Base station, communication method, and communication program

Abstract

Provided is a base station that relays communication between terminals and can identify, at an early stage, a precoding matrix to be applied to a terminal. This base station relays wireless communication between a plurality of terminals by multiple input multiple output (MIMO) transmission. The base station comprises: an acquisition unit that acquires position information related to a first terminal; an estimation unit that estimates the position of the first terminal after a prescribed time period on the basis of the position information; an identification unit that identifies a second terminal which was present in the past within a prescribed range from the position estimated by the estimation unit and which is different from the first terminal; and a communication unit that performs communication by executing beamforming for the first terminal by using, as a precoding matrix for the first terminal estimated to be present at the position estimated by the estimation unit, a precoding matrix which has been used for the second terminal identified by the identification unit.

Description

Base station, communication method and communication program

[0001] The present invention relates to a base station that relays communication between terminals, a communication method therefor, and a communication program.

[0002] In recent years, when communication is performed using MIMO (Multiple Input Multiple Output) transmission, a base station controls the directivity of an antenna in communication (also known as beamforming) to communicate with a terminal, thereby avoiding crosstalk between terminals. Patent Literature 1 discloses a method for specifying a precoding matrix when a terminal performs handover from one base station to another.

[0003] JP 2017-118462 A

[0004] In recent years, the precoding matrix has been calculated for each terminal, and depending on the number of terminals around the base station, the amount of calculation can become enormous. Furthermore, when a terminal is moving, especially at high speed, if the calculation is delayed, the beamforming cannot keep up, and communication with that terminal may be temporarily disabled or communication quality may deteriorate.

[0005] Therefore, the present invention has been made in consideration of the above problems, and aims to provide a base station that can identify a precoding matrix to be used for a terminal earlier than conventional methods, as well as a communication method and communication program for the base station.

[0006] In order to solve the above problem, a base station according to one aspect of the present invention is a base station that relays wireless communication between multiple terminals using MIMO (Multiple Input Multiple Output) transmission, and includes: an acquisition unit that acquires location information of a first terminal; an estimation unit that estimates the location of the first terminal after a predetermined time based on the location information; an identification unit that identifies a second terminal that is different from the first terminal that previously existed within a predetermined range from the location estimated by the estimation unit; and a communication unit that performs beamforming on the first terminal, using the precoding matrix used for the second terminal identified by the identification unit as the precoding matrix for the first terminal estimated to be present at the location estimated by the estimation unit, and communicates with the first terminal.

[0007] In addition, the base station may include a memory unit that stores correspondence information that associates the precoding matrix used for the second terminal with location information of the second terminal when the precoding matrix was used, and the identification unit may identify the second terminal based on the correspondence information.

[0008] In addition, in the above base station, the correspondence information may further be associated with speed information indicating the movement speed of the second terminal, the estimation unit may further estimate the movement speed of the first terminal at the position of the first terminal after a predetermined time, and the identification unit may further identify the second terminal based on the movement speed.

[0009] In addition, in the above base station, the correspondence information may further be associated with directional information indicating the movement direction of the second terminal, the estimation unit may further estimate the movement direction of the second terminal at the position of the first terminal after a predetermined time, and the identification unit may further identify the second terminal based on the movement direction.

[0010] In addition, in the above base station, if the communication unit is unable to communicate with the first terminal estimated to be located at the position estimated by the estimation unit using the precoding matrix used for the second terminal, it may return to the precoding matrix most recently used for the first terminal and perform beamforming to communicate.

[0011] In addition, the base station may be provided with a transmission unit that transmits location information indicating the location of the first terminal to other base stations that cover the location when the location of the first terminal after a predetermined time determined by the estimation unit is outside the communication range of the base station.

[0012] Furthermore, the base station may include a receiving unit that receives location information indicating an estimated location of a third terminal after a predetermined time from another base station, an identifying unit that identifies a second terminal that is present within a predetermined range from the location information, and a communication unit that performs beamforming for the third terminal using the precoding matrix used for the second terminal identified by the identifying unit as the precoding matrix for the third terminal that is estimated to be present at the location estimated by the estimating unit, and communicates with the third terminal.

