WO2019245662A1

WO2019245662A1 - Methods and apparatus for harq in noma asynchronous transmission

Info

Publication number: WO2019245662A1
Application number: PCT/US2019/031059
Authority: WO
Inventors: Kao-Peng Chou
Original assignee: Google Llc
Priority date: 2018-06-18
Filing date: 2019-05-07
Publication date: 2019-12-26

Abstract

Techniques for Hybrid Automatic Repeat Request (HARQ) procedures in Non-Orthogonal Multiple Access (NOMA) asynchronous transmission are disclosed. A base station (120) transmits (602) a NOMA configuration, including first and second sets of multiple access (MA) signatures and available time-frequency resources for NOMA transmission, to multiple user equipments (UEs) (110) via a wireless link (130). The base station detects (604) and decodes (606) uplink NOMA transmissions from a UE. The base station generates (608) HARQ acknowledgements (ACKS) or negative acknowledgements (NACKS) and determines (610) a UE-specific identifier. If the base station successfully identifies the UE-specific ID and fails during decoding the uplink NOMA transmissions, then it transmits (612) a HARQ NACK in a downlink control information using the first UE-specific ID and, if the base station successfully detects the uplink NOMA transmissions using the first set of MA signatures, also transmits (614) Timing Advance information in a Media Access Control-Control Element.

Description

METHODS AND APPARATUS FOR HARQ IN NOMA ASYNCHRONOUS TRANSMISSION

BACKGROUND

[0001] In Fourth Generation Long Term Evolution (4G LTE), data transmission is scheduled by a base station through Downlink Control Information (DCI). One DCI format is an uplink (UL) grant, which indicates a physical resource, modulation type and coding scheme (MCS), Redundancy Version (RV), and so on. Although many transmission schemes used in 4G LTE can also be used in Fifth Generation New Radio (5G NR), some are inefficient in 5G NR.

SUMMARY

[0002] This document discloses procedures and apparatus for Hybrid Automatic Repeat Request (HARQ) in non-orthogonal multiple access (NOMA) asynchronous transmission. In a NOMA system, a user equipment (UE) (110) can be configured to transmit signals with multiple access (MA) signatures. By applying a multi-user detector (MUD) in a base station (120) and MA signatures in the UE (110), NOMA can increase overall system throughput. Moreover, MUD also improves NOMA robustness during MA signature collisions, making NOMA suitable for asynchronous transmission.

[0003] This summary is provided to introduce simplified concepts of HARQ in NOMA asynchronous transmission. The simplified concepts are further described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Aspects of HARQ in NOMA asynchronous transmission are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:

FIG. 1 illustrates an example wireless network system in which various aspects of HARQ in NOMA asynchronous transmission can be implemented.

FIG. 2 illustrates an example device diagram that can implement various aspects of HARQ in NOMA asynchronous transmission.

FIG. 3 illustrates two example techniques for a user equipment (UE) to transmit data to the base station through a Physical Uplink Shared CHannel (PUSCH).

FIG. 4 illustrates examples of multi-layer transmission.

FIG. 5 shows an example implementation of parallel HARQ processes that LTE supports simultaneously.

FIG. 6 depicts an example method of HARQ in NOMA asynchronous transmissions for a base station in accordance with aspects of the techniques described herein.

FIG. 7 depicts an example method of HARQ in NOMA asynchronous transmissions for a user equipment in accordance with aspects of the techniques described herein.

Detailed Description

[0005] In a Non-Orthogonal Multiple Access (NOMA) system, a user equipment (UE) can be configured to transmit signals with multiple access (MA) signatures. By applying multi-user detection (MUD) in the base station and an MA signature in the UE, NOMA increases overall system throughput. Moreover, MUD also improves NOMA robustness against MA signature collision, making NOMA suitable for asynchronous transmission. [0006] UEs typically perform asynchronous transmission while in an inactive or idle state with respect to Radio Resource Control (RRC), referred to herein as RRC inactive and RRC idle states, respectively. One difference between RRC inactive and RRC idle states is that the UE in the RRC inactive state may still have a configured UE-specific resume-Radio Network Temporary Identity (RNTI), which is usable by the base station for UE-specific control signaling. Generally, Long Term Evolution (LTE) and New Radio (NR) systems use a HARQ mechanism that is based on synchronous transmission in an RRC connected state. Accordingly, the techniques described herein describe HARQ procedures usable in the RRC-inactive state.

