Method and apparatus for performing a cell reselection process based on ephemeris in a satellite network.

Abstract

The present invention provides a communication technique and system for integrating a 5G communication system with IoT technology to support a higher data transmission rate than the 4G system. The 5G communication technology and IoT-related technology can be applied to intelligent services (e.g., smart homes, smart buildings, smart cities, smart cars or connected cars, healthcare, digital education, retail, security and safety-related services, etc.). According to an embodiment of the present invention, a method and apparatus for a terminal to perform a cell reselection process in a satellite network (or a non-terrestrial network) are provided.

Description

[Technical Field]

[0001] The present invention relates to the operation of terminals and base stations in a communication system, and specifically to a method and apparatus for performing a cell reselection process in a satellite network (or a non-terrestrial network (NTN)). [Background technology]

[0002] Efforts are being made to develop improved 5G or pre-5G communication systems to meet the increasing demand for wireless data traffic since the commercialization of 4G communication systems. For these reasons, 5G communication systems or pre-5G communication systems are also called Beyond 4G Network communication systems or Post LTE systems.

[0003] To achieve high data transmission rates, 5G communication systems are being considered for implementation in ultra-high frequency (mmWave) bands (for example, the 60 gigabit (60 GHz) band). To mitigate path loss in ultra-high frequency bands and increase propagation distance, beamforming, massive MIMO, FD-MIMO (full-dimensional MIMO), array antennas, analog beamforming, and large-scale antenna technologies are being discussed for 5G communication systems.

[0004] Furthermore, to improve the system's network, 5G communication systems are undergoing technological development, including advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device communication (D2D), wireless backhaul, moving networks, cooperative communication, CoMP (Coordinated Multi-Points), and interference cancellation. In addition, 5G systems have seen the development of advanced coding modulation (ACM) methods such as FQAM (hybrid FSK and QAM modulation) and SWSC (sliding window superposition coding), as well as advanced connectivity technologies such as FBMC (filter bank multicarrier), NOMA (non orthogonal multiple access), and SCMA (sparse code multiple access).

[0005] On the other hand, the internet is evolving from a human-centered network where humans generate and consume information to an IoT (Internet of Things) network where distributed components such as objects exchange and process information. Internet of Everything (IoE) technology, which combines big data processing technologies using connections to cloud servers and other systems with IoT technologies, is also emerging. To realize the Internet of Things (IoT), technological elements such as sensing technology, wired and wireless communication and network infrastructure, service interface technology, and security technology are required. In recent years, technologies such as sensor networks, machine-to-machine (M2M), and MTC (machine type communication) for connecting things have been researched. In an IoT environment, intelligent IT (internet technology) services can be provided that collect and analyze data generated by connected devices to create new value for people's lives. IoT can be applied to fields such as smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart home appliances, and advanced medical services through the integration and combination of existing IT (information technology) technologies and various industries.

[0006] Accordingly, various attempts are being made to apply 5G communication systems to IoT networks. For example, 5G communication technologies such as sensor networks, machine-to-machine (M2M), and machine-type communication (MTC) are being implemented using techniques such as beamforming, MIMO, and array antennas. The application of cloud wireless access networks (cloud RAN) as a big data processing technology, as mentioned earlier, can be seen as another example of the convergence of 5G and IoT technologies. [Overview of the project] [Problems that the invention aims to solve]

[0007] Unlike conventional terrestrial networks, the difference in received signal strength between terminals supporting satellite networks (or non-terrestrial networks: hereinafter referred to as NTN) located at the center of a satellite cell and those located at the edge of a satellite cell is small. This can lead to problems such as re-selecting a surrounding cell even when the terminal is at the center of the cell, or frequent ping-pong cell reselection. Therefore, it is necessary to devise a method and apparatus for performing the cell reselection process at NTN. [Means for solving the problem]

[0008] To solve the aforementioned problems, according to one aspect of the present invention, a method for a terminal at NTN is provided. The terminal method comprises the steps of: receiving configuration information from a base station's serving cell, including at least one cell reselection parameter; confirming cell reselection conditions based on the at least one cell reselection parameter and location information relating to the serving cell; and reselecting a new cell based on the cell reselection conditions.

[0009] Furthermore, according to one aspect of the present invention, an NTN terminal is provided. The terminal includes a transmitting / receiving unit and a control unit connected to the transmitting / receiving unit, which receives configuration information including at least one cell reselection parameter from a base station's serving cell, confirms cell reselection conditions based on the at least one cell reselection parameter and location information relating to the serving cell, and reselects a new cell based on the cell reselection conditions. [Effects of the Invention]

[0010] According to one aspect of the present invention, the method and terminal for an NTN terminal can perform the cell reselection process more efficiently. Specifically, since the terminal can perform a cell reselection process that takes into account the satellite's ephemeris, it can solve problems that occur during cell reselection at NTN. The effects that can be obtained with the present invention are not limited to those described above, and other effects not mentioned will be clearly understood from the following description by a person with ordinary skill in the art to which the present invention pertains. [Brief explanation of the drawing]

[0011] The above-mentioned and other objectives, features and advantages of the present invention will be further clarified by the following description of embodiments of the present invention with reference to the accompanying drawings. [Figure 1] This figure shows the structure of an LTE system according to one embodiment of the present invention. [Figure 2] This is a diagram showing the wireless protocol structure in an LTE system according to one embodiment of the present invention. [Figure 3] This figure shows the structure of a next-generation mobile communication system according to one embodiment of the present invention. [Figure 4] This figure shows the wireless protocol structure of a next-generation mobile communication system according to one embodiment of the present invention. [Figure 5] This diagram illustrates the procedure for a base station to disconnect a terminal, for the terminal to switch from RRC connected mode (RRC_CONNECTED) to RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE), and for a terminal in RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE) to perform a cell reselection process. [Figure 6] This diagram compares the received signal strength when the terminal is located in the center of a cell and when it is located at the edge of a cell in a terrestrial network or NTN network. [Figure 7]This figure shows a procedure according to one embodiment of the present invention in which a base station disconnects a terminal, the terminal switches from RRC connected mode (RRC_CONNECTED) to RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE), and then the terminal in RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE) performs the satellite cell reselection process. [Figure 8] This is a block diagram showing a schematic configuration of a terminal according to one embodiment of the present invention. [Figure 9] This is a block diagram illustrating the schematic configuration of a base station according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] The operating principle of the present invention will be described in detail below with reference to the attached drawings. In describing the present invention below, if a detailed explanation of a related known function or configuration is deemed likely to obscure the gist of the invention, such detailed explanation will be omitted. Furthermore, the terms described later are defined in consideration of the functions in this invention, and these may be changed according to the intentions or conventions of the user or operator. Therefore, the definition should be based on the content of this specification as a whole.

[0013] In describing the present invention below, if a detailed explanation of a related known function or configuration is deemed likely to obscure the gist of the invention, such detailed explanation will be omitted. Embodiments of the present invention will be described below with reference to the attached drawings.

[0014] The terms used in the following explanation to identify connected nodes, network entities, messages, interfaces between network entities, and various other forms of identification are illustrative examples provided for the sake of clarity. Therefore, the present invention is not limited to the terms described below, and other terms that refer to subjects with equivalent technical meanings may be used.

[0015] For the sake of explanation, the present invention uses terms and names defined in the 3GPP® LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present invention is not limited by the above terms and names, and can be applied identically to systems according to other standards. In this invention, eNB may be used interchangeably with gNB for the sake of explanation. In other words, the base station described as eNB can also represent gNB.

[0016] Figure 1 shows the structure of an LTE system according to one embodiment of the present invention. Referring to Figure 1, as shown in the figure, the LTE system's radio access network consists of next-generation base stations (Evolved Node B, hereinafter referred to as ENB, Node B, or base station) (1-05, 1-10, 1-15, 1-20), an MME (mobility management entity) (1-25), and an S-GW (Serving-Gateway) (1-30). User equipment (hereinafter referred to as UE or terminal) (1-35) connects to the external network via ENB (1-05 to 1-20) and S-GW (1-30).