[0013] In addition, in order to solve the above problem, a communication method according to one aspect of the present invention includes an acquisition step in which a computer of a base station that relays wireless communication between multiple terminals via MIMO (Multiple Input Multiple Output) transmission acquires location information of a first terminal; an estimation step in which the location of the first terminal after a predetermined time based on the location information; an identification step in which a second terminal different from the first terminal that previously existed within a predetermined range from the location estimated in the estimation step is identified; and a communication step in which beamforming is performed on the first terminal using the precoding matrix used for the second terminal identified in the identification step as the precoding matrix for the first terminal estimated to be present at the location estimated in the estimation step, thereby communicating.

[0014] In addition, in order to solve the above problem, a communication program according to one aspect of the present invention provides a computer of a base station that relays wireless communication between multiple terminals via MIMO (Multiple Input Multiple Output) transmission with the following functions: an acquisition function that acquires location information of a first terminal; an estimation function that estimates the location of the first terminal after a predetermined time based on the location information; a determination function that identifies a second terminal that is different from the first terminal that previously existed within a predetermined range from the location estimated by the estimation function; and a communication function that performs beamforming on the first terminal, using the precoding matrix used for the second terminal identified by the determination function as the precoding matrix for the first terminal estimated to be located at the location estimated by the estimation function, to communicate.

[0015] According to the base station of the present invention, it is possible to predict the movement of a terminal and perform beamforming at the new location using a precoding matrix that was assigned to a terminal that had previously been there, thereby making it possible to determine the precoding matrix for the terminal earlier than before and to start communication earlier than before.

[0016] Fig. 1 is a schematic diagram showing an overview of a communication system; Fig. 2 is a block diagram showing an example of the configuration of a base station; Fig. 3 is a data conceptual diagram showing an example of the configuration of precoding information; Fig. 4 is a flowchart showing an example of an operation when a base station determines a precoding matrix for a terminal; Fig. 5 is a flowchart showing an example of an operation when a terminal is handed over from its own station to another station; Fig. 6 is a flowchart showing an example of an operation when a terminal is handed over from another station to its own station.

[0017] A base station according to the present invention will be described below with reference to the drawings.

[0018] <Overview> Fig. 1 is a schematic diagram showing an overview of a communication system. In Fig. 1, the upper side shows an example of a communication state between base station 100 and a terminal at a certain time t1, and the lower side shows an example of a communication state between base station 100 and a terminal at a time t2 after time t1.

[0019] The base station 100 is a communication device that relays communications between terminals 200 within its coverage area and is an information processing device (computer system) having so-called base station functionality. The base station 100 is a base station that performs MIMO (Multiple Input Multiple Output) communications. The base station 100 performs beamforming (forming antenna directivity) for the terminals 200 to communicate with them. This allows for favorable communication with the terminals 200 for which beamforming is being performed, while also making communication with terminals 200 outside the beamforming range difficult, thereby reducing the occurrence of crosstalk. When performing beamforming, the base station 100 determines a precoding matrix to be used for each terminal 200 and performs beamforming based on the determined precoding matrix. Precoding refers to beamforming to support multi-stream transmission when performing wireless communication using multiple antennas, and a precoding matrix is ​​a coefficient by which a signal (baseband signal) transmitted from base station 100 to terminal 200 is multiplied. If y is the received signal received by base station 100 from terminal 200, H is the channel matrix, W is the precoding matrix, s is the transmitted symbol, and n is the received noise, then y = HWs + n holds, and it is generally known that by solving this equation for W, the precoding matrix to be used for terminal 200 can be calculated. The precoding matrix can be uniquely estimated from the channel estimation value from base station 100 to terminal 200.

[0020] The upper diagram in Figure 1 shows an example in which base station 100 performs beamforming using precoding matrix α for terminal 200a, and performs beamforming using precoding matrix β for terminal 200b.

[0021] Here, the terminal 200 is a portable terminal held by a user and moves along with the user's movements. Note that the terminal 200 may be, for example, a mobile communication module such as a smartphone, a tablet terminal, or a mobile phone, but is not limited to these.

[0022] Therefore, when terminal 200 moves and is likely to move outside the beamforming range, base station 100 needs to determine a new precoding matrix for the moving terminal 200 and perform beamforming, and it is desirable to adjust the beamforming direction as appropriate.