[0007] In aspects, a method for a base station to configure and communicate with a user equipment is disclosed. The method includes transmitting, by the base station, a NOMA configuration to a plurality of UEs via a wireless link. The NOMA configuration may include a first set of MA signatures, a second set of MA signatures, and available time-frequency resources for NOMA transmission. The method also includes detecting, by the base station, uplink NOMA transmissions in a time-frequency resource from a UE of the plurality of UEs via the wireless link. In addition, the method includes the base station decoding the uplink NOMA transmissions, generating a plurality of Hybrid Automatic Repeat Request (HARQ) acknowledgments (ACKS) or negative acknowledgments (NACKS), and determining a first UE-specific identifier. The method further includes, in an event that the base station successfully identifies the first UE-specific identifier and fails decoding at least a portion of the uplink NOMA transmissions: the base station transmitting a HARQ NACK in a downlink control information (DCI) with cyclical redundancy check (CRC) scrambled by the first UE-specific identifier and, if the base station successfully detects the uplink NOMA transmissions by the first set of MA signatures, transmitting Timing Advance information in a Medium Access Control-Control Element (MAC-CE). [0008] In aspects, a method for a UE to communicate with a base station is disclosed. The method includes receiving, at the UE, a NOMA configuration from the base station via a wireless link. The NOMA configuration may include a first set of MA signatures, a second set of MA signatures, and available time-frequency resources for NOMA transmission. The method also includes transmitting, by the UE, an uplink signal corresponding to the NOMA configuration and the first set of MA signatures via the wireless link for receipt by the base station. The method further includes monitoring, by the UE, a downlink control information to detect HARQ negative acknowledgments based on the first UE-specific identifier. In addition, the method includes monitoring, by the UE, a MAC-CE to detect Timing Advance information. Further, in an event that both the hybrid automatic repeat request negative acknowledgment and the Timing Advance information are detected, the method includes retransmitting, by the UE, the uplink signal with an adjusted Timing Advance and based on the second set of MA signatures.

[0009] FIG. 1 illustrates an example environment 100, which includes a user equipment 110 (UE 110) that can communicate with base stations 120 (illustrated as base stations 121 and 122) through wireless communication links 130 (wireless link 130), illustrated as wireless links 131 and 132. For simplicity, the UE 110 is implemented as a smartphone but may be implemented as any suitable computing or electronic device, such as a mobile communication device, modem, cellular phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, smart appliance, vehicle-based communication system, or an Intemet-of- Things (IoT) device such as a sensor or an actuator. The base stations 120 ( e.g an Evolved Universal Terrestrial Radio Access Network Node B, E-UTRAN Node B, evolved Node B, eNodeB, eNB, Next Generation Node B, gNode B, gNB, or the like) may be implemented in a macrocell, microcell, small cell, picocell, and the like, or any combination thereof.

[0010] The base stations 120 communicate with the user equipment 110 using the wireless links 131 and 132, which may be implemented as any suitable type of wireless link. The wireless links 131 and 132 include control and data communication, such as downlink of data and control information communicated from the base stations 120 to the user equipment 110, uplink of other data and control information communicated from the user equipment 110 to the base stations 120, or both. The wireless links 130 may include one or more wireless links ( e.g ., radio links) or bearers implemented using any suitable communication protocol or standard, or combination of communication protocols or standards, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), Fifth Generation New Radio (5G NR), and so forth. Multiple wireless links 130 may be aggregated in a carrier aggregation to provide a higher data rate for the UE 110. Multiple wireless links 130 from multiple base stations 120 may be configured for Coordinated Multipoint (CoMP) communication with the UE 110.

