WO2018071050A1

WO2018071050A1 - RETRANSMISSION PROCEDURES FOR FIFTH GENERATION (5G) NEW RADIO (NR) THINGS SIDELINK (tSL) COMMUNICATION

Info

Publication number: WO2018071050A1
Application number: PCT/US2016/059387
Authority: WO
Inventors: Satish C. Jha; Yaser M. FOUAD; Qian Li; Guangjie Li; Xiaoyun May Wu; Geng Wu; JoonBeom Kim; Vesh Raj SHARMA BANJADE; Lu LU; Dawei YING; Hassan GHOZLAN; Song Noh
Original assignee: Intel Corporation
Priority date: 2016-10-14
Filing date: 2016-10-28
Publication date: 2018-04-19

Abstract

Retransmission techniques for a tSL-HL (5G (Fifth Generation) NR (New Radio) Things (t) SL (Sidelink) HL (higher layer)) are discussed. One example involves a User Equipment (UE), comprising a memory; and one or more processors configured to: receive one or more tSL-HL PDUs (Protocol Data Units) from a tSL-PHY (Physical layer); assign each of the one or more tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN (Sequence Number) associated with a first data field element of a data field of that tSL-HL PDU; sort the tSL-HL PDUs based on the associated PDU IDs assigned to each of the tSL-HL PDUs; and generate an ARQ (Automatic Repeat Request) ACK/NACK (Acknowledgement/Negative ACK) STATUS PDU that indicates a next unreported PDU ID for an unreceived tSL-HL PDU and indicates one or more ACKs or NACKs.

Description

RETRANSMISSION PROCEDURES FOR FIFTH GENERATION (5G) NEW RADIO (NR) THINGS SIDELINK (tSL) COMMUNICATION

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

62/408,285 filed October 14, 2016, entitled "RETRANSMISSION PROCEDURES FOR NEW RADIO ACCESS TECHNOLOGIES-THINGS SIDELINK COMMUNICATION SYSTEM", the contents of which are herein incorporated by reference in their entirety.

FIELD

[0002] The present disclosure relates to wireless technology, and more specifically to retransmission procedures for Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (tSL) communications between a 5G NR Things user equipment (tUE) and a network UE (nUE) or between a tUE and a tUE.

BACKGROUND

[0003] Conventional LTE (Long Term Evolution) systems employ a higher layer protocol stack that encompasses the protocol layers between PHY (the physical layer) and the RRC (radio resource control) layer for control plane traffic or the IP (Internet protocol) or application layers for user plane traffic. In conventional LTE, these higher layer protocol layers are the MAC (medium access control), RLC (radio link control), and PDCP (packet data convergence protocol) layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a block diagram illustrating an example user equipment (UE) useable in connection with various aspects described herein.

[0005] FIG. 2 is an example diagram of a communication system that can facilitate tSL (5G (Fifth Generation) NR (New Radio) Things (t) Sidelink (SL)) communications according to various aspects described herein.

[0006] FIG. 3 is a diagram illustrating a protocol stack for a tUE (5G NR Things User Equipment)-nUE (network User Equipment) or tUE-tUE interface (e.g., the tSL (5G NR Things Sidelink) Xu-s interface discussed herein), according to various aspects described herein.

[0007] FIG. 4 is a diagram illustrating an example functional overview of two peer tSL-HL entities according to various aspects described herein. [0008] FIG. 5 is a block diagram illustrating a system that facilitate retransmission for a higher layer for 5G NR Things sidelink communication (tSL-HL) at a UE (e.g., network UE (nUE) or 5G NR Things UE (tUE)), according to various aspects described herein.

[0009] FIG. 6 is a flow diagram illustrating a method that facilitates tSL-HL

retransmission procedures at a tSL-HL Rx (reception) entity, according to various aspects described herein.

[0010] FIG. 7 is a flow diagram of a method that facilitates tSL-HL retransmission procedures at a tSL-HL Tx (transmission) entity, according to various aspects described herein.

[0011] FIG. 8 is a diagram illustrating an example of a tSL-HL ARQ ACK/NACK Status PDU for a user plane tSL-HL PDU transmission, according to various aspects described herein.

[0012] FIG. 9 is a diagram illustrating another example of a tSL-HL ARQ ACK/NACK Status PDU for a user plane tSL-HL PDUs transmission, according to various aspects described herein.

[0013] FIG. 10 is a diagram illustrating an example of a tSL-HL ARQ ACK/NACK Status PDU for a tSL-HL PDU transmitted on a Control PRA, according to various aspects described herein.

DETAILED DESCRIPTION

[0014] The present disclosure will now be described with reference to the attached drawing figures, wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures and devices are not necessarily drawn to scale. As utilized herein, terms "component," "system," "interface," and the like are intended to refer to a computer-related entity, hardware, software (e.g., in execution), and/or firmware. For example, a component can be a processor (e.g., a microprocessor, a controller, or other processing device), a process running on a processor, a controller, an object, an executable, a program, a storage device, a computer, a tablet PC and/or a user equipment (e.g., mobile phone, etc.) with a processing device. By way of illustration, an application running on a server and the server can also be a component. One or more components can reside within a process, and a component can be localized on one computer and/or distributed between two or more computers. A set of elements or a set of other components can be described herein, in which the term "set" can be interpreted as "one or more." [0015] Further, these components can execute from various computer readable storage media having various data structures stored thereon such as with a module, for example. The components can communicate via local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a network, such as, the Internet, a local area network, a wide area network, or similar network with other systems via the signal).

[0016] As another example, a component can be an apparatus with specific functionality provided by mechanical parts operated by electric or electronic circuitry, in which the electric or electronic circuitry can be operated by a software application or a firmware application executed by one or more processors. The one or more processors can be internal or external to the apparatus and can execute at least a part of the software or firmware application. As yet another example, a component can be an apparatus that provides specific functionality through electronic components without mechanical parts; the electronic components can include one or more processors therein to execute software and/or firmware that confer(s), at least in part, the functionality of the electronic components.

[0017] Use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless specified otherwise, or clear from context, "X employs A or B" is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then "X employs A or B" is satisfied under any of the foregoing instances. In addition, the articles "a" and "an" as used in this application and the appended claims should generally be construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form. Furthermore, to the extent that the terms "including", "includes", "having", "has", "with", or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term

"comprising."

[0018] As used herein, the term "circuitry" may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, circuitry may include logic, at least partially operable in hardware.

[0019] Embodiments described herein may be implemented into a system using any suitably configured hardware and/or software. FIG. 1 illustrates, for one embodiment, example components of a User Equipment (UE) device 100. In some embodiments, the UE device 100 may include application circuitry 102, baseband circuitry 104, Radio Frequency (RF) circuitry 106, front-end module (FEM) circuitry 108 and one or more antennas 1 10, coupled together at least as shown.

[0020] The application circuitry 102 may include one or more application processors. For example, the application circuitry 102 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system.

[0021] The baseband circuitry 104 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry 104 may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry 106 and to generate baseband signals for a transmit signal path of the RF circuitry 106. Baseband processing circuity 104 may interface with the application circuitry 102 for generation and processing of the baseband signals and for controlling operations of the RF circuitry 106. For example, in some embodiments, the baseband circuitry 104 may include a second generation (2G) baseband processor 104a, third generation (3G) baseband processor 104b, fourth generation (4G) baseband processor 104c, fifth generation (5G) baseband processor 104d (e.g., a 5G NR (New Radio) Things baseband processor, etc.), and/or other baseband processor(s) 104e for other existing generations, generations in development or to be developed in the future (e.g., one or more additional fifth generation (5G) baseband processors, 6G, etc.). The baseband circuitry 104 (e.g., one or more of baseband processors 104a-d) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry 106. The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry 1 04 may include Fast-Fourier Transform (FFT), precoding, and/or constellation mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry 104 may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality.

Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments.

[0022] In some embodiments, the baseband circuitry 104 may include elements of a protocol stack such as, for example, elements of an evolved universal terrestrial radio access network (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or radio resource control (RRC) elements. A central processing unit (CPU) 104e of the baseband circuitry 104 may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP) 104f. The audio DSP(s) 104f may be include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry 104 and the application circuitry 102 may be implemented together such as, for example, on a system on a chip (SOC).

[0023] In some embodiments, the baseband circuitry 104 may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry 104 may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry 104 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry.

[0024] RF circuitry 106 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 106 may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry 106 may include a receive sianal Dath which may include circuitry to down-convert RF signals received from the FEM circuitry 108 and provide baseband signals to the baseband circuitry 104. RF circuitry 106 may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry 1 04 and provide RF output signals to the FEM circuitry 108 for transmission.

[0025] In some embodiments, the RF circuitry 106 may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry 106 may include mixer circuitry 1 06a, amplifier circuitry 106b and filter circuitry 106c. The transmit signal path of the RF circuitry 106 may include filter circuitry 106c and mixer circuitry 106a. RF circuitry 106 may also include synthesizer circuitry 106d for synthesizing a frequency for use by the mixer circuitry 106a of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry 106a of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry 108 based on the synthesized frequency provided by synthesizer circuitry 106d. The amplifier circuitry 106b may be configured to amplify the down-converted signals and the filter circuitry 106c may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry 104 for further processing. In some embodiments, the output baseband signals may be zero- frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry 1 06a of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect.

[0026] In some embodiments, the mixer circuitry 106a of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry 106d to generate RF output signals for the FEM circuitry 108. The baseband signals may be provided by the baseband circuitry 104 and may be filtered by filter circuitry 1 06c. The filter circuitry 1 06c may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect.

[0027] In some embodiments, the mixer circuitry 106a of the receive signal path and the mixer circuitry 106a of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry 106a of the receive signal path and the mixer circuitry 106a of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitrv 1 06a of the receive signal path and the mixer circuitry 106a may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry 106a of the receive signal path and the mixer circuitry 106a of the transmit signal path may be configured for super-heterodyne operation.

[0028] In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry 106 may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry 104 may include a digital baseband interface to communicate with the RF circuitry 106.

[0029] In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the

embodiments is not limited in this respect.

[0030] In some embodiments, the synthesizer circuitry 106d may be a fractional-N synthesizer or a fractional N/N+1 synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry 106d may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider.

