Link recovery and sidelink beamforming

Abstract

The present disclosure provides methods, systems, and devices for implementing BFR, SL-RS for BFD, radio link monitoring, or frequency assisted beam failure recovery, etc.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 933,824, filed November 11, 2019, entitled “LINK RECOVERY AND SIDELINK BEAMFORMING,” the contents of which are incorporated herein by reference. Background Technology

[0003] Long Term Evolution (LTE) Vehicle-to-Everything (V2X) Transport Modes: Rel-14 introduces two new V2X communication modes (Mode 3 and Mode 4) specifically designed for vehicle-to-vehicle (V2V) communication. In Mode 3, the cellular network selects and manages the radio resources used by vehicles for their direct V2V communication. In Mode 4, the V2X User Equipment (UE) autonomously selects the radio resources used for its direct V2V communication. LTE V2X Mode 4 can operate without cellular coverage and is therefore considered the baseline V2V mode, as security applications cannot depend on the availability of cellular coverage. Mode 4 includes a distributed scheduling scheme for vehicles to select their radio resources and includes support for distributed congestion control. In LTE V2X, only broadcast V2X communication is supported.

[0004] New Radio (NR) V2X Transmission Modes: Similar to LTE V2X transmission modes 3 and 4, NR supports two modes: Mode 1 and Mode 2 for Rel-16 V2X transmission. In NR V2X, sidelink resource allocation modes 1 and 2 are supported. In Mode 1, the network (e.g., gNB) schedules sidelink resources for V2X UEs for sidelink transmission. In Mode 2, the V2X UE determines its sidelink resources for sidelink transmission within the sidelink resources configured by the base station or within pre-configured sidelink resources. Mode 1 allows the network (e.g., gNB) to allocate sidelink resources via the Uu interface for both dedicated sidelink carriers and shared licensed carriers between the Uu and the sidelink. Resources for sidelink transmission can be dynamically allocated or pre-configured by Radio Resource Control (RRC) or based on activation and deactivation. Section 9 "Sidelink" of 3GPP TS 36.211 V15.5.0 and Section 14 "UE procedures related to Sidelink" of 3GPP TS 36.213 V15.5.0 are incorporated in full by reference.

[0005] This background information is provided to disclose information that the applicant believes may be relevant to the present invention. It is not necessary to acknowledge, nor should it be construed, that any of the foregoing information constitutes prior art to the present invention. SUMMARY

[0006] Disclosed herein are methods, systems, and devices associated with BFR, SL-RS for BFD, wireless link monitoring, or frequency-assisted beam failure recovery, among other examples. In a first example, there can be methods or systems for implementing a beam failure recovery (BFR) procedure over a sidelink (SL). The systems can include: 1) BFR at a transmitting UE (e.g., TX UE = source UE); or 2) BFR at a receiving UE (e.g., RX UE = target UE).

[0007] In a second example, there can be methods or systems for implementing a sidelink reference signal (SL-RS) over a sidelink for beam failure detection (BFD) and candidate beam indication (CBI). The systems or methods can include: 1) beam failure detection (BFD) or candidate beam identification (CBI) based on a sidelink channel state information reference signal (SL-CSI-RS); 2) sidelink demodulation reference signal (SL-DMRS) for a physical sidelink control channel (PSCCH) based on BFD or CBI; or 3) SL-DMRS for a physical sidelink shared channel (PSSCH) based on BFD or CBI.

[0008] In a third example, there can be methods or systems for implementing a wireless link monitoring procedure over a sidelink. The systems or methods can include: 1) wireless link monitoring based on a semi-persistent scheduling (SPS) SL-CSI-RS; or 2) wireless link monitoring based on an aperiodic (AP) SL-CSI-RS.

[0009] In a fourth example, there can be methods or systems for implementing a frequency range 1 (FR1) assisted or a frequency range 2 (FR2) assisted beam failure recovery.

[0010] The purpose of the summary is to introduce a selection of concepts in a simplified form as a prelude to the more detailed description that is to follow. Neither the summary nor the following detailed description are intended to identify key or essential features of the claimed subject matter, nor are they intended to limit the scope of the claimed subject matter. Additionally, the claimed subject matter is not limited to solving any or all of the disadvantages with any part of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0011] A more detailed understanding can be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0012] Figure 1 An example method for performing BFR at a TX / source UE is illustrated;

[0013] Figure 2 An exemplary method for performing BFR at the RX / Target UE is shown;

[0014] Figure 3 An exemplary method for FR2 BFR assisted by FR1 is shown;

[0015] Figure 4 An exemplary method for BFR based on monitoring RX UE SL-CSI-RS reporting is shown;

[0016] Figure 5A An exemplary link recovery method for SL in case of data transmission is shown;

[0017] Figure 5B An exemplary link recovery method for SL in case of no data transmission due to congestion for a certain period is shown;

[0018] Figure 6 An exemplary resource selection for a beam sweep burst by TX UE and RX UE that can monitor beams is shown;

[0019] Figure 7 An exemplary (TX) UE behavior for link recovery on SL is shown;

[0020] Figure 8A An exemplary burst structure for SCS=60, PSCCH and PSSCH is shown;

[0021] Figure 8B An exemplary burst structure for SCS=60, PSCCH, PSSCH and SL-CSI-RS is shown;

[0022] Figure 8C An exemplary burst structure for SCS=60, PSCCH and SL-CSI-RS is shown;

[0023] Figure 8D An exemplary burst structure for SCS=60, PSCCH reserved repetition slots is shown;

[0024] Figure 9 An exemplary reserved acknowledgement / negative acknowledgement (ACK / NACK) resource as implicit beam indication is shown;

[0025] Figure 10 An exemplary reserved ACK / NACK resource as explicit beam indication and carried on a single SCI or first stage SCI is shown;

[0026] Figure 11 An exemplary method in which a UE can perform BFD, CBI or BFRQ is shown;

[0027] Figure 12A Example indication of SL beam failure detection (BFD) and candidate beam identification (CBI) shown: Data with SL-CSI-RS transmitted for BFD+CBI;

[0028] Figure 12B Example indication of SL beam failure detection (BFD) and candidate beam identification (CBI) shown: No BFD report found within monitoring window / monitoring interval;

[0029] Figure 13 Example (RX) UE behavior shown for link recovery on SL using Option 1 approach;

[0030] Figure 14 Example reserved BFRQ resource shown as explicit beam indication and carried on a single SCI or first stage SCI;

[0031] Figure 15 Example method shown where UE can transmit a beam sweep burst;

[0032] Figure 16 Example (RX) UE behavior shown for link recovery on SL using Option 2 approach;

[0033] Figure 17 Example SL-failureDetectionResource mapping relationship shown with multiple SLs;

[0034] Figure 18A Example SL-CSI-RS antenna port shown mapped to REs and applied with spatial filter (F): UE uses multiple panels;

[0035] Figure 18B Example SL-CSI-RS antenna port shown mapped to REs and applied with spatial filter (F): UE uses single panel to transmit SL-CSI-RS in a slot;

[0036] Figure 19 Example aperiodic SL-CSI-RS shown that can be transmitted periodically via a “zero-padded” or “zero-power” PSSCH supporting SPS SL;

[0037] Figure 20 Example AP SL-CSI-RS and “zero-padded” or “zero-power” PUSCH shown;

[0038] Figure 21 Example vehicle platooning in V2X communication shown;

[0039] Figure 22 An exemplary method for a TX / source UE to perform BFR via FR1 to assist FR2 is shown;

[0040] Figure 23 An exemplary method for a RX / target UE to perform BFR via FR1 to assist FR2 is shown;

[0041] Figure 24A An exemplary FR1-assisted FR2 BFR is shown when the TX UE and RX UE are communicating on FR2 or FR1 simultaneously: the TX UE performs BFR;

[0042] Figure 24B An exemplary FR1-assisted FR2 BFR is shown when the TX UE and RX UE are communicating on FR2 or FR1 simultaneously: the RX UE performs BFR;

[0043] Figure 25 An exemplary TX UE indicating a new beam switch for the next transmission opportunity is shown;

[0044] Figure 26 An exemplary display (e.g., graphical user interface) that can be generated based on the methods, systems, and devices of link recovery and sidelink beamforming is shown;

[0045] Figure 27A An exemplary communication system is shown;

[0046] Figure 27B An exemplary system including a RAN and a core network is shown;

[0047] Figure 27C An exemplary system including a RAN and a core network is shown;

[0048] Figure 27D An exemplary system including a RAN and a core network is shown;

[0049] Figure 27E Another exemplary communication system is shown;

[0050] Figure 27F is a block diagram of an exemplary apparatus or device, such as a WTRU; and

[0051] Figure 27G is a block diagram of an exemplary computing system. DETAILED DESCRIPTION

[0052] In NR, the BFR procedure can include the following steps: Step 1: Beam failure detection (BFD) by measuring configured periodic CSI-RS or SSB based on hypothetical block error rate (BLER); Step 2: Identifying candidate beams by measuring configured periodic channel state information reference signal (CSI-RS) or synchronization signal block (SSB) based on L1-RSRP; Step 3: Transmitting beam failure recovery request (BFRQ) after detecting beam failure based on contention-free random access (CFRA) or contention-based random access (CBRA) in Rel-15 and physical uplink shared channel (PUSCH) in Rel-16; and Step 4: Monitoring gNB response.

[0053] In LTE V2X, it only supports broadcast. Regarding the first issue, in NR V2X, it has been agreed to support unicast, groupcast and broadcast. Therefore, link monitoring can be needed to ensure that the beamformed channel is above or below a certain quality to prevent radio link failure. In NR Uu (e.g., wireless interface between UE and gNB), CSI-RS or SSB is used to derive hypothetical PDCCH BLER to determine link quality. In NR Uu, a UE can monitor link quality (e.g., beamformed PDCCH quality) based on SSB, periodic CSI-RS, or both. Sidelink synchronization signal (SLSS) can be used to provide sidelink synchronization information (SLI) and SyncRef to other SL UEs. Moreover, SLSS can not be SL UE specific, e.g., SL SS is broadcasted to neighboring UEs rather than to a specific UE. For example, some V2X UEs do not need to transmit SLSS when they have SyncRef. Therefore, it is difficult to identify which V2X UE transmitted the SLSS. In NR, it has been agreed that SL-CSI-RS cannot be transmitted alone, e.g., when there is triggered V2X communication, SL-CSI-RS is transmitted. Moreover, the network can stop SLSS transmission for a UE. Therefore, regarding SL communication, it cannot be guaranteed that both SLSS and SL-CSI-RS have periodic transmission.

[0054] Moreover, in NR Uu, a UE can compare the quality to a threshold Q out,LR When the radio link quality is worse than the threshold Q out,LR The physical layer will indicate to the upper layer. When based on RSRP, the measured CSI-RS or SSB quality is worse than the threshold Q in,LRBetter yet, the UE indicates a new candidate beam. In NRUu, the beamformed link quality can be periodically indicated to the upper layer because there are beam training reference signals such as CSI-RS and SS that can be periodically transmitted. However, in V2X SL communication, it can not be feasible to transmit periodic sidelink CSI-RS (SL-CSI-RS) and SL SS because SL-CSI-RS cannot be transmitted independently, for example, only when there is a triggering V2X communication and the V2X UE transmits SL SS under the limiting conditions such as explicitly configured by the network, or in the case where the V2X UE is in coverage and its RSRP is below a threshold. Therefore, the lack of periodic RS for performing beam failure detection is the first problem that should be addressed.

[0055] The UE can detect beam failure and can identify candidate beams based on periodic RS such as SSB and periodic CSI-RS in the NR link recovery procedure. Regarding the second problem, in the NR Rel-15 link recovery procedure, the UE transmits a beam failure recovery request (BFR) to the gNB using contention-free random access (CFRA) or contention-based random access (CBRA); and the UE monitors the response from the gNB assuming it utilizes the indicated candidate beam for QCL. However, in NR V2X communication, the random access procedure is not supported. In Rel-16, the preferred candidate beam can be reported via PUCCH or PUSCH methods.

[0056] The link recovery procedure over SL is the second problem that needs to be addressed without periodic reference signal transmission over Uu. The link recovery procedure over SL should be addressed to indicate the preferred candidate beam or reference signal and how to report BFR over SL without using the random access channel as Uu.

[0057] Link recovery procedure over SL: To establish a unicast connection over sidelink, a discovery announcement procedure should be completed where a UE (e.g., source UE) can transmit a discovery message (e.g., “I am here” or “who is there?”) to neighboring or proximate UEs via PSSCH or dedicated physical sidelink discovery channel. When a unicast connection is established after the discovery procedure has been completed between the announcing UE and the responding UE, the UE can start transmitting unicast data over sidelink to other UEs. Thereafter, the UE transmits sidelink data as a TX or source UE and the UE monitors and receives the transmitted data as a RX or target UE as described herein. Over SL, the UE can need to monitor multiple SL transmissions simultaneously whether the UE is the same SyncRef UE or not.

[0058] At the NR Uu interface, the beam failure recovery (BFR) or link recovery procedure can involve the following steps: e.g., beam failure detection (BFD), candidate beam identification (CBI), beam failure request (BFRQ), and beam recovery response (BFR) from the network. However, with respect to SL communication, the NR Uu BFR procedure can not be applicable to SL BFR. For example, on SL, due to the aperiodic transmission nature of SL communication, the transmission of periodic beamformed reference signals such as CSI-RS or SS can not be guaranteed. In addition, over a period of time, the receiving UE can move away or far from the transmitting UE. These situations can result in no SL data transmission for beam or link monitoring on sidelink during the reporting or monitoring period. In this scenario, the UE can decide whether it needs to maintain the link with respect to SL communication. In other words, if there is nothing for the transmitting UE to transmit due to data traffic congestion during the reporting or monitoring period, likewise, there can be no data reception at the receiving UE. In this case, the receiving UE cannot perform BFD, find candidate beams, and trigger a beam failure request (BFRQ). Therefore, a link recovery procedure on SL should be considered when the RX UE has nothing to measure and thus cannot report or indicate to the upper layer.

[0059] The beam failure recovery (BFR) disclosed herein can be supported for beamformed SL communication with the following options for BFR: 1) BFR performed at the TX / source UE; 2) BFR performed at the RX / target UE; or 3) FR1-aided FR2 BFR.

[0060] BFR performed at the TX / source UE: If the TX UE performs beam failure recovery, there can be no need to trigger a beam failure request (BFRQ) because the Uu link recovery procedure and link recovery procedure can be simplified. In this case, the TX UE can be responsible for beam switching and management to maintain the radio link quality. There can be no need for a BFRQ in the TX UE. The following discloses options for performing BFR at the TX / source UE side to omit the BFRQ.

[0061] For the first option, there can be a BFR based on HARQ-A / N feedback. Figure 1 At step 201, after establishing a link with the RX UE, the TX UE can start a timer T1 (e.g., in ms, slots, or subframes). The timer T1 can be equal to the duration of the intended transmission from the TX UE to the Rx UE (e.g., 100 ms). For example, the TX UE can monitor one or more unicast transmissions on SL, i = 1, … L SL This L SL Depends on the capability of the UE. Each unicast link can be associated with an independent timer T1.

