Sidelink communication method and user equipment

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Embodiments of the present application provide a sidelink communication method and a user equipment. The method comprises steps of: performing a first BED for a PC5-RRC connection with a second UE, and triggering a first BFR when the number of continuous first BFDs reaches a first preset value; transmitting a first SL-RS to the second UE; and, if the beam information reported by the second UE is received on a PSFCH resource associated with any first SL-RS resource index, determining that the first BFR succeeds. Thus, the beam failure detection and recovery of sidelink communication can be realized, so that it is convenient for the beam management of sidelink communication in an FR2 frequency band.

Description

SIDELINK COMMUNICATION METHOD AND USER EQUIPMENT

[0001] The present application relates to the technical field of wireless communication, and in particular to a sidelink communication method and a user equipment (UE).

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] In order to meet the increasing demand for wireless data communication services since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also called "Beyond 4G networks" or "Post-LTE systems".

[0009] In order to achieve a higher data rate, 5G communication systems are implemented in higher frequency (millimeter, mmWave) bands, e.g., 60 GHz bands. In order to reduce propagation loss of radio waves and increase a transmission distance, technologies such as beamforming, massive multiple-input multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming and large-scale antenna are discussed in 5G communication systems.

[0010] In addition, in 5G communication systems, developments of system network improvement are underway based on advanced small cell, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, etc.

[0011] In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies have been developed.

[0012] In a fifth-generation mobile communication (5G) new radio (NR) system, the current sidelink communication is only directed to a low frequency band (i.e., an FR1 frequency band with carrier frequency ranging from 450 MHz to 6000 MHz). Due to the serious shortage of spectrum resources of the FR1, it is necessary to support a high frequency band (i.e., an FR2 frequency band with carrier frequency ranging from 24250 MHz to 52600 MHz) in the Rel-18 release. However, the current sidelink communication does not support the FR2.

[0013] The objective of the embodiments of the present application is to solve how to perform beam measurement and reporting related to sidelink communication.

[0014] In accordance with one aspect of the embodiments of the present application, a method executed by a first UE in a communication system is provided, including steps of:

[0015] performing a first BFD for a PC5-RRC connection with a second UE, and triggering a first BFR procedure when the number of continuous first BFDs reaches a first preset value;

[0016] transmitting a first SL-RS to the second UE; and

[0017] if the beam information reported by the second UE is received on a PSFCH resource associated with any first SL-RS resource index, determining that the first BFR succeeds.

[0018] Optionally, the first BFD is determined as one time if at least one of the following conditions is met:

[0019] DTX is detected on a PSFCH reception occasion transmitted by the second UE; and

[0020] the number of continuous times when the DTX is detected on the PSFCH reception occasion transmitted by the second UE reaches a second preset value.

[0021] Optionally, the first SL-RS includes at least one of the following situations:

[0022] the first SL-RS is periodically transmitted by the first UE;

[0023] the first SL-RS is periodically transmitted by the first UE after the first UE triggers the first BFR, until the first BFR succeeds;

[0024] the first SL-RS is periodically measured by the second UE; and

[0025] the first SL-RS is periodically measured by the second UE after the second UE triggers a second BFR, until the second BFR succeeds.

[0026] Optionally, the first SL-RS is configured as at least one of the following:

[0027] SL-SSB corresponding to one set of sidelink synchronization signal block (SL-SSB) indexes; and

[0028] SL-CSI-RS corresponding to one set of sidelink channel state information reference signal (SL-CSI-RS) resources, the SL-CSI-RS transmission is standalone.

[0029] Optionally, a physical resource for transmitting the SL-CSI-RS is periodic, and the physical resource is configured to the second UE by the first UE by PC5-RRC signaling.

[0030] Optionally, if the physical resource is not configured, the method further includes at least one of the following operations:

[0031] transmitting the SL-CSI-RS to the second UE on a resource that has been indicated to be reserved by sidelink control information (SCI) by the first UE but has not been used; and

[0032] starting an initial beam pairing procedure.

[0033] Optionally, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the first SL-RS is at least one of the following:

[0034] SL-SSB corresponding to all SL-SSB indexes;

[0035] SL-CSI-RS corresponding to all SL-CSI-RS resources;

[0036] SL-RS for initial beam pairing; and

[0037] SL-CSI-RS transmitted on a resource that has been indicated to be reserved by SCI by the first UE but has not been used.

[0038] Optionally, the beam information is reported by the second UE in a case where a measurement quantity measured on at least one first SL-RS resource is greater than a first threshold.

[0039] Optionally, the measurement quantity includes at least one of the following:

[0040] layer 1 reference signal received power;

[0041] layer 1 signal to interference plus noise ratio; and

[0042] channel state information.

[0043] Optionally, the beam information being reported by the second UE in a case where the measurement quantity measured on at least one first SL-RS resource is greater than the first threshold includes:

[0044] if there are at least two first SL-RS resources whose measurement quantities measured by the second UE are greater than the first threshold, the beam information is received on a PSFCH resource associated with the largest measurement quantity in the at least two first SL-RS resources.

[0045] Optionally, the PSFCH resource associated with any first SL-RS resource index is determined in the following way:

[0046] determining a group of PSFCH resources based on at least one of the index of the time unit where the SL-RS is located, the index of the starting sub-channel of the SL-RS and the number of sub-channels occupied by the SL-RS; and

[0047] determining, from the group of PSFCH resources, the PSFCH resource associated with the SL-RS resource index according to at least one of the first UE ID, the second UE ID and the SL-RS resource index.

[0048] Optionally, the method further includes:

[0049] if the beam information reported by the second UE is not received on the PSFCH resource associated with any first SL-RS resource index within a first preset period of time after the first SL-RS is transmitted, determining that the first BFR fails; and

[0050] returning to the initial beam pairing procedure.

[0051] In accordance with another aspect of the embodiments of the present application, a method executed by a second UE in a communication system is provided, including steps of:

[0052] periodically measuring a first SL-RS transmitted by a first UE; and

[0053] if the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold, reporting beam information to the first UE on a corresponding PSFCH resource.

[0054] In accordance with still another aspect of the embodiments of the present application, another method executed by a second UE in a communication system is provided, including steps of:

[0055] performing a second BFD for a PC5-RRC connection with a first UE, and triggering a second BFR when the number of continuous second BFDs reaches a third preset value;

[0056] measuring a first SL-RS transmitted by a first UE;

[0057] if the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold, reporting beam information to the first UE on a corresponding PSFCH resource; and

[0058] if a PSCCH and / or PSSCH transmitted by the first UE is received, determining that the second BFR succeeds.

[0059] Optionally, any second BFD is determined according to at least one of the following situations:

[0060] the measurement quantity measured based on the second SL-RS transmitted by the first UE is less than a second threshold;

[0061] the number of continuous times when the measurement quantity measured based on the second SL-RS is less than the second threshold reaches a fifth preset value;

[0062] based on the second SL-RS, the block error rate (BLER) of hypothetical PSCCH or PSSCH transmission is inferred to be greater than a sixth preset value; and;

[0063] based on the second SL-RS, the number of continuous times when the BLER of hypothetical PSCCH or PSSCH transmission is greater than the sixth preset value is inferred to reach a seventh preset value.

[0064] Optionally, the first SL-RS includes at least one of the following situations:

[0065] the first SL-RS is periodically transmitted by the first UE;

[0066] the first SL-RS is periodically transmitted by the first UE after the first UE triggers the first BFR, until the first BFR succeeds;

[0067] the first SL-RS is periodically measured by the second UE; and

[0068] the first SL-RS is periodically measured by the second UE after the second UE triggers a second BFR, until the second BFR succeeds.

[0069] Optionally, at least one of the third preset value, the first threshold, the second threshold, the fifth preset value, the sixth preset value and the seventh preset value is configured to the second UE by the first UE by PC5-RRC signaling.

[0070] Optionally, the second SL-RS is configured as at least one of the following:

[0071] SL-SSB corresponding to one set of SL-SSB indexes; and

[0072] SL-CSI-RS corresponding to one set of SL-CSI-RS resources, the SL-CSI-RS transmission is standalone.

[0073] Optionally, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the second SL-RS is at least one of the following:

[0074] the DMRS of the PSCCH and / or the DMRS of the PSSCH;

[0075] the SL-SSB associated with an available set of candidate beams of the PSCCH; and

[0076] the SL-CSI-RS associated with the available set of candidate beams of the PSCCH.

[0077] Optionally, the measurement quantity includes at least one of the following:

[0078] layer 1 reference signal received power;

[0079] layer 1 signal to interference plus noise ratio; and

[0080] channel state information.

[0081] Optionally, the first SL-RS is configured as at least one of the following:

[0082] SL-SSB corresponding to one set of SL-SSB indexes; and

[0083] SL-CSI-RS corresponding to one set of SL-CSI-RS resources, the SL-CSI-RS transmission is standalone.

[0084] Optionally, a physical resource for transmitting the SL-CSI-RS is periodic, and the physical resource is configured to the second UE by the first UE by PC5-RRC signaling.

[0085] Optionally, if the physical resource is not configured, the method further includes at least one of the following operations:

[0086] receiving the SL-CSI-RS transmitted by the first UE on a resource that has been indicated to be reserved by SCI by the first UE but has not been used; and

[0087] starting an initial beam pairing procedure.

[0088] Optionally, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the first SL-RS is at least one of the following:

[0089] SL-SSB corresponding to all SL-SSB indexes;

[0090] SL-CSI-RS corresponding to all SL-CSI-RS resources;

[0091] SL-RS for initial beam pairing; and

[0092] SL-CSI-RS received on a resource that has been indicated to be reserved by SCI by the first UE but has not been used.

[0093] Optionally, the reporting beam information to the first UE on the corresponding PSFCH resource if the measurement quantity measured on at least one first SL-RS resource is greater than the first threshold includes:

[0094] if there are at least two first SL-RS resources whose measurement quantities are greater than the first threshold, reporting beam information to the first UE on a PSFCH resource associated with the largest measurement quantity in the at least two first SL-RS resources.

[0095] Optionally, the PSFCH resource associated with any first SL-RS resource index is determined in the following way:

[0096] determining a group of PSFCH resources based on at least one of the index of the time unit where the SL-RS is located, the index of the starting sub-channel of the SL-RS and the number of sub-channels occupied by the SL-RS; and

[0097] determining, from the group of PSFCH resources, the PSFCH resource associated with the SL-RS resource index according to at least one of the first UE ID, the second UE ID and the SL-RS resource index.

[0098] Optionally, the method further includes:

[0099] if the PSCCH and / or PSSCH transmitted by the first UE is not received within a second preset period of time after the beam information is reported, determining that the second BFR fails; and

[0100] returning to the initial beam pairing procedure.

[0101] In accordance with yet another aspect of the embodiments of the present application, another method executed by a first UE in a communication system is provided, including steps of:

[0102] periodically transmitting a first SL-RS to a second UE; and

[0103] reception beam information reported by the second UE on a PSFCH resource associated with any first SL-RS resource.

[0104] In accordance with yet another aspect of the embodiments of the present application, a user equipment is provided, including:

[0105] a transceiver, which is configured to transmit and receive signals; and

[0106] a processor, which is coupled to the transceiver and configured to execute the method executed by a UE provided in the embodiments of the present application.

[0107] In accordance with yet another aspect of the embodiments of the present application, a computer-readable storage medium is provided, the computer-readable storage medium having computer programs stored thereon that, when executed by a processor, implement the method executed by a UE provided in the embodiments of the present application.

[0108] In accordance with yet another aspect of the embodiments of the present application, a computer program product is provided, including computer programs that, when executed by a processor, implement the method executed by a UE provided in the embodiments of the present application.

[0109] In the sidelink communication method and the user equipment provided in the embodiments of the present application, a BED is performed for a PC5-RRC connection with a second UE, and a BFR is triggered when the number of continuous BFDs reaches a first preset value; a first SL-RS used for the BFR is transmitted to the second UE; and, if the beam information reported by the second UE is received on a PSFCH resource associated with any first SL-RS resource index, it is determined that the BFR succeeds. Thus, the beam failure detection and recovery of sidelink communication can be realized, so that it is convenient for the beam management of sidelink communication in an FR2 frequency band.

[0110] Embodiments of the present disclosure provide a sidelink communication method and a user equipment (UE).

[0111] In order to explain the technical solutions in the embodiments of the present application more clearly, the accompanying drawings to be used in the description of the embodiments of the present application will be briefly illustrated below.

[0112] FIG. 1 is a schematic diagram of an overall structure of a wireless network according to an embodiment of the present application;

[0113] FIG. 2a is a schematic diagram of a transmission path according to an embodiment of the present application;

[0114] FIG. 2b is a schematic diagram of a reception path according to an embodiment of the present application;

[0115] FIG. 3a is a schematic structure diagram of a UE according to an embodiment of the present application;

[0116] FIG. 3b is a schematic structure diagram of a base station according to an embodiment of the present application;

[0117] FIG. 4 is a schematic diagram of a method executed by a first UE according to an embodiment of the present application;

[0118] FIG. 5 is a schematic diagram of a method executed by a second UE according to an embodiment of the present application;

[0119] FIG. 6 is a schematic diagram of another method executed by a second UE according to an embodiment of the present application;

[0120] FIG. 7 is a schematic diagram of another method executed by a first UE according to an embodiment of the present application;

[0121] FIG. 8 is a schematic diagram of the beam failure detection and recovery scheme 1 according to an embodiment of the present application;

[0122] FIG. 9 is a schematic diagram of the beam failure detection and recovery scheme 2 according to an embodiment of the present application;

[0123] FIG. 10 is a schematic diagram of the beam failure detection and recovery scheme 3 according to an embodiment of the present application;

[0124] FIG. 11a is a schematic diagram of time division multiplexing of SL-CSI-RS and 2-stage SCI according to an embodiment of the present application;

[0125] FIG. 11b is another schematic diagram of time division multiplexing of SL-CSI-RS and 2-stage SCI according to an embodiment of the present application;

[0126] FIG. 12a is a schematic diagram of the SCI for scheduling SL-CSI-RS doing not include 2-stage SCI according to an embodiment of the present application;

[0127] FIG. 12b is another schematic diagram of the SCI for scheduling SL-CSI-RS doing not include 2-stage SCI according to an embodiment of the present application;

[0128] FIG. 13a is a schematic diagram of resources used for PSCCH transmission being also used for SL-CSI-RS transmission according to an embodiment of the present application;

[0129] FIG. 13b is another schematic diagram of resources used for PSCCH transmission being also used for SL-CSI-RS transmission according to an embodiment of the present application;

[0130] FIG. 14a is a schematic diagram of repetitively mapping SL-CSI-RS signal sequence in time domain according to an embodiment of the present application;

[0131] FIG. 14b is another schematic diagram of repetitively mapping SL-CSI-RS signal sequence in time domain according to an embodiment of the present application;

[0132] FIG. 15 is a schematic diagram of repetitively mapping SL-CSI-RS signal sequence in frequency domain according to an embodiment of the present application;

[0133] FIG. 16a is a schematic diagram of repetitively mapping SL-CSI-RS signal sequence in time domain and frequency domain according to an embodiment of the present application;

[0134] FIG. 16b is another schematic diagram of repetitively mapping SL-CSI-RS signal sequence in time domain and frequency domain according to an embodiment of the present application;

[0135] FIG. 17 is a schematic diagram of the SL-CSI-RS including a plurality of SL-CSI-RS resources in one slot according to an embodiment of the present application;

[0136] FIG. 18 is a schematic diagram of the SL-CSI-RS including one SL-CSI-RS resource in one slot according to an embodiment of the present application;

[0137] FIG. 19 is another schematic diagram of the SL-CSI-RS including a plurality of SL-CSI-RS resources in one slot according to an embodiment of the present application; and

[0138] FIG. 20 is a schematic structure diagram of an electronic device according to an embodiment of the present application.