[0017] In Figure 1, ENB(1-05~1-20) corresponds to existing node B of the UMTS system. The ENB is connected to the UE (1-35) via a wireless channel and performs a more complex role than the existing Node B. In LTE systems, all user traffic, including real-time services such as VoIP (Voice over IP) using the Internet Protocol, is served via a shared channel. Therefore, a device is needed to collect status information such as the UE's buffer state, available transmit power state, and channel state, and to schedule them. This is the role of the ENB (1-05~1-20).

[0018] A single ENB typically controls multiple cells. For example, to achieve a transmission speed of 100 Mbps, an LTE system might use orthogonal frequency division multiplexing (OFDM) as its wireless connection technology with a bandwidth of 20 MHz. Furthermore, an adaptive modulation coding (AMC) method is applied, which determines the modulation scheme and channel coding rate according to the channel status of the terminal. S-GW(1-30) is a device that provides data bearers and generates or removes data bearers according to the control of MME(1-25). The MME is a device responsible for mobility management and various control functions for terminals, and is connected to multiple base stations.

[0019] Figure 2 shows the wireless protocol structure in an LTE system according to one embodiment of the present invention. Referring to Figure 2, the wireless protocols of the LTE system consist of PDCP (packet data convergence protocol) (2-05, 2-40), RLC (radio link control) (2-10, 2-35), and MAC (medium access control) (2-15, 2-30) at the terminal and ENB, respectively.

[0020] PDCP (Packet Data Convergence Protocol) (2-05, 2-40) is responsible for operations such as IP header compression / decompression. The main functions of PDCP can be summarized as follows:

[0021] • Header compression and decompression function (ROHC only) • User data transmission function • Sequential delivery function (In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM) • Reordering function (For split bearers in DC (only support for RLC AM): PDCP PDU routing for transmission and PDCP PDU reordering for reception) • Duplicate detection function (Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM) • Retransmission function (for PDCP SDUs at handover and for split bearers in DC, for PDCP PDUs at PDCP data-recovery procedure, and for RLC AM) • Encryption and deciphering functions • Timer-based SDU deletion function (SDU discard in uplink).

[0022] Radio link control (RLC) (2-10, 2-35) reconfigures the PDCP PDU (protocol data unit) to an appropriate size to perform ARQ operations, etc. The main functions of RLC can be summarized as follows:

[0023] • Data transmission function (Transfer of upper layer PDUs) ·ARQ function (Error Correction through ARQ(only for AM data transfer)) • Concatenation, segmentation, and reassembly functions (only for UM and AM data transfer) • Re-segmentation function (Re-segmentation of RLC data PDUs (only for AM data transfer)) • Reordering function for RLC data PDUs (only for UM and AM data transfer) • Duplicate detection function (only for UM and AM data transfer) • Error detection function (Protocol error detection (only for AM data transfer)) • RLC SDU deletion function (RLC SDU discard (only for UM and AM data transfer)) ·RLC re-establishment function

[0024] MAC (2-15, 2-30) is connected to multiple RLC hierarchical devices configured in a single terminal and performs the operation of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of a Mac can be summarized as follows:

[0025] • Mapping function (Mapping between logical channels and transport channels) • Multiplexing and demultiplexing of MAC SDUs belonging to one or different logical channels into / from transport blocks (TB) delivered to / from the physical layer on transport channels. • Scheduling information reporting function • HARQ function (Error correction through HARQ) • Priority handling between logical channels of one UE (Logical User Interface) • Priority adjustment function between UEs (User Interfaces) by means of dynamic scheduling. • MBMS service verification function • Transmission format selection function • Padding function

[0026] The PHY layers (2-20, 2-25) perform the following operations: channel coding and modulation of higher-level data to generate OFDM symbols and transmit them to the radio channel, or demodulate and channel decoding OFDM symbols received via the radio channel and transmit them to the higher layer.

[0027] Figure 3 shows the structure of a next-generation mobile communication system according to one embodiment of the present invention. Referring to Figure 3, as shown in the figure, the radio access network of the next-generation mobile communication system (hereinafter referred to as NR or 2g) consists of a next-generation base station (new radio Node B, hereinafter referred to as NR gNB or NR base station) (3-10) and an NR CN (new radio core network) (3-05). The user terminal (new radio user equipment, hereinafter referred to as NR UE or terminal) (3-15) connects to the external network via NR gNB (3-10) and NR CN (3-05).

[0028] In Figure 3, NR gNB(3-10) corresponds to the eNB (Evolved Node B) of an existing LTE system. NR gNB is connected to NR UE(3-15) via wireless channels and provides superior service compared to existing Node B. In next-generation mobile communication systems, all user traffic is served via a shared channel. Therefore, a device is needed to collect status information such as the UE's buffer state, available transmit power state, and channel state, and to schedule it. This is the role of the NR NB(3-10).

[0029] A single NR gNB typically controls multiple cells. To achieve ultra-high-speed data transmission compared to current LTE, it is possible to have a bandwidth exceeding the existing maximum bandwidth, and orthogonal frequency division multiplexing (OFDM) is used as the wireless connection technology, with beamforming technology added as an additional feature. Furthermore, an Adaptive Modulation & Coding (AMC) method is applied, which determines the modulation scheme and channel coding rate according to the channel status of the terminal.

[0030] NR CN(3-05) provides functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device responsible for mobility management and various control functions for terminals, and is connected to multiple base stations. Furthermore, the next-generation mobile communication system can also be linked with existing LTE systems, with the NR CN connected to the MME(3-25) via a network interface. The MME connects to the existing base station, eNB(3-30).

[0031] Figure 4 shows the wireless protocol structure of a next-generation mobile communication system according to one embodiment of the present invention. Referring to Figure 4, the wireless protocols for the next-generation mobile communication system consist of NR SDAP (service data adaptation protocol) (4-01, 4-45), NR PDCP (packet data convergence protocol) (4-05, 4-40), NR RLC (radio link control) (4-10, 4-35), and NR MAC (medium access control) (4-15, 4-30) at the terminal and NR base station, respectively.

[0032] The main functions of NR SDAP (4-01, 4-45) may include some of the following functions:

[0033] • User data transfer function • Mapping between a QoS flow and a DRB for both DL and UL (Uplink and Downlink) • A function to mark QoS flow IDs in both uplink and downlink packets. • A function that maps reflective QoS flow to DRB mapping for the UL SDAP PDUs.

[0034] The terminal receives settings via RRC messages from the SDAP tiering device, specifying whether to use the SDAP tiering device header or the SDAP tiering device functions, for each PDCP tiering device, bearer, or logical channel. When the SDAP header is configured, the NAS QoS reflective setting 1-bit indicator (NAS reflective QoS) and the AS QoS reflective setting 1-bit indicator (AS reflective QoS) in the SDAP header instruct the terminal to update or reconfigure the mapping information for the uplink and downlink QoS flow and data bearer. The SDAP header contains "QoS flow ID" information, which represents QoS. QoS information is used to prioritize data processing, schedule information, and other information to support smooth service delivery.

[0035] The main functions of NR PDCP (4-05, 4-40) may include some of the following functions:

[0036] • Header compression and decompression function (ROHC only) • User data transmission function • Sequential delivery of upper layer PDUs • Out-of-sequence delivery of upper layer PDUs • Reordering function (PDCP PDU reordering for reception) • Duplicate detection function (Duplicate detection of lower layer SDUs) • Retransmission function (Retransmission of PDCP SDUs) • Encryption and deciphering functions • Timer-based SDU deletion function (SDU discard in uplink).

[0037] The aforementioned reordering function of the NR PDCP device is a function that rearranges the PDCP PDUs received at lower levels in order based on the PDCP SN (sequence number), and may include a function to transmit the data to higher levels in the rearranged order, or it may include a function to transmit the data directly without considering the order. Furthermore, the system may include a function to reorder and record the leaked PDCP PDUs, a function to report the status of the leaked PDCP PDUs to the sender, and a function to request retransmission of the leaked PDCP PDUs.

