Patent Publication Number: US-2022225198-A1

Title: Methods and apparatuses for sl carrier aggregation enhancement

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 17/091,582, filed on Nov. 6, 2020, entitled “Methods and Apparatuses for SL Carrier Aggregation Enhancement,” which claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/931,401, filed on Nov. 6, 2019, entitled “Sidelink Carrier Aggregation Enhancement,” the contents of all of which are hereby incorporated fully by reference into the present application. 
    
    
     FIELD 
     The present disclosure is related to wireless communication, and more particularly to methods and apparatuses for sidelink (SL) carrier aggregation enhancement in wireless communication networks. 
     BACKGROUND 
     With the tremendous growth in the number of connected devices and the rapid increase in user/network traffic volume, various efforts have been made to improve different aspects of wireless communication for cellular wireless communication systems, such as fifth generation (5G) New Radio (NR), by improving data rate, latency, reliability and mobility. 
     The 5G NR system is designed to provide flexibility and configurability to optimize the network services and types, accommodating various use cases such as Vehicle to Vehicle (V2V), Vehicle to Pedestrian (V2P), and Vehicle to Everything (V2X) communications. 
     However, as the demand for radio access continues to increase, there exists a need for further improvements in the art. 
     SUMMARY 
     The present disclosure is related to methods and apparatuses for sidelink (SL) carrier aggregation enhancement in wireless communication networks. 
     According to a first aspect of the present disclosure, a user equipment (UE) includes one or more non-transitory computer-readable media containing computer-executable instructions embodied thereon and at least one processor coupled to the one or more non-transitory computer-readable media. The at least one processor is configured to execute the computer-executable instructions to cause the UE to receive, through a serving cell of a first Radio Access Technology (RAT), an SL resource configuration of a second RAT, determine first validity area information associated with the first RAT and second validity area information associated with the second RAT, and identify a validity area of the SL resource configuration based on the first validity area information and the second validity area information. 
     In an implementation of the first aspect, the at least one processor is further configured to execute the computer-executable instructions to cause the UE to access an SL resource associated with the validity area after the validity area is identified as valid. 
     In another implementation of the first aspect, the first validity area information is associated with a first Public Land Mobile Network (PLMN) identity (PLMNidentity) in a PLMNidentity list or a first Non-Public Network (NPN) identity (NPNidentity) in an NPNidentity list, and the PLMNidentity list and the NPNidentity list are broadcast by the serving cell. 
     In yet another implementation of the first aspect, the second validity area information is associated with at least one of one or more SL transmission resource pools, one or more SL reception resource pools, and one or more exceptional transmission resource pools. 
     In yet another implementation of the first aspect, the first RAT is a 5 th  Generation New Radio (5G NR) RAT. 
     In yet another implementation of the first aspect, NR SL communication is considered as part of the 5G NR RAT (or is associated with the 5G NR RAT). 
     In yet another implementation of the first aspect, the NR SL communication is implemented based on the 5G NR RAT. 
     In yet another implementation of the first aspect, the second RAT is an Evolved Universal Terrestrial Radio Access (E-UTRA) RAT. 
     In yet another implementation of the first aspect, the SL resource configuration of the second RAT is for Long Term Evolution (LTE) Vehicle to Everything (V2X) SL communication associated with an Evolved Universal Terrestrial Radio Access (E-UTRA) RAT. 
     In yet another implementation of the first aspect, V2X SL communication and SL communication/discovery are considered as part of the E-UTRA RAT (or are associated with the E-UTRA RAT). 
     In yet another implementation of the first aspect, V2X SL communication and SL communication/discovery are implemented based on the E-UTRA RAT. 
     In yet another implementation of the first aspect, the SL resource configuration of the second RAT (e.g., V2X SL communication) is received through system information broadcast by the serving cell of the first RAT. 
     In yet another implementation of the first aspect, the SL resource configuration of the first RAT (e.g., NR SL communication) is received through system information broadcast by the serving cell of the second RAT. 
     In yet another implementation of the first aspect, the validity area of the SL resource configuration is composed of at least one system information area identifier (systeminformationAreaID) broadcast by the serving cell of the first RAT. 
     In yet another implementation of the first aspect, a first validity area of the first RAT is composed of a cell identity of the serving cell of the first RAT, when the SL resource configuration is not indicated by the systeminformationAreaID broadcast by the serving cell or the systeminformationAreaID is absent from system information broadcast by the serving cell. 
     In yet another implementation of the first aspect, the SL resource configuration associated with the validity area is invalidated by the UE after the UE moves out of either a first validity area associated with the first validity area information and/or a second validity area associated with the second validity area information. 
     According to a second aspect of the present disclosure, a method performed by a UE is provided. The method includes receiving, through a serving cell of a first Radio Access Technology (RAT), an SL resource configuration of a second RAT, determining first validity area information associated with the first RAT and second validity area information associated with the second RAT, and identifying a validity area of the SL resource configuration based on the first validity area information and the second validity area information. 
     In an implementation of the second aspect, the method further includes accessing an SL resource associated with the validity area after the validity area is identified as valid. 
     In another implementation of the second aspect, the first validity area information is associated with a first Public Land Mobile Network (PLMN) identity (PLMNidentity) in a PLMNidentity list or a first Non-Public Network (NPN) identity (NPNidentity) in an NPNidentity list, and the PLMNidentity list and the NPNidentity list are broadcast by the serving cell. 
     In yet another implementation of the second aspect, after cell (re)selection procedures triggered by a UE mobility event, the UE may also check the first validity area information by checking whether the first PLMN identity (or the first NPN identity) of the serving cell has changed. Moreover, the UE may check the first PLMN identity (in the PLMNidentity list broadcast by the serving cell) while the UE is checking the validity of the first validity area information and the UE is not under the Stand-alone Non-Public Network (SNPN) access mode. On the other hand, the UE may check the first NPN identity (in the NPNidentity list broadcast by the serving cell) while the UE is checking the validity of the first validity area information and the UE is under the SNPN access mode. 
     In yet another implementation of the second aspect, the second validity area information is associated with at least one of one or more SL transmission resource pools, one or more SL reception resource pools, and one or more exceptional transmission resource pools. 
     In yet another implementation of the second aspect, the first RAT is a 5 th  Generation New Radio (5G NR) RAT. 
     In yet another implementation of the second aspect, the second RAT is an Evolved Universal Terrestrial Radio Access (E-UTRA) RAT. 
     In yet another implementation of the second aspect, the SL resource configuration of the second RAT is for Long Term Evolution (LTE) Vehicle to Everything (V2X) SL communication associated with an Evolved Universal Terrestrial Radio Access (E-UTRA) RAT. 
     In yet another implementation of the second aspect, the SL resource configuration of the second RAT (e.g., a V2X SL resource configuration associated with the E-UTRA RAT) is received through system information broadcast by the serving cell of the first RAT (e.g., an NR Cell). 
     In yet another implementation of the second aspect, the validity area of the SL resource configuration is composed of at least one system information area identifier (systeminformationAreaID) broadcast by the serving cell of the first RAT. 
     In yet another implementation of the second aspect, a first validity area of the first RAT is composed of a cell identity of the serving cell of the first RAT, when the SL resource configuration is not indicated by the systeminformationAreaID broadcast by the serving cell or the systeminformationAreaID is absent from system information broadcast by the serving cell. 
     In yet another implementation of the second aspect, the SL resource configuration associated with the validity area is invalidated by the UE after the UE moves out of either a first validity area associated with the first validity area information or a second validity area associated with the second validity area information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the disclosure are best understood from the following detailed description when read with the accompanying drawings. Various features are not drawn to scale. Dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a diagram illustrating LTE/NR (V2X) SL operations, in accordance with an example implementation of the present disclosure. 
         FIG. 2A  and  FIG. 2B  are diagrams illustrating carrier aggregation for (LTE) V2X SL communication/NR SL communication, in accordance with example implementations of the present disclosure. 
         FIG. 3  is a flowchart of a method performed by a UE for NR SL operations, in accordance with an example implementation of the present disclosure. 
         FIG. 4  illustrates a diagram showing a UE performing SL synchronization and SL cell (re)selection procedures under a fallback mechanism to a cross-carrier validity area configuration, in accordance with an example implementation of the present disclosure. 
         FIG. 5  illustrates a range-based SL resource association in accordance with an example implementation of the present disclosure. 
         FIG. 6  is a block diagram illustrating a node for wireless communication in accordance with various aspects of the present disclosure. 
     
    
    