[0139] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0140] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

[0141] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0142] The term "include" or "may include" refers to the existence of a corresponding disclosed function, operation or component which can be used in various embodiments of the present disclosure and does not limit one or more additional functions, operations, or components. The terms such as "include" and / or "have" may be construed to denote a certain characteristic, number, step, operation, constituent element, component or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, constituent elements, components or combinations thereof.

[0143] The term "or" used in various embodiments of the present disclosure includes any or all of combinations of listed words. For example, the expression "A or B" may include A, may include B, or may include both A and B.

[0144] Unless defined differently, all terms used herein, which include technical terminologies or scientific terminologies, have the same meaning as that understood by a person skilled in the art to which the present disclosure belongs. Such terms as those defined in a generally used dictionary are to be interpreted to have the meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present disclosure.

[0145] FIG. 1 illustrates an example wireless network 100 according to various embodiments of the present disclosure. The embodiment of the wireless network 100 shown in FIG. 1 is for illustration only. Other embodiments of the wireless network 100 can be used without departing from the scope of the present disclosure.

[0146] The wireless network 100 includes a gNodeB (gNB) 101, a gNB 102, and a gNB 103. gNB 101 communicates with gNB 102 and gNB 103. gNB 101 also communicates with at least one Internet Protocol (IP) network 130, such as the Internet, a private IP network, or other data networks.

[0147] Depending on a type of the network, other well-known terms such as "base station" or "access point" can be used instead of "gNodeB" or "gNB". For convenience, the terms "gNodeB" and "gNB" are used in this patent document to refer to network infrastructure components that provide wireless access for remote terminals. And, depending on the type of the network, other well-known terms such as "mobile station", "user station", "remote terminal", "wireless terminal" or "user apparatus" can be used instead of "user equipment" or "UE". For convenience, the terms "user equipment" and "UE" are used in this patent document to refer to remote wireless devices that wirelessly access the gNB, no matter whether the UE is a mobile device (such as a mobile phone or a smart phone) or a fixed device (such as a desktop computer or a vending machine).

[0148] gNB 102 provides wireless broadband access to the network 130 for a first plurality of User Equipments (UEs) within a coverage area 120 of gNB 102. The first plurality of UEs include a UE 111, which may be located in a Small Business (SB); a UE 112, which may be located in an enterprise (E); a UE 113, which may be located in a WiFi Hotspot (HS); a UE 114, which may be located in a first residence (R); a UE 115, which may be located in a second residence (R); a UE 116, which may be a mobile device (M), such as a cellular phone, a wireless laptop computer, a wireless PDA, etc. GNB 103 provides wireless broadband access to network 130 for a second plurality of UEs within a coverage area 125 of gNB 103. The second plurality of UEs include a UE 115 and a UE 116. In some embodiments, one or more of gNBs 101-103 can communicate with each other and with UEs 111-116 using 5G, Long Term Evolution (LTE), LTE-A, WiMAX or other advanced wireless communication technologies.

[0149] The dashed lines show approximate ranges of the coverage areas 120 and 125, and the ranges are shown as approximate circles merely for illustration and explanation purposes. It should be clearly understood that the coverage areas associated with the gNBs, such as the coverage areas 120 and 125, may have other shapes, including irregular shapes, depending on configurations of the gNBs and changes in the radio environment associated with natural obstacles and man-made obstacles.

[0150] As will be described in more detail below, one or more of gNB 101, gNB 102, and gNB 103 include a 2D antenna array as described in embodiments of the present disclosure. In some embodiments, one or more of gNB 101, gNB 102, and gNB 103 support codebook designs and structures for systems with 2D antenna arrays.

[0151] Although FIG. 1 illustrates an example of the wireless network 100, various changes can be made to FIG. 1. The wireless network 100 can include any number of gNBs and any number of UEs in any suitable arrangement, for example. Furthermore, gNB 101 can directly communicate with any number of UEs and provide wireless broadband access to the network 130 for those UEs. Similarly, each gNB 102-103 can directly communicate with the network 130 and provide direct wireless broadband access to the network 130 for the UEs. In addition, gNB 101, 102 and / or 103 can provide access to other or additional external networks, such as external telephone networks or other types of data networks.

[0152] FIGs. 2a and 2b illustrate example wireless transmission and reception paths according to the present disclosure. In the following description, the transmission path 200 can be described as being implemented in a gNB, such as gNB 102, and the reception path 250 can be described as being implemented in a UE, such as UE 116. However, it should be understood that the reception path 250 can be implemented in a gNB and the transmission path 200 can be implemented in a UE. In some embodiments, the reception path 250 is configured to support codebook designs and structures for systems with 2D antenna arrays as described in embodiments of the present disclosure.

[0153] The transmission path 200 includes a channel coding and modulation block 205, a Serial-to-Parallel (S-to-P) block 210, a size N Inverse Fast Fourier Transform (IFFT) block 215, a Parallel-to-Serial (P-to-S) block 220, a cyclic prefix addition block 225, and an up-converter (UC) 230. The reception path 250 includes a down-converter (DC) 255, a cyclic prefix removal block 260, a Serial-to-Parallel (S-to-P) block 265, a size N Fast Fourier Transform (FFT) block 270, a Parallel-to-Serial (P-to-S) block 275, and a channel decoding and demodulation block 280.

[0154] In the transmission path 200, the channel coding and modulation block 205 receives a set of information bits, applies coding (such as Low Density Parity Check (LDPC) coding), and modulates the input bits (such as using Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM)) to generate a sequence of frequency-domain modulated symbols. The Serial-to-Parallel (S-to-P) block 210 converts (such as demultiplexes) serial modulated symbols into parallel data to generate N parallel symbol streams, where N is a size of the IFFT / FFT used in gNB 102 and UE 116. The size N IFFT block 215 performs IFFT operations on the N parallel symbol streams to generate a time-domain output signal. The Parallel-to-Serial block 220 converts (such as multiplexes) parallel time-domain output symbols from the Size N IFFT block 215 to generate a serial time-domain signal. The cyclic prefix addition block 225 inserts a cyclic prefix into the time-domain signal. The up-converter 230 modulates (such as up-converts) the output of the cyclic prefix addition block 225 to an RF frequency for transmission via a wireless channel. The signal can also be filtered at a baseband before switching to the RF frequency.

[0155] The RF signal transmitted from gNB 102 arrives at UE 116 after passing by the wireless channel, and operations in reverse to those at gNB 102 are performed at UE 116. The down-converter 255 down-converts the received signal to a baseband frequency, and the cyclic prefix removal block 260 removes the cyclic prefix to generate a serial time-domain baseband signal. The Serial-to-Parallel block 265 converts the time-domain baseband signal into a parallel time-domain signal. The Size N FFT block 270 performs an FFT algorithm to generate N parallel frequency-domain signals. The Parallel-to-Serial block 275 converts the parallel frequency-domain signal into a sequence of modulated data symbols. The channel decoding and demodulation block 280 demodulates and decodes the modulated symbols to recover the original input data stream.

[0156] Each of gNBs 101-103 may implement a transmission path 200 similar to that for transmitting to UEs 111-116 in the downlink, and may implement a reception path 250 similar to that for receiving from UEs 111-116 in the uplink. Similarly, each of UEs 111-116 may implement a transmission path 200 for transmitting to gNBs 101-103 in the uplink, and may implement a reception path 250 for receiving from gNBs 101-103 in the downlink.

[0157] Each of the components in FIGs. 2a and 2b can be implemented using only hardware, or using a combination of hardware and software / firmware. As a specific example, at least some of the components in FIGs. 2a and 2b may be implemented in software, while other components may be implemented in configurable hardware or a combination of software and configurable hardware. For example, the FFT block 270 and IFFT block 215 may be implemented as configurable software algorithms, in which the value of the size N may be modified according to the implementation.

[0158] Furthermore, although described as using FFT and IFFT, this is only illustrative and should not be interpreted as limiting the scope of the present disclosure. Other types of transforms can be used, such as Discrete Fourier transform (DFT) and Inverse Discrete Fourier Transform (IDFT) functions. It should be understood that for DFT and IDFT functions, the value of variable N may be any integer (such as 1, 2, 3, 4, etc.), while for FFT and IFFT functions, the value of variable N may be any integer which is a power of 2 (such as 1, 2, 4, 8, 16, etc.).

[0159] Although FIGs. 2a and 2b illustrate examples of wireless transmission and reception paths, various changes may be made to FIGs. 2a and 2b. For example, various components in FIGs. 2a and 2b can be combined, further subdivided or omitted, and additional components can be added according to specific requirements. Furthermore, FIGs. 2a and 2b are intended to illustrate examples of types of transmission and reception paths that can be used in a wireless network. Any other suitable architecture can be used to support wireless communication in a wireless network.

[0160] FIG. 3a illustrates an example UE 116 according to the present disclosure. The embodiment of UE 116 shown in FIG. 3a is for illustration only, and UEs 111-115 of FIG. 1 can have the same or similar configuration. However, a UE has various configurations, and FIG. 3a does not limit the scope of the present disclosure to any specific implementation of the UE.

[0161] UE 116 includes an antenna 305, a radio frequency (RF) transceiver 310, a transmission (TX) processing circuit 315, a microphone 320, and a reception (RX) processing circuit 325. UE 116 also includes a speaker 330, a processor / controller 340, an input / output (I / O) interface 345, an input device(s) 350, a display 355, and a memory 360. The memory 360 includes an operating system (OS) 361 and one or more applications 362.

[0162] The RF transceiver 310 receives an incoming RF signal transmitted by a gNB of the wireless network 100 from the antenna 305. The RF transceiver 310 down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is transmitted to the RX processing circuit 325, where the RX processing circuit 325 generates a processed baseband signal by filtering, decoding and / or digitizing the baseband or IF signal. The RX processing circuit 325 transmits the processed baseband signal to speaker 330 (such as for voice data) or to processor / controller 340 for further processing (such as for web browsing data).

[0163] The TX processing circuit 315 receives analog or digital voice data from microphone 320 or other outgoing baseband data (such as network data, email or interactive video game data) from processor / controller 340. The TX processing circuit 315 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver 310 receives the outgoing processed baseband or IF signal from the TX processing circuit 315 and up-converts the baseband or IF signal into an RF signal transmitted via the antenna 305.

[0164] The processor / controller 340 can include one or more processors or other processing devices and execute an OS 361 stored in the memory 360 in order to control the overall operation of UE 116. For example, the processor / controller 340 can control the reception of forward channel signals and the transmission of backward channel signals by the RF transceiver 310, the RX processing circuit 325 and the TX processing circuit 315 according to well-known principles. In some embodiments, the processor / controller 340 includes at least one microprocessor or microcontroller.

[0165] The processor / controller 340 is also capable of executing other procedures and programs residing in the memory 360, such as operations for channel quality measurement and reporting for systems with 2D antenna arrays as described in embodiments of the present disclosure. The processor / controller 340 can move data into or out of the memory 360 as required by an execution procedure. In some embodiments, the processor / controller 340 is configured to execute the application 362 based on the OS 361 or in response to signals received from the gNB or the operator. The processor / controller 340 is also coupled to an I / O interface 345, where the I / O interface 345 provides UE 116 with the ability to connect to other devices such as laptop computers and handheld computers. I / O interface 345 is a communication path between these accessories and the processor / controller 340.

[0166] The processor / controller 340 is also coupled to the input device(s) 350 and the display 355. An operator of UE 116 can input data into UE 116 using the input device(s) 350. The display 355 may be a liquid crystal display or other display capable of presenting text and / or at least limited graphics (such as from a website). The memory 360 is coupled to the processor / controller 340. A part of the memory 360 can include a random access memory (RAM), while another part of the memory 360 can include a flash memory or other read-only memory (ROM).

[0167] Although FIG. 3a illustrates an example of UE 116, various changes can be made to FIG. 3a. For example, various components in FIG. 3a can be combined, further subdivided or omitted, and additional components can be added according to specific requirements. As a specific example, the processor / controller 340 can be divided into a plurality of processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Furthermore, although FIG. 3a illustrates that the UE 116 is configured as a mobile phone or a smart phone, UEs can be configured to operate as other types of mobile or fixed devices.

[0168] FIG. 3b illustrates an example gNB 102 according to the present disclosure. The embodiment of gNB 102 shown in FIG. 3b is for illustration only, and other gNBs of FIG. 1 can have the same or similar configuration. However, a gNB has various configurations, and FIG. 3b does not limit the scope of the present disclosure to any specific implementation of a gNB. It should be noted that gNB 101 and gNB 103 can include the same or similar structures as gNB 102.