[0011] The base stations 120 are collectively a Radio Access Network 140 (e.g., RAN, Evolved Universal Terrestrial Radio Access Network, E-UTRAN, 5G NR RAN or NR RAN). The base stations 121 and 122 in the RAN 140 are connected to a core network 150. The base stations 121 and 122 connect, at 102 and 104 respectively, to the core network 150 through an NG2 interface for control- plane signaling and using an NG3 interface for user-plane data communications when connecting to a 5G core network, or using an S 1 interface for control-plane signaling and user-plane data communications when connecting to an Evolved Packet Core (EPC) network. The base stations 121 and 122 can communicate using an Xn Application Protocol (XnAP) through an Xn interface, or using an X2 Application Protocol (X2AP) through an X2 interface, at 106, to exchange user- plane and control-plane data. The user equipment 110 may connect, via the core network 150, to public networks, such as the Internet 160 to interact with a remote service 170.

[0012] FIG. 2 illustrates an example device diagram 200 of the UE 110 and the base stations 120. The UE 110 and the base stations 120 may include additional functions and interfaces that are omitted from FIG. 2 for the sake of clarity. The UE 110 includes antennas 202, a radio frequency front end 204 (RF front end 204), an LTE transceiver 206, a 5G NR transceiver 208, and a 6G transceiver 210 for communicating with base stations 120 in the RAN 140. The RF front end 204 of the UE 110 can couple or connect the LTE transceiver 206, the 5G NR transceiver 208, and the 6G transceiver 210 to the antennas 202 to facilitate various types of wireless communication. The antennas 202 of the UE 110 may include an array of multiple antennas that are configured similarly to or differently from each other.

[0013] The antennas 202 and the RF front end 204 can be tuned to, and/or be tunable to, one or more frequency bands defined by the 3 GPP LTE, 5G NR, and 6G communication standards and implemented by the LTE transceiver 206, the 5G NR transceiver 208, and/or the 6G transceiver 210. Additionally, the antennas 202, the RF front end 204, the LTE transceiver 206, the 5G NR transceiver 208, and/or the 6G transceiver 210 may be configured to support beamforming for the transmission and reception of communications with the base stations 120. By way of example and not limitation, the antennas 202 and the RF front end 204 can be implemented for operation in sub-gigahertz bands, sub-6 GHZ bands, and/or above 6 GHz bands that are defined by the 3 GPP LTE, 5G NR, and 6G communication standards.

[0014] The UE 110 also includes processor(s) 212 and computer-readable storage media 214 (CRM 214). The processor 212 may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media described herein excludes propagating signals. CRM 214 may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data 216 of the UE 110. The device data 216 includes user data, multimedia data, beamforming codebooks, applications, and/or an operating system of the UE 110, which are executable by processor(s) 212 to enable user-plane communication, control-plane signaling, and user interaction with the UE 110. [0015] In some implementations, the CRM 214 may also include a communication manager 218. Alternately or additionally, the communication manager 218 may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the UE 110. In at least some aspects, the communication manager 218 can communicate with the antennas 202, the RF front end 204, the LTE transceiver 206, the 5G NR transceiver 208, and/or the 6G transceiver 210 to monitor the quality of the wireless communication links 130. Additionally, the communication manager 218 can configure the antennas 202, the RF front end 204, the LTE transceiver 206, the 5G NR transceiver, and/or the 6G transceiver 210 to implement the techniques for HARQ in NOMA asynchronous transmission described herein.

[0016] The device diagram for the base stations 120, shown in FIG. 2, includes a single network node ( e.g a gNode B). The functionality of the base stations 120 may be distributed across multiple network nodes or devices and may be distributed in any fashion suitable to perform the functions described herein. The base stations 120 include antennas 252, a radio frequency front end 254 (RF front end 254), one or more LTE transceivers 256, one or more 5G NR transceivers 258, and/or one or more 6G transceivers 260 for communicating with the UE 110. The RF front end 254 of the base stations 120 can couple or connect the LTE transceivers 256, the 5G NR transceivers 258, and/or the 6G transceivers 260 to the antennas 252 to facilitate various types of wireless communication. The antennas 252 of the base stations 120 may include an array of multiple antennas that are configured similarly to or differently from each other.

[0017] The antennas 252 and the RF front end 254 can be tuned to, and/or be tunable to, one or more frequency band defined by the 3 GPP LTE, 5G NR, and 6G communication standards, and implemented by the LTE transceivers 256, one or more 5G NR transceivers 258, and/or one or more 6G transceivers 260. Additionally, the antennas 252, the RF front end 254, the LTE transceivers 256, one or more 5G NR transceivers 258, and/or one or more 6G transceivers 260 may be configured to support beamforming, such as Massive-MIMO, for the transmission and reception of communications with the UE 110.