[0031] The synthesizer circuitry 106d may be configured to synthesize an output frequency for use by the mixer circuitry 106a of the RF circuitry 1 06 based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry 106d may be a fractional N/N+1 synthesizer.

[0032] In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry 104 or the applications processor 102 depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a look-up table based on a channel indicated by the applications processor 1 02.

[0033] Synthesizer circuitry 1 06d of the RF circuitry 106 may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+1 (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip- flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

[0034] In some embodiments, synthesizer circuitry 1 06d may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLO). In some embodiments, the RF circuitry 106 may include an IQ/polar converter.

[0035] FEM circuitry 108 may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas 1 10, amplify the received signals and provide the amplified versions of the received signals to the RF circuitry 106 for further processing. FEM circuitry 108 may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry 106 for transmission by one or more of the one or more antennas 1 1 0.

[0036] In some embodiments, the FEM circuitry 108 may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry 106). The transmit signal path of the FEM circuitry 108 may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry 106), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 1 1 0.

[0037] In some embodiments, the UE device 100 may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface.

[0038] Additionally, although the above example discussion of device 100 is in the context of a UE device (e.g., a tUE (Fifth Generation (5G) New Radio (NR) Things (t) User Equipment) or a nUE (network UE)), in various aspects, a similar device can be erriDloved in connection with a base station (BS) such as an Evolved NodeB (eNB), etc. [0039] In various aspects, retransmission techniques discussed herein can be employed in connection with a simplified higher layer design for communication between a tUE and a nUE, involving a single layer - referred to herein as tSL-HL (5G NR Things Sidelink (SL) Higher Layer (HL)) - between an upper layer (e.g., an IP (Internet Protocol) layer, an application layer, etc.) and tSL-PHY (the tSL physical layer) for the user plane, or between a tRRC (5G NR Things Radio Resource Control (RRC)) layer and tSL-PHY for the control plane. Retransmission techniques discussed herein can facilitate retransmission of tSL-HL PDUs (protocol data units) in the absence of a PDU Sequence Number (PDU-SN).

[0040] To enhance transmission reliability, a retransmission mechanism can be employed at the tSL-HL layer when an unsuccessful tSL-HL PDU is retransmitted.

Generally, such a retransmission can be initiated at the transmit entity after getting NACK (Negative Acknowledgement) for a tSL-HL PDU from receive entity. The receive entity can prepare (e.g., periodically or upon trigger of an event) a report for sending ACK (Acknowledgement) and/or NACK for one or more tSL-HL PDUs. Such a report is called an ARQ (Automatic Repeat reQuest) ACK/NACK STATUS REPORT. In order to reduce header overhead per PDU, a sequence number (SN) per PDU can be omitted at the transmit entity. However, in conventional LTE (Long Term Evolution) systems, the PDU-SN is employed to identify a PDU and hence to prepare ARQ ACK/NACK

STATUS REPORT. As a result of omitting a PDU-SN, in various embodiments, the receive entity can employ an alternate technique to identify a unique ID for each PDU (referred to herein as a PDU ID or PDUJD) and then use that ID in preparing the STATUS REPORT. To facilitate correct retransmission, the transmit entity can also understand the PDUJD so that the transmit entity can retransmit the correct original PDU in case of NACK. In various embodiments, procedures and techniques discussed herein can be employed in connection with an ARQ mechanism of tSL-HL PDUs for tSL-HL PDUs that do not have PDU-SNs.

[0041] tSL-HL PDUs can be generated at a transmit entity for control PRAs (physical resource assignments that can comprise one or more PRBs (physical resource blocks)) and for non-control/regular PRAs. Due to the contention environment, the PDU size can be limited to a few tens of bytes in order to minimize the impact of collision. As a result, packet header size can be a significant portion of the PDU size, and packet header size reduction can significantly improve the ratio of packet header to payload to maintain a reasonable ratio. Several techniques can be employed to minimize the packet header added at tSL-HL. Among those techniques to improve the proposed packet header design, the sequence number per PDU can be omitted to further reduce the header size. With no SN per PDU, the tSL-HL PDU level retransmission mechanism called automatic repeat request (ARQ) cannot employ the conventional LTE retransmission mechanism based on a SN per PDU. However, in various aspects discussed herein, a retransmission mechanism based on other techniques of identifying PDUs (e.g., based on a PDU ID as discussed herein) can be employed to ensure transmission reliability.

[0042] In various embodiments, techniques discussed herein can be employed in connection with an ARQ procedure. These techniques can include techniques to identify each PDU uniquely at a receive entity when there is no PDU sequence number in the PDU packet header, such as techniques to determine a unique PDU ID for each PDU from its header field(s) when there is no PDU sequence number in the PDU packet header. These techniques can also include: techniques to enable sorting of PDUs based on PDU IDs when there is no PDU sequence number in PDU packet header; techniques to employ a retransmission request mechanism at receive entity to request retransmission of a PDU or a PDU segment by sending an ARQ ACK/NACK STATUS PDU to the transmit entity; techniques to employ a mechanism to generate an ARQ ACK/NACK STATUS PDU at the receive entity in the absence of a PDU sequence number in PDU packet header; and techniques to employ an ARQ procedure at a transmit entity to retransmit a PDU based on an ARQ ACK/NACK STATUS PDU and/or a Timer.

[0043] Referring to FIG. 2, illustrated is an example diagram of a communication system 200 that can facilitate tSL (5G (Fifth Generation) NR (New Radio) Things (t) Sidelink (SL)) communications according to various aspects described herein. In system 200, Things devices (e.g., wearable devices, etc.) can be supported over a 5G NR- Things interface referred to herein as Xu-s. The communication system of FIG. 2 shows the following network nodes and interfaces: (1 ) a nUE (network UE) with full sidelink and direct link protocol stacks (e.g., with full C/U (control/user)-plane functions), which can act as a master UE in a sidelink cell/PAN (personal area network); (2) three tUEs (Things UEs, e.g., wearable UEs), which have a full sidelink protocol stack and can have (or can omit) a standalone direct link protocol stack, and can act as a slave UE in the sidelink cell/PAN; (3) a sidelink cell/PAN comprising the nUE and associated tUEs, which can employ mutual authentication to form the PAN; (4) the Xu-d interface, the radio link interface between the nUE/tUE and the 5G infrastructure; (5) the Xu-s interface, the radio link interface between the nUE and a tUE or between two tUEs; (6) the 5G-RAN (5G Radio Access Network); and (7) the 5G Core Network (5G-CN). [0044] Various embodiments discussed herein relate to the Xu-s interface shown in FIG. 2. In various situations, a tUE can communicate with the 5G-RAN via the nUE. Each nUE can have several tUEs associated with it which together form a PAN (which can also be referred to herein as a Sidelink Cell). In general, there can be a large number of nUEs in a geographical region, each with their own PANs, which can create a high density network scenario. The 5G-RAN (or E-UTRAN (Evolved Universal Terrestrial Radio Access Network)) can assign a common resource pool for 5G NR- Things Sidelink Communication. This resource pool can be shared among multiple PANs in a close geographical area and among tUEs within each PAN on a contention based resource access basis. Each nUE can have at least the following two higher layer protocol stacks: (a) one for the 5G NR-Things Sidelink (tSL) Communication interface between tUE and nUE and (b) one for the 5G NR-Things Directlink Communication interface between nUE and 5G-RAN. The Higher Layer protocol stack for the interface nUE-5G-RAN can be the LTE Uu stack or a LTE evolved 5G protocol stack. As used herein, higher layer protocol stack refers mainly to protocol layer(s) in between tSL-PHY (the physical layer, also referred to herein as lower layer) and IP (Internet

Protocol)/Application layers (also referred to herein as upper layer) in a user plane, and protocol layer(s) in between tSL-PHY and a RRC (radio resource control, e.g., tSL- RRC) layer in a control plane. For example, higher layer refer to MAC (Medium Access Control), RLC (Radio Link Control), and PDCP (Packet Data Convergence Protocol) layers of a conventional LTE system.

[0045] Due to the contention environment for communication over the Xu-s interface, it is expected that each packet transmission (i.e. tSL-PHY transport block TB size) can be shorter in 5G NR-Things Sidelink (tSL) Communication in order to reduce the impact of collision on system performance. For example, the TB (Transport Block) size can be of only a few Bytes (as an example, in some embodiments, the TB size can be less than 75 Bytes, although greater or lesser sizes can be employed in other embodiments). In such scenarios, reducing the size of the packet header added at the higher layer can maintain a reasonable data-to- Packet Header ratio. The higher layer protocol design and packet processing procedure design discussed herein for higher layer can minimize the higher layer protocol header overhead per packet transmission. In various embodiments, the 5G NR Things higher layer design for the user plane discussed herein can have the following features: (1 ) A simplified higher layer protocol design, which can simplify higher layer functionalities and to avoid addition of packet headers by multiDle lavers: (2) functionalities of higher layer protocol customized for 5G NR-Things Sidelink Communication features; (3) Reduced number of protocol-layer-specific header fields (e.g., avoiding multiple levels of packet ID (such as sequence number) addition); (4) Shorter size of various packet header fields; (5) Packet segmentation and

Combination with lower Packet header overhead; and (6) Retransmission of packets with lower Packet header overhead.

[0046] In various aspects, all higher layer functionalities (such as conventional LTE MAC/RLC/PDCP functionalities) for user plane data processing and/or control plane data processing can be merged into a single layer referred to herein as 5G NR-Things Sidelink Higher Layer (tSL-HL), which can reduce packet header during transmission over the air-interface Xu-s. The packet header reduction can provide significant advantages in throughput, given that each tSL-PHY-SDU (i.e. tSL-PHY TB) can typically be of very small size (e.g., 180 -600 bits, which is 22.5-75 Bytes) for the Xu-s, which is very small in comparison to that of conventional LTE.

