terminal

Abstract

Provided is a terminal capable of quickly eliminating a PDCP SN gap due to transmission of an incremented count value. The terminal comprises: a control unit that, in a lower layer than a radio resource control layer, executes transition to a candidate cell without requesting a base station for the transition; and a transmission unit that transmits, to the candidate cell, a message including a count value for deriving a necessary security key each time the candidate cell is changed. When the message is not received, the control unit includes, in the message to be transmitted to another candidate cell, a count value obtained by incrementing the count value and an instruction to cause a timer for detecting a packet loss in a packet data convergence protocol (PDCP) layer to expire.

Description

Terminal

[0001] The present disclosure relates to a terminal.

[0002] The 3rd Generation Partnership Project (3GPP (registered trademark)) has developed specifications for 5th generation mobile communication systems (5G, also known as New Radio (NR) or Next Generation (NG)), and is also developing specifications for next-generation mobile communication systems known as Beyond 5G, 5G Evolution, or 6G.

[0003] In 3GPP Release 18, extensions to Layer 1 / Layer 2 mobility (L1 / L2 mobility) are being discussed. L1 / L2 mobility, also known as Lower Layer Triggered Mobility (LTM), is a technology related to the mobility of terminals (User Equipment, UE) in L1 / L2, such as handover (HO) (see Non-Patent Document 1). HO in L1 / L2 is controlled by a lower layer, which is a layer lower than the Radio Resource Control (RRC) layer. As mentioned above, mobility in L1 / L2 is sometimes referred to as LTM, but for convenience of explanation, HO in L1 / L2 will be referred to as LTM below.

[0004] In addition, in LTM, it has been agreed that fast recovery to a candidate cell will be supported when a radio link failure (RLF) or an LTM execution failure (hereinafter also referred to as an LTM failure) occurs (Non-Patent Document 2).

[0005] In LTM, an LTM failure (hereinafter also referred to as an LTM cell switch failure) may occur after an RRC reconfiguration complete message including a count value in the security key derivation (keystream) is transmitted to a candidate cell. In this case, all state variables including the count value are also restored to their original state, and the count value is not incremented. This may result in an RRC reconfiguration complete message including the same count value being transmitted to another candidate cell. In other words, the same count value may be reused (Non-Patent Document 3).

[0006] “Further NR Mobility Enhancements”, RP-222332, 3GPP TSG RAN Meeting #97-e, 3GPP, September 12-16, 2022 “Status Report to TSG”, RP-231311, 3GPP TSG RAN Meeting #100, 3GPP, June 12-14, 2023 “Keystream reuse issue caused by fast recovery after LTM cell switch”, R2-2313310, 3GPP TSG-RAN WG2 Meeting #124, 3GPP, November 13-17, 2023

[0007] Therefore, even if an LTM cell switch failure occurs after the transmission of the RRC reconfiguration complete, it is possible to maintain the increment of the PDCP state variable TX_NEXT count value instead of restoring it to its original value. This prevents the reuse of the count value in the keystream. However, a PDCP SN gap occurs when the incremented count value (N+1) is transmitted instead of the original count value (e.g., N). The PDCP SN gap cannot be resolved until the PDCP t-reordering timer expires. In other words, the UE waits until the PDCP t-reordering timer expires, which may hinder the fast cell transition (fast recovery), which is the original purpose of LTM.

[0008] Therefore, the present disclosure has been made in consideration of such circumstances, and aims to provide a terminal that can quickly eliminate a PDCP SN gap caused by transmitting an incremented count value.

[0009] One aspect of the disclosure is a terminal (UE) (200) that includes: a control unit (control unit 240) that performs a transition to a candidate cell without requesting the transition from a base station at a layer lower than a radio resource control layer; and a transmission unit (transmission / reception unit 210) that transmits a message to the candidate cell including a count value for deriving a security key required each time the candidate cell is changed, and if the message is not received, the control unit includes in the message to be sent to another candidate cell a count value obtained by incrementing the count value and an instruction to expire a timer that detects packet loss in a Packet Data Convergence Protocol (PDCP) layer.

[0010] FIG. 1 is a diagram showing an overall schematic configuration of a wireless communication system. FIG. 2 is a diagram showing a frequency range used in the wireless communication system. FIG. 3 is a diagram showing an example configuration of a wireless frame, subframe, slot, and symbol used in the wireless communication system. FIG. 4 is a functional block diagram of a terminal. FIG. 5 is a functional block diagram of a base station. FIG. 6 is a sequence diagram showing an example of LTM. FIG. 7 is a flowchart showing an example of fast recovery in LTM when RLF / HOF / LTM Failure occurs. FIG. 8 is a sequence diagram showing an example of fast recovery in LTM when BF occurs. FIG. 9 is a flowchart showing an example of fast recovery in LTM when BF occurs. FIG. 10 is a flowchart showing an example of fast recovery when the count value increment is maintained. FIG. 11 is a diagram showing an example of the hardware configuration of a base station and a terminal. FIG. 12 is a diagram showing an example of the configuration of a vehicle.

[0011] Hereinafter, embodiments will be described with reference to the drawings. Note that the same or similar reference numerals are used to designate the same functions or configurations, and descriptions thereof will be omitted as appropriate.

[0012] (1) Overall Schematic Configuration of Wireless Communication System The wireless communication system 10 shown in Fig. 1 is a wireless communication system conforming to a method called 5G. Alternatively, the wireless communication system 10 may be a wireless communication system conforming to a method called Beyond 5G, 5G Evolution, or 6G.

[0013] The wireless communication system 10 can support Massive Multiple-Input Multiple-Output (Massive MIMO), which generates more directional beams by controlling wireless signals transmitted from multiple antenna elements, Carrier Aggregation (CA), which uses multiple component carriers (CCs) as a bundle, and Dual Connectivity (DC), which enables simultaneous communication with two base stations.

[0014] As shown in FIG. 1 , the wireless communication system 10 includes a base station (gNodeB, gNB) 100 connected to a Next Generation-Radio Access Network (NG-RAN) 20, and a terminal (User Equipment, UE) 200 that performs wireless communication with the gNB 100. The NG-RAN 20 is connected to a core network (CN) (not shown). The CN is configured by a network function (NF) such as an access and mobility management function (AMF). The NG-RAN 20 and the CN may be simply referred to as a "network," and may or may not be considered to be included in the wireless communication system 10. Note that the specific configuration of the wireless communication system 10, for example, the number of gNBs 100 and UEs 200, is not limited to the example shown in FIG. 1 .

[0015] The UE 200 of the embodiment supports HO (hereinafter also referred to as LTM) controlled in Layer 1 / Layer 2 (L1 / L2, e.g., Medium Access Control (MAC) layer), which is a layer lower than Layer 3 (L3, e.g., RRC layer). That is, the UE 200 can transition to a selected cell or a candidate cell in a lower layer transition (hereinafter also referred to as an LTM candidate cell or simply as a candidate cell) based on control of a lower layer. LTM has an advantage that the time required for HO is shorter than that of conventional HO controlled in L3. Note that HO may also be referred to as transition hereinafter.

[0016] Furthermore, the UE 200 of the embodiment supports fast recovery in LTM. Fast recovery in LTM is a mechanism in which, similar to that in CHO, when a predetermined condition is satisfied, the UE 200 transitions to a candidate cell without requesting the gNB 100 to transition to the candidate cell. Note that the request for transition to the candidate cell may be interpreted as a request for RRC reconnection to the candidate cell or transmission of an RRC re-establishment request to the candidate cell.

[0017] Fast recovery in LTM is performed, for example, when UE200 detects a communication failure with gNB100. Note that the failure referred to here may be understood as a concept including not only the above-mentioned RLF and LTM Failure, but also handover failure (HOF) and beam failure (BF). In other words, RLF, LTM Failure, HOF, and BF may be interpreted as interchangeable in terms of a communication failure with gNB100.

[0018] The wireless communication system 10 may also support multiple frequency ranges (FR). That is, as shown in Fig. 2, the wireless communication system 10 may support the following FRs: FR1: 410 MHz to 7.125 GHz FR2-1: 24.25 GHz to 52.6 GHz FR2-2: Over 52.6 GHz to 71 GHz

[0019] In FR1, a subcarrier spacing (SCS) of 15, 30, or 60 kHz and a bandwidth (BW) of 5 to 100 MHz may be used, while in FR2-1, an SCS of 60 or 120 kHz (including 240 kHz) and a BW of 50 to 400 MHz may be used.

[0020] In FR2-2, to avoid an increase in phase noise, Cyclic Prefix-Orthogonal Frequency Division Multiplexing (CP-OFDM) or Discrete Fourier Transform-Spread-Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) with a larger SCS may be applied.

