Patent Description:
To meet the demand for wireless data traffic having increased since deployment of <NUM>th generation (<NUM>) communication systems, efforts have been made to develop an improved <NUM>th generation (<NUM>) or pre-<NUM> communication system. Therefore, the <NUM> or pre-<NUM> communication system is also called a "Beyond <NUM> Network" or a "Post LTE System". In the <NUM> system, hybrid frequency shift key (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

For example, technologies, such as a sensor network, machine type communication (MTC), and machine-to-machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas.

The publication "<NPL>) discusses impacts of multiRAT operation on system information and cell reselection.

3GPP Technical Specification <NUM> (Version <NUM>. <NUM>) specifies the Access Stratum (AS) part of the UE procedures in RRC_IDLE state (also called Idle mode) and RRC_INACTIVE state.

In next-generation mobile communication new radio (NR), V2X SL communication may be designed to provide not only basic safety services but also various enhanced services. Therefore, NR V2X SL communication may be designed to support not only a broadcast transmission type but also unicast and/or groupcast transmission types.

Accordingly, an aspect of the disclosure is to provide a method for handling cell reselection and frequency priorities for vehicle to everything sidelink (V2X SL) communication of a user equipment (UE) in a radio resource control (RRC) inactive mode.

In accordance with an embodiment of the disclosure, a method performed by a terminal in a wireless communication system is provided as defined in the appended claims.

In accordance with another embodiment of the disclosure, a terminal in a wireless communication system is provided as defined in the appended claims.

According to an embodiment of the disclosure, a UE in an RRC inactive mode is allowed to reselect a cell and to handle frequency priorities, thereby supporting V2X SL communication for providing various enhanced services.

The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in conjunction with the accompanying drawings.

<FIG> illustrates a structure of an LTE system according to an embodiment of the disclosure.

Referring to <FIG>, a radio access network of the LTE system may include an evolved node B (hereinafter, referred to as an eNB, a Node B, or a base station) 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, or 1a-<NUM>, a mobility management entity (MME) 1a-<NUM>, and a serving gateway (S-GW) 1a-<NUM>. A user equipment (hereinafter, referred to as a UE or terminal) 1a-<NUM> may access an external network through the eNBs 1a-<NUM> to 1a-<NUM> and the S-GW 1a-<NUM>.

Referring to <FIG>, the eNBs 1a-<NUM> to 1a-<NUM> correspond to existing Node Bs of a universal mobile telecommunication system (UMTS). The eNBs may be connected to the UE 1a-<NUM> over a wireless channel, and may perform a more complex role than that of the existing Node Bs. In the LTE system, all user traffic based on real-time service, such as a voice over Internet protocol (VoIP) service, is provided through a shared channel. Therefore, a device that collects state information, such as UEs' buffer status, available transmission power state, and channel state, and performs scheduling is required. The eNBs 1a-<NUM> to 1a-<NUM> may be responsible for these functions.

One eNB may generally control a plurality of cells. For example, in order to realize a transmission speed of <NUM> Mbps, the LTE system may use orthogonal frequency-division multiplexing (OFDM) as a radio access technology, for example, at a bandwidth of <NUM>. In addition, the LTE system may apply adaptive modulation & coding (AMC), which determines a modulation scheme and a channel coding rate according to the channel state of a UE. The S-GW 1a-<NUM> is a device that provides a data bearer, and may generate or remove a data bearer under the control of the MME 1a-<NUM>. The MME is a device that performs not only a mobility management function for the UE but also various control functions, and may be connected to a plurality of base stations.

<FIG> illustrates a wireless protocol structure of an LTE system according to an embodiment of the disclosure.

Referring to <FIG>, a wireless protocol of the LTE system may include packet data convergence protocols (PDCPs) 1b-<NUM> and 1b-<NUM>, radio link controls (RLCs) 1b-<NUM> and 1b-<NUM>, and media access controls (MACs) 1b-<NUM> and 1b-<NUM> respectively at a UE and an eNB. The PDCPs may be responsible for IP header compression/decompression or the like. The main functions of the PDCPs may be summarized as follows.

The RLCs 1b-<NUM> and 1b-<NUM> may reconstruct a PDCP PDU to have an appropriate size, and may perform an automatic repeat request (ARQ) operation. The main functions of the RLCs may be summarized as follows.

The MACs 1b-<NUM> and 1b-<NUM> may be connected to a plurality of RLC-layer devices configured in one UE, may multiplex RLC PDUs into a MAC PDU, and may demultiplex a MAC PDU into RLC PDUs. The main functions of the MACs may be summarized as follows.

Physical (PHY) layers 1b-<NUM> and 1b-<NUM> may perform channel coding and modulation of upper-layer data, and may convert the data into OFDM symbols to transmit the OFDM symbols via a wireless channel, or may demodulate OFDM symbols received via a wireless channel and may perform channel decoding of the OFDM symbols to deliver the OFDM symbols to an upper layer.

