Patent Description:
The subject matter disclosed herein relates generally to wireless communications and more particularly relates to sidelink HARQ operation.

The following abbreviations are herewith defined, at least some of which are referred to within the following description: Third Generation Partnership Project ("<NUM> GPP"), Fifth Generation Core Network ("5CG"), Fifth Generation System ("5GS"), Authentication, Authorization and Accounting ("AAA"), Access and Mobility Management Function ("AMF"), Positive-Acknowledgment ("ACK"), Application Programming Interface ("API"), Access Stratum ("AS"), Base Station ("BS"), Control Element ("CE"), Channel State Information ("CSI"), Connection Mode ("CM", this is a NAS state in 5GS), Core Network ("CN"), Control Plane ("CP"), Data Radio Bearer ("DRB"), Downlink Control Information ("DCI"), Downlink ("DL"), Discontinuous Transmission ("DTX"), Evolved Node-B ("eNB"), Evolved Packet Core ("EPC"), Evolved Packet System ("EPS"), EPS Mobility Management ("EMM", this is a NAS state in EPS), Evolved UMTS Terrestrial Radio Access Network ("E-UTRAN"), Frequency Division Duplex ("FDD"), Frequency Division Multiple Access ("FDMA"), General Packet Radio Service ("GPRS"), Global System for Mobile Communications ("GSM"), Hybrid Automatic Repeat Request ("HARQ"), Home Subscriber Server ("HSS"), Home Public Land Mobile Network ("HPLMN"), Information Element ("IE"), Long Term Evolution ("LTE"), Mobility Management ("MM"), Mobility Management Entity ("MME"), Negative-Acknowledgment ("NACK") or ("NAK"), New Generation (<NUM>) Node-B ("gNB"), New Generation Radio Access Network ("NG-RAN", a RAN used for 5GS networks), New Radio ("NR", a <NUM> radio access technology; also referred to as "<NUM> NR"), Non-Access Stratum ("NAS"), Network Exposure Function ("NEF"), Network Slice Selection Assistance Information ("NSSAI"), Packet Data Unit ("PDU", used in connection with 'PDU Session'), Packet Switched ("PS", e.g., Packet Switched domain or Packet Switched service), Physical Broadcast Channel ("PBCH"), Physical Downlink Control Channel ("PDCCH"), Physical Downlink Shared Channel ("PDSCH"), Physical Hybrid ARQ Indicator Channel ("PHICH"), Physical Random Access Channel ("PRACH"), Physical Resource Block ("PRB"), Physical Sidelink Control Channel ("PSCCH"), Physical Sidelink Shared Channel ("PSSCH"), Physical Uplink Control Channel ("PUCCH"), Physical Uplink Shared Channel ("PUSCH"), Public Land Mobile Network ("PLMN"), Quality of Service ("QoS"), Radio Access Network ("RAN"), Radio Resource Control ("RRC"), Random-Access Channel ("RACH"), Receive ("RX"), Radio Link Control ("RLC"), Shared Channel ("SCH"), Session Management ("SM"), Session Management Function ("SMF"), Single Network Slice Selection Assistance Information ("S-NSSAI"), System Information Block ("SIB"), Transport Block ("TB"), Transport Block Size ("TBS"), Time-Division Duplex ("TDD"), Time Division Multiplex ("TDM"), Transmit ("TX"), Unified Data Management ("UDM"), User Data Repository ("UDR"), Uplink Control Information ("UCI"), User Entity/Equipment (Mobile Terminal) ("UE"), Uplink ("UL"), User Plane ("UP"), Universal Mobile Telecommunications System ("UMTS"), UMTS Terrestrial Radio Access ("UTRA"), UMTS Terrestrial Radio Access Network ("UTRAN"), Visited Public Land Mobile Network ("VPLMN"), and Worldwide Interoperability for Microwave Access ("WiMAX"). As used herein, "HARQ-ACK" may represent collectively the Positive Acknowledge ("ACK") and the Negative Acknowledge ("NACK") and Discontinuous Transmission ("DTX"). ACK means that a TB is correctly received while NACK (or NAK) means a TB is erroneously received. DTX means that no TB was detected.

In certain wireless communication systems, V2X communication allows vehicles to communicate with moving parts of the traffic system around them. Two resource allocation modes are used in LTE V2x communication and similar modes were introduced for NR v2x communication. Mode-<NUM> corresponds to a NR network-scheduled V2X communication mode. Mode-<NUM> corresponds to a NR UE-scheduled V2X communication mode. Mode-<NUM> corresponds to an LTE network-scheduled V2X communication mode. Mode-<NUM> corresponds to an LTE UE-scheduled V2X communication mode.

In LTE V2X HARQ operation is limited to blind retransmission without any HARQ feedback. NR V2X communication may support HARQ feedback signaling for SL transmission. However, it is unclear how SL HARQ processes are managed, e.g., for NR V2X communication.

Known methods are disclosed in <NPL>) and <NPL>).

Code for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object-oriented programming language such as Python, Ruby, Java, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the "C" programming language, or the like, and/or machine languages such as assembly languages.

The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart diagrams and/or block diagrams.

Generally, the present disclosure describes systems, methods, and apparatus for sidelink HARQ operation for UEs engaged in V2X communication. "V2X" (vehicle-to-everything) refers sidelink communications may include one or more of: "V2I "(vehicle-to-infrastructure) communications, "V2N" (vehicle-to-network), "V2V" (vehicle-to-vehicle) communications, "V2P" (vehicle-to-pedestrian), "V2D" (vehicle-to-device) and "V2G" (vehicle-to-grid) communications. A V2X UE refers to a UE capable of vehicular communication using 3GPP protocol(s).

