WO2021229362A1

WO2021229362A1 - Transmitting a sidelink buffer status report for an empty buffer

Info

Publication number: WO2021229362A1
Application number: PCT/IB2021/053739
Authority: WO
Inventors: Joachim Löhr; Prateek Basu Mallick; Karthikeyan Ganesan; Ravi Kuchibhotla
Original assignee: Lenovo (Singapore) Pte. Ltd.
Priority date: 2020-05-11
Filing date: 2021-05-04
Publication date: 2021-11-18

Abstract

Apparatuses, methods, and systems are disclosed for transmitting a sidelink buffer status report for an empty buffer. One method (600) includes determining (602), at a user equipment, that a sidelink transmission buffer is empty for a destination. The method (600) includes triggering (604) a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. The method (600) includes transmitting (606) the sidelink buffer status report to a network unit.

Description

TRANSMITTING A SIDELINK BUFFER STATUS REPORT FOR AN EMPTY BUFFER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to United States Patent Application Serial Number 63/022,951 entitled “APPARATUSES, METHODS, AND SYSTEMS FOR A BSR/SR PROCEDURE FOR A HARQ-BASED RLF MECHANISM” and filed on May 11, 2020 for Joachim Loehr, which is incorporated herein by reference in its entirety.

FIELD

[0002] The subject matter disclosed herein relates generally to wireless communications and more particularly relates to transmitting a sidelink buffer status report for an empty buffer.

BACKGROUND

[0003] In certain wireless communications networks, a sidelink buffer status report may be made. Generally, a sidelink buffer status report is for a buffer that has data.

BRIEF SUMMARY

[0004] Methods for transmitting a sidelink buffer status report for an empty buffer are disclosed. Apparatuses and systems also perform the functions of the methods. One embodiment of a method includes determining, at a user equipment, that a sidelink transmission buffer is empty for a destination. In some embodiments, the method includes triggering a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. In certain embodiments, the method includes transmitting the sidelink buffer status report to a network unit.

[0005] One apparatus for transmitting a sidelink buffer status report for an empty buffer includes a user equipment. In some embodiments, the apparatus includes a processor that: determines that a sidelink transmission buffer is empty for a destination; and triggers a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. In various embodiments, the apparatus includes a transmitter that transmits the sidelink buffer status report to a network unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] A more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only some embodiments and are not therefore to be considered to be limiting of scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: [0007] Figure 1 is a schematic block diagram illustrating one embodiment of a wireless communication system for transmitting a sidelink buffer status report for an empty buffer;

[0008] Figure 2 is a schematic block diagram illustrating one embodiment of an apparatus that may be used for transmitting a sidelink buffer status report for an empty buffer;

[0009] Figure 3 is a schematic block diagram illustrating one embodiment of an apparatus that may be used for transmitting a sidelink buffer status report for an empty buffer;

[0010] Figure 4 is a schematic block diagram illustrating one embodiment of a system for transmitting a sidelink buffer status report for an empty buffer;

[0011] Figure 5 is a schematic block diagram illustrating another embodiment of a system for transmitting a sidelink buffer status report for an empty buffer; and

[0012] Figure 6 is a flow chart diagram illustrating one embodiment of a method for transmitting a sidelink buffer status report for an empty buffer.

DETAILED DESCRIPTION

[0013] As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, apparatus, method, or program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments may take the form of a program product embodied in one or more computer readable storage devices storing machine readable code, computer readable code, and/or program code, referred hereafter as code. The storage devices may be tangible, non-transitory, and/or non-transmission. The storage devices may not embody signals. In a certain embodiment, the storage devices only employ signals for accessing code.

[0014] Certain of the functional units described in this specification may be labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom very-large-scale integration (“VLSI”) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0015] Modules may also be implemented in code and/or software for execution by various types of processors. An identified module of code may, for instance, include one or more physical or logical blocks of executable code which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may include disparate instructions stored in different locations which, when joined logically together, include the module and achieve the stated purpose for the module.

[0016] Indeed, a module of code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different computer readable storage devices. Where a module or portions of a module are implemented in software, the software portions are stored on one or more computer readable storage devices.

[0017] Any combination of one or more computer readable medium may be utilized. The computer readable medium may be a computer readable storage medium. The computer readable storage medium may be a storage device storing the code. The storage device may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

[0018] More specific examples (anon-exhaustive list) of the storage device would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (“RAM”), a read-only memory (“ROM”), an erasable programmable read-only memory (“EPROM” or Flash memory), a portable compact disc read only memory (“CD-ROM”), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0019] Code for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object oriented programming language such as Python, Ruby, lava, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the "C" programming language, or the like, and/or machine languages such as assembly languages. The code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (“LAN”) or a wide area network (“WAN”), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0020] Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.

[0021] Furthermore, the described features, structures, or characteristics of the embodiments may be combined in any suitable manner. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of an embodiment.

[0022] Aspects of the embodiments are described below with reference to schematic flowchart diagrams and/or schematic block diagrams of methods, apparatuses, systems, and program products according to embodiments. It will be understood that each block of the schematic flowchart diagrams and/or schematic block diagrams, and combinations of blocks in the schematic flowchart diagrams and/or schematic block diagrams, can be implemented by code. The code may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

[0023] The code may also be stored in a storage device that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the storage device produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

[0024] The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

[0025] The schematic flowchart diagrams and/or schematic block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of apparatuses, systems, methods and program products according to various embodiments. In this regard, each block in the schematic flowchart diagrams and/or schematic block diagrams may represent a module, segment, or portion of code, which includes one or more executable instructions of the code for implementing the specified logical function(s).