<FIG> illustrates a structure of a next-generation mobile communication system according to an embodiment of the disclosure.

Referring to <FIG>, a radio access network of the next-generation mobile communication system (hereinafter, referred to as NR or <NUM>) may include a new radio node B (hereinafter, an NR gNB, or NR base station) 1c-<NUM> and a new radio core network (NR CN) 1c-<NUM>. A new radio user equipment (hereinafter, an NR UE or terminal) 1c-<NUM> may access an external network 1c-<NUM> through the NR gNB 1c-<NUM> and the NR CN 1c-<NUM>.

Referring to <FIG>, the NR gNB 1c-<NUM> may correspond to an evolved node B (eNB) of an existing LTE system. The NR gNB is connected to the NR UE 1c-<NUM> over a wireless channel, and may provide a more advanced service than that of the existing eNB. In the next-generation mobile communication system, all user traffic may be served through a shared channel. Therefore, a device that collects state information, such as UEs' buffer status, available transmission power state, and channel state, and performs scheduling is required. The NR gNB 1c-<NUM> may be responsible for these functions. One NR gNB may generally control a plurality of cells. The next-generation mobile communication system may apply a bandwidth greater than the existing maximum bandwidth in order to realize ultrahigh-speed data transmission compared to current LTE. Further, the next-generation mobile communication system may employ a beamforming technique in addition to OFDM as a radio access technology. In addition, the next-generation mobile communication system may apply AMC, which determines a modulation scheme and a channel coding rate according to the channel state of a UE.

The NR CN 1c-<NUM> may perform functions of mobility support, bearer setup, and QoS setup. The NR CN is a device that performs not only a mobility management function for a UE but also various control functions, and may be connected to a plurality of base stations. The next-generation mobile communication system may also interwork with the existing LTE system, in which case the NR CN may be connected to an MME 1c-<NUM> through a network interface. The MME is connected to the eNB 1c-<NUM>, which is an existing base station.

<FIG> illustrates a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the disclosure.

Referring to <FIG>, a wireless protocol of the next-generation mobile communication system includes NR service data adaptation protocols (SDAPs) 1d-<NUM> and 1d-<NUM>, NR PDCPs 1d-<NUM> and 1d-<NUM>, NR RLCs 1d-<NUM> and 1d-<NUM>, NR MACs 1d-<NUM> and 1d-<NUM>, and NR PHYs 1d-<NUM> and 1d-<NUM> respectively at a UE and an NR base station.

The main functions of the NR SDAPs 1d-<NUM> and 1d-<NUM> may include some of the following functions.

Regarding the SDAP-layer devices, the UE may receive a configuration about whether to use a header of the SDAP-layer devices or whether to use a function of the SDAP-layer devices for each PDCP-layer device, each bearer, or each logical channel via a radio resource control (RRC) message. When an SDAP header is configured, a one-bit non-access stratum (NAS) quality of service (QoS) reflective indicator (NAS reflective QoS) and a one-bit AS QoS reflective indicator (AS reflective QoS) of the SDAP header may be used for indication to enable the UE to update or reconfigure uplink and downlink QoS flows and mapping information for a data bearer. The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used as a data-processing priority, scheduling information, or the like in order to support a desired service.

The main functions of the NR PDCPs 1d-<NUM> and 1d-<NUM> may include some of the following functions.

Among the above functions, the reordering function of the NR PDCP devices refers to a function of rearranging PDCP PDUs received in a lower layer in sequence based on the PDCP sequence number (SN). The reordering function of the NR PDCP devices may include a function of transmitting the data to an upper layer in the rearranged order or a function of immediately transmitting the data regardless of order. In addition, the reordering function may include a function of recording lost PDCP PDUs via reordering, may include a function of reporting the state of lost PDCP PDUs to a transmitter, and may include a function of requesting retransmission of lost PDCP PDUs.

The main functions of the NR RLCs 1d-<NUM> and 1d-<NUM> may include some of the following functions.

Among the above functions, the in-sequence delivery function of the NR RLC devices refers to a function of delivering RLC SDUs received from a lower layer to an upper layer in order. The in-sequence delivery function of the NR RLC devices may include a function of reassembling and delivering a plurality of RLC SDUs when one original RLC SDU which is divided into the plurality of RLC SDUs is received.

The in-sequence delivery function of the NR RLC devices may include a function of rearranging received RLC PDUs based on the RLC SN or the PDCP SN, may include a function of recording lost RLC PDUs via reordering, may include a function of reporting the state of lost RLC PDUs to a transmitter, and may include a function of requesting retransmission of lost RLC PDUs.