Mode-<NUM> and Mode-<NUM> support direct LTE V2X communications but differ on how they allocate the radio resources. For Mode-<NUM>, resources are allocated by the cellular network, e.g., eNB. Mode-<NUM> does not require cellular coverage, and vehicles (UEs) autonomously select their radio resources using a distributed scheduling scheme supported by congestion control mechanisms. Mode-<NUM> is considered the baseline mode and represents an alternative to <NUM>. 11p or dedicated short range communications (DSRC).

Both resource allocation Mode-<NUM> and <NUM> have been designed to satisfy the latency requirements and accommodate high Doppler spreads and high density of vehicles for V2X communications. Here, the maximum allowed latency varies between <NUM> and <NUM>, depending on the application. Mode-<NUM> uses the centralized eNB scheduler as mentioned before. The vehicular UE and eNB use the Uu interface to communicate, e.g., sending of BSR/SR from the transmitting V2X UE to the eNB and receiving in response a SL grant on the PDCCH (carried in DCI).

Mode-<NUM> uses the PC5 interface, which offers direct LTE sidelink (SL) between two vehicular UEs. Mode-<NUM> employs distributed UE scheduling and operates without infrastructure support, even when the UEs is in eNB coverage. Note that LTE sidelink resources are shared with the LTE uplink. Both LTE duplexing modes (e.g., time and frequency division duplexing) are supported. Mode-<NUM> uses a specific resource pool configuration and Semi-Persistent Scheduling ("SPS") to select and reserve resources for transmission.

SPS was introduced in LTE for supporting services that require deterministic latency, such as voice. Mode-<NUM> adopts this concept and uses sensing to determine suitable semi-persistent transmission opportunities, e.g., the set of subframes and sub-channels for V2X transmission. A candidate single-subframe resource consists of from one up to L contiguous subchannels in a single subframe, depending on the message size. The UE selects a set of candidate resources within the selection window that spans a number of subframes and contains M single-subframe resources. Parameters T1 and T2 define the selection window. T2 is determined as a function of the latency requirement. The UE continuously monitors subframes and takes notes of decoded SCI and SL received signal strength indicator (S-RSSI) measurements. In certain embodiments, the UE considers the last <NUM> subframes for selecting candidate resources.

As mentioned above, NR V2X design uses LTE V2X operation as a baseline. NR V2X also supports both a centralized scheduling mode (e.g., network-scheduled) and a distributed scheduling mode (e.g., UE-scheduled). The two resource allocation modes in NR V2X are referred to as resource allocation Mode-<NUM> and Mode-<NUM>.

In various embodiments, NR V2X operation supports HARQ with HARQ feedback signaling for SL transmissions, e.g., at least for unicast and potentially for groupcast SL transmission. As noted above, LTE V2X HARQ operation is limited to blind retransmissions without any HARQ feedback and is thus unable to provide a baseline for NR V2X HAR operation with HARQ feedback for SL transmission. This raises several questions on how the sidelink HARQ processes are managed respectively maintained for the different cast types, e.g., unicast, groupcast and broadcast, and resource allocation modes.

The present disclosure outlines several methods for an efficient SL HARQ protocol operation for NR V2X. In particular, the HARQ operation for a SL transmission in the resource allocation Mode-<NUM> is disclosed. Furthermore, the UE behavior for cases when the transmitting V2X UE switches the cast type for different HARQ (re)transmissions of a TB transmitted on the PSSCH is disclosed.

<FIG> depicts a wireless communication system <NUM> for sidelink HARQ operation in NR V2X communication for wireless devices communicating V2X messages <NUM>, according to embodiments of the disclosure. In one embodiment, the wireless communication system <NUM> includes at least one remote unit <NUM>, a radio access network ("RAN") <NUM>, and a mobile core network <NUM>. The RAN <NUM> and the mobile core network <NUM> form a mobile communication network. The RAN <NUM> may be composed of a base unit <NUM> with which the remote unit <NUM> communicates using wireless communication links <NUM>. Even though a specific number of remote units <NUM>, base units <NUM>, wireless communication links <NUM>, RANs <NUM>, and mobile core networks <NUM> are depicted in <FIG>, one of skill in the art will recognize that any number of remote units <NUM>, base units <NUM>, wireless communication links <NUM>, RANs <NUM>, and mobile core networks <NUM> may be included in the wireless communication system <NUM>.

In one implementation, the RAN <NUM> is compliant with the <NUM> system specified in the 3GPP specifications. In another implementation, the RAN <NUM> is compliant with the LTE system specified in the 3GPP specifications. More generally, however, the wireless communication system <NUM> may implement some other open or proprietary communication network, for example WiMAX, among other networks.

In one embodiment, the remote units <NUM> may include computing devices, such as desktop computers, laptop computers, personal digital assistants ("PDAs"), tablet computers, smart phones, smart televisions (e.g., televisions connected to the Internet), smart appliances (e.g., appliances connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, modems), or the like. Moreover, the remote units <NUM> may be referred to as the UEs, subscriber units, mobiles, mobile stations, users, terminals, mobile terminals, fixed terminals, subscriber stations, user terminals, wireless transmit/receive unit ("WTRU"), a device, or by other terminology used in the art.

The remote units <NUM> may communicate directly with one or more of the base units <NUM> in the RAN <NUM> via uplink ("UL") and downlink ("DL") communication signals. Furthermore, the UL and DL communication signals may be carried over the wireless communication links <NUM>. Here, the RAN <NUM> is an intermediate network that provides the remote units <NUM> with access to the mobile core network <NUM>.

