 from UE 102 operating in coverage enhancement (CE) mode on a PRACH frequency resource. The PRACH preamble may be received based on an uplink access repetition number, which may refer to the number of repetitions of the PRACH preamble sent by UE 102. In some embodiments, the uplink access repetition number may be based at least in part on the CE category of the UE, which may be selected from a group of candidate CE categories, as previously described. The uplink access repetition number for each CE category may be different and may also be known at eNB 104 for use in receiving the PRACH at operation 605.

At operation 610, a CE category may be determined for the UE 102 from the group of candidate CE categories, and the determination may be based at least in part on the PRACH frequency resources used for the PRACH preamble. As previously described, some or all of the candidate CE categories may be associated with different PRACH frequency resources, which may be mutually exclusive. The mapping or allocation of PRACH frequency resources to candidate CE categories may be known at the eNB 104. Thus, the eNB 104 may determine the CE category of the UE 102 based on which PRACH frequency resources are used. In some embodiments, the PRACH frequency resources used by the UE 102 when operating in CE mode may be separate from the PRACH frequency resources used by the UE 102 when not operating in CE mode.

At operation 615, a random access response (RAR) may be sent according to a downlink repetition number, which may be based at least in part on the CE category of the UE 102. In some embodiments, a PDSCH frequency resource based at least in part on the CE category of the UE 102 may be used for transmission of the RAR, and the PDSCH frequency resource may be separate from a second PDSCH frequency resource for UEs not operating in CE mode. In some embodiments, the RAR message may be sent in response to receiving the PRACH preamble at operation 605.

A physical downlink control channel (PDCCH) data block including PDSCH resource assignments for UEs not operating in CE mode may be transmitted. Furthermore, the eNB 104 may refrain from transmitting PDCCH data blocks for UEs operating in CE mode. Consequently, UEs operating in CE mode may receive RARs on predetermined PDSCH frequency resources. Such an arrangement may be considered "PDCCH-less" operation, as UEs operating in CE mode may receive RARs (or other messages) on PDSCH resources without decoding PDCCH data blocks.

In addition, a control message may also be sent by the eNB 104 for reception at the UE 102, which may include an allocation of PDSCH frequency resources. The control message may also include other information, such as a modulation and coding scheme (MCS) indicator for the RAR transmission. The MCS indicator may be an index that refers to an MCS from a set of predetermined candidate MCSs, and each candidate MCS may refer to a modulation type (e.g., BPSK, QPSK, QAM, or other) and a forward error correction (FEC) coding rate. The timing relationship between the PRACH transmission at the UE 102 and the RAR transmission may also be included in the control message. In some embodiments, the timing relationship may be fixed. In some embodiments, the control message may be a SIB-2 or other system information block (SIB) message of 3GPP or other standards.

At operation 620, an uplink control message may be received from UE 102 on the PUSCH resource according to the uplink control repetition number. In some embodiments, the uplink control repetition number may be based at least in part on the CE category of UE 102 and may be predetermined. In some embodiments, the RAR (or another message from eNB 104) sent at operation 615 may include the uplink control repetition number for UE 102 to use. In some cases, the value sent in the RAR may override or replace a predetermined value for the uplink control repetition number (that the UE may otherwise use), e.g., a value based on the CE category as described above.

PUSCH frequency resources based at least in part on the CE category of UE 102 may be used for reception of uplink control messages at eNB 104 and may be separate from second PUSCH frequency resources for UEs not operating in CE mode.

At operation 625, a contention resolution message may be sent based on the downlink repetition number. As previously described, the downlink repetition number may be based at least in part on the CE category of UE 102. Furthermore, the downlink repetition number used at operation 625 may be the same as the downlink repetition number used at operation 615, but is not limited thereto. In some embodiments, a PDSCH frequency resource based at least in part on the CE category of UE 102 may be used to send the contention resolution message. The PDSCH frequency resource may or may not overlap with the PDSCH frequency resource used to send the RAR at operation 615.

At operation 630 of method 600, a second PRACH preamble may be received from a second UE that is not operating in CE mode. The second PRACH preamble may be received on a second PRACH frequency resource allocated for the UE that is not operating in CE mode. In some embodiments, the second PRACH frequency resource may be mutually exclusive with a PRACH frequency resource allocated for the UE that is operating in CE mode. It should also be noted that the UE that is not operating in CE mode may include a legacy UE that does not support coverage enhancement.