[0038] The main functions of NR RLC (4-10, 4-35) may include some of the following functions:

[0039] • Data transmission function (Transfer of upper layer PDUs) • Sequential delivery of upper layer PDUs • Out-of-sequence delivery of upper layer PDUs • ARQ function (Error Correction through ARQ) • Concatenation, segmentation, and reassembly of RLC SDUs • Re-segmentation function (Re-segmentation of RLC data PDUs) • Reordering function (Reordering of RLC data PDUs) • Duplicate detection function • Error detection function (Protocol error detection) ·RLC SDU deletion function (RLC SDU discard) ·RLC re-establishment function

[0040] In the above, the in-sequence delivery function of an NR RLC device is a function that sequentially transmits RLC SDUs received from lower levels to higher levels. If a single RLC SDU is originally received as multiple RLC SDUs, it can include a function to reassemble and transmit them. The system may include a function to rearrange received RLC PDUs based on RLC SN (sequence number) or PDCP SN (sequence number), a function to record RLC PDUs that have been lost due to the rearrangement, a function to report the status of lost RLC PDUs to the sender, and a function to request retransmission of lost RLC PDUs.

[0041] If an RLC SDU is lost, the system may include a function to sequentially transmit only the RLC SDUs received up to the point before the lost RLC SDU to the next level. Alternatively, if a predetermined timer expires even if an RLC SDU is lost, the system may include a function to sequentially transmit all RLC SDUs received before the timer started to the next level. Alternatively, if a predetermined timer expires even if an RLC SDU is lost, the system may include a function to sequentially transmit all RLC SDUs received up to the present to the next level. Furthermore, the RLC PDUs can be processed in the order they are received (regardless of the sequence number order, in the order of arrival) and transmitted to the PDCP device in an out-of-sequence delivery manner. In the case of segments, they can be stored in a buffer, or later segments can be received, reconstructed into a single complete RLC PDU, processed, and then transmitted to the PDCP device. The above NR RLC hierarchy may not include concatenation functionality; this functionality can be performed by the NR MAC hierarchy or replaced by the multiplexing functionality of the NR MAC hierarchy.

[0042] In the above, the out-of-sequence delivery function of the NR RLC device is a function that directly transmits RLC SDUs received from lower levels to higher levels regardless of their order. If a single RLC SDU is received split into multiple RLC SDUs, the system may include a function to reassemble and transmit them, store the RLC SN or PDCP SN of the received RLC PDUs to sort them, and record any lost RLC PDUs.

[0043] An NR MAC (4-15, 4-30) can be connected to multiple NR RLC hierarchical devices configured in a single terminal, and the main functions of the NR MAC may include some of the following functions:

[0044] • Mapping function (Mapping between logical channels and transport channels) ·Multiplexing / demultiplexing of MAC SDUs • Scheduling information reporting function • HARQ function (Error correction through HARQ) • Priority handling between logical channels of one UE (Logical User Interface) • Priority adjustment function between UEs (User Interfaces) by means of dynamic scheduling. • MBMS service verification function • Transmission format selection function • Padding function

[0045] The NR PHY layers (4-20, 4-25) perform the operation of channel coding and modulation of higher-level data to generate OFDM symbols and transmitting them to the radio channel, or demodulating and channel decoding OFDM symbols received via the radio channel and transmitting them to the higher layer.

[0046] Figure 5 shows the procedure in which a base station disconnects a terminal, the terminal switches from RRC connected mode (RRC_CONNECTED) to RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE), and then the terminal in RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE) performs the cell reselection process.

[0047] In the present invention, the cell reselection process (or cell reselection procedure) means a procedure in which a terminal in RRC idle mode (RRC_IDLE) or RRC inactive mode (RRC_INACTIVE) decides whether to maintain the current serving cell or reselect a cell to a neighbor cell when, for a predetermined reason or due to movement, the service quality of the serving cell becomes lower than the service quality of the neighbor cell.

[0048] In the case of handover, the network (MME or AMF (access and mobility management function) or source eNB or source gNB) determines whether or not to perform the handover operation, whereas in the case of cell reselection, the terminal itself decides whether or not to perform the cell reselection operation based on the cell measurement value. The cell that the terminal re-selects while moving means a cell that uses the same NR frequency (NR intra-frequency) as the currently camp-on serving cell, a cell that uses a different NR frequency (NR inter-frequency) than the serving cell, or a cell that uses the frequency used in other radio access technologies (RATs) (inter-RAT frequency).

[0049] Referring to Figure 5, terminal (5-01) is in RRC connection mode (5-05) (RRC_CONNECTED). (5-10) In step (5-01), the terminal (5-01) in RRC connection mode receives an RRC disconnection message (RRCRelease message) from the base station (5-02). The message may contain deactivation configuration information (e.g., suspendConfig). The message may include single-cell reselection priority setting information for each RAT (e.g., NR EUTRA, UTRA-FDD, UTRA-TDD, etc.) per frequency, and a timer value that is applicable in common regardless of the RAT (e.g., t320 timer value).

[0050] (5-15) In step (5-15), depending on whether the received RRC disconnection message contains deactivation setting information, the terminal transitions to (or enters) either RRC deactivation mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE). For example, if a terminal in RRC connection mode successfully receives an RRC disconnection message containing deactivation setting information, it will transition to RRC deactivation mode. Conversely, if an RRC disconnection message that does not contain deactivation setting information is successfully received, the terminal in RRC connection mode will transition to RRC idle mode.

[0051] (5-20) In step (5-20), the terminal performs the cell selection procedure in RRC idle mode or RRC deactivation mode. The cell selection procedure refers to the process by which the terminal searches for a suitable cell in the selected PLMN (public land mobile network) or SNPN (stand-alone non-public network) and camps it on. The cell that is camped on after searching for a suitable cell in RRC idle mode or RRC deactivated mode is referred to as the serving cell. The terminal receives system information (e.g., MIB and / or SIB1) to be broadcast in the cell in order to perform the cell selection procedure.

[0052] For example, a terminal can select cells according to cell selection criteria (which can be referred to as S criteria or Formula 1). For example, select the cells that satisfy formula 1 shown below.

number

[0053] For each parameter used in Equation 1, the definition can refer to the 3GPP (registered trademark) standard document TS38.304, and the parameters are included in the system information (e.g., SIB1, SIB2) broadcast by the cell. In the following, the parameters are the same for the embodiments of the present invention to which Equation 1 is applied.

[0054] For example, Srxlev is the cell selection reception level value (in dB), Squal is the cell selection quality value (in dB), Q rxlevmeas is the measured cell reception level value (RSRP), Q rxlevmin is the minimum required reception level value (in dBm) for the cell, Q rxlevminoffset is Q considering the Srxlev evaluation rxlevmin the offset for, P compensation is the compensation power value, Q offsettemp is the offset temporarily applied to the cell, Q qualmin is the minimum required quality level (in dB) for the cell, Q qualminoffset is Q considering the Squal evaluation qualmin means the offset for.

[0055] In steps (5-25), the terminal acquires (or receives) system information (SIB3, SIB4,..., SIB8, SIB24). Each system information may include one cell reselection priority setting information and cell reselection parameters for each frequency for each RAT. For example, SIB2 may include information (or parameters) commonly applied for a terminal in the RRC idle mode or RRC deactivated mode to reselect "NR intra-frequency", "NR inter-frequency", "inter-RAT frequency" cells.

[0056] For example, SIB3 includes information / parameters applied only for a terminal in the RRC idle mode or RRC deactivated mode to reselect an "NR intra-frequency" cell. For example, SIB4 includes information / parameters that are only applied to terminals in RRC idle mode or RRC deactivated mode for re-selecting an "NR inter-frequency" cell. For example, SIB5 includes information / parameters that apply only to terminals in RRC idle mode or RRC deactivation mode in order to re-select an "LTE frequency (inter-RAT frequency)" cell.

[0057] (5-30) In this stage, the terminal performs a cell reselection evaluation process. The cell reselection evaluation procedure refers to the following series of steps:

[0058] • Frequency priority application method (Reselection priorities handling) • Measurement rules for cell reselection • Cell reselection criteria

[0059] The method for applying frequency priority is determined by whether the RRC disconnection message received by the terminal in steps (5-10) includes cell reselection priority setting information for each frequency specific to each RAT and a timer value that applies to all RATs in common. For example, frequency priority is determined based on the following method. On the other hand, the methods described below are merely examples, and the present invention is not limited thereto; frequency priority can be determined based on a variety of methods.