     DESCRIPTION 
     The following description contains specific information related to implementations of the present disclosure. The drawings and their accompanying detailed description are merely directed to implementations. However, the present disclosure is not limited to these implementations. Other variations and implementations of the present disclosure will be obvious to those skilled in the art. 
     Unless noted otherwise, like or corresponding elements among the drawings may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations in the present disclosure are generally not to scale and are not intended to correspond to actual relative dimensions. 
     For the purposes of consistency and ease of understanding, like features may be identified (although, in some examples, not illustrated) by the same numerals in the drawings. However, the features in different implementations may be differed in other respects and shall not be narrowly confined to what is illustrated in the drawings. 
     The phrases “in one implementation,” or “in some implementations,” may each refer to one or more of the same or different implementations. The term “coupled” is defined as connected whether directly or indirectly through intervening components and is not necessarily limited to physical connections. The term “comprising” means “including, but not necessarily limited to” and specifically indicates open-ended inclusion or membership in the so-described combination, group, series, or equivalent. The expression “at least one of A, B and C” or “at least one of the following: A, B and C” means “only A, or only B, or only C, or any combination of A, B and C.” 
     The terms “system” and “network” may be used interchangeably. The term “and/or” is only an association relationship for describing associated objects and represents that three relationships may exist such that A and/or B may indicate that A exists alone, A and B exist at the same time, or B exists alone. The character “I” generally represents that the associated objects are in an “or” relationship. 
     For the purposes of explanation and non-limitation, specific details such as functional entities, techniques, protocols, and standards are set forth for providing an understanding of the disclosed technology. In other examples, detailed description of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the description with unnecessary details. 
     Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) disclosed may be implemented by hardware, software, or a combination of software and hardware. Disclosed functions may correspond to modules which may be software, hardware, firmware, or any combination thereof. 
     A software implementation may include computer-executable instructions stored on a computer-readable medium such as memory or other types of storage devices. One or more microprocessors or general-purpose computers with communication processing capability may be programmed with corresponding executable instructions and perform the disclosed network function(s) or algorithm(s). 
     The microprocessors or general-purpose computers may include Application-Specific Integrated Circuits (ASICs), programmable logic arrays, and/or using one or more Digital Signal Processor (DSPs). Although some of the disclosed implementations are oriented to software installed and executing on computer hardware, alternative implementations implemented as firmware or as hardware or as a combination of hardware and software are well within the scope of the present disclosure. The computer readable medium includes but is not limited to Random Access Memory (RAM), Read Only Memory (ROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory, Compact Disc Read-Only Memory (CD-ROM), magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions. 
     A radio communication network architecture such as a Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system, an LTE-Advanced Pro system, or a 5G NR Radio Access Network (RAN) typically includes at least one base station (BS), at least one UE, and one or more optional network elements that provide connection within a network. The UE communicates with the network such as a Core Network (CN), an Evolved Packet Core (EPC) network, an Evolved Universal Terrestrial RAN (E-UTRAN), a 5G Core (5GC), or an internet via a RAN established by one or more BSs. 
     A UE may include but is not limited to a mobile station, a mobile terminal or device, or a user communication radio terminal. The UE may be a portable radio equipment that includes but is not limited to a mobile phone, a tablet, a wearable device, a sensor, a vehicle, or a Personal Digital Assistant (PDA) with wireless communication capability. The UE is configured to receive and transmit signals over an air interface to one or more cells in a RAN. 
     The BS may be configured to provide communication services according to at least a Radio Access Technology (RAT) such as Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM) that is often referred to as 2G, GSM Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunication System (UMTS) that is often referred to as 3G based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), LTE, LTE-A, evolved LTE (eLTE) that is LTE connected to 5GC, NR (often referred to as 5G), and/or LTE-A Pro. However, the scope of the present disclosure is not limited to these protocols. 
     The BS may include but is not limited to a node B (NB) in the UMTS, an evolved node B (eNB) in LTE or LTE-A, a radio network controller (RNC) in UMTS, a BS controller (BSC) in the GSM/GERAN, an ng-eNB in an Evolved Universal Terrestrial Radio Access (E-UTRA) BS in connection with 5GC, a next generation Node B (gNB) in the 5G-RAN, or any other apparatus capable of controlling radio communication and managing radio resources within a cell. The BS may serve one or more UEs via a radio interface. 
     The BS is operable to provide radio coverage to a specific geographical area using a plurality of cells forming the RAN. The BS supports the operations of the cells. Each cell is operable to provide services to at least one UE within its radio coverage. 
     Each cell (often referred to as a serving cell) provides services to serve one or more UEs within its radio coverage such that each cell schedules the downlink (DL) and optionally uplink (UL) resources to at least one UE within its radio coverage for DL and optionally UL packet transmissions. The BS can communicate with one or more UEs in the radio communication system via the plurality of cells. 
     A cell may allocate sidelink (SL) resources for supporting Proximity Service (ProSe), SL service (e.g., (LTE) SL communication service and/or (LTE) SL discovery service) or Vehicle to Everything (V2X) service (e.g., NR SL communication and/or (LTE) V2X SL communication). Each cell may have overlapped coverage areas with other cells. 
     As discussed previously, the frame structure for NR supports flexible configurations for accommodating various next generation (e.g., 5G) communication requirements such as Enhanced Mobile Broadband (eMBB), Massive Machine Type Communication (mMTC), and Ultra-Reliable and Low-Latency Communication (URLLC), while fulfilling high reliability, high data rate, and low latency requirements. The Orthogonal Frequency-Division Multiplexing (OFDM) technology in the 3rd Generation Partnership Project (3GPP) may serve as a baseline for an NR waveform. The scalable OFDM numerology such as adaptive sub-carrier spacing, channel bandwidth, and Cyclic Prefix (CP) may also be used. 
     Two coding schemes are considered for NR, specifically Low-Density Parity-Check (LDPC) code and Polar Code. The coding scheme adaption may be configured based on channel conditions and/or service applications. 
     When a transmission time interval (TTI) of a single NR frame includes DL transmission data, a guard period, and UL transmission data, the respective portions of the DL transmission data, the guard period, and the UL transmission data may be configured based on the network dynamics of NR. SL resources may also be provided in an NR frame to support ProSe services or V2X services. 
     Example descriptions of some selected terms used in this disclosure are given below. 
     Primary Cell (PCell): For dual connectivity (DC) operation or carrier aggregation (CA) operation, PCell is the master cell group (MCG) cell, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure. 
     Primary SCG Cell (PSCell): For DC operation, PSCell is the secondary cell group (SCG) cell in which the UE performs random access when performing the Reconfiguration with Sync procedure. 
     Special Cell: For DC operation the term Special Cell (SpCell) refers to the PCell of the MCG or the PSCell of the SCG, otherwise (e.g., for CA operation), the term Special Cell refers to the PCell. 
     Secondary Cell: For a UE configured with carrier aggregation (CA), a cell providing additional radio resources on top of Special Cell. 
     Serving Cell: For a UE in RRC_CONNECTED not configured with CA/DC, there is only one serving cell, which may be referred to as the primary cell. For a UE in an RRC_CONNECTED state configured with CA/DC, the term “serving cells” may be used to denote the set of cells including the SpCell(s) and all secondary cells. 
     Listen Before Talk (LBT) is a feature available in Wi-Fi that allows coexistence with other Wi-Fi nodes. LBT is a mechanism by which an equipment applies clear channel assessment (CCA) before using the channel. The 3rd Generation Partnership Project (3GPP) chose to specify a conservative LBT scheme similar to what Wi-Fi nodes use in order to ensure coexistence of Licensed Assisted Access (LAA) with Wi-Fi. LAA uses carrier aggregation in DL to combine LTE in the unlicensed spectrum (e.g., 5 GHz) with LTE in the licensed band. In NR, LBT may be also required prior to any transmission when operating on the unlicensed spectrum. 
     In the present disclosure, various implementations focus on the functionality of NR cells to support SL operation under SL carrier aggregation. In the present disclosure, both Frequency Range 1 (FR1) and Frequency Range 2 (FR2) may be considered to support (NR-V2X) SL operations. The UE may require additional power to support SL operations, such as SL synchronization, SL resource (pools) configuration, and SL (serving/non-serving) cell (re)selection cross multiple SL component carriers (CCs). In an effort to reduce power consumption by the UE supporting these SL operations, various implementations of the present disclosure provide, among other things, a cross-carrier validity area configuration in an SL resource configuration, as discussed in IMPLEMENTATION 1 of the present disclosure. Moreover, various implementations of the present disclosure provide, among other things, fallback mechanisms when a cross-carrier validity area configuration is absent, as discussed in IMPLEMENTATION 2 of the present disclosure. 
     In various implementations of the present disclosure, to maintain channel quality (e.g., beam management) in FR2, a range-based SL resource association is provided to enable an SL logical channel (LCH) to be associated with different combinations of SL component carrier(s), (so as to be the SL resource configuration on these configured SL components) based on the distance (e.g., physical distance) between the UEs (e.g., transmission (Tx)/reception (Rx) UEs), as discussed in IMPLEMENTATION 2 of the present disclosure. 
     Under an SL carrier aggregation scenario, in some implementations of the present disclosure, an NR Non-standalone (NSA) cell may not support LTE/NR SL operations. In addition, the UE may not attempt to decode the system information broadcast by an NR NSA cell (e.g., SIB1) to obtain system information about SL resource configuration for LTE V2X SL (communication) services and NR V2X services/NR sidelink (communication) service (e.g., the NSA cell is not a suitable cell to the UE and the UE cannot access V2X services if the UE is in a limited-service state). In some implementations of the present disclosure, some component carriers may be deployed with NR NSA cells. As a result, the UE may select to camp on an NR NSA cell. For example, the UE may be in a ‘camped on any cell’ state, and the camped NSA cell is an ‘acceptable cell’ to the UE. However, these NSA cells may still support NR/LTE SL operations and these NSA cells can still broadcast one or more SL configurations in system information to the UEs. The UEs may be in a limited service state and able to access (public safety) V2X service(s) or public safety related SL service(s). IMPLEMENTATION 3 of the present disclosure describes how an NR NSA cell supports NR/LTE SL operations. 
     In addition, with the introduction of FR2 for SL carrier aggregation, implementations of the present disclosure provide assistance information regarding how channel quality or packet delivery status may be delivered by the component carriers in FR1. As discussed below, IMPLEMENTATION 4 of the present disclosure provides support for ‘FR2 assistance information exchange’ on FR1. In the present disclosure, the range of FR1 may be specified to the SL component carriers in a lower frequency range (e.g., less than 7 GHz), and the range of FR2 may be specified to the SL component carriers in a higher frequency range (e.g., greater than equal to 7 GHz). Implementations of the present disclosure may be applicable to SL unicast group scenarios, SL multi-cast/group-cast group scenarios, and SL broadcast scenarios. In addition, implementations of the present disclosure may be applicable to public-safety V2X services, non-public safety (e.g., commercial) V2X services, and (public-safety/non-public-safety) SL communication/discovery services. 
     IMPLEMENTATION 5 of the present disclosure provides stored validity area and SL resource configuration cross serving frequency(ies) and non-serving frequency(ies) while cell (re)selection may be implemented on the serving frequency(ies) and non-serving frequency(ies). 
     Implementation 1: Cross-Carrier Validity Area Configuration 
     Referring to  FIG. 1 ,  FIG. 1  is a diagram  100  illustrating V2X SL operations, in accordance with an example implementation of the present disclosure. In  FIG. 1 , at least two UEs (e.g., UE1 and UE2) may be configured in an (Access Stratum (AS)-layer/Non-Access Stratum (NAS)) unicast group to implement NR-SL (which is also referred to as NR-V2X in some applications) services and/or LTE-V2X (sidelink) services based on configured NR and/or LTE SL configurations (e.g., the NR SL configuration and LTE V2X configuration). It should be noted that, in some implementations, the LTE V2X services may include the LTE V2X communication through an LTE Uu interface (e.g., packet exchange through downlink/uplink direction between the UE(s) and serving Radio Access Network) and/or the LTE V2X SL packet exchange (e.g., LTE V2X SL communication and/or LTE V2X SL discovery between UEs) through an LTE PC5 interface. Thus, in some implementations, the LTE V2X configuration may include the configuration for LTE V2X communication through the LTE Uu interface and/or the configuration for LTE V2X SL communication/LTE V2X SL discovery through the LTE PC5 interface (e.g., LTE V2X SL configuration). It should also be noted that, in some implementations, the NR SL service may include NR SL packet exchange (e.g., NR SL communication and/or NR SL discovery between UEs) through an NR PC5 interface. Therefore, in some implementations, the NR SL configuration may include the configuration for NR SL communication and/or NR SL discovery. Furthermore, the NR SL communication may include NR SL transmission (e.g., one UE transmits NR SL packets and/or SL NR control messages (e.g., SL Control Information (SCI) and/or PC5 Radio Resource Control (RRC) signaling and/or SL Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement/Non-Acknowledgement messages) and/or NR SL synchronization signals (NR SL synchronization burst sets) to nearby UEs in the same NR SL unicast/multi-cast (group-cast)/broadcast groups) and/or NR SL reception (e.g., one UE receives NR SL packets and/or NR SL control messages (e.g., SCI or PC5 RRC signaling) and/or NR SL synchronization signals (NR SL synchronization burst sets) to nearby UEs in the same NR SL unicast/Multi-cast(group-cast)/broadcast groups). 
     In various implementations of the present disclosure, the serving cell (e.g., an NR cell in  FIG. 1 ) may configure multiple SL CCs and the associated RATs (or associated RANs) in the corresponding SL CCs. In accordance with an example implementation of the present disclosure, with reference to  FIG. 1 , at least two UEs (e.g., UE1 and UE2) may be configured in an (Access Stratum (AS)-layer/Non-Access Stratum (NAS)) multi-cast group to implement NR-SL (which is also referred to as NR-V2X (sidelink) in some applications) services and/or LTE-V2X (sidelink) services based on configured NR and/or LTE SL configurations. In various implementations of the present disclosure, the serving cell (e.g., an NR cell in  FIG. 1 ) may configure multiple SL CCs and the associated RATs (or associated RANs) in the corresponding SL CCs. In accordance with an example implementation of the present disclosure, with reference to  FIG. 1 , at least two UEs (e.g., UE1 and UE2) may be configured in an AS-layer/NAS layer) broadcast group to implement NR-SL (which is also referred to as NR-V2X in some applications) services and/or LTE-V2X services based on configured NR and/or LTE SL configurations. In various implementations of the present disclosure, the serving cell (e.g., an NR cell in  FIG. 1 ) may configure multiple SL CCs and the associated RATs (or associated RANs) in the corresponding SL CCs. It should be noted that, in some implementations, the UEs in one unicast group/multi-cast group/broadcast group may be served by one or more cells, which may be served by one or more RATs (e.g., New Radio, E-UTRA). In some other implementations, one or more UEs in the unicast group/multi-cast group/broadcast group may be out of the coverage of cellular networks (e.g., the UE(s) could not find out at least one cell which the downlink reference signaling quality, such as the DL Reference Signal Received Power (RSRP), is higher than a pre-defined threshold). In addition, one out-of-coverage UE may communicate with other UEs in the same unicast/multi-cast/broadcast group based on SL-pre-configuration or configurations obtained from the neighboring UEs (e.g., through SL-Master Information Block (MIB) reception or PC5 RRC signaling exchange or PC5-S signaling). A UE may join in one or more unicast/multi-cast/broadcast group(s) and each group may be associated with one Layer 2 Identifier independently. 