[0062] At step 202, the TX UE (e.g., PHY layer or MAC layer) can count the number of consecutive (e.g., cumulative) NACK feedbacks or no feedbacks (e.g., DTX) received from the RX UE. If the number of consecutive NACKs or no feedbacks exceeds a (pre)configured threshold N, the TX UE physical layer can report a beam failure indication to the upper layer to indicate a link failure (e.g., failure on link i). The threshold can be (pre)configured by RRC for mode 1 or by PC5 RRC for mode 2. The RRC or PC5 RRC can provide a list of thresholds (or multiple levels of thresholds) for different QoS or priority requirements for the TX UE to select the threshold. For example, it can be based on the priority of the intended transmission, the number of transmissions, or network congestion, etc. Another approach is that no feedback and NACK feedback can be treated differently, such as (1) having different thresholds for NACK feedback and no feedback, respectively; (2) giving a larger weight (e.g., higher score) for no feedback case than NACK case. The sidelink can determine no feedback case and NACK case separately, since no feedback case can be considered as a worse or bad channel condition than NACK case. For sidelink, when the RX UE fails to decode the control information on PSCCH, the RX UE has no feedback (e.g., NACK) to the TX UE, or still can decode PSSCH and transmit feedback (e.g., NACK or ACK) to the TX UE.

[0063] At step 203, after one or more beam failures are received from the physical layer at upper layers, and if no ACK indication (including no feedback) is received from the physical layer before the expiry of timer T1, the TX UE can attempt to reserve resources in the resource pool to transmit a beam sweeping burst. In mode 2, the TX UE can reserve the resource pool based on sensing (e.g., long-term or short-term sensing) to transmit a beam sweeping burst, or the TX UE can transmit a beam sweeping burst on a certain resource in the resource pool. The beam sweeping burst is a combination of several blocks, where for example PSCCH and PSSCH will be transmitted in each block. The content of PSSCH can be based on retransmission of previous data. The number of blocks in a burst can depend on numerology, for example on FR2 with subcarrier spacing (SCS) equal to 120 KHz, the maximum number of blocks per burst is 32. The HARQ-ACK / NACK resources reserved in the resource pool can be for RX UE to feedback or acknowledge, so the TX UE can know which preferred beam to use for link recovery. In mode 1, the TX UE can send a request to reserve resources to the network, or use the configured grant resources to transmit the beam sweeping burst and HARQ-ACK / NACK feedback resources. More details of the beam sweeping burst and feedback resources are set forth herein. After the beam sweeping burst transmission, the TX UE can start timer T2 and the behavior as in Table 1 below.

[0064] Table 1

[0065]

[0066] At step 204, if no sidelink failure occurs, or no beam failure indication is sent to upper layers after the expiry of timer T1, the TX UE upper layers (e.g., MAC) can determine that when the TX UE still has data to transmit to the RX UE (e.g., based on sidelink buffer status report), the T1 timer is restarted or reset to continue this SL, or if there is no intention to send data to the RX UE, the TX UE can decide to terminate this SL and perform a re-discovery procedure.

[0067] For the second option, Figure 2), there can be a BFR based on detecting "no feedback" when HARQ-A / N is enabled. Step 211 can be the same as step 201. At step 212, the TX UE can count the number of (e.g., consecutive or cumulative) no feedback (e.g., no ACK feedback and no NACK feedback in between) from the RX UE that exceeds a certain (pre)configured threshold N', and then the TX UE physical layer can report a beam failure indication to upper layer to indicate this link (e.g., link i) failure. When the RX UE fails to decode PSCCH successfully, it will result in no feedback (e.g., NACK) to the TX UE. This threshold can be (pre)configured by RRC for mode 1 or (pre)configured by PC5 RRC for mode 2.

[0068] Step 213 can be the same as step 203.

[0069] Step 214 can be the same as step 204.

[0070] Regarding the method of Figure 1 and Figure 2 , there can be a case that if the number of measured samples is too low, it can affect the beam failure detection. This impact is because the threshold setting can be incorrect, thus affecting the announcement of beam failure detection. The measured samples can be defined as the number of collected feedback (e.g., number of NACK or no feedback) in one period. However, if the number of measured samples in one period is too low, this can be equivalent to the case that the number of PSSCH transmissions in the same period is low. Therefore, the following discloses ways that can solve this problem. In a first way, the TX UE can force to transmit "dummy data" (or "zero padding" data) to the RX UE to increase the number of measured samples in one period. The detailed implementation of "zero padding" data please refer to "zero padding" PSSCH in this document. In a second way, the TX UE can use a multi-level threshold to determine whether to announce beam failure. The multi-level threshold can depend on the number of transmitted PSCCH and PSSCH, for example, the number of expected feedback from the RX UE if HARQ feedback is enabled.

[0071] For a third option ( Figure 3 ), there can be a BFR based on monitoring the feedback channel (e.g., measuring the PSFCH channel quality). Step 221 can be the same as step 201.

[0072] At step 222, the TX UE can monitor the feedback channel PSFCH quality. This measurement can be based on a (pre-)configured threshold of a (pre-)defined metric (e.g., L1-RSRP, RSRQ, SINR, or hypothetical BLER) below which the TX UE physical layer can report a beam failure indication to upper layers to indicate this link (e.g., link i) failure. When there is no SL-CSI-RS, RSRP, RSRQ, or hypothetical BLER can be based on other SL reference signals, e.g., SL-DMRS of PSFCH, as performance metrics for determining SL channel quality. For sequence-based PSFCH, e.g., similar to PUCCH-Format-0, RSSI or SINR can be used as performance metrics. The feedback channel PSFCH can share spatial information as PSCCH. If PSFCH is sequence-based, the PSFCH signal (e.g., sequence) can be used for measurement. If PSFCH is SL-DMRS modulated (e.g., SL-DMRS encoded), the SL-DMRS for PSFCH can be used for measurement (e.g., RSRP). The feedback PSFCH can use the following feedback channels: 1) PSFCH for HARQ-ACK / NACK; 2) PSFCH for HARQ-ACK / NACK with CSI; or 3) PSFCH for CSI.

[0073] Monitoring PSFCH quality can be similar to monitoring PSCCH quality from RX UE when PSFCH uses the same spatial information of SL-DMRS as PSCCH. In addition, if TX UE detects “no feedback” from RX UE, TX UE can also count this sample into L1-RSRP SINR or hypothetical BLER computation.

[0074] Step 223 can be the same as step 203.

[0075] Step 224 can be the same as step 203.

[0076] For the fourth option, there can be BFR (beam failure recovery) based on monitoring RX UE SL-CSI-RS reporting. Figure 4 Step 231 can be the same as step 201.

[0077] At step 232, the SL-CSI-RS channel quality can be used to determine if a beam failure occurs. The RX UE can measure the received SL-CSI-RS and report the metric (e.g., L1-RSRP / RSRQ, SINR or hypothetical BLER) to the TX UE. The feedback of SL-CSI-RS reporting can use PSFCH or PSCCH and PSSCH. When the TX UE receives the channel quality report, then the TX UE can decide if there is a beam failure that should be reported to upper layer to indicate this link (e.g., link i) failure. In mode 2, if the feedback report uses the sidelink control channel (e.g., PSCCH) and data channel (e.g., PSSCH) for the RX UE, the feedback resource for the RX UE can be based on the following methods: (1) via channel sensing, the RX UE can reserve or select the resource; or (2) the TX UE can pre-reserve the resource for the RX UE for transmitting the feedback. If the feedback channel is based on dedicated SL data channel, e.g., PFSCH, the TX UE can pre-reserve the resource for the RX UE for the RX UE to transmit the feedback. For SL mode 1, the network can pre-reserve the resource for the RX UE. When the SL-CSI-RS is QCLed with the RX UE PSCCH, the SL-CSI-RS quality can be similar to monitoring the PSCCH quality. If the TX UE cannot detect the RX UE SL-CSI-RS, where there is expected feedback from the RX UE, the TX UE can also count this sample into the L1-RSRP SINR / RSRQ, hypothetical BLER calculation.

[0078] Step 233 can be the same as step 203.

[0079] Step 234 can be the same as step 204.

[0080] Figure 5A And Figure 5B respectively show the timing relationship of the disclosed method for a certain link when there is data transmission, or no data transmission due to congestion. If the TX UE cannot send unicast data to the RX UE during the T1 period due to congestion (e.g., no resource reserved for data transmission during T1), the TX UE can continue running the timer T1, and when the T1 timer expires as shown in Figure 5B “no transmission due to congestion” to the upper layer. In this case, the TX UE can decide whether to maintain this link or perform a re-discovery procedure.

[0081] The TX UE processing of link recovery can have the following advantages compared to the processing at the RX UE. First, the RX UE cannot know the PSCCH transmission from the TX UE when the PSCCH decoding fails. Second, the accurate PSCCH decoding performance can be difficult to measure by a small number of PSCCH receptions. Figure 3 The UE procedures for the disclosed methods are summarized.

[0082] With continued reference to Figure 3 At step 253, a discovery announcement procedure can occur. The discovery announcement procedure can involve UE 241 and UE 242. After the discovery announcement procedure, at UE 241, there can be a start of TX and a start / reset of timer Tl. At step 245, it is determined whether Tl times out. If Tl times out, proceed to step 252, and if Tl does not time out, proceed to step 260. Step 260 can include sending PSCCH+PSSCH to UE 242 or receiving PSFCH ACK / NACK from UE 242. At step 246, UE 241 can determine if there is a link failure. If there is no link failure, proceed to step 245, but if there is a link failure, proceed to step 247 (start timer T2). At step 248, UE 241 performs a TX beam sweep burst. At step 259, more PSCCH+PSSCH can be sent to UE 242 or more PSFCH ACK / NACK can be received from UE 242. At step 249, UE 241 determines whether T2 times out, if so, proceed to step 251. If T2 does not time out, at step 250, it is determined whether the link is recovered. If the link is not recovered, proceed to step 251, and if the link is recovered, proceed to step 245.

[0083] At step 252, it is determined whether to continue communicating with UE 241. If not, at step 253, it is determined whether re-discovery should be performed. If so, proceed to step 254 to perform re-discovery, and if not, at step 255, UE 241 can discard the communication with UE 242.

[0084] With continued reference to Figure 3 At step 257 and step 258, UE 242 can decode the received PSCCH and PSSCH or select a new beam.

[0085] Beam sweep burst: A TX UE (e.g., UE 241) can transmit a beam sweep burst for link recovery. A beam sweep burst consists of multiple beamformed blocks, and a beamformed block can be one NR (SL) slot, multiple SL slots, or one SL slot can contain more than one beamformed block. For example, in one beamformed block, a PSCCH, PSSCH, or SL-CSI-RS can be included. The content of the PSSCH can be based on initial transmission of new data, retransmission of previous data, or dummy data. In one burst, the maximum number of beamformed blocks can depend on numerology. For example, the actual number of beamformed blocks transmitted within one burst period can be (pre)configured for the supported NR numerologies, as shown in Table 2.

[0086] Table 2

[0087]

[0088] This can depend on the TX UE (e.g., UE 241 or WTRU 102a); the TX UE can decide the number of beamformed blocks in one (beam sweep) burst and for link recovery. For example, for 60 kHz SCS, the UE can transmit 1, 2, 4, 8, or 16 beamformed blocks. The UE (e.g., UE 241) can assume that each beamformed block duration can be equal to one slot or mini-slot duration.

[0089] In Mode 2, when the TX UE transmits a data packet at slot n, the TX UE can reserve resources for the next transmission at slot n+k, e.g., at a slot k slots later, or the RX UE can derive the reserved resources for PSSCH transmission. For example, the reserved resource information can be carried via TX SCI for the next transmission reserved by the TX UE. Thus, the RX UE can transmit to the TX UE in the next reserved resource with RX beams (i.e., the TX UE and RX UE have established beam correspondence). The TX UE can also reselect resources for transmission resources based on the number of TX blocks and HARQ-ACK / NACK feedback (e.g., the TX UE can reserve new resources for both data and feedback resources of the RX UE). In addition, the RX UE should monitor SL resources for transmissions from other UEs unless the RX UE knows the reserved resources (e.g., slots) from a specific TX UE (e.g., from previous transmissions from the TX UE). As Figure 2As shown, the RX UE monitors for data received from the TX UE at time slot n with the corresponding beam, and the TX UE also reserves the next transmission opportunity after k time slots. Thus, the RX UE expects to receive data after k time slots using the same (corresponding) RX beam. However, if a beam failure is detected / occurs before the next transmission reserved by the TX UE, the TX UE can reselect new resources to transmit a beam sweep burst for link recovery. In this way, via a (semi-)omni beam pattern, the RX UE can attempt to receive the beam sweep burst and try to decode it (e.g., the beam sweep burst includes multiple beamformed blocks). When a block is successfully detected (e.g., PSCCH and PSSCH are successfully decoded), then the RX UE identifies the new beam for link recovery.

[0090] In Mode 1, the TX UE can send a request to the network (e.g., NodeB 140a, 140b, or 140c) to reserve and select resources for the beam sweep burst transmission. Similar to the case of Mode 2, the newly selected resources, as well as the dynamically scheduled SL resources, will not overlap with the resources reserved by the previous transmission.

[0091] In each time slot, the beam sweep block can consist of PSCCH and PSSCH, PSCCH and PSSCH and SL-CSI-RS, or PSCCH and SL-CSI-RS. When the subcarrier spacing is equal to 60 kHz for (a) PSCCH and PSSCH, (b) PSCCH, PSSCH and SL-CSI-RS, and (c) PSCCH and SL-CSI-RS, respectively, Figure 4 A- Figure 4 D shows an exemplary burst with 4 blocks for 60 kHz SCS and 8 blocks for 120 kHz SCS. If the SL-CSI-RS and PSCCH are transmitted in the same time slot or within a time duration (e.g., multiple time slots), the RX UE can assume that the SL-CSI-RS and SL-DMRS PSCCH are QCLed. In addition, the TX UE can decide the spatial information for each beamformed block in the beam sweep burst. If multiple time slots are reserved for PSCCH retransmission to enhance reception (the repetition can be signaled by PSCCH, SL-MAC-CE, or SL-RRC signaling), the RX UE can assume that the time slots reserved for PSCCH retransmission are QCLed (e.g., use the same spatial information), as shown in Figure 8D For example, in Figure 8D two time slots are reserved for retransmission.

[0092] To avoid unnecessary beam switching between PSCCH and PSSCH for SL transmission, RX UE can assume PSCCH and PSSCH are QCLed in the same slot (e.g., SL-DMRS for PSCCH and PSSCH have Doppler shift, Doppler spread, average delay, delay spread, spatial Rx parameter) (or we suggest PSSCH and PSCCH use the same beam / space information). The last symbol in the slot is reserved for the gap symbol. RX UE’s feedback can be based on implicit or explicit method, as described herein.