[0018] The base stations 120 also include processor(s) 262 and computer- readable storage media 264 (CRM 264). The processor 262 may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. CRM 264 may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data 266 of the base stations 120. The device data 266 includes network scheduling data, radio resource management data, beamforming codebooks, applications, and/or an operating system of the base stations 120, which are executable by processor(s) 262 to enable communication with the UE 110.

[0019] CRM 264 also includes a base station manager 268. Alternately or additionally, the base station manager 268 may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the base stations 120. In at least some aspects, the base station manager 268 configures the LTE transceivers 256, the 5G NR transceivers 258, and the 6G transceiver(s) 260 for communication with the UE 110, as well as communication with a core network, such as the core network 150, and routing user-plane and control-plane data for joint communication.

[0020] The base stations 120 include an inter-base station interface 270, such as an Xn and/or X2 interface, which the base station manager 268 configures to exchange user-plane and control-plane data between other base stations 120, to manage the communication of the base stations 120 with the UE 110. The base stations 120 include a core network interface 272 that the base station manager 268 configures to exchange user-plane and control-plane data with core network functions and/or entities. [0021] FIG. 3 illustrates two example techniques for a UE to transmit data to the base station through Physical Uplink Shared CHannel (PUSCH). One technique includes persistent scheduling, in which an LTE base station (eNB) transmits a UL grant to the UE in every subframe. In this case, if the UE has any data to send, the UE can use the resources allocated in the grant. Another technique includes non-persistent scheduling. Using non-persistent scheduling, if a UE has UL data to send, it sends a Scheduling Request (SR) by Physical Uplink Control CHannel (PUCCH) to the eNB. The eNB can then schedule a UL grant to the UE for the following UL data transmission.

[0022] In Fifth Generation New Radio (5G NR), massive machine type communication (mMTC) supports a large number of devices in a cell. As a result, increased UL scheduling is required and the overhead of control signaling increases accordingly. To solve this problem, grant-free transmission can be used as a generic function in 5G NR.

[0023] Generally, grant-free transmission enables a 5G base station (gNB) to allocate a physical resource as a shared physical resource, and subsequently, the gNB can instruct a group of UEs to transmit UL data on the shared resource without a UL grant.

[0024] Non-orthogonal multiple access (NOMA) spreads signals onto a larger and shared resource grid at a bit and symbol level, where the shared resource grid corresponds to one or more of frequency domain, a time domain, a code domain, or a spatial domain. The spreading can be exploited by the base station with multiple user detection (MUD) to distinguish signals from distinct UEs. Accordingly, assisted by NOMA spreading, the base station with NOMA MUD can distinguish signals from these UEs regardless of whether their signals are mapped on the same frequency, time, and/or code resource, or using the same antenna configuration.

[0025] Moreover, because the receiving power is recognized as a general multiple access (MA) signature, a UE with the same NOMA spreading, mapped on the same frequency, time, and code resource, and using the same antenna configuration, but with a different receiving power in the base station, may also be distinguished. Bit-level and symbol-level signal processing such as spreading, repetition, scrambling, sparse resource mapping, and forward error control (FEC) coding can be used. In aspects, an MA signature can be utilized in any suitable signal processing scheme, such as UE-specific bit-level scrambling, UE-specific bit-level interleaving, UE-specific symbol-level spreading (usable with 5G NR legacy modulation or modified modulation), UE-specific symbol-level scrambling, UE-specific symbol-level interleaving (with symbol-level zero padding), UE- specific power assignment, UE-specific sparse RE mapping, cell-specific MA signature, or multi-branch/MA signature transmission (irrespective of rank) per UE.

[0026] Another NOMA application is multi-branch transmission, which is illustrated in FIG. 4. A UE can transmit multiple signals with different MA signatures in parallel. This technique provides an additional dimension of time, frequency, and space. Multi-layer linear superposition per user can be considered in order to achieve high per-user spectral efficiency. This multi-layer processing can be common to multiple ones of the above-mentioned schemes, where UE- specific MA signature should be replaced by layer-specific MA signature if multi layer transmission is applied, and the layer-specific MA signatures can be either orthogonal or non-orthogonal. In the illustrated example depicted in FIG. 4, different operations exist for multi-layer transmission, including before FEC (scenario 402) and after modulation (scenario 404).