[0026] It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more blocks, or portions thereof, of the illustrated Figures.

[0027] Although various arrow types and line types may be employed in the flowchart and/or block diagrams, they are understood not to limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and/or flowchart diagrams, and combinations of blocks in the block diagrams and/or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and code.

[0028] The description of elements in each figure may refer to elements of proceeding figures. Like numbers refer to like elements in all figures, including alternate embodiments of like elements.

[0029] Figure 1 depicts an embodiment of a wireless communication system 100 for transmitting a sidelink buffer status report for an empty buffer. In one embodiment, the wireless communication system 100 includes remote units 102 and network units 104. Even though a specific number of remote units 102 and network units 104 are depicted in Figure 1, one of skill in the art will recognize that any number of remote units 102 and network units 104 may be included in the wireless communication system 100.

[0030] In one embodiment, the remote units 102 may include computing devices, such as desktop computers, laptop computers, personal digital assistants (“PDAs”), tablet computers, smart phones, smart televisions (e.g., televisions connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e g., routers, switches, modems), aerial vehicles, drones, or the like. In some embodiments, the remote units 102 include wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, the remote units 102 may be referred to as subscriber units, mobiles, mobile stations, users, terminals, mobile terminals, fixed terminals, subscriber stations, UE, user terminals, a device, or by other terminology used in the art. The remote units 102 may communicate directly with one or more of the network units 104 via UL communication signals. In certain embodiments, the remote units 102 may communicate directly with other remote units 102 via sidelink communication.

[0031] The network units 104 may be distributed over a geographic region. In certain embodiments, a network unit 104 may also be referred to and/or may include one or more of an access point, an access terminal, a base, a base station, a location server, a core network (“CN”), a radio network entity, a Node-B, an evolved node-B (“eNB”), a 5G node-B (“gNB”), a Home Node-B, a relay node, a device, a core network, an aerial server, a radio access node, an access point (“AP”), new radio (“NR”), a network entity, an access and mobility management function (“AMF”), a unified data management (“UDM”), a unified data repository (“UDR”), a UDM/UDR, a policy control function (“PCF”), a radio access network (“RAN”), a network slice selection function (“NSSF”), an operations, administration, and management (“OAM”), a session management function (“SMF”), a user plane function (“UPF”), an application function, an authentication server function (“AUSF”), security anchor functionality (“SEAF”), trusted non- 3 GPP gateway function (“TNGF”), or by any other terminology used in the art. The network units 104 are generally part of a radio access network that includes one or more controllers communicably coupled to one or more corresponding network units 104. The radio access network is generally communicably coupled to one or more core networks, which may be coupled to other networks, like the Internet and public switched telephone networks, among other networks. These and other elements of radio access and core networks are not illustrated but are well known generally by those having ordinary skill in the art. [0032] In one implementation, the wireless communication system 100 is compliant with NR protocols standardized in third generation partnership project (“3GPP”), wherein the network unit 104 transmits using an OFDM modulation scheme on the downlink (“DL”) and the remote units 102 transmit on the uplink (“UL”) using a single-carrier frequency division multiple access (“SC-FDMA”) scheme or an orthogonal frequency division multiplexing (“OFDM”) scheme. More generally, however, the wireless communication system 100 may implement some other open or proprietary communication protocol, for example, WiMAX, institute of electrical and electronics engineers (“IEEE”) 802.11 variants, global system for mobile communications (“GSM”), general packet radio service (“GPRS”), universal mobile telecommunications system (“UMTS”), long term evolution (“LTE”) variants, code division multiple access 2000 (“CDMA2000”), Bluetooth®, ZigBee, Sigfoxx, among other protocols. The present disclosure is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol.

[0033] The network units 104 may serve a number of remote units 102 within a serving area, for example, a cell or a cell sector via a wireless communication link. The network units 104 transmit DL communication signals to serve the remote units 102 in the time, frequency, and/or spatial domain.

[0034] In various embodiments, a remote unit 102 may determine that a sidelink transmission buffer is empty for a destination. In some embodiments, the remote unit 102 may trigger a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. In certain embodiments, the remote unit 102 may transmit the sidelink buffer status report to a network unit. Accordingly, the remote unit 102 may be used for transmitting a sidelink buffer status report for an empty buffer.

[0035] Figure 2 depicts one embodiment of an apparatus 200 that may be used for transmitting a sidelink buffer status report for an empty buffer. The apparatus 200 includes one embodiment of the remote unit 102. Furthermore, the remote unit 102 may include a processor 202, a memory 204, an input device 206, a display 208, a transmitter 210, and a receiver 212. In some embodiments, the input device 206 and the display 208 are combined into a single device, such as a touchscreen. In certain embodiments, the remote unit 102 may not include any input device 206 and/or display 208. In various embodiments, the remote unit 102 may include one or more of the processor 202, the memory 204, the transmitter 210, and the receiver 212, and may not include the input device 206 and/or the display 208.