7 , an example of a RAR message or MAC RAR message is shown according to some embodiments. The RAR message 705 may include other parameters or information 710 that may or may not be related to coverage enhancement or connection or reconnection operations. The RAR message 705 may also include an uplink grant 715, which may include a PUSCH repetition level 725 and other parameters or information 720 that may or may not be related to coverage enhancement or connection or reconnection operations. As will be described below, the PUSCH repetition level 725 may be the same as or serve the same purpose as the uplink control repetition level previously described with respect to methods 500 and 600.

Another example RAR 755 may include other parameters or information 760 that may or may not be related to coverage enhancement or connection or reconnection operations. The RAR 755 may also include an uplink grant 765 and a PUSCH repetition level 770. Thus, in contrast to the PUSCH repetition level 725 that may be included in the uplink grant 715, the PUSCH repetition level 770 may be external to the uplink grant 765.

In some embodiments, the PUSCH repetition level 725 may be included as part of the RAR 705 sent by the eNB 104 at operation 615, or may be included as part of the RAR 705 received at the UE 102 at operation 515. In some embodiments, the PUSCH repetition level 770 may be included as part of the RAR 755 sent by the eNB 104 at operation 615, or may be included as part of the RAR 755 received at the UE 102 at operation 515. It should be noted that the RARs 705, 755 are used to illustrate the concept of RARs and are not limiting, and other suitable arrangements for using RARs may be used.

8 , a signal flow diagram illustrates an example of a method 800 for connection or reconnection between UE 102 and eNB 104. It should be noted that some operations of method 800 may be similar to those included in methods 500 or 600. In such cases, the description of such operations in methods 500 or 600 may apply to the corresponding operations included in method 800. Furthermore, the method 800 illustrated in FIG8 may be used to illustrate the concepts of the connection or reconnection process, but is not intended to be limiting. Fewer or additional operations may be included in other embodiments of the connection or reconnection method, and the temporal order of the operations is not limited to the order illustrated in FIG8 .

At operation 805, a PRACH preamble may be transmitted from UE 102 to eNB 104 according to the uplink access repetition number. At operation 810, eNB 104 may transmit a random access response (RAR) to UE 102 according to the downlink repetition number. At operation 815, UE 102 may adjust its uplink timing. It should be noted that UE 102 may perform operation 805 without being synchronized with the timing of eNB 104 and may require or refine its timing during reception of the RAR at operation 810. At operation 820, UE 102 may transmit an uplink control message (e.g., an L2/L3 message) to eNB 104 according to the uplink control repetition number. At operation 825, eNB 104 may transmit a contention resolution message to UE 102 according to the same downlink repetition number used at operation 810.

As previously described, the repetition number can quantify how many times a message (e.g., a PRACH preamble or RAR) can be repeated and can depend on the CE category of the UE 102. For example, the uplink access repetition number can refer to the number of repetitions of the PRACH preamble. For the connection or reconnection process, the messages exchanged between the UE 102 and the eNB 104 can be repeated according to a predetermined value, which can be determined through simulation or analysis. In some embodiments, a table can include repetition values for different CE categories and can be used for the operations described previously.

An example of such a table 900 is shown in FIG9 . Column 910 includes three CE categories 912, 914, 916, which correspond to 5, 10, and 15 dB in this example. The rows associated with each of the three CE categories 912, 914, 916 may include a repetition value used when the UE 102 operates in that particular CE category. The values of columns 920, 930, 940, 950 may correspond to a PRACH repetition level 920, an (E)PDCCH repetition level 930, a PDSCH repetition level 940, and a PUSCH repetition level 950. These designations on columns 920, 930, 940, 950 may be the same as or related to the repetition values previously described. As an example, the PRACH repetition level 920 may be the same as or related to the uplink access repetition number. As another example, the PDCCH repetition level 930 or the PDSCH repetition level 940 may be the same as or related to the downlink repetition number. As another example, the PUSCH repetition level 950 may be the same as or related to the uplink control repetition number.

Disclosed herein is a user equipment (UE) operating in accordance with a coverage enhancement (CE) mode. The UE may include hardware processing circuitry configured to determine a CE category of the UE from a group of candidate CE categories based, at least in part, on downlink channel statistics related to reception of one or more downlink signals from an evolved Node B (eNB) at the UE. The hardware processing circuitry may also be configured to send a physical random access channel (PRACH) preamble in PRACH frequency resources based on an uplink access repetition number. In some embodiments, these PRACH frequency resources and the uplink access repetition number may be based, at least in part, on the CE category of the UE. In some embodiments, the CE category of the UE may reflect one of a system resource level and an additional link margin level that brings performance to a performance threshold associated with a normal operating mode of the UE or above the performance threshold. In some embodiments, the downlink channel statistics include a reference signal received power (RSRP) or a path loss measurement at the UE.