If there is a lost RLC SDU, the in-sequence delivery function of the NR RLC devices 1d-<NUM> and 1d-<NUM> may include a function of delivering only RLC SDUs before the lost RLC SDU to an upper layer in order. Further, the in-sequence delivery function of the NR RLC devices may include a function of delivering all RLC SDUs received before a timer starts to an upper layer in order when the timer has expired despite the presence of a lost RLC SDU. Further, the in-sequence delivery function of the NR RLC devices may include a function of delivering all RLC SDUs received up to that point in time to an upper layer in order when the timer expires despite the presence of a lost RLC SDU.

The NR RLC devices 1d-<NUM> and 1d-<NUM> may process RLC PDUs in the order of reception thereof regardless of the order of SNs, and may deliver the RLC PDUs to the NR PDCP devices 1d-<NUM> and 1d-<NUM> in an out-of-sequence manner.

When receiving a segment, the NR RLC devices 1d-<NUM> and 1d-<NUM> may receive segments that are stored in a buffer or are to be subsequently received, may reconstruct the segments into one whole RLC PDU, and may deliver the RLC PDU to the NR PDCP devices.

The NR RLC layers may not include a concatenation function, and the concatenation function may be performed in the NR MAC layers, or may be replaced with a multiplexing function of the NR MAC layers.

The out-of-sequence delivery function of the NR RLC devices refers to a function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order. The out-of-sequence delivery function of the NR RLC devices may include a function of reassembling and delivering a plurality of RLC SDUs when one original RLC SDU is divided into the plurality of RLC SDUs to be received. In addition, the out-of-sequence delivery function of the NR RLC devices may include a function of recording lost RLC PDUs by storing and reordering the RLC SNs or PDCP SNs of received RLC PDUs.

The NR MACs 1d-<NUM> and 1d-<NUM> may be connected to a plurality of NR RLC-layer devices configured in one device, and the main functions of the NR MACs may include some of the following functions.

The NR PHY layers 1d-<NUM> and 1d-<NUM> may perform channel coding and modulation of upper-layer data and convert the data into OFDM symbols to transmit the OFDM symbols via a wireless channel, or demodulate OFDM symbols received via a wireless channel and perform channel decoding of the OFDM symbols to deliver the OFDM symbols to an upper layer.

<FIG> illustrates V2X communication in a next-generation mobile communication system according to an embodiment of the disclosure.

Referring to <FIG>, vehicle-to-everything (V2X) according to the embodiment collectively refers to communication technology based on a vehicle and all interfaces and may be vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), vehicle-to-network (V2N), and the like according to the form and components for establishing communication.

Referring to <FIG>, a base station 1e-<NUM> may include at least one vehicle terminal 1e-<NUM> or 1e-<NUM> and a portable pedestrian UE 1e-<NUM> located in a cell 1e-<NUM> supporting V2X. Here, V2X may be supported through a Uu interface and/or a PC5 interface. When V2X is supported through the Uu interface, for example, the vehicle terminal 1e-<NUM> or 1e-<NUM> may perform V2X cellular communication with the base station 1e-<NUM> using a vehicle-terminal/base-station uplink (UL)/downlink (DL) 1e-<NUM> or 1e-<NUM>, or the portable pedestrian UE 1e-<NUM> may perform V2X cellular communication using a portable-pedestrian-UE/base-station uplink (UL)/downlink (DL) 1e-<NUM>. When V2X is supported through the PC5 interface, V2X sidelink (SL) communication may be performed using a UE-UE sidelink (SL) 1e-<NUM> and 1e-<NUM>. For example, the vehicle terminal 1e-<NUM> in the coverage area of the base station terrestrial radio access (E-UTRA/NR) may transmit and receive V2X packets to and from other vehicle terminals 1e-<NUM> and 1e-<NUM> and/or portable pedestrian UEs 1e-<NUM> and 1e-<NUM> through SLs 1e-<NUM>, 1e-<NUM>, 1e-<NUM>, and 1e-<NUM> as transmission channels. The V2X packets may be transmitted and received in a broadcast transmission type and/or a unicast and/or groupcast transmission type.

A UE supporting V2X sidelink communication may transmit and receive a V2X packet according to a resource allocation mode (scheduled resource allocation or UE autonomous resource selection). Scheduled resource allocation (mode <NUM> and/or mode <NUM>) is a mode in which a base station allocates a resource used for sidelink transmission to a UE in an RRC-connected mode based on a dedicated scheduling scheme. This mode enables the base station to manage sidelink resources, and may thus be efficient for interference management and/or management of a resource pool (dynamic allocation and semi-persistent transmission). When there is data to be transmitted to other UE(s), the UE in the RRC-connected mode may report that there is data to be transmitted to other UE(s) to the base station using an RRC message or a MAC control element (hereinafter, "CE"). For example, the RRC message may be a SidelinkUEInformation or UEAssistanceInformation message, and the MAC CE may be a buffer status report MAC CE in a new format (including at least an indicator indicating that a buffer status report is for V2X communication and information about the size of data buffered for sidelink communication).