[0047] Referring to FIG. 3, illustrated is a protocol stack for a tUE-nUE (or tUE-tUE) interface (e.g., the tSL (5G NR Things Sidelink) Xu-s interface discussed herein), according to various aspects described herein. For the UL (uplink) transmission, a CP/UP (control plane/user plane) data packet to be transmitted over the air-interface can be received as a tSL-HL service data unit (tSL-HL SDU) from the IP/host (for user plane data) layer or the 5G NR Things Sidelink-RRC (tSL-RRC) (for control plane data) layer. The tSL-RRC layer can handle the configuration of the tSL-HL. tSL-HL can store the data in a relevant transmission (Tx) Buffer (e.g., UP Tx buffer, CP Tx buffer) until tSL-PHY indicates a UL grant. The tSL-HL can form a tSL-HL packet data unit (tSL-HL PDU) based on the TB size indicated by tSL-PHY. The tSL-HL can then pass the tSL- HL PDU to tSL-PHY for transmission. The data packet tSL-HL SDU can go through several operations during its lifetime in the tSL-HL protocol layer. Functions of the tSL- HL layer can be performed by tSL-HL entities. For a tSL-HL entity configured at the nUE (or at one tUE, for tUE-tUE communication), a peer tSL-HL entity can be configured at the tUE (or the other tUE, for tUE-tUE communication) and vice versa.

[0048] Referring to FIG. 4, illustrated is an example diagram showing a functional overview of two peer tSL-HL entities according to various aspects described herein. A tSL-HL entity can receive/deliver tSL-HL SDUs from/to upper layer (e.g., IP/application for UP) and can send/receive tSL-HL PDUs to/from its peer tSL-HL entity via lower layers. Although a tSL-HL PDU can either be a tSL-HL data PDU (e.g., user plane or control plane PDU, or a tSL-HL PDU segment) or a tSL-HL control PDU (e.g. ARQ (automatic reDeat request) ACK (acknowledgement)/NACK (negative acknowledgement) Status PDU), various embodiments discussed herein relate to tSL- HL UP data PDUs and/or segments thereof. If a tSL-HL entity receives tSL-HL SDUs from an upper layer, it can receive them through either a user plane SAP (service access point) or a control plane SAP between tSL-HL and the upper layer, and after forming tSL-HL data PDUs from the received tSL-HL SDUs, the tSL-HL entity can deliver the tSL-HL data PDUs or PDU segments to a lower layer (tSL-PHY). When a tSL-HL entity receives tSL-HL data PDUs or PDU segments from the lower layer, after forming tSL-HL SDUs from the received tSL-HL data PDUs and PDU segments, the tSL-HL entity can deliver the tSL-HL SDUs to the upper layer through either the user plane SAP or control plane SAP between tSL-HL and upper layer. A tSL-HL entity can also deliver/receive tSL-HL control PDUs to/from lower layer.

[0049] A tSL-HL entity can comprise a transmitting side and a receiving side. The transmitting side of a tSL-HL entity can receives tSL-HL SDUs from an upper layer and can send tSL-HL PDUs to its peer tSL-HL entity via lower layers. The receiving side of a tSL-HL entity can deliver tSL-HL SDUs to an upper layer and can receive tSL-HL PDUs from its peer tSL-HL entity via lower layers.

[0050] In general, tSL-HL entities handle tSL-HL SDUs that can have variable sizes and can be byte aligned. Additionally, tSL-HL PDUs can be formed when a tSL-HL entity is notified of a transmission opportunity by a lower layer (e.g., by tSL-PHY), and can then be delivered to lower layer. A control plane PDU can be formed if the transmission opportunity is on one or more control PRAs (Physical Resource

Allocations, which can comprise 1 or more PRBs (physical resource blocks)), where the control PRA(s) can be indicated via higher layer signalling, predefined, etc. If the transmission opportunity is not associated with control PRA(s), a user plane tSL-HL PDU can be formed. Various embodiments discussed herein can relate to UP tSL-HL PDUs that can be transmitted via PRA(s) other than control PRA(s) (also referred to herein as non-control PRA(s)).

[0051] Referring to FIG. 5, illustrated is a block diagram of a system 500 that facilitate retransmission for a higher layer for 5G NR Things sidelink communication (tSL-HL) at a UE (e.g., network UE (nUE) or 5G NR Things UE (tUE)), according to various aspects described herein. System 500 can include one or more processors 510 (e.g., one or more baseband processors such as one or more of the baseband processors discussed in connection with FIG. 1 ), transceiver circuitry 520 (e.g., comprising one or more of transmitter circuitry or receiver circuitry, which can employ common circuit elements, distinct circuit elements, or a combination thereof), and a memory 530 (which can comprise any of a variety of storage mediums and can store instructions and/or data associated with one or more of processor(s) 510 or transceiver circuitry 520). In various aspects, system 500 can be included within a user equipment (UE), either in a 5G NR Things UE (tUE, e.g., a wearable tUE, etc.) or in a network UE (nUE). As described in greater detail below, system 500 can provide higher layer functionality to facilitate an ARQ (automatic repeat request) retransmission mechanism between a network UE (nUE) and one or more 5G NR Things UEs (tUEs) or between multiple tUEs within a personal area network (PAN).

[0052] Processor(s) 510 can implement a 5G NR Things Sidelink higher layer (tSL- HL) that can facilitate retransmission procedures associated with a tSL-HL for tSL communication between a tUE and a nUE or between two tUEs. In various aspects, processor(s) 510 can implement functions associated with a tSL-HL transmission (Tx) entity and/or functions associated with a tSL-HL reception (Rx) entity. Each of the tSL- HL Rx and Tx aspects discussed herein can implement separate retransmission techniques and associated procedures for CP (control plane) tSL-HL PDUs transmitted on control PRA(s) (physical resource assignment(s) of one or more physical resource block(s)) and for UP (user plane) tSL-HL PDUs transmitted on non-control PRA(s). Thus, in aspects, system 500 can implement one set of techniques for the CP, and can also implement a second set of techniques for the UP.

[0053] In tSL-HL Rx aspects, processor(s) 510 can implement one or more functions associated with facilitating retransmission by a tSL-HL Rx entity, such as any of the acts shown or described herein (e.g., in connection with FIG. 6, etc.). For example, processor(s) 510 can receive one or more tSL-HL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL) Higher Layer (HL)) PDUs (protocol data units) from a tSL- PHY (tSL Physical layer). The received tSL-HL PDU(s) can each comprise a header and a data field, and the data field can comprise one or more data field elements. Each data field elements can be a tSL-HL SDU (service data unit), a tSL-HL SDU segment, or a tSL-HL PDU re-segment. The header can comprise an associated sub-header for each data field element that indicates a SN (sequence number) of that data field element, and can also indicate a segment number for a tSL-HL SDU segment or a Start SO (segment offset) and an optional End SO for a tSL-HL PDU resegment (the End SO can be omitted for the last re-segment of a tSL-HL PDU and included for other re- segment(s)).

[0054] Processor(s) 510 can assign a PDU ID to each of the received tSL-HL PDUs, which Drocessor(s 510 can determine from the first data field element of the data field of that tSL-HL PDU (and the associated subheader). When the first data field element of the tSL-HL PDU is a tSL-HL SDU, processor(s) 510 can assign a PDU ID that comprises the SN of the tSL-HL SDU and can also comprise a segment number of zero (e.g., PDU ID = (SDU SN, Segment Number = 0)). When the first data field element of the tSL-HL PDU is a tSL-HL SDU Segment, processor(s) 510 can assign a PDU ID that comprises the SN of the tSL-HL SDU comprising the tSL-HL SDU segment, and can also comprise the segment number of the tSL-HL SDU segment (e.g., PDU ID = (SDU SN, Segment Number)). When the first data field element of the tSL-HL PDU is a tSL- HL PDU re-segment, processor(s) 510 can assign a PDU ID that comprises a re- segment SN and a Start SO (Segment Offset) of the tSL-HL PDU re-segment, and can also comprise an End SO of the tSL-HL PDU re-segment for a re-segment other than a final re-segment, and can omit an End SO of the tSL-HL PDU re-segment for a final re- segment.

[0055] Processor(s) 510 can sort the one or more tSL-HL PDUs based on the assigned PDU IDs. For example, the tSL-HL PDUs comprising tSL-HL SDU(s) and/or tSL-HL SDU segment(s) can be sorted first based on SDU SN, and then (for tSL-HL PDUs with the same SDU SN) based on Segment number. tSL-HL PDUs comprising tSL-HL PDU re-segment(s) can be sorted first based on a re-segment SN, and then (for tSL-HL PDUs with the same re-segment SN) based on Start SO and/or End SO.

[0056] Based on the PDU IDs, processor(s) 510 can determine a tSL-HL with a highest PDU ID among the tSL-HL PDUs (e.g., a tSL-HL with the highest PDU ID among tSL-HLs comprising tSL-HL SDU(s) and/or SDU segment(s), a tSL-HL with the highest PDU ID among tSL-HLs comprising tSL-HL PDU re-segment(s), etc.). Based on the highest PDU ID and any other PDU ID(s) of received tSL-HL PDU(s), processor(s) 51 0 can determine whether there are any missing tSL-HL PDU(s) that have not been received by processor(s) 51 0, such as based on received tSL-HL PDU(s) that have a higher PDU ID (e.g., as indicated via missing PDU ID(s) between PDU ID(s) of tSL- HL(s) that have been received, etc.).

[0057] Based on the received tSL-HL PDU(s), processor(s) 510 can generate an ARQ (automatic repeat request) ACK/NACK STATUS PDU that can comprise ARQ ACK/NACK feedback associated with the received tSL-HL PDU(s) and any missing tSL- HL PDU(s) determined by processor(s) 510. Processor(s) 510 can generate the ARQ ACK/NACK STATUS PDU to explicitly indicate an ACK for the tSL-HL PDU having the highest PDU ID and explicitly indicate a NACK for each missing tSL-HL PDU

determined bv Drocessor(s) 510. By explicitly indicating all determined NACKs and a PDU ID (e.g., via an ACK_PDU_ID field) for a next not received tSL-HL PDU (e.g., an unreceived tSL-HL PDU, which can include any tSL-HL PDU not yet received at the Rx tSL-HL entity, whether because it was not yet sent by the peer tSL-HL entity, because it was sent by the Tx tSL-HL entity but not received at the Rx tSL-HL entity, etc.) that is not reported as missing in the ARQ ACK/NACK STATUS PDU (e.g., an unreported PDU ID, which can include any PDU ID for which an ACK/NACK has not yet been reported via an ARQ ACK/NACK STATUS PDU to the peer Tx tSL-HL entity), the ARQ ACK/NACK STATUS PDU can implicitly indicate an ACK for each PDU ID not explicitly indicated that is less than the ACK PDUJD. As such, the Tx entity receiving the ARQ ACK/NACK STATUS PDU can determine an ACK (indicated either explicitly or implicitly) or a NACK (indicated explicitly) for each tSL-HL having a PDU ID greater than the PDU ID for which an ACK has not yet been received at the Tx entity.