In some embodiments, the group of candidate CE categories may include a first candidate CE category and a second candidate CE category, wherein the uplink access repetition number for the first CE category is different from the uplink access repetition number for the second CE category. In some embodiments, the group of candidate CE categories may include a first candidate CE category and a second candidate CE category, wherein the PRACH frequency resources for the first CE category and the PRACH frequency resources for the second CE category are mutually exclusive.

The hardware processing circuit may also be configured to receive a random access response (RAR) from the eNB based on a downlink repetition number based at least in part on the CE category of the UE. In some embodiments, the RAR may be received on a physical downlink shared channel (PDSCH) frequency resource based at least in part on the CE category of the UE, and the PDSCH frequency resource may be separate from a second PDSCH frequency resource for UEs not operating in CE mode. The hardware processing circuit may also be configured to receive a PDCCH data block from the eNB on a physical downlink control channel (PDCCH) frequency resource for UEs operating in CE mode. In some embodiments, the PDCCH data block may include a downlink control information (DCI) block including the downlink repetition number. The hardware processing circuit may also be configured to suppress decoding the physical downlink control channel (PDCCH) data block as part of receiving the RAR.

The hardware processing circuit may also be configured to, in response to reception of the RAR, send an uplink control message on a physical uplink shared channel (PUSCH) resource based on the uplink control repetition number. In some embodiments, the RAR may include an uplink control repetition number. In some embodiments, the RAR may include an uplink grant for the UE, and the uplink grant may include the uplink control repetition number. In some embodiments, the uplink control message may include a second CE category of the UE, the second CE category may be selected from a second group of candidate CE categories, and the second CE category may be determined at least in part based on reception of the RAR. The hardware processing circuit may also be configured to receive a contention resolution message from the eNB based on the downlink repetition number. In some embodiments, the UE may also support machine type communication (MTC). In some embodiments, the UE may operate according to the 3GPP protocol.

Disclosed herein is a non-transitory computer-readable storage medium storing instructions for execution by one or more processors to perform operations for communicating by a user equipment (UE) in coverage enhancement mode. The operations may configure the one or more processors to: determine a CE category of the UE from a group of candidate CE categories based at least in part on downlink channel statistics related to reception of one or more downlink signals from an evolved Node B (eNB) at the UE; and transmit a PRACH preamble on a physical random access channel (PRACH) frequency resource based on an uplink access repetition number. In some embodiments, the PRACH frequency resource and the uplink access repetition number may be based at least in part on the UE's CE category. The operations may further configure the one or more processors to: receive a random access response (RAR) from the eNB based on a downlink repetition number based at least in part on the UE's CE category. The operations may further configure the one or more processors to: in response to receiving the RAR, transmit an uplink control message on a physical uplink shared channel (PUSCH) resource based on an uplink control repetition number based at least in part on the UE's CE category.

Disclosed herein is a method for communicating in coverage enhancement mode performed by a user equipment (UE). The method includes determining a CE category of the UE from a group of candidate CE categories based at least in part on downlink channel statistics related to reception of one or more downlink signals from an evolved Node B (eNB) at the UE. The method may further include sending a physical random access channel (PRACH) preamble in a PRACH frequency resource based on an uplink access repetition number. In some embodiments, these PRACH frequency resources and the uplink access repetition number may be based at least in part on the CE category of the UE. The method may further include receiving a random access response (RAR) from the eNB based on the downlink repetition number, the downlink repetition number being based at least in part on the CE category of the UE. The method may further include sending an uplink control message on a physical uplink shared channel (PUSCH) resource based on the uplink control repetition number in response to receiving the RAR, the uplink control repetition number being based at least in part on the CE category of the UE.

Disclosed herein is an evolved Node B (eNB) operating in accordance with Coverage Enhancement (CE) mode. The eNB includes hardware processing circuitry configured to receive a physical random access channel (PRACH) preamble from a user equipment (UE) operating in CE mode on a PRACH frequency resource allocated for the UE. The hardware processing circuitry may also be configured to determine a CE category of the UE from a group of candidate CE categories based at least in part on the received PRACH frequency resource for the PRACH preamble; and send a random access response (RAR) based on a downlink repetition number based at least in part on the CE category of the UE. In some embodiments, the group of candidate CE categories includes a first candidate CE category and a second candidate CE category, the PRACH frequency resources for the first CE category and the second CE category being mutually exclusive. In some embodiments, the RAR may be sent on a physical downlink shared channel (PDSCH) frequency resource based at least in part on the CE category of the UE; and the PDSCH frequency resource may be separate from a second PDSCH frequency resource for UEs not operating in CE mode.

