Wireless base station

Abstract

This wireless base station receives from a terminal a measurement report including reception quality for a peripheral cell of the terminal. During handover using primary / secondary cells, the wireless base station selects, as a secondary cell, a peripheral cell estimated to be close to the handover source cell on the basis of the reception quality, and sets a secondary cell group including the primary / secondary cells.

Description

[Technical field]

[0001] The present disclosure relates to a radio base station that supports handover using primary and secondary cells. [Background technology]

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

[0003] For example, it has been agreed to study radio resource management (RRM) for NR-NR Dual Connectivity (NR-DC) and Multi-RAT Dual Connectivity (MR-DC) (Non-Patent Document 1).

[0004] Specifically, handover using a primary / secondary cell (PSCell) (HO with PSCell) is being considered for dual connectivity. In HO with PSCell, before a terminal (User Equipment, UE) executes a handover, the primary cell (PCell) of the handover destination (target) sets up a secondary cell group (SCG) including radio base stations (eNBs or gNBs, which may be read as cells) around the UE, and establishes dual connectivity as soon as the handover is completed. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "WID of REL-17 NR RRM further enhancement", RP-202053, 3GPP TSG RAN Meeting #89-e, 3GPP, September 2020 Summary of the Invention

[0006] However, the above-mentioned HO with PSCell has the following problem: Specifically, there is no standard for how to select a PSCell and an SCell that are included in the SCG for the handover destination PCell, and there is a concern that appropriate dual connectivity cannot necessarily be achieved even if the radio base stations (cells) around the UE are simply included in the SCG.

[0007] Therefore, the following disclosure has been made in consideration of the above circumstances, and aims to provide a radio base station that can execute HO with PSCell while setting an appropriate SCG.

[0008] One aspect of the present disclosure is a radio base station (radio base station 100) comprising a receiver (measurement report processing unit 120) that receives from a terminal (UE 200) a measurement report including reception quality for cells surrounding the terminal, and a control unit (control unit 140) that, in a handover using a primary and secondary cell, selects as a secondary cell the surrounding cell that is estimated to be close to a source cell of handover based on the reception quality, and sets a secondary cell group including the primary and secondary cells.

[0009] One aspect of the present disclosure is a radio base station comprising: a transceiver unit (control signal / reference signal processing unit 130) that transmits and receives reference signals to and from a terminal (UE 200); and a control unit (control unit 140) that, in a handover using a primary / secondary cell, selects a neighboring cell that is estimated to be close to the source cell of the handover as a secondary cell based on the reception state of the reference signal, and sets a secondary cell group including the secondary cell.

[0010] One aspect of the present disclosure is a radio base station (radio base station 100) comprising a receiving unit (measurement report processing unit 120) that receives measurement reports on neighboring cells from a terminal (UE 200), and a control unit (control unit 140) that estimates traffic volume in the neighboring cells based on the measurement reports, selects the neighboring cells whose traffic volume is smaller than a specified value as secondary cells, and, during handover, sets a secondary cell group including the secondary cell.

[0011] One aspect of the present disclosure is a radio base station (radio base station 100) comprising a receiving unit (control signal / reference signal processing unit 130) that receives capability information of a terminal (UE 200) from the terminal, and a control unit (control unit 140) that selects a neighboring cell of the terminal as a secondary cell according to the capability of the terminal based on the capability information, and sets a secondary cell group including the secondary cell in a handover using primary and secondary cells.

[0012] One aspect of the present disclosure is a radio base station (radio base station 100) that includes a control unit (control unit 140) that sets multiple secondary cell groups including secondary cells in a handover using primary and secondary cells, and a transceiver unit (radio communication unit 110) that transmits and receives radio signals via cells included in the secondary cell groups, and the control unit selects one of the secondary cell groups depending on the connection state of a terminal with the cells. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an overall schematic configuration of a wireless communication system 10. As shown in FIG. [Diagram 2] FIG. 2 is a diagram showing an example of handover using a PSCell (HO with PSCell). [Diagram 3] FIG. 3 is a functional block diagram of the wireless base station 100. [Figure 4] FIG. 4 is a functional block diagram of UE 200. [Diagram 5]FIG. 5 is a diagram showing a schematic communication sequence of SCG (cell) selection. [Figure 6] FIG. 6 is a diagram showing a flow of cell selection and handover operations of the radio base station 100 according to the first operation example. [Figure 7] FIG. 7 is a diagram showing a flow of cell selection and handover operations of the radio base station 100 according to the second operation example. [Figure 8] FIG. 8 is a diagram showing a flow of cell selection and handover operations of the radio base station 100 according to the third operation example. [Figure 9] FIG. 9 is a diagram showing a flow of cell selection and handover operations of the radio base station 100 according to the fourth operation example. [Figure 10] FIG. 10 is a diagram illustrating an example of a hardware configuration of the radio base station 100 and the UE 200. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment 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 the description thereof will be omitted as appropriate.

[0015] (1) Overall configuration of wireless communication system 1 is a schematic diagram of an overall configuration of a wireless communication system 10 according to the present embodiment. The wireless communication system 10 is a wireless communication system conforming to Long Term Evolution (LTE) and 5G New Radio (NR). Note that LTE may be called 4G, and NR may be called 5G.

[0016] In addition, LTE and NR may be interpreted as radio access technologies (RATs), and in this embodiment, LTE may be referred to as a first radio access technology, and NR may be referred to as a second radio access technology.

[0017] The wireless communication system 10 includes a radio access network 20 (hereinafter, RAN 20) and a user equipment 200 (hereinafter, UE 200).