[0058] If processor(s) 51 0 have not determined any missing tSL-HL PDU(s), processor(s) 510 can generate the ARQ ACK/NACK STATUS PDU to indicate an ACK associated with each of the received tSL-HL PDU(s), for example, via the ARQ

ACK/NACK STATUS PDU comprising an ACK associated with the tSL-HL PDU having the highest PDU ID and comprising no NACKs. Upon receiving an ARQ ACK/NACK STATUS PDU comprising an ACK associated with a given tSL-HL PDU and no NACKs, a tSL-HL Tx entity can determine that each tSL-HL PDU for which an ACK has not yet been received was successfully received by the tSL-HL Rx entity.

[0059] If processor(s) 51 0 have determined missing tSL-HL PDU(s), processor(s) 51 0 can generate the ARQ ACK/NACK STATUS PDU to indicate a NACK for each of the missing tSL-HL PDU(s) and an ACK for the tSL-HL PDU having the highest PDU ID among received tSL-HL PDU(s). Processor(s) 510 can indicate the NACK(s) individually (e.g., via explicitly indicating PDU ID(s)) and/or as one or more ranges of continuous tSL-HL PDUs to be NACKed. A range of continuous tSL-HL PDUs to be NACKed can be indicated via one or more of: (a) explicitly indicating Start and End PDU ID(s) of the range; (b) explicitly indicating a Start PDU ID with an implicit end PDU ID corresponding to a final segment having the same SDU SN as the Start PDU ID; (c) explicitly indicating a Start PDU ID for a range comprising all PDU IDs from the Start PDU ID up to the PDU ID for which an explicit ACK is indicated (e.g., the highest PDU ID for received tSL-HL PDU(s); etc.

[0060] In tSL-HL Tx aspects, processor(s) 510 can implement one or more functions associated with facilitating retransmission by a tSL-HL Tx entity, such as any of the acts shown or described herein (e.g., in connection with FIG. 7, etc.). For example, processor(s) 510 can store a set of tSL-HL PDU(s) generated by the tSL-HL Tx entity (e.g., via processor(s) 510) in a retransmission buffer (e.g., a CP retransmission buffer, a UP retransmission, etc.). As discussed herein, each of the tSL-HL PDUs can comprise a header and a data field comprising one or more data field elements. The header can comprise a sub-header associated with each data field element of the data field, which can indicate details of the associated data field element.

[0061] Processor(s) 510 can assign a unique PDU ID to each of the tSL-HL PDU(s) generated by the tSL-HL Tx entity. As discussed herein, processor(s) 51 0 (and similar processor(s) at the peer tSL-HL Rx entity) can determine the PDU ID for each tSL-HL PDU based on the first data field element of that tSL-HL PDU. For example, the PDU ID can be (SDU SN, Segment Number = 0) when the first data field element is a tSL-HL SDU, and can be (SDU SN, Segment Number) when the first data field element is a tSL-HL SDU segment. In situations wherein processor(s) 510 re-segment a tSL-HL PDU from the retransmission buffer for a new tSL-HL PDU (e.g., to be transmitted via a smaller allocated resource size than the original tSL-HL PDU), the re-segment can be assigned a re-segment SN that is indicated via the sub-header of the new tSL-HL PDU (e.g., along with a Start SO and (for re-segments that are not the final re-segment of the original tSL-HL PDU) an End SO). Additionally, processor(s) 510 can maintain a mapping between re-segment SN(s) and the original tSL-HL PDU, such that processor(s) 510 can determine the appropriate tSL-HL PDU when an ARQ ACK/NACK STATUS PDU indicates an ACK or a NACK for a re-segment SN, for example, when bytes of a tSL-HL PDU are to be retransmitted in response to a NACK for a re-segment SN.

[0062] Processor(s) 510 can maintain a timer with each tSL-HL PDU (e.g., the maxWaitForStatusPDUTimer described herein). If the associated timer for a tSL-HL PDU expires and ACK/NACK feedback has not yet been received for that tSL-HL PDU, processor(s) 510 can consider that tSL-HL PDU for retransmission (e.g., when a PRA (control or non-control, depending on the type of tSL-HL PDU and retransmission buffer) and allocated size are received from tSL-PHY).

[0063] Additionally or alternatively, processor(s) 510 can receive an ARQ

ACK/NACK STATUS PDU from tSL-PHY (e.g., received via the air interface Xu-s from the peer tSL-HL entity) that can indicate an ACK for at least one PDU ID associated with at least one tSL-HL PDU received by the peer tSL-HL entity, and can indicate zero or more NACKs for zero or more PDU IDs associated with tSL-HL PDUs not received bv the Deer tSL-HL entity. For each PDU ID for which a NACK is received, processor(s) 51 0 can consider the associated tSL-HL PDU for retransmission. Based on the ACK indicated in the ARQ ACK/NACK STATUS PDU, processor(s) 510 can determine one or more tSL-HL PDUs that have been successfully received at the Rx tSL-HL entity and need not be retransmitted. As discussed herein, processor(s) 51 0 can determine an ACK or a NACK from the ARQ ACK/NACK STATUS PDU for every tSL-HL PDU with a higher PDU ID than the highest PDU ID for which an ACK has previously been received by processor(s) 51 0. For example, the ARQ ACK/NACK STATUS PDU can explicitly indicate a PDU ID for a next tSL-HL PDU not received by the Rx tSL-HL entity and not reported missing via the STATUS PDU along with zero or more NACKs for zero or more PDU IDs, and implicitly indicate an ACK for all other PDU IDs lower than the PDU ID explicitly indicated for the next tSL-HL not yet received and not reported missing.

[0064] Based on an indicated PRA and allocated size received from tSL-PHY (e.g., in an UL (uplink) grant, etc.), if any tSL-HL PDUs are considered for retransmission, processor(s) 510 can retransmit a tSL-HL PDU (if the allocated size is sufficient) or a re- segment of a tSL-HL PDU. If the allocated size is insufficient to retransmit the entire tSL-HL PDU, processor(s) 510 can re-segment the tSL-HL PDU into a plurality of re- segments, and can assign each of the re-segments the same re-segment SN. When processor(s) 510 transmits a re-segment, the header of the new tSL-HL PDU

comprising that re-segment can indicate the re-segment SN along with a Start SO (and for a non-final re-segment, the End SO) of that re-segment. As described herein, processor(s) 510 can associate the re-segment SN with the PDU ID of the original tSL- HL PDU, such that processor(s) 51 0 (and the peer tSL-HL entity) can employ the re- segment SN to determine whether or not those bytes of the original tSL-HL PDU have been successfully received at the Rx tSL-HL entity.

[0065] Processor(s) 510 can pass the new tSL-HL PDU (whether comprising the original tSL-HL PDU or a re-segment thereof) to tSL-PHY for transmission via the Xu-s air interface to the peer tSL-HL entity.

[0066] Referring to FIG. 6, illustrated is a flow diagram of a method 600 that facilitates tSL-HL retransmission procedures at a tSL-HL Rx entity, according to various aspects described herein. In some aspects, method 600 can be performed at a UE (e.g., nUE or tUE). In other aspects, a machine readable medium can store instructions associated with method 600 that, when executed, can cause a UE (e.g., nUE or tUE) to perform the acts of method 600.

[0067] At 610, a set of tSL-HL PDUs can be received from a tSL-PHY. [0068] At 620, a PDU ID can be assigned to each of the one or more tSL-HL PDUs based on a SN of a first data field element of a data field of that tSL-HL PDU.

[0069] At 630, the set of tSL-HL PDUs can be sorted based on the assigned PDU IDs.

[0070] At 640, a determination can be made based on the PDU ID(s) whether there are any missing tSL-HL PDUs.

[0071] At 650, an ARQ ACK/NACK STATUS PDU can be generated that indicates an ACK or NACK status for one or more reported PDU IDs less than a PDU ID indicated via an ACK PDUJD, wherein zero or more NACK(s) can be explicitly indicated for missing tSL-HL PDUs, and an ACK can be implicitly indicated for each other reported PDU ID.

[0072] Additionally or alternatively, method 600 can include one or more other acts performed by a tSL-HL Rx entity described above in connection with system 500.

[0073] Referring to FIG. 7, illustrated is a flow diagram of a method 700 that facilitates tSL-HL retransmission procedures at a tSL-HL Tx entity, according to various aspects described herein. In some aspects, method 700 can be performed at a UE (e.g., nUE or tUE). In other aspects, a machine readable medium can store instructions associated with method 700 that, when executed, can cause a UE to perform the acts of method 700.

[0074] At 710, a set of tSL-HL PDUs can be stored in a retransmission buffer.

[0075] At 720, a unique PDU ID can be assigned to each tSL-HL PDU of the set of tSL-HL PDUs.

[0076] At 730, a distinct timer can be maintained for each tSL-HL PDU of the set of tSL-HL PDUs.

[0077] At 740, an ARQ ACK/NACK STATUS PDU can be received that indicates an ACK for at least one PDU ID and can optionally indicate NACK(s) for one or more other PDU IDs.

[0078] At 750, a determination can be made based on the timer(s) and the ARQ

ACK/NACK STATUS PDU whether to retransmit any tSL-HL PDU(s).

[0079] At 760, optionally, one or more tSL-HL PDU(s) or re-segments thereof can be retransmitted.

[0080] Additionally or alternatively, method 700 can include one or more other acts performed by a tSL-HL Rx entity described above in connection with system 500. Identifying Each PDU Uniquely - Obtaining a PDU ID for Each PDU

[0081] When a receive entity receives a PDU, the PDU can be identified uniquely, for example, for sorting PDU(s), discarding duplicate reception, sending ACK/NACK to the transmit entity, etc. An ARQ ACK/NACK Status PDU can be generated by the receive tSL-HL entity for sending ACK/NACK for several PDUs simultaneously to the transmit entity.

[0082] As described below for a variety of scenarios, a unique PDU ID (e.g., which can be indicated via a PDUJD state variable, etc.) can be obtained for each PDU.