[0093] Implicit beam ID feedback: Figure 9 An exemplary reserved ACK / NACK resource as implicit beam indication is shown. We propose the following methods for ACK / NACK feedback SL resource can be used: first, TX UE pre-reserve SL resource for feedback resource; second, RX UE can derive ACK / NACK feedback resource from the received PSCCH or PSSCH. It is disclosed herein that each transport block can be mapped to a beam (or multiple beams), and each transport block (e.g., a segment of transport block duration is a segment of SL slot duration or multiple slots) can be associated / mapped with SL resource for feedback. Once RX UE is able to successfully detect and decode one of the beamformed slots, TX UE is able to receive ACK / NACK from RX UE in the reserved SL. Thus, in this way, it is possible to avoid transmitting beam (or spatial information) identifier in SCI, PSSCH, or both. Furthermore, RX UE can determine the preferred transmit beam. For example, if second stage SCI is applied, the second stage SCI indicates the reserved ACK / NACK resource for RX UE response. For example, in this case, the first stage SCI only carries target ID, and the second stage SCI carries the reserved ACK / NACK resource. In the beam sweeping block, it can be assumed that PSCCH and PSCCH are QCLed. Since each reserved ACK / NACK (PSFCH) resource should not overlap in the same slot, TX UE is able to distinguish which block is successfully decoded by RX UE, so beam correspondence can be done without block identifier. For example, in Figure 8A- Figure 8DIn this example, two beamformed slots are transmitted and two separate ACK / NACK (PSFCH) are reserved. The first stage SCI indicates the resources reserved for PSFCH. In this example, the RX UE successfully decodes the second beamformed slot and the TX UE expects to receive the ACK / NACK after k slots of the second beamformed transmission slot. Thus, there is no uncertainty in terms of PSFCH reception and the TX UE can distinguish which PSFCH comes from which beamformed transmission slot. In this way, there is no need to embed beam or block identifiers in the SCI or data. Beam correspondence can be quickly established and the link recovered. This feedback can be based on the following: 1) the RX UE can feedback a single HARQ-ACK / NACK and transmit the feedback channel (PSFCH) to the TX UE, where the RX UE can select the best link quality for feedback; or 2) the RX UE can feedback multiple HARQ-ACK / NACK and transmit the feedback channel (PSFCH) at the corresponding reserved feedback resources.

[0094] Explicit beam ID feedback: Figure 10 An exemplary reserved ACK / NACK resource as explicit beam indication and carried on a single SCI or first stage SCI is shown. As disclosed, a single or multiple resources for ACK / NACK feedback can be reserved by the TX UE or the reserved resources for ACK / NACK feedback can be derived from the received PSSCH. Furthermore, each block ID can be mapped to a PSFCH sequence ID. If the PSFCH for HARQ-ACK / NACK is based on a sequence design, the sequence takes a Zadoff-Chu sequence. It is also defined herein that the sequence is a base sequence for HARQ-ACK / NACK as PSFCH, where 0 < n < N is the length of the PSFCH for HARQ-ACK / NACK sequence. The base sequence can be defined as a cyclic extension of a Zadoff-Chu sequence where N SC is the length of the Zadoff-Chu sequence, which is given by the largest prime number such that N SC < N. When N > 36, it is assumed that and N < 36, it is assumed that where q is the q-th Zadoff-Chu sequence. Note that the value of q is derived from the values of u and v. The HARQ-ACK / NACK information (such as {0, 1} or {00, 01, 10, 11}) can be mapped to different (cyclic shifted) values of a for root ID. For an exemplary design, via assigning different or distinct q-th roots, we can construct the PSFCH(s) for HARQ-ACK / NACK. Thus, multiple PSFCHs for HARQ-ACK / NACK sequences can be multiplexed at the same reserved resource in the resource pool. For example, if a beam sweeping burst transmits 4 blocks, and the block IDs are set as b(l) = 0, b(2) = 1, b(3) = 2, and b(4) = 3, respectively, each block ID can be mapped to a root ID, e.g., (b(m) + 10) mod N SC (Note: N SC is prime). In this way, the mapping of PSFCH sequences can be derived from the block ID, which can be signaled by SCI. The block ID can be carried by SCI, and the HARQ-ACK / NACK resource is reserved by the first stage SCI. As shown in FIG. 3B, SL resources are reserved for HARQ-ACK / NACK feedback of multiple PSSCHs. The PSFCH for HARQ-ACK / NACK can be based on sequence design. For example, a set of orthogonal sequences can be mapped to a set of block IDs. The mapping of sequence ID to block ID can be standardized. The RX UE can feedback a single or multiple PSFCHs. In one example, the RX UE can feedback a single HARQ-ACK / NACK, and at the reserved resource, transmit the corresponding PSFCH (pair of block ID link and PSFCH sequence ID) to the TX UE. The RX UE can select the best link quality for feedback. In one example, the RX UE can feedback multiple HARQ-ACK / NACKs, and at the reserved feedback resource, transmit multiple feedback channels (PSFCHs). Figure 10

[0095] ​Performing BFR at the RX / Target UE: If the RX UE performs beam fault recovery, in this case, the RX UE can be responsible for monitoring the link quality from the TX UE. The RX UE can use SL-RS (e.g., SL-DMRS for PSCCH or PSSCH) sent from the TX UE to perform hypothetical BLER measurements and determine if a beam fault exists. Furthermore, the RX UE can monitor multiple SL-CSI-RS or other SL-RS (e.g., SL-DMRS for PSCCH, SL-DMRS for PSSCH, etc.) to identify candidate beams for beam correspondence recovery. When a beam fault occurs, the RX UE can trigger a beam fault request (BFRQ) to the TX UE. Performing BFR at the RX / Target UE side is not required: SL HARQ feedback must be enabled.

[0096] This article discloses the options for performing BFR on the RX / target side.

[0097] Regarding the first option, the RX UE (e.g., UE 242) can perform BFD, CBI, or BFRQ. Figure 11 As shown, in step 281, the RX UE can start timer T1 (e.g., in milliseconds) after the discovery announcement / procedure of unicast link i is completed. The RX UE can monitor multiple unicasts of SL, for example, i = 1, ... L. SL L SL The maximum value depends on the capability of the RX UE. Each unicast link can be associated with an independent timer T1.

[0098] In step 282, while timer T1 has not yet expired, the RX UE can calculate the hypothetical BLER based on SL-RS. For example, SL-RS can be based on: (1) SL-DMRS for PSCCH; (2) SL-SL-CSI-RS with PSCCH QCL; or (3) SL-DMRS for PSSCH with or without QCL with SL-DMRS for PSCCH. Further details of SL-RS are described herein. If the hypothetical BLER of the measured SL-RS is lower than a certain (pre)configured Q... out,SL Then the UE physical layer can report a beam fault indication to the upper layer and indicate that this link (e.g., link i) is faulty. Meanwhile, when the measured SL-CSI-RS L1-RSRP exceeds a certain (pre)configured Q... in,SLAt this time, the RX UE can monitor the SL-CSI-RS for candidate beam identification. Once the candidate beam is identified, the RX UE can report the following information to the upper layer: 1) only the SL-CSI-RS configuration index; or 2) the SL-CSI-RS configuration index and the L1-RSRP / RSRQ or SINR measurement results corresponding to the upper layer.

[0099] At step 283, upon receiving one or more beam failure indications to the upper layer when the timer T1 has not expired, the RX UE can trigger a beam failure request (BFRQ). The RX UE can use the identified candidate SL-CSI-RS resource configuration index q new provided by the upper layer to transmit over the PSSCH or PSFCH channel. The TX UE can determine which beam to use for this BFRQ reception: (1) the set of candidate beams in the set new may be associated with dedicated resources reserved by the TX UE, and the RX UE maps the selected q to the corresponding resources reserved by the TX UE. Note that the set of monitored candidate beams is configured by the TX UE. More details for the transmission resource for BFRQ over PSFCH are elaborated herein. In the second example, the TX UE can determine which beam to use for this BFRQ reception based on: (2) the resource selected by the RX UE to transmit the BFRQ. If the TX UE transmits the PSCCH and PSSCH using the spatial information provided by q new , the RX UE can stop the timer T2 and the physical layer continues the reception since the wireless link has been recovered, otherwise, when the timer T2 expires but T1 does not, the RX UE can retransmit the BFRQ to the TX UE.

[0100] At step 284, if no beam failure indication is sent to the upper layer after the timer T1 expires, the RX UE can decide to terminate this SL.

[0101] Figure 12A Figure 12B The indication of the sidelink BFD, CBI, or BFRQ triggering mechanism is shown. In each BFD / CBI reporting occasion, there is an associated monitoring window (or periodic interval T1) during which the hypothetical BLER of the monitored SL-RS (e.g., SL-DMRS for PSCCH) is below a (pre-)configured threshold Q out,SLIf the RX UE indicates BFD to upper layer. In addition, upon request from upper layer, if there is a SL-RS identified as candidate beam, e.g., when the SL link quality (e.g., L1-RSRP, SIRN or hypothetical BLER) is greater than or better than (pre-)configured Q in,SL then the candidate SL-RS can be reported to upper layer. Otherwise, if no BFD is detected within the associated monitoring window / period T1, the RX UE can indicate to upper layer that there is no BFD report. Thus, based on the timer T1 operation, periodic indication of beam failure can be provided, e.g., if the TX UE resets the timer T1 after the timer expires, the UE can periodically monitor the link. Note that periodically monitoring the link does not mean that the RX UE will expect to receive data packets for this link periodically. Figure 13 The UE procedure for performing BFR at the RX UE side is summarized.

[0102] With continued reference to Figure 13 At step 261, a discovery announcement procedure can occur. The discovery announcement procedure can involve the UE 241 and the UE 242. After the discovery announcement procedure, at step 266, at the UE 242, there can be a start of RX and a start of timer T1, and at the UE 241, there can be a start of TX. At step 268, it is determined whether T1 expires. If T1 expires, proceed to step 276 (communication between the UEs is dropped), and if T1 does not expire, proceed to step 269. Step 263 can include receiving PSCCH+PSSCH from the UE 242 or receiving PSCCH+PSSCH+SL-CSI-RS from the UE 242. At step 269, the UE 242 can decode one or more PSSCHs or PSCCHs. At step 270, the UE 242 can perform link monitoring using BFD or CBI. At step 271, the UE 242 can determine link failure. If there is no link failure, proceed to step 267, but if there is a link failure, proceed to step 272 (trigger BFRQ and start T2 timer). At step 264, the UE 242 can transmit a BFRQ. At step 265, in response to the BFRQ of step 264, the UE 242 can monitor PSCCH+PSSCH. At step 274, the UE 242 determines whether data is received from the UE 241. If data is received, proceed to step 275, and if no data is received, proceed to step 273 (monitor PSCCH+PSSCH). At step 275, if it is determined that T2 has expired, proceed to step 267. If it is determined that T2 expires, proceed to step 272.

[0103] Transmission resources for sidelink beam failure recovery request (SL BFRQ) can use the following options. Regarding a first SL BFRQ option, transmission resources can be reserved by the TX UE. In one example, the TX UE reserves resources for the RX to transmit a BFRQ with PSCCH and PSSCH. In another example, the TX UE reserves PSFCH to feedback a BFRQ to the TX UE. Regarding a second SL BFRQ option, the RX UE reserves SL BFRQ resources.

[0104] Referring to the use of the first SL BFRQ option, when there is a SL-CSI-RS transmitted by the TX UE (e.g., UE 241), transmission resources can be reserved. The resources reserved by the (TX UE) can be based on the SL-CSI-RS resources configured in the set The RX UE can use these reserved resources to transmit a SL BFRQ with PSCCH and PSFCH, where it is associated with the (new) candidate beam identified in the set For example, there can be four SL-CSI-RS configurations, n, in the set and the TX UE can reserve four different resources (e.g., resource IDs 1, 2, 3, and 4). In this example, each reserved resource can be mapped one-to-one to a SL-CSI-RS configured in the set Once the RX UE identifies a candidate SL-CSI-RS (e.g., ID = 3 corresponding to a particular beam), the RX UE can select the corresponding resource to transmit a BFRQ. Thus, the TX UE can perform the appropriate receive beam for BFRQ reception.

[0105] Another approach is to design PSFCH for BFRQ indication via explicit (beam) indication. As disclosed, a single or multiple feedback resources for BFRQ feedback can be reserved by the TX UE, or the RX UE can derive from the PSSCH received from the TX UE. Each SL-CS-RS ID configured in the set can be mapped to a PSFCH sequence ID for BFRQ. If the PSFCH for BFRQ is designed based on a sequence and the sequence is a Zadoff-Chu sequence, we also define a sequence as the PSFCH for BFRQ base sequence, where N is the length of the PSFCH for BFRQ sequence. The base sequence is defined as a cyclic extension of the Zadoff-Chu sequence where N SC is the length of the Zadoff-Chu sequence, which is given by the largest prime number such that N SCN < 36, assume and N < 36, assume where q is the q-th Zadoff-Chu sequence. Note that the value of q is derived from the values of u and v. For an exemplary design, via assigning different or distinct q-th roots, we can construct the PSFCH(s) for the BFRQ sequence. Thus, multiple PSFCHs for the BFRQ sequence can be multiplexed at the same reserved resource, or can be transmitted at different resources in the resource pool. For example, if the set is configured with four SL-CSI-RSs, and each SL-CSI-RS ID is set as s(l) = 0, s(2) = 1, s(3) = 2, and s(4) = 3, respectively, each block ID can be mapped to a root ID, e.g., s(m) mod N SC (Note: N SC is a prime number). In this way, the mapping of PSFCH sequence ID to SL-CSI-RS configured in the set may have a one-to-one mapping relationship. As shown in Figure 14 , two reserved resources are reserved for two SL-CSI-RSs. The RX UE can feedback a single or multiple PSFCHs, and the TX UE can perform appropriate receive beams for BFRQ reception. In one example, the RX UE can feedback a single BFRQ, and at the reserved resource, the corresponding PSFCH (the pair of SL-CSI-RS ID link and PSFCH sequence ID) is transmitted to the TX UE. The RX UE can select the best link quality identified in the set for feedback. In one example, the RX UE can feedback multiple BFRQs, and at the reserved feedback resource, multiple feedback channels (PSFCHs) are transmitted.

[0106] If the TX UE reserves SL resources in the SL resource pool, the TX UE can apply beam direction / spatial filter to detect or receive with the RX UE selected or identified beam. If the TX UE does not reserve transmission resources or the feature for reserving BFRQ resources is not supported, the RX UE can reserve the transmission resource based on sensing, and then set a higher priority in the SCI. When the RX UE reserves the resource in the resource pool based on sensing, in this case, the BFRQ can also be used with beam sweeping as disclosed herein, e.g., the BFRQ can be transmitted with a beam sweeping burst as the following Option 2 method.

[0107] Reference the second SL BFRQ option Figure 15The RX UE can transmit the beam sweeping burst. Step 291: Same as step 281 in the first option for RX UE.

[0108] At step 292, when the timer T1 has not expired, the RX UE calculates the hypothetical BLER based on the SL-RS. For example, the SL-RS can be based on the SL-DMRS for PSCCH, or the SL-CSI-RS QCLed with PSCCH. If the hypothetical BLER of the measured SL-RS is below a certain (pre)configured Q out,SL , the UE physical layer can report a beam failure indication to upper layer and indicate this link (e.g., link i) failure.

[0109] At step 293, after the upper layer receives one or more beam failure indications when the timer T1 has not expired, the RX UE can attempt to reserve resources in the resource pool to transmit the beam sweeping burst. Note that each beam sweeping block in the burst can or can not be transmitted with a BFRQ indication. If supported, the BFRQ can be carried in SCI or PSSCH. In mode 2, the RX UE can reserve resources in the resource pool to transmit the beam sweeping burst, which can be based on sensing (e.g., long-term or short-term sensing), or the RX UE can transmit the beam sweeping burst on (SPS) resources in the resource pool, or the TX UE can inform the RX UE of the transmission resources. In mode 1, the RX UE can send a request to the network for reserving resources, or use the configured grant resources to transmit the beam sweeping burst with or without HARQ-ACK / NACK feedback resources. The details of the beam sweeping burst can refer to the beam sweeping burst associated with the above at the TX / source UE performing BFR. If the RX UE physical layer successfully decodes the data from the TX UE before the timer T1 expires, it sends an indication to the upper layer, the RX UE can reset the timer T1, and the physical layer continues transmission (retransmission) with the TX UE, as the wireless link has been recovered.

[0110] At step 294, if there is no beam failure indication, the RX UE can determine to continue monitoring or terminate this SLi after the timer T1 expires, which is sent to the upper layer.