[0021] 3, one slot in the wireless communication system 10 is composed of 14 symbols. If this configuration is maintained, the larger (wider) the SCS, the shorter the symbol period (and slot period). Note that the SCS is not limited to the frequencies shown in FIG. 3 and may be, for example, 480 kHz, 960 kHz, or other frequencies.

[0022] Furthermore, the number of symbols constituting one slot does not necessarily have to be 14, but may be, for example, 28 or 56. Furthermore, the number of slots per subframe may differ depending on the SCS.

[0023] (2) Functional Block Configuration of Wireless Communication System (2.1) Functional Block Configuration of Terminal As shown in FIG. 4, the UE 200 includes a transceiver unit 210, a detection / reporting unit 220, a generation unit 230, and a control unit 240.

[0024] The transceiver 210 transmits and receives radio signals to and from the gNB 100. Note that the transceiver 210 may be configured as a transmitter that transmits radio signals to the gNB 100 and a receiver that receives radio signals from the gNB 100.

[0025] The transceiver 210 of the embodiment transmits a measurement report to the gNB 100. The measurement report includes a conventional measurement report transmitted in L3 (e.g., an RRC layer) and an L1 measurement report transmitted in L1 (see FIG. 6 ). The transceiver 210 also transmits various messages, such as an RRC reconfiguration complete message, to the gNB 100. Note that the measurement report may be generated by the generator 230 when a failure is detected by the detector 220. Similarly, various messages may be generated by the generator 230.

[0026] The transceiver 210 of the embodiment can transmit a message (e.g., RRC reconfiguration complete) including a count value to the LTM candidate cell. The count value is a parameter for deriving a security key required each time the LTM candidate cell is changed in the LTM. The count value may be an incremented count value, as described below. The increment may be interpreted as, for example, setting the count value, which is N, to N+1.

[0027] The transceiver 210 of the embodiment receives a reconfiguration message (e.g., RRC Reconfiguration) from the gNB 100 in the RRC layer. The reconfiguration message may include various IEs, such as configuration information related to low layer transition (LTM) (e.g., LTM-Config). The reconfiguration message of the embodiment may particularly include reconfiguration information related to LTM (e.g., attemptLTM-Reconfig, attemptLTM-switch), and may further include configuration information for BFR related to an LTM candidate cell (e.g., BFR-Config for LTM). Note that attemptLTM-Reconfig and attemptLTM-switch are tentative names, and other names may be used as long as the IEs have the same function. The same applies to other IEs. IEs that may be included in the reconfiguration message will be described in detail in the section on operation examples.

[0028] In the embodiment, the transceiver 210 may receive, at the MAC layer, a MAC Control Element (CE) from the gNB 100. The MAC CE may include a Cell switch command (see FIG. 6).

[0029] The detection unit 220 detects various types of failures such as the above-mentioned RLF, LTM Failure, HOF, and BF. Specifically, the detection unit 220 measures the quality of a serving cell formed by the gNB 100 or the quality of a beam within the serving cell, and compares it with a predetermined threshold to determine whether a communication failure has occurred with the gNB 100. The detection unit 220 can also measure the quality of an LTM candidate cell, or the quality of another beam within the serving cell or a beam within the LTM candidate cell. Note that the quality of these cells or beams may be determined to be good or bad by, for example, the control unit 240, by comparing them with a predetermined threshold.

[0030] The detector 220 may output the measurement result to the generator 230 so that the generator 230 generates a measurement report. The detector 220 may also output the measurement result to the controller 240 so that the controller 240 performs cell selection or beam selection in LTM.

[0031] The generation unit 230 generates a measurement report and various messages, which will be described in detail in the section on operation examples.

[0032] The control unit 240 controls the transmission and reception of radio signals by the transceiver unit 210, the detection of various types of failures by the detector unit 220, the measurement reports by the generator unit 230, and the generation of various types of messages.

[0033] The control unit 240 in the embodiment executes HO of the UE 200. The control unit 240 may execute HO in L3, or may execute HO (LTM) in L1 / L2. Note that executing HO / LTM may mean executing HO / LTM based on control (HO / LTM determination) by the control unit 130 of the gNB 100, but particularly in the embodiment, it may mean executing fast recovery not based on HO / LTM determination by the gNB 100. In other words, the control unit 240 can transition to an LTM candidate cell without requesting the gNB 100 to transition to an LTM candidate cell. The transition to an LTM candidate cell by the control unit 240 will be briefly described below.

[0034] That is, the control unit 240 can select a cell in HO / LTM and transition to the selected cell (selected cell). At this time, if the selected cell is an LTM candidate cell and the above-mentioned LTM-related reconfiguration information is included in the reconfiguration message transmitted from the gNB 100, the control unit 240 applies the configuration related to this LTM candidate cell and can transition to the LTM candidate cell without requesting the gNB 100 to transition to the LTM candidate cell. A more detailed sequence will be described in detail in the section on operation examples (see FIG. 7 ). Note that the cell selection may be performed based on the above-mentioned measurement results, and the LTM candidate cell may be interpreted as a cell formed by the gNB 100 that supports LTM. Furthermore, the selected cell may be a cell to which transition is determined, and the candidate cell may be a cell to which transition is possible.

[0035] Furthermore, in HO / LTM, the control unit 240 can transition to an LTM candidate cell without selecting a cell. That is, the control unit 240 can determine an LTM candidate cell to transition to from among the LTM candidate cells based on a predetermined threshold, and transition to the LTM candidate cell. In this case, the control unit 240 applies the settings related to the LTM candidate cell, and can transition to the LTM candidate cell without requesting the gNB 100 to transition to the LTM candidate cell. Note that a more detailed sequence will be described in the section on operation examples (see FIG. 7).

[0036] Furthermore, before executing HO / LTM, the control unit 240 can acquire a TA for the LTM candidate cell from the gNB 100 via the transceiver unit 210. The TA is a parameter that advances the transmission timing for the LTM candidate cell. When the UE 200 holds a TA for the LTM candidate cell, it can transition to the LTM candidate cell without performing random access to the gNB 100 (omitting random access). Note that when the UE 200 does not hold a TA for the LTM candidate cell, it can transition to the LTM candidate cell by performing random access to the gNB 100. The former is also referred to as RACH-less fast recovery, and the latter is also referred to as RACH-based fast recovery.

[0037] Furthermore, in HO / LTM, if the selected cell is not an LTM candidate cell, or if the reconfiguration information related to the LTM described above is not included in the reconfiguration message transmitted from the gNB 100, the control unit 240 may request the gNB 100 to transition to an LTM candidate cell. Specifically, the control unit 240 may transmit an RRC re-establishment request to the gNB 100.

[0038] Furthermore, the control unit 240 may start a timer after applying the above-described setting related to the LTM candidate cell. This timer is, for example, an LTM-timer described later. If this timer expires before transition to the LTM candidate cell, the control unit 240 may request the gNB 100 to transition to the LTM candidate cell. Specifically, the control unit 240 may transmit an RRC re-establishment request to the gNB 100.

[0039] Furthermore, the control unit 240 may select a beam in the serving cell in HO / LTM and perform BFR. In particular, when the configuration information for BFR related to the LTM candidate cell described above is included in the reconfiguration message transmitted from the gNB 100, the control unit 240 of the embodiment can select a beam in the LTM candidate cell. For example, when a beam in the serving cell is equal to or lower than a predetermined threshold, a beam in the LTM candidate cell (exceeding the predetermined threshold) can be selected. Note that there may be multiple beams in the serving cell, and in this case, when all beams in the serving cell are equal to or lower than the predetermined threshold, a beam in the LTM candidate cell (exceeding the predetermined threshold) may be selected. Details of various configuration information (IEs) that may be included in the reconfiguration message will be described later, but the main ones will be described below.

[0040] The reconfiguration message may include configuration information related to the LTM candidate cell, and the BFR configuration information related to the LTM candidate cell may not be included in the configuration information related to the LTM candidate cell. Also, the BFR configuration information related to the LTM candidate cell may include DL configuration information and UL configuration information, and at least one of the DL configuration information and the UL configuration information may include information related to the beam in the LTM candidate cell.

[0041] Furthermore, when the quality of the beam in the serving cell described above exceeds a predetermined threshold, the control unit 240 may select a beam in the serving cell instead of selecting a beam in the LTM candidate cell. Furthermore, when the quality of the beam in the LTM candidate cell described above is equal to or lower than a predetermined threshold, the control unit 240 may request the gNB100 to transition to the LTM candidate cell. Specifically, the control unit 240 may transmit an RRC re-establishment request to the gNB100.

[0042] The control unit 240 according to the embodiment can include the count value in the RRC reconfiguration complete transmitted by the transceiver unit 210.