[0169] As shown in FIG. 3b, gNB 102 includes a plurality of antennas 370a-370n, a plurality of RF transceivers 372a-372n, a transmission (TX) processing circuit 374, and a reception (RX) processing circuit 376. In certain embodiments, one or more of the plurality of antennas 370a-370n include a 2D antenna array. gNB 102 also includes a controller / processor 378, a memory 380, and a backhaul or network interface 382.

[0170] RF transceivers 372a-372n receive an incoming RF signal from antennas 370a-370n, such as a signal transmitted by UEs or other gNBs. RF transceivers 372a-372n down-convert the incoming RF signal to generate an IF or baseband signal. The IF or baseband signal is transmitted to the RX processing circuit 376, where the RX processing circuit 376 generates a processed baseband signal by filtering, decoding and / or digitizing the baseband or IF signal. RX processing circuit 376 transmits the processed baseband signal to controller / processor 378 for further processing.

[0171] The TX processing circuit 374 receives analog or digital data (such as voice data, network data, email or interactive video game data) from the controller / processor 378. TX processing circuit 374 encodes, multiplexes and / or digitizes outgoing baseband data to generate a processed baseband or IF signal. RF transceivers 372a-372n receive the outgoing processed baseband or IF signal from TX processing circuit 374 and up-convert the baseband or IF signal into an RF signal transmitted via antennas 370a-370n.

[0172] The controller / processor 378 can include one or more processors or other processing devices that control the overall operation of gNB 102. For example, the controller / processor 378 can control the reception of forward channel signals and the transmission of backward channel signals by the RF transceivers 372a-372n, the RX processing circuit 376 and the TX processing circuit 374 according to well-known principles. The controller / processor 378 can also support additional functions, such as higher-level wireless communication functions. For example, the controller / processor 378 can perform a Blind Interference Sensing (BIS) procedure such as that performed by a BIS algorithm, and decode a received signal from which an interference signal is subtracted. A controller / processor 378 may support any of a variety of other functions in gNB 102. In some embodiments, the controller / processor 378 includes at least one microprocessor or microcontroller.

[0173] The controller / processor 378 is also capable of executing programs and other procedures residing in the memory 380, such as a basic OS. The controller / processor 378 can also support channel quality measurement and reporting for systems with 2D antenna arrays as described in embodiments of the present disclosure. In some embodiments, the controller / processor 378 supports communication between entities such as web RTCs. The controller / processor 378 can move data into or out of the memory 380 as required by an execution procedure.

[0174] The controller / processor 378 is also coupled to the backhaul or network interface 382. The backhaul or network interface 382 allows gNB 102 to communicate with other devices or systems by a backhaul connection or by a network. The backhaul or network interface 382 can support communication over any suitable wired or wireless connection(s). For example, when gNB 102 is implemented as a part of a cellular communication system, such as a cellular communication system supporting 5G or new radio access technology or NR, LTE or LTE-A, the backhaul or network interface 382 can allow gNB 102 to communicate with other gNBs by wired or wireless backhaul connections. When gNB 102 is implemented as an access point, the backhaul or network interface 382 can allow gNB 102 to communicate with a larger network, such as the Internet, by a wired or wireless local area network or by a wired or wireless connection. The backhaul or network interface 382 includes any suitable structure that supports communication by a wired or wireless connection, such as an Ethernet or an RF transceiver.

[0175] The memory 380 is coupled to the controller / processor 378. A part of the memory 380 can include an RAM, while another part of the memory 380 can include a flash memory or other ROMs. In certain embodiments, a plurality of instructions, such as the BIS algorithm, are stored in the memory. The plurality of instructions are configured to cause the controller / processor 378 to execute the BIS procedure and decode the received signal after subtracting at least one interference signal determined by the BIS algorithm.

[0176] As will be described in more detail below, the transmission and reception paths of gNB 102 (implemented using RF transceivers 372a-372n, TX processing circuit 374 and / or RX processing circuit 376) support aggregated communication with FDD cells and TDD cells.

[0177] Although FIG. 3b illustrates an example of gNB 102, various changes may be made to FIG. 3b. For example, gNB 102 can include any number of each component shown in FIG. 3a. As a specific example, the access point can include many backhaul or network interfaces 382, and the controller / processor 378 can support routing functions to route data between different network addresses. As another specific example, although shown as including a single instance of the TX processing circuit 374 and a single instance of the RX processing circuit 376, gNB 102 can include multiple instances of each (such as one for each RF transceiver).

[0178] In a communication system, the communication interface between a network base station and a UE is called a UU interface, and the UE performs data transmission with the network by the UU interface. Two UEs having communication requirements may access the same network by their respective UU interfaces and realize communication based on the data transfer in the network.

[0179] However, in a sidelink communication system, two terminals (UEs) that are close to each other can communicate directly, without transferring data by the network base station. The wireless link between two UEs is called a sidelink (SL), and the communication interface between two UEs is called a PC5 interface.

[0180] In the sidelink communication system, three communication modes are supported, i.e., broadcasting, multicasting and unicasting. The broadcasting means that one UE transmits data to all surrounding UEs, the multicasting means that one UE transmits data to a specific group of surrounding UEs, and the unicasting means that one UE transmits data to one specific surrounding UE. For unicasting, two UEs will establish a PC5 RRC connection to control the physical transmission of the underlying layer. In addition, the current sidelink communication system mainly has the following four physical channels: physical sidelink broadcast channels (PSBCHs), physical sidelink control channels (PSCCHs), physical sidelink shared channels (PSSCHs), and physical sidelink feedback channels (PSFCHs).

[0181] PSBCHs are used to synchronize and indicate important broadcast information. PSCCHs are used to indicate the transmission parameters (e.g., physical resources, etc.) of PSSCHs and other control information (e.g., destination UE ID (identity or identifier), etc.). PSSCHs are used to carry data. PSFCHs are used to feed back the decoding results of PSSCHs (including acknowledgement (ACK) of successful decoding and negative acknowledgement (NACK) of unsuccessful decoding).

[0182] The sidelink communication in Rel-16 release and Rel-17 release is only directed to an FR1 frequency band. Due to the serious shortage of spectrum resources of the FR1, it is necessary to support the sidelink communication in an FR2 frequency band. The FR2 communication mainly differs from the FR1 communication in that the FR2 communication realizes transmission by using directional beams, that is, all channels / signals are transmitted in a specific beam direction, in order to gather the transmitting power in a certain direction to improve the signal power at the receiving terminal, thus improving the coverage range. Due to the transmission characteristics of directional beams, beam management is essential. The beam management mainly includes the following aspects: initial beam pairing, beam refinement, beam measurement and reporting, beam indication and switching, beam failure detection and beam failure recovery. Since the current sidelink communication does not support the FR2, the details about beam management in the sidelink communication are not clear. The embodiments of the present application mainly provide the technical details about beam failure detection and recovery in the sidelink communication.

[0183] The technical solutions in the embodiments of the present application and the technical effects achieved by the technical solutions in the present application will be explained below by describing several exemplary implementations. It should be noticed that the following implementations can be referred to, learned from or combined with each other, and the same terms, similar features and similar implementation steps in different implementations will not be repeated.

[0184] An embodiment of the present application provides a method executed by a first UE in a communication system. As shown in FIG. 4, the method includes the following steps.

[0185] In step S401, a first beam failure detection (BFD) is performed for a PC5-RRC connection with a second UE, and a first beam failure recovery (BFR) procedure is triggered when the number of continuous first BFDs reaches a first preset value.

[0186] In step S402, a first sidelink reference signal (SL-RS) is transmitted to the second UE.

[0187] In step S403, if the beam information reported by the second UE is received on a PSFCH resource associated with any first SL-RS resource index, it is determined that the first BFR succeeds.

[0188] In the embodiment of the present application, the UE that transmits data is called a first UE or transmission UE (TX UE), the UE that receives data is called a second UE or reception UE (RX UE), and a PC5 RRC connection will be established between the TX UE and the RX UE. The ID of the TX UE is called a first UE ID or source ID, and the ID of the RX UE is called a second UE ID or destination ID.

[0189] The beam failure detection (BFD) means that the UE continuously monitors the communication quality of beams, and the UE determines a beam failure when the communication quality is poor (for example, the communication quality is lower than a certain preset value). A beam failure means that the current beam may not be able to support reliable communication due to UE movement or scatterer movement, that is, the current beam is not the best beam. After multiple beam failures occur continuously, the UE will trigger a beam failure recovery procedure to obtain a new best beam and re-establish beam pairing.

[0190] Correspondingly, an embodiment of the present application provides a method executed by a second UE in a communication system. As shown in FIG. 5, the method includes the following steps.

[0191] In step S501, a first SL-RS transmitted by a first UE is periodically measured.

[0192] In step S502, if the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold, beam information is reported to the first UE on a corresponding PSFCH resource.

[0193] The method executed on the second UE side in the embodiment of the present application corresponds to the method executed on the first UE side, the detailed functional description and the achieved beneficial effects can specifically refer to the description of the method executed on the first UE side, and the same processing procedure may not be repeated.

[0194] An embodiment of the present application further provides a method executed by a second UE in a communication system. As shown in FIG. 6, the method includes the following steps.

[0195] In step S601, a second BFD is performed for a PC5-RRC connection with a first UE, and a second BFR is triggered when the number of continuous second BFDs reaches a third preset value.

[0196] In step S602, a first SL-RS transmitted by a first UE is measured.

[0197] In step S603, if the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold, beam information is reported to the first UE on a corresponding PSFCH resource.

[0198] In step S604, if a PSCCH and / or PSSCH transmitted by the first UE is received, it is determined that the second BFR succeeds.

[0199] Correspondingly, an embodiment of the present application provides another method executed by a first UE in a communication system. As shown in FIG. 7, the method includes the following steps.

[0200] In step S701, a first SL-RS is periodically transmitted to a second UE.

[0201] In step S702, beam information reported by the second UE on a PSFCH resource associated with any first SL-RS resource is received.

[0202] In the embodiment of the present application, the UE can determine a beam failure detection when at least one of the following conditions is satisfied (that is, any BFD is determined according to at least one of the following situations):

[0203] 1. Discontinuous transmission (DTX) is detected on a PSFCH reception occasion (transmitted by the second UE), that is, no PSFCH is detected.

[0204] 2. The number of continuous times when the DTX is detected on the PSFCH reception occasion (transmitted by the second UE) reaches a second preset value.

[0205] 3. The measurement quantity (e.g., sidelink layer 1 reference signal received power (SL-L1-RSRP) and / or sidelink layer 1 signal to interference plus noise ratio (SL-L1-SINR), etc.) measured based on the sidelink reference signal (second SL-RS) transmitted by the first UE is less than a second threshold.

[0206] 4. The number of continuous times when the measurement quantity (e.g., SL-L1-RSRP and SL-L1-SINR, etc.) measured based on the sidelink reference signal (second SL-RS) is less than the second threshold reaches a fifth preset value.

[0207] 5. Based on the sidelink reference signal (second SL-RS), the block error rate (BLER) of hypothetical PSCCH or PSSCH transmission is inferred to be greater than a sixth preset value, for example, the BLER is greater than 10%. The UE may infer the BLER of hypothetical PSCCH or PSSCH transmission based on the measured L1-SINR value.

[0208] 6. Based on the sidelink reference signal (second SL-RS), the number of continuous times when the BLER of hypothetical PSCCH or PSSCH transmission is greater than the sixth preset value is inferred to reach a seventh preset value.

[0209] The conditions 1 and 2 correspond to the determination conditions of any first BFD, and the conditions 3-6 correspond to the determination conditions of any second BFD.

[0210] Optionally, for the above conditions 2, 4 and 6, the UE determines in a third preset period of time whether the number of continuous times reaches the corresponding preset value. That is, in the third preset period of time, the UE determines a beam failure detection only when the number of continuous occurrence of the event reaches the corresponding preset value.

[0211] The measurement quantity includes at least one of the following: layer 1 reference signal received power (L1-RSRP), layer 1 signal inference noise ratio (L1-SINR), and channel state information (CSI). In the sidelink communication, for the purpose of distinguishing with UU, the corresponding measurement quantities may be called SL-L1-RSRP, SL-L1-SINR, and sidelink channel state information reference signal (SL-CSI), etc., but it is not limited thereto.

[0212] In the above conditions, the preset value for the number of continuous times, the preset value for the measurement quantity (e.g., SL-L1-RSRP and / or SL-L1-SINR, etc.) and / or the preset value for the BLER may be configured to the RX UE by the TX UE by PC5-RRC signaling. That is, at least one of the third preset value, the first threshold, the second threshold, the fifth preset value, the sixth preset value and the seventh preset value is configured to the second UE by the first UE by PC5-RRC signaling. However, for the TX UE, these values may be determined autonomously by the TX UE, or these values may be preconfigured. For example, if the TX UE is within the network coverage, these values may be configured to the TX UE by the base station by UE-specific RRC signaling; and, if the TX UE is not within the network coverage, the TX UE may determine these values by preconfigured RRC parameters that are stored in the terminal device in a hard-coded manner.

[0213] In the above conditions 2, 4 and 6, since the number of continuous occurrence of the event needs to be counted, the medium access control (MAC) layer may be an entity of the UE to determine the beam failure detection. Whenever an event occurs, the physical layer needs to report it to the MAC layer, and the MAC layer determines a beam failure detection when the number of continuous times reaches the corresponding preset value. However, in the conditions 1, 3 and 5, the physical layer may be an entity of the UE to determine the beam failure detection. When the physical layer determines the beam failure detection, the beam failure detection may be reported to the MAC layer because the MAC layer is the entity that performs beam management.

[0214] In the communication system based on the UU interface, the beam failure detection is performed by the UE. When the UE detects multiple beam failures, a beam failure recovery (BFR) is triggered. After the BFR (first BFR and / or second BFR, which may be called BFR for short for the convenience of description), the UE performs measurement on the reference signal used for BFR transmitted by the base station to re-acquire the best downlink transmission beam and then reports it to the base station based on the non-contention based random access procedure. Since the physical resource (RACH occasion, RO) used for random access is associated with the index of the synchronization signal block (SSB), the base station can obtain the information of the best downlink transmission beam reported by the UE. Then, the base station transmits a physical downlink control channel (PDCCH) and the reconfigured downlink transmission beam to the UE based on the best downlink transmission beam. Upon receiving the PDCCH, the UE can consider that the BFR succeeds.