UE autonomous resource selection (mode <NUM> and/or mode <NUM>) is a mode in which a base station provides sidelink resource information/pool to a UE supporting V2X sidelink communication via system information and/or an RRC message and the UE selects a resource according to a set rule. For example, the base station may provide sidelink resource information to the UE by signaling SIB21, SIB26, or SIBx to be newly defined for an NR V2X UE. The base station may provide sidelink resource information by signaling an RRC message, for example, an RRC connection reconfiguration message (RRCReconfiguration message) and/or connection resumption message (RRCResume message), to the UE. Further, UE autonomous resource selection may enable the UE to assist other UEs in selecting a resource to be used for a sidelink through a PC5 RRC message and/or MAC CE, or may allocate a resource to be used for sidelink transmission through direct or indirect scheduling. For example, the UE autonomous resource selection mode may refer to one or more of the following.

Resource selection methods for a UE may include zone mapping, sensing-based resource selection, random selection, configured-grant-based resource selection, and the like.

The UE supporting V2X sidelink communication may transmit and receive a V2X packet based on a preconfigured resource pool (preconfigured resource) included in SL-V2X-Preconfiguration, which is an information element (hereinafter, "IE"). For example, when the UE exists in the coverage area of the base station but cannot perform V2X sidelink communication based on the scheduled resource allocation and/or UE autonomous resource selection mode for some reason, the UE may perform V2X sidelink communication through a sidelink transmission/reception resource pool preconfigured in SL-V2X-Preconfiguration as the information element (IE). In addition, a vehicle terminal 1e-<NUM> out of the coverage area of terrestrial radio access/new radio (E-UTRA/NR) vehicle terminal 1e-<NUM> may perform V2X sidelink communication with another vehicle terminal 1e-<NUM> or a portable pedestrian UE 1e-<NUM>, based on the foregoing preconfigured sidelink resource, through sidelinks (SL) 1e-<NUM> and 1e-<NUM> as transmission channels.

LTE V2X SL communication is designed primarily for basic safety services. For example, a UE supporting LTE V2X SL communication is designed to provide basic safety services to all neighboring UEs supporting LTE V2X SL communication through a broadcast transmission type. Therefore, the UE does not need to perform a process for establishing a session with another particular UE or to perform a sidelink connection establishment procedure.

However, in next-generation mobile communication (NR), V2X SL communication may be designed to provide not only basic safety services but also various and enhanced services (e.g., a self-driving service, a platooning service, a remote driving service, or an in-vehicle infotainment service). Therefore, NR V2X SL communication may be designed to support not only a broadcast transmission type but also a unicast and/or groupcast transmission type.

<FIG> illustrates a procedure in which a base station releases a connection with a UE to switch from an RRC-connected mode (RRC_CONNECTED) to an RRC inactive mode (RRC_INACTIVE) and a method in which a UE in the RRC inactive mode (RRC_INACTIVE) handles frequency priorities when performing a cell reselection process according to an embodiment of the disclosure.

Referring to <FIG>, the UE 1f-<NUM> may establish an RRC connection to the NR base station 1f-<NUM> and thus enter the RRC connected mode (RRC_CONNECTED) by in operation 1f-<NUM>. The UE may transmit and receive data to and from the base station 1f-<NUM> in the RRC connected mode. Alternatively, in the RRC connected mode, the UE may obtain V2X sidelink communication configuration information from the base station 1f-<NUM> and may transmit and receive data related to V2X sidelink communication to and from another UE 1f-<NUM>.

In operation 1f-<NUM>, the UE may receive an RRC connection release message (RRCRelease) including suspension configuration information (suspendConfig) from the base station when there is no data to be transmitted or received for some reason. The message may also include cell reselection priority information (cellReselectionPriorities). Upon receiving the message, the UE may transition from the RRC connected mode to the RRC inactive mode (RRC_INACTIVE).

In operation 1f-<NUM>, the UE in the RRC inactive mode may perform a cell selection procedure to find a suitable NR cell and may camp on the NR cell. The cell that the UE camps on by finding a suitable cell in the RRC inactive mode may be referred to as a serving cell. To perform the cell selection procedure, the UE may receive system information (e.g., master information block (MIB) or system information block <NUM> (SIB1)) broadcast by the cell. Specifically, the UE may derive the reception level (Srxlev) and the reception quality (Squal) of the serving cell using a parameter included in received SIB1. For example, the reception level and reception quality of the serving cell may be obtained using Equation <NUM> below. <MAT> <MAT>.

Parameters used in Equation <NUM> are defined in <NPL>". In the following, the same applies to embodiments to which Equation <NUM> is applied.