[0043] In the embodiment, the control unit 240 increments the count value (N) after the transceiver unit 210 transmits an RRC reconfiguration complete including the count value (N) in the LTM. As a result, when performing LTM again, the control unit 240 can include the incremented count value (N+1) in the RRC reconfiguration complete transmitted by the transceiver unit 210 to other LTM candidate cells. With this mechanism, a secure connection with each LTM candidate cell can be established in the LTM.

[0044] Furthermore, even if an LTM cell switch failure occurs after the transceiver unit 210 transmits an RRC reconfiguration complete including the count value (N), the control unit 240 of the embodiment can maintain the increment of the count value without returning the incremented count value (N+1) to the original count value (N).

[0045] In the embodiment, when an LTM cell switch failure occurs, that is, when the RRC reconfiguration complete transmitted to the LTM candidate cell is not received, or when the original count value (N) is not used normally, the control unit 240 can include an incremented count value (N+1) in the RRC reconfiguration complete transmitted by the transceiver unit 210 to another LTM candidate cell when performing LTM again. In this case, the control unit 240 can include, in the RRC reconfiguration complete transmitted by the transceiver unit 210 to another LTM candidate cell, an instruction to cause the gNB 100 to expire a timer (e.g., a t-reordering timer) that detects packet loss in the Packet Data Convergence Protocol (PDCP) layer. Alternatively, the control unit 240 can include, in the RRC reconfiguration complete transmitted by the transceiver unit 210 to another LTM candidate cell, an instruction to stop and reset this timer. The term "packet" may be replaced with terms such as data unit, protocol data unit (PDU), and service data unit (SDU).

[0046] The control unit 240 of the embodiment can include an instruction to clear buffer data of the PDCP layer in the RRC reconfiguration complete transmitted by the transceiver unit 210 to other LTM candidate cells.

[0047] The control unit 240 according to the embodiment can include an instruction indicating that the LTM is an intra-CU LTM in the RRC reconfiguration complete transmitted to other LTM candidate cells by the transceiver unit 210. Note that LTM may be interchangeably read as LTM fast recovery.

[0048] In the embodiment, the control unit 240 can include an instruction to consider the packet of the count value (N), i.e., the count value before incrementing, as already received in the RRC reconfiguration complete sent by the transceiver unit 210 to other LTM candidate cells.

[0049] The control unit 240 of the embodiment can include the count value (N), i.e., a dummy packet of the count value before incrementing, in the RRC reconfiguration complete transmitted by the transceiver unit 210 to other LTM candidate cells.

[0050] In the embodiment, the control unit 240 can include an instruction indicating that the RRC reconfiguration complete is to be treated as out of order delivery in the RRC reconfiguration complete transmitted to other LTM candidate cells by the transceiver unit 210. Note that out of order delivery may mean that a packet or a message is not in the transmission order.

[0051] (2.2) Functional block configuration of base station As shown in FIG. 5, the gNB 100 includes a transceiver unit 110, a generator unit 120, and a controller unit 130.

[0052] The transmission / reception unit 110 transmits and receives radio signals to and from the UE 200. Note that the transmission / reception unit 110 may be configured as a transmission unit that transmits radio signals to the UE 200 and a reception unit that receives radio signals from the UE 200.

[0053] The transceiver 110 of the embodiment transmits a reconfiguration message (e.g., RRC Reconfiguration) to the UE 200 in the RRC layer. The reconfiguration message may include various IEs, such as configuration information (e.g., LTM-Config) related to low layer transition (LTM). The reconfiguration message of the embodiment may particularly include reconfiguration information related to LTM (e.g., attemptLTM-Reconfig, attemptLTM-switch), and may further include configuration information for BFR related to an LTM candidate cell (e.g., BFR-Config for LTM). Note that IEs that may be included in the reconfiguration message will be described in detail in the section on operation examples.

[0054] The transceiver 110 according to the embodiment may transmit a MAC Control Element (CE) in the MAC layer to the UE 200. The MAC CE may include a Cell switch command (see FIG. 6).

[0055] The transceiver 110 of the embodiment receives the above-mentioned measurement report and various messages from the UE 200.

[0056] The generation unit 120 generates various messages such as the above-mentioned reset message and Cell switch command.

[0057] The control unit 130 controls the transmission and reception of radio signals by the transmission and reception unit 110 and the generation of various messages by the generation unit 120 .

[0058] The control unit 130 of the embodiment may prepare an LTM candidate cell based on the measurement report received via the transceiver unit 110. Furthermore, configuration information related to this LTM candidate cell may be included in the above-mentioned reconfiguration message.

[0059] Furthermore, the control unit 130 may control HO / LTM of the UE 200. The control unit 130 may control HO in L3, or may control HO (LTM) in L1 / L2. Note that controlling HO / LTM may mean determining HO / LTM by the UE 200.

[0060] (3) Operation of Wireless Communication System (3.1) Issues (3.1.1) Issue 1 Fast recovery in LTM, similar to that in conditional handover (CHO), is a mechanism for transitioning to a candidate cell when certain conditions are met without requesting a base station to transition to the candidate cell. However, fast recovery in LTM differs from fast recovery in CHO in the parts involving the RRC layer, which poses a problem in that the fast recovery mechanism in CHO cannot be applied as is. In fast recovery in CHO, if the cell selected by the UE for reconnection after a failure occurs is a candidate cell and if reconfigurationWithSync is present, fast recovery is performed; if reconfigurationWithSync is not present, an RRC re-establishment request is transmitted. This problem poses a problem in that such a mechanism cannot be applied as is to fast recovery in LTM.

[0061] (3.1.2) Problem 2 When a beam failure occurs in LTM, if another beam in the serving cell does not satisfy a predetermined condition (for example, the quality of the other beam exceeds a predetermined threshold), the base station is requested to transition to a candidate cell other than the serving cell. However, even in such a case, there are cases where a beam in the candidate cell satisfies the predetermined condition. In such cases, there is a demand for recovering from the beam failure by utilizing a beam in the candidate cell that satisfies the predetermined condition.

[0062] (3.1.3) Issue 3: Even if an LTM cell switch failure occurs after the transmission of an RRC reconfiguration complete, it is possible to maintain the increment of the PDCP state variable TX_NEXT count value instead of restoring it to its original value. This prevents the reuse of the count value in the keystream. However, a PDCP SN gap occurs when an incremented count value (N+1) is transmitted instead of the original count value (e.g., N). The PDCP SN gap cannot be resolved until the PDCP t-reordering timer expires. In other words, the UE must wait until the PDCP t-reordering timer expires, which may hinder the fast cell transition (fast recovery), which is the original purpose of LTM.

[0063] (3.2) Operational Example (3.2.0) Overview The LTM sequence that is the premise of the operational example will be explained with reference to Figure 6. The LTM sequence is roughly executed in the following order: LTM preparation (step S01), early sync (step S02), LTM execution (step S03), and LTM completion (step S04).

[0064] First, assuming that UE200 is in an RRC connected state with gNB100, UE200 transmits a measurement report to gNB100 (step S01-1). The measurement report includes, for example, measurement results for the quality of the serving cell of UE200. Next, gNB100 prepares an LTM candidate cell (step S01-2) and transmits an RRC reconfiguration message to UE200 (step S01-3). The RRC reconfiguration message includes LTM-Config. LTM-Config includes, for example, LTM-CandidateConfig, which is configuration information for the LTM candidate cell. In response to this, UE200 transmits an RRC reconfiguration complete message (step S01-4).

[0065] Next, UE200 performs DL / UL early synchronization with the LTM candidate cell formed by gNB100 (step S02). Specifically, DL / UL early synchronization is performed using SSB / RACH or the like. This allows UE200 to acquire a TA for the LTM candidate cell. TA is a parameter that advances the transmission timing for the LTM candidate cell. Note that UE200 does not need to acquire a TA for the LTM candidate cell.

[0066] Next, UE200 transmits an L1 measurement report to gNB100 (step S03-1). The L1 measurement report includes, for example, measurement results for the quality of the serving cell of UE200. Next, gNB100 determines an LTM (step S03-2) and transmits a MAC CE to UE200 (step S03-3). The MAC CE includes a cell change command. In response to this, UE200 releases its connection with the serving cell and applies settings related to the LTM candidate cell (step S03-4). Finally, UE200 performs RACH with gNB100 (step S03-5), thereby completing the transition to the LTM candidate cell (step S04). Note that if UE200 holds a TA, step S03-5 can be omitted.

[0067] (3.2.1) Operation Example 1 Operation example 1 will be described with reference to Figures 6 and 7. In operation example 1, LTM-Config (see step S01-3) may include an IE indicating that UE 200 supports LTM fast recovery. This IE is, for example, attemptLTM-Reconfig, which is reconfiguration information related to low layer transition. As described above, attemptLTM-Reconfig is a provisional name, and any other name may be used as long as the IE has the function of causing UE 200 to support fast recovery in LTM.