[0060] If the RRC disconnection message includes one cell reselection priority setting information per frequency for each RAT and a timer value applicable to all RATs, while the T320 timer is running, the RAT-specific cell reselection priority setting information per frequency in the system information obtained in step (5-25) is ignored, and the cell reselection priority setting information contained in the RRC disconnection message is applied to determine the frequency priority. If the T320 timer expires, the frequency-specific cell reselection priority setting information for each RAT, obtained in the system information at stage (5-25), is applied to determine the frequency priority.

[0061] If the RRC disconnection message contains one cell reselection priority setting information per frequency for each RAT, and does not contain a timer value that can be applied to all RATs, the RAT-specific frequency cell reselection priority setting information in the system information obtained in step (5-25) is ignored, and the frequency priority is determined by applying the cell reselection priority setting information contained in the RRC disconnection message.

[0062] If the RRC disconnection message does not include cell reselection priority settings for each frequency specific to each RAT and timer values ​​applicable to all RATs, the frequency priority is determined by applying the cell reselection priority settings for each frequency specific to each RAT, as obtained in the system information in step (5-25).

[0063] The above measurement rules apply to the terminal, which applies frequency priority for a predetermined reason or to minimize battery consumption, and performs neighbor cell measurement based on the following measurement rules. On the other hand, the following measurement rules are merely examples, and the present invention is not limited thereto; the terminal can perform peripheral cell measurements based on a variety of measurement rules.

[0064] • If the receiving level and receiving quality of the serving cell are greater than the critical value (S rxlev >S IntraSearchP and Squal >S IntraSearchQ The terminal does not perform "NR intra-frequency" measurements. Otherwise, the device performs an "NR intra-frequency" measurement. Here, S IntraSearchP This refers to the Srxlev critical value for "NR intra-frequency" measurement, and S IntraSearchQ This refers to the Squal critical value for "NR intra-frequency" measurement.

[0065] For "NR inter-frequency" or "inter-RAT frequency" frequencies that have a higher cell reselection priority than the current serving cell frequency, the terminal performs surrounding cell measurements in accordance with 3GPP® standard document TS38.133.

[0066] • If the receiving level and receiving quality of the serving cell are greater than the critical value (S rxlev >S nonIntraSearchP and S qual >S nonIntraSearchQ The terminal does not perform measurements for "NR inter-frequency" frequencies that have a lower or equal cell reselection priority than the current serving cell frequency, or for "inter-RAT frequency" frequencies that have a higher cell reselection priority than the current serving cell frequency. Otherwise, for "NR inter-frequency" or "inter-RAT frequency" with a cell reselection priority lower than or equal to the current serving cell frequency, the terminal performs a peripheral cell measurement in accordance with 3GPP® standard document TS38.133. For reference, the critical value (for example, S mentioned above) IntraSearchP S IntraSearchQ S nonIntraSearchP S nonIntraSearchQ The reception level and reception quality of the serving cell are obtained or derived via the system information received in steps (5-30).

[0067] Here, S nonIntraSrachPThis refers to the Srxlev critical value for "NR inter-frequency" or "inter-RAT frequency" measurements, and S nonIntraSearchQ This refers to the Squal critical value for "NR inter-frequency" or "inter-RAT frequency" measurements.

[0068] On the other hand, the cell reselection evaluation criteria apply different criteria depending on the frequency priority determined by the terminal. Specifically, the device applies different cell reselection criteria in the following cases: On the other hand, the present invention is not limited to the examples below, and there may be a variety of cases in which the cell reselection criteria are applied.

[0069] ■Case 1: ● If there is at least one "NR inter-frequency" or "inter-RAT frequency" with a higher priority than the current serving frequency. ■Second case: ● If there is at least one "NR inter-frequency" or "inter-RAT frequency" with a lower priority than the current serving frequency. ■Case 3: ● If there is at least one "NR inter-frequency" that is the current serving frequency or has the same priority as the current serving frequency. ■Case 4: ● If there are multiple NR cells that meet the cell reselection criteria according to either the first or second case.

[0070] If multiple cells that meet the cell reselection criteria have different priorities, the terminal will prioritize the higher-priority RAT / frequency over the lower-priority RAT / frequency when performing cell reselection. For example, the terminal prioritizes the first case, or the fourth case resulting from the first case, and performs cell reselection. If the above conditions are not met, the terminal will perform cell reselection according to the third condition. If none of the above conditions are met, the cell selection is performed according to the second condition, or the fourth condition that arises from the second condition.

[0071] When applying the cell reselection criteria according to the first case, terminals in RRC idle mode or RRC deactivation mode shall be subject to the "Higher priority NR Inter-frequency and inter-RAT cell reselection criteria". Here, the "Higher priority NR Inter-frequency and inter-RAT cell reselection criteria" are as follows:

[0072] • If Thresh is broadcast by system information (e.g., SIB2) in a serving cell Serving、LowQ When the broadcast is made and the terminal camp-on to the current serving cell, 1 second has passed (where Thresh Serving、LowQ This refers to the Squal critical value used for serving cells when reselecting towards lower priority.

[0073] ● The terminal determines whether one or more cells in each frequency meet the following condition A, and derives a list of candidate target cells for each frequency. Treselection used in condition A RAT Parameters and Thresh X、HighQ The parameters are included in the system information. For example, for cells with a higher priority than the serving frequency ("NR frequency"), the parameter values ​​are included in SIB4, and for cells with a higher priority than the serving frequency ("inter-RAT frequency"), the parameter values ​​are included in SIB5. Here, Treselection RAT This refers to the cell reselection timer value, Thresh X、HighQ This refers to the Squal critical value when reselecting towards a RAT or frequency with a higher priority than the serving frequency.

[0074] ■Condition A: The reception quality (Squal) of a cell or E-UTRAN RAT cell on a high-priority NR frequency is Treselection RAT During the period Thresh X、HighQ If larger (A cell of a higher priority NR or E-UTRAN RAT / frequency fulfils Squal>Thresh) X、HighQ during a time internal Treselection RAT )

[0075] • Otherwise

[0076] ● The terminal determines whether one or more cells in each frequency meet the following condition B, and derives a list of candidate target cells for each frequency. Treselection used in condition B RAT Parameters and Thresh X、HighP The parameters are included in the system information. For example, for cells with a higher priority than the serving frequency ("NR frequency"), the parameter values ​​are included in SIB4, and for cells with a higher priority than the serving frequency ("inter-RAT frequency"), the parameter values ​​are included in SIB5. Here, Thresh X、HighP This refers to the Srxlev critical value when reselecting towards a RAT or frequency with a higher priority than the serving frequency.

[0077] ■Condition B: The terminal has camped on the current serving cell for more than 1 second, and the received level (Srxlev) of the higher priority RAT cell or frequency cell is in Treselection. RAT During the period Thresh X、HighP If larger (A cell of a higher priority RAT / frequency fulfils Srxlev>Thresh) X、HighP during a time internal Treselection RAT )

[0078] This determines whether there are multiple cells that satisfy the "Higher priority NR Inter-frequency and inter-RAT cell reselection criteria". In this context, "multiple cells" refers to multiple cells at a single frequency with the highest priority, or, when there are multiple frequencies with the highest priority and one or more cells for each frequency, it refers to multiple cells for all frequencies that satisfy this condition. If multiple cells exist, the device will, if the "highest-priority frequency" is an NR frequency, additionally derive a cell-specific ranking and re-select the cell as the "highest ranked cell". In other words, when applying the cell reselection criteria based on the fourth case that occurred in the first case, the cell reselection to the "highest ranked cell" will be performed according to the following conditions.

[0079] The terminal performs ranking of all cells that fulfill the cell selection criterion S. For cells that meet the cell selection criteria, the terminal derives a cell-specific Rank based on RSRP measurements. The ranks of the serving cell and surrounding cells are calculated according to Formula 2 shown below. The serving cell rank and surrounding cell rank are calculated according to formula 2 shown below.