     The ProSe (Proximity Service) unicast group (or SL unicast group in the AS-layer) may be in-coverage, partial-coverage, or out-of-coverage with a serving RAN, that is an NR RAN connected to a 5GC (5G Core) and/or a Evolved Packet Core (EPC) as shown in  FIG. 1 . In another implementation, the ProSe unicast group (or SL unicast group in the AS-layer) may be in-coverage, partial-coverage, or out-of-coverage with a serving RAN, that is an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) connected to an EPC (Evolved Packet Core) and/or an 5GC (5G Core). 
     In  FIG. 1 , a (NR) gNB in an NR-RAN (or an LTE eNB in an E-UTRAN) may provide physical resource(s) to support NR-V2X SL operation(s) and/or LTE-V2X SL operation(s). The interface between UE1 and UE2 to support NR-V2X SL operation(s) is referred to as an NR PC5 interface. For example, an NR PC5 interface may be configured by a serving RAN (e.g., an NR-RAN or an E-UTRAN) or by pre-configuration, which may be stored in the memory modules or USIMs (UMTS Subscriber Identity Modules) of the UEs, to support NR V2X service(s). The interface between the vehicles to support LTE-V2X SL operation(s) is referred to as an LTE PC5 interface. The LTE PC5 interface may be configured by the serving RAN (e.g., an NR-RAN or an E-UTRAN) or by pre-configuration, which is stored in the memory module(s) or USIM(s) of the UEs, to support LTE V2X service(s). In some implementations, the serving NR cell is the PCell (primary cell) to the UE. In some implementations, the serving NR cell may be the PSCell (primary SCell) to the UE(s) while the UE(s) is/are configured with an additional secondary node based on an NR dual-connectivity (or multi-connectivity) configuration. In addition, the serving PSCell may transmit SL resource configuration to the UE(s) directly through a configured radio bearer (e.g., Signaling Radio Bearer 3 (SRB3)). It should be noted that, in the implementations of the present disclosure, the serving RAN is not limited to an NR RAN. For example, the serving RAN may be an E-UTRAN. In addition, implementations of the present disclosure may cover both an intra-RAT SL resource configuration (e.g., an NR cell may provide an NR SL resource configuration and an LTE cell may provide an LTE (V2X) SL resource configuration) and an inter-RAT SL resource configuration (e.g., an NR cell may provide an LTE SL resource configuration and an LTE cell may provide an NR SL resource configuration). 
     Referring to  FIGS. 2A and 2B ,  FIGS. 2A and 2B  are diagrams illustrating V2X SL carrier aggregation, in accordance with example implementations of the present disclosure. As shown in diagram  200 A in  FIG. 2A , one or more UEs (e.g., UE1 and UE2) may be served by a serving cell (Cell #1) via an SL component carrier (e.g., CC #1). As shown in diagram  200 B in  FIG. 2B , Cell #1 is deployed in CC #1, where is in FR1. Also shown in diagram  200 B, there are several cells (Cell #A, Cell #B, and Cell #C) deployed in another SL component carrier (e.g., CC #2). In one example, CC #2 is in FR2. Both CC #1 and CC #2 support (NR/LTE) SL operation(s). In addition, CC #2 may have a paired DL frequency carrier (e.g., also in FR2) in Cell #A, Cell #B, Cell #C in the (LTE/NR) Uu interface. It should be noted that CC #1/CC #2 may or may not be the secondary frequency carrier to the UE(s) while the UE(s) is configured with carrier aggregation in an (LTE/NR) Uu interface. Furthermore, in some additional implementations, CC #1/CC #2 may or may not be the serving frequency carrier to the UE(s) while the UE(s) is implementing SL operations with non-serving cell(s), which are operating on the non-serving frequency carrier. 
     In the present disclosure, Cell #1 may configure an SL resource configuration indicating CC #2 to the UE(s) (e.g., UE1 and UE2) with a cross-carrier validity area configuration. In addition, the UE(s) may not need to perform SL synchronization and SL cell (re)selection on the associated SL frequency carrier of CC #2. The UE(s) may not be configured with special cell(s) and secondary cell(s) in the concerned frequency carrier. In other words, the concerned CC #2 is neither a primary frequency carrier nor a secondary frequency carrier to the UEs. In some implementations, the serving cell (e.g., Cell #1 in  FIG. 2 ) may transmit timing adjustment instructions (e.g., timing advance instructions) to the UE(s) to adjust their transmission timing(s) based on the instructions from the serving cell. 
     In comparison, in LTE V2X protocols, SL resources among multiple SL carriers may be configured through a v2x-InterFreqInfoList (e.g., by broadcasting system information or by dedicated RRC signaling on a Uu interface). It should be noted that, in some implementations, the UE(s) may need to implement SL synchronization and SL cell (re)selection on the concerned frequency (or on the paired DL frequency carrier with the one used to transmit V2X SL communication), while the concerned frequency carrier is not a serving frequency to the UE(s). In some other implementations, the UE(s) may be optionally configured with a SyncFreqList, which specifies a list of candidate SL synchronization carrier frequencies for V2X SL communications on these non-serving frequency carriers. Additional SL synchronization may require additional power consumption by the UE(s). 
     In the implementations of the present disclosure, as shown in  FIG. 2A , Cell #1 may deliver an SL resource configuration associated with CC #2 (and the cross-carrier validity area configuration) to the UE(s) through control signaling (e.g., by broadcasting system information or (UE-specific) dedicated RRC signaling). In addition, the associated validity area may be composed of cells in CC #1 and Cell #1 and may also be located in the given validity area. In some implementations, the validity area may be composed of one or more cell identity(ies), physical cell identity(ies), systeminformationAreaID(s), RAN notification Area Code(s) or Tracking Area Code(s), etc. The cells in CC #1 may also deliver the assistance information (e.g., cell identity(ies), physical cell identity(ies), systemInformationAreaID(s), RAN notification Area Code(s), Tracking Area Code(s), and/or zone ID(s) which the cell belongs to) for the UE(s) to identify the range of the validity area. 
     Based on the associated validity area configuration, the UE(s) may transmit SL packet(s) on CC #2 directly without implementing SL synchronization or SL cell (re)selection on CC #2 (or the DL frequency carrier associated with CC #2). The UE(s) may transmit SL packets on CC #2 based on the timing reference which the UE(s) obtains from CC #1. In addition, the UE(s) may not need to use the DL frequency carrier associated with CC #2 in the LTE/NR Uu interface (which may also be the operating DL frequency carrier of Cell #A, Cell #B, and/or Cell #C) as the timing reference when the UE(s) is/are transmitting SL packets on CC #2. In some additional implementations, the UE may still implement sidelink synchronization and/or (non-serving) cell (re)selection on the CC #2. However, the UE may only need to check whether the selected cell on CC #2 is located on the sidelink resource validity area based on the pre-stored validity area information associated with CC #2 (e.g., the UE may receive the MIB and/or System information block Type1 (SIB1) of the selected cell after the cell (re)selection procedure (e.g., for cell identity reception and/or system information area ID reception, which may be broadcast by the selected cell in the MIB/SIB1). Then, the UE may check the validity of stored sidelink resource configuration based on the received cell identity/system information area ID broadcast by the selected cell and the stored validity area information associated with the stored sidelink resource configuration. However, the UE may not need to monitor the other system information or broadcasting control signaling broadcast by the selected cell for sidelink resource configuration reception while the stored sidelink resource configuration is still valid. 
     In some implementations, Cell #1 (e.g., an NR cell) may support both a normal uplink (NUL) carrier and at least one supplementary uplink (SUL) carrier. In addition, Cell #1 may provide SL resource configurations in both the NUL carrier and SUL carrier(s). For example, at least one SL Bandwidth Part (BWP) configuration is associated with the NUL carrier, and at least one SL BWP configuration is associated with the SUL carrier. As such, the UE(s) may transmit SL packets by accessing the SL resource(s) on the NUL carrier and/or the SUL carrier(s). In some implementations, the UE(s) may transmit SL packets on the NUL carrier and the SUL carrier(s) simultaneously. In some implementations, the UE(s) may only choose the SL resource(s) on either the NUL carrier or the SUL carrier(s) (e.g., depending on whether a NUL or a SUL is used in the UL direction). 
     In some implementations, the UE may need to transmit the UE&#39;s capability of SL carrier aggregation to the serving cell. 
     As shown in  FIG. 2B , a validity area configuration in FR2 may be associated with Cell #1 in FR1. Implementations of the present disclosure may improve the UE&#39;s power consumption since the UE(s) does not need to perform SL synchronization and SL cell (re)selection in FR2. 
     As discussed above, the SL synchronization on CC #1 may be with a Global Navigation Satellite System (GNSS), a base station (eNB or gNB), or a neighboring UE (LTE UE or NR UE). In addition, in some implementations, the UE may be in an NR-RRC Idle state, an NR-RRC Inactive state, an LTE-RRC Idle state, or an LTE-RRC Inactive state. In some implementations of the present disclosure, the UE may receive the above-mentioned configurations through system information. In some implementations of the present disclosure, the UE may receive the above-mentioned configurations while the UE is in an NR-RRC Connected state or an LTE-RRC Connected state. In some implementations of the present disclosure, the UE may receive the above-mentioned configurations through (UE-specific) dedicated RRC signaling. In some implementations of the present disclosure, the UE may receive the above-mentioned configurations through dedicated RRC signaling (e.g., an RRC Connection Resume message, an RRC Release with suspend configuration message), while the UE is an NR-RRC Inactive state or an LTE-RRC Inactive state. 
     As shown in  FIG. 2A , the UE (e.g., UE1 and/or UE2) is camped on Cell #1 in CC #1 (located on FR1). The UE may be in an NR-RRC Inactive state/NR-RRC Idle state/NR-RRC Connected state. 
     In some implementations, the SL resource configuration on FR1 (e.g., CC #1) and FR2 (e.g., CC #2) may be configured with one associated validity area. On the UE side, the UE (e.g., UE1 and/or UE2) may know that the SL resource configuration on CC #2 is valid under the coverage of the configured validity area associated with cells in CC #1 (e.g., Cell #1). In addition, the UE (e.g., UE1 and/or UE2) may not need to perform SL synchronization or SL cell (re)selection in CC #2 when the UE is accessing the configured SL resource (e.g., while the UE is transmitting SL packets on the configured SL resource). In some additional implementations, the UE may still implement sidelink synchronization and/or (non-serving) cell (re)selection on the CC #2. However, the UE may only need to check whether the selected cell on CC #2 is located on the sidelink resource validity area based on the pre-stored validity area information associated with CC #2. In other words, the UE may not need to monitor other DL control signaling for sidelink resource configuration delivered by the selected cell on the CC #2. 
     In some implementations, the configured SL resource may include dynamic SL grant, Type 1 SL configured grant, Type 2 SL configured grant, SL resource pool, and SL exceptional pool in the appointed SL component carrier (e.g., CC #2 in  FIG. 2B ). In addition, it is noted that the serving cell (e.g., Cell #1) may transmit the configuration of Type 1 SL configured grant to the UE (e.g., UE1 and/or UE2) through broadcasting message (e.g., system information) or dedicated control signaling (e.g., (UE-specific) RRC signaling). On the UE side, the configuration of Type 1 SL configured grant is valid to the UE (e.g., UE1 and/or UE2) right after the UE decoding the configuration from the serving cell successfully. So, the UE (e.g., UE1 and/or UE2) can transmit SL packets by accessing the configured Type 1 SL configured grant. 
     The serving cell (e.g., Cell #1) may transmit part of the configuration of Type 2 SL configured grant (e.g., the periodicity in time domain for the Type 2 SL configured grant) to the UE (e.g., UE1 and/or UE2) through broadcasting message (e.g., system information) or dedicated control signaling (e.g., RRC signaling). Then, the serving cell may configure the other part of Type 2 SL configured grant (e.g., the locations of SL resource blocks, such as sub-channel and symbols in frequency domain and time domain respectively) by transmitting other dedicated control signaling (e.g., Downlink control information scrambled by C-RNTI of the UE or Medium Access Control Control Element (MAC CE)) to the UE. So, after receiving the DCI from the serving cell (e.g., Cell #1 in CC #1), the configured Type 2 SL configured grant is activated to the UE, and so the UE can transmit SL packets on the configured Type 2 SL configured grant. On the other hand, to an activated SL configured grant, the serving cell may transmit another DCI to de-activate this SL configured grant. After receiving the de-activation message, the UE may stop accessing the configured Type 2 SL configured grant and release the stored configurations which the UE receives through the activation DCI message. In other words, the configurations received through RRC signaling may still be kept by the UE, so that next time the serving cell may configure other SL resource in another activation DCI to activate one Type 2 SL configured grant. 
     The SL resource pool configuration or SL exceptional resource pool configuration may be provided to the UE (e.g., UE1 and/or UE2) so that the UE can select SL grant autonomously with/without sensing (e.g., by random selection) or through partial sensing mechanism. 
     The SL resource configuration may be associated with (at least) one SL bandwidth part (SL-BWP) configuration in one SL component carrier. Each SL bandwidth part configuration may include the numerology of the operating SL component carrier (e.g., the length of cyclic prefix, subcarrier spacing, etc.). 
     It should be noted that, in various implementations of the present disclosure, RRC signaling may cover the RRC signaling in (LTE/NR) Uu interface, such as RRC(Connection)(Re)Establishment message, RRC(Connection)Setup message, RRC(Connection)Resume message, RRC(Connection)Release message with/without suspend configuration, RRC(Connection)Reconfiguration message with/without mobilitycontrolinfoV2X, or RRC(Connection)Reconfiguration message with/without reconfigurationwithsync message, etc. In addition, the reconfigurationwithsync/mobilitycontrolinfoV2X message may be delivered when the serving RAN is instructing the UE to implement (intra-RAT/inter-RAT) handover procedure, Secondary Cell Group change, etc. 
     It should be noted that the above-mentioned configurations may also be applicable during an intra-RAT (e.g., from a source LTE cell to a target LTE cell or from a source NR cell to a target NR cell) handover procedure, an inter-RAT (e.g., from a source LTE/NR cell to a target NR/LTE cell respectively) handover procedure, an inter-system handover procedure in LTE protocols, a conditional handover procedure, and a Dual Active Protocol Stack (DAPS) handover procedure. In some additional implementations, the above-mentioned configuration may also be applicable during an MCG-change/SCG-change procedure. In addition, during the handover procedure, the serving cell may apply a delta signaling approach to re-configure the SL resource configuration (e.g., SL resource configuration of CC #2 in this disclosure). For example, to provide a new SL resource (pool) configuration, the serving cell may transmit SL_Resource_(Pool)_ToAdd list to transmit a new SL resource (pool) configuration to the UE. Then, the UE may store the new SL resource (pool) configuration with the stored SL resource (pool) configuration. In addition, all of the stored SL resource (pool) configuration may be further associated an SL resource (pool) index. So, the serving cell may instruct the UE to release one SL resource (pool) configuration by indicating the associated SL resource (pool) index in another SL_Resource_(Pool)_ToRemove list. The SL_Resource_(Pool)_ToAdd list &amp; SL_Resource_(Pool)_ToRemove list may be included in the IE reconfigurationwithsync (in NR protocols)/mobilitycontrolinfoV2X (in LTE protocols) when the serving cell is transmitting an RRC Connection Reconfiguration message to initiate a handover procedure. It should be noted that the above-mentioned mechanisms and signaling may also be applicable to a conditional handover procedure. It should be noted that the sidelink resource pool configuration may include a normal sidelink resource pool configuration and/or an exceptional sidelink resource pool configuration. It should be noted that the delta signaling approach may be applicable to a (Type1/Type2) sidelink configured grant configuration. 
     In some implementations, the UE may start to access the configured SL resource (pool) after the handover procedure is finished successfully. In some implementations, the UE could access the configured SL resource (pool) during the handover procedure. In some additional implementations, the UE could access the configured SL resource (pool) during the conditional handover procedure. 
     In some implementations, the UE may obtain the timing advance instruction or timing offset value represented in symbols, microseconds, etc. (or assistance information for the UE to adjust timing when the UE is transmitting/receiving SL packets) for SL packet delivery on FR2 by receiving the timing reference or timing advance instructions from the serving cell on FR1 (e.g., Cell #A). 
     Table 1 shows a validity area configuration of an SL resource on FR1 (e.g., CC #1 in  FIG. 3 ) or FR2 (e.g., CC #2 in  FIG. 2A ). 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Cross-Carrier Validity Area Configuration 
               