[0068] Furthermore, the RRC reconfiguration message (see step S01-3) may include not only LTM-Config but also other IEs necessary for UE 200 to support LTM fast recovery. The other IEs may be, for example, SpCellConfig. SpCellConfig includes, for example, LTM-CellSwitchInfo, which is information related to a cell change in a lower layer, and LTM-timer, which is a timer for determining completion of fast recovery in LTM.

[0069] First, when UE200 detects RLF / HOF / LTM Failure in the LTM sequence shown in FIG. 6 (specifically, step S02 or step S03) (step S11), it measures the quality of the LTM candidate cell, and if it exceeds a predetermined threshold, it decides to transition to the LTM candidate cell (YES in step S12). Furthermore, when LTM-Config includes attemptLTM-Reconfig (YES in step S15), UE200 transitions to the LTM candidate cell determined in YES in step S12. Specifically, it applies the configuration (LTM-CandidateConfig) related to the LTM candidate cell, and can perform fast recovery from step S16 onwards, which will be described later. In LTM, for example, in the above-mentioned steps S01-3, a reference signal (RS) of the LTM candidate cell may be configured in advance for UE200, and UE200 can measure the quality of the LTM candidate cell based on this RS.

[0070] On the other hand, if the quality of the LTM candidate cell does not exceed the predetermined threshold (NO in step S12), UE200 selects a cell to reconnect to (transition destination cell) (step S13). UE200 may also start timer T311 when starting cell selection. Note that step S12 may be omitted, and in that case, the process proceeds from step S11 to step S13.

[0071] If the cell selected in step S13 (hereinafter also referred to as selected cell) is an LTM candidate cell (YES in step S14) and if attemptLTM-Reconfig is included in LTM-Config (YES in step S15), UE200 applies the configuration (LTM-CandidateConfig) related to the LTM candidate cell and can execute fast recovery from step S16 onwards, which will be described later. Note that, for the reasons described above, "LTM-Config includes attemptLTM-Reconfig" may be interpreted as "LTM-Config includes attemptLTM-Reconfig, and SpCellConfig includes CellSwitchInfo and LTM-timer".

[0072] After applying the LTM-CandidateConfig in step S15 (YES), the UE 200 may start the LTM-timer included in the SpCellConfig. The LTM-timer may be, for example, the timer T304.

[0073] After YES in step S15, if UE200 has acquired TA in the above-mentioned step S02 (YES in step S16), UE200 executes RACH-less fast recovery (step S17-1). RACH-less fast recovery allows transition to an LTM candidate cell without executing RACH, i.e., random access, to gNB100 (i.e., transmitting RRCReconfigurationComplete according to the resource allocation of the UL grant previously set by gNB100), thereby shortening the time required for recovery. Note that if the TA acquired by UE200 is not valid (for example, if the TA timer has expired), YES in step S16 may be interpreted as NO in step S16, and the process may proceed to step S17-2, which will be described later.

[0074] If RACH-less fast recovery is successful (YES in step S18-1), the flow ends. If RACH-less fast recovery fails because the LTM-timer expires before fast recovery is completed (NO in step S18-1), the UE 200 requests the gNB 100 to transition to an LTM candidate cell (step S19). Specifically, the UE 200 transmits an RRC re-establishment request. After transmitting the RRC re-establishment request, the UE 200 may start a timer T301.

[0075] On the other hand, if the UE 200 has not acquired the TA in step S02 (NO in step S16), the UE 200 executes RACH-based fast recovery (step S17-2). The RACH-based fast recovery executes RACH, i.e., random access, to the gNB 100 to transition to an LTM candidate cell (see step S03).

[0076] If the RACH-based fast recovery is successful (YES in step S18-2), the flow ends. If the RACH-based fast recovery fails because the LTM-timer expires before the fast recovery is completed (NO in step S18-2), the UE 200 requests the gNB 100 to transition to an LTM candidate cell (step S19). Specifically, the UE 200 transmits an RRC re-establishment request. After transmitting the RRC re-establishment request, the UE 200 may start a timer T301.

[0077] Furthermore, if the results of steps S14 and S15 are NO, UE200 may proceed to step S19 and may start timer T301 in step S19. Specifically, if the selected cell is not an LTM candidate cell (NO in step S14) or if attemptLTM-Reconfig is not included in LTM-Config (NO in step S15), UE200 proceeds to step S19. Note that, for the reasons described above, "LTM-Config does not include attemptLTM-Reconfig, or SpCellConfig does not include either CellSwitchInfo or LTM-timer."

[0078] (3.2.2) Operation Example 2 Operation Example 2 will be described with reference to Fig. 8 and Fig. 9. First, fast recovery in LTM when BF occurs will be described with reference to Fig. 8. The fast recovery sequence in LTM when BF occurs has many parts in common with the LTM sequence shown in Fig. 6. For example, step S22 is common to the above-mentioned step S02, so its description will be omitted.

[0079] Also, in step S21, steps S21-1, S21-2, and S21-4 are common to steps S01-1, S01-2, and S01-4, respectively, and therefore description thereof will be omitted. Therefore, only step S21-3 will be described. In step S21-3, the gNB 100 transmits an RRC reconfiguration message to the UE 200. The RRC reconfiguration message includes an LTM-Config. The LTM-Config includes, for example, an LTM-CandidateConfig, which is configuration information for an LTM candidate cell. Furthermore, the RRC reconfiguration message includes a configuration for performing beam failure recovery (BFR) for the LTM candidate cell (hereinafter also referred to as a BFR configuration for the LTM candidate cell, or a BFR-Config for LTM). The BFR-Config for LTM is configuration information for BFR related to the LTM candidate cell.

[0080] The BFR-Config for LTM may be located below the LTM-Config in terms of the hierarchy of IEs included in the RRC reconfiguration message, but may also be located above it. In other words, the BFR-Config for LTM may be located so as to be included in the LTM-Config, but may also be located so as not to be included in the LTM-Config. Similarly, the BFR-Config for LTM may be located below the LTM-CandidateConfig included in the LTM-Config, but may also be located above it. In other words, the BFR-Config for LTM may be located so as to be included in the LTM-CandidateConfig, but may also be located so as not to be included in the LTM-CandidateConfig. In the latter case, the BFR-Config for LTM may be located so as to be included in the LTM-Config, but not to be included in the LTM-CandidateConfig.

[0081] The BFR-Config for LTM may include, for example, BWP-Downlink, which is configuration information for the downlink related to the LTM candidate cell, and BWP-Uplink, which is configuration information for the uplink related to the LTM candidate cell.

[0082] The BWP-Downlink may include IEs such as BWP-Id, BWP-Common, and BWP-Dedicated. The BWP-Dedicated may include BeamFailureRecoveryRSConfig. Furthermore, the BeamFailureRecoveryRSConfig may include configuration information related to the beam of the LTM candidate cell (UL configuration information). Specifically, the CandidateBeamRSList in the BeamFailureRecoveryRSConfig may include configuration information related to the beam of the LTM candidate cell (UL configuration information).

[0083] The BWP-Uplink may include IEs such as BWP-Id, BWP-Common, and BWP-Dedicated. The BWP-Dedicated may include BeamFailureRecoveryConfig. Furthermore, the BeamFailureRecoveryConfig may include configuration information related to the beam of the LTM candidate cell (downlink configuration information). Specifically, the CandidateBeamRSList in the BeamFailureRecoveryConfig may include configuration information related to the beam of the LTM candidate cell (downlink configuration information).

[0084] As described above, in step S21-3, the configuration information for BFR related to the LTM candidate cell may be configured for the UE 200, and further, the configuration information related to the beam of the LTM candidate cell may be configured.

[0085] Furthermore, UE200 may select a beam in an LTM candidate cell when it holds both BeamFailureRecoveryRSConfig and BeamFailureRecoveryConfig.

[0086] Returning to FIG. 8 , step S23 will be described. It is assumed that BF occurs after step S22, which has not been described, is completed. In L1, UE200 measures the quality of a beam in a serving cell formed by gNB100 or the quality of a beam in a candidate cell (step S23-1). Since the RS for measuring the beam quality is the same as in Operation Example 1, detailed description thereof will be omitted. After measuring the beam quality, UE200 selects a beam whose beam quality exceeds a predetermined threshold and performs BFR (step S23-2). Furthermore, UE200 applies the settings for the selected new beam (step S23-3). Finally, UE200 performs RACH with gNB100 (step S23-4), thereby completing the selection of a new beam (step S24). If UE200 maintains TA, step S23-4 can be omitted.

[0087] Note that the second operation example may be applied to either the inter-CU LTM or the intra-CU LTM.