[0023] In the past, when determining this precoding matrix, the base station 100 transmitted a codebook specifying multiple precoding matrices to the terminal 200, the terminal 200 reported a suitable precoding matrix to the base station 100, and the base station 100 performed beamforming using the reported precoding matrix. In recent years, the flow has shifted to performing channel estimation between the base station 100 and the terminal 200 to calculate a precoding matrix and then perform beamforming. However, since the base station 100 communicates with countless terminals 200 in the vicinity, it is desirable to reduce the processing load as much as possible.

[0024] 1, the base station 100 predicts the movement of the terminal 200b, determines whether or not the terminal 200 previously existed at the predicted post-movement position, and if so, performs beamforming by applying the precoding matrix α that was used for the terminal 200a previously existed at the post-movement position. This allows beamforming to be performed for the post-movement terminal 200b earlier than in the past, and also reduces the processing load on the base station 100 because it is not necessary to perform communication with the terminal 200b to determine the precoding matrix.

[0025] The base station 100 according to this embodiment will be described in detail below.

[0026] <Configuration> <Configuration of Base Station 100> FIG. 2 is a block diagram showing an example configuration of the base station 100. The base station 100 functions as a base station that relays communications between terrestrial terminals 200 and is a computer system that operates according to a predetermined program. The base station 100 may be configured to construct a virtual radio access network (vRAN) implemented by a CPU and a GPU. In the base station 100, the communication unit 110 described below may be an RU (Radio Unit) in 5G communication. The function implemented by the control unit 130 may be implemented by a DU (Distribution Unit) or a CU (Central Unit) in 5G communication, or may be implemented by an RU. The base station 100 may be configured to implement a radio access network intelligent controller (RIC) or may operate under the control of an RIC.

[0027] 2, the base station 100 includes a communication unit 110, a control unit 130, and a storage unit 140. The base station 100 may also include an input unit 120 and an output unit 150.

[0028] The communication unit 110 is a communication interface having a function of communicating with a device external to the base station 100. The communication unit 110 has a function of communicating with the terminal 200 as an external device. The communication unit 110 may perform beamforming in a specified direction in accordance with an instruction from the control unit 130 to communicate with the terminal 200.

[0029] The input unit 120 has a function of receiving input from an operator of the base station 100 or the like and transmitting the input content to the control unit 130. The input unit 120 may be realized by an input device such as a mouse, a keyboard, or a touch panel, or in the case of voice input, by a microphone.

[0030] The control unit 130 is a processor having the function of controlling each unit of the base station 100. The control unit 130 may be realized by a single core or a multi-core. The control unit 130 executes various programs stored in the storage unit 140 and uses various data to realize the functions of the base station 100.

[0031] The control unit 130 relays communication between the terminals 200 in the same manner as a normal base station 100. At this time, the control unit 130 calculates a precoding matrix for performing beamforming (forming antenna directivity) for communication with the terminals 200, and causes the communication unit 110 to perform beamforming in accordance with the calculated precoding matrix, thereby executing communication.

[0032] The control unit 130 has a function of storing precoding information 141 in the storage unit 140 as a history of communication with the terminal 200 via the communication unit 110. The precoding information 141 is information that associates at least a terminal identifier 302, location information 303, and a precoding matrix 307 used for the terminal 200 at that time.

[0033] The control unit 130 includes an acquisition unit 131, an estimation unit 132, and an identification unit 133 as functions realized by the control unit 130.

[0034] The acquisition unit 131 acquires location information of the terminal 200. The acquisition unit 131 may acquire location information acquired by the terminal 200 from the terminal 200 using GPS or the like. Alternatively, the acquisition unit 131 may estimate and acquire the location of the terminal 200 based on a signal received from the terminal 200. Estimating the location of the terminal 200 based on the signal received from the terminal 200 may, for example, acquire the location information of the terminal 200 using a learning model that learns the relationship between the reception strength and waveform of a signal received from the terminal 200 (which may be, for example, an SRS (Sounding Reference Signal), but is not limited to, an SRS) and the relative position (or absolute position coordinates) of the terminal 200 with respect to a base station at that time. Alternatively, the acquisition unit 131 may acquire the location information of the terminal 200 by using identification information of the terminal 200 to inquire about the location information of the terminal 200 from a service providing device that stores the location information of the terminal 200. The acquisition unit 131 transmits the acquired location information of the terminal 200 to the estimation unit 132 .