[0083] PDU ID in the case of new Transmission and Retransmission without PDU segmentation: A tSL-HL PDU can comprise 0 or more SDUs and 0 or more SDU segments (e.g., with the PDU comprising at least one SDU or SDU segment). Each of these SDU(s) (or SDU segment(s)) can have a unique ID, such that a SDU can be identified by an SDU SN, and a SDU segment can be identified by an SDU SN and a segment number (also referred to herein as SegN). In various aspects, the unique ID of the first data field of the PDU (e.g., SDU SN for an SDU, or SDU SN plus segment number for a segment) can be employed as the PDU ID. Therefore, a tSL-HL PDU can be uniquely identified by the SDU sequence number (alone, or with a segment number in case of an SDU segment) of the first data field element (SDU/SDU segment) of the tSL-HL PDU.

[0084] PDU ID in the case of tSL-HL PDU Retransmission with PDU segmentation: In the case of PDU segmentation during retransmission, the segment of an original PDU can be identified by a re-segmentation SN, a start segment offset (SO) and an end segment offset. The transmit entity can maintain a mapping between the re- segmentation SN and the original PDU ID (wherein the PDU ID can be the SDU SN of the first data field element if the first data field of the tSL-HL PDU is an SDU, or can be the SDU SN plus the Segment Number of the first data field element if first data field of the tSL-HL PDU is an SDU Segment). The entire original PDU (the original Header plus the Original payload) can be considered as data during retransmission to specify the byte number for segment offsets.

[0085] Thus, in various embodiments, the PDU ID can be: (1 ) the SDU SN of the first SDU in the PDU, if the first data field element of the tSL-HL PDU is an SDU; (2) The SDU SN and Segment Number of the first SDU segment in the PDU if the first data field element of the tSL-HL PDU is an SDU Segment; or (3) The Re-segmentation SN, Start SO and possibly End SO, if the retransmission PDU is a segment of an original PDU durina retransmission. Thus, the PDU ID can comprise a SN (e.g., SDU SN or re- segmentation SN) of the first data field element, and can also comprise a Segment Number or (in the case of resegmentation) a Start SO and possibly an End SO.

[0086] Note that the PDU ID in case of a PDU segment (e.g., in case of

segmentation of an original PDU during retransmission) can comprise a non-negative integer called Re-segment SN (along with start SO and possibly end SO). The Re- Segment SN can be associated with a unique PU at the transmit entity, which can facilitate retransmission. In other cases (not involving a Re-segment SN), the PDU ID can be as discussed below.

Performing Arithmetic Operation on PDU ID:

[0087] Various state variables and parameters are described below that can be used in tSL-HL entities in order to specify the ARQ procedures. All state variables can be non-negative integers. The following details can relate to PDU ID(s) for PDU(s) comprising SDU(s) and/or SDU segment(s), wherein SDUJD and Seg_N can be variables representing the SDU identity and segment number, respectively.

[0088] PDUJD: A tSL-HL PDU can be identified by a PDU ID via a PDUJD state variable, which can comprise: (1 ) an SDU PDUJD of the first SDU in the PDU, if the first data field (SDU/SDU segment field) of the tSL-HL PDU is an SDU (In this case, the PDUJD can be (SDU_SN, Seg_N =0)); or (2) (SDU SN, Segment Number) of the first SDU segment in the PDU if the first data field (SDU/SDU segment field) of the tSL-HL PDU is an SDU Segment (In this case, the PDUJD can be (SDU_SN, Seg_N)).

[0089] Therefore, PDUJD can be defined as a duple PDUJD = (SDU_SN, Seg_N), wherein Seg_N can be 0 for a complete (non-segmented) SDU. Comparison between two PDUJDs can be based on both parts (the SDU_SN and the Seg_N) of the

PDUJD, wherein sorting can be based first on the SDU_SN, and then (e.g., for

PDUJDs with a common SDU_SN) on the Seg_N. For example, assume PDUJD1 = (SDU_SN1 , Seg_N1 ), PDUJD2 = (SDU_SN2, Seg_N2), and PDUJD3 = (SDU_SN3, Seg_N3). If SDU_SN2 > SDU_SN1 , then PDUJD2 > PDUJD1 . If SDU_SN2 =

SDU_SN3 and Seg_N2 < Seg_N3, PDUJD2 <PDUJD3.

[0090] Next PDUJD: The next PDUJD after PDUJD1 =(SDU_SN1 , Seg_N1 ) can depend on whether or not Seg_N1 is the last segment of the SDU with SDU SN = SDU_SN1 .

[0091] If Seg_N1 is the last segment of the SDU with SDU SN = SDU_SN1 , the Next PDUJD can be either the SDU with SDU SN (SDU_SN1 +1 ) or the first segment of the SDU SN (SDU SN1 +1 ). Thus, the next PDUJD can be (SDU_SN1 +1 , 0) or (SDU_SN1 +1 , 1 ). Segment number 0 implies that this SDU is not segmented, that is, a whole SDU is the first data field in the corresponding PDU. In various aspects described herein, the receive entity can always know whether a received segment is the last segment of a SDU, because the last segment can be indicated in the PDU header field.

[0092] If Seg_N1 is not the last segment of the SDU with SDU SN = SDU_SN1 , then the Next PDUJD is the next segment of the SDU with SDU SN = SDU_SN1 . Thus, the next PDUJD can be (SDU_SN1 , Seg_N1 +1 ).

[0093] All state variables related to PDUJD can perform arithmetic operations on the SDU_SN and/or the Seg_N of the PDUJD. The SDU_SN can take a value from 0 to MaxSN -1 , where MaxSN can be a maximum sequence number (e.g., 1024 for user plane tSL-HL SDUs/PDUs and 128 for control plane tSL-HL SDUs/PDUs, although in various aspects, other values can be employed). All arithmetic operations described herein on SDU_SN can be affected by the modulus (e.g., the final value can be [value from arithmetic operation] modulo MaxSN).

[0094] When performing arithmetic comparisons of state variables or SDU_SN values, a modulus base can be used.

[0095] VT(ACK) and VR(R) can be state variables that can be assumed as the modulus base at the transmitting side and receiving side of a tSL-HL entity,

respectively. The value of VT(ACK) can represent the next tSL-HL PDU for which a positive acknowledgment is to be received in-sequence at the Tx side, while VR(R) can represent the PDUJD following the last in-sequence completely received tSL-HL PDU at the Rx side. These modulus bases can be subtracted from all the values involved (depending whether at the Tx side or Rx side), and then an absolute comparison can be performed (e.g., VR(R) < SDU_SN < VR(ACK_PDUJD) can be evaluated as [VR(R) - VR(R)] modulo MaxSN < [SDU_SN - VR(R)] modulo MaxSN < [VR(ACK_PDUJD) - VR(R)] modulo Max_SN).

[0096] Using the above arithmetic operations, receive entity can sort PDUs. In various aspects, the transmit entity can ensure that the difference between the next PDUJD for which the transmit entity is waiting to obtain ACK/NACK from the receive entity and the PDUJD of the last transmitted PDU is less than MaxSN/2 so that the modulus operation at the receive side for sorting works properly (which can prevent a potential overflow problem). ARQ ACK/NACK STATUS PDU

[0097] ARQ ACK/NACK STATUS PDU is used by the receiving side of tSL-HL entity to inform the peer tSL-HL entity (i.e., transmitting side of tSL-HL entity) about tSL-HL data PDUs that are received successfully, and tSL-HL data PDUs that are detected to be lost by the receiving side of tSL-HL entity.

[0098] The ARQ ACK/NACK Status PDU for user plane data transmission are transmitted separately than the status PDU for the data transmission on control PRA.

ARQ ACK/NACK STATUS PDU Parameters

[0099] ARQ ACK/NACK STATUS PDU Header fields: the following fields/parameters can be employed for ARQ ACK/NACK STATUS PDU.

[00100] wCPT (tSL-HL Control PDU-Type) field: this field can have a Length of 4 bits. The wCPT field can indicate the type of the tSL-HL internal control PDUs. The interpretation of the wCPT field can be as provided below in Table 1 .

[00101 ] Acknowledge PDU ID Field (ACK-PDU-ID): This can be a variable field length as described in Table 1 , below. It can provide the PDUJD of the next packet expected by the receiving side of the tSL-HL entity. The ACK-PDU-ID field can indicate the PDU ID of the next not yet received tSL-HL Data PDU which is not reported as missing in the STATUS PDU. When the transmitting side of a tSL-HL entity receives a STATUS PDU, it can interpret that all PDUs up to but not including the tSL-HL PDU with PDUJD = ACK-PDU-ID have been received by its peer tSL-HL entity, excluding those PDUs indicated in the STATUS PDU with NACK-PDU-ID (SDU SN or SDU SN+Seg-N), NACK-PDU-Range-ID, and portions of PDUs indicated in the STATUS PDU with NACK- PDU-ID (Rseg-SN, Start segment offset (SO) and End SO) (End SO is not needed if a NACK is sent for portion from byte start SO of a PDU to the end of the PDU).

Table 1 : Description of various fields for ARQ ACK/NACK STATUS PDU.

Header field Header field Header field Description

Value

R (1 bit) 0 Reserved for future use

PDU Type 00 User plane Data PDU for UP PRAs

(2 bit) (PDU 01 PDU for Control PRAs

Type 10 tSL-HL Internal Control PDU

indicates 1 1 Reserved for future use

what type is.) wCPT (tSL- 000 ARQ ACK/NACK Status PDU for user plane data PDU HL Control 001 transmission

PDU-Type) 01 0-1 1 1 ARQ ACK/NACK Status PDU for data PDU (3 bits) transmitted on control PRA

Reserved for future use

PDU-ID- 0000 SDU SN (10 bits for User plane PDU and 7 bits for Type (4 PDU on Control PRA) of first SDU in the PDU

bits) 0001 SDU SN (10 bits for User plane PDU and 7 bits for

PDU on Control PRA) and Segment Number (7 or 9 bits for User plane PDU and 7 bits for PDU on Control PRA) of first SDU segment in the PDU

0010 Re-segmentation SN, Start SO (segment offset) and

End SO

10 bits + 7 bits + 7 bits (User plane PDU);

3 bits + 7 bits + 7 bits (PDU on Control PRA)

001 1 Re-segmentation SN, Start SO (segment offset). In this case, End SO is end of original PDU.