[0027] For the multi-layer splitting at bit-level, each layer’s data is individually encoded. Minimum mean squared error (MMSE) can be applied with hard successive interference cancellation (SIC) at the receiver where each layer’s data is decoded one-by-one. Additional Cyclical Redundancy Check (CRC) overhead may be required for the hard interference cancellation and reconstruction of each layer’s data, which may result in some performance loss due to the higher coding rate. [0028] For the multi-layer splitting at symbol-level, each layer’s data shares the same FEC and modulation, and there is no need of additional CRC overhead compared with the above-described multi-layer splitting at bit-level mode. However, interference of each layer’s data cannot be fully cancelled with hard-SIC since the CRC check can only be performed after the combination of each user’s data from the multiple layers. In this case, soft parallel interference cancellation (PIC) may be implemented to reduce the inter-layer interferences.

[0029] Figure 5 shows an example implementation 500 of parallel HARQ processes that LTE supports simultaneously. Generally, LTE can support up to eight HARQ processes simultaneously. The HARQ procedures can be classified in synchronous/asynchronous and adaptive/non-adaptive schemes according to the freedom to schedule a retransmission in time and frequency.

[0030] In an example, using a downlink (DL) adaptive HARQ, the eNB sends downlink control information (DCI) to schedule the UE to receive a signal from an indicated physical resource with a HARQ process identifier (ID). If the UE successfully receives and decodes the signal, the UE sends an acknowledgment (ACK) to the eNB. If, however, the UE failed to receive and decode the signal, the UE sends a negative acknowledgment (NACK) to the eNB. After the eNB receives the NACK, the eNB can send a new DCI to schedule a retransmission of the signal in another physical resource with the same HARQ process ID. When the UE receives the retransmitted signal with the same HARQ ID, the UE can soft-combine these two signals and try to decode again. The retransmission may repeat until a successful transmission or until the procedure exceeds the maximum HARQ number.

[0031] In 5G NR, HARQ ACK feedback with one bit per transport block (TB) is supported. Operation of more than one DL HARQ process is supported for a given UE while operation of one DL HARQ process is supported for some UEs. Generally, the UE supports a set of minimum HARQ processing times. 5G NR also supports different minimum HARQ processing times across UEs. The HARQ processing time includes at least one delay between DL data reception timing and the corresponding HARQ ACK transmission timing, and another delay between UL grant reception timing and the corresponding UL data transmission timing. In these scenarios, the UE is required to indicate its capability of minimum HARQ processing time to the gNB.

[0032] Asynchronous and adaptive DL HARQ is supported at least for enhanced Mobile Broadband (eMBB) and Ultra Reliable Low Latency Communication (URLLC). Lrom a UE perspective, HARQ ACK/NACK feedback for multiple DL transmissions in time can be transmitted in one UL data/control region. Timing between DL data reception and corresponding acknowledgement is indicated by a field in the DCI from a set of values and the set of values is configured by a higher layer. The timing(s) is (are) defined at least for the case where the timing(s) is (are) unknown to the UE.

[0033] To reduce Random Access Channel (RACH) overhead and delay, a simplified RACH procedure, such as a 2-step RACH procedure, can be implemented. This simplified RACH procedure is particularly useful when a small packet is to be transmitted. Compared to conventional 4-step RACH transmitting four messages (Msg), 2-step RACH UE combines Msg-1 and Msg-3 as the initial transmission, and the base station returns a signal combining Msg-2 (Random Access Response (RAR)) and Msg-4.