[0035] The estimation unit 132 estimates the location of the terminal 200 after a predetermined time based on the location information of the terminal 200 acquired by the acquisition unit 131. The predetermined time may be, for example, one minute later, but is not limited to this and may be any time such as five minutes later, ten minutes later, or 30 seconds later. The estimation unit 132 identifies the movement path and movement speed of the terminal 200 based on the location information of the multiple terminals 200 acquired by the acquisition unit 131 and the time at which the location information was acquired, and estimates the location of the terminal 200 after a predetermined time based on the identified movement path and movement speed. The estimation unit 132 transmits the estimated location of the terminal 200 after the predetermined time to the identification unit 133. At this time, the estimation unit 132 may also transmit the identified movement path and movement speed of the terminal 200 to the identification unit 133.

[0036] The identification unit 133 identifies another terminal 200 that is different from the terminal 200 that was previously present within a predetermined range (for example, within 3 m, but not limited to this) from the position of the terminal 200 after a predetermined time transmitted from the estimation unit 132. More specifically, the identification unit 133 identifies precoding information 141 having position information 303 within a predetermined range from the position of the terminal 200 after a predetermined time transmitted from the estimation unit 132. At this time, the identification unit 133 may further identify precoding information 141 of another terminal 200 that is within a predetermined speed (for example, within 1 km / h around the transmitted speed, or within 10% around the transmitted speed, but not limited to this) based on the movement speed 305 of the precoding information 141. Furthermore, the identification unit 133 may further identify the direction of movement of the terminal 200 after a predetermined time based on the movement path transmitted by the estimation unit 132 and the precoding information 141 of other terminals 200 within a predetermined range (within a predetermined angle (for example, 5 degrees, but not limited to this) to the left and right of the direction of movement) based on the movement direction 306 of the precoding information 141.

[0037] The control unit 130 refers to the precoding matrix 307 in the precoding information 141 to identify the precoding matrix that was used at the time for the terminal 200 identified by the identification unit 133 and that was previously located at the position estimated by the estimation unit 132. Then, the control unit 130 instructs the communication unit 110 to perform beamforming using the identified precoding matrix after the above-mentioned predetermined time period, and to communicate with the terminal 200. Therefore, the communication unit 110 performs beamforming in accordance with the precoding matrix instructed by the control unit 130, and executes communication with the terminal 200.

[0038] The control unit 130 registers the information such as the location information, moving speed, and moving direction of the terminal 200 acquired by the above-mentioned method, along with the precoding matrix used, in the precoding information 141 in association with the terminal identifier of the terminal 200.

[0039] Furthermore, if the location of terminal 200 after a predetermined time estimated by estimation unit 132 will be outside the coverage area (communication range) of the own device, control unit 130 identifies another base station that will cover the estimated location of terminal 200 after the predetermined time. Then, control unit 130 transmits information indicating the location of terminal 200 and the moving speed and moving direction at that time to the base station via communication unit 110. Terminal 200 that has moved out of the coverage area of ​​the own device will be handed over to another base station, but at this time, since information about terminal 200 has been transmitted from base station 100 to this other base station, the other base station can use the above-mentioned method to perform beamforming on terminal 200 that will be handed over early.

[0040] Conversely, if there is a terminal 200 that is about to be handed over to the own terminal, information indicating the position, moving speed, and moving direction of that terminal 200 after a predetermined time is received from another base station via communication unit 110, and the precoding matrix to be applied to terminal 200 that has handed over after the predetermined time can be identified using precoding information 141, thereby enabling beamforming to be realized early.

[0041] The storage unit 140 has a function of storing various programs and data required for the operation of the base station 100. The storage unit 140 can be realized, for example, by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, etc., but is not limited to these. The storage unit 140 may store various programs and various data for realizing the functions to be performed by the base station 100. The storage unit 140 may store, for example, a program that estimates the movement of the terminal 200 and, based on the estimated position after the movement, identifies a precoding matrix used for a terminal that was previously located at that position and causes the communication unit 110 to perform beamforming. The storage unit 140 may also store precoding information 141. Details of the precoding information 141 will be described later.