10 bits + 7 bits (User plane PDU);

3 bits + 7 bits (PDU on Control PRA)

01 00 It indicates that next field is a range of continuous 01 01 PDUs to be NACKED, where range is identified by 01 10 PDU_ID_Range_Start and PDU_ID_Range_End. 01 1 1 PDU_ID_Start and PDU_ID_End are specified based on PDU-ID-Type as follows:

0100: Range specified by [SDU SN, SDU SN]

0101 : Range specified by [SDU SN, SDU SN +

Segment Number]

01 10: Range specified by [SDU SN + Segment Number, SDU SN]

01 1 1 : Range specified by [SDU SN + Segment Number, SDU SN + Segment Number]

1000 It indicates a NACK for a PDU range starting from a given PDU ID (SDU SN + Segment Number) until the last segment of this SDU SN. Note that the end of this range is not needed to be transmitted.

1001 It indicates that the next field is a range of continuous 1010 PDUs to be NACKED due to insufficient grant for the

Status PDU. The ending point for the range is equal to the ACKED PDU ID and is not transmitted while the beginning of the range is equal to PDU_ID_Range_Start and is specified by:

1001 : Range start specified by[ SDU SN1; 1010: Range start specified by[ SDU SN + Segment

Number].

101 1 -1 1 1 1 Reserved for future use

ARQ ACK/NACK STATUS PDU Structure

[00102] A STATUS PDU can comprise a STATUS PDU payload and a tSL-HL control PDU header.

[00103] The tSL-HL control PDU header can comprise a R, PDU-Type, and a wCPT fields.

[00104] The STATUS PDU payload can start from the first bit following the tSL-HL control PDU header. The payload can comprise at least one E field and an ACK-PDU- ID, and can also comprise one or more of (1 ) zero or more sets of an E and a NACK- PDU-ID to indicate missing PDU(s); (2) zero or more sets of an E, and NACK-PDU- Range-ID (Range-Start PDU ID and Range-End PDU ID) to indicate missing

consecutive PDU(s); (3) zero or more sets of an E, a NACK-PDU-ID, a start SO, and an end SO to indicate missing segment(s) of PDU(s); and/or (4) zero or more sets of an E, a NACK-PDU-ID, and a Start SO (wherein an End SO can be omitted as the End SO is end byte of the original PDU) to indicate missing segment(s) of PDU(s).

[00105] The STATUS PDUs for UP tSL-HL PDUs ARQ retransmissions and for CP tSL-HL PDUs ARQ retransmissions can be generated separately. The wCPT field can indicate whether the STATUS PDU is for UP tSL-HL PDUs ARQ retransmission(s) or CP tSL-HL PDUs ARQ retransmission(s).

[00106] Referring to FIG. 8, illustrated is an example of a tSL-HL ARQ ACK/NACK Status PDU for user plane tSL-HL PDU transmission(s), according to various aspects described herein. Referring to FIG. 9, illustrated is another example of a tSL-HL ARQ ACK/NACK Status PDU for user plane tSL-HL PDUs transmission(s), according to various aspects described herein. Referring to FIG. 10, illustrated is an example of a tSL-HL ARQ ACK/NACK Status PDU for tSL-HL PDU(s) transmitted on a Control PRA, according to various aspects described herein.

Sending Request for Retransmission from Receive Entity

[00107] The tSL-HL receive entity can generate and send an ARQ ACK/NACK STATUS PDU based on the expiry of a timer associated with sending the STATUS PDU (e.g., a PeriodicStatusPDUTimer). [00108] The ARQ ACK/NACK STATUS PDU can be sent by the receiving side of a tSL-HL entity to inform the peer tSL-HL entity about the tSL-HL data PDUs that are received successfully, and the tSL-HL data PDUs that are detected to be lost by the receiving side of a tSL-HL entity. The receive entity can expect retransmission of negatively acknowledged PDU and/or PDU segment from the transmit side.

[00109] After sending an ARQ ACK/NACK STATUS PDU, the

PeriodicStatusPDUTimer can be restarted or stopped. The PeriodicStatusPDUTimer can be restarted if (1 ) There is at least one NACK for a PDU or PDU segment included in the current STATUS PDU; or (2) the Receive entity knows that there is at least one PDU for which ACK/NACK is not included in current STATUS PDU (e.g., when grant size is not sufficient to include all NACKed PDU information). Otherwise the

PeriodicStatusPDUTimer can be stopped.

[00110] If the PeriodicStatusPDUTimer is not running and the Receive entity receives a PDU or PDU Segment from transmit entity, the PeriodicStatusPDUTimer can be started.

Retransmission Procedure at Transmit Entity:

ARQ Parameters/Variables:

[00111 ] The transmitting side of each tSL-HL entity can maintain the following state variables for ARQ procedures.

[00112] VT(ACK) - Acknowledgement state variable. This state variable can hold the value of the PDUJD of the next tSL-HL PDU for which a positive acknowledgment is to be received in-sequence and it can serve as the lower edge of the transmitting window. It can be initially set to 0, and can be updated whenever the tSL-HL entity receives a positive acknowledgment for a tSL-HL PDU with PDUJD = VT(ACK).

[00113] The transmitting side of tSL-HL entity can maintain the following counters.

[00114] RETX COUNT - Counter. This counter can count the number of

retransmissions of a tSL-HL PDU. There can be one RETX COUNT counter per PDU that needs to be retransmitted.

[00115] TX_PDU_COUNT - Counter. This counter can count the number of tSL-HL PDUs which have been transmitted and have not been acknowledged so far from the receiving tSL-HL entity. It can enable maintaining a Transmission window in terms of the number of PDUs. It can be initially set to 0, and can be updated (e.g., can decrease) whenever the tSL-HL entity receives a positive acknowledgment for an tSL-HL PDU with PDUJD = VT(ACK). Upon each tSL-HL PDU transmission, it can be incremented by 1 . The maximum value of TX_PDU_COUNT at any time can be MaxSN/2.

Retransmission:

[00116] tSL-HL can support tSL-HL PDU level retransmission. The transmitting side can perform retransmission of a tSL-HL PDU based on either of the following two events: (1 ) Reception of NACK from the receiving side; or (2) Expiry of a timer associated with waiting for an ACK/NACK status associated with that PDU (e.g., the maxWaitForStatusPDUTimer as discussed below).

[00117] maxWaitForStatusPDUTimer can be used to resolve deadlock cases of infinitely waiting for ARQ ACK/NACK STATUS PDU. If this timer is not running, it can be started upon (re)transmission of a tSL-HL PDU. The timer can be restarted upon reception of ARQ ACK/NACK STATUS PDU if any data (including PDUs NACKed in the current STATUS PDU) is still available for transmission or retransmission. The timer can stopped upon reception of ARQ ACK/NACK STATUS PDU if no more data is available for transmission or retransmission.

[00118] The transmitting side of a tSL-HL entity can receive a negative

acknowledgement (notification of reception failure by its peer receiving tSL-HL entity) for a tSL-HL PDU or a portion of a tSL-HL PDU by an ARQ ACK/NACK STATUS PDU from its peer tSL-HL entity.

[00119] When receiving a negative acknowledgement (NACK) for a tSL-HL PDU or a portion of an tSL-HL PDU by a STATUS PDU from its peer tSL-HL entity, the

transmitting side of the tSL-HL entity can, if the PDUJD of the corresponding tSL-HL PDU > VT(ACK), consider the tSL-HL PDU or the portion of the tSL-HL PDU for which a negative acknowledgement was received for retransmission.

[00120] When maxWaitForStatusPDUTimer expires, the transmitting side of the tSL- HL entity can consider tSL-HL PDU with PDUJD = VT(ACK) or the portion of the tSL- HL PDU with PDUJD = VT(ACK) for retransmission.

[00121 ] When a tSL-HL PDU or a portion of a tSL-HL PDU is considered for retransmission, the transmitting side of the tSL-HL entity can: (1 ) If the tSL-HL PDU is considered for retransmission for the first time, set the RETX COUNT associated with the tSL-HL PDU to zero; or (2) otherwise, if it (the tSL-HL PDU or the portion of the tSL- HL PDU that is considered for retransmission) is not pending for retransmission already, or a portion of it is not pending for retransmission already, the tSL-HL entity can ncrement the RETX COUNT and can (a) If RETX_COUNT = maxRetxThreshold, indicate to upper layers that max retransmission has been reached and stop the retransmission or (b) otherwise, proceed with the retransmission.

[00122] When retransmitting a tSL-HL PDU, the transmitting side of a tSL-HL entity can: (1 ) If the tSL-HL PDU can entirely fit within the total size of tSL-HL PDU grant indicated by lower layer at the particular transmission opportunity, deliver the tSL-HL PDU as it is; or (2) Else if the grant is bigger than original tSL-HL PDU, add padding to fit the grant; or (3) Otherwise, (a) Segment the tSL-HL PDU, form a new tSL-HL PDU segment which can fit within the total size of tSL-HL PDU grant indicated by lower layer at the particular transmission opportunity and deliver the new tSL-HL PDU segment to lower layer, and (b) Assign a new Resegment SN to the original PDU (to be

retransmitted by segmenting) and maintain a mapping between Resegment SN to the PDUJD of the original PDU (The new tSL-HL PDU segment can be identified by Resegment SN, Start offset and (optional) End offset values).

[00123] When retransmitting a portion of a tSL-HL PDU, the transmitting side of a tSL- HL entity can segment the portion of the tSL-HL PDU as appropriate, and can form a new tSL-HL PDU segment which can fit within the total size of tSL-HL PDU grant indicated by lower layer at the particular transmission opportunity, and can deliver the new tSL-HL PDU segment to lower layer.

[00124] When forming a new tSL-HL PDU segment, the transmitting side of a tSL-HL entity can: (1 ) Map the Data field and the header field (excluding padding) of the original tSL-HL PDU to the Data field of the new tSL-HL PDU segment in case of retransmission of user plane data (the segment offset can be specified based on assuming the data field and the header field (excluding padding) of the original tSL-HL PDU as a new data); (2) Map the Data field and the Header field (excluding padding, BSR and PHR subheaders) of the original tSL-HL PDU to the Data field of the new tSL-HL PDU segment in case of retransmission of control plane data (the segment offset can be specified based on assuming the data field and the header field (excluding padding, BSR and PHR subheaders) of the original tSL-HL PDU as a new data); and/or (3) Set the header of the new tSL-HL PDU segment.