In operation 1f-<NUM>, the UE may receive system information (e.g., SIB2, SIB3, SIB4, or SIB5) broadcasted by the cell before or after camping on the cell. SIB2 may include information/parameters commonly applied when the UE in the RRC inactive mode reselects an NR intra-frequency cell, an NR inter-frequency cell, and an inter-RAT frequency cell. SIB3 may include information/parameters applied only when the UE in the RRC inactive mode reselects an NR intra-frequency cell. SIB4 may include information/parameters applied only when the UE in the RRC inactive mode reselects an NR inter-frequency cell. SIB5 may include information/parameters applied only when the UE in the RRC inactive mode reselects an inter-RAT frequency cell. The system information may also include per-frequency cell reselection priority information (cellReselectionPriority).

Alternatively, in operation 1f-<NUM>, when the UE in the RRC inactive mode is capable of performing V2X sidelink communication, the UE may receive system information (one or a plurality of new SIBs) including V2X sidelink communication configuration information from the serving cell. The serving cell may separately broadcast the system information for each radio access technology (RAT). For example, the V2X sidelink communication configuration information may include V2X sidelink communication reception resource pool (e.g., v2x-CommRxPool), a V2X sidelink communication transmission resource pool (e.g., v2x-CommTxPoolNormalCommon), a V2X sidelink communication transmission resource pool available for an exceptional occasion (e.g., v2x-CommTxPoolExceptional), or an inter-frequency information list for V2X sidelink communication (v2x-InterFreqInfiList). Alternatively, the system information may include an anchor carrier frequency list (anchorCarrierFreqList) including V2X sidelink communication configuration information. For example, the SIB may have the following ASN1 structure.

The IE SystemInformationBlockTypex contains NR V2X and/or LTE V2X sidelink communication configuration.

There may be one or a plurality of pieces of system information.

In operation 1f-<NUM>, the UE in the RRC inactive mode may be configured to perform V2X sidelink communication. Here, the UE may be configured to perform V2X sidelink communication according to the following three cases.

Performing V2X sidelink communication may mean transmitting V2X sidelink communication (i.e., transmitting V2X sidelink data), receiving V2X sidelink communication (i.e., receiving V2X sidelink data), or transmitting and receiving V2X sidelink communication. Operation 1f-<NUM> may occur in operation 1f-<NUM> or operation 1f-<NUM>.

In operation 1f-<NUM>, the UE in the RRC inactive mode may perform a cell reselection evaluation procedure. The cell reselection evaluation procedure may mean performing the following series of processes.

When the RRC connection release message received in operation 1f-<NUM> includes the cell reselection priority information (cellReselectionPriorities), the UE may perform the cell reselection evaluation procedure by applying the cell reselection priority information. When the RRC connection release message received in operation 1f-<NUM> does not include the cell reselection priority information (cellReselectionPriorities), the UE may perform the cell reselection evaluation procedure by applying the per-frequency cell reselection priority information (cellReselectionPriority) included in the system information received in operation 1f-<NUM>. If the UE 1f-<NUM> capable of V2X sidelink communication is configured to perform V2X sidelink communication, an embodiment proposes an operation in which the UE handles reselection priorities by applying at least one of the following methods according to Case <NUM>, Case <NUM>, and Case <NUM> described above.

In operation 1f-<NUM>, the UE in the RRC inactive mode may perform measurement based on frequency priorities, may apply cell reselection criteria, and may perform a suitability check, thereby finally reselecting a cell.

When an NR cell is reselected through operation 1f-<NUM> in operation 1f-<NUM>, the UE may maintain the RRC inactive mode in operation 1f-<NUM>, and may perform V2X sidelink communication with the other UE 1f-<NUM> in operation 1f-<NUM>.

When an LTE cell is reselected through operation 1f-<NUM> in operation 1f-<NUM>, the UE may transition to the RRC idle mode in operation 1f-<NUM>, and may perform V2X sidelink communication with the other UE 1f-<NUM> in operation 1f -<NUM>.

The embodiment may be applied equally to the UE in the RRC idle mode (RRC_IDLE). For example, when an NR cell is reselected by applying the same cell reselection priorities, the UE stays in the NR RRC idle mode, when an LTE cell is reselected, the UE transitions to the LTE RRC idle mode.

Referring to <FIG>, the UE <NUM>-<NUM> may establish an RRC connection to the LTE base station <NUM>-<NUM> connected to a <NUM> core and thus enter the RRC connected mode (RRC_CONNECTED) by in operation <NUM>-<NUM>. The UE may transmit and receive data to and from the base station <NUM>-<NUM> in the RRC connected mode. Alternatively, in the RRC connected mode, the UE may obtain V2X sidelink communication configuration information from the base station <NUM>-<NUM> and may transmit and receive data related to V2X sidelink communication to and from another UE <NUM>-<NUM>.