               
                 Cross-Carrier Validity Area Configuration with SL Resource Configuration 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Cellidentitylist 
                 (1) 
                 In some implementations, the SL resource configuration 
               
               
                   
                   
                 on FR2 (in SL CC#2) may be associated to a 
               
               
                   
                   
                 cellidentitylist, which includes at least one cell identity in 
               
               
                   
                   
                 another component carrier (e.g., CC#1 in FIG. 3). 
               
               
                   
                 (2) 
                 In addition, each cell identity may be associated with one 
               
               
                   
                   
                 cell operating on CC#1 (which is also the serving 
               
               
                   
                   
                 frequency to the UE). 
               
               
                   
                 (3) 
                 The cell identity may be physical cell identity (PCI) or 
               
               
                   
                   
                 cellidentity which is unique with associated network 
               
               
                   
                   
                 (e.g., PLMN or NPN). 
               
               
                   
                 (4) 
                 In some additional implementations, at least one cell 
               
               
                   
                   
                 configured in the cellidentitylist may be further 
               
               
                   
                   
                 associated with one PLMN identity or one NPN identity. 
               
               
                   
                 (5) 
                 In some implementations, UE would implicitly know 
               
               
                   
                   
                 that the configured SL resource on CC#2 is valid only 
               
               
                   
                   
                 in the coverage of serving cell in CC#1 (e.g., Cell#1 in 
               
               
                   
                   
                 FIG. 3) while no explicit validity area configuration is 
               
               
                   
                   
                 provided with the SL resource configuration. 
               
               
                 Systeminformationarea 
                 (1) 
                 In some implementations, the SL resource configuration 
               
               
                 configuration 
                   
                 on FR2 (e.g., CC#2) may be associated with one 
               
               
                   
                   
                 systemInformationAreaID, which is broadcast by cells in 
               
               
                   
                   
                 FR1 (e.g., CC#1). 
               
               
                   
                 (2) 
                 So, the UE would know that the UE can still access the 
               
               
                   
                   
                 configured SL resource of CC#2 while the UE is still 
               
               
                   
                   
                 camping on CC#1 while the serving cell to the UE is 
               
               
                   
                   
                 broadcasting the same systemInformationAreaID. 
               
               
                   
                 (3) 
                 In some implementations, the systemInformationAreaID 
               
               
                   
                   
                 is generally applied to all or a subset of of the system 
               
               
                   
                   
                 information broadcast by the serving cell (e.g., the 
               
               
                   
                   
                 system information which contains the (LTE) V2X 
               
               
                   
                   
                 sidelink configuration (V2X-SL SIB) and/or the system 
               
               
                   
                   
                 information which contains the NR sidelink 
               
               
                   
                   
                 configuration (NR-SL SIB)), such as the SIB12, SIB13, 
               
               
                   
                   
                 and SIB14 in the NR protocols. 
               
               
                   
                 (4) 
                 In some other implementations, a specific area ID (e.g., 
               
               
                   
                   
                 systemInformationAreaID_V2X may be configured to 
               
               
                   
                   
                 be associated with the system information to support 
               
               
                   
                   
                 (LTE/NR) V2X (sidelink) service. 
               
               
                 RAN notification area 
                 (1) 
                 In some implementations, the validity area may be 
               
               
                 Code or Tracking Area 
                   
                 associated with one RAN Notification Area Code 
               
               
                 Code 
                   
                 (RANAC). In addition, each RAN Notification Area may 
               
               
                   
                   
                 cover one or more cells in one PLMN and each RANAC 
               
               
                   
                   
                 may be unique in one PLMN. 
               
               
                   
                 (2) 
                 In some implementations, the validity area may be 
               
               
                   
                   
                 associated with one Tracking Area Code (TAC). In 
               
               
                   
                   
                 addition, each Tracking area may cover one or more cells 
               
               
                   
                   
                 in one PLMN/NPN and each TAC may be unique in one 
               
               
                   
                   
                 PLMN. 
               
            
           
           
               
               
            
               
                 Area defined by GNSS 
                 In some implementations, the validity area may be 
               
               
                   
                 configured based on an area defined by GNSS (e.g., based 
               
               
                   
                 on the coordinates provided by GNSS). 
               
               
                 Reuse Supplementary 
                 In NR protocols, a NR cell may support uplink resource 
               
               
                 uplink carrier (SUL) 
                 configuration on both Normal uplink carrier and 
               
               
                 configuration 
                 supplementary uplink carrier. So, the camped Cell#1 may 
               
               
                   
                 also broadcast SUL configuration in system information 
               
               
                   
                 (e.g., SIB1). 
               
               
                   
                 (1) In some implementations, the serving cell to the UE is 
               
               
                   
                 camped on CC#2. In addition, the serving cell may broadcast 
               
               
                   
                 SL resource configuration on the operating normal uplink 
               
               
                   
                 (NUL) carrier (e.g., NUL carrier in CC#2 or other 
               
               
                   
                 component carrier in FR2) and/or supplementary uplink 
               
               
                   
                 (SUL) carrier (in CC#1 or other component carrier in FR1). 
               
               
                   
                 In addition, the serving cell may also deliver supplementary 
               
               
                   
                 uplink carrier configuration in system information. 
               
               
                   
                 (3) So, to the UE side, the UE would know that it can 
               
               
                   
                 access the SL resource configured on the NUL carrier (in 
               
               
                   
                 FR2) and SUL carrier (in FR1). In addition, the UE may not 
               
               
                   
                 need to do SL cell (re)selection in the SUL carrier (in a 
               
               
                   
                 time division duplex (TDD) scenario) or try to find out the 
               
               
                   
                 downlink frequency carrier associated with the SUL carrier. 
               
            
           
           
               
               
               
            
               
                 PLMN-specific 
                 (1) 
                 In RAN, one cell (e.g., Cell#1 in CC#1) may be shared 
               
               
                 association to the 
                   
                 by different PLMNs and so the cell would broadcast 
               
               
                 validity area design 
                   
                 PLMN identity(-ies) to indicate the PLMN(s) supported 
               
               
                   
                   
                 by the cell. In addition, Cell#1 may also support V2X 
               
               
                   
                   
                 services of different PLMN(s). Each PLMN may have 
               
               
                   
                   
                 individual SL resource configurations. 
               
               
                   
                 (2) 
                 To the UE side, the UE may subscribe the NR-V2X/LTE- 
               
               
                   
                   
                 V2X (sidelink) service with its registered telecom 
               
               
                   
                   
                 operator and the operator may deploy (at least) one 
               
               
                   
                   
                 PLMN(s) to support the subscribed UEs. So, the UE 
               
               
                   
                   
                 could access the RAN and implement SL operation based 
               
               
                   
                   
                 on the given configuration associated with the registered 
               
               
                   
                   
                 PLMN (e.g., Home PLMN or equivalent HPLMN). To 
               
               
                   
                   
                 enable UEs to implement NR-V2X/LTE-V2X SL 
               
               
                   
                   
                 operation based on the SL resource configurations of 
               
               
                   
                   
                 their registered PLMNs, RAN may deliver the validity 
               
               
                   
                   
                 configurations associated with PLMN identity(-ies) to 
               
               
                   
                   
                 the UEs. 
               
               
                   
                 (3) 
                 In some implementations, an implicit approach may also 
               
               
                   
                   
                 be configured to the UE (e.g., the transmitted SL resource 
               
               
                   
                   
                 configuration may be implicitly associated to the 1 st   
               
               
                   
                   
                 PLMN shown in the PLMN list, which is broadcast in the 
               
               
                   
                   
                 SIB1 of the serving cell). In some additional 
               
               
                   
                   
                 implementations, the cells in the cellidentitylist may be 
               
               
                   
                   
                 associated with more than one PLMN. So, each 
               
               
                   
                   
                 cellidentity in the cellidentitylist may be further indicated 
               
               
                   
                   
                 the associated PLMN identity. 
               
               
                   
                 (4) 
                 The serving cell may deliver the validity area 
               
               
                   
                   
                 configurations with associated PLMN(s) through 
               
               
                   
                   
                 broadcasting system information (e.g., system 
               
               
                   
                   
                 information broadcasting or SI-on-demand procedure) or 
               
               
                   
                   
                 dedicated signaling (e.g., RRC signaling). 
               
               
                   
                 (5) 
                 Also, in some additional implementations, the mapping 
               
               
                   
                   
                 information with one associated PLMN may be 
               
               
                   
                   
                 represented by a ‘PLMN index’. The ‘PLMN index’ is 
               
               
                   
                   
                 decided based on the sequence of PLMN shown in the 
               
               
                   
                   
                 PLMN identity list, which is broadcast by the cell in 
               
               
                   
                   
                 system information (e.g., SIB1 broadcast by Cell#1). 
               
               
                   
                 (6) 
                 Please also note that the PLMN in this disclosure may 
               
               
                   
                   
                 also cover the Non-Public-Network (NPN) scenario. The 
               
               
                   
                   
                 validity configuration may associate to NPN identity 
               
               
                   
                   
                 (e.g., PLMN ID and/or NID for SNPN, PLMN ID and/or 
               
               
                   
                   
                 CAG ID for PNI-NPN). In some implementations, The 
               
               
                   
                   
                 NPN scenario may be a Stand-alone Non-Public 
               
               
                   
                   
                 Network (SNPN), i.e., the RAN is operated by an NPN 
               
               
                   
                   
                 operator and it does not rely on network functions 
               
               
                   
                   
                 provided by a PLMN. In some other implementations, 
               
               
                   
                   
                 the NPN scenario may be a Public network integrated 
               
               
                   
                   
                 NPN (PNI-NPN), i.e., a non-public RAN is deployed 
               
               
                   
                   
                 with the support of a PLMN. The SNPN(s) may be 
               
               
                   
                   
                 identified by UEs based on the PLMN ID and/or 
               
               
                   
                   
                 Network ID (NID) broadcast in SIB1 of a cell which 
               
               
                   
                   
                 supports SNPN. The PNI-NPN may be identified by 
               
               
                   
                   
                 PLMN ID and/or Cell Access Group (CAG) ID broadcast 
               
               
                   
                   
                 in SIB1 of a cell supporting PNI-NPN. 
               
               
                   
                 (7) 
                 In some additional implementations, one UE may receive 
               
               
                   
                   
                 the SL resource configuration (with the validity area 
               
               
                   
                   
                 configuration with/without associated PLMN identities) 
               
               
                   
                   
                 through PC5 interface (e.g., by receiving the 
               
               
                   
                   
                 broadcasting MIB-SL (MasterInformationBlock_SL) or 
               
               
                   
                   
                 the (broadcasting/multi-casting(group- 
               
               
                   
                   
                 casting)/unicasting) PC5 RRC signaling transmitted by 
               
               
                   
                   
                 neighbor UEs). 
               
               
                   
               
               
                 It should be noted that the sidelink resource configuration on CC#2 and the RAN on CC#1 may be implemented by different RATs. In some implementations, sidelink resource configurations for (LTE) V2X sidelink communication may be configured on CC#2 and the associated cross-carrier validity area configuration may be implemented on an NR-RAN, which is operating on CC#1. In some additional implementations, sidelink resource configurations for NR sidelink communication may be configured on CC#2 and the associated cross-carrier validity area configuration may be implemented on an E-UTRAN, which is operating on CC#1. 
               
               
                 It should also be noted that, in some implementations, a cross-carrier validity area configuration may be implemented jointly with other validity area information. For example, while the UE is camping on a serving cell in CC#1, the CC#1 may configure the sidelink resource configuration of CC#2 with one additional cellidentitylist, which is composed by one or more cell identities of the cells operating on CC#2. In addition, the UE may need to implement a non-serving cell (re)selection procedure on CC#2 for sidelink operations. So, the UE needs to check the validity of the sidelink resource configuration based on the cross-carrier validity area configuration (associated with CC#1) and the cellidentitylist (associated with CC#2). 
               
