Secondary HARQ feedback resource allocation for sidelink communication in the unlicensed spectrum

Abstract

An example embodiment relates to secondary HARQ feedback resource allocation for sidelink communication in an unlicensed spectrum. An apparatus may perform the following: receiving a sidelink transmission from a user equipment, determining Hybrid Automatic Repeat Request (HARQ) feedback for the sidelink transmission, determining whether primary resources for transmitting the HARQ feedback are available, and determining secondary resources for transmitting the HARQ feedback if the primary resources are unavailable.

Description

[Technical Field]

[0001] The exemplary embodiments described herein relate, in general, to communication technology, and more particularly to apparatus and methods for secondary hybrid automatic retransmission request (HARQ) feedback resource allocation in sidelink communications in the unlicensed spectrum. [Background technology]

[0002] 5G New Radio (NR) supports sidelinks, providing reliable, low-latency, and high-speed device-to-device (D2D) communication for various applications, particularly in vehicle-to-vehicle / vehicle-to-infrastructure (V2X) scenarios. In NR sidelinks, user equipment (UEs) can transmit to one or more UEs via unicast, groupcast, or broadcast, with or without network control. A Hybrid Automatic Retransmission Request (HARQ) mechanism has also been introduced to NR sidelinks to ensure the reliability of sidelink transmissions. [Overview of the Initiative]

[0003] To provide a basic understanding of several aspects of various embodiments, a brief summary of exemplary embodiments is provided below. It should be noted that this summary is not intended to identify key features of essential elements or define the scope of the embodiments, but rather its sole purpose is to introduce some concepts in a simplified form as a prelude to the more detailed description provided below.

[0004] In a first embodiment, an exemplary embodiment of the apparatus is provided. The apparatus may comprise at least one processor and at least one memory containing computer program code. The at least one memory and computer program code may be configured by at least one processor to cause the apparatus to at least receive sidelink transmissions from user equipment, determine hybrid automatic retransmission request (HARQ) feedback regarding sidelink transmissions, determine whether a primary resource is available for sending HARQ feedback, and, if the primary resource is unavailable, determine a secondary resource for sending HARQ feedback.

[0005] In a second embodiment, exemplary embodiments of the apparatus are provided. The apparatus may comprise at least one processor and at least one memory containing computer program code. The at least one memory and computer program code may be configured by at least one processor to cause at least the apparatus to cause a sidelink transmission to be sent to a user device, to determine whether a primary resource is available for receiving Hybrid Automatic Retransmission Request (HARQ) feedback relating to the sidelink transmission, and, if the primary resource is unavailable, to determine a secondary resource for receiving the HARQ feedback.

[0006] Exemplary embodiments of methods, apparatus, and computer program products are also provided. Such exemplary embodiments generally correspond to the exemplary embodiments described above, and for convenience, a repeated description is omitted here.

[0007] Other features of the exemplary embodiments of this disclosure and, preferably, the accompanying drawings illustrating the principles of the exemplary embodiments of this disclosure will also become apparent from the following description of specific embodiments. [Brief explanation of the drawing]

[0008] Next, several exemplary embodiments will be described, as non-limiting examples, with reference to the attached drawings. [Figure 1] Figure 1 is a schematic diagram showing a communication network in which exemplary embodiments of the present disclosure can be implemented. [Figure 2A] Figure 2A is a schematic diagram showing examples of sidelink slots with and without physical sidelink feedback channel symbols. [Figure 2B] Figure 2B is a schematic diagram showing examples of sidelink slots with and without physical sidelink feedback channel symbols. [Figure 3] Figure 3 is a schematic diagram showing an example of the mapping between a physical sidelink shared channel and a physical sidelink feedback channel. [Figure 4] Figure 4 is a schematic diagram showing the duration of channel occupancy time (COT) obtained by the listen-before-talk (LBT) procedure. [Figure 5] Figure 5 is a schematic message flowchart illustrating sidelink communication between multiple UEs. [Figure 6] Figure 6 is a schematic diagram illustrating an example where Hybrid Automatic Retransmission Request (HARQ) feedback is blocked due to an LBT failure in a sidelink (SL-U) in the unlicensed spectrum. [Figure 7] Figure 7 is a schematic diagram illustrating an example of secondary physical sidelink feedback channel (PSFCH) resource allocation according to an exemplary embodiment of the present disclosure. [Figure 8] Figure 8 is a schematic message flowchart illustrating the procedure for secondary PSFCH resource allocation in an exemplary embodiment of the present disclosure. [Figure 9] Figure 9 is a schematic diagram showing an example of secondary PSFCH resource allocation according to an exemplary embodiment of the present disclosure. [Figure 10] Figure 10 is a schematic diagram showing an example of secondary PSFCH resource allocation according to an exemplary embodiment of the present disclosure. [Figure 11]Figure 11 is a schematic message flowchart illustrating the procedure for sending HARQ feedback based on a secondary PSFCH resource according to an exemplary embodiment of the present disclosure. [Figure 12] Figure 12 is a schematic block diagram of an apparatus according to an exemplary embodiment of the present disclosure. Throughout the drawings, the same or similar reference numerals indicate the same or similar elements. Repeated descriptions of the same elements are omitted. [Modes for carrying out the invention]

[0009] The following describes several exemplary embodiments in detail with reference to the accompanying drawings. The following description includes specific details intended to ensure a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts can be implemented without these specific details. In some examples, known circuits, techniques, and components are shown in block diagrams to avoid obscuring the described concepts and features.

[0010] As used herein, the term “network equipment” refers to any suitable entity or device capable of providing a cell or coverage through which terminal equipment can access the network and receive services. Network equipment may generally be referred to as a base station. As used herein, the term “base station” can represent a Node B (NodeB or NB), an evolved Node B (eNodeB or eNB), or a gNB. A base station may be embodied as a macro base station, a relay node, or a low-power node such as a pico base station or a femto base station. A base station may consist of multiple distributed network units, such as a central unit (CU), one or more distributed units (DU), and one or more remote radio heads (RRHs) or remote radio units (RRUs). The number and functionality of these distributed units depend on the chosen split RAN architecture.

[0011] As used herein, the term "terminal device" or "user equipment" (UE) refers to a network device or any entity or device capable of wireless communication with each other. Examples of terminal devices include mobile phones, mobile terminals (MTs), mobile stations (MSs), subscriber stations (SSs), portable subscriber stations (PSSs), access terminals (ATs), computers, wearable devices, in-vehicle communication devices, machine-type communication (MTC) devices, D2D communication devices, V2X communication devices, sensors, and the like. The term "terminal device" can be used interchangeably with UE, user equipment, mobile terminal, mobile station, or wireless device.