In operation <NUM>-<NUM>, the UE may receive an RRC connection release message (RRCConnectionRelease) including RRC inactivation configuration information (rrc-InactiveConfig) from the base station when there is no data to be transmitted or received for some reason. The message may also include cell reselection priority information (cellReselectionPriorities). Upon receiving the message, the UE may transition from the RRC connected mode to the RRC inactive mode (RRC_INACTIVE).

In operation <NUM>-<NUM>, the UE in the RRC inactive mode may perform a cell selection procedure to find a suitable LTE cell and may camp on the LTE cell. The cell that the UE camps on by finding a suitable cell in the RRC inactive mode may be referred to as a serving cell. To perform the cell selection procedure, the UE may receive system information (e.g., MIB, SIB1, or SIB2) broadcast by the cell. Specifically, the UE may derive the reception level (Srxlev) and the reception quality (Squal) of the serving cell using a parameter included in the received system information. For example, the reception level and reception quality of the serving cell may be obtained using Equation <NUM> below. <MAT> <MAT>.

Parameters used in Equation <NUM> are defined in 3GPP TS <NUM>: "User Equipment (UE) Procedures in Idle Mode". In the following, the same applies to embodiments to which Equation <NUM> is applied.

In operation <NUM>-<NUM>, the UE may receive system information (e.g., SIB3, SIB4, SIB5, or SIB24) broadcasted by the cell before or after camping on the cell. SIB3 may include information/parameters commonly applied when the UE in the RRC inactive mode reselects an LTE intra-frequency cell, an LTE inter-frequency cell, and an inter-RAT frequency cell. SIB4 may include information/parameters applied only when the UE in the RRC inactive mode reselects an LTE intra-frequency cell. SIB5 may include information/parameters applied only when the UE in the RRC inactive mode reselects an LTE inter-frequency cell. SIB24 may include information/parameters applied only when the UE in the RRC inactive mode reselects an inter-RAT frequency NR cell. The system information may also include per-frequency cell reselection priority information (cellReselectionPriority).

Alternatively, in operation <NUM>-<NUM>, when the UE in the RRC inactive mode is capable of performing V2X sidelink communication, the UE may receive system information (SIB21, SIB26, or one or a plurality of new SIBs) including V2X sidelink communication configuration information from the serving cell. The serving cell may separately broadcast the system information for each radio access technology (RAT). For example, the V2X sidelink communication configuration information may include a V2X sidelink communication reception resource pool (e.g., v2x-CommRxPool), a V2X sidelink communication transmission resource pool (e.g., v2x-CommTxPoolNormalCommon), a V2X sidelink communication transmission resource pool available for an exceptional occasion (e.g., v2x-CommTxPoolExceptional), or an inter-frequency information list for V2X sidelink communication (v2x-InterFreqInfiList). For example, SIB21 and SIB26 may have the ASN1 structure mentioned in 3GPP TS <NUM>: "Radio Resource Control (RRC)". Alternatively, the system information may include an anchor carrier frequency list (anchorCarrierFreqList) including V2X sidelink communication configuration information. The new SIB may have the following abstract syntax notation <NUM> (ASN1) structure.

There may be one or a plurality of new SIBs.

In operation <NUM>-<NUM>, the UE in the RRC inactive mode may be configured to perform V2X sidelink communication. Here, the UE may be configured to perform V2X sidelink communication according to the following three cases.

Performing V2X sidelink communication may mean transmitting V2X sidelink communication (i.e., transmitting V2X sidelink data), receiving V2X sidelink communication (i.e., receiving V2X sidelink data), or transmitting and receiving V2X sidelink communication. Operation <NUM>-<NUM> may occur in operation <NUM>-<NUM> or operation <NUM>-<NUM>.

In operation <NUM>-<NUM>, the UE in the RRC inactive mode may perform a cell reselection evaluation procedure. The cell reselection evaluation procedure may mean performing the following series of processes.

When the RRC connection release message received in operation <NUM>-<NUM> includes the cell reselection priority information (cellReselectionPriorities), the UE may perform the cell reselection evaluation procedure by applying the cell reselection priority information. When the RRC connection release message received in operation <NUM>-<NUM> does not include the cell reselection priority information (cellReselectionPriorities), the UE may perform the cell reselection evaluation procedure by applying the per-frequency cell reselection priority information (cellReselectionPriority) included in the system information received in operation <NUM>-<NUM>. If the UE <NUM>-<NUM> capable of V2X sidelink communication is configured to perform V2X sidelink communication, an embodiment proposes an operation in which the UE handles reselection priorities by applying at least one of the following methods according to Case <NUM>, Case <NUM>, and Case <NUM> described above.

In operation <NUM>-<NUM>, the UE in the RRC inactive mode may perform measurement based on frequency priorities, may apply cell reselection criteria, and may perform a suitability check, thereby finally reselecting a cell.