[0042] The output unit 150 has a function of outputting designated information in accordance with an instruction from the control unit 130. The output unit 150 may, for example, output text information or image information, in which case the output unit 150 is realized by a monitor provided in or connected to the base station 100. The output unit 150 may, for example, output audio information, in which case the output unit 150 is realized by a speaker provided in or connected to the information processing device.

[0043] The above is an example of the configuration of the base station 100.

[0044] The terminal 200 is similar to a typical information processing device having a configuration similar to that of a communication terminal such as a smartphone or tablet terminal, and therefore a detailed description using a block diagram will be omitted.

[0045] <Data> Fig. 3 is a conceptual data diagram showing an example configuration of the precoding information 141. As shown in Fig. 3, the precoding information 141 is correspondence information in which a management number 301, a terminal identifier 302, location information 303, a movement speed 305, a movement direction 306, and a precoding matrix 307 are associated with each other.

[0046] The management number 301 is a management number assigned by the control unit 130 for the purpose of managing each piece of precoding information 141 for convenience.

[0047] The terminal identifier 302 is identification information that can uniquely identify each terminal 200 .

[0048] The location information 303 is information indicating the location of the terminal 200 indicated by the corresponding terminal identifier 302, and may be, but is not limited to, information on longitude and latitude. The location information 303 may be relative coordinates with the base station 100, as long as it is possible to know the location as seen from the base station 100.

[0049] The time 304 is information indicating the time (date and time) when the corresponding position information 303 was measured.

[0050] The moving speed 305 is information indicating the moving speed of the terminal 200 when the terminal 200 was moving and was located at the position indicated by the corresponding terminal identifier 302 and the position information 303. When the terminal 200 was not moving, 0 may be registered in the moving speed 305, indicating that the terminal 200 was not moving.

[0051] The movement direction 306 is information indicating the movement direction of the terminal 200 when the terminal 200 was moving and was located at the position indicated by the corresponding terminal identifier 302 and the position information 303. When the terminal 200 was not moving, 0 may be registered in the movement direction 306, indicating that the terminal 200 was not moving.

[0052] The precoding matrix 307 is information indicating the precoding matrix that the base station 100 used for the terminal 200 indicated by the corresponding terminal identifier 302 when the terminal 200 was located at the location indicated by the corresponding location information 303.

[0053] That is, the precoding information 141 is information that records the precoding matrix that the base station 100 used for the terminal 200 indicated by the terminal identifier 302 under the conditions indicated by the corresponding moving speed 305 and moving direction 306 when the terminal 200 was located at the position indicated by the location information 303. The presence of the precoding information 141 allows the control unit 130 to quickly identify the precoding matrix to be used for communication without performing processing to calculate a precoding matrix for communication.

[0054] Note that the precoding information 141 shown in Figure 3 may include information other than that shown in the figure, and unnecessary information shown in Figure 3 may not be stored. For example, the precoding information 141 may also include information on the height of the terminal 200 in addition to the information shown in the figure. Furthermore, the management number 301 of the precoding information 141 shown in Figure 3 may not be stored. Similarly, the movement speed 305 and the movement direction 306 may not be stored. This is because the movement speed 305 and the movement direction 306 can be calculated based on past position information of the terminal.

[0055] <Operation> The operation of the base station 100 in the communication system 1 according to this embodiment will be described with reference to FIGS.

[0056] FIG. 4 is a flowchart showing an example of the operation of base station 100 when base station 100 identifies a precoding matrix to be used for terminal 200 and communicates with terminal 200.

[0057] 4, the acquisition unit 131 of the control unit 130 of the base station 100 acquires location information of the communicating terminal 200 (step S401). The acquisition unit 131 transmits the acquired location information of the terminal 200 to the estimation unit 132.

[0058] The estimation unit 132 estimates the location of the terminal 200 after a predetermined time based on the transmitted location information of the terminal 200 and past location information of the terminal (step S402). The estimation unit 132 may also estimate the moving speed and moving direction of the terminal 200. The estimation unit 132 transmits information on the estimated location, moving speed, and moving direction of the terminal 200 to the identification unit 133.