In some embodiments, the remote units <NUM> communicate with an application server <NUM> via a network connection with the mobile core network <NUM>. For example, an application <NUM> (e.g., web browser, media client, telephone/VoIP application) in a remote unit <NUM> may trigger the remote unit <NUM> to establish a PDU session (or other data connection) with the mobile core network <NUM> via the RAN <NUM>. The mobile core network <NUM> then relays traffic between the remote unit <NUM> and the application server <NUM> in the packet data network <NUM> using the PDU session. Note that the remote unit <NUM> may establish one or more PDU sessions (or other data connections) with the mobile core network <NUM>. As such, the remote unit <NUM> may concurrently have at least one PDU session for communicating with the packet data network <NUM> and at least one PDU session for communicating with another data network (not shown).

The base units <NUM> may be distributed over a geographic region. In certain embodiments, a base unit <NUM> may also be referred to as an access terminal, an access point, a base, a base station, a Node-B, an eNB, a gNB, a Home Node-B, a relay node, or by any other terminology used in the art. The base units <NUM> are generally part of a radio access network ("RAN"), such as the RAN <NUM>, that may include one or more controllers communicably coupled to one or more corresponding base units <NUM>. These and other elements of radio access network are not illustrated but are well known generally by those having ordinary skill in the art. The base units <NUM> connect to the mobile core network <NUM> via the RAN <NUM>.

The base units <NUM> may serve a number of remote units <NUM> within a serving area, for example, a cell or a cell sector, via a wireless communication link <NUM>. The base units <NUM> may communicate directly with one or more of the remote units <NUM> via communication signals. Generally, the base units <NUM> transmit DL communication signals to serve the remote units <NUM> in the time, frequency, and/or spatial domain. Furthermore, the DL communication signals may be carried over the wireless communication links <NUM>. The wireless communication links <NUM> may be any suitable carrier in licensed or unlicensed radio spectrum. The wireless communication links <NUM> facilitate communication between one or more of the remote units <NUM> and/or one or more of the base units <NUM>.

In one embodiment, the mobile core network <NUM> is a <NUM> core ("5GC") or the evolved packet core ("EPC"), which may be coupled to a packet data network <NUM>, like the Internet and private data networks, among other data networks. A remote unit <NUM> may have a subscription or other account with the mobile core network <NUM>. Each mobile core network <NUM> belongs to a single public land mobile network ("PLMN").

The mobile core network <NUM> includes several network functions ("NFs"). As depicted, the mobile core network <NUM> includes multiple user plane functions ("UPFs") <NUM>. The mobile core network <NUM> also includes multiple control plane functions including, but not limited to, an Access and Mobility Management Function ("AMF") <NUM> that serves the RAN <NUM>, a Session Management Function ("SMF") <NUM>, and a Policy Control Function ("PCF") <NUM>. In certain embodiments, the mobile core network <NUM> may also include an Authentication Server Function ("AUSF"), a Unified Data Management function ("UDM") <NUM>, a Network Repository Function ("NRF") (used by the various NFs to discover and communicate with each other over APIs), or other NFs defined for the 5GC.

In various embodiments, the mobile core network <NUM> supports different types of mobile data connections and different types of network slices, wherein each mobile data connection utilizes a specific network slice. Here, a "network slice" refers to a portion of the mobile core network <NUM> optimized for a certain traffic type or communication service. A network instance may be identified by a S-NSSAI, while a set of network slices for which the remote unit <NUM> is authorized to use is identified by NSSAI. In certain embodiments, the various network slices may include separate instances of network functions, such as the SMF <NUM> and UPF <NUM>. In some embodiments, the different network slices may share some common network functions, such as the AMF <NUM>. The different network slices are not shown in <FIG> for ease of illustration, but their support is assumed.

Although specific numbers and types of network functions are depicted in <FIG>, one of skill in the art will recognize that any number and type of network functions may be included in the mobile core network <NUM>. Moreover, where the mobile core network <NUM> is an EPC, the depicted network functions may be replaced with appropriate EPC entities, such as an MME, S-GW, P-GW, HSS, and the like. In certain embodiments, the mobile core network <NUM> may include a AAA server.

While <FIG> depicts components of a <NUM> RAN and a <NUM> core network, the described embodiments for sidelink HARQ operation in NR V2X communication apply to other types of communication networks and RATs, including IEEE <NUM> variants, GSM, GPRS, UMTS, LTE variants, CDMA <NUM>, Bluetooth, ZigBee, Sigfoxx, and the like. For example, in an LTE variant involving an EPC, the AMF <NUM> may be mapped to an MME, the SMF mapped to a control plane portion of a PGW and/or to an MME, the UPF map to an SGW and a user plane portion of the PGW, the UDM/UDR maps to an HSS, etc..

In various embodiments, the remote units <NUM> may communicate directly with each other (e.g., device-to-device communication) using V2X communication signals <NUM>. Here, V2X transmissions may occur on V2X resources. As discussed above, a remote unit <NUM> may be provided with different V2X communication resources for different V2X modes. Mode-<NUM> corresponds to a NR network-scheduled V2X communication mode. Mode-<NUM> corresponds to an NR UE-autonomous V2X communication mode. Mode-<NUM> corresponds to an LTE network-scheduled V2X communication mode. Mode-<NUM> corresponds to an LTE UE-scheduled V2X communication mode.

Moreover, the remote units <NUM> implement SL HARQ processes for at least some data transferred over V2X communication signals <NUM>. In certain embodiments, a transmitting remote unit <NUM> selects the HARQ process for a SL transmission on PSSCH. In certain embodiments, the HARQ processes are shared between Mode-<NUM> and Mode-<NUM> SL communications. In certain embodiments, the HARQ processes are shared between unicast, groupcast, and broadcast transmissions.

For SL HARQ operation in Mode-<NUM>, the transmitting remote unit <NUM> may select the HARQ process autonomously, which may be different to the HARQ process ID signaled within a SL grant. As the purpose of HARQ process ID in SL grant is to identify together with the NDI whether SL resource for a HARQ retransmission of a previously scheduled SL TB are allocated or whether SL resources for an initial HARQ transmissions are allocated, the base unit <NUM> may alternatively use another identifier, such as a SL grant ID, to identify a retransmission or an initial grant.