When an LTE cell is reselected through operation <NUM>-<NUM> in operation <NUM>-<NUM>, the UE may maintain the RRC inactive mode in operation <NUM>-<NUM> and may perform V2X sidelink communication with the other UE <NUM>-<NUM> in operation <NUM>-<NUM>.

When an NR cell is reselected through operation <NUM>-<NUM> in operation <NUM>-<NUM>, the UE may transition to the RRC idle mode in operation <NUM>-<NUM>, and may perform V2X sidelink communication with the other UE <NUM>-<NUM> in operation <NUM> -<NUM>.

The embodiment may be applied equally to the UE in the RRC idle mode (RRC_IDLE). For example, when an LTE cell is reselected by applying the same cell reselection priorities, the UE stays in the LTE RRC idle mode, when an NR cell is reselected, the UE transitions to the NR RRC idle mode.

<FIG> illustrates a configuration of a UE according to an embodiment of the disclosure.

Referring to <FIG>, the UE may include a radio frequency (RF) processor <NUM>-<NUM>, a baseband processor <NUM>-<NUM>, a storage unit <NUM>-<NUM>, and a controller <NUM>-<NUM>.

The RF processor <NUM>-<NUM> according to an embodiment may perform a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. For example, the RF processor <NUM>-<NUM> may upconvert a baseband signal, provided from the baseband processor <NUM>-<NUM>, into an RF band signal to transmit the RF band signal through an antenna, and may downconvert an RF band signal, received through the antenna, into a baseband signal. For example, the RF processor <NUM>-<NUM> may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC).

Although <FIG> shows only one antenna, the UE may include a plurality of antennas.

In addition, the RF processor <NUM>-<NUM> may include a plurality of radio frequency (RF) chains. Further, the RF processor <NUM>-<NUM> may perform beamforming. For beamforming, the RF processor <NUM>-<NUM> may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor <NUM>-<NUM> may perform multiple-input and multiple-output (MIMO) and may receive a plurality of layers when performing MIMO. The RF processor <NUM>-<NUM> may perform reception beam sweeping by appropriately setting the plurality of antennas or antenna elements under the control of the controller <NUM>-<NUM>, or may adjust the orientation and width of a reception beam such that the reception beam is coordinated with a transmission beam.

The baseband processor <NUM>-<NUM> may perform a function of converting a baseband signal and a bit stream according to the physical-layer specification of a system. For example, in data transmission, the baseband processor <NUM>-<NUM> may encode and modulate a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor <NUM>-<NUM> may demodulate and decode a baseband signal, provided from the RF processor <NUM>-<NUM>, thereby reconstructing a reception bit stream. For example, according to OFDM, in data transmission, the baseband processor <NUM>-<NUM> may generate complex symbols by encoding and modulating a transmission bit stream, may map the complex symbols to subcarriers, and may construct OFDM symbols through an inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion. In data reception, the baseband processor <NUM>-<NUM> may divide a baseband signal, provided from the RF processor <NUM>-<NUM>, into OFDM symbols, may reconstruct signals mapped to subcarriers through a fast Fourier transform (FFT), and may reconstruct a reception bit stream through demodulation and decoding.

As described above, the baseband processor <NUM>-<NUM> and the RF processor <NUM>-<NUM> may transmit and receive signals. Accordingly, the baseband processor <NUM>-<NUM> and the RF processor <NUM>-<NUM> may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. At least one of the baseband processor <NUM>-<NUM> and the RF processor <NUM>-<NUM> may include a plurality of communication modules to support a plurality of different radio access technologies. Further, at least one of the baseband processor <NUM>-<NUM> and the RF processor <NUM>-<NUM> may include different communication modules for processing signals in different frequency bands. For example, the different radio access technologies may include an LTE network, an NR network, and the like. In addition, the different frequency bands may include a superhigh-frequency (SHF) band (e.g., <NUM> or <NUM>) and a millimeter (mm)-wave band (e.g., <NUM>).

The storage unit <NUM>-<NUM> may store data, such as a default program, an application, and configuration information for operating the UE. The storage unit <NUM>-<NUM> may provide stored data upon request from the controller <NUM>-<NUM>.

The controller <NUM>-<NUM> may control the overall operation of the UE. For example, the controller <NUM>-<NUM> may transmit and receive signals through the baseband processor <NUM>-<NUM> and the RF processor <NUM>-<NUM>. Further, the controller <NUM>-<NUM> may record and read data in the storage unit <NUM>-<NUM>. To this end, the controller <NUM>-<NUM> may include at least one processor (e.g., a multi-connection processor <NUM>-<NUM>). For example, the controller <NUM>-<NUM> may include a communication processor (CP) to perform control for communication and an application processor (AP) to control an upper layer, such as an application.

<FIG> illustrates a configuration of a base station according to an embodiment of the disclosure.