[0012] FIG. 1 shows an exemplary communication network 100 in which an exemplary embodiment of the present disclosure can be implemented. Referring to FIG. 1, the communication network 100 may include a first UE 110a, a second UE 110b, and a base station (BS) 120. The base station 120 is shown as a 5G base station gNB in FIG. 1, but it can also be implemented as a long-term evolution (LTE) base station eNB or a beyond 5G base station. The base station 120 can communicate with the UEs 110a, 110b via an uplink (UL) and a downlink (DL) through the Uu interface. The base station 120 in other embodiments may implement other radio access technologies to communicate with the UEs 110a, 110b.

[0013] UEs 110a and 110b may be vehicle-mounted terminals, roadside units, mobile phones, etc. In addition to network communication via the Uu interface with the base station 120, UEs 110a and 110b can also perform direct communication, referred to as sidelink (SL) communication, with each other via, for example, the PC5 interface. Each of UEs 110a and 110b can function as an SL transmission (TX) UE that transmits information on the sidelink or an SL reception (RX) UE that receives information on the sidelink. The SL TX UE can transmit to one or more SL RX UEs by unicast, groupcast, or broadcast, under the control of the network or without control. For example, the sidelink may be established between UEs 110a and 110b when both are within the network coverage (in-coverage scenario), when both are outside the network coverage (out-of-coverage scenario), or when one is within the network coverage and the other is outside the network coverage (partial-coverage scenario).

[0014] UEs 110a and 110b can use the same or different spectra for network communication on the Uu link and sidelink communication on the sidelink. In some exemplary embodiments, UEs 110a and 110b can perform network communication in unlicensed spectra, such as LTE or NR bands, and perform sidelink communication in unlicensed spectra. Unlicensed spectra may refer to any frequency band that does not require a license from a relevant regulatory agency, and the frequency band can be used not only by devices having a license for using a specific frequency band but also by any device. Examples of unlicensed spectra available worldwide include 2.4 GHz, 5 GHz, and 60 GHz.

[0015] The 3GPP® specification designs two radio resource allocation modes, and an SL TX UE can be configured to one of them to perform its sidelink transmission. In Mode 1, the network allocates sidelink transmission resources to the SL TX UE. The SL TX UE can send a Sidelink Scheduling Request (SL-SR) to base station 120, and base station 120 can respond to the received SL-SR by sending a resource allocation to the SL TX UE. In Mode 2, the SL TX UE can autonomously select its sidelink transmission resources. For example, the SL TX UE can first perform a sensing procedure on the configured sidelink transmission resource pool(s) to obtain information about reserved resources from other nearby SL TX UE(s). Based on the information obtained from the sensing procedure, the SL TX UE can select a resource from the available SL resources.

[0016] In order for the SL UE to perform sensing and obtain the information necessary to receive SL transmissions, the SL UE needs to decode sidelink control information (SCI). SCI related to data transmission may have a two-stage SCI structure, including a first-stage SCI and a second-stage SCI, to support size differences between SCIs for various NR V2X sidelink service types (e.g., broadcast, groupcast, and unicast). The first-stage SCI, including SCI format 1-A, is transmitted by the physical sidelink control channel (PSCCH) and includes, in particular, information that enables sensing operations and information necessary to determine resource allocation on the physical sidelink shared channel (PSSCH) and decode the second-stage SCI. The second-stage SCI, including SCI formats 2-A and 2-B, is transmitted by the PSSCH and includes source and destination IDs, information for identifying and decoding the associated sidelink shared channel (SL-SCH) transport block (TB), HARQ feedback control information, and channel status information (CSI) feedback trigger information.

[0017] The configuration of resources within the sidelink resource pool defines the minimum information necessary for the SL RX UE to decode sidelink transmissions, including the number of subchannels, the number of physical resource blocks (PRBs) per subchannel, the number of symbols in the PSCCH, and the slots containing physical sidelink feedback channels (PSFCH). The actual sidelink transmission details, i.e., the payload transmitted within the PSCCH, are provided in the PSCCH (First Stage SCI) for each individual transmission, and include time and frequency resources, the demodulation reference signal (DMRS) configuration of the PSCCH, the modulation and coding scheme (MCS), and the PSFCH. The SL RX UE must decode the PSCCH before it can decode the payload of the sidelink transmission.

[0018] Figure 2A shows an example of a sidelink slot containing PSCCH and PSSCH symbols, and Figure 2B shows an example of a sidelink slot containing PSCCH, PSSCH, and PSFCH symbols. In both slots, the first symbol (symbol #0) is used for automatic gain control (AGC), which may be a duplicate symbol of the second symbol (symbol #1), and the last symbol (symbol #13) is used for the guard period (GP). PSCCH is transmitted with the second and third symbols (symbols #1 and #2). If HARQ feedback is enabled, the second-to-last symbol (symbol #12, the last symbol excluding guard symbol #13) is used for PSFCH, and a guard symbol (symbol #10) may be included between the PSSCH and PSFCH symbols. Alternatively, the symbol preceding the PSFCH symbol may be used for AGC and may be a symbol that overlaps with the PSFCH symbol. As mentioned above, the configuration of the PSCCH (e.g., DMRS, MCS, number of symbols used) is part of the resource pool configuration, and the indication of which slots contain PSFCH symbols is also part of the resource pool configuration. The configuration of the PSSCH (number of symbols used, DMRS pattern, MCS, etc.) is provided by the first-stage SCI, which is the payload transmitted within the PSCCH.

[0019] PSFCH was introduced to enable HARQ feedback via sidelink from the receiver UE (i.e., RX UE) to the UE that initiated the transmission (i.e., TX UE) of a PSSCH transmission. If the RX UE successfully receives and decodes the PSSCH transmission, it generates a positive HARQ acknowledgment (ACK) and sends a HARQ ACK on the PSFCH to the TX UE to confirm the transmission. If the RX UE fails to receive or decode the PSSCH transmission, it generates a negative HARQ acknowledgment (NACK) and sends a HARQ NACK on the PSFCH to the TX UE to request a retransmission of the PSSCH. In the case of NACK-only HARQ feedback, the RX UE may not send HARQ ACK feedback even if it successfully receives and decodes the PSSCH transmission. The Rx UE always knows when a PSSCH transmission was intended, for example, based on the TX ID and RX ID indicated in the second stage SCI. Within the PSFCH, as shown in Figure 2B, a Zadoff-Chu sequence for one PRB is repeated across two OFDM symbols. The Zadoff-Chu sequence as the base sequence is configured or pre-configured for each sidelink resource pool.