[0080] In this invention, the rank of the serving cell is R s It points to the surrounding cells, and the Rank of the surrounding cells is R n He points to it.

number

[0081] Here, Q meas (Q meas、s and Q meas、n ) refers to the RSRP measurement result (RSRP measurement quality) used for cell reselection. Qoffset is the opposite of "intra-frequency". s、n If valid, Qoffset s、n It is identical to Qoffset s、n If it is not valid, the value is "0". Furthermore, Qoffset is the opposite of "inter-frequency". s、n If enabled, Qoffset s、n and Qoffset frequency It is the same as adding Qoffset s、n If it is not enabled, Qoffset frequecy It is identical to [the other one]. Qoffset temp This represents an offset that is temporarily applied to the cell.

[0082] For a terminal to re-select a new cell (e.g., the highest-ranked cell), the following conditions must be met:

[0083] ■If rangeToBestCell is not set in SIB2, the cell with the highest ranking will be selected. Here, rangeToBestCell refers to a range of values.

[0084] ■If rangeToBestCell is set in SIB2, cell reselection will be performed to the cell with the highest number of beams above the threshold (i.e., absThreshSS-BlocksConsolidation) among the cells whose R value is within rangeToBestCell of the highest ranked cell. Here, "absThreshSS-BlocksConsolidation" refers to the critical values ​​for L1 measurement consolidation, which are signaled by NR frequency and RS index.

[0085] ■Trselection RAT Cells that meet the cell reselection criteria during a time interval are superior to the current serving cell (TreselectionRAT).

[0086] • The device must have been camp-on to the current serving cell for at least one second.

[0087] In the case where cell reselection criteria are applied according to the second case, terminals in RRC idle mode or RRC deactivation mode shall be subject to the "Lower priority NR Inter-frequency and inter-RAT cell reselection criteria". The "Lower priority NR Inter-frequency and inter-RAT cell reselection criteria" are as follows:

[0088] • If Thresh is broadcast by system information (e.g., SIB2) in a serving cell Serving、LowQ If the broadcast is made and 1 second has passed since the device camp-on to the current serving cell

[0089] ● The terminal determines whether one or more cells in each frequency meet the following condition C, and derives a list of candidate target cells for each frequency. Treselection used in condition C RAT Parameters, Thresh Serving、LowQ Parameters, ThreshX、LowQ The parameters are included in the system information. For example, parameters for serving frequency (e.g., Thresh Serving、LowQ ) is included in SIB2, and for cells in the "NR frequency" which has a lower priority than the serving frequency, the parameter value (for example, Treselection) is added to SIB4. RAT Thresh X、LowQ ) is included, and for cells in the "inter-RAT frequency" which has a lower priority than the serving frequency, the SIB5 contains parameter values ​​(e.g., Treselection RAT Thresh X、LowQ ) is included.

[0090] ■Condition C: Treselection RAT During the period, the current serving cell's receiving quality (Squal) is Thresh Serving、LowQ The reception quality (Squal) of cells or E-UTRAN / RAT cells with smaller, lower priority NR frequencies is Thresh X、LowQ If it is greater than (The serving frequency fulfills Squal <Thresh Serving、LowQ and a cell of a lower priority NR or E-UTRAN RAT / frequency fulfils Squal>Thresh X、LowQ during a time internal Treselection RAT )

[0091] • Otherwise

[0092] ● The terminal determines whether one or more cells in each frequency meet the following condition D, and derives a list of candidate target cells for each frequency. Treselection used in condition D RAT Parameters, Thresh Serving、LowP Parameters, Thresh X、LowP The parameters are included in the system information. For example, parameters for serving frequency (e.g., Thresh Serving、LowP ) is included in SIB2 and is an NR with a lower priority than the serving frequency. frequency For cells located in the SIB4, the parameter value (for example, Treselection) RAT Thresh X、LowP ) is included, and for cells in the "inter-RAT frequency" which has a lower priority than the serving frequency, the SIB5 contains parameter values ​​(e.g., Treselection RAT Thresh X、LowP ) is included.

[0093] ■Condition D: If the terminal has camped on the current serving cell for more than 1 second, Treselection will be disabled. RAT During the period, the current serving cell's receive level (Srxlev) is Thresh Serving、LowP The received level (Srxlev) of a RAT cell or cell at a smaller, lower priority frequency is Thresh X、LowP If it is greater (The serving frequency fulfills Srxlev <Thresh Serving、LowP and a cell of a lower priority RAT / frequency fulfils Srxlev>Thresh X、LowP during a time internal Treselection RAT )

[0094] Determine whether there are multiple cells that satisfy the "Lower priority NR Inter-frequency and inter-RAT cell reselection criteria". If multiple cells exist (i.e., if the cell reselection criteria are applied according to the fourth case resulting from the second case), the terminal will additionally derive cell-specific rankings using the method described above and reselect the cell to the "highest ranked cell".

[0095] In the third case, when applying the cell reselection criteria, the cell-specific ranking is derived using the method described above, and the cell is reselected to the "highest ranked cell".

[0096] (5-35) In step (5-35), the terminal re-selects a cell at the final target cell using the cell re-selection evaluation procedure described above. At this time, the MIB and SIB1 broadcast in the cell in question are received, and if the cell status is not indicated as “barred” or not to be treated as if the cell status is “barred”, the reception level and reception quality of the cell in question are newly derived based on the received SIB1, and it is determined whether the cell re-selection criteria (Srxlev>0 AND Squal>0) are met, and the cell in question is ultimately re-selected.

[0097] On the other hand, in the aforementioned existing terrestrial network, when comparing the case where the terminal is located at the cell center with the case where it is located at the cell edge, there are large differences in reception level (Srxlev), reception quality (Squal), absolute signal strength (reference signal received power, RSRP), and relative signal quality (reference signal received quality, RSRQ). Therefore, when the terminal is located at the cell center, the problem of reselecting surrounding cells, or the problem of frequent ping-pong cell reselection, is minimal. However, problems may arise if the device supports non-terrestrial networks (NTN) (or satellite networks). The specific details will be explained by referring to Figure 6.

[0098] Figure 6 compares the received signal strength when the terminal is located in the center of a cell and when it is located at the edge of a cell in a terrestrial network or NTN. Referring to Figure 6(a), it can be seen that there is a large difference in the measured values ​​received from the terrestrial network cell (e.g., received level (Srxlev), received quality (Squal), absolute signal strength (reference signal received power: RSRP)) when the terminal is located at the center of the terrestrial network cell or at the edge of the terrestrial network cell.

[0099] On the other hand, referring to Figure 6(b), it can be seen that there is almost no difference in the measured values ​​received from the satellite cell (e.g., received level (Srxlev), received quality (Squal), absolute signal strength (reference signal received power: RSRP)) when the terminal is located at the center of the satellite cell or at the edge of the satellite cell. In this case, even if the terminal is in the center of a satellite cell network, problems may occur, such as re-selecting a surrounding cell or frequent ping-pong cell reselection issues.

[0100] Therefore, in order to solve the aforementioned problems, the present invention proposes an ephemeris-based cell reselection process. The cell reselection process based on the ephemeris proposed in this invention will be explained below with reference to Figure 7.

[0101] Figure 7 shows a procedure according to one embodiment of the present invention in which a base station disconnects a terminal, the terminal switches from RRC connected mode (RRC_CONNECTED) to RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE), and then the terminal in RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE) performs the satellite cell reselection process.

[0102] One embodiment of the present invention proposes a procedure for a terminal in a non-terrestrial network (NTN) that is in RRC inactive mode (RRC_INACTIVE) or RRC idle mode (RRC_IDLE) to perform a satellite cell reselection process. Specifically, the terminals and satellite cells that support NTN have the following characteristics:

[0103] • NTN terminals: Terminals that support NTN have GNSS (Global Navigation Satellite System) capabilities. Terminals that utilize GNSS can determine their own location. For example, a terminal that drives a GNSS can determine its own position based on Earth-centered coordinates. • Satellite cell: The satellite cell provides ephemeris information to terminals supporting NTN via system information. For example, ephemeris information refers to satellite position information. Ephemeris information is provided to NTN-supporting terminals via newly defined system information or existing system information. On the other hand, satellite cells are connected to NR base stations and forward the information provided by the NR base stations to terminals that support NTN. In this invention, "satellite cell" also refers to an NTN base station.

[0104] If the NTN-supporting terminal does not drive GNSS, the cell reselection process is performed according to the embodiment described above. In other words, a terminal that cannot determine its own position performs the cell reselection process according to the embodiment described above. In contrast, if a terminal supporting NTN drives GNSS, it performs the cell reselection process using its own position and ephemeris information provided by the base station. In other words, a terminal that can determine its own location uses its location and ephemeris information provided by the base station to perform the cell reselection process. On the other hand, in this invention, the cell reselection process is performed using ephemeris information provided by the base station, and this is called ephemeris-based cell reselection. In this invention, compared to the cell reselection parameters described in the embodiments described above, a new cell reselection parameter for NTN terminals is introduced, although it serves the same purpose as the cell reselection parameter used for cell reselection. Such a new cell reselection parameter can be broadcast via system information.

[0105] Specifically, if no new cell reselection parameters are introduced for the NTN terminal, the NTN terminal will perform the cell reselection evaluation procedure by applying the cell reselection parameters described in the above embodiment. If new cell reselection parameters are introduced for NTN terminals and broadcast via system information, the NTN terminal will apply the newly introduced cell reselection parameters for cell reselection and perform the cell reselection procedure. In the following explanation, for the sake of clarity, the present invention will primarily focus on the case where a new cell reselection parameter is introduced and the terminal performs the cell reselection process based on the newly introduced cell reselection parameter. However, this is merely for illustrative purposes, and the present invention is not limited thereto.

[0106] Referring to FIG. 7, the NTN terminal (7-01) sets up an RRC connection with the "NTN gNB or satellite cell" (7-02) and is in the RRC connection mode (7-05) (RRC_CONNECTED).

[0107] (7-10) In this stage, the RRC-connected mode terminal (7-01) receives an RRC connection release message (e.g., RRCRelease) from the "NTN gNB or satellite cell" (7-02). The message stores (or includes) configuration information (e.g., suspendConfig) for transitioning to the RRC inactive mode. Alternatively, the message stores one cell reselection priority configuration information for each frequency for each RAT (e.g., NR, EUTRA, etc.) and timer values (e.g., t320 value) that are commonly applicable regardless of RAT. In the present invention, an indicator indicating whether the frequency supported by NTN is included in the message, or a predetermined cell identifier (e.g., Physical Cell Id) representing a satellite cell for each frequency, the type of satellite (low earth orbit, geostationary satellite, HAPS, etc.), and the S IntraSearchP S IntraSearchQ S nonIntraSearchP S nonIntraSearchQ It includes an indicator or information element that can be activated (enable) or deactivated (disable) to determine whether to perform measurement based on the distance difference between the terminal and the serving satellite, considering at least one of them.

[0108] (7-15) In this stage, the terminal (7-01) that has received the RRC connection release message transitions to the RRC idle mode or the RRC inactive mode. If the RRC connection release message stores configuration information for transitioning to the inactive mode, the terminal applies this and transitions to the RRC inactive mode. Otherwise, the terminal transitions to the RRC idle mode.

[0109] (7-20) In step (7-20), terminals (7-01) that are in RRC idle mode or RRC deactivation mode perform the cell selection procedure. The cell selection procedure is as described in the embodiment above.

[0110] In stage (7-25), the terminal (7-01) acquires / receives system information (e.g., SIB3, SIB4, SIB5, etc.) broadcast by the "NTN gNB or satellite cell" (7-02) in order to perform the cell reselection process. In one embodiment of the present invention, in addition to the information specified in the above-described embodiment, "NTN gNB or satellite cell" (7-02) can broadcast the following information via existing system information or new system information.

[0111] • Ephemeris information for the serving (satellite) cell (e.g., SIB2 or new SIB) • Ephemeris information of surrounding (satellite) cells at a given NR frequency (e.g., SIB3, SIB4, or new SIB) ■Includes a (satellite) cell identifier (e.g., PCI) that can identify the (satellite) cell mapped to the ephemeris information.

[0112] • The predetermined distance critical value (Dserving) and offset value (Qoffset) between the terminal and the serving (satellite) cell. location、serving (For example, SIB2 or new SIB) ■Qoffset location、serving If the distance between the terminal and the serving (satellite) cell is less than or equal to the Dserving distance, the terminal will use Qoffset when deriving the serving cell ranking. location、serving Apply this.

[0113] • The predetermined distance critical value (Dneighbor) and offset value (Qoffset) between the terminal and surrounding (satellite) cells. location、neighbor (For example, SIB3 or SIB4 or new SIB) ■Qoffset location、neighborWhen the distance between the terminal and the neighboring (satellite) cell is less than Dneighbor or less than or equal to Dserving, the terminal applies Qoffset when deriving the neighboring cell ranking. location、neighbor Apply it. ■ The Dneighbor value is signaled by frequency and can also be signaled by cell. ■ Qoffset location、neighbor is signaled by frequency and can also be signaled by cell.

[0114] · The aforementioned Dserving and Dneighbor are signaled with one value. · The aforementioned offset (for example, Qoffset location、serving or Qoffset location、neighbor ) can also have different values signaled depending on the type of satellite (low Earth orbit, geostationary satellite, HAPS, etc.). · S IntraSearchP 、S IntraSearchQ 、S nonIntraSearchP 、S nonIntraSearchQ It can also include an indicator or information element that can activate (enable or activate) or deactivate (disable or deactivate) determining whether to perform the measurement based on the distance difference between the terminal and the serving satellite by considering at least one of them.

[0115] For example, based on the distance difference between the terminal and the serving satellite, it can be enabled or disabled to determine whether to perform "intra-frequency" measurement, "inter-frequency" measurement, or "inter-RAT frequency" measurement.

[0116] (In step (7-30), the terminal (7-01) performs an ephemeris based cell reselection evaluation process based on the celestial calendar. The cell reselection evaluation process means the following series of processes.

[0117] • Frequency priority application method (Reselection priorities handling) • Measurement rules for cell reselection (According to one embodiment, these may be modified measurement rules.) • Cell reselection criteria

[0118] The method for applying frequency priority is as described in the embodiment above. The measurement rules are as described in the embodiments mentioned above. In one embodiment of the present invention, the measurement rule described above is applied as a modified measurement rule that can be enabled or disabled to measure surrounding (satellite) cells or the frequencies to which surrounding (satellite) cells belong, based on the distance between the terminal and the serving (satellite) cell. For example, instead of determining whether or not to measure surrounding cells based on the measurement value of the serving (satellite) cell, as in the conventional method, it is also possible to measure surrounding cells only when the distance difference between the terminal and the serving (satellite) cell is less than or equal to a predetermined distance difference. On the other hand, the distance critical value related to a predetermined distance standard is provided to the terminal by the base station through system information or an RRC disconnection message.

[0119] The distance critical value refers to the Dserving mentioned above, or to a separately defined distance critical value. The terminal can enable or disable itself to decide whether or not to perform measurements based on the distance difference to the serving (satellite) cell, or the base station can explicitly enable or disable the decision to perform measurements based on the distance difference to the serving (satellite) cell (for example, through an indicator, the decision to perform serving cell measurements based on the distance difference to the serving (satellite) cell can be enabled or disabled). Alternatively, in one embodiment of the present invention, the measurement rules described above can be applied as modified measurement rules that enable or disable whether to measure the surrounding cell or the frequency to which the surrounding cell belongs, based on the distance between the terminal and the surrounding (satellite) cell.

[0120] For example, it is also possible to measure a surrounding cell or the frequency to which a surrounding cell belongs only if the distance difference between the terminal and the surrounding (satellite) cell is less than or equal to a predetermined distance difference. The distance critical value for a predetermined distance standard is provided to the terminal by the base station via system information or an RRC disconnection message. The distance critical value can refer to the aforementioned Dneighbor, or it can refer to a different predetermined distance critical value. A terminal can enable or disable surrounding cell measurement based on the distance difference to surrounding (satellite) cells, or a base station can explicitly enable or disable surrounding cell measurement based on the distance difference to surrounding (satellite) cells (for example, enabling or disabling surrounding cell measurement through an indicator).