[0088] Finally, with reference to Figure 9, a specific flow of fast recovery in LTM when BF occurs will be described. First, when UE200 detects BF in the LTM sequence when BF occurs (for example, between step S02 and step S03) shown in Figure 8 (step S31), and when BFR-Config for LTM is configured in the above-mentioned step S21-3 (YES in step S32), it measures beams in the same cell (serving cell). When the quality of the beam with the best quality among the beams in the serving cell exceeds a predetermined threshold (YES in step S33-1), UE200 performs BFR to the beam with the best quality (using the beam with the best quality) using BeamFailureRecoveryConfig of the serving cell (step S34). Note that BeamFailureRecoveryConfig may be included in the RRC reconfiguration message in the above-mentioned step S21-3 and configured in UE200.

[0089] On the other hand, if the BFR-Config for LTM is not set in the above-mentioned step S21-3 (NO in step S32), UE200 may search for a beam within the same cell (serving cell) (step S33-2) and proceed to step S34.

[0090] Returning to step S33-1, UE200 measures the beam in the LTM candidate cell if the quality of the beam with the best quality among the beams in the serving cell is equal to or less than a predetermined threshold (NO in step S33-1). If the quality of the beam with the best quality among the beams in the LTM candidate cell exceeds a predetermined threshold (YES in step S35), UE200 performs BFR to the beam with the best quality (using the beam with the best quality) using the BFR-Config for LTM (step S36-1).

[0091] On the other hand, if the quality of the beam with the best quality among the beams in the LTM candidate cell is equal to or lower than a predetermined threshold (NO in step S35), the UE 200 requests the gNB 100 to transition to the LTM candidate cell (step S36-2). Specifically, the UE 200 transmits an RRC re-establishment request. After transmitting the RRC re-establishment request, the UE 200 may start a timer T301.

[0092] (3.2.3) Operation Example 3 Operation Example 3 will be described with reference to Fig. 10 . As a premise of Operation Example 3, it is assumed that an IE indicating that UE 200 supports LTM fast recovery, for example, attemptLTM-switch, which is reconfiguration information related to low layer transition, is configured in UE 200. Note that, as described above, attemptLTM-switch is a provisional name, and any other name may be used as long as the IE has the function of causing UE 200 to support fast recovery in LTM. Furthermore, Operation Example 3 will be described as being applied to SRB1, as will be described later, but is not limited to this, and may be applied to other SRBs or DRBs.

[0093] Furthermore, the gNB100 in Operation Example 3 is not limited to being a Master Node (MN) in the DC, and may be a Secondary Node (SN). Accordingly, the LTM in Operation Example 3 may be replaced with an inter-SN PSCell LTM.

[0094] The UE 200 receives a Cell switch command from the connected cell X. Note that this Cell switch command may be understood to be the same as the Cell switch command in step S03-3 of FIG.

[0095] Here, if an LTM failure occurs, UE 200 performs cell selection while timer T311 is running. If the selected cell is an LTM candidate cell (e.g., Cell A in the figure), a RACH-based LTM cell switch procedure is performed (RACH in the figure).

[0096] Next, the UE 200 transmits RRCReconfigurationComplete including the count value (N) to the cell A via the SRB1. At this time, the UE 200 increments the count value (N) in the SRB1 to N+1.

[0097] Here, suppose that the transmission of RRCReconfigurationComplete is unsuccessful and an LTM cell switch failure occurs (for example, the timer T304 expires). In this case, the UE 200 does not need to restore the incremented count value (N+1) in the SRB1 to the source-configured count value (N). That is, the UE 200 can maintain the incremented count value (N+1).

[0098] Furthermore, UE200 performs cell selection again and selects another LTM candidate cell (for example, Cell B in the figure). UE200 transmits RRCReconfigurationComplete including the incremented count value (N+1) to Cell B via SRB1. Here, in order to eliminate the waiting of UE200 due to the occurrence of the above-mentioned PDCP SN gap, that is, to eliminate the delay due to the occurrence of the PDCP SN gap, UE200 can include at least one of the following a to f in the RRCReconfigurationComplete transmitted to Cell B.

[0099] a: An instruction to expire the t-reordering timer in gNB100, or an instruction to stop and reset the t-reordering timer b: An instruction to clear PDCP buffer data c: An instruction indicating intra-CU LTM fast recovery d: An instruction to consider the packet of PDCP SN with count value (N) in gNB100 as already received (for example, to advance RX_DELIV to the next) e: A dummy PDCP PDU (empty data) with count value (N) *In the case of e, instead of including a dummy PDCP PDU (empty data) with count value (N) in RRCReconfigurationComplete, a dummy PDCP PDU (empty data) with count value (N) may be sent before RRCReconfigurationComplete. f: An instruction to treat the RRCReconfigurationComplete message itself as out of order delivery

[0100] Furthermore, the instructions a to d may be transmitted in any of the following locations: PDCP header PDCP control PDU MAC CE, MAC PDU header, PUCCH

[0101] Furthermore, upon receiving instructions a to d, or f (or dummy e), the gNB100 may perform at least one of the following actions A to E. A: Immediately expire the t-reordering timer in the gNB100. Perform the action described in TS38.323 Chapter 5.2.2.2. B: Immediately stop the t-reordering timer in the gNB100 and reset the t-reordering timer. C: Shorten the timer value of the t-reordering timer in the gNB100 (for example, 0 ms or 1 ms). D: The gNB100 considers the packet of the PDCP SN with count value (N) as having been received (for example, advances RX_DELIV to the next). E: The gNB100 treats the RRCReconfigurationComplete message containing instructions a to d, or f (or dummy e) as out of order delivery.

[0102] (4) Actions and Effects According to the above-described Operation Example 1, the mechanism of fast recovery in LTM is streamlined, enabling wireless communication that is resistant to RLF / HOF / LTM Failure. Also, according to the above-described Operation Example 2, the mechanism of BFR in LTM is improved, enabling wireless communication that is resistant to BF.

[0103] Furthermore, according to the above-described operation example 3, when preventing reuse of the keystream in intra-CU LTM fast recovery, it is possible to suppress the delay caused by the PDCP SN gap.

[0104] (5) Other Embodiments The contents of the present invention have been described above in accordance with the embodiments, but it will be obvious to those skilled in the art that the present invention is not limited to these descriptions and that various modifications and improvements are possible.

[0105] In the above disclosure, "exceeding a predetermined threshold" may be read as "above a predetermined threshold." In this case, "below a predetermined threshold" shall be read as "below a predetermined threshold."

[0106] In the above disclosure, step S12 for checking whether a good LTM candidate exists may be omitted, but other steps may also be omitted as appropriate. For example, step S16 for determining whether UE 200 holds a TA may be omitted, and the process may proceed to step S17-2 for executing RACH-based fast recovery. Also, steps S02 and S22 for performing early sync may be omitted, and in this case, the omission of step S16 described above may be combined.

[0107] In the above disclosure, the wireless communication system 10 may include a relay station (not shown) that relays wireless communication between the UE 200 and the gNB 100. The relay station is, for example, a satellite such as a geostationary Earth orbit (GEO) satellite, a middle Earth orbit (MEO) satellite, or a low Earth orbit (LEO) satellite. The relay station may also be a high altitude platform station (HAPS) mounted on an airship, a balloon, or a commercial aircraft (air to ground, ATG). When a relay station is included, propagation delay tends to be large, so RACH-less fast recovery by obtaining the TA in advance as described above is more effective.

[0108] The above-described operation examples may be combined and applied in a composite manner, as long as no contradiction occurs.

[0109] In the above disclosure, configure, activate, update, indicate, enable, specify, and select may be interchangeable. Similarly, link, associate, correspond, and map may be interchangeable, and allocate, assign, monitor, and map may be interchangeable.

[0110] Furthermore, specific, dedicated, UE-specific, and UE-dedicated may be interchangeable. Similarly, common, shared, group-common, UE-common, and UE-shared may be interchangeable.

[0111] The block diagrams (FIGS. 4 and 5) used to explain the above-described embodiments show functional blocks. These functional blocks (components) are realized by any combination of hardware and / or software. Furthermore, the method for realizing each functional block is not particularly limited. That is, each functional block may be realized using a single device that is physically or logically coupled, or may be realized using two or more physically or logically separated devices that are directly or indirectly connected (e.g., wired, wireless, etc.) and these multiple devices. The functional block may be realized by combining software with the single device or multiple devices.

[0112] Functions include, but are not limited to, judgment, determination, judgment, calculation, computation, processing, derivation, investigation, search, confirmation, reception, transmission, output, access, resolution, selection, election, establishment, comparison, assumption, expectation, regard, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, and assignment. For example, a functional block (component) that performs transmission is called a transmitting unit or transmitter. As mentioned above, there are no particular limitations on how each is implemented.