The hardware processing circuitry may also be configured to transmit a physical downlink control channel (PDCCH) data block including a PDSCH resource allocation for UEs not operating in CE mode, and suppress transmission of PDCCH data blocks for UEs operating in CE mode. The hardware processing circuitry may also be configured to transmit a control message including an allocation for PDSCH frequency resources, a modulation and coding scheme (MCS) indicator for the RAR transmission, and a timing relationship between the PRACH transmission and the RAR transmission at the UE.

The hardware processing circuitry may also be configured to receive an uplink control message from the UE on a physical uplink shared channel (PUSCH) resource based on an uplink control repetition number. In some embodiments, the uplink control repetition number may be based at least in part on the CE category of the UE. In some embodiments, the RAR includes the uplink control repetition number. The hardware processing circuitry may also be configured to, in response to receiving the uplink control message, send a contention resolution message based on the downlink repetition number. The hardware processing circuitry may also be configured to receive, from a second UE that is not operating in CE mode, a second PRACH preamble on a second PRACH frequency resource allocated for a UE that is not operating in CE mode. In some embodiments, the second PRACH frequency resource is mutually exclusive with a PRACH frequency resource allocated for a UE that is operating in CE mode. In some embodiments, the eNB may operate in accordance with 3GPP protocols.

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

Claims (30)