[0036] The processor 202, in one embodiment, may include any known controller capable of executing computer-readable instructions and/or capable of performing logical operations. For example, the processor 202 may be a microcontroller, a microprocessor, a central processing unit (“CPU”), a graphics processing unit (“GPU”), an auxiliary processing unit, a field programmable gate array (“FPGA”), or similar programmable controller. In some embodiments, the processor 202 executes instructions stored in the memory 204 to perform the methods and routines described herein. The processor 202 is communicatively coupled to the memory 204, the input device 206, the display 208, the transmitter 210, and the receiver 212.

[0037] The memory 204, in one embodiment, is a computer readable storage medium. In some embodiments, the memory 204 includes volatile computer storage media. For example, the memory 204 may include a RAM, including dynamic RAM (“DRAM”), synchronous dynamic RAM (“SDRAM”), and/or static RAM (“SRAM”). In some embodiments, the memory 204 includes non-volatile computer storage media. For example, the memory 204 may include a hard disk drive, a flash memory, or any other suitable non-volatile computer storage device. In some embodiments, the memory 204 includes both volatile and non-volatile computer storage media. In some embodiments, the memory 204 also stores program code and related data, such as an operating system or other controller algorithms operating on the remote unit 102.

[0038] The input device 206, in one embodiment, may include any known computer input device including a touch panel, a button, a keyboard, a stylus, a microphone, or the like. In some embodiments, the input device 206 may be integrated with the display 208, for example, as a touchscreen or similar touch-sensitive display. In some embodiments, the input device 206 includes a touchscreen such that text may be input using a virtual keyboard displayed on the touchscreen and/or by handwriting on the touchscreen. In some embodiments, the input device 206 includes two or more different devices, such as a keyboard and a touch panel.

[0039] The display 208, in one embodiment, may include any known electronically controllable display or display device. The display 208 may be designed to output visual, audible, and/or haptic signals. In some embodiments, the display 208 includes an electronic display capable of outputting visual data to a user. For example, the display 208 may include, but is not limited to, a liquid crystal display (“LCD”), a light emitting diode (“LED”) display, an organic light emitting diode (“OLED”) display, a projector, or similar display device capable of outputting images, text, or the like to a user. As another, non-limiting, example, the display 208 may include a wearable display such as a smart watch, smart glasses, a heads-up display, or the like. Further, the display 208 may be a component of a smart phone, a personal digital assistant, a television, a table computer, a notebook (laptop) computer, a personal computer, a vehicle dashboard, or the like. [0040] In certain embodiments, the display 208 includes one or more speakers for producing sound. For example, the display 208 may produce an audible alert or notification (e.g., a beep or chime). In some embodiments, the display 208 includes one or more haptic devices for producing vibrations, motion, or other haptic feedback. In some embodiments, all or portions of the display 208 may be integrated with the input device 206. For example, the input device 206 and display 208 may form a touchscreen or similar touch-sensitive display. In other embodiments, the display 208 may be located near the input device 206.

[0041] In some embodiments, the processor 202: determines that a sidelink transmission buffer is empty for a destination; and triggers a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. In various embodiments, the transmitter 210 transmits the sidelink buffer status report to a network unit.

[0042] Although only one transmitter 210 and one receiver 212 are illustrated, the remote unit 102 may have any suitable number of transmitters 210 and receivers 212. The transmitter 210 and the receiver 212 may be any suitable type of transmitters and receivers. In one embodiment, the transmitter 210 and the receiver 212 may be part of a transceiver.

[0043] Figure 3 depicts one embodiment of an apparatus 300 that may be used for transmitting a sidelink buffer status report for an empty buffer. The apparatus 300 includes one embodiment of the network unit 104. Furthermore, the network unit 104 may include a processor 302, a memory 304, an input device 306, a display 308, a transmitter 310, and a receiver 312. As may be appreciated, the processor 302, the memory 304, the input device 306, the display 308, the transmitter 310, and the receiver 312 may be substantially similar to the processor 202, the memory 204, the input device 206, the display 208, the transmitter 210, and the receiver 212 of the remote unit 102, respectively.

[0044] In some embodiments, such as using a user equipment (“UE”) to network (“Uu”) interface (e.g., NR, LTE), radio link monitoring (“RLM”) may be performed. If a RLM procedure indicates that the UE is out of sync with respect to DL (e.g., a hypothetical block error rate (“BLER”) target for a physical downlink control channel (“PDCCH”) exceeds a threshold such as 10%) for a time duration, the UE may declare a radio link failure (“RLF”) and may initiate a recovery procedure. The recovery on Uu may include trying to re-establish a radio resource control (“RRC”) connection on a different cell. In direct communication between UEs (“PC5”), it may be meaningful to perform radio link monitoring to determine if a radio link between two UEs is sufficiently good and, if not, the UEs may not unnecessarily attempt transmission to the other UE. In certain embodiments, after having declared RLF, UEs may immediately or later clear a context for another UE and free memory space.

[0045] In various embodiments, a RLF mechanism at a transmit (“TX”) UE may be based on hybrid automatic repeat request UHARQ ) feedback. In certain embodiments, a TX UE counts a number of consecutive discontinuous transmissions (“DTX”) received from a receive (“RX”) UE in response to a physical sidelink shared channel (“PSSCH”) transmission. In some embodiments, RLF may be declared and subsequent actions may be carried out if a counter exceeds a predefined threshold (e.g., x number of consecutive DTX received from the RX UE for a specific link and/or connection).

[0046] In certain embodiments, if a TX UE is configured for a mode 1 sidelink (“SL”) resource allocation mode and there is an absence of higher layer SL data at the TX UE, it may be unknown how the TX UE requests SL resources from a network (“NW”) entity (e.g., gNB) to make PSSCH transmissions (e.g., with special content such as padding which may trigger the transmission of a HARQ feedback required for a HARQ-based RLF mechanism).

[0047] In some embodiments, UE behavior may be defined if a SL grant from aNW entity (e.g., gNB) is provided for a transmission buffer is empty for a destination for which RLF is enabled. In such embodiments, a logical channel prioritization (“LCP”) procedure may enable a TX UE to generate a transport block (“TB”) (e.g., with padding only or with other special content) for a destination, even though a corresponding transmission buffer is empty (e.g., destination selection process may account for destinations having no data for transmission available).

[0048] In a first embodiment, a SL buffer status report (“BSR”) trigger condition (e.g., new SL BSR trigger condition) may be used to inform a NW entity (e.g., gNB) about an empty transmission buffer for a destination. In such an embodiment, aUE (e.g., TX UE) may start anew SL BSR related timer in response to the transmission buffer becoming empty for an intended destination. In certain embodiments, a RX UE may support multiple destinations with reference to a TX UE. As used herein, the term “empty transmission buffer” may refer to embodiments in which none of the logical channels that belong to logical channel groups (“LCGs”) belonging to the same destination contain any available SL data (e.g., there is no SL data available for transmission to a destination) . In various embodiments, a BSR timer may be started if there is no SL data available for transmission for a destination. In such embodiments, if SL data becomes available for any of the SL logical channels belonging to the destination, the BSR timer is stopped (e.g., if running). Upon expiration of the BSR timer, a SL BSR is triggered. The triggered SL BSR may be a new SL BSR (e.g., new SL BSR medium access control (“MAC”) control element (“CE”)) which indicates to a gNB that there is no SL data available for a specific destination. In response to receiving such a SL BSR indicating an empty transmission buffer for a destination, the gNB may allocate SL resources to the TX UE so that the TX UE may send a PSSCH transmission to be able to receive HARQ feedback. The BSR timer may have one instance per destination. In some embodiments, a BSR trigger and/or BSR timer is configured per destination (e.g., only for specific destinations for which a HARQ-based RLF mechanism is performed by a UE). In various embodiments, a BSR timer value may be autonomously adapted by a TX UE (e g., based on a traffic pattern and/or periodicity of data sent for an intended destination).

[0049] In a second embodiment, a TX UE reports a SL BSR (e.g., with one or more fields of a SL BSR MAC CE set to a predefined value) to a gNB if there is no SL data available for transmission for a destination (e.g., upon expiration of a BSR timer). In certain embodiments, a SL BSR indicates a zero buffer size for a predefined LCG of a destination. It should be noted that, in some network configurations, a SL BSR contains only a buffer status for LCGs having data available for transmission (e.g., a buffer status of zero is not reported in a SL BSR). In some embodiments, by triggering and/or reporting a zero size buffer status for the LCGs of a destination, a gNB may be made aware of an empty transmission buffer at a TX UE and may act based on this (e.g., schedule SL resources for a PSSCH transmission which in turn triggers HARQ feedback signaling from an RX UE being used for a HARQ-based RLF).

[0050] In various embodiments, a TX UE triggers and/or sends a SL BSR to a gNB if there is no SL data available for a destination. In such embodiments, the SL BSR may indicate the same content for the destination (e.g., for which no SL data is available for transmission) as previously reported for the destination to the gNB (e.g., buffer status is repeated for the destination to indicate that there is no SL data available for transmission).

[0051] In certain embodiments, a UE triggers and/or sends a SL BSR to a gNB which corresponds to a last transmitted TB for a destination that has no further SL data available for transmission. In such embodiments, the last transmitted TB may be stored in a corresponding HARQ TX buffer. Reporting a SL BSR corresponding to a stored TB (e.g., TB stored in the HARQ TX buffer) enables the gNB to schedule SL resources that match a size of the stored TB (e.g., a TX UE may send the stored TB on allocated SL resources to request HARQ feedback from an RX UE for RLF).

[0052] In some embodiments, a SL BSRtype (e.g., new SL BSR type) is reported by a TX UE if there is no SL data available for a destination for which HARQ-based RLF is applied. The SL BSR type may be referred to as a SL RLF BSR. In such embodiments, the SL RLF BSR contains only information for LCGs for a particular destination for which no SL data is available for transmission (e.g., no buffer size information is reported for other destinations that may have SL data available for transmission). Moreover, the SL BSR type may be identified by a new reserved logical channel identifier (“LCID”) (e.g., different LCID than what is used for a regular and/or truncated SL BSR). In various embodiments, a SL RLF BSR MAC CE may have the same format as a regular SL BSR MAC. In such embodiments, the SL RLF BSR MAC CE may only report a predefined buffer size for destinations having no SL data available for transmission. In certain embodiments, a SL RLF BSR MAC CE may contain only destination index fields that identify destinations for which there is no SL data available for transmission. In some embodiments, triggering and or transmitting a SL RLF BSR may not affect certain SL BSR related timers (e.g., periodicBSR-Timer is not started and/or restarted if the SL RLF BSR is sent).

[0053] In various embodiments, a TX UE may switch to a mode 2 SL resource allocation procedure for a destination and/or HARQ process ID if there is no SL data for the destination and if the TX UE wants to transmit dummy data to the destination for RLF purposes. In such embodiments, a priority value signaled in sidelink control information (“SCI”) and/or used for a mode 2 resource allocation and/or candidate resource selection may be based on a fixed (e.g., configured, reconfigured) value reserved for a RLF specific purpose. In certain embodiments, a priority value in the SCI and/or for a mode 2 resource allocation and/or candidate may be the same as that of the priority of a logical channel (“LCH”) and/or destination for which RLF is triggered. In some embodiments, a packet delay budget (“PDB”) for resource selection (e.g., T2 min, T2 value) may be set so that it is less than a RLF timer.

[0054] In certain embodiments, a TX UE triggers a packet data convergence protocol (“PDCP”) retransmission of previously transmitted PDCP SDUs if there is no SL data available for transmission. If there is no SL data available for transmission for a destination for which a HARQ-based RLF is running at a TX UE, the TX UE may trigger a retransmission of PDCP SDUs (e.g., the last PDCP SDU delivered to radio link control (“RLC”) layer for transmission). In various embodiments, a TX UE triggers a PDCP retransmission of PDCP SDUs (e.g., last PDCP SDU delivered to a lower layer) upon a predetermined trigger condition. The triggering condition may be that no SL data is available for transmission for a destination for a predetermined time period. In some embodiments, aNW (e.g., gNB) may configure which SLRB a TX UE to trigger a PDCP retransmission if there is no SL data available for transmission (e.g., only for SLRB for which HARQ-based RLF has applied PDCP retransmission which is enabled if there is an empty transmission buffer).

[0055] In some embodiments, a UE may be configured by aNW entity (e.g., gNB) with a virtual data arrival pattern for a SLRB for a destination. In certain embodiments, a gNB configures a vehicle-to-everything (“V2X”) UE with a SLRB configuration which may include parameters such as periodicity of data arrival, a size of the data, a priority of an associated logical channel, and so forth. Based on the configuration, the UE considers an arrival of higher layer data (e.g., PDCP data) for the corresponding SLRB logical channel for a layer 2 (“L2”) procedure (e.g., such as buffer status reporting and scheduling request procedures) (e.g., TX UE assumes that for a SL BSR and/or scheduling request (“SR”) procedure that SL data is available for transmission for a SL logical channel according to a configured data pattern configuration). The configuration of a virtual data arrival pattern for a SLRB and/or LCH of a destination enables a TX UE to request SL resources for a PSSCH transmission with a configured periodicity such that a link for a destination may be kept alive and HARQ feedback can be gathered at the TX UE for the HARQ-based RLF. In various embodiments, a gNB autonomously configures resources for a TX UE for use to keep the link alive and monitor link availability.

[0056] In certain embodiments, a PDCP control protocol data unit (“PDU”) type is used (e.g., which may be referred to as RLF PDCP control PDU). The PDCP control PDU type may be generated for a SLRB and/or LCH with a given configured periodicity. The PDCP control PDU type (e.g., in addition to an already existing PDCP status report and interspersed robust header compression (“ROHC”) feedback) may only consist of a PDU header.

[0057] In various embodiments, a TX UE indicates to a higher layer (e.g., application layer) that there is no SL data available for transmission for a destination based on predefined criteria. Such criteria may be that there is no SL data available for transmission for a destination for a predetermined period of time. In some embodiments, a UE starts a timer as soon as there is no SL data available for transmission for a destination. Upon expiration of the timer (e.g., the timer value may be configured by a network to some specific value), a TX UE indicates to a higher layer and/or application layer that there is no SL data available for transmission for the destination. The application layer may, in response to this indication, generate some higher layer and/or application layer message for a SLRB of the destination.

[0058] In certain embodiments, a TX UE may be configured with a SL configured grant type (e.g., new SL configured grant type). In such embodiments, the SL configured grant may be associated with a destination and/or a SL LCH (e.g., only data for a configured destination for the data for the configured SL LCH may use the allocated configured grant resources). Moreover, in such embodiments, the SL configured grant type allocates SL resources to the TX UE with a given configured periodicity. In some embodiments, if there is no SL data available for transmission for the linked destination and/or SL LCH in slots in which SL resources are allocated by a new SL CG, a TX UE uses configured grant resources for a PSSCH transmission (e.g., transmission of padding bits or any other virtual data) . The PSSCH transmission allows the TX UE to seek HARQ feedback from a receiving UE to be able to check a link quality (e.g., HARQ feedback from RX UEs is used for HARQ based RLF) . If there is SL data available for transmission for a destination associated with a linked SL LCH, the TX UE skips the PSSCH transmissions on the configured grant resources. [0059] In some embodiments, a dedicated SR configuration may be configured for HARQ- based RLF reporting. The SR configuration may be used to indicate to a gNB that there is no SL data available for transmission for a destination. In such embodiments, a dedicated SR configuration may be configured for each destination. In certain embodiments, a RLF -specific SR configuration may be configured per UE. [0060] In various embodiments, a RLF-specific SR configuration per destination may be beneficial because a gNB may only configure the SR for destinations for which RLF reporting is to be applied. In such embodiments, if a Tx UE triggers and/or sends a SR on the RLF-specific SR configuration, the gNB may allocate (e.g., in response to receiving a RLF SR) SL resources to the TX UE to allow the TX UE to test a link quality by seeking HARQ feedback for a PSSCH transmission used for HARQ-based RLF. In some embodiments, triggering and/or sending a RLF- specific SR may be triggered by the expiration of a timer that is started once there is no SL data available for transmission for a destination. The timer may be set to a predetermined value.

[0061] In various embodiments, a SL MAC CE is used to indicate that there is no SL data available for transmission for a destination. In such embodiments, the transmission of the SL MAC CE may be triggered upon expiration of a timer that is started once there is no SL data available for transmission for the destination. If the SL MAC CE is triggered (e.g., upon expiration of the timer) and a MAC entity of a TX UE has no SL resources allocated for a new transmission, the TX UE may trigger a scheduling request on a Uu interface. In certain embodiments, a TX UE triggers a RLF-specific SR indicating to a gNB that there is no SL data available for transmission. In response to reception of the RLF-specific SR, the gNB may allocate SL resource to the TX UE that matches the size of the SL MAC CE (e.g., TX UE transmits the SL MAC CE on the allocated PSSCH resources to seek HARQ feedback from an RX UE.

[0062] In some embodiments, a SL MAC CE may have an associated priority that is higher than a priority of a sidelink radio bearer (“SLRB”) and/or sidelink channel (“SLCH”) to ensure that a SL grant received from a gNB is used for the transmission of the SL MAC CE. The SL MAC CE may be identified by a LCID. In certain embodiments, a priority of a logical channel for a SR may be the same as that of that of a logical channel of a destination for which a SL BSR is triggered (e.g., to receive a SL grant to transmit SL dummy data). In various embodiments, a TX UE may prioritize a SR to avoid SR collision (e.g., multiple SR physical uplink control channel (“PUCCH”) resources occur at the same time (e.g., slot and/or symbol), other SR PUCCHs - SRs for RLF have a lower priority than other SRs).

[0063] In certain embodiments, a TX UE, upon receiving a SL grant, selects a destination during a LCP procedure even though there is no SL data available for transmission for the selected destination In such embodiments, the TX UE may select the destination that has no SL data available for transmission if a HARQ-based RLF transmission is used for the destination In various embodiments, a TX UE may select a destination for which there is no SL data available for transmission if there is no other SL data for other destinations that are of high priority (e.g., priority of a highest priority LCH among SL LCHs associated with a different destination is below a configured threshold). In some embodiments, a TX UE, upon receiving a SL grant and selecting a destination during LCP for which there is no SL data available, generates a SL MAC PDU that contains only padding.

[0064] In various embodiments, a TX UE generates, upon reception of a SL grant from a gNB, a SL MAC PDU including only random data. In such embodiments, the random data may be identified by a reserved logical channel ID. The SL MAC PDU may be generated for a SL grant if there is no SL data available for a destination for which HARQ-based RLF is used. In certain embodiments, a MAC layer, after having delivered such a special MAC PDU to a physical (“PHY”) layer for transmission, may indicate that SCI is to indicate “HARQ-enabled” in the SCI (e.g., an RX UE may send HARQ feedback for a corresponding PSSCH transmission). In some embodiments, a reserved LCID identifying random data indicates to a receiving UE that there is no higher layer data contained in a TB and a sole purpose of the TB is to gather HARQ feedback for RLF.

[0065] As may be appreciated, any embodiment described herein may be configured for a given destination ID, a pair of source layer-2 ID and destination layer-2 ID corresponding to a PC5-RRC connection, and/or a SL LCH. For specific destinations and/or LCHs, a UE may rely on upper layer keep alive messages.

[0066] Figure 4 is a schematic block diagram illustrating one embodiment of a system 400 for transmitting a sidelink buffer status report for an empty buffer. The system 400 includes a user equipment 402, a destination 404 (e.g., a UE), and a network unit 406. Moreover, the user equipment 402 includes a sidelink transmission buffer 408. In embodiments described herein, in response to the sidelink transmission buffer 408 being empty for the destination 404, a sidelink buffer status report 410 may be triggered. The sidelink buffer status report 410 may be used to indicate that the sidelink transmission buffer 408 is empty for the destination 404. The user equipment 402 may transmit 412 the sidelink buffer status report 410 to the network unit 406. [0067] Figure 5 is a schematic block diagram illustrating another embodiment of a system 500 for transmitting a sidelink buffer status report for an empty buffer. The system 500 includes a user equipment 502, a destination 504 (e.g., a UE), and a network unit 506. Moreover, the user equipment 502 includes a sidelink transmission buffer 508. In embodiments described herein, in response to the sidelink transmission buffer 508 being empty for the destination 504, a sidelink buffer status report 510 may be triggered. The sidelink buffer status report 510 may be used to indicate that the sidelink transmission buffer 508 is empty for the destination 504. The user equipment 502 may transmit 512 the sidelink buffer status report 510 to the network unit 506. In certain embodiments, the sidelink buffer status report 510 may be triggered in response to a timer 514 expiring.

[0068] Figure 6 is a flow chart diagram illustrating one embodiment of a method 600 for transmitting a sidelink buffer status report for an empty buffer. In some embodiments, the method 600 is performed by an apparatus, such as the remote unit 102. In certain embodiments, the method 600 may be performed by a processor executing program code, for example, a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

[0069] In various embodiments, the method 600 includes determining 602, at a user equipment, that a sidelink transmission buffer is empty for a destination. In some embodiments, the method 600 includes triggering 604 a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination. In certain embodiments, the method 600 includes transmitting 606 the sidelink buffer status report to a network unit.

[0070] In certain embodiment, the method 600 further comprises starting a timer in response to determining that the sidelink transmission buffer is empty for the destination. In some embodiments, the method 600 further comprises stopping the timer in response to determining that the sidelink transmission buffer for the destination is no longer empty. In various embodiments, triggering the sidelink buffer status report comprises triggering formation of the sidelink buffer status report in response to the timer expiring.

[0071] In one embodiment, the timer value is configured based on the destination. In certain embodiment, the timer value is determined autonomously by the user equipment. In some embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report via a medium access control control element.

[0072] In various embodiments, at least one field of the medium access control control element comprises a predetermined value indicating that the sidelink transmission buffer is empty for the destination. In one embodiment, the sidelink buffer status report indicates a zero buffer size for a logical channel group of the destination. In certain embodiment, the sidelink buffer status report comprises the same content as a last sent sidelink buffer status report for the destination or a last transmitted transport block.

[0073] In some embodiments, the sidelink buffer status report comprises a sidelink radio link failure buffer status report. In various embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report using resources autonomously allocated by the user equipment. In one embodiment, transmitting the sidelink buffer status report to the network unit comprises retransmitting a previously transmitted packet data convergence protocol service data unit. [0074] In certain embodiment, transmitting the sidelink buffer status report to the network unit comprises transmitting a virtual data arrival pattern for a sidelink radio bearer for the destination. In some embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting an indication to an application layer of the user equipment. In various embodiments, transmitting the sidelink buffer status report to the network unit comprises requesting sidelink resources for the transmission of the sidelink buffer status report using a dedicated scheduling request configuration.

[0075] In one embodiment, the method 600 further comprises, in response to transmitting the sidelink buffer status report to the network unit, receiving a sidelink grant for making a transmission to the destination. In certain embodiment, the method 600 further comprises making a transmission to the destination for which the sidelink transmission buffer is empty.

[0076] In some embodiments, the transmission comprises a sidelink medium access control protocol data unit. In various embodiments, the sidelink medium access control protocol data unit comprises only padding. In one embodiment, the sidelink medium access control protocol data unit comprises random data. [0077] In one embodiment, a method comprises: determining, at a user equipment, that a sidelink transmission buffer is empty for a destination; triggering a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination; and transmitting the sidelink buffer status report to a network unit.

[0078] In certain embodiment, the method further comprises starting a timer in response to determining that the sidelink transmission buffer is empty for the destination.

[0079] In some embodiments, the method further comprises stopping the timer in response to determining that the sidelink transmission buffer for the destination is no longer empty.

[0080] In various embodiments, triggering the sidelink buffer status report comprises triggering formation of the sidelink buffer status report in response to the timer expiring. [0081] In one embodiment, the timer value is configured based on the destination.

[0082] In certain embodiment, the timer value is determined autonomously by the user equipment.

[0083] In some embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report via a medium access control control element.

[0084] In various embodiments, at least one field of the medium access control control element comprises a predetermined value indicating that the sidelink transmission buffer is empty for the destination. [0085] In one embodiment, the sidelink buffer status report indicates a zero buffer size for a logical channel group of the destination.

[0086] In certain embodiment, the sidelink buffer status report comprises the same content as a last sent sidelink buffer status report for the destination or a last transmitted transport block.

[0087] In some embodiments, the sidelink buffer status report comprises a sidelink radio link failure buffer status report.

[0088] In various embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report using resources autonomously allocated by the user equipment.

[0089] In one embodiment, transmitting the sidelink buffer status report to the network unit comprises retransmitting a previously transmitted packet data convergence protocol service data unit.

[0090] In certain embodiment, transmitting the sidelink buffer status report to the network unit comprises transmitting a virtual data arrival pattern for a sidelink radio bearer for the destination. [0091] In some embodiments, transmitting the sidelink buffer status report to the network unit comprises transmitting an indication to an application layer of the user equipment.

[0092] In various embodiments, transmitting the sidelink buffer status report to the network unit comprises requesting sidelink resources for the transmission of the sidelink buffer status report using a dedicated scheduling request configuration. [0093] In one embodiment, the method further comprises, in response to transmitting the sidelink buffer status report to the network unit, receiving a sidelink grant for making a transmission to the destination.

[0094] In certain embodiment, the method further comprises making a transmission to the destination for which the sidelink transmission buffer is empty. [0095] In some embodiments, the transmission comprises a sidelink medium access control protocol data unit.

[0096] In various embodiments, the sidelink medium access control protocol data unit comprises only padding.

[0097] In one embodiment, the sidelink medium access control protocol data unit comprises random data.

[0098] In one embodiment, an apparatus comprises a user equipment. The apparatus further comprises: a processor that: determines that a sidelink transmission buffer is empty for a destination; and triggers a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination; and a transmitter that transmits the sidelink buffer status report to a network unit.