[0215] However, in the sidelink system, the communication parties are TX UE and RX UE, respectively, and the executors of beam failure detection and recovery are different. There may be the following schemes.

[0216] Scheme 1 (as shown in FIG. 8): the beam failure detection and recovery are executed by the TX UE because the TX UE is the initiator of the establishment of the PC5 RRC connection. It is necessary for the TX UE to maintain the communication quality of the PC5 RRC connection. For example, the TX UE determines, based on the above condition 1 and / or 2, whether to perform a beam failure detection (that is, for the first UE, the BFD is the first BFD determined according to the above condition 1 and / or 2). When multiple continuous beam failure detections are detected (for example, the number of continuous times reaches the first preset value), the TX UE triggers a BFR (first BFR). Then, the TX UE transmits, to the RX UE, a first sidelink reference signal (SL-RS) used for the first BFR on the preconfigured sidelink resource. After the available candidate beam information reported by the RX UE is received, it is considered that the first BFR succeeds. In this scheme, since the RX UE does not know when the first BFR is triggered, the RX UE needs to periodically measure the first SL-RS used for the first BFR. When the measurement result satisfies a preset condition (for example, but not limited to, being greater than the first threshold), the corresponding beam is determined as an available candidate beam, and the beam information is reported to the TX UE. For example, the beam information is reported to the first UE on the PSFCH resource associated with this beam, but it is not limited thereto. It can be seen that scheme 1 can be regarded as the combination of the method executed by a first UE shown in FIG. 4 and the method executed by a second UE shown in FIG. 5, wherein the first SL-RS is periodically transmitted by the first UE after the first UE triggers the first BFR, until the first BFR succeeds; and, the first SL-RS is periodically measured by the second UE.

[0217] Scheme 2 (as shown in FIG. 9): the beam failure detection and recovery are executed by the RX UE because the RX UE is the first to perceive the sidelink communication quality. If the beam failure detection is performed by the RX UE, the change of the beam communication quality can be found in time, and intervention can be performed as early as possible. For example, the RX UE determines, based on at least one of the above conditions 3-6, whether to perform a beam failure detection (that is, for the second UE, the BFD is the second BFD determined according to at least one of the above conditions 3-6). When multiple continuous beam failure detections are detected (for example, the number of continuous times reaches the first preset value), the RX UE triggers a BFR (second BFR). Then, the RX UE measures the first SL-RS used for the second BFR transmitted by the TX UE on the preconfigured sidelink resource. When the measurement result satisfies a preset condition (for example, but not limited to, being greater than the first threshold), the corresponding beam is determined as an available candidate beam, and the available candidate beam information is reported to the TX UE. For example, the beam information is reported to the first UE on the PSFCH resource associated with this beam, but it is not limited thereto. Upon receiving the PSCCH / PSSCH transmitted by the TX UE, the RX UE considers that the second BFR succeeds. In this scheme, since the TX UE does not know when the second BFR is triggered, the TX UE needs to periodically transmit the first SL-RS used for the second BFR. It can be seen that scheme 2 can be regarded as the combination of the method executed by a first UE shown in FIG. 7 and the method executed by a second UE shown in FIG. 6, wherein the first SL-RS is periodically transmitted by the first UE, and the first SL-RS is periodically measured by the second UE after the second UE triggers the second BFR, until the second BFR succeeds.

[0218] Scheme 3 (as shown in FIG. 10): the beam failure detection and recovery are jointly performed by the TX UE and the RX UE. This scheme can establish beam recovery between the TX UE and the RX UE, and also simplify the behavior of the TX UE or the RX UE. For example, the TX UE determines whether to perform a beam failure detection based on the condition 1 and / or 2. When multiple continuous beam failure detections are detected (for example, the number of continuous times reaches the first preset value), the TX UE triggers the first BFR of the transmitting terminal (which may also be called TX-BFR hereinafter). Then, the TX UE transmits, to the RX UE, a first SL-RS used for the BFR on the preconfigured sidelink resource. After the available candidate beam information reported by the RX UE is received, it is considered that the TX-BFR succeeds. In addition, the RX UE also determines whether to perform a beam failure detection based on at least one of the conditions 3-6. When multiple continuous beam failure detections are detected (for example, the number of continuous times reaches the first preset value), the RX UE triggers the second BFR of the receiving terminal (which may also be called RX-BFR hereinafter). Then, the RX UE measures the first SL-RS used for the BFR transmitted by the TX UE on the preconfigured sidelink resource. When the measurement result satisfies a preset condition (for example, but not limited to, being greater than the first threshold), the corresponding beam is determined as an available candidate beam, and the available candidate beam information is reported to the TX UE. For example, the beam information is reported to the first UE on the PSFCH resource associated with this beam, but it is not limited thereto. After the PSCCH / PSSCH transmitted by the TX UE is received, it is considered that the RX-BFR succeeds. In this scheme, the TX UE transmits the first SL-RS used for the BFR only after the TX-BFR is triggered, and the RX UE measures the first SL-RS used for the BFR and reports the available candidate beam information only after the RX-BFR is triggered. It can be seen that scheme 3 can be regarded as the combination of the method executed by a first UE shown in FIG. 4 and the method executed by a second UE shown in FIG. 6, wherein the first SL-RS is periodically transmitted by the first UE after the first UE triggers the first BFR, until the first BFR succeeds; and, the first SL-RS is periodically measured by the second UE after the second UE triggers the second BFR, until the second BFR succeeds.

[0219] Further, for the first UE, the method executed by the first UE may further include the following steps.

[0220] In the step S404, if the beam information reported by the second UE is not received on the PSFCH resource associated with any first SL-RS resource index within a first preset period of time after the first SL-RS is transmitted, it is determined that the first BFR fails.

[0221] In step S405, the procedure returns to the initial beam pairing procedure.

[0222] Correspondingly, for the second UE, the method executed by the second UE may further include the following steps.

[0223] In step S605, if the PSCCH and / or PSSCH transmitted by the first UE is not received within a second preset period of time after the beam information is reported, it is determined that the second BFR fails.

[0224] In step S606, the procedure returns to the initial beam pairing procedure.

[0225] In the embodiment of the present application, in the conditions 3-6 for determining the BFD, the UE needs to measure a second SL-RS used for determine the second BFD. The sidelink reference used for the measurement of the second BFD may be configured by the TX UE as at least one of the following by PC5-RRC signaling (that is, the second SL-RS may be configured as at least one of the following).

[0226] (1) SL-SSB corresponding to one set of SL-SSB indexes.

[0227] If the TX UE happens to also transmit a PSBCH for synchronization of other UEs in the surrounding range, the TX UE may instruct the RX UE to determine the second BFD based on the SL-SSB. In the sidelink communication system, a UE will transmit a PSBCH only when a certain condition is satisfied, that is, not every TX UE will transmit a PSBCH. Therefore, other sidelink reference signals may also be used for the measurement of the second BFD.

[0228] (2) SL-CSI-RS corresponding to one set of SL-CSI-RS resources, the SL-CSI-RS transmission is standalone.

[0229] Standalone transmission means that the SL-CSI-RS is not transmitted together with the PSSCH, and the SL-CSI-RS may be aperiodic or periodic.

[0230] Generally, in order to reduce the measurement complexity of BFD, the beam used for BFD measurement is a subset of all transmission beams supported by the TX UE. If it is assumed that the SL-SSB is used for BFD measurement, the TX UE will configure an index set of SL-SSB for BFD measurement by PC5-RRC signaling, and the RX UE will perform measurement on the corresponding SSB. If it is assumed that the SL-CSI-RS is used for BFD measurement, the TX UE will configure SL-CSI-RS resource index set for BFD measurement by PC5-RRC signaling, and the RX UE will perform measurement on the corresponding SL-CSI-RS resource.

[0231] Optionally, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the second SL-RS may be at least one of the following:

[0232] (3) the demodulation reference signal (DMRS) of the PSCCH and / or the DMRS of the PSSCH;

[0233] (4) the SL-SSB associated with the available set of candidate beams of the PSCCH; and

[0234] (5) the SL-CSI-RS associated with the available set of candidate beams of the PSCCH.

[0235] If the TX UE does not configure for the RX UE the sidelink reference signal (second SL-RS) used for the measurement of the second BFD, that is, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the RX UE performs measurement based on the SL-CSI-RS or SL-SSB associated with the available candidate beam of the PSCCH. The "associated" means that the PSCCH and the associated SL-CSI-RS or SL-SSB correspond to the same beam. The available candidate beam of the PSCCH may be configured as a set of beams. For example, the available candidate beam of the PSCCH may be indicated by a beam ID, a beam index, an associated SL-SSB index or an associated SL-CSI-RS resource index; or, the available candidate beam of the PSCCH may be indicated by a transmission configuration indicator (TCI). The TX UE configures the corresponding beam ID, beam index, associated SL-SSB index or associated SL-CSI-RS resource index for each TCI state by PC5 RRC signaling to indicate the corresponding beam.

[0236] In the embodiment of the present application, after the TX UE triggers the TX-BFR, the TX UE transmits the sidelink reference signal (first SL-RS) used for the first BFR; and, after the RX UE triggers the RX-BFR, the RX UE measures the sidelink reference signal (first SL-RS) used for the second BFR. The sidelink reference signal used for the BFR (first BFR and / or second BFR) may be configured as at least one of the following by the TX UE by PC5-RRC signaling (that is, the first SL-RS may be configured as at least one of the following):

[0237] (1) SL-SSB corresponding to one set of SL-SSB indexes. If the TX UE happens to also transmit a PSBCH, the SL-SSB transmitted by this TX UE may be used for the BFR measurement of the RX UE.

[0238] (2) SL-CSI-RS corresponding to one set of SL-CSI-RS resources, the SL-CSI-RS transmission is standalone. Optionally, the physical resource used for transmitting the SL-CSI-RS is periodic. That is, the SL-CSI-RS is a periodic SL-CSI-RS transmission that is standalone. The periodic physical resource is configured to the second UE by the first UE by PC5-RRC signaling. For example, the TX UE preconfigures a periodic SL-CSI-RS (including the preconfigured time-frequency domain resources, period, related parameters, etc.) for the RX UE by PC5-RRC signaling.

[0239] In the embodiment of the present application, if the periodic physical resource is not configured, the method executed by a first UE further includes at least one of the following operations: transmitting the SL-CSI-RS to the second UE on a resource that has been indicated to be reserved by sidelink control information (SCI) by the first UE but has not been used; and, starting the initial beam pairing procedure. Correspondingly, the method executed by a second UE further includes at least one of the following operations: receiving the SL-CSI-RS transmitted by the first UE on a resource that has been indicated to be reserved by SCI by the first UE but has not been used; and, starting the initial beam pairing procedure.

[0240] Generally, in order to reduce the measurement complexity of the beam re-acquiring procedure, the beam used for BFR (first BFR and / or second BFR) measurement may be a subset of all transmission beams supported by the TX UE. In the initial beam pairing procedure, the RX UE measures all transmission beams supported by the TX UE, then selects an available candidate beam and reports the available candidate beam information to the TX UE. However, in the beam re-acquiring procedure triggered by the BFR, the RX UE does not need to measure all beams, but only needs to measure a set of candidate beams and determine at least an available candidate beam in this set of candidate beams and report it to the TX UE. In addition, it is not hard to understand that the set of beams used for BFR (first BFR and / or second BFR) measurement may be different from the set of beams used for BFD measurement.

[0241] If it is assumed that the SL-SSB is used for BFR measurement, the TX UE will configure an index set of SL-SSB for BFR measurement by PC5-RRC signaling, and the RX UE will perform measurement on the corresponding SSB.

[0242] Optionally, if the set of SL-SSB indexes is not configured, the first SL-RS is SL-SSB corresponding to all SL-SSB indexes. That is, if the set of SL-SSB indexes is not configured, the RX UE performs measurement on all SSBs by default.

[0243] If it is assumed that the SL-CSI-RS is used for BFR measurement, the TX UE will configure SL-CSI-RS resource index set for BFR measurement by PC5-RRC signaling, and the RX UE will perform measurement on the corresponding SL-CSI-RS resource.

[0244] Optionally, if the set of SL-CSI-RS resources is not configured, the first SL-RS is SL-CSI-RS corresponding to all SL-CSI-RS resources. That is, if the set of SL-CSI-RS resources is not configured, the RX UE performs measurement on all SL-CSI-RS resources by default.

[0245] Optionally, if the TX UE does not preconfigure periodic SL-CSI-RS for the RX UE and if the TX UE happens to transmit SL-SSB, the RX UE performs BFR measurement based on the SL-SSB by default.

[0246] Optionally, if the set of SL-CSI-RS resources is not configured, the first SL-RS is the SL-RS used for initial beam pairing. That is, if the TX UE does not preconfigure a periodic SL-CSI-RS for the RX UE, the beam re-acquiring procedure triggered by the BFR returns to the initial beam pairing procedure. For example, after the TX-BFR is triggered, the TX UE transmits the sidelink reference signal used for initial beam pairing; and, after the RX-BFR is triggered, the RX UE measures the sidelink reference signal used for initial beam pairing. Generally, the sidelink reference signal used for initial beam pairing is transmitted on the predefined time-frequency domain resource. The initial beam pairing procedure will not be described in detail in the embodiment of the present application.

[0247] Optionally, if the set of SL-CSI-RS resources is not configured, the first SL-RS is the SL-CSI-RS (transmitted by the first UE, received by the second UE) on a resource that has been indicated to be reserved by SCI by the first UE but has not been used. That is, if the TX UE does not preconfigure a periodic SL-CSI-RS for the RX UE and if the TX UE has resources that have been indicated to be reserved by SCI but have not been used, this resource or these resources may be used to transmit the SL-CSI-RS for BFR measurement. For example, after the TX-BFR is triggered, the TX UE transmits, on the resource that has been indicated to be reserved by SCI but has not been used, the SL-CSI-RS for BFR measurement; and, after the RX-BFR is triggered, the RX UE measures the SL-CSI-RS on the resource that has been indicated to be reserved by SCI by the TX UE but has not been used. If this TX UE has no resource that has been indicated to be reserved by SCI but has not been used, the beam re-acquiring procedure triggered by the BFR returns to the initial beam pairing procedure. Here, the resource of the TX UE that has been indicated to be reserved by SCI but has not been used is the resource reserved for the RX UE, or the resource of the TX UE that has been indicated to be reserved by SCI but has not been used may be the resource reserved for the RX UE or other UEs.