[00125] Examples herein can include subject matter such as a method, means for performing acts or blocks of the method, at least one machine-readable medium including executable instructions that, when performed by a machine (e.g., a processor with memory, an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like) cause the machine to perform acts of the method or of an apparatus or system for concurrent communication using multiple communication technologies according to embodiments and examples described.

[00126] Example 1 is an apparatus configured to be employed within a User

Equipment (UE), comprising: a memory; and one or more processors configured to: receive one or more tSL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL))-HL (Higher Layer) PDUs (Protocol Data Units) from a tSL-PHY (Physical layer), wherein each tSL-HL PDU comprises a header and a data field; assign each of the one or more tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU; sort the one or more tSL-HL PDUs based on the associated PDU IDs assigned to each of the one or more tSL-HL PDUs; and generate an ARQ (Automatic Repeat Request) ACK/NACK (Acknowledgement/Negative ACK) STATUS PDU that explicitly indicates a next unreported PDU ID for an unreceived tSL-HL PDU, and indicates an ACK or a NACK for each PDU ID of a set of reported PDU IDs less than the next unreported PDU ID, wherein the set of reported PDU IDs comprises one or more of the associated PDU IDs, and wherein the ARQ ACK/NACK STATUS PDU implicitly indicates the ACK for each PDU ID of the one or more of the associated PDU IDs.

[00127] Example 2 comprises the subject matter of any variation of any of example(s)

1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit), and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU.

[00128] Example 3 comprises the subject matter of any variation of any of example(s)

2, wherein the first PDU ID comprises a segment number equal to zero.

[00129] Example 4 comprises the subject matter of any variation of any of example(s) 1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit) segment of a tSL-HL SDU, and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number of the tSL-HL SDU segment.

[00130] Example 5 comprises the subject matter of any variation of any of example(s) 1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL PDU resegment, and wherein the one or more processors are further confiaured to assian the first tSL-HL PDU a first PDU ID that comprises a Resegment SN of the tSL-HL PDU resegment and a start SO (segment offset) of the tSL-HL PDU resegment.

[00131 ] Example 6 comprises the subject matter of any variation of any of example(s) 5, wherein the first PDU ID comprises an end SO of the tSL-HL PDU resegment.

[00132] Example 7 comprises the subject matter of any variation of any of example(s) 5, wherein the tSL-HL PDU resegment is a final resegment, and wherein the first PDU ID consists of the Resegment SN of the tSL-HL PDU resegment and the start SO of the tSL-HL PDU resegment.

[00133] Example 8 comprises the subject matter of any variation of any of example(s) 1 -7, wherein the ARQ ACK/NACK STATUS PDU explicitly indicates at least one NACK for at least one PDU ID distinct from the PDU IDs associated with the one or more tSL- HL PDUs received from the tSL-HL PHY.

[00134] Example 9 comprises the subject matter of any variation of any of example(s) 8, wherein the at least one NACK comprises a plurality of NACKs, and wherein the ARQ ACK/NACK STATUS PDU explicitly indicates the plurality of NACKs for a range of continuous PDU IDs.

[00135] Example 10 comprises the subject matter of any variation of any of example(s) 1 -7, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a CP (control plane) tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a control PRA (physical resource assignment).

[00136] Example 1 1 comprises the subject matter of any variation of any of example(s) 1 -7, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a UP (user plane) tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a set of UP PRAs (physical resource assignments).

[00137] Example 12 comprises the subject matter of any variation of any of example(s) 1 -9, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a CP (control plane) tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a control PRA (physical resource assignment).

[00138] Example 13 comprises the subject matter of any variation of any of example(s) 1 -9 or 12, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a UP (user plane) tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a set of UP PRAs (physical resource assignments).

[00139] Example 14 is an apparatus configured to be employed within a User Equipment (UE), comprising: a memory; and one or more processors configured to: store a set of tSL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL))-HL (Higher Layer) PDUs (Protocol Data Units) in a retransmission buffer, wherein each tSL- HL PDU of the set of tSL-HL PDUs comprises a header and a data field; assign a unique PDU ID (identifier) to each of tSL-HL PDU of the set of tSL-HL PDUs based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU; and determine, for each tSL-HL PDU of the set of tSL-HL PDUs, whether to retransmit that tSL-HL PDU, based at least in part on a timer for that tSL-HL PDU or on an ARQ (Automatic Repeat Request) ACK/NACK

(Acknowledgement/ Negative ACK) STATUS PDU received from a tSL-PHY (physical layer).

[00140] Example 15 comprises the subject matter of any variation of any of example(s) 14, wherein the ARQ ACK/NACK STATUS PDU indicates an ACK for a first PDU ID associated with a first tSL-HL PDU of the set of tSL-HL PDUs, and wherein the one or more processors are further configured to determine not to retransmit at least the first tSL-HL PDU of the set of tSL-HL PDUs based on the ACK associated with the first tSL-HL PDU.

[00141 ] Example 16 comprises the subject matter of any variation of any of example(s) 15, wherein the ARQ ACK/NACK STATUS PDU indicates at least one NACK for at least one PDU ID associated with at least one tSL-HL PDU of the set of tSL-HL PDUs, and wherein the one or more processors are configured to determine to retransmit the at least one tSL-HL PDU.

[00142] Example 17 comprises the subject matter of any variation of any of example(s) 16, wherein the at least one NACK comprises a plurality of NACKs, and wherein the ARQ ACK/NACK STATUS PDU indicates the plurality of NACKs via a continuous range of PDU IDs.

[00143] Example 18 comprises the subject matter of any variation of any of example(s) 14, wherein the one or more processors are further configured to determine to retransmit a first tSL-HL PDU of the set of tSL-HL PDUs based on an expiration of the timer for the first tSL-HL PDU.

[00144] Example 19 comprises the subject matter of any variation of any of example(s) 14-18, wherein the one or more processors are further configured to:

determine to retransmit a first tSL-HL PDU of the set of tSL-HL PDUs; and receive, from the tSL-PHY, a PRA (physical resource assignment) and an allocated size for a tSL-HL PDU retransmission.

[00145] Example 20 comprises the subject matter of any variation of any of exarriDle(s) 19. wherein the allocated size is less than a size for retransmission of the first tSL-HL PDU, and wherein the one or more processors are further configured to: resegment the first tSL-HL PDU into a plurality of tSL-HL resegments; assign a common resegment SN to each tSL-HL resegment of the plurality; and associate the common resegment SN with the PDU ID.

[00146] Example 21 comprises the subject matter of any variation of any of example(s) 20, wherein the one or more processors are further configured to: generate a new tSL-HL PDU comprising a data field and a header, wherein the data field comprises a first tSL-HL resegment of the plurality of tSL-HL resegments, and wherein the header indicates the common resegment SN and a start SO (segment offset) of the first tSL-HL resegment.

[00147] Example 22 comprises the subject matter of any variation of any of example(s) 21 , wherein the header indicates an end SO of the first tSL-HL resegment.

[00148] Example 23 comprises the subject matter of any variation of any of example(s) 14-18, wherein the ARQ ACK/NACK STATUS PDU indicates an ACK or a NACK associated with a resegment SN, and wherein the one or more processors are further configured to determine a tSL-HL PDU associated with the resegment SN based on a stored mapping between the resegment SN and the PDU ID of the tSL-HL PDU.

[00149] Example 24 comprises the subject matter of any variation of any of example(s) 14-18, wherein the retransmission buffer is a CP (control plane)

retransmission buffer, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a CP tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a CP.

[00150] Example 25 comprises the subject matter of any variation of any of example(s) 14-18, wherein the retransmission buffer is a UP (user plane)

retransmission buffer, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a UP tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a UP.

[00151 ] Example 26 is a machine readable medium comprising instructions that, when executed, cause a UE to: receive a set of tSL-HL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL) Higher Layer (HL)) PDUs (protocol data units) from a tSL-PHY (physical layer), wherein each tSL-HL PDU of the set of tSL-HL PDUs comprises a header and a data field; assign each tSL-HL PDU of the set of tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU, wherein the SN associated with the first data field element is indicated via the header of that tSL-HL PDU; sort the one or more tSL-HL PDUs based on the associated PDU IDs assigned to each of the one or more tSL; determine whether one or more additional tSL- HL PDUs are missing based on the associated PDU IDs; and generate an ARQ

(Automatic Repeat Request) ACK/NACK (Acknowledgement/Negative ACK) STATUS PDU that explicitly indicates a next unreported PDU ID for an unreceived tSL-HL PDU, and indicates an ACK or a NACK for each PDU ID of a set of reported PDU IDs less than the next unreported PDU ID, wherein the set of reported PDU IDs comprises one or more of the associated PDU IDs, and wherein the ARQ ACK/NACK STATUS PDU implicitly indicates the ACK for each PDU ID of the one or more of the associated PDU IDs.

[00152] Example 27 comprises the subject matter of any variation of any of example(s) 26, wherein the instructions, when executed, cause the UE to determine that the one or more additional tSL-HL PDUs are missing, and wherein the ARQ

ACK/NACK STATUS PDU explicitly indicates one or more NACKs for the one or more additional tSL-HL PDUs.

[00153] Example 28 comprises the subject matter of any variation of any of example(s) 26-27, wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit), and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number equal to zero.

[00154] Example 29 comprises the subject matter of any variation of any of example(s) 26-27, wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit) segment of a tSL-HL SDU, and wherein the one or more processors are further configured to assign the first tSL- HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number of the tSL-HL SDU segment.

[00155] Example 30 is an apparatus configured to be employed within a User

Equipment (UE), comprising: means for receiving a set of tSL-HL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL) Higher Layer (HL)) PDUs (protocol data units) from a tSL-PHY (physical layer), wherein each tSL-HL PDU of the set of tSL-HL PDUs comprises a header and a data field; means for assigning each tSL-HL PDU of the set of tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN

(Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU, wherein the SN associated with the first data field element is indicated via the header of that tSL-HL PDU; means for sorting the one or more tSL-HL PDUs based on the associated PDU IDs assigned to each of the one or more tSL; means for determining whether one or more additional tSL-HL PDUs are missing based on the associated PDU IDs; and means for generating an ARQ (Automatic Repeat Request) ACK/NACK (Acknowledgement/Negative ACK) STATUS PDU that explicitly indicates a next unreported PDU ID for an unreceived tSL-HL PDU, and indicates an ACK or a NACK for each PDU ID of a set of reported PDU IDs less than the next unreported PDU ID, wherein the set of reported PDU IDs comprises one or more of the associated PDU IDs, and wherein the ARQ ACK/NACK STATUS PDU implicitly indicates the ACK for each PDU ID of the one or more of the associated PDU IDs.