[0121] The cell re-selection evaluation criteria are as described in the embodiment above. If a terminal according to one embodiment of the present invention needs to derive a cell ranking, the cell ranking can be derived through the following formula 3.

number

[0122] Here, ■Qoffset location、serving Qoffset: If the distance between the terminal and the serving (satellite) cell is less than or equal to the distance critical value (e.g., Dserving), then Qoffset location、serving This applies to equation 3. Alternatively, if the distance between the terminal and the serving (satellite) cell is greater than or equal to the distance critical value (e.g., Dserving), Qoffset location、serving This is not used in the derivation of the cell ranking, and in this case, R in formula 2. s The formula for R s This leads to the conclusion.

[0123] ■Qoffset location、neighbor : Qoffset if the distance between the terminal and the surrounding (satellite) cell is less than or equal to the distance critical value (e.g., Dneighbor), or less than or equal to the distance critical value. location、neighbor This applies to equation 3. Alternatively, if the distance between the terminal and the surrounding (satellite) cell is greater than or equal to the distance critical value (e.g., Dneighbor), Qoffset location、neighbor This is not used in the derivation of the cell ranking, and in this case, R in formula 2. n The formula for R n This leads to the conclusion.

[0124] Meanwhile, Qoffset location、serving and Qoffset location、neighbor This may apply only when specified by the satellite frequency, or only to certain surrounding cells specified by the satellite frequency. In other words, for cells that are not satellite cells, the cell ranking is derived without applying an offset. In this case, for cells that are not satellite cells, the cell ranking is derived using Equation 2. Furthermore, according to one embodiment, an offset (for example, Qoffset) location、serving or Qoffset location、neighbor ) may also have different values ​​applied depending on the type of satellite.

[0125] (7-35) In step (7-01) of one embodiment of the present invention, the terminal (7-01) re-selects the "highest ranked cell". Alternatively, you can re-select the "highest ranked cell" from among the cells that meet the distance criteria. If no cell satisfies the distance criteria, the terminal re-selects the cell that satisfies the S criteria and has the shortest distance between the terminal and the cell. Alternatively, the terminal can re-select the cell with the shortest distance between it and the cell. Here, a cell that satisfies the distance condition is a cell whose distance from the terminal is less than (or equal to) a specific distance. Here, the specific distance can be any one of the aforementioned critical distance values, or it can be a value set separately. Alternatively, use an offset (for example, Qoffset). location、serving or Qoffset location、neighbor If this is not implemented, the terminal can also re-select the "highest ranked cell" from among the cells that meet the distance conditions between the terminal and the cell.

[0126] The cell reselection process based on the ephemeris according to one embodiment of the present invention is carried out considering at least one of the following characteristics:

[0127] 1. "nonIntraSearch" (deciding whether to perform "inter-frequency" measurements or "inter-RAT frequency" measurements) and "intraSearch" (deciding whether to perform "intra-frequency" measurements) are activated or disabled based on the distance difference to the serving satellite, not on signal strength (or activated or disabled considering both nonIntraSearch and intraSearch).

[0128] 2. Define the "cell edge condition" based on distance. For example, whether or not the aforementioned cell selection criteria (S criteria) are met is defined based on distance.

[0129] 3. In ephemeris-based "cell reselection," the ephemeris offset is applied only when measuring the ranking of surrounding cells corresponding to a given frequency (for example, the ephemeris offset is applied only to surrounding frequencies indicated by the satellite frequency to determine the cell ranking for the corresponding frequency).

[0130] 4. The serving frequency is used to announce the PCI (physical cell ID) of the surrounding satellite cells, and the terminal then uses an ephemeris offset (e.g., the aforementioned Qoffset) for the surrounding satellite cells. location、serving or Qoffset location、neighbor The cell ranking is determined by applying the ) method, and for non-satellite cells (e.g., cells that are not satellite cells), the cell ranking is determined without applying an offset based on the ephemeris.

[0131] 5. Offset (for example, Qoffset) location、serving or Qoffset location、neighbor This value varies (or is determined) depending on the type of satellite (e.g., low Earth orbit, geostationary satellite, HAPS, etc.).

[0132] 6. The terminal may re-select the "highest ranked cell," or re-select the "highest ranked cell" from among the cells that meet the specified distance conditions, or re-select the cell with the shortest distance between the terminal and the cell (from among the cells that meet the S criteria).

[0133] Figure 8 is a block diagram showing the schematic configuration of a terminal according to one embodiment of the present invention. Referring to Figure 8, the terminal includes an RF (Radio frequency) processing unit (8-10), a baseband processing unit (8-20), a storage unit (8-30), and a control unit (8-40).

[0134] The RF processing unit (8-10) performs functions such as signal bandwidth conversion and amplification for transmitting and receiving signals via the wireless channel. In other words, the RF processing unit (8-10) converts the baseband signal provided by the baseband processing unit (8-20) upwards to an RF band signal and transmits it via the antenna, and converts the RF band signal received via the antenna downwards to a baseband signal. For example, the RF processing unit (8-10) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog converter), an ADC (analog to digital converter), and so on.

[0135] Although only one antenna is shown in the diagram, a terminal can be equipped with multiple antennas. Furthermore, the RF processing unit (8-10) may include multiple RF chains. Furthermore, the RF processing unit (8-10) can perform beamforming. For beamforming, the RF processing unit (8-10) can adjust the phase and intensity of each signal transmitted and received through multiple antennas or antenna elements. Furthermore, the RF processing unit can perform MIMO and receive multiple layers when MIMO operation is performed.

[0136] The baseband processing unit (8-20) performs conversion functions between baseband signals and bit sequences according to the system's PHY hierarchy standard. For example, when transmitting data, the baseband processing unit (8-20) generates a complex symbol by encoding and modulating the transmitted bit sequence. Furthermore, upon receiving data, the baseband processing unit (8-20) reconstructs the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (8-10). For example, when supporting the OFDM (orthogonal frequency division multiplexing) method, during data transmission, the baseband processing unit (8-20) generates a complex symbol by encoding and modulating the transmitted bit sequence, maps the complex symbol to a subcarrier, and then constructs the OFDM symbol by performing an IFFT (inverse fast Fourier transform) operation and inserting a CP (cyclic prefix). Furthermore, upon receiving data, the baseband processing unit (8-20) divides the baseband signal provided by the RF processing unit (8-10) into OFDM symbol units, reconstructs the signal mapped to the subcarrier using the FFT (fast Fourier transform), and then reconstructs the received bit sequence through demodulation and decoding.

[0137] The baseband processing unit (8-20) and the RF processing unit (8-10) transmit and receive signals as described above. As a result, the baseband processing unit (8-20) and the RF processing unit (8-10) can be referred to as the transmitting unit, receiving unit, transceiver unit, or communication unit. Furthermore, at least one of the baseband processing unit (8-20) and the RF processing unit (8-10) may include multiple communication modules to support multiple different wireless connectivity technologies. Furthermore, at least one of the baseband processing unit (8-20) and the RF processing unit (8-10) may include different communication modules for processing signals in different frequency bands. For example, different wireless connectivity technologies may include wireless LAN (e.g., IEEE 802.11) and cellular networks (e.g., LTE). Furthermore, these different frequency bands may include the super high frequency (SHF) band (e.g., 2.NRHz, NRhz) and the millimeter wave (e.g., 60GHz) band.

[0138] The storage unit (8-30) stores data such as basic programs, applications, and configuration information necessary for the operation of the terminal. In particular, the storage unit (8-30) can store information related to a second connection node that performs wireless communication using a second wireless connection technology. The storage unit (8-30) then provides the stored data in response to a request from the control unit (8-40).

[0139] The control unit (8-40) controls the overall operation of the terminal. For example, the control unit (8-40) transmits and receives signals via the baseband processing unit (8-20) and the RF processing unit (8-10). Furthermore, the control unit (8-40) records and reads data from the storage unit (8-40). For this purpose, the control unit (8-40) includes at least one processor. For example, the control unit (8-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls higher layers such as applications.