[0248] In the embodiment of the present application, the beam information is reported by the second UE in a case where the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold. As an example, if the SL-L1-RSRP or SL-L1-SINR measured by the RX UE on the candidate beam used for BFR measurement exceeds the first threshold, it is determined that the corresponding candidate beam is an available candidate beam, and the available candidate beam information is reported to the TX UE. The first threshold value is configured to the RX UE by the TX UE by PC5-RRC signaling.

[0249] Optionally, the RX UE reports the available candidate beam information by a PSFCH. For example, each candidate beam used for BFR measurement corresponds to one PSFCH resource. If the SL-L1-RSRP or SL-L1-SINR measured by the RX UE on a candidate beam exceeds the first threshold, one piece of state information (e.g., ACK) is fed back on the corresponding PSFCH resource; or, the RX UE does not give feedback. If the TX UE receives the state information on one PSFCH resource, it implies that the available candidate beam of the RX UE is the candidate beam corresponding to the PSFCH resource. In the present application, the beam information fed back by the RX UE on the PSFCH may also be called "ACK" or "successful information", etc.

[0250] Optionally, if the RX UE measures that the SL-L1-RSRP or SL-L1-SINR of a plurality of beams in a group of candidate beams exceeds the first threshold, one piece of state information (e.g., ACK) is fed back on the PSFCH resource associated with the best beam. That is, the step S502 or S603 includes: if there are at least two first SL-RS resources whose measurement quantities are greater than the first threshold, reporting beam information to the first UE on a PSFCH resource associated with the largest measurement quantity in the at least two first SL-RS resources. Correspondingly, for the first UE, if there are at least two first SL-RS resources whose measurement quantities measured by the second UE are greater than the first threshold, the beam information is received on a PSFCH resource associated with the largest measurement quantity in the at least two first SL-RS resources.

[0251] In the embodiment of the present embodiment, the PSFCH resource associated with any first SL-RS resource index is determined in the following way: determining a group of PSFCH resources based on at least one of the index of the time unit where the SL-RS is located, the index of the starting sub-channel of the SL-RS and the number of sub-channels occupied by the SL-RS; and, determining, from the group of PSFCH resources, the PSFCH resource associated with the SL-RS resource index according to at least one of the first UE ID, the second UE ID and the SL-RS resource index.

[0252] The mapping relationship between candidate beams used for BFR measurement and PSFCH resource may reuse the existing mapping relationship between PSCCH / PSSCH resources and PSFCH resources. For example, if it is assumed that the standalone SL-CSI-RS transmission is used for BFR measurement, that is, if all the resources used for PSSCH resource transmission may be used for the standalone SL-CSI-RS transmission, the existing mapping relationship between PSSCH resources and PSFCH resources may be reused.

[0253] It is to be noted that, in the embodiment of the present application, one time unit may refer to one OFDM symbol or one slot including a plurality of OFDM symbols. In addition, the "OFDM symbol" may be called "symbol" for short, and the same content will not be repeated hereinafter.

[0254] Optionally, a group of PSFCH resources may be determined in the corresponding PSFCH slot according to the index i of the slot where the standalone SL-CSI-RS transmission is located, the index j of the starting sub-channel and the number of the occupied sub-channels.

[0255] Specifically, according to the configuration of the resource pool, it can be determined that PSSCH slots are associated with one PSFCH slot, and one PSFCH slot includes total physical resource blocks (PRBs) for PSFCH transmission, so that the PSFCH PRB corresponding to the jthsub-channel in the ithPSSCH slot is a PRB numbered as among PRBs, where , and . The index of the PRB is determined by ascending i, followed by j. is the number of PSFCH PRBs corresponding to a sub-channel in a PSSCH slot, , and is the maximum number of sub-channels included in a PSSCH slot.

[0256] In addition, each PSFCH PRB incudes PFSCH code domain resources, and is the number of cyclic shift pairs determined according to the resource pool configuration parameter sl-NumMuxCS-Pair. Thus, the UE may determine that the total number of available PSFCH resources is . If sl-PSFCH-CandidateResourceType is configured as startSubCH, that is, if available PSFCH resources are determined according to the starting sub-channel, ; and, if sl-PSFCH-CandidateResourceType is configured as allocSubCH, that is, if available PSFCH resources are determined according to the number of sub-channels, . Therefore, a group of PSFCH resources with a size of may be determined according to the index of the slot where the SL-CSI-RS is located, the index of the starting sub-channel and the number of occupied sub-channels.

[0257] Further, if one slot includes only one SL-CSI-RS resource, the index of a PSFCH resource for reporting beam information or rough beam quality may be determined among PSFCH resources by the following formula:

[0258]

[0259] Or, if one slot includes one or more SL-CSI-RS resources, the index of a PSFCH resource for reporting beam information or rough beam quality may be determined among PSFCH resources by the following formula:

[0260]

[0261] where , is the maximum index of the SL-CSI-RS resource, is the index of the SL-CSI-RS resource associated with the beam information to be reported, is the physical layer source ID indicated in the SCI for scheduling the SL-CSI-RS, and is the physical layer destination ID indicated in the SCI, the UE ID indicated by a higher layer, or 0.

[0262] In the embodiment of the present application, the BFR and BFR procedures may be controlled by an MAC layer.

[0263] The BFR is controlled by the MAC entity of the UE, and at least one of the following parameters needs to be used in the related procedure:

[0264] (1) slBeamFailureDetectionTimer, which is a timer for controlling the accumulation of the number of beam failures, wherein the count is accumulated only when a beam failure occurs within a period of time controlled by the timer;

[0265] (2) slBeamFailureInstanceMaxCount, which is the maximum count of continuous beam failures, wherein the BFR is triggered if the number of continuous beam failures is greater than or equal to this parameter;

[0266] (3) slBeamFaiureRecoveryTimer, which is a timer for controlling the time of the beam recovery procedure, wherein it is considered as a beam recovery failure if the beam failure recovery is not successful within a period of time corresponding to the timer; and

[0267] (4) SL_BFI_COUNTER, which is a counter for beam failures.

[0268] In an example, the BFR control procedure related to the MAC layer can be described as at least one of the following:

[0269] 1> If one beam failure indication is received:

[0270] 1.1> the slBeamFailureDetectionTimer is started or restarted;

[0271] 1.2> the counter SL_BFI_COUNTER is added by 1;

[0272] 1.3> if the counter SL_BFI_COUNTER is greater than or equal to the slBeamFailureInstanceMaxCount:

[0273] 1.3.1> the BFR triggered; or, if the UE is a TX UE, the TX-BFR is triggered; or, if the UE is a RX UE, the RX-BFR is triggered;

[0274] 2> if the BFR (TX-BFR) is triggered (the BFR triggered by the TX UE):

[0275] 2.1> the physical layer is instructed to transmit a sidelink reference signal used for BFR measurement on the preconfigured resource;

[0276] 2.2> if no transmission resource is preconfigured for the sidelink reference signal used for BFR measurement:

[0277] 2.2.1> the physical layer is instructed to transmit, on a resource that has been indicated to be reserved by SCI but has not been used, a sidelink reference signal used for BFR measurement; or, the procedure returns to the initial beam pairing procedure;

[0278] 2.2.2> if there is no resource that has been indicated to be reserved by SCI but has not been used:

[0279] 2.2.2.1> the procedure returns to the initial beam pairing procedure;

[0280] 3> if the BFR (RX-BFR) is triggered (the BFR triggered by the RX UE):

[0281] 3.1> the physical layer is instructed to measure the sidelink reference signal used for BFR on the preconfigured resource and report the available candidate beam information in the set of candidate beams used for BFR;

[0282] 3.2> if no transmission resource is preconfigured for the sidelink reference signal used for BFR measurement:

[0283] 3.2.1> the physical layer is instructed to measure, on a resource that has been indicated to be reserved by SCI but has not been used, the sidelink reference signal used for BFR measurement and report the available candidate beam information in the set of candidate beams used for BFR; or, the procedure returns to the initial beam pairing procedure;

[0284] 3.2.2> if there is no resource that has been indicated to be reserved by SCI but has not been used:

[0285] 3.2.2.1> the procedure returns to the initial beam pairing procedure;

[0286] 4> if the slBeamFailureDetectionTimer is expired; or, if the parameter slBeamFailureDetectionTimer, slBeamFailureInstanceMaxCount or the sidelink reference signal used for BFD is reconfigured:

[0287] 4.1> the counter SL_BFI_COUNTER is set as 0;

[0288] 5> if the available candidate beam information reported by the RX UE is received, it is considered that the BFR or TX-BFR is completed successfully; or, if the PSCCH / PSSCH from the TX UE is received, it is considered that the BFR or RX-BFR is completed successfully;

[0289] 5.1> the counter SL_BFI_COUNTER is set as 0;

[0290] 5.2> the timer slBeamFaiureRecoveryTimer is stopped;

[0291] 6> if the available candidate beam information based on the set of candidate beams used for BFR is reported (the RX-BFR triggered for the RX UE); or, if the sidelink reference signal used for BFR measurement is transmitted (the TX-BFR triggered for the TX UE):

[0292] 6.1> the slBeamFaiureRecoveryTimer is started or restarted;

[0293] 7> if the timer slBeamFaiureRecoveryTimer is expired;

[0294] 7.1> a BFR failure is considered and reported to a higher layer;

[0295] 7.2> the procedure returns to the initial beam pairing procedure.

[0296] In the embodiment of the present application, the sidelink reference signal (second SL-RS) used for BFD measurement and the sidelink reference signal (second SL-RS) used for BFR measurement may be standalone SL-CSI-RS transmissions. The standalone SL-CSI-RS transmission means that it is not bound to the PSSCH for transmission, so all the existing time-frequency domain resources used for PSSCH transmission can be used for SL-CSI-RS transmission.

[0297] The resource allocation of the aperiodic SL-CSI-RS can adopt the same resource allocation method as the PSSCH. That is, the used frequency domain resources and the related information are indicated by the SCI, and the occupied time domain symbols are defaulted as all symbols except for other transmission symbols in a slot. The other transmission symbols include automatic gain control (AGC), PSCCH, PSFCH, guard period or other symbols.

[0298] Since the beam of the SL-CSI-RS may be different from the beam used by the SCI, the SL-CSI-RS should be completely time-multiplexed with the SCI, including being completely time-multiplexed with the PSCCH (1-stage SCI) and 2-stage SCI. As shown in FIGS. 11a and 11b, the 2-stage SCI completely occupies first one or more symbols of the SL-CSI-RS resource, where FIG. 11a corresponds to a situation where there is no PSFCH resource in the slot, and FIG. 11b corresponds to a situation where there are PSFCH symbols in the slot. In addition, other time units further include AGC, PSCCH (1-stage SCI), GP, etc.

[0299] Since the related control information transmitted by the SL-CSI-RS is less, the related control information can be carried by the existing 1-stage SCI, so that the 2-stage SCI can also be omitted, as shown in FIGS. 12a and 12b, where FIG. 12a corresponds to a situation where there is no PSFCH symbols in the slot, and FIG. 12b corresponds to a situation where there are PSFCH symbols in the slot. In addition, other time units further include AGC, GP, etc.

[0300] For the resource allocation of the periodic SL-CSI-RS, the frequency domain sources, the time domain starting position and the period may be configured to the RX UE by the TX UE by PC5-RRC signaling. In the existing resource allocation method based on Mode 1, the base station may preconfigure for the TX UE a periodic resource for SL-CSI-RS transmission; and, in the resource allocation mode of Mode 2, the TX UE may reserve a periodic resource for SL-CSI-RS transmission in a resource pool by sensing. This resource pool may be specific for SL-CSI-RS transmission, or this resource pool may be shared with PSCCH / PSSCH transmission. Since the time-frequency domain resources of the periodic SL-CSI-RS are preconfigured to the RX UE, the SL-CSI-RS transmission does not need to include the SCI, and the resources originally corresponding to SCI transmission may be left blank (that is, nothing will be transmitted), or the resources originally corresponding to SCI transmission may also be used for SL-CSI-RS transmission, as shown in FIGS. 13a and 13b, where FIG. 13a corresponds to a situation where there is no PSFCH symbol in the slot, and FIG. 13b corresponds to a situation where there are PSFCH symbols in the slot. In addition, other time units further include AGC, GP, etc.

[0301] In the existing communication system, for the SL-CSI-RS with a single antenna port, the mapping pattern only occupies one OFDM symbol in time domain. However, in the embodiment of the present application, the resource used for standalone SL-CSI-RS transmission may include a plurality of symbols in the slot. Therefore, it is necessary to map one SL-CSI-RS to a plurality of symbols. Specifically, the standalone SL-CSI-RS transmission includes at least one SL-CSI-RS resource, and each SL-CSI-RS resource is mapped to at least two consecutive time units. The mapping mode may be at least one of the following.

[0302] (1) One SL-CSI-RS resource is mapped to at least two consecutive time units by repeating on time units. One SL-CSI-RS signal sequence is mapped to more symbols by repeating in time domain. When repeating in time domain, the starting mapping RE position of each symbol may be kept the same; or, the starting mapping RE position of each subsequent symbol is sequentially moved by a first preset number of REs, for example, being sequentially moved by one RE. By taking a pattern in which the frequency domain density is three SL-CSI-RS REs per PRB as an example, the repetition mode is as shown in FIGS. 14a and 14b. FIG. 14a corresponds to a situation where the starting RE position is kept the same on all symbols, and FIG. 14b corresponds to a situation where the starting RE position is cyclically shifted by one RE on different symbols.

[0303] (2) One SL-CSI-RS resource is mapped to at least two consecutive time units by cyclic shifting. For example, one SL-CSI-RS signal sequence is cyclically shifted and then mapped to other symbols. The difference from the above repetition on time units is that the signal sequence mapped to other symbols is a signal sequence obtained by cyclically shifting the signal sequence on the first symbol by a preset gap.