Where retransmission is required, the remote unit <NUM> may switch transmission cast type for the retransmission. For example, if the initial HARQ transmission is done in group cast manner, then HARQ retransmission(s) may be done in unicast manner. In various embodiments, the remote unit <NUM> uses the same HARQ process for transmitting HARQ retransmission to multiple receiving V2X remote units <NUM>.

In the following descriptions, the term RAN node is used for the base station, but it is replaceable by any other radio access node, e.g., BS, eNB, gNB, AP, NR, etc. Further the operations are described mainly in the context of <NUM> NR. However, the proposed solutions/methods are also equally applicable to other mobile communication systems supporting serving cells/carriers being configured for Sidelink Communication over PC5 interface.

<FIG> depicts a signaling flow diagram <NUM> for SL HARQ operation by a V2X transmitting UE <NUM> ("V2X Tx UE"), according to a first solution. In the first solution, a UE <NUM> that receives a SL grant <NUM> on PDCCH from the RAN node <NUM> (e.g., via the Uu interface <NUM>), then chooses autonomously a SL HARQ process for the corresponding SL transmission, e.g., PSSCH transmission <NUM>. The V2X Tx UE <NUM> sends a feedback message <NUM> to the RAN node <NUM> (e.g., gNB) after a predefined time offset. Here, the feedback message <NUM> either indicates the successful reception of the scheduled SL transmission or, respectively, requests an additional SL resource for the HARQ retransmission of the SL transmission scheduled by the SL grant. Note that the depicted V2X Tx UE <NUM> operates in a network-scheduled V2X mode (e.g., Mode-<NUM>).

As depicted in the signaling flow diagram <NUM>, the UE <NUM> first sends a SL buffer status report ("SL BSR") <NUM> to the RAN node <NUM> indicating the amount of SL data available for transmission. In response, the RAN node <NUM> may allocate SL resources for the transmission of the indicated SL data by sending a SL grant <NUM> (i.e., in DCI) on the PDCCH.

According to one implementation of the first solution, the SL grant <NUM> contains an indication of a HARQ process ID and a New Data Indicator (NDI). Both fields are merely used to identify whether the SL grant <NUM> is allocating SL resource for a HARQ retransmission of a previously scheduled SL TB or allocating SL resources for an initial HARQ transmission. For example, a SL grant received with an un-toggled NDI value (compared to the NDI value of the last received SL grant for the same HARQ process ID) allocates SL resources for a HARQ retransmission, whereas a SL grant received with a toggled NDI value allocates SL resources for an initial HARQ transmission.

According to an alternative implementation, instead of a HARQ process ID field, a new field may be signaled within the DCI which identifies the SL grant, e.g., referred to as "SL grant identifier (ID). " Here, the "SL grant ID" field together with the NDI field indicates to a V2X Tx UE <NUM> whether the SL grant allocates SL resources for <NUM>) an initial HARQ transmission or <NUM>) a HARQ retransmission. Accordingly, a SL grant received with an un-toggled NDI value (compared to the NDI value of the last received SL grant for the same SL grant ID or HARQ process ID) allocates SL resources for a HARQ retransmission, whereas a SL grant received with a toggled NDI value allocates SL resources for an initial HARQ transmission.

The SL grant <NUM> may further allocate resources, e.g., PUCCH resources, and/or HARQ feedback timing related information, providing information on which resource and/or when the HARQ feedback should be transmitted, e.g., relative to the reception of the SL grant on PDCCH. Such feedback <NUM> indicates to the RAN node <NUM> whether the PSSCH transmission <NUM> scheduled by the SL grant <NUM> was successfully received/decoded by the receiving V2X UE(s) <NUM> or whether the V2X Tx UE <NUM> requests SL resource for a HARQ retransmission of the TB sent on the PSSCH.

The SL grant <NUM> may further signal the redundancy version ("RV") which the V2X Tx UE <NUM> is to use for the corresponding transmission of the TB on the PSSCH. According to a further implementation, the SL grant <NUM> may also allocate SL resources for the HARQ feedback <NUM> corresponding to the PSSCH transmission <NUM> on the PC5 interface <NUM>.

Upon reception of the SL grant <NUM> on PDCCH, the V2X Tx UE <NUM> generates the TB according to the assigned transmission parameter signaled within the SL grant and transmits it on the SL resources allocated by the SL grant <NUM>. To be more specific, the V2X Tx UE <NUM> selects a SL HARQ process for the transmission of the TB (SL-SCH), e.g., one of the transmitting Sidelink HARQ processes associated with the Sidelink HARQ Entity for which there is no pending HARQ retransmission. The ID of the selected HARQ process is signaled within the SCI <NUM> accompanying the PSSCH <NUM>.

The SCI <NUM> transmitted on the PSCCH may further contain the SL resource for the SL HARQ feedback <NUM>, e.g., ACK/NACK, to be sent by the V2X receiving UE(s) <NUM> as e.g., allocated by the SL grant <NUM> sent from the RAN node <NUM>. The SCI <NUM> may further contain a new data indicator ("NDI"), providing information to the receiving UE(s) <NUM> on whether the PSSCH transmission <NUM> conveys an initial HARQ transmission or a HARQ retransmission. The HARQ process ID together with the NDI is used by the receiving V2X UE(s) <NUM> for the HARQ soft buffer management, e.g., soft combining.