               
                 It should be also noted that, in some implementations, the validity area of the sidelink resource configuration may be implicitly associated with the cell identity of the serving cell of the first RAT (e.g., NR cell#1 in CC#1). This condition may happen when the sidelink resource configuration is not indicated by the systemInformationAreaID broadcast by the serving cell. For example, when the system information related to NR/LTE (V2X) sidelink operation (e.g., SIB12, SIB13, SIB14 in NR protocols, which contains the sidelink resource configuration) is not configured with ‘AreaScope = {true}’ by the serving cell in the SIB1, or when the systemInformationAreaID is absent from the system information broadcast by the serving cell, the validity area of the first RAT is composed by the cell identity of the serving cell of the first RAT. 
               
            
           
         
       
     
       FIG. 3  is a flowchart  300  of a method performed by a UE for NR SL operations, in accordance with an example implementation of the present disclosure. 
     In action  302 , the UE may receive, through a serving cell of a first (e.g., 5G NR) Radio Access Technology (RAT), an SL resource configuration of a second RAT (e.g., E-UTRA). 
     In action  304 , the UE may determine first validity area information associated with the first RAT and second validity area information associated with the second RAT, the first validity area information and the second validity area information being associated with different frequency carriers. 
     In action  306 , the UE may identify a validity area of the SL resource configuration based on the first validity area information and the second validity area information. 
     In action  308 , the UE may access an SL resource associated with the validity area after the validity area is identified as valid. 
     Implementation 2: Fallback Mechanism to Cross-Carrier Validity Area Configuration 
     Referring to  FIG. 4 ,  FIG. 4  illustrates a diagram showing a UE performing SL synchronization and SL cell (re)selection procedures under a fallback mechanism to a cross-carrier validity area configuration, in accordance with an example implementation of the present disclosure. 
     In the present implementation, the cross-carrier SL resource configuration associated with a validity area (e.g., Validity Area #1) may be invalidated by a UE after the UE moves out of the validity area to another validity area (e.g., Validity Area #2). 
     In some implementations, the UE may release the invalidated cross-carrier SL resource configuration after the UE moves out of the validity area associated with the stored SL resource configuration. 
     In some implementations, the UE may start performing SL synchronization and SL cell (re)selection procedures on FR2 when one of more of the following fallback conditions are met: 
     Condition 1: the UE may not be configured with another SL resource configuration nor validity area in FR2 (e.g., but CC #2 still supports SL in the areas out of Validity Area #1). In this condition, the UE may initiate SL synchronization and SL cell (re)selection in the SL CC #2 by the UE itself. 
     Condition 2: In some other conditions, the UE may be configured with another validity Area #2 in FR1 but the UE may temporarily fail to find a suitable cell (e.g., while the UE moves to a coverage hole). In this condition, the UE may implement SL synchronization and SL cell (re)selection in the SL CC #2 by the UE itself. 
     Condition 3: the serving cell in FR1 does not provide a validity area in FR1. Instead, the serving cell in FR1 may configure SL resource configuration in FR2 with a validity area indicated in FR2 (e.g., the Validity Area #2 in  FIG. 3 ). For example, the Validity Area #2 may be composed of the cells operating in CC #2. In some additional implementations, the Validity Area #2 is composed of the cellidentity/PCI/RANAC/Tracking area code/SysteminformationareaID broadcast by cells in FR2. In this condition, the UE may implement SL synchronization and SL cell (re)selection in the SL CC #2 by the UE itself. 
     It is noted that, after the SL cell (re)selection procedure, the UE may start monitoring the system information broadcast by the selected (non-serving) cell for sidelink resource configuration reception (on the CC #2). 
     Referring to  FIG. 5 ,  FIG. 5  illustrates a range-based SL resource association in accordance with an example implementation of the present disclosure. In the present implementation, each SL LCH may have one or more associated SL carriers. One or more range-based SL resource configurations may be configured to a UE. For example, SL-Resource Configuration #1 and SL-Resource Configuration #2 may be provided to the UE with a distance-based threshold, R 1  (e.g., in the unit of meters). 
     In one example, a UE (e.g., UE #2 in  FIG. 2B ) may apply SL-Resource Configuration #1 to transmit SL packets with a paired UE (e.g., UE #1 in  FIG. 2B ) while the physical distance between the Tx UE/Rx UE is smaller than R 1 . For example, the value of R 1  may be up to several hundred meters. 
     In another example, a UE (e.g., UE #2 in  FIG. 2B ) may apply SL-Resource Configuration #2 to transmit SL packets with a paired UE (e.g., UE #1 in  FIG. 2B ) while the physical distance between the Tx UE and Rx UE is larger than R 1 . 
     In some implementations, a UE (e.g., UE #2 in  FIG. 2B ) may estimate the physical distance from another UE (e.g., UE #1 in  FIG. 2B ) by receiving the SL control information (SCI) (e.g., based on the received 1 st  SCI and/or the 2 nd  SCI during the two-stage SCI transmission procedure) transmitted by the (Tx) UE (e.g., by decoding the location information, such as zone ID or GNSS location information, of the Tx UE). In some other implementations, a UE may estimate the physical distance from another UE through other radio access technologies, such as an NR positioning technique or a GNSS information exchange. 
     It should be noted that the SL packet delivery may become more critical when UE #1 and UE #2 are close to each other. In addition, the channel effect (e.g., pathloss) on different SL CC may also need to be considered. Therefore, to one SL LCH, associations with different SL CCs (and so the SL resource configurations, such as Type1/Type2 SL configured grant(s), SL dynamic grant(s), resource pool(s), exceptional resource pool(s) associated with the SL CC) may be helpful to preserve the QoS (Quality of Service) of SL packet delivery. As shown in Table 2, SL logical channel #1 may be associated with CC #1 (in FR1) in the SL-Resource Configuration #2 since the pathloss effect in FR1 is smaller than that in FR2. Then, while the physical distance between the Tx UE/Rx UE is smaller than R 1 , the SL logical channel #1 may be associated with CC #2 (e.g., in FR2) in the SL-Resource Configuration #2. In addition, in some other implementations, one SL LCH may be associated with more than one SL component carrier. As shown in Table 2, the SL logical channel #2 may be associated {CC #1} in the SL-Resource configuration #2 and the same SL logical channel #2 may be associated {CC #1, CC #2, CC #3} in the SL-Resource configuration #2 and so the UE may implement SL multiplexing to an SL grant (based on the received SL resource configuration in one SL CC, such as Type1/Type2 SL configured grant(s), SL dynamic grant(s), resource pool(s), resource pool(s) with zone configuration, exceptional resource pool(s) associated with the SL CC) based on the range-based association with the SL LCH and SL CC. Also, it is noted that, in some implementations, the operating SL CC(s) for SL HARQ or SL Automatic Repeat reQuest (ARQ) packet re-transmission or SL packet repetition may be decided while the UE is preparing to transmit a first SL packet. So, the UE may not change the operating SL CC while the UE is implementing SL HARQ/ARQ packet re-transmission and SL packet repetition to the same SL packets after the UE sending the first SL packet. In some implementations, the UE may decide the operating SL CC(s) (based on the configured rules) of each SL packet delivery independently every time when the UE is preparing to transmit one or more SL packet(s) (no matter whether the SL packet is a first transmission, (SL-HARQ) re-transmission, or repetition). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Range-Based SL Resource Association 
               
            
           
           
               
               
               
            
               
                   
                 SL-Resource config. #2 
                 SL-Resource config. #1 
               
               
                   
               
               
                 SL logical 
                 {CC#1} 
                 {CC#2} 
               
               
                 channel#1 
                   
                   
               
               
                 SL logical 
                 {CC#1} 
                 {CC#1, CC#2, 
               
               
                 channel#2 
                   
                 CC#3} 
               
               
                   
               
            
           
         
       
     
     In some implementations, a default SL resource association (e.g., SL-Resource config. #1) may be indicated to the UEs in the SL-group (e.g., unicast group or groupcast group). Thus, if the location information is (temporarily) unavailable to the Tx UE side, then the Tx UE may apply the default SL resource association to transmit SL packets. In some implementations, the default SL resource association may be obtained through SL pre-configuration or through broadcasting message (e.g., System Information (SI)) or through an SI on-demand procedure which the Tx UE obtains from the serving RAN. 
     Implementation 3: NR Non-Standalone Cell Broadcasting SL Configuration 
     An NR non-standalone cell (NR-NSA cell) may also broadcast system information to support NR (public safety) V2X service/LTE V2X service or public safety SL communication service. In some implementation, a NR-NSA cell may not broadcast a tracking area code (TAC) while the NR-NSA cell is broadcasting system information, and so the UE could identify whether a cell is an NSA cell by checking the TAC. In addition, the UE may consider the NR-NSA cell as a non-suitable cell while the UE is performing cell (re)selection (e.g., cell (re)selection in (LTE/NR) Uu interface). However, it is still possible that the UE may select one NR-NSA cell during (serving/non-serving) cell (re)selection as the cell to provide SL communication. So, an NSA cell may become the serving cell to the UE and the concerned SL CC is also the serving frequency to the UE. At this stage, the NR-NSA cell may be an ‘acceptable cell’ to the UE and the UE may select to camp on a NR-NSA cell after the (serving/non-serving) cell (re)selection procedure (so the UE may also move to a ‘camped on any cell’ state). The UE may stay in a ‘limited service’ state. However, even in the ‘limited service’ state, the UE may still be able to access some (limited) LTE/NR V2X service through NR/LTE SL while the UE is camping on an NR-NSA cell. In addition, one UE may still be able to exchange PC5 RRC signaling with neighboring UEs while the UE is in the ‘limited service’ state (so, the PC5 RRC signaling exchange may not be impacted if one of the UEs move to the ‘camped on any cell’ state). Thus, an NR-NSA cell may broadcast NR/LTE SL configurations, which may include an SL resource pool configuration, an SL exceptional pool configuration, and an SL synchronization configuration, to support SL operations for NR/LTE V2X service. In addition, the UE may think it is in-coverage while it is camping on an NR-NSA cell (or while the UE selects an NR-NSA cell). It should be noted, in some implementations, the NSA cell may broadcast an SL transmission resource pool configuration (e.g., v2x-CommTxPoolNormalCommon or p2x-CommTxPoolNormalCommon or discovery resource pool based on the 3GPP TS 36.331.f.6.0) associated with the camped frequency in the broadcasting system information. In addition, the UE may not initiate an RRC connection with the NSA cell when the NSA cell does broadcast SL information about V2X service, but the NSA cell does not transmit an SL transmission resource pool configuration which the UE needs (e.g., for V2X service, P2X service or for discovery service) in the broadcast system information. In some implementations, the UE may not expect an NSA cell would broadcast SL resource configuration without delivering the SL transmission resource pool configuration (e.g., v2x-del CommTxPoolNormalCommon or p2x-CommTxPoolNormalCommon) in the camped frequency carrier. 
     In some implementations, the NSA cell may operate on a non-serving frequency, the NSA cell may also be included while the UE is implementing cell selection and reselection for SL operations (by taking the cell selection and reselection for SL mechanism in 3GPP TS 36.304.15.6.0 as the baseline). Moreover, the NSA cell may also transmit SL resource configuration associated with the concerned SL frequency carrier (with or without SL resource configuration associated with other SL CCs), the UE may transmit and/or receive SL packets on the concerned SL CC based on the received SL resource configuration and based on the timing information (e.g., DL timing) obtained from the NSA cell. 
     Implementation 4: FR2 Assistance Information Delivery Through FR1 
     In IMPLEMENTATION 4, further association between an SL CC on FR1 (e.g., CC #1) and an SL CC on FR2 (e.g., CC #2) may be configured. For example, a UE may be configured to deliver FR2 assistance information of SL operation on FR2 through the SL CC #1. In some implementations, the UE may transmit FR2 assistance information to the serving cell in FR1 (e.g., CC #1 in  FIG. 2B ) through LTE/NR Uu interface. In some implementations, the UE may transmit FR2 assistance information to neighboring UEs (e.g., an SL group leader in an SL multi-cast (/group-cast) group, such as UE #1 in  FIG. 2A ) through LTE/NR PC5 interface. In some implementations, FR2 assistance information may be transmitted to a serving cell (through (LTE/NR) Uu interface) or a paired UE (through PC5 RRC signaling (LTE/NR) PC5 interface) by transmitting an SL-measurement report. 
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 FR2 Assistance Information 
               
               
                 FR2 Assistance Information (e.g., CC#2 in FIG. 1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Measurement 
                 UE may transmit SL measurement report on FR2 (e.g., CC#2 in 
               
               
                 Report on 
                 FIG. 2), which may include (which is called FR2 measurement 
               
               
                 CC#2 
                 configuration in this disclosure): 
               
               
                   
                 1) SL Channel State Information Reference Signal (CSI-RS) 
               
               
                   
                 report (with one associated destination ID); 
               
               
                   
                 2) SL beam measurement report (with one associated destination 
               
               
                   
                 ID); 
               
               
                   
                 3) SL beam failure indication on CC#2 (with one destination ID); 
               
               
                   
                 4) SL radio failure indication on CC#2 (e.g., T310_SL is configured 
               
               
                   
                 to CC#2. The MAC entity may receive in-sync/out-of-sync 
               
               
                   
                 indications, which is decided by the lower layers based on the 
               
               
                   
                 channel conditions (e.g., SL RSRP value) on CC#2, from the lower 
               
               
                   
                 layers). 
               