[0304] (3) One SL-CSI-RS resource is mapped to at least two consecutive time units by generating a longer SL-CSI-RS signal sequence, for example, being mapped to more symbols by generating a longer SL-CSI-RS signal sequence. The mapping mode may be mapping in time domain first and then in frequency domain, or mapping in frequency domain first and then in time domain. The starting mapping RE position on each symbol may be kept the same, or the starting mapping RE position on each symbol is sequentially moved by a second preset number of REs.

[0305] In the existing communication system, for the SL-CSI-RS with a single antenna port, the mapping pattern is discrete in frequency domain, and the frequency domain density is fixed as one SL-CSI-RS RE per PRB. However, the standalone SL-CSI-RS transmission may occupy all REs in frequency domain, i.e., frequency domain density is 12 SL-CSI-RS REs per PRB. Therefore, it is necessary to map one SL-CSI-RS to all REs in the allocated PRBs in a symbol. That is, the SL-CSI-RS may be mapped to all REs in the allocated PRBs in at least one time unit. For example, 12 REs in one PRB are all used for the SL-CSI-RS. The mapping mode may be at least one of the following.

[0306] (1) The SL-CSI-RS is mapped to all REs in the allocated PRBs in at least one time unit by repeating on REs. For example, one SL-CSI-RS is mapped to all REs in the allocated PRBs in a symbol by repeating in frequency domain. By taking a pattern in which the frequency domain density is three SL-CSI-RS REs per PRB as an example, the repetition mode is as shown in FIG. 15. The signal on one SL-CSI-RS RE is repetitively mapped to other two REs.

[0307] (2) The SL-CSI-RS is mapped to all REs in the allocated PRBs in at least one time unit by generating a longer SL-CSI-RS signal sequence. For example, the SL-CSI-RS is mapped to all REs in the allocated PRBs in a symbol by generating a longer SL-CSI-RS signal sequence, that is, the frequency domain density of the SL-CSI-RS is maximized (fully occupying the frequency domain, i.e., 12 SL-CSI-RS REs per PRB).

[0308] In addition, one SL-CSI-RS signal sequence may be repetitively mapped in time domain and frequency domain, and the coverage of the SL-CSI-RS is boosted by energy accumulation, for example, as shown in FIGS. 16a and 16b, where FIG. 16a corresponds to a situation where the starting RE position is kept the same on all symbols, and FIG. 16b corresponds to a situation where the starting RE position is cyclically shifted by one RE on different symbols.

[0309] A plurality of SL-CSI-RS resources may be transmitted in one slot. That is, the standalone SL-CSI-RS transmission may include a plurality of SL-CSI-RS resources in one slot. As an example, as shown in FIG. 17, each SL-CSI-RS corresponds to one symbol, and eight SL-CSI-RS resources (i.e., resources {#0, #1, #2, #3, #4, #5, #6, #7}) may be transmitted in one slot. If it is assumed that the eight SL-CSI-RS resources correspond to different transmission beams, that is, if eight times of sweeping of transmission beams may be completed in one slot, the RX UE may complete the measurement of different beams in one slot, and thus may quickly determine the best transmission beam. Or, only one SL-CSI-RS resource may be transmitted in one slot. As shown in FIG. 18, one SL-CSI-RS resource occupies eight symbols by repeating in time slot. Since one SL-CSI-RS resource (i.e., resource {#0}) corresponds to only one transmission beam, the repetition of the SL-CSI-RS signal sequence is the repetition of the same transmission beam, so the RX UE may receive different repetitions by using different reception beams, that is, eight times of sweeping of reception beams may be completed in one slot, so that the best reception beam may be quickly determined. Or, a plurality of SL-CSI-RS resources may be transmitted in one slot, and each SL-CSI-RS resource may be repeated on a plurality of consecutive symbols. As shown in FIG. 19, the number of SL-CSI-RS resources included in one slot is 4 (i.e., resources {#0, #1, #2, #3}), and each SL-CSI-RS resource is repeated on two consecutive symbols. This transmission mode can consider the sweeping of transmission beams and the sweeping of reception beams in one slot.

[0310] In the embodiment of the present application, the standalone SL-CSI-RS transmission may also be discretely mapped in the frequency domain. For example, similar to the CSI-RS in the communication system based on the UU interface, the frequency domain density of the SL-CSI-RS is configurable. Specifically, the SL-CSI-RS is mapped to some REs in at least one time unit, and the transmitting power on other REs is boosted to the some REs. As an example, the maximum frequency domain density may be three REs per PRB, that is, other 9 REs in the PRB are blank REs. That is, the TX UE does not transmit anything on these REs. Thus, the TX UE may concentrate the transmitting power, which is originally allocated to the blank REs, on SL-CSI-RS REs, that is, power boosting is performed on the REs of the SL-CSI-RS. In this example, if it is assumed that the existing power allocation method for the PSSCH is reused, when the transmitting power (i.e., the transmitting power to be allocated) remains unchanged at the given bandwidth, the energy per resource element (EPRE) of the SL-CSI-RS may be boosted to 4 times (i.e., 8 dB, increased by 6 dB) of the EPRE (assumed as 2 dB) of the PSSCH.

[0311] In the embodiment of the present application, similar to other physical channels in the sidelink communication system, the standalone SL-CSI-RS transmission may have a priority. The priority may be indicated in the SCI associated with the SL-CSI-RS. In the resource allocation mode of Mode 2, the UE will use the priority of the SL-CSI-RS when autonomously allocating resources, and the priority of the SL-CSI-RS will also be used to solve the transmission collision of the TX UE, the reception collision of the RE UE, etc. The priority of the SL-CSI-RS may be predefined or preconfigured.

[0312] The related design schemes of the SL-CSI-RS used for BFD or BFR measurement mentioned in the above embodiments are also applicable to the SL-CSI-RS used for initial beam pairing before PC5-RRC establishment, and the method for reporting, by a RX UE in BFR, available candidate beam information by a PSFCH mentioned in the above embodiments is also applicable to the procedure of initial beam pairing before PC5-RRC establishment. For example, the SL-CSI-RS used for BFR measurement and the SL-CSI-RS used for initial beam pairing before PC5-RRC establishment are the same RS, but may have different time-frequency domain positions and transmission periods. In the initial beam pairing procedure, the SL-CSI-RS may be transmitted in a sparser cycle; while in the BFR, the SL-CSI-RS may be transmitted in a denser cycle.

[0313] Optionally, the TX UE transmits a candidate beam determination reference signal (CBD-RS) based on dynamic scheduling.

[0314] In an embodiment of the present application, when a beam failure recovery procedure is triggered, the TX UE shall transmit a sidelink reference signal to the RX UE for measurement to recover beam pairing. For the convenience of description, the sidelink reference signal used for the measurement by the RX UE to recover beam pairing may be referred to as candidate beam determination reference signal (CBD-RS). As described above, the CBD-RS may be an SL-SSB, an SL-CSI-RS, or a DMRS of the PSSCH, where the SL-CSI-RS transmission may be standalone or non-standalone. In the resource allocation mode of Mode 1, since sidelink resources are centrally allocated by the base station, the base station may allocate periodic transmission resources for the CBD-RS. In the resource allocation mode of Mode 2, the UE allocates resources autonomously based on its sensing of a resource pool, and it is very difficult to ensure that the periodic transmission resources are preempted, thereby it is more suitable to transmit the CBD-RS by means of dynamic scheduling to achieve the flexibility in resource allocation.

[0315] In an optional scheme, the CBD-RS is transmitted based on dynamic scheduling. That is, the CBD-RS is non-periodic, resources used for CBD-RS transmission are dynamically allocated, the TX UE is unable to pre-configure the resources used for CBD-RS transmission to the RX UE, the CBD-RS needs to have an accompanying SCI to indicate its transmission resources, and the RX UE determines the resources used for CBD-RS transmission by monitoring the SCI, thereby measuring the CBD-RS on the transmission resources indicated by the monitored SCI.

[0316] Here, by taking the SL-CSI-RS as the CBD-RS as an example, the SL-CSI-RS for determining candidate beams is transmitted by means of beam sweeping. That is, the TX UE transmits the SL-CSI-RS sequentially using different beams, and beams used for beam sweeping may be all beams supported by the TX UE, or a subset thereof, and the number of beams included in the subset may be pre-configured, or determined autonomously by the TX UE. The SL-CSI-RS transmission used for beam sweeping includes transmission of multiple SL-CSI-RS resources corresponding to the different beams. The SL-CSI-RS corresponding to different resource indexes may be transmitted on different slots, that is, the SL-CSI-RS transmission used for beam sweeping includes multiple consecutive or discontinuous slots. Alternatively, the SL-CSI-RS corresponding to different resource indexes may be transmitted on different symbols of the same slot. The RX UE determines the candidate beams by measuring the SL-CSI-RS on different resource indexes.

[0317] In a scenario where the BFR is triggered by the TX UE, after the TX UE triggers the BFR, the transmission of the SL-CSI-RS for determining candidate beams is also triggered by the TX UE. Since the BFR procedure needs to be completed within a period of time, e.g., by controlling the maximum execution time of the BFR procedure by a timer beamFailureRecoveryTimer, the transmission of the SL-CSI-RS for determining candidate beams shall also be completed within a preset period of time. For example, after the BFR is triggered, the TX UE shall transmit the SL-CSI-RS used for determining the candidate beams within a preset time window thereafter. That is, the latest transmission time of the SL-CSI-RS shall not exceed a pre-configured parameter value (e.g., SL-CSI-RS-lantencyBound), and the starting time position corresponding to the latest transmission time is the moment when the BFR is triggered.

[0318] In addition, the MAC layer of the TX UE may also control the transmission of the SL-CSI-RS used for determining candidate beams by a timer SL-CSI-RS-TransmissionTimer. That is, the size of the SL-CSI-RS-lantencyBound is the same as the size of the timer SL-CSI-RS-TransmissionTimer, where the size of the SL-CSI-RS-TransmissionTimer shall be smaller than the size of beamFailureRecoveryTimer to have sufficient time for the RX UE to transmit a beam failure recovery request (i.e., to report measurement results) and for the TX UE to transmit a beam failure recovery response (i.e., to indicate recovered beam information). On the TX UE side, when the BFR is triggered, both timers beamFailureRecoveryTimer and SL-CSI-RS-TransmissionTimer shall be started.

[0319] Optionally, in the resource allocation mode of Mode 1, after the TX UE triggers the BFR, the transmission of the SL-CSI-RS for determining candidate beams is triggered. That is, the timer SL-CSI-RS-TransmissionTimer shall be started, and if there are no resources available for sidelink transmission at the TX UE, the TX UE may trigger a scheduling request to request to the base station sidelink resources used for the SL-CSI-RS transmission, i.e., request SL-CSI-RS transmission resources corresponding to multiple times of beam sweeping. The base station may allocate resources on multiple consecutive slots for the SL-CSI-RS transmission used for beam sweeping to save signaling overhead.

[0320] In an example, when the TX UE transmits a scheduling request to the base station for SL-CSI-RS transmission used for beam sweeping, it may report to the base station the number of beams used for sweeping, and / or beam information for sweeping, where the number of beams may also be represented by the number of SL-CSI-RS resources, or the number of slots, and the beam information may be represented by an SL-CSI-RS resource index, or a TCI ID.

[0321] In an example, when the TX UE transmits a scheduling request to the base station for the SL-CSI-RS transmission, it may report to the base station the size of remaining time for the SL-CSI-RS transmission, to ensure that the base station can allocate resources for the SL-CSI-RS within the remaining time. Alternatively, the TX UE reports to the base station the size of the SL-CSI-RS-TransmissionTimer or the SL-CSI-RS-lantencyBound.

[0322] Optionally, in the resource allocation mode of Mode 2, after the TX UE triggers the BFR, the transmission of the SL-CSI-RS for determining candidate beams is triggered, that is, the timer SL-CSI-RS-TransmissionTimer is started. The MAC layer of the TX UE requests to the physical layer to determine a subset of resources for SL-CSI-RS transmission used for beam sweeping, i.e., to determine the SL-CSI-RS transmission resources corresponding to multiple times of beam sweeping.

[0323] In an example, when the MAC layer of the TX UE requests a resource allocation to the physical layer for the SL-CSI-RS transmission used for beam sweeping, the MAC layer may indicate to the physical layer the number of beams for sweeping, and / or beam information for sweeping, where the number of beams may also be represented by the number of SL-CSI-RS resources, or the number of slots, and the beam information may be represented by an SL-CSI-RS resource index, or a TCI ID.

[0324] In an example, the physical layer of the TX UE, in the process of determining the subset of the resources for SL-CSI-RS transmission, the end position of a resource selection window used for determining a set of initial candidate resources (as determined by a parameter T2) shall not extend beyond the latest transmission timepoint of the SL-CSI-RS (as determined by the SL-CSI-RS-lantencyBound), or, the end position of the resource selection window is selected as the latest transmission timepoint of the SL-CSI-RS, which has the advantage of ensuring that the SL-CSI-RS is transmitted before the latest transmission timepoint of the SL-CSI-RS, and that the latest transmission timepoint of the SL-CSI-RS can be indicated to the physical layer by the MAC layer of the TX UE. Alternatively, the MAC layer of the TX UE indicates to the physical layer the size of the SL-CSI-RS-lantencyBound.

[0325] Since the dynamically scheduled SL-CSI-RS may be miss-detected by the RX UE, to ensure that the RX UE is able to monitor the SL-CSI-RS to perform measurement, the TX UE may transmit multiple times of SL CSI-RS beam sweeping to reduce the probability of missing detection. For example, the TX UE may transmit up to N SL-CSI-RS beam sweeping after the BFR has been triggered, where one time of SL CSI-RS beam sweeping denotes a plurality of SL-CSI-RS transmissions corresponding to different candidate beams, that is, one time of SL CSI-RS beam sweeping may include SL-CSI-RS transmissions on a plurality of consecutive or discontinuous slots, and the value of N is pre-configured.

[0326] Optionally, the number of times the TX UE transmits CBD-RS beam sweeping cannot exceed a preset number, where one time of CBD-RS beam sweeping includes multiple CBD-RS transmissions corresponding to different candidate beams. For example, the MAC layer of the TX UE controls the number of times of CBD-RS beam sweeping by a counter, and whenever each time of CBD-RS beam sweeping is triggered (or transmitted), the TX UE increases the number of times of SL-CSI-RS beam sweeping by 1. If the number of times of SL-CSI-RS beam sweeping exceeds the preset value N, it is considered that the BFR procedure failed, the beamFailureRecoveryTimer is stopped, and the TX UE may start an establishment procedure for initial beam pairing of the RX UE.

[0327] Optionally, the TX UE expects to receive measurement reports from the RX UE within the preset time window after each time of CBD-RS beam sweeping, and if the TX UE does not receive measurement reports from the RX UE within the preset time window after the last CBD-RS transmission in the one time of CBD-RS beam sweeping, the TX UE is required to transmit the CBD-RS beam sweeping again , i.e. to trigger the transmission of the SL-CSI-RS for determining candidate beams, e.g. to start the SL-CSI-RS-TransmissionTimer etc..

[0328] Optionally, the TX UE continuously transmits multiple times of beam sweeping and does not stop transmitting the CBD-RS until it receives measurement reports transmitted by the RX UE, or until the allowed maximum number of times of CBD-RS beam sweeping is reached. A preset interval needs to be satisfied between two adjacent times of CBD-RS beam sweeping. For example, the TX UE triggers the transmission of the next CBD-RS beam sweeping at a position satisfying the preset interval after the previous CBD-RS beam sweeping. Alternatively, when to trigger the CBD-RS transmission is dependent on the implementation of the TX UE, and the TX UE shall ensure that the interval between two adjacent times of CBD-RS beam sweeping is greater than or equal to a pre-configured parameter value (e.g. CBD-RS-interval), where the interval between two adjacent times of CBD-RS beam sweeping refers to the interval between the last CBD-RS transmission in the previous CBD-RS beam sweeping and the first CBD-RS transmission in the subsequent CBD-RS beam sweeping.

[0329] Optionally, the RX UE notifies of the TX UE that the BFR is triggered, requesting the TX UE to transmit the CBD-RS.

[0330] In a scenario where the BFR is triggered by the RX UE, the RX UE needs to notify of the TX UE that the BFR is triggered by signaling, to request the TX UE to transmit the CBD-RS for determining the candidate beams. The signaling may be referred to as a BFR indication signaling, CBD-RS request signaling, and, by taking the SL-CSI-RS as the CBD-RS as an example, the CBD-RS request signaling may also be referred to as an SL-CSI -RS request signaling, etc.

[0331] Correspondingly, the TX UE triggers the transmission of the CBD-RS after receiving the CBD-RS request signaling transmitted by the RX UE, and / or, triggers a tx-ue-beamFailureRecoveryTimer on the TX UE side, where the size of the tx-ue-beamFailureRecoveryTimer on the TX UE side and the size of a rx-ue-beamFailureRecoveryTimer on the RX UE side can be different, and both are configured separately.

[0332] As described above, the TX UE can transmit the CBD-RS based on dynamic scheduling. For example, the TX UE transmits the transmission of the CBD-RS within a preset time window after receiving the CBD-RS request signaling from the RX UE. As described above, the starting position of a time window determined by the latest transmission time SL-CSI-RS-lantencyBound is the first symbol or the first slot after the TX UE receives the CBD-RS request signaling. Alternatively, the starting position of a time window determined by the latest transmission time SL-CSI-RS-lantencyBound is the first symbol or the first slot after the TX UE receives the CBD-RS request signaling.

[0333] The CBD-RS request signaling can be indicated by an SL MAC-CE or an SCI. As the BFR is triggered, beam pairing between the TX UE and the RX UE is no longer available, and the RX UE can only transmit the CBD-RS request signaling by means of beam sweeping. That is, the CBD-RS request signaling is transmitted sequentially by using different beams, and beams used for beam sweeping can be all transmitting beams supported by the RX UE, or a subset thereof, and the number of beams included in the subset can be either pre-configured or autonomously determined by the RX UE, and the beams included in the subset may also be autonomously determined by the RX UE.

[0334] Optionally, in order to enable the BFR procedure to be completed within a preset time, the transmission of the CBD-RS request signaling needs to be controlled to be within a preset time window. For example, the RX UE transmits the CBD-RS request signaling to the TX UE within the preset time window after triggering the BFR. That is, the transmission of the CBD-RS request signaling should not be later than a preset parameter value CBD-RS-request-lantencyBound, and the starting position of the time window determined by the CBD-RS-request-lantencyBound may be the first symbol or the first slot after the BFR is triggered.

[0335] In addition, the MAC layer of the RX UE may further control the transmission of the CBD-RS request by a timer CBD-RS-requestTimer, the size of which is the same as the size of the CBD-RS-request-lantencyBound. For example, the RX UE, at the first symbol or the first slot after triggering the BFR, triggers the transmission of the CBD-RS request, and correspondingly starts a timer BFR-requestTimer.

[0336] In the resource allocation mode of Mode 1, if the transmission of the CBD-RS request signaling is triggered (e.g., the timer CBD-RS-requestTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the CBD-RS request, the RX UE may transmit a scheduling request to the base station to request the sidelink resources for transmission of the PSSCH. In the resource allocation mode of Mode 2, if the transmission of the CBD-RS request signaling is triggered (e.g., the timer CBD-RS-requestTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the CBD-RS request signaling, the MAC layer of the RX UE may request the physical layer to allocate a subset of resources for PSSCH transmission.

[0337] In an embodiment of the present application, a feasible implementation is provided for transmission of a beam failure recovery reQuest (BFRQ).

[0338] In the above, the PSFCH-based measurement reporting method is introduced, and due to the less information content that can be carried by the PSFCH, the reporting of CBD-RS measurements by the RX UE can also be transmitted via an SL MAC-CE in order to report more information content. Herein, the reporting of CBD-RS measurements by the RX UE is referred to as a beam failure recovery request (BFRQ).

[0339] Optionally, by taking the SL-CSI-RS as the CBD-RS as an example, the BFRQ may indicate SL-CSI-RS indexes corresponding to one or M candidate beams. Alternatively, the BFRQ indicates SL-CSI-RS indexes corresponding to one or M candidate beams, and their corresponding RSRP values. For the case of reporting the SL-CSI-RS indexes corresponding to the M candidate beams, these M SL-CSI-RS indexes may be indicated in the order of magnitude of the RSRP values. For example, the corresponding SL-CSI-RS indexes are indicated from small to big according to the measured RSRP values. In addition, the determination of candidate beams needs to satisfy preset conditions, e.g., the RSRP values measured by the RX UE on the SL-CSI-RS corresponding to the candidate beams should exceed a preset RSRP threshold, and for the case of reporting one candidate beam, the RSRP values measured by the RX UE on the SL-CSI-RS corresponding to this candidate beam should be the best one of the RSRP values measured in all CBD-RSs, but for the case of reporting M candidate beams, the RSRP values measured by the RX UE on the SL-CSI-RS corresponding to the M candidate beams should be the top M RSRP values measured in all CBD-RSs. M may be a predefined or pre-configured positive integer value.

[0340] Optionally, in order to enable the BFR procedure to be completed within a preset time, the transmission of the BFRQ needs to be controlled to be within a preset time window. For example, the RX UE transmits the BFRQ within a preset time window after monitoring the CBD-RS corresponding to the last beam. That is, the transmission of the BFRQ should not be later than a preset parameter value BFR-request-lantencyBound, and the starting position of a time window determined by the BFR-request-lantencyBound may be the first symbol or the first slot after the last CBD-RS transmission (i.e. corresponding to the last beam) monitored by the RX UE, or, the starting position of the time window determined by the BFR-request-lantencyBound may be the first symbol or the first slot satisfying a preset interval after the last CBD-RS transmission monitored by the RX UE.

[0341] In addition, the MAC layer of the RX UE may further control the transmission of the BFRQ by a timer BFR-requestTimer, the size of which is the same as the size of the BFR-request-lantencyBound. For example, the RX UE, at the first symbol or the first slot after the monitored last CBD-RS transmission, triggers the transmission of the BFRQ, and correspondingly starts the timer BFR-requestTimer. Alternatively, the RX UE, at the first symbol or the first slot after the last CBD-RS transmission that satisfies the preset interval after the monitored last CBD-RS transmission, triggers the transmission of the BFRQ, and correspondingly starts the timer BFR-requestTimer.

[0342] In the resource allocation mode of Mode 1, if the BFRQ transmission is triggered (e.g. the timer BFR-requestTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the BFRQ, the RX UE may transmit a scheduling request to the base station to request sidelink resources for PSSCH transmission. Alternatively, in the resource allocation mode of Mode 2, if the BFRQ transmission is triggered (e.g. the timer BFR-requestTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the BFRQ, the MAC layer of the RX UE may request the physical layer to allocate a subset of resources for PSSCH transmission.

[0343] Optionally, assuming that the RX UE has beam symmetry, that is, each receiving beam of the RX UE corresponds to a transmitting beam, the RX UE may transmit the BFRQ using the transmitting beam corresponding to a candidate beam corresponding to the best RSRP value in the CBD-RS measurements, and the transmitting beam corresponding to the candidate beam means that the transmitting beam of the RX UE is symmetric to the receiving beam paired with the candidate beam. Alternatively, the RX UE may transmit the BFRQ by means of beam sweeping, whereby it uses different beams to transmit the BFRQ. For example, assuming that the RX UE reports M candidate beams in the BFRQ, then the RX UE transmits the BFRQ in turn using transmitting beams corresponding to these M candidate beams. Alternatively, the transmitting beams used for the BFRQ transmission are dependent on the implementation of the RX UE. For example, the RX UE may use a transmitting beam corresponding to one of the M candidate beams reported in the BFRQ to transmit the BFRQ.

[0344] Optionally, in a scenario where the BFR is triggered by the TX UE, if the TX UE receives the BFRQ transmitted by the RX UE before the tx-ue-beamFailureRecoveryTimer expires, it is considered that the BFR procedure is completed successfully, the BFI counter tx-ue-BFI-COUNTER is set to 0, and the tx-ue-beamFailureRecoveryTimer is stopped. When the timer tx-ue-beamFailureRecoveryTimer expires, if the TX UE has not yet received the BFRQ transmitted by the RX UE, it is considered that the BFR procedure failed, and the TX UE may trigger an establishment procedure for initial beam pairing of the RX UE.

[0345] Optionally, in a scenario where the BFR is triggered by the RX UE, if the RX UE completes the transmission of the BFRQ before the rx-ue-beamFailureRecoveryTimer expires, or the RX UE determines that there are sidelink resources available for transmission of the BFRQ before the rx-ue-beamFailureRecoveryTimer expires, it is considered that the BFR procedure is completed successfully, the BFI counter rx-ue-BFI-COUNTER is set to 0, and the rx-ue-beamFailureRecoveryTimer is stopped. When the timer rx-ue-beamFailureRecoveryTimer expires, if the RX UE has not yet transmitted the BFRQ, or if the RX UE has not yet determined that sidelink resources are available for transmission of the BFRQ, it is considered that the BFR procedure failed, and the RX UE may trigger the establishment procedure of initial beam pairing of the corresponding TX UE.

[0346] In an embodiment of the present application, a feasible implementation is provided for transmission of a beam failure recovery response (BFRR).

[0347] The TX UE, after receiving the BFRQ transmitted by the RX UE, shall transmit a corresponding response to the RX UE, that is, indicates to the RX UE new beam information after beam pairing is recovered, after which the TX UE will use the indicated new beam to perform subsequent data transmission until the beam information is updated. Herein, the new beam information for beam pairing recovery indicated by the TX UE to the RX UE is referred to as a beam failure recovery response (BFRR), and the BFRR may indicate a TCI ID, an SL-SSB index, or an SL-CSI-RS resource index, etc., corresponding to the recovered new beam. In addition, the BFRR may also indicate effective time of the recovered new beam. Assuming that the RX UE reports M candidate beams in the BFRQ, the new beam indicated by the BFRR may be one of the M candidate beams indicated by the RX UE in the BFRQ. And, assuming that the RX UE reports one candidate beam in the BFRQ, then the new beam indicated by the BFRR is the reported one.

[0348] Optionally, the BFRR is transmitted by an SL MAC CE or an SCI. Similar to the BFRQ, in order to ensure that the BFR is completed within a preset time, the BFRR should be transmitted within a preset time window. For example, the TX UE transmits the BFRR within a preset time window after receiving the BFRQ. That is, the transmission of the BFRR should not be later than a preset parameter value BFR-response-lantencyBound, and the starting position of a time window determined by the BFR-response-lantencyBound may be the first symbol or the first slot after the TX UE receives the BFRQ. Alternatively, the starting position of the time window determined by the BFR-response-lantencyBound may be the first symbol or first slot satisfying a preset interval after the TX UE receives the BFRQ.

[0349] In addition, the MAC layer of the TX UE can also control the transmission of the BFRR by a timer BFR-responseTimer, the size of which is the same as the size of the BFR-response-lantencyBound. For example, the TX UE, at the first symbol or the first slot after the reception of the BFRQ, triggers the transmission of the BFRR, and correspondingly starts a timer BFR-responseTimer. Alternatively, the TX UE, at the first symbol or the first slot satisfying the preset interval after the reception of the BFRQ, triggers the transmission of the BFRR, and correspondingly starts the timer BFR-responseTimer.

[0350] In the resource allocation mode of Mode 1, if BFRR transmission is triggered (e.g. the timer BFR-responseTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the BFRR, the TX UE may transmit a scheduling request to the base station to request sidelink resources for PSSCH transmission. Alternatively, in the resource allocation mode of Mode 2, if the BFRR transmission is triggered (e.g., the timer BFR-responseTimer is running), and if there are no sidelink resources available for transmission of the PSSCH carrying the BFRR, the MAC layer of the TX UE may request the physical layer to allocate a subset of resources for PSSCH transmission.

[0351] Optionally, the TX UE may use a new beam indicated by the BFRR to transmit the BFRR to the RX UE. Alternatively, the TX UE may transmit the BFRR by means of beam sweeping, that is, the BFRR is transmitted sequentially by using different beams. For example, assuming that the RX UE reports M candidate beams in the BFRQ, then the TX UE uses these M candidate beams to transmit the BFRR in sequence. Alternatively, the transmitting beams used for BFRR transmission are dependent on the implementation of the TX UE. For example, the TX UE may use one of the M candidate beams reported by the RX UE in the BFRQ to transmit the BFRR.