[0111] If the RX UE reserves resources in the resource pool, the TX UE is able to detect this beam sweeping burst, as the TX UE continues to sense all resources in the resource pool when there is no data to send. If the TX UE is informed of the reserved resources for the RX to transmit the beam sweeping burst, the TX UE is able to detect the beam sweeping burst transmitted by the RX UE.

[0112] Figure 16A UE procedure for performing BFR at the RX UE side without using BFRQ is summarized.

[0113] Sidelink beam failure detection (BFD) or candidate beam identification (CBI): In the NR Uu detection beam failure (BFD) procedure, the UE evaluates the radio link quality according to the periodic CSI-RS resource configuration or SS / PBCH block in the failureDetectionResource set and the PDCCH reception monitored by the UE. The periodic CSI-RS resource configuration or SS / PBCH block in the failureDetectionResource set may be explicitly indicated by the upper layer or implicitly indicated by the TCI state.

[0114] The radio link quality (e.g., SL BFD) on SL communication can be used to indicate the status to the upper layer. After the discovery announcement between the announcing UE and the responding UE has been established, the UE monitors the radio link quality on SL.

[0115] Based on the sidelink reference signal (SL-RS), the source UE can perform BFD measurement. In NR V2X, SL-RS cannot be transmitted alone, e.g., it shall be transmitted with the sidelink data channel PSSCH. If the numerology supported by the SL communication supports multi-beam operation, the UE can be explicitly configured with a set of resource indices by a corresponding set of upper layer parameters SL-failureDetectionResource per each monitored unicast SL. If the SL-failureDetectionResource is not explicitly configured by the upper layer, the RX UE can use the SL-DMRS for PSCCH, the SL-DMRS for PSSCH (if QCLed with the SL-DMRS for PSCCH), or the configured SL-CSI-RS QCLed with PSCCH in the search space (or in the CORESET).

[0116] The following explicit configuration method for SL BFD operation is disclosed:

[0117] - The UE can be explicitly configured with one or more SL-failureDetectionResources set and candidateBeamRSList for SL radio link quality measurement to support beam failure detection (BFD) with single or multiple UE SL transmission, respectively, where N represents the number of simultaneously monitored sidelinks (from source UE to target UE).

[0118] - The UE is not expected to monitor more than N max unicast more items.

[0119] - And each set of k = 1…N can be independently associated with multiple resource sets of SL-RS, and each resource set contains multiple configured SL-RS resource indices. The SL-failureDetectionResources can be a set of non-periodic NZP SL-CSI-RS resources.

[0120] - The UE is expected to monitor a set of includes up to M (e.g., two) RS resource indices. The UE is expected that in each set of , a single resource (single port or multiple ports) has one SL-RS resource index.

[0121] - According to a threshold Q out,LR of resource configuration sets relative to N links The UE’s physical layer evaluates the radio link quality.

[0122] - For each set of The UE only evaluates the radio link quality according to the aperiodic SL-CSI-RS resource configuration that is quasi co-located with the SL-DMRS of the PSCCH reception that the UE monitors.

[0123] - The upper layer provides a set of candidateBeamRSList for candidate beam identification for SL k.

[0124] This paper shows the SL-failureDetectionResource set between different UEs mapping relationship. In Figure 17 , it can be assumed that the total number of multi-unicast SL is N. Each wireless link is associated with one or more transmission panels. This paper discloses that each SL-failureDetectionResource set of link k can be independently provided by the upper layer, and each can be associated with an SL-RS resource configuration index.

[0125] If no SL-failureDetectionResources are provided to the RX UE (e.g., implicit configuration for BFD), the RX UE can determine the SL-failureDetectionResources set for the kth link includes aperiodic CSI-RS resource configuration index with the same value as the RS index in the RS set indicated by the TCI state for the RX UE to monitor SL-DMRS for PSCCH or PSCCH and PSSCH. In this case, when upper layer does not provide any SL-failureDetectionResources to the UE, the SL-DMRS for the kth link can be indicated via the TCI-state. Each set of SL-failureDetectionResources is associated with to indicate the corresponding aperiodic SL-CSI-RS.

[0126] SL reference signals for BFD and CBI: SL-failureDetectionResources set SL-RS configuration of

[0127] If SL-RS is explicitly configured by upper layer, the RX UE is expected to monitor one or more of the following SL-RS for evaluating beam failure detection (BFD):

[0128] - SL-CSI-RS QCLed with PSCCH

[0129] - SL-CSI-RS QCLed with PSSCH

[0130] - SL-DMRS for PSCCH

[0131] - SL-DMRS for PSSCH

[0132] - SLSS

[0133] If SL-RS is explicitly configured by upper layer, the RX UE can monitor one or more of the following SL-RS for evaluating BFD:

[0134] - SL-DMRS for PSCCH

[0135] - SL-DMRS for PSSCH

[0136] - SLSS

[0137] For candidate beam identification, candidateBeamRSList set SL-RS configuration of

[0138] SL-CSI-RS: A UE can be configured with one or several SL-CSI-RS resource sets, referred to as NZP-SL-CSI-RSResourceSet. Each such resource set includes one or several configured SL-CSI-RS resources, each of which can be mapped to a single or multiple SL-CSI-RS antenna ports. The transmission of all SL-CSI-RS within an aperiodic resource set is jointly triggered by the SCI. The configuration of SL-CSI-RS can consider the following configuration options:

[0139] - Option 1: For each transmission occasion, all SL-CSI-RS resources on a SL-CSI-RS resource set can be applied with the same TX spatial filter. This can enable TX beam sweeping across different SL-CSI-RS resource sets.

[0140] - Option 2: For each transmission occasion, different SL-CSI-RS resources in the same SL-CSI-RS resource set can be applied with different TX spatial filters. This can enable TX beam sweeping across SL-CSI-RS resources in the resource set.

[0141] In practice, a SL-CSI-RS is associated with a specific beam. The RX UE measures the set of signals within one or multiple resource sets and reports the results to the TX UE as input for beam management (e.g., SL-CSI-RS can be used for BM), candidate beam identification, or beam failure monitoring. A SL-CSI-RS can be configured to cover the full SL bandwidth of the bandwidth part or only a part of it. In the latter case, the SL-CSI-RS bandwidth and the frequency domain starting position are provided as part of the SL-CSI-RS configuration. Within one instance of a SL-CSI-RS transmission occasion, SL-CSI-RS resources from a SL-CSI-RS resource set can be allocated.

[0142] Within the configured SL-CSI-RS bandwidth, a SL-CSI-RS can be configured for transmission in every resource block, referred to as SL-CSI-RS density equal to one. A single-port SL-CSI-RS occupies a single resource element within a block, which corresponds to one resource block in the frequency domain and one slot in the time domain. A SL-CSI-RS can be configured with a single-port CSI-RS with density d (e.g., d = 3), in which case the SL-CSI-RS occupies three subcarriers within each resource block.

[0143] SL-CSI-RS can be configured for aperiodic transmission. In case of aperiodic SL-CSI-RS (e.g., no periodicity is configured), the SL-CSI-RS is transmitted with PSSCH. Note: PSSCH is always associated with PSCCH or SL-CSI-RS is only transmitted with PSCCH. Instead, the RX UE is explicitly informed about (“triggered”) each SL-CSI-RS transmission instant by signaling in the single-stage SCI or the second-stage SCI. The RX UE can assume that the transmission of the configured SL-CSI-RS does not collide with the SL-DMRS of the PSSCH transmission and the SL SS block.

[0144] The mapping of a SL-CSI-RS to one such panel is an example from the spatial information (filter) F of the set of physical antennas to the SL-CSI-RS antenna port. Then, the transmission from different panels would correspond to different spatial filters F as shown in Figure 18A and Figure 18B In practice, depending on the UE capability, the UE can be equipped with a single panel or multiple panels for SL-CSI-RS transmission. To support different spatial transmissions of SL-CSI-RS in a slot, different SL-CSI-RS can be separated by at least one or multiple OFDM symbols in a slot. Thus, the TX UE can perform beam switching to apply with different spatial filters. If the UE is equipped with multiple panels, the UE can transmit multiple SL-CSI-RS with different spatial filters simultaneously or the multiple panels transmit on the same antenna port. In Figure 18A two different panels and spatial filters are used to transmit two SL-CSI-RS simultaneously, while in Figure 18B a single panel with two different spatial filters is used to transmit two SL-CSI-RS at different OFDM symbols. The SL-CSI-RS transmission is at the last M (e.g., 6) symbols in a slot or with a time pattern, e.g., such as at symbol l = 5, 7, 9, 11 or l = 9, 10, 11, 12 positions in a slot.

[0145] A multi-port SL-CSI-RS can be seen as multiple orthogonally transmitted individual antenna port CSI-RSs that share the total set of resource elements allocated for the configured multi-port SL-CSI-RS. A multi-port SL-CSI-RS corresponds to a set of antenna ports and the SL-CSI-RS can be used to probe the channel corresponding to these antenna ports.

[0146] This sharing can be based on one or more of the following:

[0147] - Code domain sharing (CDM, e.g. orthogonal cover codes), implying that different antenna port SL-CSI-RSs are transmitted on the same set of resource elements, where separation is achieved by modulating the SL-CSI-RSs with different orthogonal patterns;

[0148] - Frequency domain sharing (FDM), implying that different antenna port SL-CSI-RSs are transmitted on different subcarriers within an OFDM symbol;

[0149] - Time domain sharing (TDM), implying that different antenna port SL-CSI-RSs are transmitted in different OFDM symbols within a time slot.

[0150] In frequency domain with CDM over two adjacent subcarriers (2x CDM), code domain sharing between two antenna port SL-CSI-RSs is allowed. In frequency and time domain with CDM over two adjacent subcarriers and four adjacent OFDM symbols (8x CDM), code domain sharing between up to eight antenna port SL-CSI-RSs is allowed.

[0151] The UE can assume that the reference signal sequence r(m) for the SL-CSI-RS is defined by

[0152]

[0153] The SL-CSI-RS can be constructed from one gold sequence; the gold sequence g(n) can be specified as follows:

[0154] g(n) = (x1(n+N c )+x2(n+N c )) mod 2

[0155] x1(n+31) = (x1(n+3) + x1(n)) mod 2

[0156] x2(n+31) = (x2(n+3) + x2(n+2) + x2(n+1) + x2(n)) mod 2

[0157] where N c is a constant (e.g. = 1600) and the operator "+" is modulo-2 addition. x1 and x2 are polynomials of length 31. The pseudo-random sequence generator for the SL CSI-S should be initialized as follows.

[0158]

[0159] where is the slot number within the SL radio frame, l is the OFDM symbol number within the slot, and is the SL-CSI-RS sequence ID, where and M ≥ 10.

[0160] SL-DMRS for PSCCH: One advantage of measuring PSCCH is that it can not involve additional signal detection complexity in systems with sensing and occasional no channel access for TX / source UEs. RX UEs can monitor PSSCH and PSCCH anyway and when PSCCH is successfully decoded, it can reliably provide the measurement result instance. Another advantage can be that the measured interference will more accurately reflect PSCCH interference. Therefore, when there is no explicitly configured set of SL-failureDetectionResources or SL-CSI-RS is not transmitted with PSSCH, RX / target UEs can assume SL-DMRS for PSCCH as the default SL-RS for the assumed BLER computation for BFD. Furthermore, to support using SL-CSI-RS for assumed BLER computation, QCL and TCI state concepts can be considered for SL communication to support beam switching with SL-CSI-RS.

[0161] Pseudo-SCI: If a TX / source UE does not transmit any regular PSCCH and PSSCH for scheduling in a period, the UE can transmit a special PSCCH with “pseudo-SCI” that does not schedule / indicate anything. Instead, the pseudo-SCI will be transmitted over PSCCH with the purpose to provide RX UEs with a link monitoring occasion. RX UEs can be configured with a timer T1, where after the period, the RX UE PHY evaluates the link quality to determine whether to send BFD or no indication to upper layers (e.g., MAC). For example, the period is typically set to the BFD-RS periodicity as in Uu. On SL, this period (timer T1) can be RRC or PC5 RRC configurable or based on a (pre-)configured fixed value in the specification, e.g., 10 ms.

[0162] SL-DMRS for PSSCH: If SL-DMRS for PSCCH is supported for SL-RS, when SL-DMRS for PSCCH and SL-DMRS for PUSCH are QCLed, RX UEs can jointly derive the assumed BLER using SL-DMRS for PSSCH. In this case, when there is no explicitly configured set of SL-failureDetectionResources or SL-CSI-RS is not transmitted with PSSCH, SL-DMRS for PSCCH can always be associated with SL-DMRS for PSSCH for BFD assumed BLER computation.

[0163] “zero-padding” PSSCH or “zero-power” PSSCH: If the TX / source UE does not transmit any regular PSSCH for scheduling within a period (e.g., timer T1), the UE can transmit a “zero-padding” or “zero-power” dedicated PSSCH. In contrast, for the case of zero-padding PSSCH, dummy data will be transmitted over the PSSCH, the purpose of which is to provide a link monitoring occasion to the RX UE via the use of both SL-DMRS for PSCCH and PSSCH. For the case of zero-power PSSCH, the transmission of PSSCH is set to zero. In addition, SL-CSI-RS can be transmitted with PSSCH for the RX UE to monitor the link quality, ensuring sufficient samples for the hypothetical BLER computation. In this case, the transmission of SL-CSI-RS with PSSCH can be indicated by a single SCI or a form of second-stage SCI. The RX UE can be configured with a timer T1, where after this period, the RX UE evaluates the link quality to determine whether to send a BFD or no indication to the upper layer (e.g., MAC). For example, this period can be set to the BFD-RS periodicity as in Uu. On SL, this period (timer T1) can be RRC or PC5 RRC configurable or based on a (pre-)configured fixed value in the specification, e.g., 10 ms.

[0164] In addition, given the more intermittent nature of SL, if semi-persistent (SPS) transmission for SL transmission is supported, SL can be (de)activated, e.g., based on semi-persistent. Thus, SL-CSI-RS can be configured to (or for) support SPS SL, which supports the use of dedicated PSSCH, where even when there is no expected data to be sent at the same time, a “zero-padding” or “zero-power” PSSCH is on SL. In this way, SL-CSI-RS can be transmitted periodically, and similar to periodic SL-CSI-RS. As shown in FIG. 6, it shows that via support of “zero-padding” PSSCH for SPS SL transmission, aperiodic SL-CSI-RS can be transmitted periodically. In the presence of transmission occasion / chance but no actual data to be transmitted, then the upper layer (e.g., MAC) can decide to transmit “zero-padding” PSSCH and SL-CSI-RS. In this way, via “zero-padding” PSSCH, a similar periodic transmission of SL-CSI-RS can be achieved. Figure 19

[0165] ​In addition, the UE can activate / deactivate the BFD function of SL (e.g., semi-persistent (SP) or aperiodic (AP) sidelink) even if the corresponding signal (e.g., PSCCH, PSSCH, etc.) continues or does not continue to transmit. The activation / deactivation of the BFD function can be indicated by SCI or MAC-CE.