It should be noted that in addition to the HARQ process ID and the NDI, the Source Layer-<NUM> ID may also need to be considered for the HARQ soft buffer management at a receiving UE <NUM>, e.g., only PSSCH transmission from the same source ID are to be soft combined. Upon having sent the SCI <NUM> (PSCCH) and the SL MAC PDU (TB) <NUM> on the PSSCH, the V2X Tx UE <NUM> receives the SL HARQ feedback <NUM> on the allocated SL resource. In case the SL HARQ feedback <NUM> indicates a NACK (e.g., indicating that the TB was not successfully received), the V2X Tx UE <NUM> requests a SL resource for the retransmission of the TB from the RAN node <NUM>. Such retransmission request is transmitted on the resources allocated by the SL grant, e.g., on PUCCH. Note that the V2X Tx UE <NUM> may track SL HARQ feedback responses to ensure that each V2X receiving UE successfully receives the SL MAC PDU (TB) at least once.

<FIG> depicts a signaling flow diagram <NUM> for SL data transfer, according to embodiments of the disclosure. The signaling flow diagram <NUM> involves a V2X Tx UE <NUM>, the RAN node <NUM>, and at least one V2X Rx UE <NUM>. The V2X Tx UE <NUM> sends a SL BSR to the RAN node <NUM> (see messaging <NUM>). The RAN node <NUM> then allocates SL resources to the V2X Tx UE <NUM> (see messaging <NUM>). Note that in this case, the SL resources are for the initial HARQ transmission of a first TB ("TB-A"). Here, the SL grant also allocates a PUCCH resource for HARQ feedback (i.e., ACK/NACK) and a SL resource for SL HARQ feedback.

As depicted, the RAN node <NUM> indicates a first HARQ process ID (e.g., HPID=X) in the SL grant. The V2X Tx UE <NUM> maps the first HARQ process ID to a SL HARQ process having a second HARQ process ID (e.g., HPID=Y) for the SL transmission on the PC5 interface. The V2X Tx UE <NUM> transmits SCI to the V2X Rx UE(s) <NUM> and further transmits the TB-A on PSSCH (see messaging <NUM> and <NUM>).

The SCI (PSCCH) accompanying a SL-SCH transmission on PSSCH signals the second HARQ process ID of the UE-selected HARQ process and an NDI (see messaging <NUM>). Note that the second HARQ process ID and the NDI only needs to be signaled within the SCI, when SL HARQ feedback, e.g., ACK/NACK, is requested from the receiving UE <NUM> in response to the SL-SCH transmission. Therefore, there may be two different SCI formats for NR V2X operation, one which is used when HARQ feedback is requested from the receiving UE <NUM> and one SCI for SL-SCH transmissions without HARQ feedback. According to a further implementation, the SCI which is used for SL-SCH with HARQ feedback may also allocate SL resources for the HARQ feedback from the receiving UE(s) <NUM>. Alternatively, and/or additionally, the SCI may indicate the timing of the HARQ feedback relative to the PSSCH or PSCCH reception.

In the depicted embodiment, at least one V2X Rx UE <NUM> does not receive the TB-A successfully and thus sends negative feedback (i.e., HARQ NACK) corresponding to the SL HARQ process ID 'Y' to the V2X Tx UE <NUM> (see messaging <NUM>). Consequently, the V2X Tx UE <NUM> sends HARQ NACK to the RAN node <NUM> on PUCCH for the SL grant corresponding to the HARQ process ID 'X' (see messaging <NUM>). The RAN node <NUM> then allocates SL resources to the V2X Tx UE <NUM> (see messaging <NUM>). Note that in this case, the SL resources are for the HARQ retransmission of the TB-A. Again, the SL grant also allocates a PUCCH resource for HARQ feedback (i.e., ACK/NACK) and a SL resource for SL HARQ feedback. Note that the SL grant is for the same HARQ process (i.e., HPID = 'X').

The V2X Tx UE <NUM> transmits SCI to the V2X Rx UE(s) <NUM> and further retransmits the TB-A on PSSCH (see messaging <NUM> and <NUM>). Again, the SCI indicates the same second HARQ process ID (i.e., HPID = 'Y') and a non-toggled NDI (see messaging <NUM>). This time the V2X Rx UE <NUM> successfully receives the TB-A and thus sends positive feedback (i.e., HARQ ACK) corresponding to the SL HARQ process ID 'Y' to the V2X Tx UE <NUM> (see messaging <NUM>). Consequently, the V2X Tx UE <NUM> sends HARQ ACK to the RAN node <NUM> on PUCCH for the SL grant corresponding to the HARQ process ID 'X' (see messaging <NUM>). Recall that the V2X Tx UE <NUM> may track the SL HARQ feedback received from the V2X Rx UEs <NUM> to ensure that each V2X Rx UE <NUM> successfully receives the TB-A at least once.

According to a second solution, for each carrier/serving cell there is one Sidelink HARQ Entity at the MAC entity for transmission(s) on SL-SCH, which maintains a number of parallel Sidelink HARQ processes. The Sidelink HARQ processes are shared across all SL transmissions irrespective of the cast type of the SL transmission, e.g., unicast, groupcast or broadcast SL transmission, and irrespective of the resource allocation mode, e.g., RAN-scheduled mode (Mode-<NUM>) or UE-autonomous mode (Mode-<NUM>).

According to one implementation of the second solution, a SL grant and its associated HARQ information are associated with a Sidelink HARQ process. The V2X Tx UE <NUM> selects the HARQ process for a SL transmission autonomously according to this embodiment and delivers the HARQ information to the corresponding SL HARQ process. The HARQ information contains at least the HARQ process ID of the selected HARQ process for a SL transmission and may further contain a New Data Indicator (NDI), indicating whether the corresponding SL transmission is an initial HARQ transmission or a HARQ retransmission.