[0020] The time resource for a PSFCH may be set or pre-configured to occur once every N slots, where N may be 0, 1, 2, 4, or any other value. The HARQ feedback resource (PSFCH) is derived from the resource location of the PSSCH. A slot-based parameter K is set for PSSCH-to-HARQ timing, and the time occasion of a PSFCH may be determined from parameter K. For example, for a PSSCH transmission with the last symbol in slot n, its HARQ feedback is expected to be in slot n+a, where a is the smallest integer greater than or equal to K, and slot n+a contains the PSFCH resource. A time difference of at least K slots allows for consideration of the processing delay of the RX UE when decoding the PSCCH and PSSCH and generating the HARQ feedback. Parameter K can be 2, 3, 4, or any other value, and a single value for K may be set or pre-configured per resource pool. This allows multiple RX UEs using the same resource pool to utilize the same mapping of PSFCH resources for HARQ feedback. The parameter K determines the N PSSCH slots associated with the slot that has a PSFCH.

[0021] Figure 3 shows an example of the mapping between PSSCH slots and PSFCH slots. Referring to Figure 3, the period of the PSFCH is set to N=4, and the PSSCH-to-HARQ time gap is set to K=2, for example, via the information element sl-MinTimeGapPSFCH. Therefore, four PSSCH slots are associated with a PSFCH, and the time gap from the last PSSCH to the PSFCH is two slots. If there are L subchannels in the resource pool and N PSSCH slots are associated with the slot containing the PSFCH, then there will be N*L PSSCH transmissions associated with the PSFCH symbol. If there are M PRBs available for the PSFCH within the PSFCH symbol, then there will be M PRBs available for HARQ feedback of PSSCH transmissions via L subchannels and N slots, and Mset =M / (N*L) separate sets of PRBs can be associated with the HARQ feedback of each PSSCH transmission within the PSFCH period, where M is set to be a multiple of N*L. set The first set of PRBs is associated with the HARQ feedback of the PSSCH transmission in the first subchannel in the first slot, and M of the M PRBs set A second set of PRBs is associated with the HARQ feedback for PSSCH transmission in the first subchannel in the second slot, and so on.

[0022] In the example shown in Figure 3, the resource pool consists of L=3 subchannels, and all PRBs within the PSFCH symbol are available to the PSFCH. There are 12 PSSCH transmissions in the L=3 subchannels and N=4 slots, and the HARQ feedback for PSSCH transmission x is M within the corresponding PSFCH symbol. set It is sent in the x-th set of PRBs (x=1,...,12).

[0023] In the case of ACK / NACK feedback in groupcast communication, or when different PSSCH transmissions occur within the same subchannel, the M associated with the subchannel set A set of PRBs may be shared among multiple RX UEs. For each PRB available in the PSFCH, there are Q cyclic shift pairs available to support ACK or NACK feedback for Q RX UEs within the PRB. For the resource pool, the number of cyclic shift pairs Q may be set or pre-configured to 1, 2, 3, 6, or any other value.

[0024] There are F PSFCH resources that can be used to support HARQ feedback for a certain transmission. If one RX UE uses each PSFCH resource, the F PSFCH resources can be used for the ACK / NACK feedback of up to F RX UEs. The F PSFCH resources available for multiplexing the HARQ feedback of PSSCH are determined based on the following two options. a) Based on the L PSSCH subchannels used by PSSCH, F is calculated as follows. F = L * M set * Q, provided that the F PSFCH resources are related to the L subchannels of PSSCH. Or, b) Based only on the starting subchannel used by PSSCH (i.e., based on only one subchannel if L > 1), F can be calculated as follows. F = M set * Q, provided that the F PSFCH resources are related to the starting subchannel of PSSCH.

[0025] Similar to the physical uplink control channel (PUCCH) on the NR Uu interface, the available F PSFCH resources may be indexed based on the PRB index (frequency domain) and the cyclic shift pair index (code domain). For the mapping between the PSFCH index i (i = 1, 2,..., F) and the PRB and Q cyclic shift pairs, first, the PSFCH index i increases with the PRB index until the maximum number of available PRBs for PSFCH is reached. Next, the PSFCH index i increases with the cyclic shift pair index and then increases again with the PRB index. Among the F PSFCH resources available for the HARQ feedback of a given transmission, the RX UE can select the PSFCH resource for which the index i is given by the following equation for HARQ feedback, i = (T ID + R ID ) mod F, provided that T IDThis is the Layer 1 ID of the TX UE shown in the second stage SCI, and for unicast ACK / NACK feedback and groupcast NACK-only feedback (option 1), R ID = 0, and in the case of group cast ACK / NACK feedback (option 2), R ID This is equal to the ID of the RX UE within the group shown in the higher layer.

[0026] For a number X of RX UEs in a group, the ID of an RX UE is an integer from 0 to X-1. An RX UE can determine the PRB and cyclic shift pair to use for sending HARQ feedback based on its PSFCH index i. An RX UE can use the first or second cyclic shift from the cyclic shift pair associated with the selected PSFCH index i, respectively, to send a NACK or ACK. By selecting a PSFCH with index i, an RX UE can distinguish between HARQ feedback from a different RX UE (via the RX UE's ID, e.g., in groupcast option 2) and HARQ feedback intended for the TX UE (via the TX UE's Layer 1 ID, e.g., in unicast). In groupcast option 1, R ID Since = 0, the RX UE is the ID of the TX UE on Layer 1, T ID Based solely on this, the same PSFCH index i can be selected for NACK-only feedback.

[0027] As mentioned above, sidelink communication can be performed in unlicensed spectrum that may also be used by other communication systems. For example, the 2.4 GHz and 5 GHz frequency bands are also used for WiFi® communication. Considering coexistence with other systems (such as IEEE 802.11), the TX UE must perform a clear channel evaluation procedure to assess whether the channel resources obtained by resource allocation mode 1 or mode 2 are available for sidelink transmission. A listen-before-talk (LBT) channel access mechanism is introduced for channel availability evaluation, and a UE attempting to perform sidelink transmission must first pass an LBT check before initiating transmission. For a UE to pass the LBT check, it must confirm that the channel is available for a series of clear channel evaluation (CCA) slots. In the unlicensed spectrum below 7 GHz, the duration of these slots is 9 μs. The TX UE determines that the channel is available in a CCA slot if the measured power (i.e., energy collected during the CCA slot) falls below a predetermined threshold that varies depending on the operating bandwidth and geographical area.

[0028] When a UE initiates sidelink communication (i.e., the UE acts as the initiator), it must acquire the "right" to access the channel for a certain period called Channel Occupancy Time (COT) by applying an "extended" LBT procedure, which considers the channel to be free for the entire duration of the Contention Window (CW). This "extended" LBT procedure is commonly known as LBT Type 1 (or LBT Cat. 4). An example of the Contention Window and Channel Occupancy Time is shown in Figure 4. The duration of COT and CW may depend on the Channel Access Priority Class (CAPC) associated with the UE's traffic. Control plane traffic (such as PSCCH) has CAPC=1, while user plane traffic has CAPC>1.

[0029] Upon successful completion of LBT Type 1 and execution of a transmission, the UE (Initiator) obtains a COT (Conditioning Time) for the duration associated with the corresponding CAPC (Capacitor-Assisted Transmission). The obtained COT remains valid even if the initiator pauses transmissions. If the initiator wishes to execute a new transmission within the COT, it must perform a "reduced" LBT procedure. The "reduced" LBT procedure is commonly known as LBT Type 2 and has the following variations: • Type 2A (also known as 25μs LBT or LBT Cat.2) - For sidelink transmissions within a starting device that has obtained COT (when the gap between two sidelink transmissions is 25μs or more, and for sidelink transmissions following other sidelink transmissions). • Type 2B (also known as 16μs LBT or LBT Cat.2) - For sidelink transmissions within a starter that has obtained COT (used only for sidelink transmissions following other sidelink transmissions with a transmit gap equal to 16μs). • Type 2C (without LBT, also known as LBT Cat.1) - For sidelink transmissions following other sidelink transmissions with a transmit gap of less than 16 μs, with an allowable sidelink transmission duration of 584 μs or less.

[0030] The initiator can share the acquired COT with the receiving receiver (responder). For this purpose, the initiator can notify the responder of the COT duration using a control signal or similar method. The responder can then use this information to determine which type of LBT to apply when the receiving receiver, which is the initiator, performs a transmission. If the responder's transmission goes outside the COT range, the responder must acquire a new COT using LBT type 1 with the appropriate CAPC.

[0031] Figure 5 shows an example of sidelink communication between multiple UEs. Referring to Figure 5, the first UE 110a can transmit a PSCCH / PSSCH to the second UE 110b when it acquires the first COT by performing an "extended" LBT (LBT type 1). The first UE 110a can also share the first COT with the second UE 110b via control signaling. Within the first COT, the second UE 110b can perform a "decreased" LBT (LBT type 2) to check channel availability in response to the PSCCH / PSSCH received from the first UE 110a and transmit a PSFCH to the first UE 110a. If the second UE110b wants to perform a transmission to the first UE110a, but the first COT has an expiration date, the second UE110b can perform an LBT type 1 to acquire the second COT and then forward the PSCCH / PSSCH to the first UE110a. Alternatively, the second UE110b can share the second COT with the first UE110a via control signaling. Within the second COT, the first UE110a can perform an LBT type 2 to check channel availability and, in response to the PSCCH / PSSCH received from the second UE110b, can transmit a PSFCH to the second UE110b.

[0032] Due to the listen-before-talk requirement, there is some uncertainty about whether a transmission will occur when intended when operating on unlicensed spectrum. This particularly affects procedures where a fixed timing relationship is assumed between two or more transmissions. One such example is the HARQ procedure, where for a PSSCH transmission with the last symbol in slot n, the HARQ feedback transmission is predicted to be in slot n+a, where a is the smallest integer greater than or equal to the PSSCH-to-HARQ time gap parameter K, and slot n+a contains a PSFCH resource. However, there is no guarantee that the HARQ feedback transmission on the PSFCH is possible in slot n+a, at least if the TX UE (transmitting PSSCH and PSCCH) must perform LBT before occupying each channel.

[0033] One possible scenario is when the RX UE lacks the capability to perform LBT and can only transmit within the channel occupancy initiated by the TX UE. An example of a relevant scenario to which this assumption applies is reduced-capability devices (devices without LBT functionality), such as sensors and actuators, where communication is always initiated via a control device (device with LBT functionality). This is a reasonable assumption because LBT implementations require devices to transition from a receiving state (such as performing LBT) to a transmitting state within a few microseconds, which introduces significant complexity to the device.

[0034] Figure 6 shows an example where HARQ feedback is blocked due to an LBT failure. Referring to Figure 6, the TX UE obtains the first COT (COT#1) by executing LBT type 1 (LBT Cat.4) and sends a PSCCH / PSSCH to the RX UE in slot n-1. Within the COT, the TX UE also executes LBT type 2 (LBT Cat.2) during the guard period between two adjacent slots and sends a PSCCH / PSSCH to the RX UE in the subsequent slot. In this embodiment, the period of the PSFCH is set to N=1 slot and the HARQ delay is set to a=2 slots. In this case, the RX UE will send a PSFCH two slots after receiving the corresponding PSCCH / PSSCH. For example, the RX UE sends a PSFCH in slot n+1 in response to the PSCCH / PSSCH received in slot n-1. However, if the LBT type 2 fails at the end of slot n+1 and the first COT ends, the HARQ feedback associated with slot n+2 cannot be delivered because there is no PSFCH resource in slot n+2. The TX UE can perform another LBT type 1 and obtain a second COT (COT#2) to send to the RX UE. Since the PSFCH resource is available in slot n+3, the RX UE can send a PSFCH in slot n+3 in response to the PSCCH / PSSCH received in slot n+1.

[0035] An exemplary embodiment provides a secondary resource allocation mechanism for HARQ feedback on a PSFCH that cannot be transmitted on the primary PSFCH resource as intended, for example, due to an LBT failure. The secondary PSFCH resource may be allocated, for example, to one or more slots following one or more empty slots that have no transmissions due to an LBT failure. An example of secondary resource allocation is shown in Figure 7, which is similar to the case shown in Figure 6. Referring to Figure 7, the TX UE suffers an LBT failure before the start of slot n+2, and therefore cannot perform a PSCCH / PSSCH transmission in slot n+2. As a result, the RX UE cannot transmit HARQ feedback for the PSSCH transmission in slot n on the PSFCH of slot n+2. Also, because the LBT failed before slot n+2, there is no PSSCH transmission in slot n+2, and therefore there is no HARQ feedback corresponding to that slot in slot n+4, and the PSFCH resource for slot n+4 is not occupied. This unoccupied resource can then be used as a secondary resource for HARQ feedback that failed to be transmitted on the primary resource due to the LBT failure.

[0036] The exemplary embodiment can be applied to RX UEs with or without LBT functionality. Secondary PSFCH resources are allocated in a shared COT initiated by the TX UE (i.e., the UE transmitting the PSCCH / PSSCH), and the RX UE may or may not perform LBT before transmitting the PSFCH. The RX UE may determine the secondary PSFCH resource from explicit notification from the TX UE, or the RX UE may determine the secondary PSFCH resource independently based on predetermined rules or the like. The secondary resource allocation mechanism does not significantly increase the signaling overhead of sidelink communication.

[0037] Figure 8 shows a secondary PSFCH resource allocation procedure according to an exemplary embodiment of the present disclosure. This procedure can be performed by UEs having sidelink capabilities, for example, UE110a, 110b described with respect to Figure 1. In some exemplary embodiments, UE110a is described as the TX UE and UE110b is described as the RX UE, but it will be understood that any one of UE110a, 110b can function as both the TX UE and the RX UE. In some exemplary embodiments, UE110a, 110b may include, or be configured with, a plurality of components, modules, means, or elements for performing the operations in the procedure, and these components, modules, means, or elements may be implemented in various ways, including, but not limited to, software, hardware, firmware, or any combination thereof.

[0038] Referring to Figure 8, in operation 210, TX UE110a can transmit a sidelink transmission to RX UE110b. The sidelink transmission may include, for example, a payload carried on the PSSCH and information necessary to decode the payload carried on the PSCCH. The sidelink transmission may be transmitted on an unlicensed spectrum, and TX UE110a may perform LBT type 1 or type 2 before the sidelink transmission. RX UE110b recognizes whether there is a transmission for it based on, for example, a second-stage SCI, which includes a source ID indicating the TX UE and a destination ID indicating the RX UE. In operation 210, RX UE110b can receive the sidelink transmission and decode the first-stage SCI carried on the PSCCH first, and then decode the second-stage SCI carried on the PSSCH according to the first-stage SCI. The first and second-stage SCIs allow RX UE110b to decode the payload of the sidelink transmission.

[0039] In operation 212, RX UE110b may determine the HARQ feedback for the sidelink transmission received in operation 210. The determined HARQ feedback may be an affirmative acknowledgment (ACK) confirming that the sidelink transmission was successfully received and decoded, or a negative acknowledgment (NACK) notifying TX UE110a that RX UE110b failed to decode the sidelink transmission. In response to the HARQ NACK feedback, TX UE110a may retransmit as necessary.

[0040] In operation 214, TX UE110a may determine whether a primary PSFCH resource is available for HARQ feedback related to the sidelink transmission transmitted in operation 210. Here, the primary PSFCH resource refers to the resource determined for normal transmission of HARQ feedback based on the resources used for sidelink transmission and the PSFCH channel configuration. For example, the primary PSFCH resource may be determined as described above with respect to Figures 2B and 3. In an exemplary embodiment, TX UE110a may perform a clear channel evaluation procedure, such as a listen-before-talk (LBT) channel access procedure, to evaluate whether a primary PSFCH resource is available for HARQ feedback. In operation 214, either Cat.4 LBT or Cat.2 LBT can be performed to check the availability of the primary PSFCH resource.

[0041] In operation 216, RX UE110b may also determine whether the primary PSFCH resource for HARQ feedback determined in operation 212 is available. In an exemplary embodiment where RX UE110b is a low-capacity device that does not implement LBT, RX UE110b may detect, based on control signaling received from TX UE110a, whether a shared channel occupation initiated by TX UE110a to transmit HARQ feedback on the primary PSFCH resource is available. If RX UE110b is capable of performing LBT, RX UE110b may, additionally or alternatively, perform LBT (e.g., Cat.2 LBT) to check whether the primary PSFCH resource is available.

[0042] If the primary PSFCH resource is available, RX UE110b can use the primary PSFCH resource to send HARQ feedback to TX UE110a in operation 218. If the received HARQ feedback is a HARQ ACK, TX UE110a knows that the sidelink transmission was successfully received by RX UE110a and can initiate a new transmission. If the received HARQ feedback is a HARQ NACK, TX UE110a knows that RX UE110a failed to receive the sidelink transmission and can retransmit if necessary.

[0043] If the primary PSFCH resource is unavailable, the TX UE110a can initiate a new Channel Occupancy Time (COT) by performing an "extended" LBT (Cat.4 LBT) in operation 220, and share the COT with the RX UE110b. Here, the new COT is referred to as the second COT, and the previous COT for sidelink transmission in operation 210 is referred to as the first COT. Prior to the "extended" LBT for the second COT, the TX UE110a can select any available resources, for example, any combination of future slots and subchannels. In this embodiment, the TX UE110a can select available resources by following the Mode 2 resource selection procedure.

[0044] In operation 222, TX UE110a may determine a secondary PSFCH resource for HARQ feedback that was not transmitted on the primary PSFCH resource. TX UE110a may determine a secondary PSFCH resource in the second COT based on predetermined rules. For example, TX UE110a may determine a secondary PSFCH resource based on the location and number of one or more unavailable (empty) slots between the first COT and the second COT, as described later with reference to some examples shown in Figures 7 and 9.

[0045] Referring to Figure 7, the PSFCH period is set to slot N=1 and the HARQ delay is set to slot a=2. The first COT ends at the end of slot n+1 due to an LBT failure, and TX UE110a starts the second COT from slot n+3. Subsequently, since slot n+2 is unavailable, HARQ feedback for the sidelink transmission in slot n cannot be transmitted over the primary PSFCH resource. As an example, TX UE110a may determine that the secondary PSFCH resource is in the first available slot n+K+a*x, where n is the slot number of the side transmission for which the primary PSFCH resource is available, K is the set PSFCH-to-HARQ timing, a is the smallest integer greater than or equal to K, and x is the smallest positive integer satisfying that slot n+K+a*x is in the second COT. The value of x can be determined based on the location and number of empty (unavailable) slots between the first COT and the second CTO initiated by the TX UE110a. In the example shown in Figure 7, the secondary PSFCH resource may be determined in slot n+4.

[0046] In another example shown in Figure 9, the TX UE110a obtains the second COT from slot n+5, and another embodiment is the same as the example in Figure 7. In this embodiment, sidelink transmissions in slots n and n+1 do not have a primary PSFCH resource for HARQ feedback because slots n+2 through n+4 are unavailable. Since the second COT starts from slot n+5, the secondary PSFCH resource for sidelink transmissions in slot n may be determined to be in slot n+6 according to the formula n+K+a*x, where x is 2 in this embodiment, and the secondary PSFCH resource for sidelink transmissions in slot n+1 may be determined to be in slot n+5, where x is 1.

[0047] The formula n+K+a*x is given merely as an example for determining secondary PSFCH resources, and it should be understood that other algorithms may also be used. For example, TX UE110a can assign an unoccupied PSFCH slot with a smaller index to a previous sidelink transmission for which no HARQ feedback has been sent. Referring to Figure 10, no HARQ feedback has been delivered for sidelink transmissions in slots n and n+1, and the PSFCHs in slots n+5 and n+6 are unoccupied. In this case, TX UE110a can determine that the secondary PSFCH resource for the sidelink transmission in slot n is assigned to slot n+5, and the secondary PSFCH resource for the sidelink transmission in slot n+1 is assigned to slot n+6.

[0048] Generally, the TX UE110 can determine available PSFCH resources in the second COT based on the location and number of unavailable slots that do not deliver transmissions between the first COT and the second COT, and these available PSFCH resources may be used as secondary PSFCH resources.

[0049] Optionally, in operation 224, the TX UE110a may notify the RX UE110b of a secondary PSFCH resource. For example, the TX UE110a may notify the RX UE110b of the slot of the secondary PSFCH resource. The slot is indicated, for example, by a y-bit bitmap [b(0), b(1), b(y-1)] (where y≧K). Each bit indicates whether the secondary PSFCH resource exists in slot (b0), slot (b1), etc. For example, as shown in Figure 7, the TX UE110a may send the bitmap [b(0), b(1)] to the RX UE110b in slot n+3, and the bitmap may include b(0)=0 and b(1)=1, indicating that the secondary PSFCH resource is not located in the current slot n+3 but in the subsequent slot n+4. In the example shown in Figure 9, the bitmap [b(0), b(1)] may include b(0)=1, b(1)=1, which is sent to the RX UE110b in slot n+5 and indicates that the secondary PSFCH resource is located in the current slot n+5 and the subsequent slot n+6.

[0050] If the bitmap indicates two or more slots containing secondary PSFCH resources, the RX UE110b can select a slot / secondary PSFCH resource for HARQ feedback of a given sidelink transmit based on a predetermined rule. This predetermined rule may be set or pre-configured to maintain the same secondary PSFCH-to-slot mapping in both the TX UE110a and the RX UE110b. For example, in Figure 9, the bitmap indicates slots n+5 and n+6 for HARQ feedback of sidelink transmits in slots n and n+1. According to the rule n+K+a*x described above, the RX UE110b can select slot n+5 for HARQ feedback of sidelink transmits in slot n+1, and slot n+6 for HARQ feedback of sidelink transmits in slot n. In the example shown in Figure 10, the RX UE110b can select slots n+5 and n+6 for HARQ feedback of sidelink transmits in slots n and n+1. As mentioned above, different rules / algorithms may be applied, but the same rules / algorithms are maintained for both the TX UE110a and RX UE110b.

[0051] In some exemplary embodiments, alternatively or additionally, TX UE110a may notify RX UE110b of PSFCH opportunities, for example, by a bitmap. For example, bit b(0) may indicate the next first PSFCH opportunity in the current or subsequent slot, and bit b(1) may correspond to the next second PSFCH opportunity after the next first PSFCH opportunity. The bitmap may also indicate two or more PSFCH opportunities, and RX UE110b may select a PSFCH opportunity for HARQ feedback of a given sidelink transmission based on a predetermined rule which may be set / pre-configured in TX UE110a and RX UE110b.

[0052] In an exemplary embodiment, a secondary PSFCH resource notification may be sent to the RX UE110b, for example, on the PSCCH in the first stage SCI and / or on the PSSCH in the second stage SCI. This notification may be sent in the first slot in the second COT, or in the starting slot of one or more unoccupied PSFCH slots in the second COT.

[0053] In an exemplary embodiment, the secondary PSFCH resource notification may also include an enable / disable bit indicating whether the secondary PSFCH resource should / can be used to verify a previous sidelink transmission(s) for which HARQ feedback was not delivered. Based on this bit, the RX UE110b can determine whether to use the secondary PSFCH resource to send HARQ feedback for the previous sidelink transmission.

[0054] Returning to Figure 8, in operation 226, RX UE110b may determine a secondary PSFCH resource for transmitting HARQ feedback for a sidelink transmission where HARQ feedback was not transmitted on the primary PSFCH resource due to an LBT failure, for example. In an exemplary embodiment, RX UE110b may determine a secondary PSFCH resource based at least in part on a notification received from TX UE110a in operation 224. For example, RX UE110b may determine a slot and / or PSFCH opportunity for a secondary PSFCH resource based on a notification received from TX UE110a, and other aspects of the secondary PSFCH resource may depend on the corresponding primary PSFCH resource. For example, the mapping of secondary PSFCH resources may follow the same principles as the mapping of primary PSFCH resources in the frequency domain and code domain.

[0055] In other exemplary embodiments, operation 214 may be omitted, and RX UE110b may determine the secondary PSFCH resource itself. In the exemplary embodiment of this embodiment, RX UE110b may determine the secondary PSFCH resource in the time domain according to the same principle as TX UE110a does in operation 222, and for convenience, a repeated explanation of that is omitted here. Another aspect of the secondary PSFCH resource may depend on the corresponding primary PSFCH resource. For example, the mapping of the secondary PSFCH resource may follow the mapping of the primary PSFCH resource in the frequency domain and code domain. As described above, of the F PSFCH resources available for HARQ feedback of a given transmission, RX UE110b determines i=(T ID +R ID A PSFCH having index i given by mod F can be selected. By using different cyclic shift pairs, different resource blocks, and different Zadoff-Chu sequences, the secondary PSFCH resource determined for a given sidelink transmission may be orthogonal to other primary PSFCH resources on other RX UEs receiving the given sidelink transmission, and to primary PSFCH resources corresponding to other sidelink transmissions received by RX UE110b from other TX UEs at the same time as receiving the given sidelink transmission. In this way, there will be no PSFCH collisions between different RX UEs on the TX UE110a side.

[0056] Next, in operation 228, the RX UE110b can use the secondary PSFCH resource to send HARQ feedback to the TX UE110a. Since the TX UE110a is also aware of the secondary PSFCH resource, it will monitor and receive the HARQ feedback on the secondary PSFCH resource.

[0057] Figure 10 shows an exemplary procedure for sending HARQ feedback based on a secondary HARQ resource, according to an exemplary embodiment of the present disclosure. This procedure may be implemented in the RX UE110b and may be incorporated as part of the procedure described above with respect to Figure 8.

[0058] Referring to Figure 10, in operation 310, the RX UE110b may start a timer to monitor the effectiveness of HARQ feedback. In one embodiment, the timer may be started when the RX UE110b receives a sidelink transmission. If HARQ feedback is sent to the TX UE110a using the primary PSFCH resource, the RX UE110b may stop the timer. In another embodiment, the timer may be started when it is detected that the primary PSFCH resource is unavailable. The timer may be configured to have a duration of S slots, which are set / pre-configured in the RX UE110b or set by the base station to which the TX UE110a or RX UE110b is connected. The parameter S may have values ​​of 2, 4, 8, 16, 32, or other values.

[0059] In operation 312, if RX UE110b determines a secondary PSFCH resource for a given sidelink transmission, RX UE110b can detect whether another UE is reserving the slot where the secondary PSFCH resource is located, using the same PSFCH mapping as the secondary PSFCH resource determined by RX UE110b. If the answer is "Y (yes)", RX UE110b may refrain from sending HARQ feedback using the secondary PSFCH resource in operation 314. Otherwise, the procedure proceeds to operation 316.

[0060] In operation 316, RX UE110b may detect whether TX UE110a has reserved a resource in the slot where the secondary PSFCH resource is located for a new transmission to RX UE110b. If not, RX UE110b may refrain from transmitting HARQ feedback using the secondary PSFCH resource.

[0061] If TX UE110a reserves the resources in the slot where the secondary PSFCH resource is located for a new transmission to RX UE110b, and no other UE reserves the resources in that slot, RX UE110b may attempt to send and retransmit HARQ feedback based on the determined secondary PSFCH resource until the timer expires. If RX UE110b fails to send HARQ feedback before the timer expires, RX UE110b may abandon the HARQ feedback and flush the HARQ buffer.

[0062] Figure 12 is a schematic block diagram of the apparatus 500 according to an exemplary embodiment of the present disclosure. The apparatus 500 may be implemented as the TX UE110a and / or RX UE110b described above.

[0063] Referring to Figure 12, the device 500 may include one or more processors 511, one or more memories 512, and one or more transceivers 513 interconnected via one or more buses 514. One or more buses 514 may be an address bus, a data bus, or a control bus, and may include any interconnection mechanism such as a series of wires on a motherboard or integrated circuit, fiber, optical, or other optical communication equipment. Each of the one or more transceivers 513 may include a receiver and a transmitter connected to one or more antennas 516. The device 500 can wirelessly communicate with network equipment or terminal equipment via one or more antennas 516. One or more memories 512 may contain computer program code 515. One or more memories 512 and computer program code 515 may be configured, when executed by one or more processors 511, to cause the device 500 to perform operations related to TX UE110a and / or operations related to RX UE110b, as described above.

[0064] The one or more processors 511 described above may be of any suitable type appropriate for a local technology network and may include one or more general-purpose processors, special-purpose processors, microprocessors, digital signal processors (DSPs), processor-based multicore processor architectures, and dedicated processors such as those developed based on field-programmable gate arrays (FPGAs) and application-specific integrated circuits (ASICs). The one or more processors 511 may be configured to control and cooperate with other elements of the UE / network device to perform the procedures described above.

[0065] One or more memories 512 may include at least one storage medium of various forms, such as volatile memory and / or non-volatile memory. Volatile memory includes, but is not limited to, random access memory (RAM) or cache. Non-volatile memory includes, but is not limited to, read-only memory (ROM), hard disks, flash memory, and the like. Furthermore, one or more memories 512 may include, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any combination thereof.

[0066] Some exemplary embodiments further provide computer program code or instructions that, when executed by one or more processors, can cause a device or apparatus to perform the steps described above. The computer program code for performing the steps of the exemplary embodiments can be written in any combination of one or more programming languages. The computer program code may be provided to one or more processors or controllers of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the program code is executed by the processor or controller, a particular function / operation is performed in a flowchart and / or block diagram. The program code may run entirely on a machine, partially on a machine, as a standalone software package, partially on a machine, partially on a remote machine, or entirely on a remote machine or server.

[0067] Some exemplary embodiments further provide computer program products or computer-readable media having computer program code or instructions stored therein. A computer-readable medium may be any tangible medium that contains or can store a program for use by or in connection with an instruction execution system, apparatus, or device. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, semiconductor systems, apparatus, or devices, or any suitable combination thereof. More specific examples of machine-readable storage media include electrical connections having one or more wires, portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM, or flash® memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0068] It will be understood that the blocks in the drawing may be implemented in various ways, including software, hardware, firmware, or any combination thereof. In some embodiments, one or more blocks may be implemented using software and / or firmware, for example, machine-executable instructions stored on a storage medium. In addition to, or instead of, machine-executable instructions, some or all of the blocks in the drawing may be implemented at least partially by one or more hardware logic components. For example, but not limited to, exemplary types of hardware logic components that can be used include field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific general-purpose integrated circuits (ASSPs), systems on a chip (SOCs), and complex-programmable logic devices (CPLDs).

[0069] Furthermore, although the operations are described in a specific order, this should not be interpreted as requiring that such operations be performed in a specific order or sequentially, or that all illustrated operations be performed, in order to achieve the desired result. In certain circumstances, multitasking and parallel processing are preferred. Similarly, although some specific implementation details are included in the above discussion, these should not be interpreted as limiting the scope of this disclosure, but rather as descriptions of features specific to a particular embodiment. Certain features described in the context of a separate embodiment may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately or in any suitable subcombination in multiple embodiments.