               
                   
                 5) In some implementations, the MAC entity may receive up to N 
               
               
                   
                 consecutive SL HARQ Discontinuous Transmission (DTX) 
               
               
                   
                 indications from the lower layers. Here, one SL HARQ DTX 
               
               
                   
                 indication means the Tx UE has not received any response (neither 
               
               
                   
                 HARQ ACK/NACK message) after one SL HARQ packet 
               
               
                   
                 transmission to the Rx UE (e.g., with one Layer 2 Destination ID). 
               
               
                   
                 Under this condition, the MAC entity may report this event (e.g., 
               
               
                   
                 reaches up to N consecutive SL HARQ DTX indications in MAC 
               
               
                   
                 entity associated with one Layer2/Layer1 Destination UE ID) to the 
               
               
                   
                 upper layers (e.g., the RRC layer). Then, the RRC layer may trigger 
               
               
                   
                 an SL radio failure to the associated with Rx UE (e.g., Sidelink Radio 
               
               
                   
                 Link Failure event happens to the PC5 RRC connection associated 
               
               
                   
                 with the Layer 2 Destination ID). 
               
               
                   
                 6) Channel busy ratio (CBR) report in CC#2. 
               
               
                   
                 7) Channel Occupancy ratio (CR) report in CC#2. 
               
               
                   
                 Here, the destination ID may be an identifier provided by higher 
               
               
                   
                 layer (e.g., V2X layer) or a Layer-2/Layer-1 ID (for example, when 
               
               
                   
                 the UE#2 (as shown in FIG. 3) is transmitting FR2 assistance 
               
               
                   
                 information to the serving cell or UE#1). The UE#2 may also 
               
               
                   
                 transmit the UE#1&#39;s ID (e.g., Layer 2 UE ID) with FR2 assistance 
               
               
                   
                 information as the destination ID. 
               
            
           
           
               
               
               
            
               
                 SL Radio 
                 1) 
                 UE may be configured to report SL radio link failure indication 
               
               
                 Link Failure 
                   
                 or physical layer problem on CC#2 (with one associated 
               
               
                 Report 
                   
                 destination ID); 
               
            
           
           
               
               
            
               
                   
                 Here, the destination ID may be an identifier provided by higher 
               
               
                   
                 layer (e.g., V2X layer) or a Layer-2/Layer-1 ID of the paired UE. 
               
               
                 Resource 
                 In some implementations, the UE may be configured with a resource 
               
               
                 configuration 
                 in NR/LTE Uu interface which is specified for the UE to report 
               
               
                 for the 
                 FR2 assistance information reporting to the serving cell (e.g., 
               
               
                 assistance 
                 Cell#1 in FR1). For example, 
               
            
           
           
               
               
               
            
               
                 information 
                 1) 
                 The UE is configured with Type 1/Type 2 configured grant for 
               
               
                 delivery in 
                   
                 periodic FR2 assistance information report to the serving cell. 
               
               
                 Uu interface 
                   
                 In addition, explicit association may be provided in the 
               
               
                   
                   
                 configuration that one (Type 1/Type 2) configured grant on 
               
               
                   
                   
                 CC#1 is reserved for FR2 assistance information reporting 
               
               
                   
                   
                 (e.g., by configuring one configured grant to be associated with 
               
               
                   
                   
                 one FR2 measurement configuration) and so the UE would 
               
               
                   
                   
                 transmit FR2 assistance information through the associated 
               
               
                   
                   
                 configured grant. 
               
               
                   
                 2) 
                 In some additional implementations, the UE (e.g., UE#2) may be 
               
               
                   
                   
                 configured with FR2 measurement configuration of more than 
               
               
                   
                   
                 one paired UE(s) (or more than one destination ID). In addition, 
               
               
                   
                   
                 these FR2 assistance information may share configured grant(s) 
               
               
                   
                   
                 for the UE to transmit FR2 assistance information. 
               
            
           
           
               
               
            
               
                 SL resource 
                 In some implementations, the UE may be configured with SL 
               
               
                 configuration 
                 resource which is specified for FR2 assistance information 
               
               
                 for the 
                 reporting. For example, 
               
            
           
           
               
               
               
            
               
                 assistance 
                 1) 
                 The UE is configured with Type 1/Type 2 SL configured grant(s) 
               
               
                 information 
                   
                 on CC#1 for periodic FR2 assistance information report. 
               
               
                 delivery in 
                   
                 In addition, explicit association may be provided in the 
               
               
                 PC5 interface 
                   
                 configuration of SL configured grant to configure that one (Type 
               
               
                   
                   
                 1/Type 2) SL configured grant on CC#1 is reserved for FR2 
               
               
                   
                   
                 assistance information (e.g., by configuring one SL configured 
               
               
                   
                   
                 grant to be associated with FR2 assistance information) and so 
               
               
                   
                   
                 the UE may transmit FR2 assistance through the associated Type 
               
               
                   
                   
                 1/Type 2 SL configured grant. 
               
               
                   
                 2) 
                 In some additional implementations, the UE (e.g., UE#2) may be 
               
               
                   
                   
                 configured with FR2 measurement configuration of more than 
               
               
                   
                   
                 one paired UE(s) (or more than one destination ID). In addition, 
               
               
                   
                   
                 these FR2 assistance information may share configured grant(s) 
               
               
                   
                   
                 for the UE to transmit FR2 assistance information. 
               
               
                   
                 3) 
                 Small Data Transmission: in some additional implementations, 
               
               
                   
                   
                 the serving cell may configure Type 1/Type 2 UL configured 
               
               
                   
                   
                 grant(s) on CC#1 for (periodic/non-periodic) FR2 assistance 
               
               
                   
                   
                 information reporting while the UE is staying in the RRC 
               
               
                   
                   
                 Connected state/RRC Inactive state. In some additional 
               
               
                   
                   
                 implementations, the UE may be enabled to transmit a FR2 
               
               
                   
                   
                 assistance information report through a (2-step/4-step) random 
               
               
                   
                   
                 access procedure. It is noted that, in addition to (periodic/non- 
               
               
                   
                   
                 periodic) FR2 assistance information reporting, the UE may also 
               
               
                   
                   
                 be enabled (e.g., the serving cell may deliver one explicit DL 
               
               
                   
                   
                 control signaling to enable the UE to do sidelink UE information 
               
               
                   
                   
                 delivery through small data transmission approaches during 
               
               
                   
                   
                 RRC inactive state) to transmit sidelink-related information to 
               
               
                   
                   
                 the serving cell through the (Type1/Type2) UL Configured Grant 
               
               
                   
                   
                 Configuration and/or the (2-step/4-step) random access 
               
               
                   
                   
                 procedures while the UE is staying in the RRC Inactive state. In 
               
               
                   
                   
                 some implementations, the sidelink-related information may 
               
               
                   
                   
                 include SidelinkUEInformationNR, a sidelink radio link failure 
               
               
                   
                   
                 report (with one ore more Layer 2 Destination UE ID(s)), an SL- 
               
               
                   
                   
                 measurement report, etc. In addition, the small data transmission 
               
               
                   
                   
                 may not be limited by FR2 Assistance Information but also 
               
               
                   
                   
                 include other SL reporting (e.g., Channel Busy Ratio Report in 
               
               
                   
                   
                 one or more SL CCs). 
               
            
           
           
               
               
            
               
                 SL- 
                 In some of the presented implementations, the FR2 Assistance 
               
               
                 measurement 
                 Information may be transmitted through (LTE/NR) Uu interface or 
               
               
                 report 
                 (LTE/NR) PC5 interface by transmitting SL-measurement to the 
               
               
                   
                 serving cell or other UEs. 
               
               
                   
                 SL-measurement report may cover the following Information 
               
               
                   
                 Elements: 
               
            
           
           
               
               
               
            
               
                   
                 (1) 
                 SL-measurement report may include (at least) one 
               
               
                   
                   
                 CarrierFreq_SL (e.g., represented by NR-ARFCN (absolute 
               
               
                   
                   
                 radio-frequency channel number) value), which indicates the 
               
               
                   
                   
                 target of corresponding SL component. 
               
               
                   
                 (2) 
                 In the indicated CarrierFreq_SL, the UE may report the SL 
               
               
                   
                   
                 CSI-RS transmitted by one target UE to obtain the {Sidelink 
               
               
                   
                   
                 Reference Signal Received Power Result (rsrpResult_SL), 
               
               
                   
                   
                 Sidelink Reference Signal Received Quality Result 
               
               
                   
                   
                 (rsrqResult_SL), Sidelink Signal to Interference &amp; Noise Result 
               
               
                   
                   
                 (sinrResult_SL)} corresponding to the target UE (the target UE 
               
               
                   
                   
                 is associated with one Layer 2 Destination UE ID in the SL- 
               
               
                   
                   
                 measurement report). 
               
               
                   
                 (3) 
                 In some additional implementations, in the indicated 
               
               
                   
                   
                 CarrierFreq_SL, the UE may report the observed CBR of the 
               
               
                   
                   
                 concerned SL-CC. 
               
               
                   
                 (4) 
                 In some additional implementations, to one specific destination 
               
               
                   
                   
                 UE ID, the UE may report SL-measurement result 
               
               
                   
                   
                 corresponding to one MeasResultSL-Synchronization Signal 
               
               
                   
                   
                 Block (SSB)-index. The UE may include the index of the SL- 
               
               
                   
                   
                 SSB (being associated with one Destination UE ID and one 
               
               
                   
                   
                 CarrierFreq_SL) and the measurement result of the associated 
               
               
                   
                   
                 SL-SSB index (e.g., {rsrpResult_SL, rsrqResult_SL, 
               
               
                   
                   
                 sinrResult_SL}). In some other implementations, the SL- 
               
               
                   
                   
                 measurement report may not be associated with SL-SSB but be 
               
               
                   
                   
                 associated with one configured SL reference signal (e.g., SL 
               
               
                   
                   
                 CSI-RS with one associated reference signal index). 
               
               
                   
                 (5) 
                 In some additional implementations, the UE may include 
               
               
                   
                   
                 MeasResultCBR (e.g, CBR-PSSCH, CBR-PSCCH) associated 
               
               
                   
                   
                 with (at least) one indicated resource pool identity (e.g., with 
               
               
                   
                   
                 one SLresourcepoolidentity, which may be configured by 
               
               
                   
                   
                 serving RAN) in one FR2 SL-CC (e.g, being indicated by 
               
               
                   
                   
                 CarrierFreq_SL). 
               
               
                   
                 (6) 
                 In some additional implementations, the UE may indicate 
               
               
                   
                   
                 channel occupancy ratio (e.g, channelOccupancy_SL = integer 
               
               
                   
                   
                 (0, 100) to indicate the percentage of channel occupancy ratio) 
               
               
                   
                   
                 with (at least) one FR2 SL-CC (e.g, being indicated by 
               
               
                   
                   
                 CarrierFreq_SL). The channel occupancy ratio is obtained by 
               
               
                   
                   
                 monitoring the percentage of samples when the RSSI in the 
               
               
                   
                   
                 concerned SL-CC was above a pre-configured 
               
               
                   
                   
                 channelOccupancyThreshold. 
               
               
                   
               
            
           
         
       
     
     In some of the present implementations, a UE may be configured with event-based SL measurement objects to provide SL-measurement reports after an SL radio link failure event (or SL physical layer problem) occurs. In the present disclosure, an additional timer, T 312 _SL, is introduced where the T 312 _SL may be configured to a UE with configured SL measurement objects. Moreover, in the present disclosure, the SL measurement objects may include the SL-measurement report to serving cell(s) (e.g., special cell, such as PCell and PSCell of the UE), the SL-measurement report to a paired UE in an SL unicast group, or other UEs. So, it is clear that an SL-measurement report corresponding to one SL-measObject may be transmitted through a (LTE/NR) Uu interface or a (LTE/NR) PC5 interface based on the target of an associated SL-measObject. 
     In some implementations, the UE needs to report to the serving RAN that it supports T 312 _SL during an SL-radio link failure (RLF) event. In an example, an Information Element, ‘Timer 312 _SL=support’, may be explicitly indicated by the UE in the UE (NR/LTE) capability information to the serving cell. It should be noted that an SL-measurement report initiated while a T 312 _SL starts counting/running may cover the SL-measurement report for an LTE PC5 interface (e.g., a CBR report on LTE SL resource pools) and/or an NR PC5 interface (CBR report on NR SL resource pools). In some implementations, the ‘Timer 312 _SL=support’ IE may only be applied to an SL-measurement report for an LTE PC5 interface or an NR PC5 interface. In some implementations, the ‘Timer 312 _SL=support’ IE may be applied to an SL-measurement report for an LTE PC5 interface or an NR PC5 interface. In addition, on the UE side, the UE may not support the Timer 312 _SL in a default setting. Thus, the UE need not indicate Timer 312 _SL not supported if the UE does not support an SL-measurement report initiated after T 312 _SL starts counting. 
     
       
         
           
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 SL-Measurement Object with T312_SL 
               
               
                 SL-Measurement object 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 SL- 
                 (1) 
                 One UE may be configured with event-triggered measurement 
               
               
                 measObject 
                   
                 objects. 
               