[0113] Furthermore, the above-described gNB 100 and UE 200 (the devices) may function as a computer that performs processing of the wireless communication method of the present disclosure. Figure 11 is a diagram showing an example of the hardware configuration of the devices. As shown in Figure 11, the devices may be configured as a computer including a processor 1001, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, etc.

[0114] In the following description, the term "apparatus" can be interpreted as a circuit, a device, a unit, etc. The hardware configuration of the apparatus may be configured to include one or more of the apparatuses shown in the drawings, or may be configured to exclude some of the apparatuses.

[0115] Each functional block of the device (FIGS. 4 and 5) is realized by any hardware element of the computer device or a combination of the hardware elements.

[0116] In addition, each function of the device is realized by loading specified software (programs) onto hardware such as processor 1001 and memory 1002, causing processor 1001 to perform calculations, control communication via communication device 1004, and control at least one of reading and writing data in memory 1002 and storage 1003.

[0117] The processor 1001 controls the entire computer by running, for example, an operating system, and may be configured as a central processing unit (CPU) including an interface with peripheral devices, a control unit, an arithmetic unit, and registers.

[0118] The processor 1001 also reads programs (program codes), software modules, data, etc. from at least one of the storage 1003 and the communication device 1004 into the memory 1002 and executes various processes in accordance with these. The programs used are those that cause a computer to execute at least some of the operations described in the above-described embodiments. Furthermore, the various processes described above may be executed by a single processor 1001, or may be executed simultaneously or sequentially by two or more processors 1001. The processor 1001 may be implemented by one or more chips. The programs may be transmitted from a network via a telecommunications line.

[0119] The memory 1002 is a computer-readable recording medium and may be configured by at least one of, for example, a read-only memory (ROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a random access memory (RAM), etc. The memory 1002 may also be called a register, a cache, a main memory (primary storage device), etc. The memory 1002 may store a program (program code), a software module, etc., capable of executing a method according to an embodiment of the present disclosure.

[0120] Storage 1003 is a computer-readable recording medium, and may be, for example, at least one of an optical disk such as a Compact Disc ROM (CD-ROM), a hard disk drive, a flexible disk, a magneto-optical disk (e.g., a compact disk, a digital versatile disk, a Blu-ray disc), a smart card, a flash memory (e.g., a card, a stick, a key drive), a floppy disk, a magnetic strip, etc. Storage 1003 may also be referred to as an auxiliary storage device. The above-mentioned recording medium may be, for example, a database, a server, or other suitable medium including at least one of memory 1002 and storage 1003.

[0121] The communication device 1004 is hardware (transmission / reception device) for communicating between computers via at least one of a wired network and a wireless network, and is also called, for example, a network device, a network controller, a network card, or a communication module.

[0122] The communication device 1004 may be configured to include a high-frequency switch, a duplexer, a filter, a frequency synthesizer, etc. to realize, for example, at least one of Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

[0123] The input device 1005 is an input device (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, etc.) that receives input from the outside. The output device 1006 is an output device (e.g., a display, a speaker, an LED lamp, etc.) that outputs to the outside. Note that the input device 1005 and the output device 1006 may be integrated into one device (e.g., a touch panel).

[0124] Furthermore, each device such as the processor 1001 and the memory 1002 is connected to a bus 1007 for communicating information. The bus 1007 may be configured using a single bus, or may be configured using different buses between each device.

[0125] Furthermore, the device may be configured to include hardware such as a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA), and some or all of the functional blocks may be realized by the hardware. For example, the processor 1001 may be implemented using at least one of these pieces of hardware.

[0126] Furthermore, the notification of information is not limited to the aspects / embodiments described in the present disclosure, and may be performed using other methods. For example, the notification of information may be performed by physical layer signaling (e.g., Downlink Control Information (DCI), Uplink Control Information (UCI)), higher layer signaling (e.g., RRC signaling, Medium Access Control (MAC) signaling), broadcast information (Master Information Block (MIB), System Information Block (SIB)), other signals, or a combination thereof. Furthermore, the RRC signaling may be referred to as an RRC message, and may be, for example, an RRC Connection Setup message, an RRC Connection Reconfiguration message, or the like.

[0127] Each aspect / embodiment described in the present disclosure may be applied to at least one of a system using Long Term Evolution (LTE), LTE-Advanced (LTE-A), SUPER 3G, IMT-Advanced, a 4th generation mobile communication system (4G), a 5th generation mobile communication system (5G), Future Radio Access (FRA), New Radio (NR), W-CDMA (registered trademark), GSM (registered trademark), CDMA2000, Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, Ultra-WideBand (UWB), Bluetooth (registered trademark), or other suitable system, and a next-generation system enhanced based on these. Furthermore, a combination of multiple systems (e.g., a combination of at least one of LTE and LTE-A and 5G) may also be applied.

[0128] The order of the procedures, sequences, flowcharts, etc. of each aspect / embodiment described in this disclosure may be changed unless it is consistent. For example, the methods described in this disclosure present elements of various steps using an example order, and are not limited to the particular order presented.

[0129] In the present disclosure, a specific operation described as being performed by a base station may be performed by its upper node in some cases. In a network consisting of one or more network nodes having a base station, it is clear that various operations performed for communication with a terminal may be performed by at least one of the base station and another network node other than the base station (for example, an MME or an S-GW, etc., but are not limited to these). Although the above example illustrates a case where there is one other network node other than the base station, a combination of multiple other network nodes (for example, an MME and an S-GW) may also be used.

[0130] Information, signals (information, etc.) may be output from a higher layer (or a lower layer) to a lower layer (or a higher layer), or may be input / output via multiple network nodes.

[0131] The input and output information may be stored in a specific location (for example, a memory) or may be managed using a management table. The input and output information may be overwritten, updated, or added. The output information may be deleted. The input information may be transmitted to another device.

[0132] The determination may be made based on a value represented by one bit (0 or 1), a Boolean value (true or false), or a numerical comparison (e.g., comparison with a predetermined value).

[0133] The aspects / embodiments described in this disclosure may be used alone, in combination, or switched depending on the implementation. Notification of predetermined information (e.g., notification that "X is true") is not limited to explicit notification, but may be implicit (e.g., not notifying the predetermined information).

[0134] Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0135] Software, instructions, information, etc. may also be transmitted or received over a transmission medium. For example, if software is transmitted from a website, server, or other remote source using wired technologies (such as coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL)), and / or wireless technologies (such as infrared, microwave), then these wired and / or wireless technologies are included within the definition of transmission media.

[0136] The information, signals, etc. described in this disclosure may be represented using any of a variety of different technologies. For example, data, instructions, commands, information, signals, bits, symbols, chips, etc. that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, optical fields or photons, or any combination thereof.

[0137] Note that terms described in this disclosure and terms necessary for understanding this disclosure may be replaced with terms having the same or similar meanings. For example, at least one of a channel and a symbol may be a signal (signaling). Furthermore, a signal may be a message. Furthermore, a component carrier (CC) may be called a carrier frequency, a cell, a frequency carrier, etc.

[0138] As used in this disclosure, the terms "system" and "network" are used interchangeably.

[0139] Furthermore, the information, parameters, etc. described in the present disclosure may be expressed using absolute values, may be expressed using relative values ​​from a predetermined value, or may be expressed using other corresponding information. For example, a radio resource may be indicated by an index.

[0140] The names used for the above-described parameters are not intended to be limiting in any way. Furthermore, the mathematical expressions using these parameters may differ from those explicitly disclosed in this disclosure. The various channels (e.g., PUCCH, PDCCH, etc.) and information elements may be identified by any suitable names, and therefore the various names assigned to these various channels and information elements are not intended to be limiting in any way.

[0141] In this disclosure, terms such as "base station (BS)," "radio base station," "fixed station," "NodeB," "eNodeB (eNB)," "gNodeB (gNB)," "access point," "transmission point," "reception point," "transmission / reception point," "cell," "sector," "cell group," "carrier," and "component carrier" may be used interchangeably. Base stations may also be referred to by terms such as macrocell, small cell, femtocell, and picocell.

[0142] A base station can accommodate one or more (e.g., three) cells (also called sectors). When a base station accommodates multiple cells, the overall coverage area of ​​the base station can be divided into multiple smaller areas, and each smaller area can be provided with communication services by a base station subsystem (e.g., a small indoor base station (Remote Radio Head: RRH)).

[0143] The terms "cell" or "sector" refer to part or all of the coverage area of ​​a base station and / or base station subsystem that provides communication services within that coverage area.

[0144] In this disclosure, the terms "Mobile Station (MS)," "user terminal," "User Equipment (UE)," "terminal," etc. may be used interchangeably.

[0145] A mobile station may also be referred to by those skilled in the art as a subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, or some other suitable terminology.