[0018] The RAN 20 includes a radio base station 100. The radio base station 100 may be a gNB conforming to NR or an eNB conforming to LTE. A specific configuration of the radio communication system 10 including the number of gNBs / eNBs and UEs is not limited to the example shown in FIG. 1.

[0019] The wireless communication system 10 supports FR1 and FR2. The frequency bands of each FR are as follows.

[0020] FR1: 410MHz~7.125GHz FR2: 24.25GHz~52.6GHz FR1 may use a Sub-Carrier Spacing (SCS) of 15, 30 or 60 kHz and a bandwidth (BW) of 5 to 100 MHz. FR2 is a higher frequency than FR1, and may use an SCS of 60 or 120 kHz (240 kHz may be included) and a bandwidth (BW) of 50 to 400 MHz.

[0021] Furthermore, the wireless communication system 10 may also support a frequency band higher than the FR2 frequency band. Specifically, the wireless communication system 10 may support a frequency band exceeding 52.6 GHz up to 114.25 GHz.

[0022] The radio base station 100 performs radio communication according to LTE or NR with the UE 200. The radio base station 100 and the UE 200 can support Massive MIMO, which generates a more directional beam by controlling radio signals transmitted from multiple antenna elements, Carrier Aggregation (CA), which uses a bundle of multiple component carriers (CCs), and Dual Connectivity (DC), which simultaneously communicates between the UE and each of multiple NG-RAN nodes.

[0023] The type of DC may be Multi-RAT Dual Connectivity (MR-DC) that uses multiple radio access technologies, or NR-NR Dual Connectivity (NR-DC) that uses only NR. In addition, MR-DC may be E-UTRA-NR Dual Connectivity (EN-DC) in which the eNB constitutes the master node (MN) and the gNB constitutes the secondary node (SN), or NR-E-UTRA Dual Connectivity (NE-DC) in which the eNB constitutes the secondary node (SN).

[0024] In the DC, a master cell group (MCG) and a secondary cell group (SCG) may be configured. The MCG may include a primary cell (PCell), and the SCG may include a secondary cell (SCell).

[0025] In addition, the SCell may include a primary / secondary cell (PSCell). The PSCell is a type of SCell, but may be interpreted as a special SCell having the same functions as the PCell. The PSCell may perform functions such as transmitting the PUCCH (Physical Uplink Control Channel), performing a contention-based random access procedure (CBRA), and monitoring the radio link quality of the downlink, just like the PCell.

[0026] Furthermore, in the wireless communication system 10, handover using a PSCell (which may be referred to as HO with PSCell) is performed. In HO with PSCell, before the UE 200 in which a DC is set executes a handover, the PCell of the handover destination (target) sets up an SCG including a radio base station (eNB or gNB, which may be read as a cell) around the UE 200, and establishes a DC at the same time as the handover is completed.

[0027] Fig. 2 shows an example of handover using a PSCell (HO with PSCell). Specifically, Fig. 2 shows an example of HO with PSCell when UE 200 performs handover from an NR standalone (NR SA) network to an EN-DC network.

[0028] 2, a handover request (HO Request) is transmitted from the radio base station 100 in the NR-SA network to the radio base station 100 in the EN-DC network ((0) in the figure). In response to the handover request, the radio base station 100 in the EN-DC network sets up an SCG in the EN-DC network ((1) in the figure).

[0029] The radio base station 100 in the NR-SA network receives a response to the handover request (HO response) and information about the target SCG to be the handover destination (2 in the figure), and instructs the UE 200 to perform a handover (HO instruction) (3 in the figure).

[0030] Based on the HO command, the UE 200 executes handover to the EN-DC network, and executes synchronization processing with the radio base station 100 (eNB) and the SCG in the EN-DC network ((4) in the figure).

[0031] In the case of 3GPP Release 15, after completing handover to the eNB of the handover destination (target PCell), the UE 200 performs measurement of neighboring cells (eNB / gNB), adds an SCG (PSCell and SCell), and establishes an EN-DC.

[0032] Also, HO with PSCell may be supported in the case of 3GPP Release 16. In HO with PSCell, the target PCell may set up an SCG before the UE 200 executes handover, and may establish an EN-DC simultaneously with the completion of the handover.

[0033] Specifically, in (1) in the figure, before handover is performed, the target PCell sets up the surrounding eNBs / gNBs (cells formed by them) as SCGs.

[0034] In (2) in the figure, after the SCG setup by the target PCell is completed, the target PCell transmits SCG information and an HO response to the handover source PCell.

[0035] In (3) in the figure, when a handover command (HO command) is transmitted from the source PCell to the UE 200, information on the target SCG to be added when moving to the target PCell is also transmitted at the same time. In (4) in the figure, based on the information in the HO command, the UE 200 executes synchronization processing for both the target PCell and the target SCG, and the handover is completed.

[0036] Compared to handover in 3GPP Release 15, HO with PSCell can omit measurements of neighboring cells and enables early establishment of EN-DC. This contributes to improving data rates even during handover.

[0037] (2) Functional block configuration of wireless communication system Next, a description will be given of a functional block configuration of the wireless communication system 10. Specifically, a description will be given of a functional block configuration of the wireless base station 100 and the UE 200.

[0038] (2.1) Wireless base station 100 3 is a functional block diagram of the radio base station 100. As shown in FIG. 3, the radio base station 100 includes a radio communication unit 110, a measurement report processing unit 120, a control signal / reference signal processing unit 130, and a control unit 140.

[0039] The wireless communication unit 110 transmits and receives wireless signals conforming to LTE or NR. Specifically, the wireless communication unit 110 transmits downlink signals (DL signals) conforming to LTE or NR, and receives uplink signals (UL signals) conforming to LTE or NR.

[0040] In particular, in this embodiment, the wireless communication unit 110 supports dual connectivity and transmits and receives wireless signals via a cell group, specifically, a cell included in an MCG and / or an SCG. In this embodiment, the wireless communication unit 110 may constitute a transceiver unit that transmits and receives wireless signals.

[0041] The measurement report processing unit 120 executes processing related to a measurement report transmitted from the UE 200. Specifically, the measurement report processing unit 120 can receive from the UE 200 a measurement report including a measurement result regarding a serving cell and its peripheral cells (which may be called neighboring cells or adjacent cells, etc.) performed by the UE 200, in particular, a reception quality regarding the peripheral cells of the UE 200. In this embodiment, the wireless communication unit 110 may configure a receiving unit that receives a measurement report from a terminal.

[0042] The reception quality may include at least one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and Signal-to-Interference plus Noise power Ratio (SINR).

[0043] The control signal / reference signal processing unit 130 performs processing related to various control signals transmitted and received by the wireless communication unit 110, and processing related to various reference signals transmitted and received by the wireless communication unit 110.

[0044] Specifically, the control signal and reference signal processing unit 130 receives various control signals, for example, control signals of a radio resource control layer (RRC), transmitted from the wireless communication unit 110 via a predetermined control channel. Also, the control signal and reference signal processing unit 130 transmits various control signals to the wireless communication unit 110 via a predetermined control channel. In particular, in this embodiment, the control signal and reference signal processing unit 130 can receive capability information of the UE 200 (UE Capability Information) from the UE 200. In this embodiment, the control signal and reference signal processing unit 130 may constitute a receiving unit that receives capability information from the terminal.

[0045] The capability information may include at least a capability related to dual connectivity (DC), for example, the number of cells of the SCG supported by the UE 200, and a frequency band (which may be FR) to which the UE 200 can connect. Note that the capability information is not limited to such a capability of the UE 200, and may include, for example, capabilities related to transmission power, transmission beams, antennas, and the like.

[0046] The channels may include a control channel and a data channel. The control channels may include a PDCCH (Physical Downlink Control Channel), a PUCCH (Physical Uplink Control Channel), a RACH (Random Access Channel, Downlink Control Information (DCI) including a Random Access Radio Network Temporary Identifier (RA-RNTI)), and a Physical Broadcast Channel (PBCH).

[0047] Moreover, the data channel includes a physical downlink shared channel (PDSCH) and a physical uplink shared channel (PUSCH), etc. Data may refer to data transmitted via a data channel.

[0048] The control signal / reference signal processor 130 executes processing using reference signals (RS) such as a Demodulation Reference Signal (DMRS) and a Channel State Information-Reference Signal (CSI-RS).

[0049] The DMRS is a reference signal (pilot signal) known between a base station and a terminal for estimating a fading channel used for data demodulation, and the CSI-RS is a downlink reference signal for measuring the channel state.

[0050] In addition to the DMRS and the CSI-RS, the reference signal may include a Phase Tracking Reference Signal (PTRS), a Sounding Reference Signal (SRS), a Positioning Reference Signal (PRS) for location information, etc. In other words, the reference signal may include a reference signal transmitted by the radio base station 100 and a reference signal transmitted by the UE 200 (received by the radio base station 100).

[0051] In this manner, the control signal and reference signal processor 130 can transmit and receive the reference signal to and from the UE 200. In this embodiment, the control signal and reference signal processor 130 may configure a transceiver that transmits and receives the reference signal.

[0052] The control unit 140 controls each functional block constituting the radio base station 100. In particular, in this embodiment, the control unit 140 executes control related to handover of the UE 200. Note that handover may be interpreted as an expression such as cell selection, cell reselection, or cell transition. Furthermore, in this embodiment, it may be interpreted as HO with PSCell using the PSCell.

[0053] The control unit 140 can execute control related to handover that supports dual connectivity (DC) in particular. Specifically, the control unit 140 can select a neighboring cell that is estimated to be close to the handover source cell of the UE 200 as an SCell (or a PSCell) based on the reception quality (RSRP, etc.) included in the measurement report (MR) received from the UE 200. The control unit 140 can set an SCG that includes the selected SCell.

[0054] There is no particular limitation on the method for estimating neighboring cells that are estimated to be close to the source cell of the handover based on reception quality. For example, the neighboring cell with the best reception quality or whose reception quality is equal to or greater than a predetermined value may be estimated to be close to the source cell of the handover.

[0055] The control unit 140 can select a neighboring cell that is estimated to be close to the handover source cell as an SCell (or a PSCell) based on the reception state of a reference signal transmitted and / or received by the UE 200. The control unit 140 can set an SCG including the selected SCell.

[0056] For example, the control unit 140 can acquire a round trip time (RTT) between the UE 200 and the radio base station 100 using a reference signal (RS), and estimate the location of the UE 200 based on the acquired RTT value (time). The control unit 140 may select a cell close to the estimated location of the UE 200. At this time, the control unit 140 may use arrangement information (station placement information) of cells (radio base stations) owned by the operator of the radio communication system 10, if available.

[0057] The control unit 140 can estimate the traffic volume in the neighboring cell based on the measurement report received from the UE 200. The control unit 140 can select a neighboring cell in which the estimated traffic volume is smaller than a specified value as an SCell (or a PSCell), and can set an SCG including the SCell in handover (particularly, HO with PSCell).

[0058] The method for estimating the traffic volume is not particularly limited, but for example, the traffic volume transmitted and received by each of the neighboring cells may be estimated by obtaining information such as the transmission power and modulation method of UE200 based on the reception quality included in the MR, and calculating the amount of data transmitted and received by each of UE200 from the obtained information.

[0059] Based on the capability information of UE 200 (UE Capability Information), control unit 140 can select a neighboring cell of UE 200 according to the capability of UE 200 as an SCell (or a PSCell), and set an SCG including the SCell during handover (particularly, HO with PSCell).

[0060] For example, the control unit 140 may select an SCG with an appropriate number of cells depending on the number of cells of the SCG supported by the UE 200, or may select an SCG that includes cells that use FR1 depending on a frequency band to which the UE 200 can connect (e.g., only FR1) (i.e., not select an SCG that includes cells that use FR2).

[0061] Furthermore, in handover (particularly, in HO with PSCell), control unit 140 may set up a plurality of SCGs including an SCell (which may include a PSCell). For example, in HO with PSCell, control unit 140 may set up three SCGs and select one of the SCGs depending on the connection state between UE 200 and the cell.

[0062] Specifically, the control unit 140 can select one of the SCGs depending on the connection state (e.g., whether or not synchronization can be established) between the UE 200 and any cell (which may be a PSCell) included in the set SCG. For example, if the UE 200 attempts to connect to a cell of the first SCG but is unable to establish synchronization, the control unit 140 may attempt to connect to a cell of the second SCG. Alternatively, the UE 200 may connect to each of the three SCGs, and the SCG with the best state may be selected.

[0063] A specific method for selecting an SCG (SCell including a PSCell) will be described later. Also, "during handover (HO with PSCell)" may be interpreted as any of the following, prior to the handover, and during the execution of the handover.

[0064] Further, in addition to the above-mentioned method of selecting an SCG (cell), the control unit 140 may select a cell close to the handover source cell of the UE 200 in HO with PSCell by using station information of a cell (radio base station) owned by the operator of the wireless communication system 10. Alternatively, the control unit 140 may select a cell close to the handover source cell of the UE 200 by using a handover destination candidate cell list. For example, a Neighbor list (see 3GPP TS38.133) may be used as the handover destination candidate cell list. An example of the handover destination candidate cell list will be described later.

[0065] (2.2)UE200 4 is a functional block diagram of the UE 200. As shown in FIG. 4, the UE 200 includes a radio communication unit 210, a control signal / reference signal processing unit 220, a quality measurement unit 230, and a control unit 240.

[0066] The wireless communication unit 210 transmits and receives wireless signals conforming to NR. Specifically, the wireless communication unit 210 transmits uplink signals (UL signals) conforming to NR and receives downlink signals (DL signals) conforming to NR.

[0067] The wireless communication unit 210 supports Massive MIMO, CA that uses a bundle of multiple CCs, and DC that simultaneously communicates between a UE and each of two RAN nodes.

[0068] The control signal / reference signal processor 220 executes processing related to various control signals transmitted and received by the UE 200, and processing related to various reference signals transmitted and received by the UE 200.

[0069] Specifically, the control signal / reference signal processor 220 receives various control signals, for example, control signals of a radio resource control layer (RRC), transmitted from the radio base station 100 via a predetermined control channel. In addition, the control signal / reference signal processor 220 transmits various control signals to the radio base station 100 via a predetermined control channel.

[0070] The control signal / reference signal processor 220 performs processing using reference signals (RS) such as DMRS and CSI-RS.

[0071] DMRS is a known reference signal (pilot signal) between a base station and a terminal for estimating a fading channel used for data demodulation. PTRS is a terminal-specific reference signal for estimating phase noise, which is an issue in high frequency bands.

[0072] In addition to the DMRS and PTRS, the reference signals may include a Channel State Information-Reference Signal (CSI-RS), a Sounding Reference Signal (SRS), and a Positioning Reference Signal (PRS) for position information.

[0073] Furthermore, the control signal and reference signal processor 220 can execute processing related to capability information (UE Capability Information) of the UE 200. For example, the control signal and reference signal processor 220 can transmit UE Capability Information in response to a capability information inquiry (UE Capability Enquiry) from the radio base station 100.

[0074] The quality measurement unit 230 measures the reception quality of the serving cell of the UE 200 and neighboring cells formed around the serving cell.

[0075] Specifically, the quality measurement unit 230 can measure the reception quality using a synchronization signal block (SSB: SS / PBCH Block) or CSI-RS, etc. As described above, the reception quality may include at least one of RSRP, RSRQ, and SINR.

[0076] RSRP is the reception level of the reference signal measured at UE 200, and RSRQ is the reception quality of the reference signal measured at UE 200 (which may be interpreted as the ratio of the power of the cell-specific reference signal to the total power within the reception bandwidth).

[0077] In the SSB measurement, a measurement window that can be set for each carrier (or subcarrier) called SSB based RRM Measurement Timing Configuration (SMTC) may be used. Specifically, the SMTC window may be interpreted as a measurement window set in the UE 200 by the network (radio base station 100) so that the UE 200 recognizes the measurement start timing, measurement period, and measurement cycle for each cell to be measured when the UE 200 performs reception quality measurement using SSB.

[0078] The control unit 240 controls each functional block constituting the UE 200. In particular, in this embodiment, the control unit 240 executes control related to the transmission of UE Capability Information by the control signal / reference signal processing unit 220, the transmission and reception of reference signals, and the measurement of reception quality (RSRP, RSRQ, and SINR) by the quality measurement unit 230.

[0079] (3) Operation of wireless communication system Next, a description will be given of the operation of the wireless communication system 10. Specifically, a description will be given of the operation related to the selection of an SCG (SCell) when HO with PSCell is applied.

[0080] (3.1) Operation overview From the perspective of Radio Resource Management (RRM), the following handover scenarios are assumed for HO with PSCell.

[0081] NR SA to EN-DC EN-DC to EN-DC NE-DC to NE-DC NR-DC to NR-DC Assuming such a scenario, the following specifies the operation of the handover destination PCell (see Figure 2) selecting an eNB / gNB as an SCG. Specifically, this specifies the method of setting up (may be read as setting) the SCG in HO with PSCell.

[0082] 5 shows a schematic communication sequence of SCG (cell) selection. As described above, the RAN 20 (specifically, the radio base station 100) can receive the capability information (UE capability information) of the UE 200. The capability (UE capability) of the UE 200 may include the number of cells of the SCG supported by the UE 200, which are used for selecting the SCG, the frequency bands to which the UE 200 can connect, and the like.

[0083] The RAN 20 can select a neighboring cell of the UE 200 according to the capability of the UE 200 as an SCell (or a PSCell).

[0084] Furthermore, the RAN 20 can receive a measurement report (MR) including the RSRP, RSRQ, SINR, etc. measured by the UE 200 and / or a measurement result (such as the transmission power of the UE 200) used to estimate the traffic volume of the radio base station. The RAN 20 (radio base station 100) can select a neighboring cell that is estimated to be close to the handover source cell of the UE 200 as the SCell (or a PSCell), based on the reception quality of the RSRP, etc.

[0085] Note that the radio base station 100 can also select an SCG (SCell) based on a basis other than the capability information or measurement report of the UE 200, but a specific operation example will be described further below.

[0086] (3.2) Example of operation The following describes examples of the operation of selecting an SCG (SCell) by the radio base station 100. Specifically, operation examples 1 to 4 will be described.

[0087] (3.2.1) Example 1 6 shows a flow of cell selection and handover operations of the radio base station 100 according to operation example 1. In this operation example, a cell close to the source PCell is selected.

[0088] 6, the radio base station 100 (source PCell) acquires information on neighboring cells (S10). For example, the radio base station 100 may acquire the positions of neighboring cells by using station placement information of cells held by an operator.

[0089] Alternatively, the radio base station 100 may obtain information on surrounding cells (which may be read as adjacent cells, neighboring cells, etc.) using a candidate cell list for handover destinations.

[0090] The handover destination candidate cell list includes the Neighbor list (see 3GPP TS38.133), Neighbor A cell list (see 3GPP TS36.133) or a neighbor relation table regarding neighbor relations may be used.

[0091] Furthermore, as described above, the radio base station 100 may acquire (estimate) the positions of neighboring cells based on the reception quality (RSRP, RSRQ and / or SINR) included in the measurement report (MR).

[0092] Alternatively, the radio base station 100 may estimate the location of the UE 200 using a reference signal (RS) and select a cell close to the source PCell from the location of the UE 200.

[0093] As described above, when using RS, a method using RTT can be used. Specifically, using RS, RTT between X (for example, X=3) radio base stations 100 and UE 200 may be acquired, and the location of UE 200 may be estimated based on the RTT value. Such measurement of RTT may be called Multi RTT.

[0094] Furthermore, the radio base station 100 may estimate the location of the UE 200 with respect to X (for example, X=3) radio base stations 100 from the reception timing difference of the RS. Such measurement of the timing difference may be called downlink / uplink (DL / UL)-TDOA (Timing Difference of Arrival).

[0095] Alternatively, the radio base station 100 may estimate the position of the UE 200 from the radio base station 100 by using X (e.g., X=3) arrival angles (e.g., indexes of beams (which may be SSBs)) of DL / UL-RS. Such measurement of the arrival angles may be called DL-AoD (Angle of departure) and UL-AoA (Angle of arrival).

[0096] The radio base station 100 selects a cell close to the source PCell by any of the methods described above (S20).

[0097] The radio base station 100 sets up an SCG including the selected cell (SCell), and executes handover of the UE 200, specifically, HO with PSCell (S30).

[0098] If the radio base station 100 cannot estimate a cell close to the source PCell and has difficulty in selecting an SCG cell, the radio base station 100 may perform a normal handover instead of HO with PSCell.

[0099] (3.2.2) Example 2 7 shows a flow of cell selection and handover operations of the radio base station 100 according to operation example 2. In this operation example, the eNB / gNB (cell) with the least traffic is selected.

[0100] 7, the radio base station 100 (source PCell) acquires information on traffic transmitted and received by neighboring cells (radio base stations) (S110). For example, as described above, the radio base station 100 acquires information such as the transmission power and modulation method of the UE 200 based on the reception quality included in the MR, and calculates the amount of data transmitted and received by each of the UEs 200 from the acquired information, thereby estimating the amount of traffic transmitted and received by each of the neighboring cells.

[0101] That is, the radio base station 100 may estimate the traffic being handled in the neighboring cells based on the MR information reported from the UE 200, and select an eNB / gNB based on the estimated traffic.

[0102] Here, the radio base station 100 selects the neighboring cell (eNB / gNB) handling the least amount of traffic (S120).

[0103] The radio base station 100 sets up an SCG including the selected cell (SCell), and executes handover of the UE 200, specifically, HO with PSCell (S130).

[0104] If the radio base station 100 cannot estimate the traffic volume and has difficulty in selecting an SCG cell, the radio base station 100 may perform a normal handover instead of HO with PSCell.

[0105] (3.2.3) Example 3 8 shows a flow of cell selection and handover operations of the radio base station 100 according to the operation example 3. In this operation example, an eNB / gNB (cell) according to the capability of the UE 200 is selected.

[0106] As shown in Fig. 8, the radio base station 100 (source PCell) acquires capability information (UE capability information) of the UE 200 (S210). As described above, the capability information may include the number of cells of the SCG supported by the UE 200 and the frequency bands to which the UE 200 can connect. The number of cells may be an absolute value or a relative value to some reference value. In addition, the frequency band may be in FR units or a specific band (or band combination) finer than the FR.

[0107] For example, when a UE that does not support FR2 performs a handover, a cell that uses FR2 does not need to be selected as a cell included in the SCG.

[0108] In addition, the UE Capability Information may be notified from the source PCell to the target PCell at the time of a handover request (see (0) in FIG. 2).

[0109] The radio base station 100 selects a cell according to the acquired capability information of the UE 200 (S220).

[0110] The radio base station 100 sets up an SCG including the selected cell (SCell), and executes handover of the UE 200, specifically, HO with PSCell (S230).

[0111] If the radio base station 100 cannot acquire capability information and has difficulty selecting an SCG cell, the radio base station 100 may perform a normal handover instead of HO with PSCell.

[0112] (3.2.4) Example 4 9 shows a flow of cell selection and handover operations of the radio base station 100 according to operation example 4. In this operation example, a plurality of SCGs are set up, and an optimal SCG (cell) is selected from the set up SCGs.

[0113] 9, the radio base station 100 (source PCell) sets up multiple target SCGs (S310). The number of SCGs to be set up is not particularly limited, but Y SCGs (for example, Y=3) may be set up.

[0114] The radio base station 100 selects one of the SCGs depending on the connection state (eg, whether or not synchronization can be established) between the UE 200 and one of the cells (which may be a PSCell) included in the set-up SCG (S320).

[0115] For example, if UE 200 attempts to connect to a cell of a first SCG but is unable to establish synchronization, UE 200 may attempt to connect to a cell of a second SCG. Alternatively, UE 200 may connect to each of three SCGs, and the SCG with the best status may be selected.

[0116] The connection state may be whether or not synchronization can be established in a predetermined layer (not necessarily limited to a specific layer). Alternatively, other parameters such as reception quality may be used instead of or in addition to synchronization establishment.

[0117] The radio base station 100 sets the selected SCG and executes handover of the UE 200, specifically, HO with PSCell (S330).

[0118] (3.2.5) Other In the above-described operation examples 1 to 4, the SCG (cell) is selected by different selection methods, but any two or more of the operation examples may be combined.

[0119] In addition, when multiple operation examples are combined, handover (HO with PSCell) is performed only if the SCGs (cells) selected by all the selection methods match, and if not, a normal handover may be performed.

[0120] (4) Actions and Effects According to the above-described embodiment, the following advantageous effects can be obtained: Specifically, in HO with PSCell, the radio base station 100 can select a neighboring cell estimated to be close to the handover source cell of the UE 200 as an SCell (or a PSCell) based on the reception quality (such as RSRP) included in the measurement report (MR) received from the UE 200, and can set an SCG including the selected SCell.

[0121] Furthermore, the radio base station 100 can also select a neighboring cell that is estimated to be close to the handover source cell as the SCell (or a PSCell), based on the reception state of a reference signal transmitted and / or received from the UE 200.

[0122] Alternatively, the radio base station 100 can estimate the traffic volume in the neighboring cells based on the measurement report received from the UE 200, and select a neighboring cell in which the estimated traffic volume is smaller than a specified value as the SCell (or a PSCell).

[0123] Furthermore, the radio base station 100 can select a neighboring cell of the UE 200 according to the capability of the UE 200 as the SCell (or a PSCell), based on capability information of the UE 200 (UE Capability Information).

[0124] Furthermore, the radio base station 100 can configure a plurality of SCGs including an SCell (which may include a PSCell) and select one of the SCGs depending on the connection state of the UE 200 with the cell.

[0125] Therefore, particularly when HO with PSCell is executed, it is possible to set an appropriate SCG according to the capability or state of the UE 200 or the radio base station 100. This makes it possible to achieve appropriate dual connectivity even when HO with PSCell is applied.

[0126] (5) Other embodiments Although the embodiment has been described above, it will be apparent to those skilled in the art that the present invention is not limited to the description of the embodiment and that various modifications and improvements are possible.

[0127] For example, in the above-described embodiment, the wireless communication system 10 supports LTE and NR, but may support only NR. Also, the wireless communication system 10 may be a wireless communication system conforming to a scheme called Beyond 5G, 5G Evolution, or 6G.

[0128] In the above-described embodiment, dual connectivity to which HO with PSCell is applied is assumed, but if the application conditions are met, the above-described cell (cell group) selection method may be applied to handover other than HO with PSCell.

[0129] Moreover, the block diagrams (FIGS. 3 and 4) used in the description of the above-mentioned embodiments show functional blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. Furthermore, the method of realizing each functional block is not particularly limited. That is, each functional block may be realized by using one device that is physically or logically combined, or may be realized by using two or more devices that are physically or logically separated and directly or indirectly connected (for example, by using wires, wirelessly, etc.). The functional blocks may be realized by combining the one device or the multiple devices with software.

[0130] Functions include, but are not limited to, judgment, determination, judgment, calculation, computation, processing, derivation, investigation, search, confirmation, reception, transmission, output, access, resolution, selection, selection, establishment, comparison, assumption, expectation, consideration, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, and assignment. For example, a functional block (component) that performs the function of transmission is called a transmitting unit or a transmitter. As described above, there is no particular limitation on the method of realization of any of these.

[0131] Furthermore, the above-mentioned radio base station 100 and UE 200 (the device) may function as a computer that performs processing of the wireless communication method of the present disclosure. Fig. 10 is a diagram showing an example of a hardware configuration of the device. As shown in Fig. 10, the device may be configured as a computer device 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, and the like.

[0132] In the following description, the term "apparatus" may 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.

[0133] Each functional block of the device (see FIGS. 3 and 4) is realized by any hardware element of the computer device, or a combination of the hardware elements.

[0134] In addition, each function in the device is realized by loading a specific software (program) onto hardware such as the processor 1001, memory 1002, etc., so that the processor 1001 performs calculations, controls communication by the communication device 1004, and controls at least one of reading and writing of data in the memory 1002 and storage 1003.

[0135] The processor 1001 controls the entire computer by running, for example, an operating system, and may be configured by a central processing unit (CPU) including an interface with peripheral devices, a control unit, an arithmetic unit, a register, and the like.

[0136] Furthermore, the processor 1001 reads out 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 according to these. As the programs, programs that cause a computer to execute at least a part of the operations described in the above-mentioned embodiments are used. Furthermore, the above-mentioned various processes may be executed by one 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.

[0137] 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 can store a program (program code), a software module, etc., capable of executing a method according to an embodiment of the present disclosure.

[0138] Storage 1003 is a computer-readable recording medium, and may be composed of at least one of, for example, 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 (registered trademark) disk), a smart card, a flash memory (e.g., a card, a stick, a key drive), a floppy (registered trademark) disk, a magnetic strip, and the like. Storage 1003 may 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.

[0139] The communication device 1004 is hardware (transmission / reception device) for performing communication 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.

[0140] The communication device 1004 may be configured to include a high-frequency switch, a duplexer, a filter, a frequency synthesizer, and the like to realize, for example, at least one of Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

[0141] The input device 1005 is an input device (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, etc.) that accepts input from the outside. The output device 1006 is an output device (e.g., a display, a speaker, an LED lamp, etc.) that performs output to the outside. The input device 1005 and the output device 1006 may be integrated into one device (e.g., a touch panel).

[0142] In addition, each device such as the processor 1001 and the memory 1002 is connected by 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.

[0143] 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), a field programmable gate array (FPGA), etc., 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.

[0144] 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 of these. Furthermore, the RRC signaling may be called an RRC message, and may be, for example, an RRC Connection Setup message, an RRC Connection Reconfiguration message, or the like.

[0145] 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, 4th generation mobile communication system (4G), 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), other suitable systems, and next-generation systems extended based on these. In addition, a combination of multiple systems (e.g., a combination of at least one of LTE and LTE-A and 5G, etc.) may be applied.

[0146] The order of the steps, sequences, flow charts, etc. of each aspect / embodiment described in this disclosure may be changed unless inconsistent. 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.

[0147] In the present disclosure, a specific operation 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 other network nodes other than the base station (e.g., MME or S-GW, etc., but are not limited to these). Although the above example illustrates a case in which there is one other network node other than the base station, it may also be a combination of multiple other network nodes (e.g., MME and S-GW).

[0148] Information, signals (information, etc.) may be output from a higher layer (or a lower layer) to a lower layer (or a higher layer), and may be input and output via multiple network nodes.

[0149] The input / output information may be stored in a specific location (e.g., memory) or may be managed using a management table. The input / output information may be overwritten, updated, or appended. The output information may be deleted. The input information may be transmitted to another device.

[0150] The determination may be based on a value represented by a single bit (0 or 1), a Boolean value (true or false), or a numerical comparison (e.g., comparison with a predetermined value).

[0151] Each aspect / embodiment described in this disclosure may be used alone, in combination, or switched according to execution. In addition, notification of specific information (e.g., notification that "X is the case") is not limited to being done explicitly, but may be done implicitly (e.g., not notifying the specific information).

[0152] 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.

[0153] Additionally, software, instructions, information, etc. may be transmitted or received over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using wired and / or wireless technologies (such as coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL)), and / or wireless technologies (such as infrared, microwave, etc.), then these wired and / or wireless technologies are included within the definition of transmission media.

[0154] The information, signals, etc. described in this disclosure may be represented using any of a variety of different technologies. For example, the 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.

[0155] In addition, the terms described in this disclosure and the 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). Also, a signal may be a message. Also, a component carrier (CC) may be called a carrier frequency, a cell, a frequency carrier, etc.

[0156] As used in this disclosure, the terms "system" and "network" are used interchangeably.

[0157] In addition, the information, parameters, etc. described in the present disclosure may be represented using absolute values, may be represented using relative values ​​from a predetermined value, or may be represented using other corresponding information. For example, a radio resource may be indicated by an index.

[0158] The names used for the above-mentioned parameters are not limiting in any way. Furthermore, the formulas 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 limiting in any way.

[0159] 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", "component carrier", etc. may be used interchangeably. A base station may also be referred to by terms such as a macro cell, a small cell, a femto cell, a pico cell, etc.

[0160] A base station can accommodate one or more (e.g., three) cells (also called sectors). When a base station accommodates multiple cells, the entire coverage area of ​​the base station can be divided into multiple smaller areas, and each smaller area can also be provided with communication services by a base station subsystem (e.g., a small indoor base station (Remote Radio Head: RRH)).

[0161] The term "cell" or "sector" refers to part or all of the coverage area of ​​a base station and / or a base station subsystem that provides communication services within that coverage.

[0162] In this disclosure, the terms "Mobile Station (MS)", "user terminal", "User Equipment (UE)", "terminal", etc. may be used interchangeably.

[0163] 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.

[0164] At least one of the base station and the mobile station may be called 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 moving body, the moving body itself, etc. The moving body may be a vehicle (e.g., a car, an airplane, etc.), an unmanned moving body (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 include a device that does not necessarily move during communication operation. 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.

[0165] Furthermore, a base station in the present disclosure may be read as a mobile station (user terminal, the same applies below). For example, each aspect / embodiment 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 communication between terminals (for example, "side"). For example, an uplink channel, a downlink channel, etc. may be read as a side channel.

[0166] 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. A radio frame may be composed of one or more frames in the time domain. Each of the one or more frames in the time domain may be called a subframe. A subframe may further be composed of one or more slots in the time domain. A subframe may have a fixed time length (e.g., 1 ms) that is independent of numerology.

[0167] Numerology may be a communication parameter that applies to the transmission and / or reception of a signal or channel, and may indicate, for example, at least one of a SubCarrier Spacing (SCS), a bandwidth, a symbol length, a Cyclic Prefix length, a Transmission Time Interval (TTI), a number of symbols per TTI, a radio frame structure, a particular filtering operation that the transceiver performs in the frequency domain, a particular windowing operation that the transceiver performs in the time domain, etc.

[0168] A slot may consist of one or more symbols in the time domain (such as an Orthogonal Frequency Division Multiplexing (OFDM) symbol, a Single Carrier Frequency Division Multiple Access (SC-FDMA) symbol, etc.) A slot may be a numerology-based unit of time.

[0169] A slot may include multiple minislots. Each minislot may be composed of one or more symbols in the time domain. A minislot may also be called a subslot. A minislot may be composed 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.

[0170] A radio frame, a subframe, a slot, a minislot, and a symbol each represent a time unit for transmitting a signal. The radio frame, the subframe, the slot, the minislot, and the symbol may each be referred to by a different name.

[0171] For example, one subframe may be called a transmission time interval (TTI), multiple consecutive subframes may be called a TTI, or one slot or one minislot may be called a TTI. That is, at least one of the subframe and the TTI may be a subframe (1 ms) in the existing LTE, a period shorter than 1 ms (for example, 1-13 symbols), or a period longer than 1 ms. Note that the unit representing the TTI may be called a slot, minislot, etc., instead of a subframe.

[0172] Here, TTI refers to, for example, the minimum time unit for scheduling in wireless communication. For example, in an LTE system, a base station performs scheduling to allocate radio resources (such as frequency bandwidth and transmission power that can be used by each user terminal) to each user terminal in TTI units. Note that the definition of TTI is not limited to this.

[0173] 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) in which a transport block, a code block, a code word, etc. are actually mapped may be shorter than the TTI.

[0174] In addition, when one slot or one minislot is called TTI, one or more TTIs (i.e., one or more slots or one or more minislots) may be the minimum time unit of scheduling. Also, the number of slots (minislots) constituting the minimum time unit of scheduling may be controlled.

[0175] A TTI having a time length of 1 ms may be called a normal TTI (TTI in LTE Rel. 8-12), a normal TTI, a long TTI, a normal subframe, a normal subframe, a long subframe, a slot, etc. A TTI shorter than a normal TTI may be called a shortened TTI, a short TTI, a partial or fractional TTI, a shortened subframe, a short subframe, a minislot, a subslot, a slot, etc.

[0176] In addition, a long TTI (e.g., a normal TTI, a subframe, etc.) may be interpreted as a TTI having a time length exceeding 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.

[0177] 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 the numerology, for example, 12. The number of subcarriers included in an RB may be determined based on the numerology.

[0178] In addition, the time domain of the RB may include one or more symbols and may be one slot, one minislot, one subframe, or one TTI in length. Each of one TTI, one subframe, etc. may be composed of one or more resource blocks.

[0179] One or more RBs may be called a physical resource block (PRB), a sub-carrier group (SCG), a resource element group (REG), a PRB pair, an RB pair, or the like.

[0180] 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.

[0181] 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 numerology on a carrier, where the common RBs may be identified by the index of the RBs relative to a common reference point of the carrier. PRBs may be defined in a BWP and numbered within the BWP.

[0182] 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.

[0183] 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 replaced with "BWP".

[0184] The above-mentioned 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 changed in various ways.

[0185] 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 at least one of one or more wires, cables, and 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.

[0186] The reference signal may also be abbreviated as Reference Signal (RS), and may be called a pilot depending on the applicable standard.

[0187] 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."

[0188] The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc.

[0189] Any reference to an element using a designation such as "first," "second," etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient way to distinguish 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.

[0190] When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, as is the term "comprising." Further, as used in this disclosure, the term "or" is not intended to be an exclusive or.

[0191] In this disclosure, where articles have been added due to translation, such as a, an, and the in English, the disclosure may include that the nouns following these articles are in the plural form.

[0192] 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, search, inquiry (e.g., searching in 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 a memory), and the like. In addition, "judgment" and "decision" can include considering resolving, selecting, choosing, establishing, comparing, etc., to be a "judgment" or "decision." In other words, "judgment" and "decision" can include considering some action to be a "judgment" or "decision." In addition, "judgment" can be interpreted as "assuming," "expecting," "considering," etc.

[0193] 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."

[0194] 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 in the present disclosure. 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. [Explanation of symbols]

[0195] 10. Wireless communication systems 20 RAN 100 Radio base station 110 Wireless Communication Division 120 Measurement report processing unit 130 Control signal / reference signal processing unit 140 Control section 200UE 210 Wireless Communication Department 220 Control signal / reference signal processing unit 230 Quality Measurement Department 240 Control Unit 1001 Processor 1002 Memory 1003 Storage 1004 Communication equipment 1005 Input Device 1006 Output device 1007 Bus

Claims

[Claim 1] A receiving unit that receives measurement reports on neighboring cells from a terminal; a control unit that estimates a traffic volume in the neighboring cell based on the measurement report, selects the neighboring cell in which the traffic volume is smaller than a specified value as a secondary cell, and sets a secondary cell group including the secondary cell in a handover; A radio base station comprising:

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