[0034] To reduce delay, a message part can be added after the preamble in Msg-1. Lor example, legacy Msg-1 can be combined with Msg-3 to form the new Msg-1 in the 2-step RACH procedure. It should be noted that the message part can be transmitted right after the preamble as a transmission reception point (TRP) should detect the preamble first and then use it to demodulate the appended message. The preamble in the new Msg- 1 can be used for a demodulation reference signal of the message part, to notify the TRP that there is an access request, and for Timing Advance (TA) measurement. The new Msg-2 can represent the combination of the legacy Msg-2 and Msg-4 in the 4-step RACH procedure used to carry out timing advance, UL grant, and contention resolution information. New Msg-2 may consist of the UL grant, timing advance, or the ID ( e.g ., an RNTI), to perform contention resolution. The UL grant is optional when the UE attempts to immediately send an urgent UL transmission or the TRP requires the UE to retransmit the message part again. When the UE has transmitted the small packet with the preamble and is not required to be scheduled after the initial message appended to the preamble, the UL grant signalling may be unnecessary. Timing advance is also optional information that depends on the network layout and TRP implementation.

Example Procedures

[0035] Example methods 600 and 700 are described with reference to FIGS. 6 and 7, respectively, in accordance with one or more aspects of HARQ in NOMA asynchronous transmission. Generally, any of the components, modules, methods, and operations described herein can be implemented using software, firmware, hardware (e.g., fixed logic circuitry), manual processing, or any combination thereof. Some operations of the example methods may be described in the general context of executable instructions stored on computer-readable storage memory that is local and/or remote to a computer processing system, and implementations can include software applications, programs, functions, and the like. Alternatively or in addition, any of the functionality described herein can be performed, at least in part, by one or more hardware logic components, such as, and without limitation, Field-programmable Gate Arrays (FPGAs), Application-specific Integrated Circuits (ASICs), Application-specific Standard Products (ASSPs), System-on-a-chip systems (SoCs), Complex Programmable Logic Devices (CPLDs), and the like.

[0036] FIG. 6 depicts an example method 600 of HARQ in NOMA asynchronous transmissions in accordance with aspects of the techniques described herein. The order in which the method blocks are described are not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement a method, or an alternate method.

[0037] At block 602, a NOMA configuration is transmitted to a plurality of UEs via a wireless link. For example, the base station 104 can transmit a NOMA configuration to a plurality of UEs 102 via the wireless link 106. In aspects, the NOMA configuration includes a first set of MA signatures, a second set of MA signatures, and available time-frequency resources for NOMA transmission.

[0038] At block 604, uplink (UL) NOMA transmissions are detected in a time-frequency resource. For example, the base station 104 can detect UL NOMA transmissions transmitted by one or more of the UEs 102 using the time-frequency resource.

[0039] At block 606, the UL NOMA transmissions are decoded. For example, the base station 104 can decode or attempt to decode the UL NOMA transmissions received from the UE 102.

[0040] At block 608, a plurality of HARQ-ACK/NACKs are generated. In an example, the base station 104 generates the plurality of HARQ-ACK/NACKs corresponding to successful and/or failed decoding of the UL signals.

[0041] At block 610, a first UE-specific identifier (ID) is determined. For example, the base station 104 can determine the UE-specific ID based on the UE- specific resume-RNTI. The RNTI can be used by the base station for UE-specific control signaling when the UE is in an RRC inactive state or an RRC idle state.

[0042] If the base station successfully identifies the first UE-specific ID but fails decoding the UL NOMA transmissions, then at block 612, a NACK is transmitted in a DCI with a CRC scrambled by the first UE-specific ID.

[0043] If the base station also successfully detects the UL NOMA transmissions by the first set of MA signatures, then at block 614, TA information is transmitted in a MAC CE.

[0044] Optionally, the base station can transmit a second UE-specific ID in a second MAC CE. In addition, the base station may detect a UL NOMA retransmission and determine that a signal transmission in the UL NOMA transmissions has a same HARQ process ID as a signal retransmission in the UL NOMA retransmission. If a New Data Indicator (NDI) is not toggled, indicating that the retransmission is not new data, then the base station can combine the signal transmission with the signal retransmission using the second UE-specific ID.

[0045] FIG. 7 depicts an example method 700 of HARQ in NOMA asynchronous transmissions in accordance with aspects of the techniques described herein. In aspects, the method 700 can be performed by a UE while in an RRC inactive state or an RRC idle state. The order in which the method blocks are described are not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement a method, or an alternate method.

[0046] At block 702, a NOMA configuration is received at a UE from a base station via a wireless link. For example, the UE 102 receives the NOMA configuration from the base station 104 via the wireless link 106. In aspects, the NOMA configuration includes a first set of MA signatures, a second set of MA signatures, and available time-frequency resources for NOMA transmission.