[0352] Optionally, in a scenario where the BFR is triggered by the TX UE, if the TX UE receives an ACK feedback corresponding to the BFRR transmitted by the RX UE before the tx-ue-beamFailureRecoveryTimer expires, it is considered that the BFR procedure is completed successfully, the BFI counter BFI-COUNTER is set to 0, and the tx-ue-beamFailureRecoveryTimer is stopped. When the timer tx-ue-beamFailureRecoveryTimer expires, if the TX UE has not received the ACK feedback corresponding to the BFRR transmitted by the RX UE, it is considered that the BFR procedure failed, and the TX UE can trigger an establishment procedure for initial beam pairing of the RX UE.

[0353] Optionally, in a scenario where the BFR is triggered by the RX UE, if the RX UE receives the BFRR transmitted by the TX UE before the rx-ue-beamFailureRecoveryTimer expires, it is considered that the BFR procedure is successfully completed, the BFI counter BFI-COUNTER is set to 0, and the rx-ue-beamFailureRecoveryTimer is stopped. When the timer rx-ue-beamFailureRecoveryTimer expires, if the RX UE has not received the BFRR transmitted by the TX UE, then it is considered that the BFR procedure failed, and the RX UE may trigger an establishment procedure for initial beam pairing of the corresponding TX UE.

[0354] In embodiments of the present application, the mentioned pre-configured parameters, preset values, etc. may be configured to the RX UE by the TX UE via a PC5 RRC signaling, or, to the TX UE by the RX UE via the PC5 RRC signaling or, alternatively, to the TX UE or the RX UE by the base station via a RRC signaling.

[0355] In an embodiment of the present application, the mentioned transmitting beam may be characterized by a sidelink transmission configuration indicator (SL TCI) status ID, and signals corresponding to the same SL TCI status ID may be understood to be transmitted by the TX UE from the same TX spatial filter. The RX UE may receive using the same RX spatial filter, and the RX UE may determine the RX spatial filter to be used based on the TCI state ID of the PSSCH / PSCCH transmission indicated by the TX UE. For example, by means of the TCI framework used in UU-interfaced communication systems, the SL TCI may indicate that a DMRS of the PSSCH / PSCCH has a Quasi-CoLocated (QCL) characteristic with a baseline sidelink reference signal in terms of large scale parameters, which baseline sidelink reference signal may be an SL-SSB or an SL-CSI-RS.

[0356] QCL means that antenna ports of two physical signals that are quasi-colocated have the same large-scale parameter, that is, the large-scale parameter of the wireless channel experienced by the PSSCH / PSCCH can be measured and obtained from the baseline reference signal QCLed with it. Depending on the type of the large-scale parameters, QCLs can be categorized into four types: Type A, Type B, Type C, and Type D. The QCL Type A means that two antenna ports have the same Delay Spread, Doppler Spread, Doppler Shift, and Average Delay, the QCL Type B means that two antenna ports have the same Doppler Spread and Doppler Shift, the QCL Type C means that two antenna ports have the same Doppler Shift and Average Delay, and the QCL Type D means that two antenna ports have the same Spatial Rx parameter. Where the QCLs Type A, Type B and Type C can be used for all frequency bands, while the QCL Type D is only used for FR2, meaning that signals from two antenna ports are transmitted using the same beam (i.e., transmitted using the same TX spatial filter), and that the receiver side can receive using the same receiving beam.

[0357] Each SL TCI state may indicate indexes of the associated baseline sidelink reference signal, e.g., the index of the SL-SSB or the SL-CSI-RS, as well as indicate the type of QCL associated with this baseline sidelink reference signal (one from Type A, Type B, Type C, Type D). Alternatively, each SL TCI state may indicate only the index of the associated baseline sidelink reference signals, e.g., the index of the SL-SSB or the SL-CSI-RS, and the QCL relationship associated with this baseline sidelink reference signal is Type D by default.

[0358] In addition to the SL TCI state, the transmitting beam of the PSSCH / PSCCH transmission may also be characterized by the index of the SL-SSB or the SL-CSI-RS. For example, the DMRS of the PSCCH / PSSCH is indicated to be associated with one baseline sidelink reference signal and the QCL relationship associated with this baseline sidelink reference signal is Type D by default. Here, the baseline sidelink reference signal may be an SL-SSB or an SL-CSI-RS.

[0359] An embodiment of the present application provides an electronic device, including: a transceiver, which is configured to transmit and receive signals; and, a processor, which is coupled to the transceiver and configured to implement the steps in the above method embodiments. Optionally, the electronic device may be a first UE or a second UE, and the processor is configured to implement the steps in the embodiments of the method executed by a first UE or a second UE. The detailed functional descriptions and the achieved beneficial effects can refer to the above description of the embodiments of the method executed by a first UE or a second UE and will not be repeated here. In practical applications, the first UE or the second UE can be interpreted as different network nodes.

[0360] An embodiment of the present application further provides an electronic device, including a processor, and may optionally include a transceiver and / or memory coupled to the processor. The processor is configured to execute the steps of the method provided in any one of the optional embodiments of the present application.

[0361] FIG. 20 shows a schematic structure diagram of an electronic device to which an embodiment of the present application is applied. As shown in FIG. 20, the electronic device 4000 in FIG. 20 includes a processor 4001 and a memory 4003. The processor 4001 is connected to the memory 4003, for example, via a bus 4002. Optionally, the electronic device 4000 may further include a transceiver 4004. The transceiver 4004 may be configured for data interaction between the electronic device and other electronic devices, for example, transmitting data and / or receiving data, etc. It is to be noted that, in practical applications, the number of the transceiver 4004 is not limited to 1, and the structure of the electronic device 4000 does not constitute any limitations to the embodiment of the present application. Optionally, the electronic device may be a first network node, a second network node or a third network node.

[0362] The processor 4001 may be a central processing unit (CPU), a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. The processor may implement or execute various exemplary logic blocks, modules and circuits described in the disclosure of the present application. The processor 4001 may also be a combination for realizing computing functions, for example, a combination of one or more microprocessors, a combination of DSPs and microprocessors, etc.

[0363] The bus 4002 may include a passageway for transferring information between the above components. The bus 4002 may be a peripheral component interconnect (PCI) bus, an extended industry standard architecture (EISA) bus, etc. The bus 4002 may be classified into address bus, data bus, control bus, etc. For ease of representation, the bus is represented by only one bold line in FIG. 15, but it does not mean that there is only one bus or one type of buses.

[0364] The memory 4003 may be, but not limited to, read only memories (ROMs) or other types of static storage devices capable of storing static information and instructions, random access memories (RAMs) or other types of dynamic storage devices capable of storing information and instructions, or electrically erasable programmable read only memories (EEPROMs), compact disc read only memories (CD-ROMs) or other optical disc storages, optical disc storages (including compact discs, laser discs, optical discs, digital versatile optical discs, Blue-ray discs, etc.), magnetic disc storage mediums or other magnetic storage devices, or any other medium that can be used to carry or store computer programs and can be accessed by a computer.

[0365] The memory 4003 is configured to store computer programs for executing the embodiments of the present application, and is controlled and executed by the processor 4001. The processor 4001 is configured to execute the computer programs stored in the memory 4003 to implement the steps in the above method embodiments.

[0366] An embodiment of the present application provides a computer-readable storage medium having computer programs stored thereon that, when executed by a processor, can implement the steps and corresponding contents in the above method embodiments.

[0367] An embodiment of the present application further provides a computer program product, including computer programs that, when executed by a processor, can implement the steps and corresponding contents in the above method embodiments.

[0368] The terms "first", "second", "third", "fourth", "1", "2", etc. (if any) in the specification and claims of the present application and the accompanying drawings are used for distinguishing similar objects, rather than describing a particular order or precedence. It　should　be　understood　that　data,　as　used　in　such　a　way,　may　be　used　interchangeably　if　appropriate,　so　that　the　embodiments　of　the　present　application　described　herein　may　be　implemented　in　an　order　other　than　those　illustrated　or　described　here.

[0369] It should be understood that although the steps in the flowchart of the embodiments of the present application are sequentially displayed by following the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless explicitly stated herein, in some implementation scenarios of the embodiments of the present application, the steps in the flowcharts may be executed in other sequences as required. In addition, based on the actual implementation scenario, some or all of the steps in the flowcharts may include multiple sub-steps or multiple stages. Some or all of the sub-steps or stages may be executed at the same moment of time, and each of the sub-steps or stages may be executed at different moments of time. In scenarios with different execution times, the execution order of these sub-steps or stages may be flexibly configured according to requirements, which is not limited in the embodiments of the present application.

[0370] The text and the accompanying drawings are merely provided as examples to help readers to understand the present application. They should not be construed as limiting the scope of the present application in any way. Although some embodiments and examples have been provided, based on the contents disclosed herein, it is obvious for those skilled in the art that the illustrated embodiments and examples can be altered without departing from the scope of the present application, and other similar implementation means based on the technical idea of the present application shall also fall into the protection scope of the embodiments of the present application.

Claims

1.A method executed by a first user equipment (UE) in a communication system, comprising steps of:performing a first beam failure detection (BFD) for a PC5 radio resource control (PC5-RRC) connection with a second UE, and triggering a first beam failure recovery (BFR) when the number of continuous first BFDs reaches a first preset value;transmitting a first sidelink reference signal (SL-RS) to the second UE; andif beam information reported by the second UE is received on a physical sidelink feedback channel (PSFCH) resource associated with any first SL-RS resource index, determining that the first BFR succeeds.2.The method of claim 1, wherein the first BFD is determined as one time if at least one of the following conditions is met:DTX is detected on a PSFCH reception occasion transmitted by the second UE; andthe number of continuous times when the DTX is detected on the PSFCH reception occasion transmitted by the second UE reaches a second preset value.3.The method of claim 1, wherein the first SL-RS comprises at least one of the following situations:the first SL-RS is periodically transmitted by the first UE;the first SL-RS is periodically transmitted by the first UE after the first UE triggers the first BFR, until the first BFR succeeds；the first SL-RS is periodically measured by the second UE; andthe first SL-RS is periodically measured by the second UE after the second UE triggers a second BFR, until the second BFR succeeds.4.The method of claim 1, wherein the first SL-RS is configured as at least one of the following:SL-SSB corresponding to one set of sidelink synchronization signal block (SL-SSB) indexes; andSL-CSI-RS corresponding to one set of sidelink channel state information reference signal (SL-CSI-RS) resources, the SL-CSI-RS transmission is standalone.5.The method of claim 4, wherein a physical resource for transmitting the SL-CSI-RS is periodic, and the physical resource is configured to the second UE by the first UE by PC5-RRC signaling.6.The method of to claim 5, wherein, if the physical resource is not configured, the method further comprises at least one of the following operations:transmitting the SL-CSI-RS to the second UE on a resource that has been indicated to be reserved by sidelink control information (SCI) by the first UE but has not been used; andstarting an initial beam pairing procedure.7.The method of claim 4, wherein, if the set of SL-SSB indexes and / or the set of SL-CSI-RS resources is not configured, the first SL-RS is at least one of the following:SL-SSB corresponding to all SL-SSB indexes;SL-CSI-RS corresponding to all SL-CSI-RS resources;SL-RS for initial beam pairing; andSL-CSI-RS transmitted on a resource that has been indicated to be reserved by SCI by the first UE but has not been used.8.The method of claim 1, wherein the beam information is reported by the second UE in a case where a measurement quantity measured on at least one first SL-RS resource is greater than a first threshold.9.The method according to claim 8, wherein the measurement quantity comprises at least one of the following:layer 1 reference signal received power;layer 1 signal to interference plus noise ratio; andchannel state information.10.The method of claim 8, wherein the beam information being reported by the second UE in a case where the measurement quantity measured on at least one first SL-RS resource is greater than the first threshold comprises:if there are at least two first SL-RS resources whose measurement quantities measured by the second UE are greater than the first threshold, the beam information is received on a PSFCH resource associated with the largest measurement quantity in the at least two first SL-RS resources.11.The method of claim 1, wherein the PSFCH resource associated with any first SL-RS resource index is determined in the following way:determining a group of PSFCH resources based on at least one of the index of the time unit where the SL-RS is located, the index of the starting sub-channel of the SL-RS and the number of sub-channels occupied by the SL-RS; anddetermining, from the group of PSFCH resources, the PSFCH resource associated with the SL-RS resource index according to at least one of the first UE ID, the second UE ID and the SL-RS resource index.12.The method of claim 1, further comprising:if the beam information reported by the second UE is not received on the PSFCH resource associated with any first SL-RS resource index within a first preset period of time after the first SL-RS is transmitted, determining that the first BFR fails; andreturning to the initial beam pairing procedure.13.A method executed by a second user equipment (UE) in a communication system, comprising steps of:performing a second BFD for a PC5-RRC connection with a first UE, and triggering a second BFR when the number of continuous second BFDs reaches a third preset value;measuring a first SL-RS transmitted by the first UE;if the measurement quantity measured on at least one first SL-RS resource is greater than a first threshold, reporting beam information to the first UE on a corresponding PSFCH resource; andif a physical sidelink control channel (PSCCH) and / or physical sidelink shared channel (PSSCH) transmitted by the first UE is received, determining that the second BFR succeeds.14.The method of claim 13, wherein any second BFD is determined according to at least one of the following situations:the measurement quantity measured based on the second SL-RS transmitted by the first UE is less than a second threshold;the number of continuous times when the measurement quantity measured based on the second SL-RS is less than the second threshold reaches a fifth preset value;based on the second SL-RS, the block error rate (BLER) of hypothetical PSCCH or PSSCH transmission is inferred to be greater than a sixth preset value; andbased on the second SL-RS, the number of continuous times when the BLER of hypothetical PSCCH or PSSCH transmission is greater than the sixth preset value is inferred to reach a seventh preset value.15.The method of claim 14, wherein at least one of the third preset value, the first threshold, the second threshold, the fifth preset value, the sixth preset value and the seventh preset value is configured to the second UE by the first UE by PC5-RRC signaling.

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