               
                   
                 (2) 
                 Besides CBR reports, the mechanisms in SL-measurement 
               
               
                   
                   
                 report (e.g., as shown in Table 3) to (at least) one target SL-CC 
               
               
                   
                   
                 may also be configured in one SL-measurement object. 
               
               
                   
                 (3) 
                 To one UE, SL-measurement object may be associated with 
               
               
                   
                   
                 (at) least one SL component carrier, which may cover the SL 
               
               
                   
                   
                 component carriers on FR1 and/or FR2. 
               
               
                   
                 (4) 
                 SL-measObject may be associated with LTE PC5 interface 
               
               
                   
                   
                 (e.g., CBR report on LTE SL resource pools) or NR PC5 
               
               
                   
                   
                 interface (CBR report on NR SL resource pools). 
               
            
           
           
               
               
            
               
                 Target of SL- 
                 After the triggering event of one SL-measObject is fulfilled, the UE 
               
               
                 measurement 
                 may report the SL-measurement report to the Target of SL- 
               
               
                 report 
                 measurement report: 
               
            
           
           
               
               
               
            
               
                   
                 a. 
                 In some implementations, the target of SL-measurement report 
               
               
                   
                   
                 may be the serving RAN (e.g., special cell, such as PCell and 
               
               
                   
                   
                 PSCell of the UE). So, in some implementations, one UE may 
               
               
                   
                   
                 implicitly know that one SL-measObject if no additional 
               
               
                   
                   
                 Target information in the SL-measObject. In some other 
               
               
                   
                   
                 implementations, the Target of SL-measObject may be 
               
               
                   
                   
                 explicitly configured in the SL-measObject (e.g., PCell, PSCell, 
               
               
                   
                   
                 etc). In addition, the SL-measurement report would be reported 
               
               
                   
                   
                 through (LTE/NR) Uu interface (e.g., through uplink physical 
               
               
                   
                   
                 channels) if the Target of this SL-measObject is serving RAN. 
               
               
                   
                 b. 
                 In some other implementations, the target of SL-measurement 
               
               
                   
                   
                 report may be associated with one SL-unicast group. For 
               
               
                   
                   
                 example, the SL-measObject may be further associated with 
               
               
                   
                   
                 one Layer-2 Destination ID of the paired UE in the SL-unicast 
               
               
                   
                   
                 group. In addition, the SL-measurement report would be 
               
               
                   
                   
                 reported through Uu interface if the Target of this SL- 
               
               
                   
                   
                 measObject is serving RAN. In addition, the SL-measurement 
               
               
                   
                   
                 report would be reported through (LTE/NR) PC5 interface 
               
               
                   
                   
                 (e.g., through PC5 RRC signaling) if the Target of this SL- 
               
               
                   
                   
                 measObject is one paired UE in one SL-unicast group. In some 
               
               
                   
                   
                 other implementations, the SL-measurement report may be 
               
               
                   
                   
                 transmitted to other members in one SL-groupcast group. 
               
            
           
           
               
               
            
               
                 T312_SL 
                 The value of T312_SL may be configured with: ENUMERATED 
               
               
                   
                 T312_SL = setup {ms0, ms50, ms100, ms200, ms300, ms400, 
               
               
                   
                 ms500, ms1000, etc} 
               
               
                   
                 ms0 represents 0 milliseconds, ms50 represents 50 milliseconds, 
               
               
                   
                 and ms100 represents 100 milliseconds, and so on. In some 
               
               
                   
                 implementations, one configured T312_SL value may be associated 
               
               
                   
                 with one or more than one SL-measurement report configuration. 
               
               
                   
                 Also note, in some additional implementations, the UE may be 
               
               
                   
                 instructed to release a configured T312_SL to (at) least one SL- 
               
               
                   
                 measurement object (e.g., T312_SL = release) by receiving the 
               
               
                   
                 instructions from the serving cell (e.g., dedicated RRC signaling). 
               
               
                 UseT312_SL 
                 One SL measurement report configuration may be associated with 
               
               
                   
                 one UseT312_SL configuration. 
               
               
                   
                 BOOLEAN = {true, false} 
               
               
                   
                 If UseT312_SL = true. Then, the UE would start to count T312_SL 
               
               
                   
                 while the triggering conditions of T312_SL is fulfilled. 
               
               
                   
                 a. SL radio link failure event happens, or 
               
               
                   
                 b. SL physical layer problem happens in one of the configured SL 
               
               
                   
                 component carrier(s) in one SL-unicast group. 
               
               
                 SL- 
                 UE may transmit SL-measurement report to serving cell through 
               
               
                 measurement 
                 (LTE/NR) Uu interface or (LTE/NR) PC5 interface. 
               
               
                 report 
                 The SL-measurement report may include: 
               
               
                 delivery 
                 a. SL radio link failure event happens, or 
               
               
                   
                 b. SL physical layer problem happen (e.g., CBR on one FR2 SL- 
               
               
                   
                 CC associated with one paired UE is higher than a pre-defined 
               
               
                   
                 threshold or S-RSRP on one FR2 SL-CC is lower than a pre- 
               
               
                   
                 defined threshold). 
               
               
                   
                 In some implementations, one UE in the RRC Inactive state may 
               
               
                   
                 be configured and be enabled to deliver an SL-measurement report 
               
               
                   
                 to the serving cell through (Type 1/Type 2) UL Configured Grant 
               
               
                   
                 configuration or through a (2-step/4-step) random access procedure 
               
               
                   
                 while the UE is staying in the RRC Inactive state. 
               
               
                   
                 While the SL physical layer problem happens to one (FR1/FR2) 
               
               
                   
                 SL-CC within one SL-unicast group, one UE may transmit SL- 
               
               
                   
                 measurement report to the paired UE through other active SL- 
               
               
                   
                 CC(s) between the paired UE. 
               
               
                   
               
            
           
         
       
     
     In some of the implementations, the initiation and stop/expiry conditions of the T 312 _SL may be tightly coupled with the initiation and stop/expiry conditions of the T 310 _SL, which are summarized in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 T310_SL Counting and Expiry 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Implementation (SL radio link failure and T310_SL counting): 
               
               
                 Start condition: In the (NR/LTE) PC5 interface, one UE in one SL-unicast group 
               
               
                 may count an SL timer, T310_SL, to zero respectively when the UE detects PHY 
               
               
                 layer related problems in (at least) one SL component carrier (e.g, when it 
               
               
                 receives N310_SL consecutive out-of-sync_SL indications (from the lower layers), 
               
               
                 which may happen periodically or in-periodically in time domain, from the lower 
               
               
                 layers (such as the Physical layer) when both of the UEs are having a PC5-RRC 
               
               
                 connection with each other in the AS layer. 
               
               
                 Stop condition: the concerned UE would stop its own T310_SL in the following 
               
               
                 conditions: 
               
               
                 a). While the UE receives N311_SL consecutive in-sync_SL indications (from the 
               
               
                 lower layers), which may be provided periodically or in-periodically in time 
               
               
                 domain, from the physical layer. 
               
               
                 Expiry condition (RRC layer does not receive up to N311_SL consecutive in- 
               
               
                 sync_SL indications before T310_SL expires): 
               
               
                 If the T310_SL expires in one UE side, the UE may release the PC5-RRC 
               
               
                 connection with the associated UE (or with the associated Layer 2 Destination 
               
               
                 ID) and then inform the released condition to the upper layer. 
               
               
                   
               
            
           
         
       
     
     Then, the initiation and stop/expiry conditions of T 312 _SL are summarized in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 T312_SL Initiation and Stop/Expiry Conditions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Implementation (T312_SL Start and Stop/Expiry Conditions): 
               
               
                 Start condition: Upon triggering an SL measurement report for which T312_SL 
               
               
                 has been configured (e.g, UseT312_SL = true) with the SL-measurement object, 
               
               
                 while T310_SL is running. 
               
               
                 For example, if the UE supports T312_SL and if useT312_SL is included for 
               
               
                 this SL-measurement report configuration and if T310_SL is running: 
               
            
           
           
               
               
            
               
                   
                     if T312_SL is not running: 
               
            
           
           
               
               
            
               
                   
                 =&gt;start timer T312_SL with the value configured in the corresponding 
               
               
                   
                 SL-measobject configuration; 
               
               
                   
                 =&gt;initiate the SL-measurement reporting procedure 
               
            
           
           
               
            
               
                 Stop Condition: UE would stop a running T312_SL upon the following 
               
               
                 conditions 
               
            
           
           
               
               
            
               
                 a. 
                 Upon receiving N311_SL consecutive in-sync indications from lower layers, 
               
               
                 b. 
                 upon triggering the handover procedure or conditional handover procedure or 
               
               
                   
                 upon initiating connection re-establishment procedure in (LTE/NR) Uu 
               
               
                   
                 interface (e.g., while the target of the SL-measurement report is serving cell). 
               
               
                 c. 
                 T312_SL may be stopped when a sidelink radio link failure event of the target 
               
               
                   
                 (e.g., one target Layer-2 Destination UE ID) of SL-measurement object is 
               
               
                   
                 triggered/initiated/announced/reported. In addition, while the SL-RLF event 
               
               
                   
                 associated with one Layer-2 Destination UE ID is announced, the stored SL- 
               
               
                   
                 measurement result associated with the Layer-2 Destination UE ID may be 
               
               
                   
                 released/removed. 
               
               
                 d. 
                 upon the expiry of T310_SL 
               
            
           
           
               
            
               
                 Expiry Condition: 
               
               
                 Release and dump the pending SL-measurement report procedure. 
               
               
                   
               
            
           
         
       
     
     In some implementations of the present disclosure, the UE may be configured with SL measurement objects to provide SL measurement reports to other UEs through a (LTE/NR) PC5 interface. In some of the implementations, the SL measurement objects may be event-triggered, as shown in Table 7A (Event V1a) and Table 7B (Event V2a), respectively. For example, the UE may trigger an SL-measurement report (e.g., a CBR report) when the inequality V1-1 is fulfilled in some of the present implementations. Similarly, the UE may stop transmitting the CBR report when the inequality V1-2 is fulfilled, as defined in Table 7A. Conversely, in some of the present implementations, the triggering event V2a may also trigger an SL-measurement report, as defined in Table 7B. It should also be noted that the Event V1a/V2a in Table 7B may be associated with the LTE (V2X) SL or NR (V2X) SL. In addition, a UE may also be configured with the Event V1a/V2a, associated with the LTE SL and/or NR SL. In some of the present implementations, different parameters may be configured for the LTE SL and NR SL in one UE. 
     In some implementations, the UE may be configured with SL measurement objects to provide SL reports to serving RAN through (LTE/NR) Uu interface, as shown in Table 7C/Table 7D. In some of the implementations, the SL measurement objects may be event-triggered, as shown in Table 7C (Event V1) and Table 7D (Event V2), respectively. 
     
       
         
           
               
             
               
                 TABLE 7A 
               
               
                   
               
               
                 CBR report (Event V1a) through NR/LTE PC5 Interface 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Event V1a (The channel busy ratio is above a threshold) 
               
               
                 UE may start a CBR report on (LTE/NR) PC5 interface if the entering condition (Inequality V1- 
               
               
                 1) is fulfilled. 
               
               
                 UE may stop the CBR report on (LTE/NR) PC5 interface if the leaving condition (Inequality 
               
               
                 V1-2) is fulfilled. 
               
               
                 The UE may: 
               
            
           
           
               
               
            
               
                  1&gt; 
                 consider the entering condition for this event to be satisfied when condition V1-1, as 
               
               
                   
                 specified below, is fulfilled; 
               
               
                  1&gt; 
                 consider the leaving condition for this event to be satisfied when condition V1-2, as 
               
               
                   
                 specified below, is fulfilled; 
               
            
           
           
               
            
               
                 Inequality V1-1 (Entering condition) 
               
               
                 Ms − Hys &gt; Thresh 
               
               
                 Inequality V1-2 (Leaving condition) 
               
               
                 Ms + Hys &lt; Thresh 
               
               
                 Ms is the measurement result of channel busy ratio of the transmission resource pool, may not 
               
               
                 taking into account any offsets. 
               
               
                 Hys is the hysteresis parameter for this event, for which the value could be decided through SL- 
               
               
                 measurement negotiation or by pre-configuration, or by base station configuration. 
               
               
                 Thresh is the threshold parameter for this event, for which the value could be decided through 
               
               
                 SL-measurement negotiation or by pre-configuration, or by serving base station configuration. 
               
               
                 Ms is expressed in decimal from 0 to 1 in steps of 0.01. 
               
               
                 Hys is expressed is in the same unit as Ms. 
               
               
                 Thresh is expressed in the same unit as Ms. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7B 
               
               
                   
               
               
                 CBR report (Event V2a) through NR/LTE PC5 interface 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Event V2a (The channel busy ratio is below a threshold) 
               
               
                 UE may start a CBR report on (LTE/NR) PC5 interface if the entering condition (Inequality V2- 
               
               
                 1) is fulfilled. 
               
               
                 UE may stop the CBR report on (LTE/NR) PC5 interface if the leaving condition (Inequality 
               
               
                 V2-2) is fulfilled. 
               