[0146] At least one of the base station and the mobile station may be referred to as a transmitting device, a receiving device, a communication device, etc. At least one of the base station and the mobile station may be a device mounted on a mobile object, the mobile object itself, etc. The mobile object may be a vehicle (e.g., a car, an airplane, etc.), an unmanned mobile object (e.g., a drone, an autonomous vehicle, etc.), or a robot (manned or unmanned). At least one of the base station and the mobile station may also include devices that do not necessarily move during communication operations. For example, at least one of the base station and the mobile station may be an Internet of Things (IoT) device such as a sensor.

[0147] Furthermore, a base station in the present disclosure may be read as a mobile station (user terminal, the same applies hereinafter). For example, the aspects / embodiments of the present disclosure may be applied to a configuration in which communication between a base station and a mobile station is replaced with communication between multiple mobile stations (which may be called, for example, Device-to-Device (D2D) or Vehicle-to-Everything (V2X)). In this case, the mobile station may be configured to have the functions of a base station. Furthermore, terms such as "uplink" and "downlink" may be read as terms corresponding to terminal-to-terminal communication (for example, "side"). For example, terms such as an uplink channel and a downlink channel may be read as a side channel.

[0148] Similarly, a mobile station in the present disclosure may be interpreted as a base station, in which case the base station may have the functions of a mobile station.

[0149] A radio frame may be made up of one or more frames in the time domain, each of which may be called a subframe.

[0150] A subframe may further be composed of one or more slots in the time domain, and may have a fixed time length (e.g., 1 ms) that is independent of numerology.

[0151] Numerology may be communication parameters that apply to the transmission and / or reception of a signal or channel, such as subcarrier spacing (SCS), bandwidth, symbol length, cyclic prefix length, transmission time interval (TTI), number of symbols per TTI, radio frame structure, specific filtering operations performed by the transceiver in the frequency domain, and specific windowing operations performed by the transceiver in the time domain.

[0152] A slot may consist of one or more symbols in the time domain (such as Orthogonal Frequency Division Multiplexing (OFDM) symbols, Single Carrier Frequency Division Multiple Access (SC-FDMA) symbols, etc.) A slot may be a time unit based on numerology.

[0153] A slot may include multiple minislots. Each minislot may consist of one or multiple symbols in the time domain. A minislot may also be called a subslot. A minislot may consist of fewer symbols than a slot. A PDSCH (or PUSCH) transmitted in a time unit larger than a minislot may be called PDSCH (or PUSCH) mapping type A. A PDSCH (or PUSCH) transmitted using a minislot may be called PDSCH (or PUSCH) mapping type B.

[0154] The radio frame, subframe, slot, minislot, and symbol all represent time units for transmitting signals, and may be referred to by other names corresponding to the radio frame, subframe, slot, minislot, and symbol.

[0155] For example, one subframe may be referred to as a transmission time interval (TTI), multiple consecutive subframes may be referred to as a TTI, or one slot or one minislot may be referred to as a TTI. That is, at least one of the subframe and the TTI may be a subframe (1 ms) in existing LTE, a period shorter than 1 ms (e.g., 1-13 symbols), or a period longer than 1 ms. Note that the unit representing the TTI may be referred to as a slot, minislot, etc. instead of a subframe.

[0156] Here, TTI refers to, for example, the smallest time unit for scheduling in wireless communication. For example, in an LTE system, a base station schedules each user terminal to allocate radio resources (such as frequency bandwidth and transmission power that can be used by each user terminal) in TTI units. Note that the definition of TTI is not limited to this.

[0157] The TTI may be a transmission time unit for a channel-encoded data packet (transport block), a code block, a code word, etc., or may be a processing unit for scheduling, link adaptation, etc. When a TTI is given, the time interval (e.g., the number of symbols) to which a transport block, a code block, a code word, etc. is actually mapped may be shorter than the TTI.

[0158] In addition, when one slot or one minislot is called a TTI, one or more TTIs (i.e., one or more slots or one or more minislots) may be the minimum time unit for scheduling. Furthermore, the number of slots (minislots) constituting the minimum time unit for scheduling may be controlled.

[0159] A TTI having a time length of 1 ms may be called a regular TTI (TTI in LTE Rel. 8-12), normal TTI, long TTI, regular subframe, normal subframe, long subframe, slot, etc. A TTI shorter than a regular TTI may be called a shortened TTI, short TTI, partial or fractional TTI, shortened subframe, short subframe, minislot, subslot, slot, etc.

[0160] In addition, a long TTI (e.g., a normal TTI, a subframe, etc.) may be interpreted as a TTI having a time length of more than 1 ms, and a short TTI (e.g., a shortened TTI, etc.) may be interpreted as a TTI having a TTI length shorter than the TTI length of a long TTI and equal to or greater than 1 ms.

[0161] A resource block (RB) is a resource allocation unit in the time domain and the frequency domain, and may include one or more consecutive subcarriers in the frequency domain. The number of subcarriers included in an RB may be the same regardless of numerology, for example, 12. The number of subcarriers included in an RB may be determined based on numerology.

[0162] The time domain of an RB may include one or more symbols and may have a length of one slot, one minislot, one subframe, or one TTI. One TTI, one subframe, etc. may each be composed of one or more resource blocks.

[0163] Note that one or more RBs may also be called a physical resource block (PRB), a sub-carrier group (SCG), a resource element group (REG), a PRB pair, an RB pair, etc.

[0164] Furthermore, a resource block may be composed of one or more resource elements (REs). For example, one RE may be a radio resource region of one subcarrier and one symbol.

[0165] A Bandwidth Part (BWP) (which may also be referred to as a fractional bandwidth) may represent a subset of contiguous common resource blocks (RBs) for a given numerology on a given carrier, where the common RBs may be identified by their index relative to a common reference point of the carrier. PRBs may be defined in a given BWP and numbered within that BWP.

[0166] The BWP may include a BWP for UL (UL BWP) and a BWP for DL ​​(DL BWP). One or more BWPs may be configured for a UE within one carrier.

[0167] At least one of the configured BWPs may be active, and the UE may not expect to transmit or receive a given signal / channel outside the active BWP. Note that the terms "cell," "carrier," etc. in this disclosure may be read as "BWP."

[0168] The above-described structures of radio frames, subframes, slots, minislots, symbols, etc. are merely examples. For example, the number of subframes included in a radio frame, the number of slots per subframe or radio frame, the number of minislots included in a slot, the number of symbols and RBs included in a slot or minislot, the number of subcarriers included in an RB, the number of symbols in a TTI, the symbol length, the cyclic prefix (CP) length, etc. may be variously changed.

[0169] The terms "connected," "coupled," or any variation thereof, refer to any direct or indirect connection or coupling between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The coupling or connection between elements may be physical, logical, or a combination thereof. For example, "connected" may be read as "access." As used in this disclosure, two elements may be considered to be "connected" or "coupled" to each other using one or more wires, cables, and / or printed electrical connections, as well as electromagnetic energy having wavelengths in the radio frequency range, microwave range, and optical (both visible and invisible) range, as some non-limiting and non-exhaustive examples.

[0170] The reference signal may also be abbreviated as Reference Signal (RS) and may be called a pilot depending on the applicable standard.

[0171] As used in this disclosure, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

[0172] The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc.

[0173] As used in this disclosure, any reference to an element using a designation such as "first," "second," etc. does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way.

[0174] When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, similar to the term "comprising." Furthermore, when the term "or" is used in this disclosure, it is not intended to be an exclusive or.

[0175] In this disclosure, where articles are added by translation, such as a, an, and the in English, the disclosure may include that the nouns following these articles are in the plural form.

[0176] As used in this disclosure, the terms "determining" and "determining" may encompass a wide variety of actions. "Determining" and "determining" may include, for example, judging, calculating, computing, processing, deriving, investigating, looking up, searching, inquiring (e.g., searching a table, database, or other data structure), ascertaining, and the like. "Determining" and "determining" may also include receiving (e.g., receiving information), transmitting (e.g., sending information), input, output, accessing (e.g., accessing data in memory), and the like, all of which are considered to be "determining." "Determining" and "determining" may also include resolving, selecting, choosing, establishing, comparing, and the like, all of which are considered to be "determining." In other words, "judgment" and "decision" can include regarding some action as having been "judged" or "decided." Also, "judgment (decision)" can be interpreted as "assuming," "expecting," "considering," etc.

[0177] In the present disclosure, the term "A and B are different" may mean "A and B are different from each other." The term may also mean "A and B are each different from C." Terms such as "separate" and "coupled" may also be interpreted in the same way as "different."

[0178] 12 shows an example of the configuration of a vehicle 2001. As shown in Fig. 12, the vehicle 2001 includes a drive unit 2002, a steering unit 2003, an accelerator pedal 2004, a brake pedal 2005, a shift lever 2006, left and right front wheels 2007, left and right rear wheels 2008, an axle 2009, an electronic control unit 2010, various sensors 2021 to 2029, an information service unit 2012, and a communication module 2013.