According to a third solution, a transmitting V2X UE <NUM> may switch the cast type for different HARQ (re)transmissions of a TB transmitted on the PSSCH. In one implementation of the third solution, a V2X Tx UE <NUM> performs the initial transmission of a TB in a groupcast mode, whereas potential HARQ retransmission are performed in the unicast mode, e.g., HARQ retransmission are performed to individual V2X receiving UEs <NUM>. For the initial transmission of the TB, the V2X Tx UE <NUM> selects one of the SL HARQ processes of the SL HARQ entity, e.g., a SL HARQ process for which there is no pending HARQ (re)transmission, as discussed above.

As mentioned above, the initial transmission may be a groupcast transmission to a group of V2X receiving UEs <NUM>. In case one or multiple UEs of the group are not able to successfully decode the TB, the V2X Tx UE <NUM> may then perform individual unicast HARQ retransmissions to those UEs. In one implementation, each unicast HARQ transmission is performed in a separate HARQ process. However, in another implementation of the third solution, the Tx UE <NUM> reuses the SL HARQ process selected for the initial transmission for the (multiple) unicast HARQ retransmissions to the different receiving UEs <NUM>.

For each HARQ retransmission to one of the receiving UEs <NUM>, the V2X Tx UE <NUM> may choose a different redundancy version. Even though only one (and the same) SL HARQ process is used for each of the multiple unicast transmissions to different Rx UEs <NUM>, the V2X Tx UE <NUM> maintains an independent HARQ status/context, e.g., RV, NDI status, received HARQ feedback, for each of the receiving UEs <NUM>. In various embodiments, the SL HARQ process can be used for a new TB transmission, e.g., initial transmission, only if all of the receiving UEs <NUM> have successfully received the TB (e.g., no retransmissions are pending for the SL HARQ process).

For unicast re-transmission, the V2X Tx UE <NUM>, while making re-transmissions, may use the destination ID of each of the receiving UE that failed in decoding the said PSSCH transmission (assume here that 'm' Rx UEs fail to successfully receive a TB in PSSCH) and make 'm' SCI/ PSSCH transmissions (where 'm' is an integer less than or equal to the number of members of the group of V2X receiving UEs <NUM>). In certain embodiments, beamforming may be used for such 'm' unicast transmissions, e.g., with knowledge of the channel state of the specific PC5 channel. In certain embodiments, if the number of unicast transmission (e.g., 'm') is greater than a certain (pre)configured number, then the Tx UE <NUM> may continue re-transmissions in groupcast manner (e.g., instead of switching to unicast re-transmission).

<FIG> depicts a user equipment apparatus <NUM> that may be used for sidelink HARQ operation in NR V2X communication, according to embodiments of the disclosure. In various embodiments, the user equipment apparatus <NUM> is used to implement one or more of the solutions described above. The user equipment apparatus <NUM> may be one embodiment of the remote unit <NUM> and/or Tx UE <NUM>, described above. Furthermore, the user equipment apparatus <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, an output device <NUM>, and a transceiver <NUM>. In some embodiments, the input device <NUM> and the output device <NUM> are combined into a single device, such as a touchscreen. In certain embodiments, the user equipment apparatus <NUM> may not include any input device <NUM> and/or output device <NUM>. In various embodiments, the user equipment apparatus <NUM> may include one or more of: the processor <NUM>, the memory <NUM>, and the transceiver <NUM>, and may not include the input device <NUM> and/or the output device <NUM>.

In various embodiments, the processor <NUM> controls the user equipment apparatus <NUM> to implement the above described UE behaviors. In some embodiments, the transceiver <NUM> receives a SL grant for data transmission using SL resources. Here, the SL grant has a first HARQ process identifier (i.e., network HARQ process ID). The processor <NUM> selects a second HARQ process identifier (i.e., SL HARQ process ID) for the data transmission using SL resources. Via the transceiver <NUM>, the processor <NUM> transmits SCI containing the second HARQ process identifier and transmits the SL data using the SL resources.

In some embodiments, the transmitter sends HARQ feedback for the first HARQ process corresponding to the SL data transmission. In such embodiments, the SL grant indicates a physical uplink control channel resource and/or HARQ feedback timing information, where transmitting HARQ feedback for the data transmission for the first HARQ process is based on the SL grant. Note that in other embodiments, the SL grant for data transmission may indicate the first HARQ process identifier without scheduling PUCCH resources.

In some embodiments, the first HARQ process identifier received in the SL grant (e.g., received in DCI) is different than the SL HARQ process identifier signaled within the SCI. In some embodiments, the selected HARQ process is associated with a SL HARQ process for which there is no pending HARQ retransmission. In various embodiments, the processor maps the first HARQ process to the SL HARQ process, where the SL HARQ process is selected independently from the first HARQ process.

In some embodiments, selecting the SL HARQ process includes autonomously selecting a SL HARQ process from a pool of configured SL HARQ processes. In certain embodiments, the pool of configured SL HARQ processes is shared between network-scheduled SL data transfer and UE-scheduled SL data transfer. In certain embodiments, the pool of configured SL HARQ processes is shared between unicast SL transmissions, groupcast SL transmission, and broadcast SL transmissions.

In some embodiments, transmitting the SL data using the SL resources includes transmitting SCI containing a SL HARQ process identifier for the SL HARQ process, the transceiver receives SL HARQ feedback for the SL HARQ process from at least one UE. In such embodiments, the SCI further contains a new data indicator, wherein a receiving UE performs soft-combining of the transmitted SL data based on at least the SL HARQ process identifier and the new data indicator. In further embodiments, the receiving UE performs soft-combining of the transmitted SL data also considering the source Layer-<NUM> identifier.