Referring to <FIG>, the base station according to the embodiment may include one or more transmission and reception points (TRPs).

The base station according to the embodiment may include an RF processor 1i-<NUM>, a baseband processor 1i-<NUM>, a communication unit 1i-<NUM>, a storage unit 1i-<NUM>, and a controller 1i-<NUM>.

The RF processor 1i-<NUM> may perform a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. For example, the RF processor 1i-<NUM> may upconvert a baseband signal, provided from the baseband processor 1i-<NUM>, into an RF band signal to transmit the RF band signal through an antenna, and may downconvert an RF band signal, received through the antenna, into a baseband signal. For example, the RF processor 1i-<NUM> may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC.

Although <FIG> shows only one antenna, the base station may include a plurality of antennas.

In addition, the RF processor 1i-<NUM> may include a plurality of RF chains. Further, the RF processor 1i-<NUM> may perform beamforming. For beamforming, the RF processor 1i-<NUM> may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor 1i-<NUM> may transmit one or more layers, thereby performing downlink MIMO.

The baseband processor 1i-<NUM> may perform a function of converting a baseband signal and a bit stream according to the physical-layer specification of a first radio access technology. For example, in data transmission, the baseband processor 1i-<NUM> may encode and modulate a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor 1i-<NUM> may demodulate and decode a baseband signal provided from the RF processor 1i-<NUM>, thereby reconstructing a reception bit stream. For example, according to OFDM, in data transmission, the baseband processor 1i-<NUM> may generate complex symbols by encoding and modulating a transmission bit stream, may map the complex symbols to subcarriers, and may construct OFDM symbols through an IFFT and CP insertion. In data reception, the baseband processor 1i-<NUM> may divide a baseband signal, provided from the RF processor 1i-<NUM>, into OFDM symbols, may reconstruct signals mapped to subcarriers through an FFT, and may reconstruct a reception bit stream through demodulation and decoding. As described above, the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> may transmit and receive signals.

Accordingly, the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

The communication unit 1i-<NUM> may provide an interface for performing communication with other nodes in a network. For example, the communication unit 1i-<NUM> may convert a bit stream, transmitted from a main base station to another node, for example, a secondary base station or a core network, into a physical signal, and may convert a physical signal, received from the other node, into a bit stream.

The storage unit 1i-<NUM> may store data, such as a default program, an application, and configuration information for operating the main base station. In particular, the storage unit 1i-<NUM> may store information on a bearer allocated to a connected UE, a measurement result reported from a connected UE, and the like. In addition, the storage unit 1i-<NUM> may store information as a criterion for determining whether to provide or stop multiple connections to a UE. The storage unit 1i-<NUM> may provide stored data in response to a request from the controller 1i-<NUM>.

The controller 1i-<NUM> may control the overall operation of the main base station. For example, the controller 1i-<NUM> may transmit and receive signals through the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> or through the communication unit 1i-<NUM>. Further, the controller 1i-<NUM> may record and read data in the storage unit 1i-<NUM>. To this end, the controller 1i-<NUM> may include at least one processor (e.g., a multi-connection processor 1i-<NUM>).

In addition, the programs may be stored in an attachable storage device which may access the electronic device through communication networks, such as the Internet, Intranet, Local Area Network (LAN), Wide LAN (WLAN), and Storage Area Network (SAN) or a combination thereof.

Claim 1:
A method performed by a terminal (1f-<NUM>) in a wireless communication system, the method comprising:
receiving (1f-<NUM>), from a base station (1f-<NUM>), a radio resource control, RRC, message for suspending an RRC connection between the terminal (1f-<NUM>) and the base station (1f-<NUM>);
identifying whether the terminal (1f-<NUM>) is configured to perform both a new radio, NR, vehicle to everything, V2X, sidelink communication on a first frequency and a long term evolution, LTE, V2X sidelink communication on a second frequency during the terminal (1f-<NUM>) being in an RRC inactive state;
in case that the terminal (1f-<NUM>) is configured to perform both the NR V2X sidelink communication and the LTE V2X sidelink communication,
identifying whether a third frequency for a cell reselection exists, the third frequency providing both an NR V2X sidelink communication configuration and an LTE V2X sidelink communication configuration;
determining the third frequency to be a highest priority for the cell reselection, in case that the third frequency exists, wherein the third frequency is for NR or LTE;
determining a fourth frequency to be the highest priority for the cell reselection, in case that the third frequency does not exist, the fourth frequency providing either the NR V2X sidelink communication configuration or the LTE V2X sidelink communication configuration, wherein the fourth frequency is for the NR or the LTE; and
in case that the terminal (1f-<NUM>) is configured to perform the NR V2X sidelink communication or the LTE V2X sidelink communication,
determining a frequency providing an intra-carrier configuration and a frequency providing an inter-carrier configuration to be the highest priority as the same priority for the cell reselection.