[0070] Although this invention is described in language specific to structural features and / or method operations, it should be understood that the invention as defined in the appended claims is not limited to the specific features or operations described above. Rather, the specific features and operations described above are disclosed as examples of implementing the claims.

[0071] Certain abbreviations found in this specification and / or in the figures are defined as follows: ACK (Affirmative Response) CAPC Channel Access Priority Class CCA Clear Channel Evaluation COT Channel Occupancy Time CSI Channel Status Information CW Contention Window HARQ Hybrid Automated Resend Request LBT Listen Before Talk NACK Negative Response PSCCH Physical Sidelink Control Channel PSFCH (Physical Sidelink Feedback Channel) PSSCH Physical Sidelink Shared Channel PRB (Physical Resource Block) RRC (Radio Resource Control) RX UE Receiving User Equipment SCI Sidelink Control Information SL-U Sidelink Unlicensed TX UE Transmitting User Equipment

Claims

1. At least one processor, A memory containing computer program code, wherein the at least one memory and the computer program code are provided to the device by the at least one processor, Receiving sidelink transmissions from user devices, To determine the Hybrid Automatic Retransmission Request (HARQ) feedback regarding the aforementioned sidelink transmission, Determining that the primary resource for sending the HARQ feedback is unavailable, Determining a secondary resource for transmitting the HARQ feedback, At least one memory, configured to execute, Equipped with, Determining that the primary resource for transmitting the HARQ feedback is available means Perform a channel evaluation procedure to evaluate the availability of the channel for transmitting the HARQ feedback. Includes, The Clear Channel Evaluation procedure includes the Listen Before Talk (LBT) channel access procedure. Device.

2. Determining a secondary resource for transmitting the HARQ feedback is, Determining the secondary resource based at least in part on the notification of the secondary resource received from the user device, The apparatus according to claim 1, including the following:

3. The apparatus according to claim 2, wherein the notification of the secondary resource indicates a slot and / or physical sidelink feedback channel opportunity of the secondary resource.

4. The at least one memory and the computer program code are provided to the device by the at least one processor, When the notification of the secondary resource indicates multiple slots and / or multiple physical side link feedback channel opportunities, select a slot and / or physical side link feedback channel opportunity from the multiple slots and / or multiple physical side link feedback channel opportunities based on a first predetermined rule. The apparatus according to claim 3, further configured to perform the following:

5. Determining a secondary resource for transmitting the HARQ feedback is, Determining the secondary resources based at least in part on the second prescribed rule, The apparatus according to claim 1, including the following:

6. The apparatus according to claim 5, wherein the second predetermined rule determines the slot of the secondary resource based on the location and number of one or more unavailable slots between a first channel occupancy time shared by the user equipment to receive the sidelink transmission and a subsequent second channel occupancy time shared by the user equipment.

7. The at least one memory and the computer program code are provided to the device by the at least one processor, To detect whether other user devices have reserved a resource in the slot where the secondary resource is located using the same physical side-link feedback channel resource mapping as the secondary resource, If the other user device reserves the resource in the slot where the secondary resource is located, the transmission of the HARQ feedback using the secondary resource will be refrained from. The apparatus according to claim 5, further configured to perform the following:

8. The at least one memory and the computer program code are provided to the device by the at least one processor, The user device detects whether it has reserved a resource in the slot where the secondary resource is located for additional sidelink transmission to the device, When the user device reserves the secondary resource in the slot where the secondary resource is located, the HARQ feedback is transmitted using the secondary resource. The apparatus according to claim 5, further configured to perform the following:

9. The apparatus according to claim 1, wherein the secondary resource depends on the primary resource in the frequency domain and / or code domain.

10. The apparatus according to claim 1, wherein the secondary resource is orthogonal to another primary resource for another user device receiving the sidelink transmission, or to a primary resource corresponding to another sidelink transmission received by the apparatus from another user device.

11. The at least one memory and the computer program code are provided to the device by the at least one processor, The timer is started at the timing of the primary resource, or at the timing of the sidelink transmission, Until the timer expires, the system attempts to send and retransmit the HARQ feedback based on the secondary resource, The apparatus according to claim 1, further configured to perform the following:

12. At least one processor, A memory containing computer program code, wherein the at least one memory and the computer program code are provided to the device by the at least one processor, Sending a side link to the user's device, Determining that the primary resource for receiving Hybrid Automatic Retransmission Request (HARQ) feedback regarding the aforementioned sidelink transmission is unavailable, Determining a secondary resource for receiving the HARQ feedback, At least one memory, configured to execute, Equipped with, Determining that a primary resource is available for receiving HARQ feedback regarding the aforementioned sidelink transmission means that Perform a channel evaluation procedure to evaluate the availability of the channel for receiving the HARQ feedback. Includes, The Clear Channel Evaluation procedure includes the Listen Before Talk (LBT) channel access procedure. Device.

13. The at least one memory and the computer program code are provided to the device by the at least one processor, Sending a notification of the secondary resource to the user device, The apparatus according to claim 12, further configured to perform the following:

14. The apparatus according to claim 13, wherein the notification of the secondary resource indicates a slot and / or physical sidelink feedback channel opportunity of the secondary resource.

15. The apparatus according to claim 14, wherein the notification of the secondary resource includes a plurality of slots and / or a plurality of physical sidelink feedback channel opportunities, and the slots and / or physical sidelink feedback channel opportunities of the secondary resource are shown in the notification based on a first predetermined rule.

16. The apparatus according to claim 13, wherein the notification of the secondary resource indicates whether the user device needs to send the HARQ feedback.

17. The apparatus according to claim 13, wherein the notification of the secondary resource is transmitted over a physical sidelink control channel and / or a physical sidelink sharing channel.

18. Sidelink communication method, In the device, receiving sidelink transmissions from user equipment, To determine the Hybrid Automatic Retransmission Request (HARQ) feedback regarding the aforementioned sidelink transmission, Determining that the primary resource for sending the HARQ feedback is unavailable, Determining a secondary resource for transmitting the HARQ feedback, Includes, Determining that the primary resource for transmitting the HARQ feedback is available means Perform a channel evaluation procedure to evaluate the availability of the channel for transmitting the HARQ feedback. Includes, The Clear Channel Evaluation procedure includes the Listen Before Talk (LBT) channel access procedure. method.

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