[0179] The drive unit 2002 is composed of, for example, an engine, a motor, or a hybrid of an engine and a motor.

[0180] The steering unit 2003 includes at least a steering wheel (also called a handle) and is configured to steer at least one of the front wheels and the rear wheels based on the operation of the steering wheel operated by the user.

[0181] The electronic control unit 2010 is composed of a microprocessor 2031, a memory (ROM, RAM) 2032, and a communication port (IO port) 2033. Signals are input to the electronic control unit 2010 from various sensors 2021 to 2027 provided in the vehicle. The electronic control unit 2010 may also be called an ECU (Electronic Control Unit).

[0182] The signals from the various sensors 2021 to 2028 include a current signal from a current sensor 2021 that senses the current of the motor, a rotation speed signal of the front and rear wheels obtained by a rotation speed sensor 2022, an air pressure signal of the front and rear wheels obtained by an air pressure sensor 2023, a vehicle speed signal obtained by a vehicle speed sensor 2024, an acceleration signal obtained by an acceleration sensor 2025, an accelerator pedal depression amount signal obtained by an accelerator pedal sensor 2029, a brake pedal depression amount signal obtained by a brake pedal sensor 2026, a shift lever operation signal obtained by a shift lever sensor 2027, and a detection signal for detecting obstacles, vehicles, pedestrians, etc. obtained by an object detection sensor 2028.

[0183] The information service unit 2012 is composed of various devices, such as a car navigation system, an audio system, speakers, a television, and a radio, for providing various types of information such as driving information, traffic information, and entertainment information, and one or more ECUs for controlling these devices. The information service unit 2012 uses information obtained from external devices via the communication module 2013, etc., to provide various types of multimedia information and multimedia services to the occupants of the vehicle 1.

[0184] The driving assistance system unit 2030 is composed of various devices that provide functions for preventing accidents and reducing the driver's driving burden, such as millimeter-wave radar, LiDAR (Light Detection and Ranging), cameras, positioning locators (e.g., GNSS, etc.), map information (e.g., high-definition (HD) maps, autonomous vehicle (AV) maps, etc.), gyro systems (e.g., IMU (Inertial Measurement Unit), INS (Inertial Navigation System), etc.), AI (Artificial Intelligence) chips, and AI processors, as well as one or more ECUs that control these devices. The driving assistance system unit 2030 also transmits and receives various information via the communication module 2013 to realize driving assistance functions or autonomous driving functions.

[0185] The communication module 2013 can communicate with the microprocessor 2031 and components of the vehicle 1 via the communication port. For example, the communication module 2013 transmits and receives data via the communication port 2033 to and from a driving unit 2002, a steering unit 2003, an accelerator pedal 2004, a brake pedal 2005, a shift lever 2006, left and right front wheels 2007, left and right rear wheels 2008, an axle 2009, a microprocessor 2031 and memory (ROM, RAM) 2032 in the electronic control unit 2010, and sensors 2021 to 2028, which are provided in the vehicle 2001.

[0186] The communication module 2013 is a communication device that can be controlled by the microprocessor 2031 of the electronic control unit 2010 and can communicate with an external device. For example, it transmits and receives various information to and from the external device via wireless communication. The communication module 2013 may be located either inside or outside the electronic control unit 2010. The external device may be, for example, a base station, a mobile station, or the like.

[0187] The communication module 2013 transmits, via wireless communication to an external device, a current signal from the current sensor that is input to the electronic control unit 2010. The communication module 2013 also transmits, via wireless communication to an external device, the rotation speed signals of the front and rear wheels acquired by a rotation speed sensor 2022, the air pressure signals of the front and rear wheels acquired by an air pressure sensor 2023, the vehicle speed signal acquired by a vehicle speed sensor 2024, the acceleration signal acquired by an acceleration sensor 2025, the accelerator pedal depression amount signal acquired by an accelerator pedal sensor 2029, the brake pedal depression amount signal acquired by a brake pedal sensor 2026, the shift lever operation signal acquired by a shift lever sensor 2027, and the detection signals for detecting obstacles, vehicles, pedestrians, etc. acquired by an object detection sensor 2028, all of which are input to the electronic control unit 2010.

[0188] The communication module 2013 receives various information (traffic information, traffic signal information, vehicle distance information, etc.) transmitted from external devices and displays it on an information service unit 2012 provided in the vehicle. The communication module 2013 also stores the various information received from the external devices in a memory 2032 that can be used by the microprocessor 2031. Based on the information stored in the memory 2032, the microprocessor 2031 may control the drive unit 2002, steering unit 2003, accelerator pedal 2004, brake pedal 2005, shift lever 2006, left and right front wheels 2007, left and right rear wheels 2008, axle 2009, sensors 2021 to 2028, and the like provided in the vehicle 2001.

[0189] Although the present disclosure has been described in detail above, it is clear to those skilled in the art that the present disclosure is not limited to the embodiments described herein. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure as defined by the claims. Therefore, the description of the present disclosure is intended to be illustrative and does not have any limiting meaning on the present disclosure.

[0190] (Additional Note) The above disclosure may be expressed as follows.

[0191] A first feature of the terminal is that it includes: a control unit, at a layer lower than a radio resource control layer, that executes a transition to a candidate cell without requesting the transition from a base station to the candidate cell; and a transmission unit that transmits to the candidate cell a message including a count value for deriving a necessary security key each time the candidate cell is changed, wherein, if the message is not received, the control unit transmits the message to another candidate cell including a count value obtained by incrementing the count value and an instruction to expire a timer that detects packet loss in a Packet Data Convergence Protocol (PDCP) layer.

[0192] A second feature is the terminal according to the first feature, wherein the control unit includes an instruction to clear buffer data of the PDCP layer in the message transmitted to the other candidate cell.

[0193] A third feature is the terminal according to the first or second feature, wherein the control unit includes, in the message transmitted to the other candidate cell, an instruction indicating that the transition is an intra-CU transition.

[0194] A fourth feature is a terminal according to any one of the first to third features, wherein the control unit includes, in the message transmitted to the other candidate cell, an instruction to consider the packets of the count value as having been received.

[0195] A fifth feature is the terminal according to any one of the first to fourth features, wherein the control unit includes a dummy of the packet of the count value in the message transmitted to the other candidate cell.

[0196] A sixth feature is the terminal according to any one of the first to fifth features, wherein the control unit includes, in the message transmitted to the other candidate cell, an instruction indicating that the message is to be treated as out of order delivery.

[0197] 10 Wireless communication system 20 NG-RAN 100 gNB 110 Transceiver unit 120 Generator unit 130 Controller 200 UE 210 Transceiver unit 220 Detector unit 230 Generator unit 240 Controller 1001 Processor 1002 Memory 1003 Storage 1004 Communication device 1005 Input device 1006 Output device 1007 Bus 2001 Vehicle 2002 Drive unit 2003 Steering unit 2004 Accelerator pedal 2005 Brake pedal 2006 Shift lever 2007 Left and right front wheels 2008 Left and right rear wheels 2009 Axle 2010 Electronic control unit 2012 Information service unit 2013 Communication module 2021 Current sensor 2022 Rotation speed sensor 2023 Air pressure sensor 2024 Vehicle speed sensor 2025 Acceleration sensor 2026 Brake pedal sensor 2027 Shift lever sensor 2028 Object detection sensor 2029 Accelerator pedal sensor 2030 Driving assistance system section 2031 Microprocessor 2032 Memory (ROM, RAM) 2033 Communication port

Claims

1. A terminal comprising: a control unit that performs a transition to a candidate cell without requesting the transition from a base station in a layer lower than a radio resource control layer; and a transmission unit that transmits a message to the candidate cell including a count value for deriving a necessary security key each time the candidate cell is changed, wherein if the message is not received, the control unit transmits the message to another candidate cell including a count value obtained by incrementing the count value and an instruction to expire a timer that detects packet loss in a Packet Data Convergence Protocol (PDCP) layer.

2. The terminal according to claim 1, wherein the control unit includes an instruction to clear buffer data of the PDCP layer in the message transmitted to the other candidate cell.

3. The terminal according to claim 1, wherein the control unit includes, in the message transmitted to the other candidate cell, an indication indicating that the transition is an intra-CU transition.

4. The terminal according to claim 1, wherein the control unit includes, in the message transmitted to the other candidate cell, an instruction to regard the packets of the count value as having been received.

5. The terminal according to claim 1, wherein the control unit includes a dummy for the packet of the count value in the message transmitted to the other candidate cell.

6. The terminal according to claim 1, wherein the control unit includes, in the message transmitted to the other candidate cell, an instruction indicating that the message is to be treated as out of order delivery.

Images