[0166] A “zero-padding” or “zero-power” PSSCH can also be coordinated with an aperiodic SL-CSI-RS transmission to support a similar periodic transmission when the TX UE can reserve the next transmission opportunity. This is because the TX UE can reserve the next PSCCH and PSSCH transmission opportunity (e.g., slot) by SCI. However, when the PSSCH transmission opportunity is reserved, the TX UE can not have actual data to transmit. Therefore, the upper layer (e.g., MAC) can transmit a “zero-padding” PSSCH and SL-CSI-RS. In this way, a similar periodic transmission of SL-CSI-RS can be achieved via a “zero-padding” or “zero-power” PUSCH with an aperiodic SL-CSI-RS. As shown in FIG. 6, the SCI can reserve the next transmission opportunity at the first transmission. However, there is no actual data to be transmitted at the reserved transmission, so the upper layer (e.g., MAC) can transmit a “zero-padding” PUSCH and SL-CSI-RS. Figure 20

[0167] In NR V2X, the SL synchronization signal (SLSS) is the only periodic signal. However, the SS / PSBCH needs to be transmitted at the SL synchronization raster, and the resources for SLSS transmission are based on one or more pre-defined resources, or the resources are scheduled by the network. In addition, the SLSS carries the SL SSID and MIB information. Furthermore, the SL MIB does not carry any target ID and source ID information. Therefore, the RX UE cannot generally distinguish who is the transmitter of the SLSS, so the sidelink synchronization signal can not be suitable for radio link monitoring unless the transmitter identifier can be identified by the neighboring RX UE or the group RX UE.

[0168] In a vehicle platooning scenario, there are multiple ways of communication: the first way is the platoon leader (PL) to platoon members (PM), e.g., PL to PM, and the platoon member (PM) to platoon member (PM), e.g., PM to PM. The PL to PM communication is point-to-multipoint (e.g., groupcast), and the PM to PM is point-to-point communication (unicast). Figure 21 PL to PM and PM to PM V2X communication is depicted.

[0169] ​In a platooning scenario, for PM, the PL can broadcast SLSS as SyncRef for PM. Thus, if SLSS carries PL identity, the PM can use periodic SLSS as SL-RS to perform BFD and CBI for link recovery between PL and PM. In this case, the SL-failureDetectionResources set and the candidateBeamRSList set can be configured SLSS. The PL identifier (ID) can be signaled via the following options:

[0170] - SL SSID, e.g., one SSID 0, …, M (e.g., M = 672) in NR SL-SSID is assigned as PL SSID. For example, SSID = 2 as PL SSID.

[0171] - SL PBCH, e.g., main bit information is transmitted through PSBCH. Regarding SL-PBCH content, a single bit indicating whether the transmitter is a PL can be introduced.

[0172] SL-DMRS or sequence of feedback channel PSFCH for measurement: When HARQ-ACK / NACK or SL-CSI-RS reporting is enabled, the TX UE can use SL-DMRS of feedback channel (e.g., PSFCH based on modulation) or sequence of feedback channel (e.g., PSFCH based on sequence) for measurement. It is disclosed herein that PSFCH can be used for the following purposes:

[0173] - HARQ-ACK / NACK only

[0174] - SL CSI only

[0175] - HARQ-ACK / NACK + SL CSI

[0176] - BFRQ indication

[0177] PSFCH can be designed by the following methods:

[0178] - based on sequence: In this case, HARQ-ACK / NACK information is based on sequence. PSFCH can occupy more than 2 symbols in one slot. If Zadoff-Chu sequence is used for this design, for example, the following can be defined as sequence where 0≤n≤N is the length of PSFCH for HARQ-ACK / NACK sequence. The HARQ-ACK / NACK information (such as {0,1} or {00,01,10,11}) can be mapped to different (cyclic shift) values of a of the root sequence derived by parameters u and v.

[0179] - UCI with SL-DMRS: In this case, UCI will use BPSK or QPSK for modulation order. PSFCH can occupy more than 2 symbols in a slot.

[0180] For example, only HARQ-ACK / NACK, BFRQ indication can be based on sequence-based PSFCH. For SL CSI and HARQ-ACK / NACK + SL CSI, they can be based on UCI with DMRS-based PSFCH.

[0181] FR1-assisted FR2 BFR: In some implementations, a UE can use both SL FR1 and FR2 bands for SL communication. For example, a UE can use FR1 as a primary carrier for SL communication and FR2 as an auxiliary band. Thus, when FR2 is blocked, the UE can still use FR1 to communicate with each other. The discovery procedure (discovery announcement) between UE 241 and UE 242 can be done within FR1 band and with the support of SL communication in FR2 band. After the discovery announcement procedure between UE 241 and UE 242, UE 241 and UE 242 can establish SL communication in the following cases.

[0182] For case 1, UE 241 and UE 242 are communicating on FR1 or FR2 at the same time. For example, if UE 241 and UE 242 have SL on FR2, but the link is failed due to beam failure. In this case, UE 241 and UE 242 can switch to the previously configured or default link on FR1 to recover the FR2 link.

[0183] For case 2, UE 241 and UE 242 have exactly (at least) two links, for example, one on FR1 and the other on FR2. In this case, if one of the links is failed, for example, the link on FR2 is failed due to beam failure, the UE can decide whether to recover the link on FR2. If the UE wants to recover the link on FR2, the UE can exchange signaling via the link on FR1 to recover the FR2 link if the link on FR1 is still available.

[0184] For the above cases, when the SL communication on FR2 is failed due to beam failure, we disclose the following methods to use FR1 to assist FR2 when BFR occurs:

[0185] - TX / Source UE performs BFR via FR1 to assist FR2 ( Figure 22 ).

[0186] o Step 301 : TX UE can start a timer T1 (in ms) when establishing link with RX UE on FR2.

[0187] o Step 302: TX UE performs beam failure detection based on the disclosed metrics (e.g. based on HARQ-ACK / NACK, no feedback or PSFCH channel quality, details can be referred to in Option 1, 2 or 3 and in the section of BFR performed by TX / Source UE in the second step).

[0188] o Step 303: The upper layer of the TX UE can trigger SL transmission to the RX UE on FR1 and indicate that beam failure occurs if no ACK indication is received from the physical layer before the expiry of the timer T1. In this case, the TX UE and RX UE can switch to the link on FR1 that was previously configured for recovering the FR2 link. The TX UE can send a beam sweeping burst to the RX UE. As mentioned above, the beam sweeping burst can consist of multiple beamformed blocks and each block duration is one slot, e.g., for SCS = 15 KHz, only one block in one burst needs to be transmitted. Since the RX UE is constantly monitoring SL on FR1 in mode 2, the RX UE can receive the BF indication without the need for the TX UE to reserve resources based on sensing. For mode 1, the network can dynamically schedule / reserve resources on FR1 for the TX UE to transmit the beam sweeping burst, thus the RX UE can monitor the data transmitted from the TX UE on FR1. When the TX UE and RX UE have (at least) two links, in this case, if one of the links fails, e.g., the link on FR2 fails due to beam failure, the UE can decide whether to recover the link on FR2. If the UE wants to recover the link on FR2, the UE can exchange signaling via the link on FR1 to recover the FR2 link if the link on FR1 is still available. For case 2 where the TX UE can try to recover the FR2 link, the TX UE can not need to transmit a beam sweeping burst since the link on FR1 is still working. Thus, the TX UE only transmits (retransmits) data (e.g., PSCCH and PSSCH) that carries the BF indication and / or retransmission data. The PSCCH and PSSCH can be applied with the beam corresponding to the RX UE. When the BF occurs on FR2, the transmitted content can include which component carrier (CC) (e.g., FR2) index, resource pool index (on FR2) with or without new beam index (e.g., one or more SL-CSI-RS). In addition, on FR2, retransmission and feedback resources can be included. Once the RX UE receives the BFR indication on FR1, the RX UE can monitor the selected resources on FR2 to perform BFR and transmit feedback back to the TX UE on FR2. If the TX UE physical layer receives one ACK from the RX / target UE on FR2 before the expiry of the timer T1, the TX UE sends an indication to the upper layer, the TX UE can reset the timer T1 and the physical layer continues transmission (retransmission) with the RX UE on FR2 since the wireless link on FR2 has been recovered.

[0189] o Step 304: If there is no beam failure indication sent to the upper layer on FR2 after the expiry of the timer T1, the TX UE determines to continue monitoring or terminate this SL.

[0190] - RX / Target UE performs BFR via FR1 to assist FR2 Figure 23 )

[0191] o Step 311: When link is established with TX UE on FR2, RX UE can start a timer T1 (in ms).

[0192] o Step 312: Based on the disclosed metrics (e.g. based on SL-RS, details can be referred to the section of BFR performed by RX / Target UE in the second step in Option 1 or 2), RX UE performs beam failure detection.

[0193] o Step 313: Upon receiving one or more beam failure indications at upper layer before timer T1 expires, RX UE:

[0194] ■may trigger a beam failure request (BFRQ) and send BFRQ indication to TX UE on frequency band (FR1). The transmission content of BFRQ can include component carrier (FR2) failure index, resource pool index (on FR2) with or without reporting candidate beam (i.e. without SL-CSI-RS or other SL-RS). If candidate beam is included in the content of BFRQ indication, RX UE can send the identified and provided by upper layer candidate SL-CSI-RS resource configuration index q newFor SL recovery, we propose two options: for option 1, the TX UE and RX UE can switch to a link on FR1 that was previously configured for recovering the FR2 link. In case 1, the RX UE can transmit a beam sweep burst on FR1 to try to recover the link on FR2. For option 2, the RX UE can only need to transmit a beam sweep block on FR1 instead of using beam sweeping when the link on FR1 is still available. For case 2, if the link on FR1 is not available (i.e., the link on FR1 also fails), similar to case 1, the RX UE can transmit a beam sweep burst on FR1 to try to recover the link on FR2. The TX UE can constantly monitor SL on FR1 in mode 2, thus, the TX UE can receive the BF indication without the RX UE reserving resources in advance; or the RX UE can inform the TX UE to reserve resources when the BF event occurs. For mode 1, the network can reserve resources on FR1 for the TX UE to monitor the occurred BF when there is a request from the RX UE. The transmission content of the BFRQ can include which component carrier (FR2) index, resource pool index (on FR2), and (if a new beam can be identified) new beam index (e.g., one or more SL-CSI-RS / other SL-RS). If the TX UE sends PSCCH and PSSCH to the RX / destination UE on FR2, and the RX UE can successfully decode the PSCCH and PSSCH before the timer T2 and T1 expire, the RX UE can stop the timer T2, and the physical layer continues to receive from the TX UE on FR2, otherwise, when the timer T2 expires but T1 does not expire, the RX UE can retransmit the BFRQ to the TX UE on FR1 again.

[0195] o Step 314: If there is no beam failure indication, the RX UE can transmit to the upper layer on FR2 after the timer T1 expires, then the RX UE can make a determination to continue monitoring or terminate this SL.

[0196] Figure 16 The disclosed method of FR1 assisting FR2 for BFR can be summarized. In Figure 24A and Figure 24B , the TX UE and RX UE communicate on FR2 or FR1 at the same time: the TX UE performs BFR Figure 24A ; or the RX UE performs BFR Figure 24B .

[0197] SL beam indication: It is disclosed herein that NR SL can support beam indication for unicast or groupcast. This can imply that a certain PSCCH or PSSCH transmission uses the same transmission beam as a configured sidelink reference signal (e.g., SL-CSI-RS). The beam indication can be based on the configuration and signaling of TCI states on SL. By associating a PSCCH or PSSCH with a certain TCI, each TCI state includes information about a SL-RS (e.g., SL-CSI-RS). Since the TCI state is an indication of the SL-RS associated with the PSCCH or PSSCH, the TCI state can be carried by the 2nd-step SCI. The UE can assume that the SL transmission is done using the same spatial filter as the reference signal associated with this TCI. On SL, a UE can be configured with up to M candidate TCI states. For beam indication of PSCCH, a subset of M configured candidate states is assigned to each configured CORESET or search space per SL bandwidth part (BWP) by upper layer RRC signaling. The UE can assume that the PSCCH transmission uses the same spatial filter as the reference signal associated with the MAC-indicated TCI. On SL, the PSSCH beam indication can be assumed to be QCLed with the PSCCH when it transmits within a slot.

[0198] To save beam sweeping overhead and RX UE can perform fast beam training (i.e., beam optimization between TX UE and RX UE), we disclose that if a TX UE reserves a next transmission opportunity and the reserved transmission opportunity is Q slots away from the current transmission slot, the TX UE can indicate a beam indication for the reserved transmission opportunity via SCI in this current transmission opportunity. Thus, the RX UE can decide whether to perform fast beam training in the next reserved transmission occasion. In Figure 25 , the TX UE indicates a new beam optimization / training for the next transmission opportunity.

[0199] It is understood that the entity performing one or more steps shown herein (such as, Figure 1- Figure 25 ) can be a logical entity. The steps can be stored in the memory of and executed on those devices, servers, or computer systems shown in Figure 19 A- Figure 19 G. It is contemplated that steps can be skipped, combined, or added between the example methods disclosed herein (e.g., Figure 1 , Figure 7 , Figure 13 , Figure 16 , Figure 22 , etc.). Table 3 shows the abbreviations and definitions of terms that can be disclosed herein.

[0200] Table 3 - Abbreviations and Definitions

[0201]

[0202]

[0203] Figure 26 Example displays (e.g., graphical user interfaces) that can be generated based on the methods, systems, and devices for link recovery and sidelink beamforming as discussed herein are shown. A display interface 901 (e.g., a touchscreen display) can provide text associated with link recovery and sidelink beamforming in block 902, such as relevant parameters, method flows, and associated current conditions. Progress of any of the steps discussed herein (e.g., messages sent or success of steps) can be displayed in block 902. In addition, graphical outputs 903 can be displayed on the display interface 901. The graphical outputs 903 can be graphical outputs of device topologies implementing the methods, systems, and devices for link recovery and sidelink beamforming, progress of any of the methods or systems discussed herein, and the like.

[0204] The Third Generation Partnership Project (3GPP) develops technical standards for cellular telecommunications network technologies, including radio access, the core transport network, and service capabilities, including coding and speech, security, and quality of service. Recent radio access technology (RAT) standards include WCDMA (commonly referred to as 3G), LTE (commonly referred to as 4G), LTE-Advanced standards, and New Radio (NR) (also referred to as “5G”). It is expected that the 3GPP NR standards will continue to evolve and include the definition of a next generation radio access technology (new RAT) that is expected to provide new flexible radio access at sub-7 GHz and new ultra-mobile broadband radio access above 7 GHz. The flexible radio access is expected to include a new non-backwards compatible radio access in new spectrum below 6 GHz, and is expected to include different operating modes that can be multiplexed together in the same spectrum to address a broad set of 3GPP NR use cases with different requirements. The ultra-mobile broadband is expected to include centimeter and millimeter wave spectrum that will provide opportunities for ultra-mobile broadband access for, e.g., indoor applications and hotspots. In particular, the ultra-mobile broadband is expected to share a common design framework with the flexible radio access below 7 GHz, while having centimeter and millimeter wave specific design optimizations.

[0205] 3GPP has identified a variety of use cases that NR is expected to support, resulting in a wide variety of user experience requirements for data rates, latency, and mobility. Use cases include the following general categories: enhanced mobile broadband (eMBB), ultra-reliable low-latency Communication (URLLC), massive machine type communication (mMTC), network operations (e.g., network slicing, routing, migration and interworking, energy savings), and enhanced vehicle-to-everything (eV2X) communications, which can include any of vehicle-to-vehicle communications (V2V), vehicle-to-infrastructure communications (V2I), vehicle-to-network communications (V2N), vehicle-to-pedestrian communications (V2P), and communications of vehicles with other entities. Particular services and applications in these categories include, for example, monitoring and sensor networks, device remote control, bi-directional remote control, personal cloud computing, video streaming, cloud-based office anyplace, first responder connectivity, automotive safety, disaster alerts, real-time gaming, multi-person video calls, autonomous driving, augmented reality, tactile internet, virtual reality, home automation, robotics, and drones, among others. All of these use cases and others are contemplated herein.

[0206] Figure 27A An exemplary communications system 100 is shown in which methods and apparatus of link recovery and sidelink beamforming, such as the systems and methods shown in FIG. 5- Figure 21 The communications system 100 can include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, 102e, 102f, or 102g, which can each be referred to generically as a WTRU 102 or WTRUs 102. The communications system 100 can include a wireless access network (RAN) 103 / 104 / 105 / 103b / 104b / 105b, a core network 106 / 107 / 109, a public switched telephone network (PSTN) 108, the Internet 110, other networks 112, and Network Services 113. The Network Services 113 can include, for example, a V2X server, V2X functions, a ProSe server, a ProSe function, IoT services, video streaming, or edge computing, among others.

[0207] It should be appreciated that the concepts disclosed herein can be used with any number of WTRUs, base stations, networks, or network elements. Each of the WTRUs 102a, 102b, 102c, 102d, 102e, 102f, or 102g can be any type of apparatus or device configured to operate or communicate in a wireless environment. Although each WTRU 102a, 102b, 102c, 102d, 102e, 102f, or 102g is often discussed in terms of a cellular phone, a wireless device, or a handheld device, as these are typical WTRUs, the scope of the subject disclosure is not so limited. For example, any WTRU 102a, 102b, 102c, 102d, 102e, 102f, or 102g can be a wearable device, a computer with wireless capability, a wireless sensor, or any other WTRU suitable for use in a wireless environment. Figure 27A , Figure 27B , Figure 27C , Figure 27D , Figure 27Eor Figure 27F WTRUs can include or embody any type of device or equipment configured to transmit or receive wireless signals as exemplified by, but not limited to, user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular phone, a personal digital assistant (PDA), a smartphone, a laptop, a tablet, a netbook, a notebook, a personal computer, a wireless sensor, a consumer electronics, a wearable device such as a smartwatch or smart clothing, a medical or eHealth device, a robot, an industrial equipment, a drone, a vehicle such as a car, a bus, a truck, a train or an airplane, etc.

[0208] The communication system 100 can also include base stations 114a and 114b. In Figure 27A In an example, each base station 114a and 114b is depicted as a single element. In practice, base stations 114a and 114b can include any number of interconnected base stations or network elements. Base station 114a can be any type of device configured to wirelessly interface with at least one of WTRUs 102a, 102b, and 102c to facilitate access to one or more communication networks, such as the core network 106 / 107 / 109, the Internet 110, the network

[0209] The TRPs 119a, 119b can be any type of device configured to wirelessly interface to at least one of the WTRUs 102d to facilitate access to one or more communication networks, such as the core network 106 / 107 / 109, the Internet 110, Network Services 113, or other networks 112. The RSUs 120a and 120b can be any type of device configured to wirelessly interface to at least one of the WTRUs 102e or 102f to facilitate access to one or more communication networks, such as the core network 106 / 107 / 109, the Internet 110, other networks 112, or Network Services 113. By way of example, the base stations 114a, 114b can be a Base Transceiver Station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a Next Generation Node-B (gNode B), a satellite, a site controller, an access point (AP), a wireless router, and the like.

[0210] The base station 114a can be part of the RAN 103 / 104 / 105, which also can include other base stations or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. Similarly, the base station 114b can be part of the RAN 103b / 104b / 105b, which also can include other base stations or network elements (not shown), such as a BSC, a RNC, relay nodes, etc. The base station 114a can be configured to transmit or receive wireless signals within a particular geographic area, which can be referred to as a cell (not shown) for methods, systems, and devices for link recovery and sidelink beamforming, as disclosed herein. Similarly, the base station 114b can be configured to transmit or receive wired or wireless signals within a particular geographic area, which can be referred to as a cell (not shown) for methods, systems, and devices for link recovery and sidelink beamforming, as disclosed herein. The cell can be further divided into cell sectors. For example, the cell associated with the base station 114a can be divided into three sectors. Thus, in one example, the base station 114a can include three transceivers, one for each sector of the cell. In one example, the base station 114a can employ multiple-input multiple-output (MIMO) technology and, therefore, can utilize multiple transceivers for each sector of the cell.

[0211] The base station 114a can communicate with one or more of the WTRUs 102a, 102b, 102c, or 102g over the air interface 115 / 116 / 117, which can be a wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, cmWave, mmWave, etc.) The air interface 115 / 116 / 117 can be established using any suitable radio access technology (RAT).

[0212] The base stations 114b can communicate with one or more of the RRHs 118a, 118b, TRPs 119a, 119b, or RSUs 120a, 120b through a wired or wireless interface 115b / 116b / 117b, which can be any suitable wired (e.g., cable, optical fiber, etc.) or wireless (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, centimeter band, millimeter band, etc.) communication link. The air interface 115b / 116b / 117b can be established using any suitable radio access technology (RAT).

[0213] The RRHs 118a, 118b, TRPs 119a, 119b, or RSUs 120a, 120b can communicate with one or more of the WTRUs 102c, 102d, 102e, 102f through an air interface 115c / 116c / 117c, which can be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, centimeter band, millimeter band, etc.). The air interface 115c / 116c / 117c can be established using any suitable radio access technology (RAT).

[0214] The WTRUs 102a, 102b, 102c, 102d, 102e, or 102f can communicate with one another through an air interface 115d / 116d / 117d, such as Sidelink communication, which can be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, centimeter band, millimeter band, etc.). The air interface 115d / 116d / 117d can be established using any suitable radio access technology (RAT).

[0215] The communications system 100 can be a multiple access system and can employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 103 / 104 / 105 and the WTRUs 102a, 102b, 102c or RRHs 118a, 118b, TRPs 119a, 119b, and RSUs 120a, 120b in the RAN 103b / 104b / 105b, or WTRUs 102c, 102d, 102e, 102f can implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which can establish the air interface 115 / 116 / 117 or 115c / 116c / 117c respectively using wideband CDMA (WCDMA). WCDMA can include communication protocols such as High-Speed Packet Access (HSPA) or Evolved HSPA (HSPA+).

[0216] In one example, the base station 114a and the WTRUs 102a, 102b, 102c or RRHs 118a, 118b, TRPs 119a, 119b, or RSUs 120a, 120b in the RAN 103b / 104b / 105b, and WTRUs 102c, 102d, can implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which can establish the air interface 115 / 116 / 117 or 115c / 116c / 117c respectively using Long Term Evolution (LTE) or LTE-Advanced (LTE-A). In the future, the air interfaces 115 / 116 / 117 or 115c / 116c / 117c can implement 3GPP NR technology. The LTE and LTE-A technology can include LTE D2D and V2X technology and interfaces such as sidelink communications. Similarly, 3GPP NR technology includes NR V2X technology and interfaces such as sidelink communications.

[0217] The base stations 114a in the RAN 103 / 104 / 105 and the WTRUs 102a, 102b, 102c, and 102g or RRHs 118a, 118b, TRPs 119a, 119b, or RSUs 120a, 120b in the RAN 103b / 104b / 105b and the WTRUs 102c, 102d, 102e, 102f can implement radio technologies such as IEEE 802.16 (e.g., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0218] Figure 27A The base station 114c in the RAN 103b / 104b / 105b can be a wireless router, Home Node B, Home eNode B, or access point, for example, and can utilize any suitable RAT for facilitating wireless connectivity access to the Internet, such as IEEE 802.11, IEEE 802.15, 3GPP, 3GPP2, iBurst®, Evolution-Data Optimized (EV-DO), IEEE 802.16, 802.20, Flash-OFDM®, Wireless Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) (e.g., LTE Rel. 8, 9, 10, 11, 12, 13, 14, etc.), LTE-Advanced (e.g., LTE-A, LTE-A Pro, LTE-A Pro 2, etc.), 5G, 5G-NR, 6G, or the like. The base station 114c and the WTRUs 102c, 102d, 102e, 102f can implement a radio technology such as IEEE 802.11 to establish a WLAN, a radio technology such as IEEE 802.15 to establish a WPAN, a radio technology such as Bluetooth® to establish a wireless personal area network (WPAN), and / or a radio technology such as WiMAX, a radio technology such as ZigBee® to establish a wireless sensor network, and / or the like. In an example, the base station 114c and the WTRUs 102c, 102d, 102e, 102f can implement a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, 5G, 6G, etc.) to establish a picocell or femtocell. As shown, the base station 114c can have a direct connection to the Internet 110. Thus, the base station 114c can not be required to access the Internet 110 via the core network 106 / 107 / 109. Figure 27A

[0219] ​The RAN 103 / 104 / 105 or RAN 103b / 104b / 105b can be in communication with a core network 106 / 107 / 109, which can be any type of network configured to provide voice, data, messaging, authorization, and authentication, application, and / or Internet Protocol voice

[0220] Although not shown in Figure 27A RAN 103 / 104 / 105 or RAN 103b / 104b / 105b and / or the core network 106 / 107 / 109 can communicate with other RANs employing the same RAT as the RAN 103 / 104 / 105 or RAN 103b / 104b / 105b or a different RAT. For example, in addition to being connected to the RAN 103 / 104 / 105 or RAN 103b / 104b / 105b, which can be utilizing E-UTRA radio technology, the core network 106 / 107 / 109 can also be

[0221] The core network 106 / 107 / 109 can also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d, 102e to access the PSTN 108, the Internet 110, or other networks 112. The PSTN 108 can include circuit-switched telephone networks that provide infrastructure for the provision of voice, video, and / or data services to users. The Internet 110 can include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) suite including TCP / IP, to communicate with each other. The networks 112 can include wired or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 can include any type of packet data network (e.g., an IEEE 802.3 Ethernet network) or another core network, which can employ the same RAT as the RAN 103 / 104 / 105 or RAN 103b / 104b / 105b or a different RAT.

[0222] Some or all of the WTRUs 102a, 102b, 102c, 102d, 102e, and 102f in the communication system 100 may include multi-mode capabilities. For example, WTRUs 102a, 102b, 102c, 102d, 102e, and 102f may include multiple transceivers for communicating with different wireless networks via different wireless links to implement the link recovery and side-link beamforming methods, systems, and apparatuses disclosed herein. For example, Figure 27A The WTRU 102g shown can be configured to communicate with a base station 114a that can employ cellular-based radio technology and with a base station 114c that can employ IEEE 802 radio technology.

[0223] Despite Figure 27A Although not shown, it should be understood that user equipment can establish a wired connection with a gateway. The gateway can be a residential gateway (RG). The RG can provide connectivity to the core network 106 / 107 / 109. It should be understood that many of the ideas contained herein are equivalent to those applied to UEs acting as WTRUs and UEs connected to the network via wired connections. For example, ideas applied to radio interfaces 115, 116, 117, and 115c / 116c / 117c are equivalent to those applied to wired connections.

[0224] Figure 27B This is a system diagram of an exemplary RAN 103 and core network 106 that enables the methods, systems, and apparatuses for link restoration and lateral link beamforming as disclosed herein. As described above, RAN 103 can communicate with WTRUs 102a, 102b, and 102c via air interface 115 using UTRA radio technology. RAN 103 can also communicate with core network 106. Figure 27B As shown, RAN 103 may include node Bs 140a, 140b, and 140c, each of which may include one or more transceivers for communicating with WTRUs 102a, 102b, and 102c via air interface 115. Node Bs 140a, 140b, and 140c may each be associated with a specific cell (not shown) within RAN 103. RAN 103 may also include RNCs 142a and 142b. It should be understood that RAN 103 may include any number of node Bs and radio network controllers (RNCs).

[0225] like Figure 27BAs shown, the Node-Bs 140a, 140b can communicate with the RNC 142a. Additionally, the Node-B 140c can communicate with the RNC 142b. The Node-Bs 140a, 140b and 140c can communicate with the respective RNCs 142a and 142b via an Iub interface. The RNCs 142a and 142b can be in communication with one another via an Iur interface. Each of the RNCs 142a and 142b can be configured to control the respective Node-Bs 140a, 140b and 140c to which it is connected. In addition, each of the RNCs 142a and 142b can be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macrodiversity, security functions, data encryption, and the like.

[0226] Figure 27B The core network 106 shown can include a media gateway (MGW) 144, a mobile switching center (MSC) 146, a serving GPRS support node (SGSN) 148, or a gateway GPRS support node (GGSN) 150. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements can be owned and / or operated by an entity other than the core network operator.

[0227] The RNC 142a in the RAN 103 can also be connected to the MSC 146 in the core network 106 via an IuCS interface. The MSC 146 can be connected to the MGW 144. The MSC 146 and the MGW 144 can provide the WTRUs 102a, 102b, and 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c, and traditional

[0228] The RNC 142a in the RAN 103 can also be connected to the SGSN 148 in the core network 106 via an IuPS interface. The SGSN 148 can be connected to the GGSN 150. The SGSN 148 and the GGSN 150 can provide the WTRUs 102a, 102b, and 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c, and IP-enabled devices.

[0229] The core network 106 can also be connected to the other networks 112, which can include other wired or wireless networks that are owned and / or operated by other service providers.

[0230] Figure 27Cis a system diagram of an exemplary RAN 104 and core network 107 that can implement methods, systems, and devices for link recovery and sidelink beamforming as disclosed herein. As described above, the RAN 104 can employ E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 can also be in communication with the core network 107.

[0231] The RAN 104 can include eNode-Bs 160a, 160b, and 160c, though it will be appreciated that the RAN 104 can include any number of eNode-Bs. The eNode-Bs 160a, 160b, and 160c can each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. For example, the eNode-Bs 160a, 160b, and 160c can implement MIMO technology. Thus, the eNode-B 160a, for example, can use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0232] Each of the eNode-Bs 160a, 160b, and 160c can be associated with a particular cell (not shown) and can be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink or downlink, and the like. As shown, the eNode-Bs 160a, 160b, and 160c can communicate with one another over an X2 interface. Figure 27C

[0233] Figure 27C The core network 107 as shown can include a mobility management gateway (MME) 162, a serving gateway 164, and a packet data network (PDN) gateway 166. While each of the foregoing elements are depicted as part of the core network 107, it will be appreciated that any of these elements can be owned and / or operated by an entity other than the core network operator.

[0234] The MME 162 can be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN 104 via an S1 interface and can serve as a control node. For example, the MME 162 can be responsible for authenticating users of the WTRUs 102a, 102b, and 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, and 102c, and the like. The MME 162 can also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0235] ​The serving gateway 164 can be connected to each of the eNode Bs 160a, 160b, and 160c in the RAN 104 via the S1 interface. The serving gateway 164 can generally route and forward user data packets to / from the WTRUs 102a, 102b, and 102c. The serving gateway 164 can also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, and 102c, managing and storing contexts of the WTRUs 102a, 102b, and 102c, and the like.

[0236] The serving gateway 164 can also be connected to the PDN gateway 166, which can provide the WTRUs 102a, 102b, and 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0237] The core network 107 can facilitate communications with other networks. For example, the core network 107 can include, or can communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 107 and the PSTN 108. In addition, the core network 107 can provide the WTRUs 102a, 102b, and 102c with access to the other networks 112, which can include other wired or wireless networks that are owned or operated by other service providers.

[0238] Figure 27D is a system diagram of an example RAN 105 and core network 109 that can implement methods, systems, and devices of link recovery and sidelink beamforming as disclosed herein. The RAN 105 can be in communication with the WTRUs 102a and 102b over the air interface 117. The RAN 105 can also be in communication with the core network 109. The non-3GPP interworking function (N3IWF) 199 can be in communication with the WTRU 102c over the air interface 198 using non-3GPP radio technology. The N3IWF 199 can also be in communication with the core network 109.

[0239] The RAN 105 can include next-generation NodeBs 180a and 180b. It will be appreciated that the RAN 105 can include any number of next-generation NodeBs. The next-generation NodeBs 180a and 180b can each include one or more transceivers for communicating with the WTRUs 102a and 102b over the air interface 117. When using integrated access and backhaul connections, the same air interface can be used between the WTRUs and the next-generation NodeBs, which can be via the core network 109 of one or more gNBs. The next-generation NodeBs 180a and 180b can implement MIMO, MU-MIMO, or digital beamforming techniques. Thus, the next-generation NodeB 180a, for example, can use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. It will be appreciated that the RAN 105 can employ other types of base stations such as an eNodeB. It will also be appreciated that the RAN 105 can include more than one type of base station. For example, the RAN can include eNodeBs and next-generation NodeBs.

[0240] The N3IWF 199 can include a non-3GPP access point 180c. It will be appreciated that the N3IWF 199 can include any number of non-3GPP access points. The non-3GPP access point 180c can include one or more transceivers for communicating with the WTRU 102c over the air interface 198. The non-3GPP access point 180c can communicate with the WTRU 102c over the air interface 198 using an 802.11 protocol.

[0241] Each of the next-generation NodeBs 180a and 180b can be associated with a particular cell (not shown) and can be configured to handle radio resource management decisions, handover decisions, scheduling of users in the downlink and / or uplink, and the like. As shown, the next-generation NodeBs 180a and 180b can communicate with one another, e.g., over an Xn interface. Figure 27D

[0242] Figure 27D The core network 109 shown in FIG. 10 can be a 5G core network (5GC). The core network 109 can provide various communication services to customers through wireless access networks. The core network 109 includes multiple entities that perform core network functions. As used herein, the term “core network entity” or “network function” refers to any entity that performs one or more functions of a core network. It will be appreciated that such core network entities can be logical entities that are implemented in the form of computer executable instructions (software) stored in the memory of, and Figure 27G executed by, a device or computer system configured for wireless or network communication, such as the system 90 shown in FIG. 10.

[0243] In Figure 27D ​In an example, the 5G core network 109 can include an Access and Mobility Management Function (AMF) 172, a Session Management Function (SMF) 174, User Plane Functions (UPFs) 176a and 176b, a User Data Management Function (UDM) 197, an Authentication Server Function (AUSF) 190, a Network Exposure Function (NEF) 196, a Policy Control Function (PCF) 184, a Non-3GPP Interworking Function (N3IWF) 199, a User Data Repository (UDR) 178. While each of the foregoing elements are depicted as part of the 5G core network 109, it will be appreciated that any of these elements can be owned or operated by an entity other than the core network operator. It will also be appreciated that the 5G core network can not include all of these elements, can include additional elements, and can include multiple instances of each of the elements. Figure 27D The network functions are shown directly connected to each other, however, it will be appreciated that they can communicate via a routing agent such as a Diameter routing agent or a message bus.

[0244] In Figure 27D In an example, the connections between the network functions are implemented via a set of interfaces or reference points. It will be appreciated that the network functions can be modeled, described, or implemented as a set of services that are invoked or called by other network functions or services. The invocation of network function services can be implemented via direct connections between network functions, exchange of messages on a message bus, invocation of software functions, etc.

[0245] The AMF 172 can be connected to the RAN 105 via an N2 interface and can serve as a control node. For example, the AMF 172 can be responsible for registration management, connection management, mobility management, access authentication, access authorization. The AMF can be responsible for forwarding user plane tunnel configuration information to the RAN 105 via an N2 interface. The AMF 172 can receive user plane tunnel configuration information from the SMF via an N11 interface. The AMF 172 can generally route and forward NAS packets to / from the WTRUs 102a, 102b, and 102c via an N1 interface. The N1 interface is not shown in Figure 27D .

[0246] The SMF 174 can be connected to the AMF 172 via an N11 interface. Similarly, the SMF can be connected to the PCF 184 via an N7 interface, and to the UPFs 176a and 176b via an N4 interface. The SMF 174 can serve as a control node. For example, the SMF 174 can be responsible for session management, IP address allocation for the WTRUs 102a, 102b, and 102c, management and configuration of traffic steering rules in the UPF 176a and UPF 176b, and generation of downlink data notifications to the AMF 172.

[0247] The UPF 176a and the UPF 176b can provide WTRUs 102a, 102b, and 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, and 102c and other devices. The UPF 176a and the UPF 176b can also provide the WTRUs 102a, 102b, and 102c with access to other types of packet-switched networks. For example, the other networks 112 can be an Ethernet network or any other type of network that exchanges data packets. The UPF 176a and the UPF 176b can receive traffic steering rules from the SMF 174 via an N4 interface. The UPF 176a and the UPF 176b can provide access to packet-switched networks by connecting to the packet-switched networks via an N6 interface or by connecting to each other and to other UPFs via an N9 interface. In addition to providing access to packet-switched networks, the UPF 176 can be responsible for packet routing and forwarding, policy rule enforcement, quality of service handling for user plane traffic, downlink packet buffering.

[0248] The AMF 172 can also be connected to the N3IWF 199, such as via an N2 interface. The N3IWF facilitates connectivity between the WTRU 102c and the 5G core network 170, such as via a radio interface technology not defined by 3GPP. The AMF can interact with the N3IWF in the same or similar manner as it interacts with the RAN 105.

[0249] The PCF 184 can be connected to the SMF 174 via an N7 interface, to the AMF 172 via an N15 interface, and to an application function (AF) 188 via an N5 interface. The N15 and N5 interfaces are not shown in FIG. 1. The PCF 184 can provide policy rules to control plane nodes, such as the AMF 172 and the SMF 174, allowing the control plane nodes to enforce the rules. The PCF 184 can send policies for the WTRUs 102a, 102b, and 102c to the AMF 172, so that the AMF can deliver the policies to the WTRUs 102a, 102b, and 102c via an N1 interface. The policies can then be enforced or applied at the WTRUs 102a, 102b, and 102c. Figure 27D

[0250] The UDR 178 can act as a repository for authentication credentials and subscription information. The UDR can be connected to network functions so that the network functions can add data to the data in the repository, read data in the repository, and modify data in the repository. For example, the UDR 178 can be connected to the PCF 184 via an N36 interface. Similarly, the UDR 178 can be connected to the NEF 196 via an N37 interface, and the UDR 178 can be connected to the UDM 197 via an N35 interface. ​

[0251] The UDM 197 can act as an interface between the UDR 178 and other network functions. The UDM 197 can authorize network functions to access the UDR 178. For example, the UDM 197 can connect to the AMF 172 via an N8 interface, and the UDM 197 can connect to the SMF 174 via an N10 interface. Similarly, the UDM 197 can connect to the AUSF 190 via an N13 interface. The UDR 178 and the UDM 197 can be tightly integrated.

[0252] The AUSF 190 performs authentication-related operations and connects to the UDM 178 via an N13 interface and to the AMF 172 via an N12 interface.

[0253] The NEF 196 exposes capabilities and services in the 5G core network 109 to Application Functions (AFs) 188. Exposure can occur over an N33 API interface. The NEF can connect to the AFs 188 via an N33 interface, and the NEF can connect to other network functions in order to expose capabilities and services of the 5G core network 109.

[0254] Application Functions 188 can interact with network functions in the 5G core network 109. Interactions between the application functions 188 and the network functions can occur via direct interfaces or can occur via the NEF 196. The application functions 188 can be considered part of the 5G core network 109 or can be external to the 5G core network 109 and deployed by an enterprise that has a business relationship with the mobile network operator.

[0255] Network slicing is a mechanism that can be used by a mobile network operator to support one or more “virtual” core networks behind the operator’s air interface. This involves “slicing” the core network into one or more virtual networks to support different RANs running across a single RAN or different service types. Network slicing enables operators to create customized networks to deliver optimized solutions for different market scenarios that require diverse requirements in terms of functionality, performance, and isolation.

[0256] 3GPP has designed the 5G core network to support network slicing. Network slicing is a good tool that network operators can use to support a wide range of 5G use cases (e.g., massive IoT, critical communications, V2X, and enhanced mobile broadband) that require very diverse and sometimes extreme requirements. Without the use of network slicing technology, the flexibility and scalability of the network architecture can be insufficient to efficiently support the wider range of use case requirements when each use case has its own specific set of performance, scalability, and availability requirements. In addition, new network services should be introduced more efficiently.

[0257] Referring again to Figure 27DIn a network slicing scenario, the WTRUs 102a, 102b, or 102c can connect to the AMF 172 via an N1 interface. The AMF can be a logical part of one or more slices. The AMF can coordinate the WTRU 102a, 102b, or 102c's connectivity or communication with one or more of the UPF 176a and 176b, the SMF 174, and other network functions. Each of the UPF 176a and 176b, the SMF 174, and other network functions can be part of the same slice or different slices. When they are part of different slices, they can be isolated from each other in the sense that they can utilize different computing resources, security credentials, etc.

[0258] The core network 109 can facilitate communications with other networks. For example, the core network 109 can include, or can communicate with, an IP gateway for facilitating communications between the 5G core network 109 and the PSTN 108, or other networks. The core network 109 can also facilitate communications with other networks between the WTRUs 102a, 102b, and 102c. For example, the core network 109 can include, or can communicate with, an Short Message Service (SMS) service center for facilitating SMS communications with other networks. For example, the 5G core network 109 can facilitate the exchange of non-IP data packets between the WTRUs 102a, 102b, and 102c and servers or applications functions 188. The core network 109 can also provide a gateway for the WTRUs 102a, 102b, and 102c to access other networks, such as networks operated by other service providers. For example, the core network 109 can serve as a gateway for the WTRUs 102a, 102b, and 102c to access the PSTN 108, the Internet 110, or a

[0259] The core network entities described herein and illustrated in Figure 27A , Figure 27C , Figure 27D or Figure 27E are identified by the names given to those entities in certain existing 3GPP specifications, but it will be understood that in the future those entities and functions can be identified by other names, and certain entities or functions can be combined in future specifications published by 3GPP, including future 3GPP NR specifications. Thus, the specific network entities and functions described and illustrated in Figure 27A , Figure 27B , Figure 27C , Figure 27D or Figure 27E are provided by way of example only, and it will be understood that the subject matter disclosed and claimed herein can be embodied in any similar communication system, whether currently defined or future defined.

[0260] Figure 27EAn example communication system 111 is shown in which systems, methods, apparatuses implementing link recovery and sidelink beamforming described herein can be used. The communication system 111 can include wireless transmit / receive units (WTRUs) A, B, C, D, E, F, a base station gNB 121, a V2X server 124, and road side units (RSUs) 123a and 123b. In practice, the concepts presented herein can be applied to any number of WTRUs, base stations gNB, V2X networks, or other network elements. One or several or all of the WTRUs A, B, C, D, E, and F can be outside the range of access network coverage 131. The WTRUs A, B, and C form a V2X group, with WTRU A being the group leader and WTRUs B and C being group members.

[0261] If the WTRUs A, B, C, D, E, and F are within the access network coverage 131, they can communicate with each other via the gNB 121 over the Uu interface 129. In Figure 27E an example, WTRUs B and F are shown to be within the access network coverage 131. The WTRUs A, B, C, D, E, and F can communicate directly with each other via a sidelink interface (e.g., PC5 or NR PC5), such as interfaces 125a, 125b, or 128, whether they are within the access network coverage 131 or outside the access network coverage 131. For example, in Figure 27E an example, WRTU D, which is outside the access network coverage 131, communicates with WTRU F, which is inside the coverage 131.

[0262] The WTRUs A, B, C, D, E, and F can communicate with the RSUs 123a or 123b via a vehicle-to-network (V2N) 133 or a sidelink interface 125b. The WTRUs A, B, C, D, E, and F can communicate with the V2X server 124 via a vehicle-to-infrastructure (V2I) interface 127. The WTRUs A, B, C, D, E, and F can communicate with another UE via a vehicle-to-pedestrian (V2P) interface 128.

[0263] Figure 27F is a block diagram of an example apparatus or device WTRU 102 that can be configured for wireless communication and operation in accordance with the systems, methods, and apparatuses implementing link recovery and sidelink beamforming described herein, such as Figure 27A , Figure 27B , Figure 27C , Figure 27D or Figure 27E or Figure 7 , Figure 13 and so on. As Figure 27FAs shown, the exemplary WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad / indicator 128, non-removable memory 130, removable memory 132, a power supply 134, a Global Positioning System (GPS) chipset 136, and other peripheral devices 138. It should be understood that the WTRU 102 may include any sub-combination of the foregoing elements. Furthermore, the nodes that base stations 114a and 114b or base stations 114a and 114b may represent (such as, but not limited to, transceiver stations (BTS), node B, site controllers, access points (APs), home node B, evolved home node B (eNodeB), home evolved node B (HeNB), home evolved node B gateway, next-generation node B (gNode-B), and proxy nodes, etc.) may include... Figure 27F Some or all of the elements drawn may be exemplary implementations of the disclosed systems and methods for link recovery and sidelink beamforming described herein.

[0264] Processor 118 can be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. Processor 118 can perform signal encoding, data processing, power control, input / output processing, or any other function that enables WTRU 102 to operate in a wireless environment. Processor 118 can be coupled to transceiver 120, which can be coupled to transmitting / receiving element 122. Although Figure 27F While the processor 118 and transceiver 120 are depicted as separate components, it should be understood that the processor 118 and transceiver 120 may be integrated together in an electronic package or chip.

[0265] The UE's transmit / receive element 122 can be configured to transmit data to a base station (e.g., via air interface 115 / 116 / 117). Figure 27A The base station 114a) transmits or receives signals from the base station, or transmits or receives signals to or from another UE via air interface 115d / 116d / 117d. For example, the transmit / receive element 122 may be an antenna configured to transmit or receive RF signals. The transmit / receive element 122 may be a transmitter / detector configured to transmit or receive, for example, IR signals, UV signals, or visible light signals. The transmit / receive element 122 may be configured to transmit and receive both RF signals and optical signals. It should be understood that the transmit / receive element 122 may be configured to transmit or receive any combination of wireless signals or wired signals.

[0266] Also, although the transmit / receive element 122 is depicted in the Figure 27F WTRU 102 can include any number of transmit / receive elements 122. More specifically, the WTRU 102 can employ MIMO technology. Thus, the WTRU 102 can include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 115 / 116 / 117.

[0267] The transceiver 120 can be configured to modulate the signals that are to be transmitted by the transmit / receive element 122 and to demodulate the signals that are received by the transmit / receive element 122. As noted above, the WTRU 102 can have multi-mode capabilities. Thus, the transceiver 120 can include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, for example NR and IEEE 802.11 or NR and E-UTRA, or to communicate with the same RAT via different RRHs, TRPs, RSUs, or nodes, via multiple beams.