[0140] Figure 9 is a block diagram showing the schematic configuration of a base station according to one embodiment of the present invention. Referring to Figure 9, the base station includes an RF processing unit (9-10), a baseband processing unit (9-20), a backhaul communication unit (9-30), a storage unit (9-40), and a control unit (9-50).

[0141] The RF processing unit (9-10) performs functions such as signal bandwidth conversion and amplification for transmitting and receiving signals via the wireless channel. In other words, the RF processing unit (9-10) converts the baseband signal provided by the baseband processing unit (9-20) upwards to an RF band signal and transmits it via the antenna, and converts the RF band signal received via the antenna downwards to a baseband signal. For example, the RF processing unit (9-10) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and so on. Although only one antenna is shown in the diagram, the first connection node can be equipped with multiple antennas. Furthermore, the RF processing unit (9-10) may include multiple RF chains. Furthermore, the RF processing unit (9-10) can perform beamforming. For beamforming, the RF processing unit (9-10) adjusts the phase and intensity of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit (9-10) can perform downward MIMO operation by transmitting one or more layers.

[0142] The baseband processing unit (9-20) performs conversion functions between baseband signals and bit sequences according to the PHY layer standard of the first wireless connection technology. For example, when transmitting data, the baseband processing unit (9-20) generates a complex symbol by encoding and modulating the transmitted bit sequence. Furthermore, upon receiving data, the baseband processing unit (9-20) reconstructs the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (9-10). For example, when supporting the OFDM method, during data transmission, the baseband processing unit (9-20) generates a complex symbol by encoding and modulating the transmitted bit sequence, maps the complex symbol to a subcarrier, and then constructs the OFDM symbol by performing an IFFT operation and CP insertion. Furthermore, upon receiving data, the baseband processing unit (9-20) divides the baseband signal provided by the RF processing unit (9-10) into OFDM symbol units, reconstructs the signal mapped to the subcarrier using FFT calculation, and then reconstructs the received bit sequence through demodulation and decoding. The baseband processing unit (9-20) and the RF processing unit (9-10) transmit and receive signals as described above. Thus, the baseband processing unit (9-20) and the RF processing unit (9-10) refer to the transmitting unit, receiving unit, transceiver unit, communication unit, or wireless communication unit.

[0143] The backhaul communication unit (9-30) provides an interface for communicating with other nodes in the network. In other words, the backhaul communication unit (9-30) converts the bit streams transmitted from the main base station to other nodes, such as auxiliary base stations and core networks, into physical signals, and converts the physical signals received from other nodes into bit streams.

[0144] The storage unit (9-40) stores data such as basic programs, applications, and configuration information for the operation of the main base station. In particular, the storage unit (9-40) stores information about bearers assigned to connected terminals, measurement results reported from connected terminals, and so on. Furthermore, the storage unit (9-40) stores information that serves as a criterion for deciding whether to provide or interrupt multiple connections to the terminal. The storage unit (9-40) then provides the stored data in response to a request from the control unit (9-50).

[0145] The control unit (9-50) controls the overall operation of the main base station. For example, the control unit (9-50) transmits and receives signals via the baseband processing unit (9-20) and the RF processing unit (9-10), or the backhaul communication unit (9-30). Furthermore, the control unit (9-50) records and reads data from the storage unit (9-40). For this purpose, the control unit (9-50) includes at least one processor. [Explanation of symbols]

[0146] 1-05, 1-10, 1-15, 1-20 Next generation base station (ENB, NR gNB) 1-25, 3-25 MME 1-30 S-GW 1-35, 3-15 User terminal (UE or terminal) 3-05 NR CN 3-30 eNB 8-10, 9-10 RF Processing Unit 8-20, 9-20 Baseband Processing Unit 8-30, 9-40 Storage Unit 8-40, 9-50 Control Unit 9-30 Backhaul Communications Department

Claims

1. In a method for a terminal in a wireless communication system, The steps include measuring the cell selection reception level value (Srxlev) and the cell selection quality value (Squal) for the serving cell, A step of identifying that the cell selection reception level value of the serving cell is equal to or greater than a first reference value, and that the cell selection quality value of the serving cell is equal to or greater than a second reference value, The process involves receiving distance reference values ​​included in the satellite support information and the associated SIB (System Information Block), A step of identifying the distance between the terminal and the reference position of the serving cell, If the serving cell satisfies the first reference value or higher for the cell selection reception level value and the second reference value or higher for the cell selection quality value, and the distance between the terminal and the reference position of the serving cell is greater than the distance reference value, then the step of measuring at least one adjacent cell, The process includes a step of re-selecting cells based on the measurement of at least one adjacent cell, A terminal method characterized in that if the aforementioned distance reference value is not received, the measurement of at least one adjacent cell is not performed.

2. The terminal method according to claim 1, characterized in that the distance between the terminal and the reference position of the serving cell is greater than the distance reference value.

3. The measurement for at least one adjacent cell is performed as follows: If the aforementioned terminal does not support location measurement for the aforementioned terminal, The terminal method according to claim 1, characterized in that it is not performed in at least one of the cases in which the location information of the terminal is not obtained.

4. The terminal method according to claim 1, characterized in that if the distance between the terminal and the reference position of the serving cell is smaller than the distance reference value, measurement for at least one adjacent cell is not performed.

5. The aforementioned SIB includes ephemeris information, The terminal method according to claim 1, characterized in that the SIB is constantly broadcast from the serving cell.

6. The terminal method according to claim 1, characterized in that the step of measuring at least one adjacent cell includes a step of performing intra-frequency measurements.

7. The step of performing the measurement of at least one adjacent cell is, The step of performing an "NR intra-frequency" measurement having the same or lower priority as the serving cell, or The terminal method according to claim 1, characterized by including at least one of the steps of measuring an "inter-RAT (Radio Access Technology) frequency" having the same or lower priority as the priority of the serving cell.

8. The terminal method according to claim 1, further comprising the step of performing measurements on at least one adjacent cell if the cell selection reception level value is lower than the first reference value or the cell selection quality value is lower than the second reference value.

9. In a terminal of a wireless communication system, Transmitter / receiver unit, It has a control unit coupled with a transmitting / receiving unit, The control unit, The cell selection reception level value (Srxlev) and cell selection quality value (Squal) for the serving cell are measured. Identify that the cell selection reception level value of the serving cell is equal to or greater than the first reference value, and that the cell selection quality value of the serving cell is equal to or greater than the second reference value. It receives distance reference values ​​contained in satellite support information and associated SIBs (System Information Blocks), Identify the distance between the terminal and the reference position of the serving cell, If the serving cell satisfies the first reference value or higher for the cell selection reception level value and the second reference value or higher for the cell selection quality value, and the distance between the terminal and the reference position of the serving cell is greater than the distance reference value, then measure at least one adjacent cell. The system is configured to perform cell reselection based on the measurement of at least one adjacent cell. A terminal characterized in that if the aforementioned distance reference value is not received, measurement of at least one adjacent cell is not performed.

10. The terminal according to claim 9, characterized in that the distance between the terminal and the reference position of the serving cell is greater than the distance reference value.

11. The measurement for at least one adjacent cell is performed as follows: If the aforementioned terminal does not support location measurement for the aforementioned terminal, The terminal according to claim 9, characterized in that the procedure is not performed in at least one of the cases in which the location information of the terminal is not obtained.

12. The terminal according to claim 9, characterized in that if the distance between the terminal and the reference position of the serving cell is smaller than the distance reference value, no measurement is performed for at least one adjacent cell.

13. The aforementioned SIB includes ephemeris information, The terminal according to claim 9, characterized in that the SIB is constantly broadcast from the serving cell.

14. The measurement for at least one adjacent cell is performed as follows: Intra-frequency measurements "NR intra-frequency" measurement having the same or lower priority as the serving cell, or The terminal according to claim 9, characterized in that it includes at least one measurement of an "inter-RAT frequency" having the same or lower priority as the priority of the serving cell.

15. The terminal according to claim 9, wherein the control unit is further configured to perform measurements on at least one adjacent cell if the cell selection reception level value is lower than the first reference value or the cell selection quality value is lower than the second reference value.

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