1. A user equipment (UE) operating according to a coverage enhancement (CE) mode, the UE including hardware processing circuitry configured to: The CE category of the UE is determined from a group of candidate CE categories based at least in part on downlink channel statistics relating to the reception of one or more downlink signals from the evolved Node B eNB at the UE; and The PRACH preamble is transmitted in the physical random access channel PRACH frequency resources according to the number of uplink access repetitions. The PRACH frequency resources and the number of uplink access duplicates are at least partially based on the UE's CE category, and the eNB determines the UE's CE category from the group of candidate CE categories based at least partially on the PRACH frequency resources used for receiving the PRACH preamble. 2. The UE of claim 1, wherein the CE category of the UE reflects one of a system resource level and an additional link margin level that causes the performance to reach or exceed a performance threshold associated with the normal operating mode of the UE. 3. The UE as described in claim 1, wherein the downlink channel statistics include the Reference Signal Received Power (RSRP) or path loss metric at the UE. 4. The UE as claimed in claim 1, wherein the group of candidate CE categories includes a first candidate CE category and a second candidate CE category, the number of uplink access duplicates for the first candidate CE category is different from the number of uplink access duplicates for the second candidate CE category, and the PRACH frequency resources for the first candidate CE category and the PRACH frequency resources for the second candidate CE category are mutually exclusive. 5. The UE of claim 1, wherein the hardware processing circuitry is further configured to: receive a Random Access Response (RAR) from the eNB based on a downlink repetition number, the downlink repetition number being at least partially based on the CE class of the UE. 6. The UE as described in claim 5, wherein: The RAR is received on the Physical Downlink Shared Channel (PDSCH) frequency resources, at least in part based on the UE's CE category; and The PDSCH frequency resources are separate from the second PDSCH frequency resources for UEs that are not operating in the CE mode. 7. The UE as claimed in claim 6, wherein: The hardware processing circuitry is also configured to receive PDCCH data blocks from the eNB on the physical downlink control channel (PDCCH) frequency resources for a UE operating in the CE mode. The PDCCH data block includes a downlink control information (DCI) block, and the DCI block includes the downlink repetition number. 8. The UE of claim 6, wherein the hardware processing circuitry is further configured to suppress the decoding of physical downlink control channel (PDCCH) data blocks as part of the reception of the RAR. 9. The UE as claimed in claim 5, wherein the hardware processing circuit is further configured to: in response to the reception of the RAR, transmit an uplink control message on the Physical Uplink Shared Channel (PUSCH) resource according to the uplink control repetition number. 10. The UE of claim 9, wherein the RAR includes the uplink control repeat number. 11. The UE of claim 10, wherein the RAR includes an uplink grant for the UE, and the uplink grant includes the number of uplink control repetitions. 12. The UE as claimed in claim 9, wherein: The uplink control message includes the UE's second CE category; The second CE category was selected from the second group of candidate CE categories; and The second CE category is determined at least in part based on the receipt of the RAR. 13. The UE of claim 9, wherein the hardware processing circuitry is further configured to: receive a contention resolution message from the eNB based on the downlink repetition number. 14. The UE as claimed in claim 1, wherein the UE further supports Machine Type Communication (MTC) and operates in accordance with 3GPP protocols. 15. A non-transitory computer-readable storage medium storing instructions executable by one or more processors to perform operations communicated by a user equipment (UE) in an overlay-enhanced CE mode, the operations configuring the one or more processors to: The CE category of the UE is determined from a group of candidate CE categories based at least in part on downlink channel statistics relating to the reception of one or more downlink signals from the evolved Node B eNB at the UE; and The PRACH preamble is transmitted in the physical random access channel PRACH frequency resources according to the number of uplink access repetitions. The PRACH frequency resources and the number of uplink access duplicates are at least partially based on the UE's CE category, and the eNB determines the UE's CE category from the group of candidate CE categories based at least partially on the PRACH frequency resources used for receiving the PRACH preamble. 16. The non-transitory computer-readable storage medium of claim 15, wherein the operation further comprises configuring the one or more processors to: receive a random access response (RAR) from the eNB based on a downlink repetition number, the downlink repetition number being at least partially based on the CE class of the UE. 17. The non-transitory computer-readable storage medium of claim 16, wherein the operation further comprises configuring the one or more processors to: in response to the reception of the RAR, transmit an uplink control message on a Physical Uplink Shared Channel (PUSCH) resource based on an uplink control repetition number, the uplink control repetition number being at least partially based on the CE class of the UE. 18. A method performed by a user equipment (UE) for communicating in a coverage enhancement CE mode, the method comprising: The CE category of the UE is determined from a group of candidate CE categories based at least in part on downlink channel statistics relating to the reception of one or more downlink signals from the evolved Node B eNB at the UE; and The PRACH preamble is transmitted in the physical random access channel PRACH frequency resources according to the number of uplink access repetitions. The PRACH frequency resources and the number of uplink access duplicates are at least partially based on the UE's CE category, and the eNB determines the UE's CE category from the group of candidate CE categories based at least partially on the PRACH frequency resources used for receiving the PRACH preamble. 19. The method of claim 18, further comprising: receiving a random access response (RAR) from the eNB based on a downlink repetition number, the downlink repetition number being at least partially based on the CE class of the UE. 20. An evolved NodeB eNB operating according to a coverage enhancement CE mode, the eNB including hardware processing circuitry configured to: Receive PRACH preamble from the UE operating in the CE mode on the physical random access channel (PRACH) frequency resources allocated for the user equipment (UE) operating in the CE mode. The CE category of the UE is determined from a group of candidate CE categories, at least in part based on the PRACH frequency resources used for receiving the PRACH preamble; and A Random Access Response (RAR) is sent based on the downlink repetition number, which is at least partially based on the UE's CE class. 21. The eNB of claim 20, wherein the group of candidate CE categories includes a first candidate CE category and a second candidate CE category, and the PRACH frequency resources for the first CE category and the PRACH frequency resources for the second CE category are mutually exclusive. 22. The eNB as claimed in claim 20, wherein: The RAR is transmitted on the Physical Downlink Shared Channel (PDSCH) frequency resources, at least in part, based on the UE's CE category; and The PDSCH frequency resources are separate from the second PDSCH frequency resources for UEs that are not operating in the CE mode. 23. The eNB of claim 22, wherein the hardware processing circuitry is further configured to: transmit PDSCH data blocks including physical downlink control channel (PDCCH) resource allocations for UEs not operating in the CE mode, and suppress the transmission of PDCCH data blocks for UEs operating in the CE mode. 24. The eNB of claim 22, wherein the hardware processing circuitry is further configured to transmit control messages, the control messages including allocation of PDSCH frequency resources, modulation and coding scheme (MCS) indicators for RAR transmissions, and timing relationships between PRACH transmissions and RAR transmissions at the UE. 25. The eNB of claim 20, wherein the hardware processing circuitry is further configured to: receive uplink control messages from the UE on the Physical Uplink Shared Channel (PUSCH) resource according to the number of uplink control repetitions. 26. The eNB of claim 25, wherein the number of uplink control repetitions is at least partially based on the CE class of the UE. 27. The eNB of claim 25, wherein the RAR includes the uplink control repeat number. 28. The eNB of claim 25, wherein the hardware processing circuitry is further configured to: in response to receiving the uplink control message, send a contention resolution message based on the downlink repetition number. 29. The eNB as claimed in claim 20, wherein: The hardware processing circuitry is further configured to receive a second PRACH preamble on a second PRACH frequency resource allocated for a second UE not operating in the CE mode; and The second PRACH frequency resource is mutually exclusive with the PRACH frequency resource allocated for the UE operating in the CE mode. 30. The eNB of claim 20, wherein the eNB further operates according to 3GPP protocols.