[0047] At block 704, the first set of MA signatures is selected for UL transmission. For example, the UE 102 selects the first set of MA signatures included in the NOMA configuration received from the base station 104. In some aspects, the UE selects the first set of MA signatures for asynchronous UL transmission and the second set of MA signatures for synchronous UL transmission. Alternatively, the UE can select the second set of MA signatures for asynchronous UL transmission and the first set of MA signatures for synchronous UL transmission. Accordingly, the UE can select any suitable set of MA signatures in the NOMA configuration for asynchronous or synchronous UL transmission.

[0048] At block 706, a UL signal, corresponding to the NOMA configuration and the first set of MA signatures, is transmitted via the wireless link for receipt by the base station. In an example, the UE 102 transmits the UL signal to the base station 104 via the wireless link 106.

[0049] At block 708, the UE monitors a DCI to detect a HARQ-NACK based on the first UE-specific ID. In an example, the DCI is received by the UE 102 from the base station 104. In particular, the UE 102 analyzes the DCI to detect a HARQ- NACK, which indicates that the UL signal failed decoding by the base station.

[0050] At block 710, a MAC CE is monitored by the UE to detect TA information. For example, the UE 102 may receive the MAC CE from the base station 104 if the UL NOMA transmission failed decoding at the base station 104 but the base station 104 successfully detected the UL NOMA transmission by the first set of MA signatures and successfully identified the first UE-specific ID.

[0051] If both the HARQ-NACK and the TA information are detected, then at block 712, the UE retransmits the UL signal with an adjusted TA and based on the second set of MA signatures. In an example, the UE 102 retransmits the UL signal via the wireless link 106 to the base station 104. Alternatively, if the UE first selected the second set of MA signatures for the UL transmission, then the UE may use the first set of MA signatures for retransmission of the UL signal.

[0052] Optionally, the UE can retransmit the UL signal with a second UE- specific ID configured by the base station. The retransmitted UL signal may have the same HARQ process ID as the first transmitted UL signal. In addition, the retransmitted UL signal includes an NDI that is not toggled. The untoggled NDI indicates that the retransmitted UL signal is not new data. The base station 104 can use the untoggled NDI to determine that the retransmitted UL signal includes the same data as the first transmitted UL signal.

[0053] Although aspects of HARQ in NOMA asynchronous transmission have been described in language specific to features and/or methods, the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of HARQ in NOMA asynchronous transmission, and other equivalent features and methods are intended to be within the scope of the appended claims. Further, various different aspects are described, and it is to be appreciated that each described aspect can be implemented independently or in connection with one or more other described aspects.

Claims

CLAIMS What is claimed is:

1. A method for a base station to configure and communicate with a user equipment, the method comprising:

transmitting, by the base station, a non-orthogonal multiple access configuration to a plurality of user equipments via a wireless link, the non- orthogonal multiple access configuration including a first set of multiple access signatures, a second set of multiple access signatures, and available time-frequency resources for non-orthogonal multiple access transmission;

detecting, by the base station, uplink non-orthogonal multiple access transmissions in at least one of the available time-frequency resources from a user equipment of the plurality of user equipments;

decoding, by the base station, the uplink non-orthogonal multiple access transmissions;

generating, by the base station, a plurality of hybrid automatic repeat request acknowledgments or negative acknowledgments; and

responsive to the base station successfully determining a first user equipment-specific identifier for the user equipment and experiencing an unsuccessful decoding of at least a portion of the uplink non-orthogonal multiple access transmissions:

transmitting, by the base station, a hybrid automatic repeat request negative acknowledgment with cyclical redundancy check scrambled using the first user equipment-specific identifier; and

transmitting, by the base station, Timing Advance information responsive to the base station successfully detecting the uplink non- orthogonal multiple access transmissions using the first set of multiple access signatures.

2. The method of claim 1, further comprising transmitting a second user equipment-specific identifier for the user equipment in a second Medium Access Control-Control Element, the second user equipment-specific identifier usable for combining the uplink non-orthogonal multiple access transmissions with uplink non-orthogonal multiple access retransmissions from the user equipment.