[0099] In certain embodiment, the processor starts a timer in response to determining that the sidelink transmission buffer is empty for the destination.

[0100] In some embodiments, the processor stops the timer in response to determining that the sidelink transmission buffer for the destination is no longer empty.

[0101] In various embodiments, triggering the sidelink buffer status report comprises triggering formation of the sidelink buffer status report in response to the timer expiring.

[0102] In one embodiment, the timer value is configured based on the destination.

[0103] In certain embodiment, the timer value is determined autonomously by the user equipment.

[0104] In some embodiments, the transmitter transmitting the sidelink buffer status report to the network unit comprises the transmitter transmitting the sidelink buffer status report via a medium access control control element.

[0105] In various embodiments, at least one field of the medium access control control element comprises a predetermined value indicating that the sidelink transmission buffer is empty for the destination.

[0106] In one embodiment, the sidelink buffer status report indicates a zero buffer size for a logical channel group of the destination.

[0107] In certain embodiment, the sidelink buffer status report comprises the same content as a last sent sidelink buffer status report for the destination or a last transmitted transport block.

[0108] In some embodiments, the sidelink buffer status report comprises a sidelink radio link failure buffer status report. [0109] In various embodiments, the transmitter transmitting the side link buffer status report to the network unit comprises the transmitter transmitting the sidelink buffer status report using resources autonomously allocated by the user equipment.

[0110] In one embodiment, the transmitter transmitting the sidelink buffer status report to the network unit comprises the transmitter retransmitting a previously transmitted packet data convergence protocol service data unit.

[0111] In certain embodiment, the transmitter transmitting the sidelink buffer status report to the network unit comprises the transmitter transmitting a virtual data arrival pattern for a sidelink radio bearer for the destination. [0112] In some embodiments, the transmitter transmitting the sidelink buffer status report to the network unit comprises the transmitter transmitting an indication to an application layer of the user equipment.

[0113] In various embodiments, the transmitter transmitting the sidelink buffer status report to the network unit comprises the transmitter requesting sidelink resources for the transmission of the sidelink buffer status report using a dedicated scheduling request configuration.

[0114] In one embodiment, the apparatus further comprises a receiver that, in response to transmitting the sidelink buffer status report to the network unit, receives a sidelink grant for making a transmission to the destination.

[0115] In certain embodiment, the processor makes a transmission to the destination for which the sidelink transmission buffer is empty.

[0116] In some embodiments, the transmission comprises a sidelink medium access control protocol data unit.

[0117] In various embodiments, the sidelink medium access control protocol data unit comprises only padding. [0118] In one embodiment, the sidelink medium access control protocol data unit comprises random data.

[0119] Embodiments may be practiced in other specific forms. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A method comprising: determining, at a user equipment, that a sidelink transmission buffer is empty for a destination; triggering a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination; and transmitting the sidelink buffer status report to a network unit.

2. The method of claim 1, further comprising starting a timer in response to determining that the sidelink transmission buffer is empty for the destination.

3. The method of claim 2, further comprising stopping the timer in response to determining that the sidelink transmission buffer for the destination is no longer empty.

4. The method of claim 2, wherein triggering the sidelink buffer status report comprises triggering formation of the sidelink buffer status report in response to the timer expiring.

5. The method of claim 2, wherein the timer value is configured based on the destination or the timer value is determined autonomously by the user equipment.

6. The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report via a medium access control control element.

7. The method of claim 6, wherein at least one field of the medium access control control element comprises a predetermined value indicating that the sidelink transmission buffer is empty for the destination.

8. The method of claim 1, wherein the sidelink buffer status report indicates a zero buffer size for a logical channel group of the destination.

9. The method of claim 1, wherein the sidelink buffer status report comprises the same content as a last sent sidelink buffer status report for the destination or a last transmitted transport block.

10 The method of claim 1, wherein the sidelink buffer status report comprises a sidelink radio link failure buffer status report.

11 The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises transmitting the sidelink buffer status report using resources autonomously allocated by the user equipment.

12 The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises retransmitting a previously transmitted packet data convergence protocol service data unit.

13. The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises transmitting a virtual data arrival pattern for a sidelink radio bearer for the destination.

14. The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises transmitting an indication to an application layer of the user equipment.

15. The method of claim 1, wherein transmitting the sidelink buffer status report to the network unit comprises requesting sidelink resources for the transmission of the sidelink buffer status report using a dedicated scheduling request configuration.

16 The method of claim 1, further comprising, in response to transmitting the sidelink buffer status report to the network unit, receiving a sidelink grant for making a transmission to the destination.

17. The method of claim 16, further comprising making a transmission to the destination for which the sidelink transmission buffer is empty.

18. The method of claim 17, wherein the transmission comprises a sidelink medium access control protocol data unit.

19. The method of claim 18, wherein the sidelink medium access control protocol data unit comprises only padding or random data.

20. An apparatus comprising a user equipment, the apparatus further comprising: a processor that: determines that a sidelink transmission buffer is empty for a destination; and triggers a sidelink buffer status report, wherein the sidelink buffer status report indicates that the sidelink transmission buffer is empty for the destination; and a transmitter that transmits the sidelink buffer status report to a network unit.