               
                 The UE may: 
               
            
           
           
               
               
            
               
                  1&gt; 
                 consider the entering condition for this event to be satisfied when condition V2-1, as 
               
               
                   
                 specified below, is fulfilled; 
               
               
                  1&gt; 
                 consider the leaving condition for this event to be satisfied when condition V2-2, as 
               
               
                   
                 specified below, is fulfilled; 
               
            
           
           
               
            
               
                 Inequality V2-1 (Entering condition) 
               
               
                 Ms + Hys &lt; Thresh 
               
               
                 Inequality V2-2 (Leaving condition) 
               
               
                 Ms − Hys &gt; Thresh 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7C 
               
               
                   
               
               
                 CBR Report (Event V1) through NR/LTE Uu Interface 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Event V1 (The channel busy ratio is above a threshold) 
               
               
                 UE may start a CBR report on (LTE/NR) Uu interface if the entering condition (Inequality V1- 
               
               
                 1) is fulfilled. 
               
               
                 UE may stop the CBR report on (LTE/NR) Uu interface if the leaving condition (Inequality V1- 
               
               
                 2) is fulfilled. 
               
               
                 The UE may: 
               
               
                 1&gt; consider the entering condition for this event to be satisfied when condition V1-1, as 
               
               
                 specified below, is fulfilled; 
               
               
                 1&gt; consider the leaving condition for this event to be satisfied when condition V1-2, as 
               
               
                 specified below, is fulfilled; 
               
               
                 Inequality V1-1 (Entering condition) 
               
               
                 Ms − Hys &gt; Thresh 
               
               
                 Inequality V1-2 (Leaving condition) 
               
               
                 Ms + Hys &lt; Thresh 
               
               
                 The variables in the formula are defined as follows: 
               
               
                 Ms is the measurement result of channel busy ratio of the transmission resource pool, may not 
               
               
                 taking into account any offsets. 
               
               
                 Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within 
               
               
                 ReportConfigEUTRA (for LTE/NR PC5 interface) or ReportConfigNR (for NR/LTE PC5 
               
               
                 interface) for this event). 
               
               
                 Thresh is the threshold parameter for this event (i.e. v1-Threshold as defined within 
               
               
                 ReportConfigEUTRA (for LTE/NR PC5 interface) or ReportConfigNR (for NR/LTE PC 
               
               
                 interface)). 
               
               
                 Ms is expressed in decimal from 0 to 1 in steps of 0.01. 
               
               
                 Hys is expressed is in the same unit as Ms. 
               
               
                 Thresh is expressed in the same unit as Ms. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7D 
               
               
                   
               
               
                 CBR report (Event V2) through NR/LTE Uu interface 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Event V2 (The channel busy ratio is below a threshold) 
               
               
                 UE may start a CBR report on (LTE/NR) Uu interface if the entering condition (Inequality 
               
               
                 V2-1) is fulfilled. 
               
               
                 UE may stop the CBR report on (LTE/NR) Uu interface if the leaving condition (Inequality 
               
               
                 V2-2) is fulfilled. 
               
               
                 The UE may: 
               
            
           
           
               
               
               
            
               
                   
                 1&gt; 
                 consider the entering condition for this event to be satisfied when condition V2-1, as 
               
            
           
           
               
               
            
               
                   
                 specified below, is fulfilled; 
               
            
           
           
               
               
               
            
               
                   
                 1&gt; 
                 consider the leaving condition for this event to be satisfied when condition V2-2, as 
               
            
           
           
               
               
            
               
                   
                 specified below, is fulfilled; 
               
            
           
           
               
            
               
                 Inequality V2-1 (Entering condition) 
               
               
                 Ms + Hys &lt; Thresh 
               
               
                 Inequality V2-2 (Leaving condition) 
               
               
                 Ms − Hys &gt; Thresh 
               
               
                 The variables in the formula are defined as follows: 
               
               
                 Ms is the measurement result of channel busy ratio of the transmission resource pool, may 
               
               
                 not taking into account any offsets. 
               
               
                 Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within 
               
               
                 ReportConfigEUTRA(for LTE/NR PC5 interface) or ReportConfigNR (for NR/LTE PC5 
               
               
                 interface) for this event). 
               
               
                 Thresh is the threshold parameter for this event (i.e. v2-Threshold as defined within 
               
               
                 ReportConfigEUTRA(for LTE/NR PC5 interface) or ReportConfigNR (for NR/LTE PC5 
               
               
                 interface)). 
               
               
                 Ms is expressed in decimal from 0 to 1 in steps of 0.01. 
               
               
                 Hys is expressed is in the same unit as Ms. 
               
               
                 Thresh is expressed in the same unit as Ms. 
               
               
                   
               
            
           
         
       
     
     The UE may obtain the configured parameters in Tables 7A through 7D by SL pre-configuration, dedicated control signaling (e.g., RRC signaling in (LTE/NR) Uu interface)/broadcasting control signaling (e.g., system information or SI on-demand procedure) from serving Cell, or dedicated control signaling (e.g., PC5 RRC signaling)/broadcasting control signaling (e.g., MIB-SL signaling) in PC5 interface. Moreover, in some implementations, the UE may also be enabled to transmit SL-measurement report (e.g., the CBR report) to the serving cell through (Type 1/Type 2) UL configured grant(s) or through a (2-step/4-step) random access procedure while the UE is staying in RRC inactive state. 
     Implementation 5: Optimization of Cell (Re)Selection for SL 
     In the present implementation, a UE may need to perform (LTE/NR) V2X SL communication/discovery services on one or more serving frequencies (e.g., the frequency carrier that the UE has a serving cell, which may be a camped cell, Primary cell (e.g., on primary frequency), secondary cell (e.g., on secondary frequency), or Primary Secondary cell (e.g., on primary frequency) in (LTE/NR) Uu interface) and/or on one or more non-serving frequency (e.g., the frequency carrier that the UE has no serving cell in (LTE/NR) Uu interface, so the UE may have a selected cell on the non-serving frequency after cell selection/reselection procedure to implement (NR/LTE) V2X (sidelink) service on this non-serving frequency) while the V2X services are supported on these frequencies. In the present implementation, a UE may check and record validity area configurations on serving cell(s) of serving frequencies and selected cell(s) of non-serving frequencies. 
     In some implementations, cells in different frequencies (e.g., CC #1 and CC #2 which may be a serving frequency and a non-serving frequency to the UE, respectively) may share the same SL resource configuration and validity area configuration. For example, the validity area for SL resource configuration may be composed of cells operating on different frequencies (which may include serving frequencies and non-serving frequencies). In some implementations, the validity area for SL resource configuration may be composed of systemInformationAreaID(s)/RAN notification area Code(s) or Tracking Area Code. Then, cells in different frequencies may also share the same systemInformationAreaID/RAN notification area Code or Tracking Area Code. Thus, in the present implementation, the UE may record the obtained SL resource configuration and the associated validity area that the UE obtains from the cells on serving frequencies and non-serving frequencies (e.g., cells in CC #1 and CC #2, respectively). For example, the UE may apply the SL resource configuration (which may cover SL resources on CC #1 and CC #2) and validity area configurations (which covers cells in CC #1 and CC #2), which are obtained from the cells of non-serving frequency(ies), when the UE is implementing (NR/LTE) V2X (sidelink) service on CC #1. In addition, if the validity area is represented by systeminformationAreaID and the SL resource configuration is broadcast in system information (or the system information may be delivered through an SI on-demand procedure), then the UE may apply the stored SL resource configuration associated with the systeminformationAreaID without reading the rest of system information about SL resource configuration (or the UE may not initiate random access procedure to request the system information to obtain the SL resource configuration), no matter whether the cell (re)selection is implementing on a serving frequency or a non-serving frequency. 
     It should be noted that the stored validity area and the associated SL resource configuration may be applied to the fallback mechanisms described in Implementation 2 above. In the fallback implementation, a UE may still keep the stored SL resource configuration and the validity area configuration while the UE camps or selects a cell (in one concerned frequency. e.g., CC #1) which does not belong to the stored validity area. The stored validity area and SL resource configuration may still be applicable in the cells operating on other SL frequencies (e.g., CC #2). In some implementations, the UE may release or remove one stored validity area and associated SL resource configuration if none of the serving cell (serving frequency)/selected cell (non-serving frequency) on all of the frequencies (which the UE is implementing SL operation) belongs to the stored validity area. In some implementations, a timer may be further configured with the validity area configuration. The timer (≥0) may be triggered after the UE finds out that none of the serving cell (serving frequency) and selected cell (non-serving frequency) on all of the frequencies (which the UE is implementing SL operations) belongs to the validity area. Then, the UE may release the stored validity area (and the associated SL resource configuration) after the timer expires. In some additional implementations, it may be up to specific UE implementations to decide when to release/remove an invalid SL resource configuration. 
       FIG. 6  is a block diagram illustrating a node  600  for wireless communication according to the present disclosure. As illustrated in  FIG. 6 , a node  600  may include a transceiver  620 , a processor  628 , a memory  634 , one or more presentation components  638 , and at least one antenna  636 . The node  600  may also include a radio frequency (RF) spectrum band module, a BS communications module, a network communications module, and a system communications management module, Input/Output (I/O) ports, I/O components, and a power supply (not illustrated in  FIG. 6 ). 
     Each of the components may directly or indirectly communicate with each other over one or more buses  640 . The node  600  may be a UE or a BS that performs various functions disclosed with reference to  FIGS. 1 through 5 . 
     The transceiver  620  has a transmitter  622  (e.g., transmitting/transmission circuitry) and a receiver  624  (e.g., receiving/reception circuitry) and may be configured to transmit and/or receive time and/or frequency resource partitioning information. The transceiver  620  may be configured to transmit in different types of subframes and slots including but not limited to usable, non-usable and flexibly usable subframes and slot formats. The transceiver  620  may be configured to receive data and control channels. 
     The node  600  may include a variety of computer-readable media. Computer-readable media may be any available media that may be accessed by the node  600  and include both volatile and non-volatile media, and removable and non-removable media. 
     The computer-readable media may include computer storage media and communication media. Computer storage media may include both volatile and non-volatile media, and removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or data. 
     Computer storage media may include RAM, ROM, EPROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices. Computer storage media may not include a propagated data signal. Communication media may typically embody computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. 
     The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Communication media may include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the previously listed components should also be included within the scope of computer-readable media. 
     The memory  634  may include computer-storage media in the form of volatile and/or non-volatile memory. The memory  634  may be removable, non-removable, or a combination thereof. Example memory may include solid-state memory, hard drives, optical-disc drives, etc. As illustrated in  FIG. 6 , the memory  634  may store computer-readable, computer-executable instructions  632  (e.g., software codes) that are configured to cause the processor  628  to perform various functions disclosed herein, for example, with reference to  FIGS. 1 through 5 . Alternatively, the instructions  632  may not be directly executable by the processor  628  but be configured to cause the node  600  (e.g., when compiled and executed) to perform various functions disclosed herein. 
     The processor  628  (e.g., having processing circuitry) may include an intelligent hardware device, e.g., a Central Processing Unit (CPU), a microcontroller, an ASIC, etc. The processor  628  may include memory. The processor  628  may process the data  630  and the instructions  632  received from the memory  634 , and information transmitted and received via the transceiver  620 , the baseband communications module, and/or the network communications module. The processor  628  may also process information to be sent to the transceiver  620  for transmission via the antenna  636  to the network communications module for transmission to a core network. 
     One or more presentation components  638  may present data indications to a person or another device. Examples of presentation components  638  may include a display device, a speaker, a printing component, and a vibrating component, etc. 
     In some implementations of the present disclosure, configurations for NR SL/LTE V2X SL synchronization rules are utilized when multiple SL CCs are configured to support (NR/LTE) (V2X) SL operations among UEs. 
     In some implementations of the present disclosure, information regarding SL CCs associated with NR (e.g., for NR sidelink communication) and/or LTE RATs (e.g., for (LTE) V2X sidelink communication) is indicated to the UE (e.g., through a Uu interface). 
     In some implementations of the present disclosure, the associations between SL CCs and the associated RATs may be network-specific (e.g., PLMN-specific or NPN-specific). 
     In some implementations of the present disclosure, SL CCs with associated NR SL/LTE V2X SL synchronization rules are indicated. 
     In some implementations of the present disclosure, the associations between SL CCs and the NR SL/LTE V2X SL synchronization rules may be PLMN-specific/NPN-specific. 
     In some implementations of the present disclosure, the associations between SL CCs and the NR SL/LTE V2X SL synchronization rules may be valid within a defined validity area. 
     In some implementations of the present disclosure, the above-mentioned indications and/or association rules may be pre-specified in technical specifications or pre-defined in the USIM or memory module in the UE so that the UE is able to interpret and apply the above-mentioned indications and/or association rules. 
     In view of the disclosure, it is obvious that various techniques may be used for implementing the concepts in the present disclosure without departing from the scope of those concepts. Moreover, while the concepts have been disclosed with specific reference to certain implementations, a person of ordinary skill in the art may recognize that changes may be made in form and detail without departing from the scope of those concepts. As such, the disclosed implementations are to be considered in all respects as illustrative and not restrictive. It should also be understood that the present disclosure is not limited to the particular implementations disclosed and many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure.