Control device, control method, and program

Abstract

This control device for a base station is provided with a control unit that executes: a step for transmitting a plurality of beams; a step for acquiring, from a mobile station, measurement results of the plurality of beams; a step for acquiring the direction of the mobile station relative to the base station; and a beam management step for determining, on the basis of the measurement results and the direction of the mobile station, which sub-procedure to start from in a beam determination procedure composed of a plurality of sub-procedures.

Description

Control device, control method, and program

[0001] The present disclosure relates to beam management in wireless communications.

[0002] Beamforming is used in wireless communications such as the 5th Generation Mobile Communication System (5G), especially in wireless communications using high-frequency radio waves. Beamforming narrows the reach of radio waves and concentrates power in a small area, making it possible to expand the communication range.

[0003] Non-Patent Document 1 describes that the Beam Management procedure includes three sub-procedures, P1 to P3. P1 is a coarse adjustment using a wide beam on the transmitting side, P2 is a fine adjustment using a narrow beam on the transmitting side, and P3 is a fine adjustment using a narrow beam on the receiving side.

[0004] Furthermore, while communicating using the determined beam, the mobile station measures the received strength of the beam and reports the measurement results to the base station. The measured value is typically the Reference Signal Received Power (RSRP) of a CSI-RS (Channel State Information Reference Signal) signal. The base station determines whether the beam to be used needs to be updated based on the measurement results, and updates the beam if necessary. This allows the base station and mobile station to continue communication using an appropriate beam.

[0005] 3GPP TR 38.802 V14.2.0 (2017-09)

[0006] When it is determined that a beam update is necessary, it is not necessary to start from the beginning of the beam determination procedure (i.e., the P1 subprocedure), but it is possible to start from the middle (the P2 or P3 subprocedure). Skipping some subprocedures enables quick beam update. On the other hand, skipping necessary subprocedures can cause the problem of not being able to select an optimal beam.

[0007] One aspect of the present disclosure aims to provide a technology that can quickly and appropriately perform beam updates.

[0008] One aspect of the present disclosure is a base station control device comprising a control unit that executes the steps of: transmitting a plurality of beams; acquiring measurement results of the plurality of beams from a mobile station; acquiring the direction of the mobile station relative to the base station; and a beam management step that determines which sub-procedure to start from in a beam determination procedure consisting of a plurality of sub-procedures based on the measurement results and the direction of the mobile station.

[0009] Another aspect of the present disclosure is a control method for a base station, comprising: a step of transmitting a plurality of beams; a step of acquiring measurement results of the plurality of beams from a mobile station; a step of acquiring the direction of the mobile station relative to the base station; and a beam management step of determining which sub-procedure to start from in a beam determination procedure consisting of a plurality of sub-procedures based on the measurement results and the direction of the mobile station.

[0010] According to the present disclosure, by taking into account not only the beam measurement results but also the direction of the mobile station, it is possible to evaluate the stability of the beam currently in use, and by performing a beam determination procedure from an appropriate sub-procedure based on the evaluation results, it is possible to quickly and appropriately update the beam.

[0011] FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of the hardware configuration of a control device according to an embodiment. FIG. 3 is a diagram illustrating an example of the functional configuration of a control device according to an embodiment. FIG. 4 is a diagram illustrating an example of the functional configuration of a base station according to an embodiment. FIG. 5 is a flowchart illustrating the overall flow of beam management processing according to an embodiment. FIG. 6 is a flowchart illustrating a detailed flow of beam determination processing according to an embodiment. FIGS. 7A to 7C are diagrams illustrating beam determination processing according to an embodiment. FIG. 8 is a flowchart illustrating the flow of start phase determination processing of beam update processing according to an embodiment. FIGS. 9A to 9C are diagrams illustrating a method of calculating the distance and direction of a mobile station. FIG. 10 is a flowchart illustrating the flow of start phase determination processing of beam update processing according to another embodiment. FIG. 11 is a flowchart illustrating the flow of start phase determination processing of beam update processing according to yet another embodiment.

[0012] (Embodiment 1) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following embodiments are merely examples for the purpose of explanation, and the present disclosure is not limited to the configurations of the embodiments. For example, an example using mobile communication, particularly 5G standard cellular communication (mobile communication), will be described below, but the technology of the present disclosure may be applied to cellular communication other than the 5G standard, or wireless communication other than cellular communication.

[0013] [System Overview] Fig. 1 is a diagram showing an example of the system configuration of a communication system 100 according to the first embodiment. The communication system 100 is a distributed MIMO system including a mobile station 3, a control device 1, and a plurality of distributed base stations. A distributed base station, together with other distributed base stations in the same communication area, provides wireless access to a mobile station 3 located within the communication area. It is assumed that the two distributed base stations shown in Fig. 1 are located in the same communication area. Each of the distributed base stations is connected to the control device 1.

[0014] A distributed base station is equipped with one or more antennas. The multiple antennas equipped in a distributed base station are, for example, adaptive array antennas. An adaptive array antenna is an array antenna in which multiple antenna elements are arranged. An adaptive array antenna can adaptively control the weighting of each antenna element according to the radio wave propagation environment and electrically change the beam pattern. The beam pattern can also be said to be the directivity of the beam formed by the adaptive array antenna. The beam pattern of the distributed base station is controlled by a control device 1.

[0015] The mobile station 3 is, for example, a smartphone, a tablet terminal, a wearable terminal, or an in-vehicle data communication device. However, the mobile station 3 is not limited to these, and may also be a stationary terminal device. The mobile station 3 is also referred to as a terminal station or a user terminal.

[0016] The example shown in Figure 1 includes two transmission points: distributed base stations RU#1 and RU#2. Three beams, b0, b1, and b2, are transmitted from distributed base station RU#1. Two beams, b3 and b4, are transmitted from distributed base station RU#2. In the example shown, mobile station 3 communicates using beam b1. It is possible that the communication quality of beam b1 will deteriorate as mobile station 3 moves or the radio wave propagation environment changes. In that case, the control device 1 changes the beam used for communication with mobile station 3.

[0017] The mobile station 3 receives from the control device 1 the specification of multiple beams, including communication beams and measurement beams, measures the received signal strength of the reference signal for the multiple beams at a predetermined interval, and reports the measurement results to the control device 1. Alternatively, the mobile station 3 may report the measurement results to the control device 1 when requested by the control device 1. Upon receiving the measurement results from the mobile station 3, the control device 1 determines whether the currently used beam needs to be updated and, if an update is necessary, which sub-procedure of the beam determination procedure should be started from, and starts the beam determination procedure from the determined sub-procedure. Note that the control device 1 determines whether the beam needs to be updated and the start phase, taking into account the beam measurement results (received signal strength) and the direction of the mobile station 3 relative to the distributed base station (transmission point). Details of the beam determination procedure will be described later.

[0018] [Configuration] Fig. 2 is a diagram illustrating an example of the hardware configuration of the control device 1. The control device 1 includes a CPU 101, a main memory device 102, an auxiliary memory device 103, an input device 104, an output device 105, and a communication device 106. The CPU 101 is also called a processor or an arithmetic unit. The CPU 101 is not limited to a single processor, and may have a multi-processor configuration. In addition to the CPU 101, a graphics processing unit (GPU), a digital signal processor (DSP), etc. may be included. The CPU 101 may also be linked to a hardware circuit such as a field programmable gate array (FPGA).

[0019] The CPU 101 executes a computer program executable in the main memory device 102 to provide processing for the control device 1. The main memory device 102 stores the computer program executed by the CPU 101, data processed by the CPU 101, etc. The main memory device 102 may be, for example, a dynamic random access memory (DRAM), a static random access memory (SRAM), a read-only memory (ROM), etc. Furthermore, the auxiliary memory device 103 is used as a storage area supporting the main memory device 102 and stores the computer program executed by the CPU 101, data processed by the CPU 101, etc. The auxiliary memory device 103 may be, for example, a hard disk drive, a solid state drive (SSD), etc. Furthermore, a drive device for a removable storage medium may be connected to the control device 1. Examples of the removable storage medium include a Blu-ray disc, a digital versatile disc (DVD), a compact disc (CD), a flash memory card, etc. The CPU 101 is an example of a "control unit" of a "control device."

[0020] The input device 104 is a device through which an operator inputs information to the control device 1, and is, for example, a keyboard, a mouse, or a touch panel with a touch sensor overlaid on a display. The output device 105 is a device for displaying information to the outside, particularly to the operator, and is, for example, a display device such as a liquid crystal display or an electroluminescence panel. The output device 105 may also include a speaker or other device for outputting sound. The communication device 106 communicates with other devices via a communication interface by wireless or wired communication. The control device 1 is configured to be able to communicate with the base station 2 and the core network 4 via the communication device 106.

[0021] FIG. 3 is a diagram illustrating an example of the functional configuration of the control device 1. The control device 1 includes a control unit 10, and sub-functional units of the control unit 10 include a measurement result acquisition unit 11, a mobile station information acquisition unit 12, a beam update determination unit 13, and a beam determination unit 14. The measurement result acquisition unit 11 acquires beam measurement results for the mobile station 3. The mobile station information acquisition unit 12 acquires information about the mobile station 3, including the distance between the base station 2 and the mobile station 3 and the direction of the mobile station 3 relative to the base station 2. The beam update determination unit 13 determines whether the beam used by the mobile station 3 needs to be updated, and if so, which sub-procedure of the beam determination procedure should be started. The beam determination unit 14 determines the beam that the mobile station 3 will use for communication. The functions of the control unit 10 and its sub-functional units are realized by the CPU 101 executing a program loaded in the main memory device 102, but some or all of the functions may be realized by dedicated hardware circuits.

[0022] FIG. 4 is a diagram illustrating an example of the functional configuration of a base station 2. The base station 2 includes a radio unit (RU) 21, a distributed unit (DU) 22, and a centralized unit (CU) 23. The RU 21 is a functional unit that controls an antenna array to communicate radio waves with a mobile station 3 and also controls MIMO, beamforming, and the like. The antenna array of the RU 21 is also called a transmission / reception point (TRP). The antenna array of the RU 21 can also be called a transmission point or a reception point. In this disclosure, the location of the base station 2 refers to the location of the antenna array (i.e., the transmission / reception point, transmission point, or reception point). The DU 22 is a functional unit that performs signal modulation / demodulation, MAC layer communication control, and the like. The CU 23 is a functional unit that controls the DU 22 and the RU 21, connects to the core network (CN) 4, performs PDCP protocol processing such as packet encryption, and RRC protocol processing such as radio resource management. Note that multiple RUs 21 may be connected to one DU 22, and multiple DUs 22 may be connected to one CU 23. The functional units of the RU 21, DU 22, and CU 23 may be located in geographically separate locations, or may be located in the same location or within the same device. The RU 21, DU 22, and CU 23 are communicatively connected to the control device 1 and perform control based on commands from the control device. The control device 1 may be located in geographically separate locations from the RU 21, DU 22, and CU 23, or may be located in the same location or within the same device.

[0023] The mobile station 3 includes a CPU, a main memory device, an auxiliary memory device, an output device, an operation device, a wireless communication device, and an antenna. The wireless communication device of the mobile station 3 connects to a wireless access network via the antenna 107 using a mobile wireless communication method such as 5G, and performs wireless communication via a base station. The wireless communication device also measures base station beams, reports the measurement results to the base station, and performs communication using beams notified from the base station.

[0024] [Processing] (1) Overall Processing of Beam Determination Procedure Figure 5 is a flowchart showing the flow of processing performed by the control device 1 when the base station 2 and the mobile station 3 communicate with each other. At the start of this processing, the mobile station 3 is in an idle state, and no connection has been established with the base station 2. The following processing is performed between the base station 2 and the mobile station 3. The processing of the base station 2 is performed under the control of the control device 1, but in the following explanation, the base station 2 may be described as being the subject of the operation.

[0025] In step S11, a beam determination procedure is performed between the base station 2 and the mobile station 3 to determine a beam to be used for communication between the base station 2 and the mobile station 3 and a beam to be used for measurement. Fig. 6 is a flowchart showing the details of the beam determination procedure S11 in step S11. Fig. 7 is a diagram explaining the beam determination procedure. The beam determination procedure will be explained below with reference to Figs. 6 and 7.

[0026] In step S111, coarse adjustment of the transmission beam is performed using a transmission beam with low angular resolution. The process of step S111 corresponds to the P1 subprocedure (first subprocedure). This procedure also involves a mobile station 3 in an idle state (RRC_IDLE) establishing a connection based on SSBs (Synchronization Signal Blocks). As shown in FIG. 7A, the base station 2 sweeps SSB beams in multiple different directions (beam sweeping). The mobile station 3 receives SSB beams (wide beams) using reception beams with low angular resolution. The mobile station 3 measures the SSB reception strength (e.g., RSRP) of each SSB beam and transmits a preamble via a Random Access Channel (RACH) at the transmission timing associated with the SSB with the highest reception strength, thereby establishing a connection. The mobile station 3 may also sweep reception beams to determine an optimal pair of transmission and reception beams. The beam determined in this procedure is a wide beam with low angular resolution and is not the optimal beam for transmitting and receiving data, so beam refinement is performed in the following procedure. Note that the wide beam used in this sub-procedure corresponds to a base station beam with the first angular resolution.

[0027] In step S112, fine adjustment of the transmission beam is performed using a transmission beam with high angular resolution. The processing of step S112 corresponds to the P2 subprocedure (second subprocedure). As shown in FIG. 7(B), the base station 2 transmits CSI-RS beams (narrow beams) with higher angular resolution in multiple different directions within the angular range of the beam determined in the P1 subprocedure. The mobile station 3 measures the reception strength (e.g., RSRP) of the CSI-RS signal contained in each beam and reports the measurement results to the base station 2. The base station 2 determines the CSI beam with the highest reception strength as the transmission beam to be used for communication between the base station 2 and the mobile station 3. The narrow beam used in this subprocedure corresponds to a base station beam with a second angular resolution, which is higher than the first angular resolution.

[0028] In step S113, fine adjustment of the receiving beam is performed using a receiving beam with high angular resolution. The processing in step S113 corresponds to the P3 subprocedure (third subprocedure). As shown in FIG. 7C, the base station 2 repeatedly transmits CSI-RS using the narrow beam determined in the P2 subprocedure, and the mobile station 3 sweeps and receives receiving beams with higher angular resolution than those in the P1 and P2 subprocedures, and determines the receiving beam with the highest reception strength (e.g., RSRP).

[0029] The above process determines a pair of transmission and reception beams to be used in communication between the base station 2 and the mobile station 3. The base station 2 determines not only the beam to be used in communication (communication beam), but also the beam to be measured by the mobile station 3 during communication (measurement beam). When determining the measurement beam, for example, a beam adjacent to the angle of the communication beam is selected, or a beam that has an intensity above the threshold in the P1 subprocedure or P2 subprocedure, or the runner-up beam, is selected.

[0030] In step S12, the base station 2 notifies the mobile station 3 of the communication beams and measurement beams determined in step S11, and performs communication using the communication beams. During communication, the mobile station 3 measures the communication beams and measurement beams and reports the measurement results to the base station 2. The timing of measurement and reporting in the mobile station 3 may be specified by the base station 2, or may be determined by the mobile station 3 itself.

[0031] In step S13, the base station 2 receives the beam measurement results (measurement report) from the mobile station 3. The beam measurement results include information on the reception strength, such as the reference signal received power (RSRP) of the beam at the mobile station 3, for example.

[0032] In step S14, the base station 2 determines whether or not it is necessary to change the beam used for communication with the mobile station 3. The determination of whether or not it is necessary to change the beam is made based on, for example, whether or not the measurement results of the mobile station 3 satisfy certain conditions, such as whether the reception strength included in the measurement results of the currently used beam is equal to or less than a threshold, or whether there is another beam with a higher reception strength than the currently used beam. If it is determined that it is not necessary to change the beam (S14-NO), the process returns to step S13 and waits for the next measurement result from the mobile station 3. On the other hand, if it is determined that it is necessary to change the beam, the process proceeds to step S15.

[0033] In step S15, the base station 2 determines which of the sub-procedures P1, P2, and P3 should be the starting phase of the beam update. Details of this process will be described later.

[0034] In step S16, the base station 2 executes the beam determination procedure from the subprocedure determined in step S15, and determines the beam to be used for communication and measurement. This process is similar to the process of step S11 described with reference to Figures 6 and 7, but the processes of steps S111 and S112 may be omitted depending on the start phase.

[0035] In step S17, the base station 2 notifies the mobile station 3 of the communication beam and measurement beam determined in step S16, and performs communication using the communication beam. After this, the processing from step S13 to step S17 is repeated until communication between the base station 2 and the mobile station 3 is completed.

[0036] (2) Start Phase Determination Process S15 Fig. 8 is a flowchart showing details of the start phase determination process of the beam determination procedure in step S15. The process of step S15 will be described with reference to Fig. 8.

[0037] In step S151, the control device 1 acquires the beam measurement results and position information of the mobile station 3. For example, the control device 1 stores the measurement results received in memory when receiving the measurement results in step S13, and in step S151, the measurement result acquisition unit 11 acquires the measurement results from the memory. The position information of the mobile station 3 may be acquired in any manner, for example, by acquiring from the mobile station 3 the position information acquired by the mobile station 3 using a GPS device or other GNSS device. The transmission of the position information from the mobile station 3 may be included in a measurement report or in another signal. Alternatively, the position information of the mobile station 3 may be determined based on the time difference of arrival (TDOA) of radio waves from the mobile station 3 at multiple base stations 2 (RUs or transmitting / receiving points).

[0038] In step S152, the control device 1 calculates the direction θ of the mobile station 3 relative to the base station 2. ０ and distance d UE,RS Here, using the base station 2 as a reference means, more precisely, using the transmitting / receiving point (TRP) of the beam as a reference.

[0039] Figure 9(A) is a diagram showing an example of the positional relationship between a base station 2 and a mobile station 3. In Figure 9(A), it is assumed that a building 902 is present in a direction 904 of the mobile station 3 as seen from the base station 2, preventing radio waves from reaching the mobile station 3, and that communication between the base station 2 and the mobile station 3 is carried out using radio waves reflected by the building 903 in a direction 905. Figure 9(B) is a diagram showing the positional relationship in Figure 9(A) projected onto a horizontal plane and viewed from above.

[0040] In step S152, the mobile station information acquisition unit 12 ０ and distance d UE,BS As shown in FIG. 9B, it can be calculated according to the following formula: In addition, (x UE , y UE ) and (x BS , y BS ) are the x and y coordinates of the mobile station 3 and the base station 2 (transmission and reception points), respectively. The coordinate system may be a global coordinate system such as latitude and longitude, or a local coordinate system based on a specific base station.

[0041] In step S153, the beam update determination unit 13 determines whether or not a beam exceeding the intensity threshold Th1 is present in the measurement report from the mobile station 3. The intensity threshold Th1 corresponds to the first threshold in the present disclosure. The intensity threshold Th1 may be determined as appropriate. For example, the intensity threshold Th1 is a value at which stable communication can be continued using that beam if the reception intensity is equal to or greater than the intensity threshold Th1. If no beam exceeds the intensity threshold Th1 (S153-NO), the process proceeds to step S157, and the beam update determination unit 13 determines to start the beam determination procedure from the P1 subprocedure (S111). On the other hand, if a beam exceeding the intensity threshold Th1 is present (S153-YES), the process proceeds to step S154.

[0042] In step S154, the beam update determination unit 13 determines whether or not there is a beam having a direction that matches the direction of the mobile station 3 among the beams exceeding the intensity threshold Th1.

[0043] Here, whether or not the beam direction coincides with the direction of the mobile station 3 is determined, for example, as follows. ０ is within the range of the half-width of the beam, the beam direction can be determined as the mobile station 3. More specifically, the beam direction exceeding the intensity threshold Th1 can be determined as θ ＯＫ The beam width (half width) of this beam is φ, and θ ＯＫ −φ / 2<θ ０ <θ ＯＫ+φ / 2 is satisfied, it is determined that the beam matches the direction of the mobile station 3. If there are multiple beams whose intensity exceeds the intensity threshold Th1, the above determination is made for each beam.

[0044] In another example, the beam direction exceeding the intensity threshold Th1 is determined as θ ＯＫ The maximum Fresnel diameter of this beam is D, and θ ＯＫ -D / d UE,BS <θ ０ <θ ＯＫ +D / d UE,BS If the above equation is satisfied, it may be determined that the direction of the beam matches the direction of the mobile station 3. UE,BS is the distance d from the base station 2 UE,BS When the wavelength of the radio wave is λ, the maximum Fresnel diameter is D = (λd UE,BS ) 1 / 2 Therefore, the above determination formula can be expressed as follows:

[0045] In the determination of step S154, if it is determined that there is no beam that matches the direction of the mobile station 3 among the beams that exceed the intensity threshold Th1 (S154-NO), the process proceeds to step S155. On the other hand, if it is determined that there is a beam that matches the direction of the mobile station 3 among the beams that exceed the intensity threshold Th1 (S154-YES), the process proceeds to step S156.

[0046] In step S155, the beam update determination unit 13 determines the distance d UE,BS is the distance threshold d ＴＨ It is determined whether the distance is equal to or greater than the distance threshold d. ＴＨ corresponds to the second threshold value in the present disclosure. UE,BS is the distance threshold d ＴＨ If the distance d is less than the predetermined distance (S155-NO), the process proceeds to step S157, and the beam update determination unit 13 determines to start the beam determination procedure from the P1 sub-procedure (S111). UE,BS is the distance threshold d ＴＨIf so (S155-YES), the process proceeds to step S158, and the beam update determination unit 13 determines to start the beam determination procedure from the P2 sub-procedure (S112).

[0047] Distance threshold d ＴＨ can be determined, for example, as follows: When a beam of beam width φ is used, the distance d ＵＥ，ＢＳ The width of the communication area (footprint) in ＵＥ，ＢＳ φ. The moving speed of the mobile station 3 is v ＵＥ and the processing delay τ required for beam update processing ＢＭ From this, the distance L that the mobile station 3 travels during the beam update process is ＢＭ is v ＵＥ ・τ ＢＭ It becomes. ＢＭ ga d ＵＥ，ＢＳ If half of φ is allowed, the distance threshold d is calculated as follows: ＴＨ is 2v ＵＥ τ ＢＭ / φ.

[0048] Distance d ＵＥ，ＢＳ is the distance threshold d ＴＨ If the distance d is less than 0.05, the mobile station 3 may move outside the footprint of the beam during the beam update process, so the beam determination process starts from an earlier sub-procedure (P1 sub-procedure). ＵＥ，ＢＳ is the distance threshold d ＴＨ In the above cases, the mobile station 3 remains within the footprint of the beam, and therefore can start the beam determination process from a later sub-procedure (P2 sub-procedure).

[0049] The control device 1 detects the moving speed v of the mobile station 3. ＵＥ For example, when the mobile station 3 moves at a speed v ＵＥ If the base station 2 has notified the base station 2 of the moving speed v ＵＥ If there is no report of the beam intensity measurement value of each beam in the beam measurement results of the most recent measurement timings, the moving speed v of the mobile station 3 can be calculated from the angle change of the beam with the maximum intensity. ＵＥ Specifically, the moving speed vＵＥ = (distance d of the mobile station) UE,BS ) × (angle change) / (beam measurement time interval). If the beam intensity measurement value is not reported, a predetermined value may be used as the moving speed of the mobile station 3.

[0050] The distance threshold dTH is further determined by the beam lifetime (the maximum time that the same beam can be used) τ ＬＴ In this case, the lifetime τ ＬＴ Adding d ＴＨ = 2v ＵＥ (τ ＢＭ +τ ＬＴ ) / φ.

[0051] In step S156, the beam update determination unit 13 performs the same determination as in step S155. The determination content is the same as in step S155, so a repeated explanation will be omitted. ＴＨ may be the same in step S155 and step S156, or may be different values.

[0052] Distance d UE,BS is the distance threshold d ＴＨ If the distance d is less than the predetermined distance (S156-NO), the process proceeds to step S158, and the beam update determination unit 13 determines to start the beam determination procedure from the P2 sub-procedure (S112). UE,BS is the distance threshold d ＴＨ If the distance d is equal to or greater than the predetermined distance (YES in S156), the process proceeds to step S159, and the beam update determination unit 13 determines to start the beam determination procedure from the P3 sub-procedure (S113). ＵＥ，ＢＳ is the distance threshold d ＴＨ If the distance d is less than 0.05, the mobile station 3 may move outside the footprint of the beam during the beam update process, so the beam update process starts from an earlier sub-procedure (P2 sub-procedure). ＵＥ，ＢＳ is the distance threshold d ＴＨ In the above cases, mobile station 3 remains within the footprint of the beam, and therefore can start the beam update process from a later sub-procedure (P3 sub-procedure).

[0053] [Advantageous Effects] According to the technique disclosed herein, when it becomes necessary to change the beam used for communication between the base station 2 and the mobile station 3, the beam determination (update) procedure, which is made up of multiple subprocedures, can be started from an intermediate subprocedure rather than from the beginning, thereby enabling rapid beam updating. Furthermore, the start phase of the beam determination procedure is determined taking into consideration not only the received strength of the beam at the mobile station 3 but also information such as the direction and distance between the base station 2 and the mobile station 3. Therefore, by executing the necessary subprocedures without skipping them, it is possible to more reliably update to an appropriate beam.

[0054] [Modification] In the above example, two-dimensional coordinates are used to calculate the direction and distance of the mobile station 3, but three-dimensional coordinates may also be used, as shown in Fig. 9C. In the case of three-dimensional coordinates, the direction of the mobile station 3 is calculated using an azimuth angle θ ０ and zenith angle φ ０ The azimuth angle θ ０ , zenith angle φ ０ and distance d UE,RS can be calculated based on the following formula:

[0055] (Embodiment 2) This embodiment differs from embodiment 1 in the process of determining the start phase of beam update (step S15). As the rest is the same as embodiment 1, only the differences will be mainly described.

[0056] FIG. 10 is a flowchart showing the beam update start phase determination process (step S15) in this embodiment. Compared to the first embodiment ( FIG. 8 ), the determination processes of steps S155 and S156 are omitted. If it is determined in step S154 that no beam matching the direction of the mobile station 3 exists among the beams exceeding the intensity threshold Th1 (S154-NO), the process proceeds to step S158, where it is determined that the beam determination procedure will start from the P2 subprocedure. On the other hand, if it is determined in step S154 that a beam matching the direction of the mobile station 3 exists among the beams exceeding the intensity threshold Th1 (S154-YES), the process proceeds to step S159, where it is determined that the beam determination procedure will start from the P3 subprocedure.

[0057] In this embodiment, as in embodiment 1, when it becomes necessary to change the beam used for communication between the base station 2 and the mobile station 3, the beam determination (update) procedure, which consists of multiple sub-procedures, can be started from an intermediate sub-procedure rather than from the beginning, thereby achieving the effect of enabling rapid beam updating.

[0058] (Embodiment 3) This embodiment differs from embodiment 1 in the process of determining the start phase of beam update (step S15). As the rest is the same as embodiment 1, only the differences will be mainly described.

[0059] 11 is a flowchart showing the beam update start phase determination process (step S15) in this embodiment. This embodiment differs from the first embodiment (FIG. 8) in that, depending on the determination result of step S154, steps S201 and S202 are performed instead of steps S155 and S156.

[0060] In step S201, a determination is made using past history. More specifically, it is determined whether the beam duration of a beam selected under the same or similar conditions in the past is sufficiently long. The determination of whether the beam duration is sufficiently long can be made by comparing the beam duration with a duration threshold. The duration threshold may be determined as appropriate, for example, using the lifetime required for the beam. If the beam duration is less than the duration threshold, the process proceeds to step S157, where the beam update determination unit 13 determines to start the beam determination procedure from the P1 subprocedure (S111). On the other hand, if the beam duration is equal to or greater than the duration threshold, the process proceeds to step S158, where the beam update determination unit 13 determines to start the beam determination procedure from the P2 subprocedure (S112).

[0061] The determination process in step S202 is the same as that in step S201, and therefore a repeated explanation will be omitted. The duration threshold may be the same in steps S201 and S202, or may be different values. In step S202, if the beam duration is less than the duration threshold, the process proceeds to step S158, where the beam update determination unit 13 determines to start the beam determination procedure from the P2 subprocedure (S112). On the other hand, if the beam duration is equal to or greater than the duration threshold, the process proceeds to step S159, where the beam update determination unit 13 determines to start the beam determination procedure from the P3 subprocedure (S113).

[0062] In steps S201 and S202, past selections included in the history that satisfy the following conditions can be determined to be selections under the same or similar conditions as the current selection. Criteria for determining identity include one or more of the following: whether the same beam as the beam currently being used for communication was selected; whether the location information of the mobile station 3 is the same; whether the moving speed of the mobile station 3 is the same; and whether the orientation of the mobile station 3 is the same. Here, "the location information of the mobile station 3 is the same" means that the distance between the current location information of the mobile station 3 and the location information of the mobile station 3 in the past selection is within a predetermined threshold, which can be determined appropriately. The same applies to the orientation and moving speed. As an example, the beam update determination unit 13 searches the history for a selection in which the location information and moving speed of the mobile station 3 are the same as those of the current one and the same beam as the beam currently being used for communication was selected. Then, the beam update determination unit 13 performs the determination in steps S201 and S202 by comparing the beam duration of the selected beam with a duration threshold. If there are multiple beam selections that meet the conditions, the statistical values ​​(average, mode, median, minimum, maximum, etc.) of the beam durations of these multiple selections may be compared with the duration threshold. As an example of the statistical value, a weighted average, in which the most recent value is given a greater weight, may be used. Alternatively, the beam duration of the most recent selection may be compared with the duration threshold.

[0063] In order to make a judgment based on history as in this embodiment, the control device 1 stores in memory the measurement results of the mobile station 3, information such as the position, orientation, and movement speed of the mobile station 3, the selected beam, and the beam duration of the selected beam each time it performs a beam update process.

[0064] As in the first embodiment, this embodiment also provides the advantage of enabling rapid beam updating when it becomes necessary to change the beam used for communication between the base station 2 and the mobile station 3, because it is possible to start from an intermediate sub-procedure rather than starting from the beginning of the beam determination (update) procedure consisting of multiple sub-procedures. In this embodiment, the stability of the beam currently in use is evaluated based on past history, and an appropriate start phase for beam updating can be determined based on the stability of the beam.

[0065] Instead of making a decision by directly referencing past history, a machine learning model may be trained using the past history as training data, with each situation as input and the duration of the selected beam as output, and the beam duration in the current situation may be determined by the machine learning model. The estimated beam duration may then be compared with a duration threshold to determine the start phase of the beam determination procedure. This approach also achieves the same effect.

[0066] (Other Modifications) The above-described embodiment is merely an example, and the present disclosure can be implemented with appropriate modifications within the scope of the gist thereof.

[0067] Although the above embodiment illustrates an example of application to 5G cellular communication, the present disclosure can also be applied to cellular communication of other standards such as 3G, 4G, and 6G, as well as wide-area wireless communication and narrow-area wireless communication other than cellular communication. Examples of wide-area wireless communication include wide-area wireless LAN (IEEE 802.11ah) and WiMax (IEEE 802.6). Examples of narrow-area wireless communication include wireless LAN (IEEE 802.11 / a / b / g / n / ac / ax), Bluetooth (registered trademark), DSRC, and ZigBee (registered trademark). Furthermore, while the above embodiment illustrates communication between a base station and a mobile station, the technique of the present disclosure can be applied to communication between any wireless communication devices.

[0068] The present disclosure can also be realized by supplying a computer program that implements the functions described in the above embodiments to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer on a non-transitory computer-readable storage medium connectable to the computer's system bus or via a network. Non-transitory computer-readable storage media include, for example, any type of disk, such as a magnetic disk (e.g., a floppy disk, a hard disk drive (HDD), etc.), an optical disk (e.g., a CD-ROM, a DVD disk, a Blu-ray disk), a read-only memory (ROM), a random access memory (RAM), an EPROM, an EEPROM, a magnetic card, a flash memory, an optical card, or any type of medium suitable for storing electronic instructions.

[0069] 1: Control device 2: Base station 3: Mobile station 10: Control unit 11: Measurement result acquisition unit 12: Mobile station information acquisition unit 13: Beam update determination unit 14: Beam determination unit

Claims

1. A control device for a base station, comprising a control unit that executes the steps of: transmitting a plurality of beams; acquiring measurement results of the plurality of beams from a mobile station; acquiring the direction of the mobile station relative to the base station; and a beam management step that determines which sub-procedure to start from in a beam determination procedure consisting of a plurality of sub-procedures based on the measurement results and the direction of the mobile station.

2. The control device described in claim 1, characterized in that in the beam management step, it is determined which sub-procedure of a beam determination procedure consisting of multiple sub-procedures to start based on the measurement results and the direction of the mobile station, as well as the distance between the base station and the mobile station.

3. The control device according to claim 1, characterized in that the control unit further executes a step of acquiring information regarding the position of the mobile station from the mobile station, and in the step of acquiring the direction of the mobile station relative to the base station, the direction of the mobile station relative to the base station is determined from the position of the mobile station and the position of the base station.

4. The control device described in claim 1, characterized in that the beam determination procedure includes, in this order: a first sub-procedure for adjusting a base station beam using a base station beam with a first angular resolution; a second sub-procedure for adjusting a base station beam using a base station beam with a second angular resolution higher than the first angular resolution; and a third sub-procedure for adjusting a mobile station beam; and in the beam management step, it is determined which of the first sub-procedure, the second sub-procedure, or the third sub-procedure to start with based on the measurement results and the direction of the mobile station.

5. The control device described in claim 4, characterized in that the beam management step includes a first judgment step of determining whether or not the measurement results include a beam whose received signal strength is higher than a first threshold, and if there is no beam whose received signal strength is higher than the first threshold, it decides to start from the first sub-procedure.

6. The control device described in claim 5, characterized in that the beam management step includes a second judgment step of judging whether or not there is a beam that matches the direction of the mobile station among the beams whose received signal strength is higher than the first threshold, and if there is a beam whose received signal strength is higher than the first threshold and none of those beams matches the direction of the mobile station, the control device starts with the first subprocedure or the second subprocedure, and if there is a beam whose received signal strength is higher than the first threshold and none of those beams matches the direction of the mobile station, the control device starts with the second subprocedure or the third subprocedure.

7. In the second determination step, the direction of the mobile station is determined as θ ０ , the direction of the beam whose received signal strength is higher than the first threshold is defined as θ ＯＫ , where φ is the beam width of the beam, and θ ＯＫ −φ / 2<θ ０ <θ ＯＫ 7. The control device according to claim 6, wherein it is determined that the direction of the beam matches the direction of the mobile station when +φ / 2 is satisfied.

8. In the second determination step, the direction of the mobile station is determined as θ ０ , the direction of the beam whose received signal strength is higher than the first threshold is defined as θ ＯＫ , the distance between the base station and the mobile station is d ＵＥ，ＢＳ , where D is the maximum Fresnel diameter of the beam, and θ ＯＫ -D / d ＵＥ，ＢＳ <θ ０ <θ ＯＫ +D / d ＵＥ，ＢＳ 7. The control device according to claim 6, wherein it is determined that the direction of the beam and the direction of the mobile station match when the following expression is satisfied:

9. The control device according to claim 6, wherein the beam management step includes a third determination step of determining whether the distance between the base station and the mobile station is greater than a second threshold, and starts from the first subprocedure if there are beams whose received signal strength is greater than a first threshold, and among those beams there is none that matches the direction of the mobile station, and the distance between the base station and the mobile station is greater than the second threshold; starts from the second subprocedure if there are beams whose received signal strength is greater than the first threshold, and among those beams there is none that matches the direction of the mobile station, and the distance between the base station and the mobile station is less than the second threshold; starts from the second subprocedure if there are beams whose received signal strength is greater than the first threshold, and among those beams there is a beam that matches the direction of the mobile station, and the distance between the base station and the mobile station is greater than the second threshold; and starts from the third subprocedure if there are beams whose received signal strength is greater than the first threshold, and among those beams there is a beam that matches the direction of the mobile station, and the distance between the base station and the mobile station is less than the second threshold.

10. The second threshold is defined as φ, which is the beam width of the beam with the highest received signal strength, and v, which is the moving speed of the mobile station. ＵＥ , the processing delay required for the beam determination procedure is τ ＢＭ As a result, 2v ＵＥ τ ＢＭ 10. The control device according to claim 9, wherein: / φ.

11. The second threshold is defined as φ, which is the beam width of the beam with the highest received signal strength, and v, which is the moving speed of the mobile station. ＵＥ , the processing delay required for the beam management sub-procedure is τ ＢＭ , the lifetime of the beam with the highest received intensity is τ ＬＴ As a result, 2v ＵＥ (τ ＢＭ +τ ＬＴ 10. The control device according to claim 9, wherein: φ=(φ) / φ.

12. The control device according to claim 10, wherein the control unit further executes a step of acquiring a moving speed of the mobile station.

13. The control device according to claim 10, characterized in that the control unit further executes a step of calculating the moving speed of the mobile station based on the angular change in the direction of the beam that maximizes the received signal strength at different measurement timings and the measurement time interval between the different measurement timings.

14. The control device described in claim 5, characterized in that the beam management step includes a second judgment step of judging whether or not there is a beam among the beams whose received signal strength is higher than the first threshold that matches the direction of the mobile station, and if there are beams whose received signal strength is higher than the first threshold and none of those beams matches the direction of the mobile station, starting with the second sub-procedure, and if there are beams whose received signal strength is higher than the first threshold and none of those beams matches the direction of the mobile station, starting with the third sub-procedure.

15. The control device according to claim 4, wherein the beam management step further includes a step of obtaining the duration of a beam selected based on measurement results under the same conditions from past history, and determining from which sub-procedure of the beam determination procedure to start based on a comparison between the duration of the beam and a duration threshold.

16. A control method for a base station, comprising: a step of transmitting a plurality of beams; a step of acquiring measurement results of the plurality of beams from a mobile station; a step of acquiring the direction of the mobile station relative to the base station; and a beam management step of determining which sub-procedure to start from in a beam determination procedure consisting of a plurality of sub-procedures, based on the measurement results and the direction of the mobile station.

17. The control method according to claim 16, characterized in that the beam determination procedure includes, in this order: a first subprocedure for adjusting a base station beam using a base station beam with a first angular resolution; a second subprocedure for adjusting a base station beam using a base station beam with a second angular resolution higher than the first angular resolution; and a third subprocedure for adjusting a mobile station beam; and the beam management step determines which of the first subprocedure, the second subprocedure, or the third subprocedure to start with, based on the measurement results and the direction of the mobile station.

18. The control method described in claim 17, characterized in that the beam management step includes a first judgment step of judging whether or not there is a beam in the measurement results whose received signal strength is higher than a first threshold, and if there is no beam whose received signal strength is higher than the first threshold, it is decided to start from the first sub-procedure.

19. The beam management step includes a third determination step of determining whether the distance between the base station and the mobile station is greater than a second threshold, and starts from the first subprocedure if there are beams whose received signal strength is greater than a first threshold, none of those beams coincides with the direction of the mobile station, and the distance between the base station and the mobile station is greater than the second threshold; starts from the second subprocedure if there are beams whose received signal strength is greater than the first threshold, none of those beams coincides with the direction of the mobile station, and the distance between the base station and the mobile station is less than the second threshold; starts from the second subprocedure if there are beams whose received signal strength is greater than the first threshold, none of those beams coincides with the direction of the mobile station, and the distance between the base station and the mobile station is greater than the second threshold; starts from the third subprocedure if there are beams whose received signal strength is greater than the first threshold, none of those beams coincides with the direction of the mobile station, and the distance between the base station and the mobile station is less than the second threshold.

18. The control method according to claim 17.

20. The control method according to claim 16, further comprising the steps of: acquiring information relating to the location of the mobile station from the mobile station; and determining, from the location of the mobile station and the location of the base station, the direction of the mobile station relative to the base station or the distance between the mobile station and the base station.

21. A computer program for causing an information processing device to execute the following steps: transmitting a plurality of beams; acquiring measurement results of the plurality of beams from a mobile station; acquiring the direction of the mobile station relative to a base station; and a beam management step of determining which sub-procedure to start from in a beam determination procedure consisting of a plurality of sub-procedures, based on the measurement results and the direction of the mobile station.

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