[0268] The processor 118 of the WTRU 102 can be coupled to, and can receive user input data from, the speaker / microphone 124, the keypad 126, or the display / touchpad / indicators 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 can also output user data to the speaker / microphone 124, the keypad 126, or the display / touchpad / indicators 128. In addition, the processor 118 can access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 or the removable memory 132. The non-removable memory 130 can include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 can include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. The processor 118 can access information from, and store data in, memory that is remote from the WTRU 102, such as a server on the Internet or cloud storage. The processor 118 can be configured to control an illumination pattern, image, or color on the display or indicators 128 in response to whether the setup of link recovery and sidelink beamforming in some examples described herein is successful or unsuccessful, or to otherwise indicate the status of link recovery and sidelink beamforming and associated components. The controlled illumination pattern, image, or color on the display or indicators 128 can reflect the figures (e.g., FIGS. 1-8) shown or discussed herein, or any other suitable figures or images. The processor 118 can also include Figure 7 Figure 13 Figure 16 ​​The status of any method procedures or components in the messages and procedures disclosed herein. Messages and procedures for link recovery and sidelink beamforming are disclosed. These messages and procedures can be extended to provide an interface / API for a user to request resources via an input source (e.g., speaker / microphone 124, keypad 126, or display / touchpad / pointer 128), as well as to request, configure, or query link recovery and sidelink beamforming related information, and other information that can be displayed on display 128, etc.

[0269] Processor 118 can receive power from power source 134 and can be configured to distribute or control power to the other components in WTRU 102. Power source 134 can be any suitable device for powering WTRU 102. For example, power source 134 can include one or more dry cell batteries, solar cells, fuel cells, and the like.

[0270] Processor 118 can also be coupled to GPS chipset 136, which can be configured to provide location information (e.g., longitude and latitude) regarding the current location of WTRU 102. In addition to, or in lieu of, the information from GPS chipset 136, WTRU 102 can receive location information from

[0271] Processor 118 can further be coupled to other peripherals 138, which can include one or more software or hardware modules that provide additional features, functionality, or wired or wireless connectivity. For example, peripherals 138 can include various sensors such as an accelerometer, biometrics (e.g., finger print) sensors, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port or other interconnect interfaces, a vibration device, a television transceiver, a a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

[0272] WTRU 102 can be included in other apparatuses or devices, such as a sensor, consumer electronics, a wearable device (such as a smartwatch or smart clothing), a medical or eHealth device, a robot, an industrial appliance, a drone, a vehicle (such as a car, truck, train, or airplane). WTRU 102 can connect to other components, modules, or systems of such apparatuses or devices via one or more interconnect interfaces, such as an interconnect interface that can include one of peripherals 138.

[0273] Figure 27G is a block diagram of an example computing system 90 in which one or more devices and link recovery and sidelink beamforming of the communication networks shown in Figure 27A , Figure 27C , Figure 27D and Figure 27E may be embodied, such as the systems and methods illustrated in FIG. 5- Figure 21 shown herein and claimed, such as certain nodes or functional entities in the RAN 103 / 104 / 105, the core network 106 / 107 / 109, the PSTN 108, the Internet 110, other networks 112, or network services 113. The computing system 90 can comprise a computer or server and can be controlled primarily by computer readable instructions, which can be in the form of software, wherever and by whatever means such software is stored or accessed. Such computer readable instructions can be executed within a processor 91 to cause the computing system 90 to work in a particular manner. The processor 91 can be a general- purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate array (FPGA) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 91 can perform signal coding, data processing, power control, input / output processing, or any other functionality that enables the computing system 90 to operate in a communication network. The coprocessor 81 is an optional processor that can be similar to the processor 91 but is different in that the coprocessor 81 is not the primary processor of the computing system 90. The processor 91 or coprocessor 81 can receive, generate, and process data related to the methods and devices for link recovery and sidelink beamforming disclosed herein, such as receiving messages.

[0274] In operation, the processor 91 fetches, decodes, and executes instructions, and transfers information to and from other resources via the computing system's main data-transfer path, system bus 80. Such a system bus connects the various components in the computing system 90 and defines the medium for data exchange. The system bus 80 typically includes a data bus for sending data, an address bus for sending addresses, and a control bus for sending interrupts and for operating the system bus. One example of such a system bus 80 is a PCI (Peripheral Component Interconnect) bus.

[0275] Memory that is coupled to system bus 80 includes random access memory (RAM) 82 and read only memory (ROM) 93. Such memory stores instructions and data that are needed by the processor 91 to implement the desired functions. ROM 93 typically contains stored data that cannot be readily modified, such as instructions for basic system functions associated with the generic processing of data by the processor 91. RAM 82 can be used to store temporary variables or other intermediate storage when implementing the functions of the present disclosure. Access to both ROM 93 and RAM 82 is typically controlled by a memory controller 92. The memory controller 92 can provide an address translation function that allows processes running on the processor 91 to access a virtual address space that is mapped to physical addresses of memory. The memory controller 92 can also provide a memory protection function that isolates processes from one another and from the system processes. Thus, a program running in a first mode can only access memory that is mapped through its own process virtual address space; it cannot access the virtual address space of another process unless memory sharing between processes has been set up.

[0276] In addition, computing system 90 can contain peripherals controller ( 83) responsible for communicating instructions from processor 91 to peripherals, such as printer 94, keyboard 84, mouse 95, and disk drive 85.

[0277] Display 86, which is controlled by display controller 96, is used to display visual output generated by computing system 90. Such visual output can include text, graphics, animated graphics, and video. The visual output can be provided in the form of a graphical user interface (GUI). Display 86 can be implemented with a CRT-based video display, an LCD-based flat-panel display, gas plasma-based flat-panel display, or a touch-panel. Display controller 96 includes electronic components required to generate a video signal that is sent to display 86.

[0278] Further, computing system 90 can contain communication circuitry, such as for example a wireless or wired network adapter 97, that can be used to connect computing system 90 to an external communications network or device, such as Figure 27A 、 Figure 27B 、 Figure 27C 、 Figure 27D or Figure 27E RAN 103 / 104 / 105, core network 106 / 107 / 109, PSTN 108, Internet 110, WTRUs 102, or other networks 112, to enable the computing system 90 to communicate with other nodes or functional entities of these networks. The communication circuitry, alone or in combination with the processor 91, can be used to perform the transmitting and receiving steps of certain apparatuses, nodes, or functional entities described herein.

[0279] It should be appreciated that any or all of the apparatuses, systems, methods, and processes described herein can be embodied in the form of computer executable instructions embodied in a computer readable storage medium such as a computer readable storage medium of a memory, such as the memory 118 or 91, of the present disclosure. Specifically, any of the steps, operations, or functions described herein can be implemented in the form of such computer executable instructions that are executed by a processor such as the processor 118 or 91 of a device or computing system configured for wireless or wired network communication. Computer readable storage media include volatile and nonvolatile, removable and non-removable media implemented in any non-transitory (e.g., tangible or physical) method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible or physical medium that can be used to store the desired information and that can be accessed by a computing system.

[0280] In describing the preferred methods, systems or apparatuses of the disclosed subject matter (link recovery and sidelink beamforming) as shown in the drawings, specific terminology is employed for the sake of clarity. The claimed subject matter, however, is not intended to be limited to the specific terms so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

[0281] The various techniques described herein can be implemented in connection with hardware, firmware, or software such as is made of computer executable instructions, or any combination thereof. Such hardware, firmware, and software can reside in apparatuses located at various nodes of a communication network. These apparatuses can operate singly or in combination with each other to implement the methods described herein. As used herein, the terms "apparatus," "network apparatus," "node," "device," "network node," and the like can be used interchangeably. Also, unless otherwise provided herein, the word "or" is generally used in the inclusive sense.

[0282] This written description uses examples to disclose the application, including the best mode, and also to enable any person skilled in the art to practice the application, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the application is defined by the claims, and can include other examples that occur to those skilled in the art (e.g., skipping steps, combining steps, or adding steps to the examples methods disclosed herein). Such other examples are intended to be within the scope of the claims if they have structural elements in common with the literal language of the claims, or if they include equivalent structural elements with non-substantial differences from the literal languages of the claims.

[0283] Types of devices in which the disclosed subject matter can be practiced can include a smartphone (consumer electronics / user equipment / smartphone); a tablet (consumer electronics / user equipment / tablet); a wearable device (consumer electronics / user equipment / wearable device); a connected vehicle (consumer electronics / user equipment / connected vehicle); or a base station (network infrastructure / wireless NW infrastructure / base station), etc.

[0284] Methods, systems, and devices associated with BFR, SL-RS for BFD, wireless link monitoring, or frequency-assisted beam failure recovery, etc. are disclosed herein. In a first example, there can be methods or systems for implementing a beam failure recovery (BFR) procedure over a sidelink (SL). The systems can include 1) a BFR at a transmitting UE or a resource UE; or 2) a BFR at a receiving UE or a target UE.

[0285] In a second example, there can be methods or systems for implementing a sidelink reference signal (SL-RS) over a sidelink for beam failure detection (BFD) and candidate beam indication (CBI). These systems or methods can include: 1) beam failure detection (BFD) or candidate beam identification (CBI) based on a sidelink channel state information reference signal (SL-CSI-RS); 2) a sidelink demodulation reference signal (SL-DMRS) for a physical sidelink control channel (PSCCH) based on BFD or CBI; or 3) a SL-DMRS for a physical sidelink shared channel (PSSCH) based on BFD or CBI.

[0286] In a third example, there can be methods or systems for implementing a wireless link monitoring procedure over a sidelink. These systems or methods can include: 1) wireless link monitoring based on a semi-persistent scheduling (SPS) SL-CSI-RS; or 2) wireless link monitoring based on an aperiodic (AP) SL-CSI-RS. In a fourth example, there can be methods or systems for implementing a frequency range 1 (FR1)-assisted or a frequency range 2 (FR2)-assisted beam failure recovery.

[0287] Methods, systems, and apparatuses as described herein can be used for an apparatus to start a timer after establishing a link with a RX UE; count a number of consecutive NACK feedbacks or no feedbacks received from the RX UE; and based on the number of consecutive NACK feedbacks or no feedbacks received exceeding a certain configured threshold N, the physical layer reports (e.g., transmits) a beam failure indication to an upper layer to indicate a link failure. Based on the upper layer receiving one or more beam failure indications from the physical layer, and if no ACK indication (including no feedback) is received from the physical layer before the timer expires, a message is sent to reserve resources in a resource pool to transmit a beam sweep burst. In a manner consistent with other portions of the DETAILED DESCRIPTION, all combinations in this paragraph and the following paragraphs (including deletions or additions of steps) can be contemplated.

[0288] Methods, systems, and apparatuses as described herein can be used for link recovery or sidelink beamforming. The method is to start a first timer in response to establishing a link with a receiving user equipment (RX UE); count a number of negative acknowledgement (NACK) feedbacks or no feedbacks received from the RX UE; and based on the number of NACK feedbacks or no feedbacks received exceeding a first threshold, the physical layer sends a beam failure indication to an upper layer to indicate a link failure. The number of NACK feedbacks or no feedbacks received can be consecutive or cumulative without regard to being consecutive. The system can be to send a message to reserve resources in a resource pool to transmit a beam sweep burst based on the upper layer receiving one or more beam failure indications from the physical layer and no acknowledgement (ACK) indication being received from the physical layer before the timer expires. The message can be sent to reserve resources in a resource pool based on sensing for transmitting a beam sweep burst. The beam sweep burst can be a combination of a plurality of blocks with PSCCH and PSSCH transmitted in each block. No ACK indication is an indication of no feedback. No ACK can be an indication of a number of ACKs less than a threshold or an indication of a number of NACKs before the timer expires. Based on no beam failure indication, after the timer expires, the upper layer is sent and the timer is restarted to continue the sidelink when data is transmitted to the RX UE. In response to performing the beam sweep burst, a second timer is started to monitor feedback from the RX UE. Resources in a resource pool are reserved to transmit a beam sweep burst based on the upper layer receiving one or more beam failure indications from the physical layer and no acknowledgement (ACK) indication being received from the physical layer before the timer expires (or a link quality being below a threshold). The reservation of resources can be based on sensing. Each of the plurality of blocks can include a SL-CSI-RS, a PSCCH, or a PSSCH+PSCCH.

Claims

1. A first wireless transmit / receive unit (WTRU), the first wireless transmit / receive unit (WTRU) comprising: Processor, the processor being configured to: Communicate with the second WTRU; Count the number of negative acknowledgments (NACK) or no feedback received from the second WTRU; If the number of received NACK responses or no responses exceeds a first threshold, a beam fault indication is sent. Report link quality indicators below the quality threshold; and A beam scan burst is transmitted based at least on the beam failure indication or the link quality indication below the quality threshold, wherein the beam scan burst comprises a plurality of blocks, and each of the plurality of blocks comprises at least a physical side link shared channel (PSSCH).

2. The first WTRU of claim 1, wherein the processor is further configured to: determine a threshold time window for a response from the second WTRU based at least on the beam fault indication and the link quality indication below the quality threshold.

3. The first WTRU of claim 1, wherein the number of no-feedback received from the second WTRU is a continuous stream of no-feedback from the second WTRU.

4. The first WTRU according to claim 1, wherein the processor is further configured to When transmitting data to the second WTRU, a threshold time window associated with communication via the side link is determined.

5. The first WTRU of claim 1, wherein the number of negative acknowledgments (NACKs) received from the second WTRU is the number of consecutive negative acknowledgments (NACKs) received from the second WTRU.

6. A method performed by a first wireless transmit / receive unit (WTRU), the method comprising: Communicate with the second WTRU; Count the number of negative acknowledgments (NACK) or no feedback received from the second WTRU; If the number of received NACK responses or no responses exceeds a first threshold, a beam fault indication is sent. Report link quality indicators that are below the quality threshold; as well as A beam scan burst is transmitted based at least on the beam fault indication and the link quality indication below the quality threshold, wherein the beam scan burst comprises a plurality of blocks, and each of the plurality of blocks comprises at least a physical side link shared channel (PSSCH).

7. The method according to claim 6, further comprising: A threshold time window is determined for the response from the second WTRU, based at least on the beam fault indication and the link quality indication below the quality threshold.

8. The method of claim 6, wherein the number of no-feedback received from the second WTRU is a continuous stream of no-feedback from the second WTRU.

9. The method of claim 6, wherein the first WTRU and the second WTRU communicate via a side link SL, and wherein the method further comprises... Terminate the SL with the second WTRU, or when transmitting data to the second WTRU, determine a threshold time window associated with communication via the side link.

10. The method of claim 6, wherein the number of negative acknowledgments (NACKs) received from the second WTRU is the number of consecutive negative acknowledgments (NACKs) received from the second WTRU.

11. A computer-readable storage medium storing computer-executable instructions, which, when executed by a computing device, cause the computing device to perform operations including: The first wireless transmitter / receiver unit (WTRU) communicates with the second WTRU. Count the number of negative acknowledgments (NACK) or no feedback received from the second WTRU; If the number of received NACK responses or no responses exceeds a first threshold, a beam fault indication is sent. Report link quality indicators below the quality threshold; and A beam scan burst is transmitted based at least on the beam failure indication or the link quality indication below the quality threshold, wherein the beam scan burst comprises a plurality of blocks, and each of the plurality of blocks comprises at least a physical side link shared channel (PSSCH).

12. The computer-readable storage medium of claim 11, wherein the instructions, when executed by the computing device, cause the computing device to determine a threshold time window for a response from the second WTRU based at least on the beam fault indication and the link quality indication below the quality threshold.

13. The computer-readable storage medium of claim 11, wherein the number of no-feedback received from the second WTRU is a continuous stream of no-feedback from the second WTRU.

14. The computer-readable storage medium of claim 11, wherein the instructions, when executed by the computing device, cause the computing device to determine a threshold time window associated with communication via the side link when transmitting data to the second WTRU.

15. The computer-readable storage medium of claim 11, wherein the number of negative acknowledgment (NACK) feedbacks received from the second WTRU is the number of consecutive negative acknowledgment (NACK) feedbacks received from the second WTRU.

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