In some embodiments, transmitting the SL data includes performing a groupcast transmission and receiving SL HARQ feedback corresponding to the SL data transmission includes receiving a negative acknowledgement indication. In such embodiments, the processor retransmits the SL data using unicast SL retransmission. In certain embodiments, the unicast SL retransmission reuses the SL HARQ process identifier. In certain embodiments, the unicast SL retransmission uses a different redundancy version than the initial SL data transmission.

In some embodiments, the memory <NUM> stores data related to SL HARQ operation. For example, the memory <NUM> may store V2X communication resources, HARQ processes, HARQ process ID mappings, and the like. In certain embodiments, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on the remote unit <NUM>.

As discussed above, the transceiver <NUM> communicates with one or more network functions of a mobile communication network via one or more access networks. The transceiver <NUM> operates under the control of the processor <NUM> to transmit messages, data, and other signals and also to receive messages, data, and other signals. For example, the processor <NUM> may selectively activate the transceiver <NUM> (or portions thereof) at particular times in order to send and receive messages.

The transceiver <NUM> may include one or more transmitters <NUM> and one or more receivers <NUM>. Although only one transmitter <NUM> and one receiver <NUM> are illustrated, the user equipment apparatus <NUM> may have any suitable number of transmitters <NUM> and receivers <NUM>. Further, the transmitter(s) <NUM> and the receiver(s) <NUM> may be any suitable type of transmitters and receivers. Additionally, the transceiver <NUM> may support at least one network interface <NUM>. Here, the at least one network interface <NUM> facilitates communication with a RAN node, such as an eNB or gNB, for example using the "Uu" interface (e.g., LTE-Uu for eNB, NR-Uu for gNB). Additionally, the at least one network interface <NUM> may include an interface used for communications with one or more network functions in the mobile core network, such as a UPF <NUM>, an AMF <NUM>, and/or a SMF <NUM>.

In one embodiment, the transceiver <NUM> includes a first transmitter/receiver pair used to communicate with a mobile communication network over licensed radio spectrum and a second transmitter/receiver pair used to communicate with a mobile communication network over unlicensed radio spectrum.

In various embodiments, one or more transmitters <NUM> and/or one or more receivers <NUM> may be implemented and/or integrated into a single hardware component, such as a multi-transceiver chip, a system-on-a-chip, an application-specific integrated circuit ("ASIC"), or other type of hardware component. In certain embodiments, one or more transmitters <NUM> and/or one or more receivers <NUM> may be implemented and/or integrated into a multi-chip module. In some embodiments, other components such as the network interface <NUM> or other hardware components/circuits may be integrated with any number of transmitters <NUM> and/or receivers <NUM> into a single chip. In such embodiment, the transmitters <NUM> and receivers <NUM> may be logically configured as a transceiver <NUM> that uses one more common control signals or as modular transmitters <NUM> and receivers <NUM> implemented in the same hardware chip or in a multi-chip module. In certain embodiments, the transceiver <NUM> may implement a 3GPP modem (e.g., for communicating via NR or LTE access networks) and a non-3GPP modem (e.g., for communicating via Wi-Fi or other non-3GPP access networks).

<FIG> depicts a base station apparatus <NUM> that may be used for protecting the user identity and credentials, according to embodiments of the disclosure. In various embodiments, the base station apparatus <NUM> is used to implement one or more of the solutions described above. The base station apparatus <NUM> may be one embodiment of the AMF, described above. Furthermore, the base station apparatus <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, an output device <NUM>, and a transceiver <NUM>. In some embodiments, the input device <NUM> and the output device <NUM> are combined into a single device, such as a touchscreen. In certain embodiments, the base station apparatus <NUM> may not include any input device <NUM> and/or output device <NUM>. In various embodiments, the base station apparatus <NUM> may include one or more of: the processor <NUM>, the memory <NUM>, and the transceiver <NUM>, and may not include the input device <NUM> and/or the output device <NUM>.

For example, the processor <NUM> may be a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or similar programmable controller.

In various embodiments, the processor <NUM> controls the base station apparatus <NUM> to implement the above described RAN node behaviors. For example, the processor <NUM> may control the transceiver <NUM> to send a SL grant to a Tx UE for data transmission using SL resources, the SL grant having a first HARQ process identifier. Where, the SL grant for data transmission schedules PUCCH resources for HARQ feedback corresponding to the first HARQ process identifier, the transmitter <NUM> receives HARQ feedback for the first HARQ process corresponding to the SL data transmission.

In some embodiments, the memory <NUM> stores data related to sidelink HARQ operation. For example, the memory <NUM> may store V2X communication resources, HARQ process IDs, UE configurations, and the like. In certain embodiments, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on the base station apparatus <NUM>.

As another, non-limiting, example, the output device <NUM> may include a wearable display separate from, but communicatively coupled to, the rest of the base station apparatus <NUM>, such as a smart watch, smart glasses, a heads-up display, or the like.

The transceiver <NUM> includes at least transmitter <NUM> and at least one receiver <NUM>. One or more transmitters <NUM> may be used to send messages to the RAN, as described herein. Similarly, one or more receivers <NUM> may be used to receive messages from the RAN, as described herein. Although only one transmitter <NUM> and one receiver <NUM> are illustrated, the base station apparatus <NUM> may have any suitable number of transmitters <NUM> and receivers <NUM>. Further, the transmitter(s) <NUM> and the receiver(s) <NUM> may be any suitable type of transmitters and receivers.

In various embodiments, the transceiver <NUM> supports one or more network interfaces <NUM> for communicating with a UE and/or network function. For example, the transceiver <NUM> may support an "Uu" interface with the UE. Additionally, the transceiver <NUM> may support various 5GC service interfaces, such as the N2 interface and/or N3 interface.