[00156] Example 31 comprises the subject matter of any variation of any of example(s) 30, wherein the means for determining are configured to determine that the one or more additional tSL-HL PDUs are missing, and wherein the ARQ ACK/NACK STATUS PDU explicitly indicates one or more NACKs for the one or more additional tSL-HL PDUs.

[00157] Example 32 comprises the subject matter of any variation of any of example(s) 30-31 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit), and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number equal to zero.

[00158] Example 33 comprises the subject matter of any variation of any of example(s) 30-31 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit) segment of a tSL-HL SDU, and wherein the one or more processors are further configured to assign the first tSL- HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number of the tSL-HL SDU segment.

[00159] The above description of illustrated embodiments of the subject disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosed embodiments to the precise forms disclosed. While specific embodiments and examples are described herein for illustrative purposes, various modifications are possible that are considered within the scope of such embodiments and examples, as those skilled in the relevant art can recognize.

[00160] In this regard, while the disclosed subject matter has been described in connection with various embodiments and corresponding Figures, where applicable, it is to be understood that other similar embodiments can be used or modifications and additions can be made to the described embodiments for performing the same, similar, alternative, or substitute function of the disclosed subject matter without deviating therefrom. Therefore, the disclosed subject matter should not be limited to any single embodiment described herein, but rather should be construed in breadth and scope in accordance with the appended claims below.

[00161 ] In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a "means") used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations. In addition, while a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.

Claims

CLAIMS What is claimed is:

1 . An apparatus configured to be employed within a User Equipment (UE), comprising:

a memory; and

one or more processors configured to:

receive one or more tSL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL))-HL (Higher Layer) PDUs (Protocol Data Units) from a tSL-PHY (Physical layer), wherein each tSL-HL PDU comprises a header and a data field; assign each of the one or more tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU;

sort the one or more tSL-HL PDUs based on the associated PDU IDs assigned to each of the one or more tSL-HL PDUs; and

generate an ARQ (Automatic Repeat Request) ACK/NACK (Acknowledgement/Negative ACK) STATUS PDU that explicitly indicates a next unreported PDU ID for an unreceived tSL-HL PDU, and indicates an ACK or a NACK for each PDU ID of a set of reported PDU IDs less than the next unreported PDU ID, wherein the set of reported PDU IDs comprises one or more of the associated PDU IDs, and wherein the ARQ ACK/NACK STATUS PDU implicitly indicates the ACK for each PDU ID of the one or more of the associated PDU IDs.

2. The apparatus of claim 1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit), and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU.

3. The apparatus of claim 2, wherein the first PDU ID comprises a segment number equal to zero.

4. The apparatus of claim 1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit) segment of a tSL-HL SDU. and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number of the tSL-HL SDU segment.

5. The apparatus of claim 1 , wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL PDU resegment, and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a Resegment SN of the tSL-HL PDU resegment and a start SO (segment offset) of the tSL-HL PDU resegment.

6. The apparatus of claim 5, wherein the first PDU ID comprises an end SO of the tSL-HL PDU resegment.

7. The apparatus of claim 5, wherein the tSL-HL PDU resegment is a final resegment, and wherein the first PDU ID consists of the Resegment SN of the tSL-HL PDU resegment and the start SO of the tSL-HL PDU resegment.

8. The apparatus of any of claims 1 -7, wherein the ARQ ACK/NACK STATUS PDU explicitly indicates at least one NACK for at least one PDU ID distinct from the PDU IDs associated with the one or more tSL-HL PDUs received from the tSL-HL PHY.

9. The apparatus of claim 8, wherein the at least one NACK comprises a plurality of NACKs, and wherein the ARQ ACK/NACK STATUS PDU explicitly indicates the plurality of NACKs for a range of continuous PDU IDs.

10. The apparatus of any of claims 1 -7, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a CP (control plane) tSL-HL PDU, and wherein the ARQ

ACK/NACK STATUS PDU indicates that it is associated with a control PRA (physical resource assignment).

1 1 . The apparatus of any of claims 1 -7, wherein each tSL-HL PDU of the one or more tSL-HL PDUs is a UP (user plane) tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a set of UP PRAs (physical resource assignments).

12. An apparatus configured to be employed within a User Equipment (UE), comprising:

a memory; and

one or more processors configured to:

store a set of tSL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL))-HL (Higher Layer) PDUs (Protocol Data Units) in a retransmission buffer, wherein each tSL-HL PDU of the set of tSL-HL PDUs comprises a header and a data field;

assign a unique PDU ID (identifier) to each of tSL-HL PDU of the set of tSL-HL PDUs based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU; and

determine, for each tSL-HL PDU of the set of tSL-HL PDUs, whether to retransmit that tSL-HL PDU, based at least in part on a timer for that tSL-HL PDU or on an ARQ (Automatic Repeat Request) ACK/NACK (Acknowledgement/ Negative ACK) STATUS PDU received from a tSL-PHY (physical layer).

13. The apparatus of claim 12, wherein the ARQ ACK/NACK STATUS PDU indicates an ACK for a first PDU ID associated with a first tSL-HL PDU of the set of tSL-HL PDUs, and wherein the one or more processors are further configured to determine not to retransmit at least the first tSL-HL PDU of the set of tSL-HL PDUs based on the ACK associated with the first tSL-HL PDU.

14. The apparatus of claim 13, wherein the ARQ ACK/NACK STATUS PDU indicates at least one NACK for at least one PDU ID associated with at least one tSL-HL PDU of the set of tSL-HL PDUs, and wherein the one or more processors are configured to determine to retransmit the at least one tSL-HL PDU.

15. The apparatus of claim 14, wherein the at least one NACK comprises a plurality of NACKs, and wherein the ARQ ACK/NACK STATUS PDU indicates the plurality of NACKs via a continuous range of PDU IDs.

16. The apparatus of claim 12, wherein the one or more processors are further configured to determine to retransmit a first tSL-HL PDU of the set of tSL-HL PDUs based on an expiration of the timer for the first tSL-HL PDU.

17. The apparatus of any of claims 12-16, wherein the one or more processors are further configured to:

18. The apparatus of claim 17, wherein the allocated size is less than a size for retransmission of the first tSL-HL PDU, and wherein the one or more processors are further configured to:

resegment the first tSL-HL PDU into a plurality of tSL-HL resegments;

assign a common resegment SN to each tSL-HL resegment of the plurality; and associate the common resegment SN with the PDU ID.

19. The apparatus of claim 18, wherein the one or more processors are further configured to:

generate a new tSL-HL PDU comprising a data field and a header, wherein the data field comprises a first tSL-HL resegment of the plurality of tSL-HL resegments, and wherein the header indicates the common resegment SN and a start SO (segment offset) of the first tSL-HL resegment.

20. The apparatus of claim 19, wherein the header indicates an end SO of the first tSL-HL resegment.

21 . The apparatus of any of claims 12-16, wherein the ARQ ACK/NACK STATUS PDU indicates an ACK or a NACK associated with a resegment SN, and wherein the one or more processors are further configured to determine a tSL-HL PDU associated with the resegment SN based on a stored mapping between the resegment SN and the PDU ID of the tSL-HL PDU.

22. The apparatus of any of claims 12-16, wherein the retransmission buffer is a CP (control plane) retransmission buffer, wherein each tSL-HL PDU of the one or more tSL- HL PDUs is a CP tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a CP.

23. The apparatus of any of claims 12-16, wherein the retransmission buffer is a UP (user plane) retransmission buffer, wherein each tSL-HL PDU of the one or more tSL- HL PDUs is a UP tSL-HL PDU, and wherein the ARQ ACK/NACK STATUS PDU indicates that it is associated with a UP.

24. A machine readable medium comprising instructions that, when executed, cause a UE to:

receive a set of tSL-HL (Fifth Generation (5G) New Radio (NR) Things (t) Sidelink (SL) Higher Layer (HL)) PDUs (protocol data units) from a tSL-PHY (physical layer), wherein each tSL-HL PDU of the set of tSL-HL PDUs comprises a header and a data field;

assign each tSL-HL PDU of the set of tSL-HL PDUs an associated PDU ID (identifier) based at least in part on a SN (Sequence Number) associated with a first data field element of the data field of that tSL-HL PDU, wherein the SN associated with the first data field element is indicated via the header of that tSL-HL PDU;

sort the one or more tSL-HL PDUs based on the associated PDU IDs assigned to each of the one or more tSL;

determine whether one or more additional tSL-HL PDUs are missing based on the associated PDU IDs; and

generate an ARQ (Automatic Repeat Request) ACK/NACK

(Acknowledgement/Negative ACK) STATUS PDU that explicitly indicates a next unreported PDU ID for an unreceived tSL-HL PDU, and indicates an ACK or a NACK for each PDU ID of a set of reported PDU IDs less than the next unreported PDU ID, wherein the set of reported PDU IDs comprises one or more of the associated PDU IDs, and wherein the ARQ ACK/NACK STATUS PDU implicitly indicates the ACK for each PDU ID of the one or more of the associated PDU IDs.

25. The machine readable medium of claim 24, wherein the instructions, when executed, cause the UE to determine that the one or more additional tSL-HL PDUs are missing, and wherein the ARQ ACK/NACK STATUS PDU explicitly indicates one or more NACKs for the one or more additional tSL-HL PDUs.

26. The machine readable medium of any of claims 24-25, wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU

(service data unit), and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number equal to zero.

27. The machine readable medium of any of claims 24-25, wherein the first data field element of a first tSL-HL PDU of the one or more tSL-HL PDUs is a tSL-HL SDU (service data unit) segment of a tSL-HL SDU, and wherein the one or more processors are further configured to assign the first tSL-HL PDU a first PDU ID that comprises a SDU SN of the tSL-HL SDU and a segment number of the tSL-HL SDU segment.