3. The method of claim 1, wherein the uplink non-orthogonal multiple access transmissions include a first signal transmission, and the method further comprises:

detecting uplink non-orthogonal multiple access retransmissions including a second signal transmission;

determining that the first signal transmission and the second signal transmission have a same hybrid automatic repeat request process identifier and that a New Data Indicator is not toggled; and

combining the first signal transmission and the second signal transmission using the second user equipment-specific identifier.

4. The method of any of the preceding claims, wherein the determining of the first user equipment-specific identifier is based on a user equipment-specific resume-Radio Network Temporary Identity.

5. The method of any of the preceding claims, wherein the method is performed while the user equipment is a Radio Resource Control inactive state or a Radio Resource Control idle state.

6. The method of any of the preceding claims, wherein the wireless link is implemented on a Fifth Generation New Radio network

7. The method of any of the preceding claims, wherein the Timing Advance information is transmitted in a Medium Access Control-Control Element.

8. The method of any of the preceding claims, wherein the hybrid automatic repeat request negative acknowledgement is transmitted in a downlink control information.

9. The method of any of the preceding claims, wherein the second set of multiple access signatures is usable for uplink non-orthogonal multiple access retransmissions by the UE with an adjusted Timing Advance.

10. A base station comprising:

a hardware-based transceiver;

computer-readable storage media storing executable instructions; and a processor configured to execute the instructions in the computer-readable storage media to implement a base station manager that configures the hardware- based transceiver for communication with the plurality of user equipments and that performs the method of any of claims 1 to 9.

11. A method for a user equipment to communicate with a base station, the method comprising:

receiving, at the user equipment, a non-orthogonal multiple access configuration from the base station via a wireless link, the non-orthogonal multiple access configuration including a first set of multiple access signatures, a second set of multiple access signatures, and available time-frequency resources for non- orthogonal multiple access transmission;

transmitting, by the user equipment, an uplink signal on at least one of the available time-frequency resources, the uplink signal corresponding to the non- orthogonal multiple access configuration and the first set of multiple access signatures;

monitoring, by the user equipment, for hybrid automatic repeat request negative acknowledgments from the base station based on a first user equipment- specific identifier for the user equipment;

monitoring, by the user equipment, for Timing Advance information from the base station; and

in an event that both the hybrid automatic repeat request negative acknowledgment and the Timing Advance information are detected, retransmitting, by the user equipment, the uplink signal with an adjusted Timing Advance and based on the second set of multiple access signatures.

12. The method of claim 11, further comprising selecting, by the user equipment, the first set of multiple access signatures for uplink transmission.

13. The method of any of claims 11 or 12, wherein the first set of multiple access signatures are selected, by the user equipment, for asynchronous uplink transmission and the second set of multiple access signatures are selected, by the user equipment, for synchronous uplink transmission.

14. The method of any of claims 11 to 13, further comprising:

retransmitting the uplink signal with a second user equipment-specific identifier configured by the base station, the retransmitted uplink signal having a same hybrid automatic repeat request process identifier as the transmitted uplink signal and a New Data Indicator that is not toggled.

15. The method of any of claims 11 to 14, wherein the receiving, the transmitting, the monitoring for hybrid automatic repeat request negative acknowledgments, the monitoring for Timing Advance information , and the retransmitting are performed while the user equipment is in a Radio Resource Control inactive state.

16. The method of any of cl ims 11 to 15, wherein the wireless link is implemented on a Fifth Generation New Radio network.

17. The method of any of cl ims 11 to 16, wherein the monitoring for hybrid automatic repeat request negative acknowledgments includes monitoring a downlink control inform tion.

18. The method of nay of cl ims 11 to 17, wherein the monitoring for Timing Advance information includes monitoring a Medium Access Control- Control Element.

19. The method of claims 11 to 18, further comprising:

receiving a second user equipment-specific identifier in a Medium Access Control-Control Element, the second user equipment-specific identifier configured at the base station for the user equipment; and

using the second user equipment-specific for uplink non-orthogonal multiple access retransmissions to the base station.

20. A user equipment comprising:

a hardware-based transceiver;

computer-readable storage media storing executable instructions; and a processor configured to execute the instructions in the computer-readable storage media to use the hardware-based transceiver to perform the method of any of claims 11 to 19.