<FIG> depicts one embodiment of a method <NUM> for sidelink HARQ operation, according to embodiments of the disclosure. In various embodiments, the method <NUM> is performed by a UE, such as the remote unit <NUM>, the Tx UE <NUM>, and/or the user equipment apparatus <NUM>, described above. In some embodiments, the method <NUM> is performed by a processor, such as a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

The method <NUM> begins and receives <NUM> a SL grant for data transmission using SL resources. Here, the SL grant indicates a first HARQ process identified by a first HARQ process identifier. The method <NUM> includes selecting <NUM> a second HARQ process identified by a second HARQ process identifier for the data transmission using SL resources.

The method <NUM> includes transmitting <NUM> SCI containing the selected second HARQ process identifier. The method <NUM> includes transmitting the SL data using the SL resources. The method <NUM> ends.

Disclosed herein is a first apparatus for sidelink HARQ operation, according to embodiments of the disclosure. The first apparatus may be implemented by a UE, such as the remote unit <NUM>, the Tx UE <NUM>, and/or the user equipment apparatus <NUM>. The first apparatus includes a transceiver that receives a SL grant for data transmission using SL resources, the SL grant having a first HARQ process identifier. The first apparatus includes a processor that selects a second HARQ process identifier for the data transmission using SL resources. Via the transceiver, the processor transmits SCI containing the second HARQ process identifier and transmits the SL data using the SL resources.

In some embodiments, the first HARQ process identifier received in the SL grant (e.g., received in DCI) is different than the second HARQ process identifier signaled within the SCI. In some embodiments, the selected HARQ process is associated with a second HARQ process for which there is no pending HARQ retransmission. In various embodiments, the processor maps the first HARQ process to the second HARQ process, where the second HARQ process is selected independently from the first HARQ process.

In some embodiments, selecting the second HARQ process includes autonomously selecting a second HARQ process from a pool of configured second HARQ processes. In certain embodiments, the pool of configured second HARQ processes is shared between network-scheduled SL data transfer and UE-scheduled SL data transfer. In certain embodiments, the pool of configured second HARQ processes is shared between unicast SL transmissions, groupcast SL transmission, and broadcast SL transmissions.

In some embodiments, transmitting the SL data using the SL resources includes transmitting SCI containing a second HARQ process identifier for the second HARQ process, the transceiver receives SL HARQ feedback for the second HARQ process from at least one UE. In such embodiments, the SCI further contains a new data indicator, wherein a receiving UE performs soft-combining of the transmitted SL data based on at least the second HARQ process identifier and the new data indicator. In further embodiments, the receiving UE performs soft-combining of the transmitted SL data also considering the source Layer-<NUM> identifier.

In some embodiments, transmitting the SL data includes performing a groupcast transmission and receiving SL HARQ feedback corresponding to the SL data transmission includes receiving a negative acknowledgement indication. In such embodiments, the processor retransmits the SL data using unicast SL retransmission. In certain embodiments, the unicast SL retransmission reuses the second HARQ process identifier. In certain embodiments, the unicast SL retransmission uses a different redundancy version than the initial SL data transmission.

Disclosed herein is a first method for sidelink HARQ operation, according to embodiments of the disclosure. The first method may be performed by a UE, such as the remote unit <NUM>, the Tx UE <NUM>, and/or the user equipment <NUM>. The first method includes receiving a SL grant for data transmission using SL resources. Here, the SL grant indicates a first HARQ process identified by a first HARQ process identifier. The first method includes selecting a second HARQ process identified by a second HARQ process identifier for the data transmission using SL resources. The first method includes transmitting SCI containing the selected second HARQ process identifier and transmitting the SL data using the SL resources.

In some embodiments, the first method includes transmitting HARQ feedback for the first HARQ process corresponding to the SL data transmission. In such embodiments, the SL grant indicates a physical uplink control channel resource and/or HARQ feedback timing information, where transmitting HARQ feedback for the data transmission for the first HARQ process is based on the SL grant. Note that in other embodiments, the SL grant for data transmission may indicate the first HARQ process identifier without scheduling PUCCH resources.

In some embodiments, the first HARQ process identifier received in the SL grant (e.g., received in DCI) is different than the second HARQ process identifier signaled within the SCI. In some embodiments, the selected HARQ process is associated with a second HARQ process for which there is no pending HARQ retransmission. In various embodiments, the first method includes mapping the first HARQ process to the second HARQ process, where the second HARQ process is selected independently from the first HARQ process.

In some embodiments, transmitting the SL data using the SL resources includes transmitting SCI containing a second HARQ process identifier for the second HARQ process, the first method further including receiving SL HARQ feedback for the second HARQ process from at least one UE. In such embodiments, the SCI further contains a new data indicator, wherein a receiving UE performs soft-combining of the transmitted SL data based on at least the second HARQ process identifier and the new data indicator. In further embodiments, the receiving UE performs soft-combining of the transmitted SL data also considering the source Layer-<NUM> identifier.

Claim 1:
A user equipment, UE, (<NUM>, <NUM>) for wireless communication, the UE (<NUM>, <NUM>) comprising:
a processor (<NUM>); and
a memory (<NUM>) coupled to the processor (<NUM>), wherein the processor (<NUM>) is configured to cause the UE (<NUM>, <NUM>) to:
receive, from a radio access node, a sidelink, SL, grant for a SL transmission using SL resources, the SL grant indicating a first hybrid automatic repeat request, HARQ, process identified by a first HARQ process identifier;
select a second SL HARQ process identified by a second SL HARQ process identifier for the SL transmission using the SL resources,
wherein the second SL HARQ process is selected independently from the first HARQ process in response to the SL grant indicating an SL initial transmission, and
wherein the second SL HARQ process is selected based on the first HARQ process identifier in response to the SL grant indicating a SL retransmission;
transmit SL control information, SCI, containing the second SL HARQ process identifier; and
perform the SL transmission using the SL resources.