[0059] The identifying unit 133 identifies whether there is precoding information 141 of another terminal that was previously present at a position close to (within a predetermined distance from) the transmitted position of the terminal 200 (step S403).

[0060] At this time, the specifying unit 133 may further narrow down the precoding information 141 using the transmitted information on the moving speed, and may specify the precoding information 141 for which the moving speed is within a predetermined forward and backward speed, for example, within 1 km / h forward and backward (step S404). Since tracking performance can be improved by changing the direction (e.g., beamforming in the direction of travel of the terminal) or range (widening the range when the moving speed is fast and narrowing the range when the moving speed is slow) of the beamforming depending on the moving speed of the terminal 200 using such past information (information on beamforming applied according to the speed of the terminal), it is possible to specify a precoding matrix suitable for the moving speed of the terminal 200 and improve communication accuracy.

[0061] Furthermore, the identification unit 133 may further narrow down the precoding information 141 using the transmitted information on the moving direction, and may identify precoding information 141 whose moving direction has a direction within a predetermined range, for example, within 10 degrees to the left or right of the transmitted moving direction (step S405). Tracking performance can be improved by changing the beamforming direction (such as to cover the direction ahead) or range (such as narrowing the range when the direction can be determined and widening the range when the direction prediction cannot be determined) depending on the moving direction of the terminal 200. Therefore, by narrowing down the precoding information 141 according to the moving direction using such past information (information on beamforming applied according to the moving direction of the terminal), it is possible to identify a precoding matrix suitable for the moving direction of the terminal 200 and improve communication accuracy.

[0062] The control unit 130 identifies the precoding matrix used for the other terminal identified by the identification unit 133 from the precoding matrix 307 in the precoding information 141. Then, the control unit 130 instructs the communication unit 110 to perform beamforming using the identified precoding matrix to communicate with the terminal 200 after a predetermined time. In accordance with the instruction from the control unit 130, the communication unit 110 performs beamforming using the specified precoding matrix to communicate with the terminal 200 after a predetermined time (step S406), and ends the process.

[0063] The control unit 130 may execute the process shown in Figure 4 individually for each terminal 200 with which the base station 100 is communicating, and may execute the process periodically (for example, every minute, but not limited to this).

[0064] Figure 5 shows an example of operation in this embodiment when base station 100 identifies a precoding matrix to be applied to terminal 200, in which terminal 200 is handed over from base station 100 to another base station, and Figure 6 shows an example of operation when terminal 200 is handed over from another base station 100 to base station 100.

[0065] The processing of steps S501 and S502 shown in Fig. 5 is the same as the processing of steps S401 and S402 shown in Fig. 4. In step S503, the control unit 130 of the base station 100 determines whether the target terminal 200 will be handed over from the base station to another base station. That is, the control unit 130 determines whether the location of the terminal 200 after a predetermined time estimated in step S502 is outside the coverage area (communication range) of the base station.

[0066] If the control unit 130 determines that the terminal 200 will not be handed over (NO in step S503), the process ends. If the control unit 130 determines that the terminal 200 will be handed over (YES in step S503), the control unit 130 identifies a base station that will cover the estimated location of the terminal 200 after a predetermined time as its communication range (step S504). This identification may be performed by storing information indicating the coverage area of ​​each base station in the storage unit 140, and identifying the base station from this information. Alternatively, if there is a higher-level device that is higher than the base station 100 in the communication system, the base station 100 may be identified by inquiring of the higher-level device for information on base stations that cover the estimated location.

[0067] When the control unit 130 identifies a base station that will cover the position of the terminal 200 after the predetermined time, the control unit 130 transmits information indicating the position, moving speed, and moving direction of the terminal 200 after the predetermined time to the base station via the communication unit 110 (step S505), and ends the processing. As a result, the handover destination base station can also easily identify the precoding matrix to be used for the terminal 200 after the predetermined time, as described above, and can perform beamforming and execute communication early. By performing the processing of FIG. 5, the base station 100 can transmit information so that other base stations can also identify the precoding matrix early.

[0068] FIG. 6 is a flowchart showing an example of operation when a new terminal is handed over from another base station to base station 100 in this embodiment.

[0069] 6, the communication unit 110 receives information including the location of a terminal scheduled to be handed over from another base station (step S601). The communication unit 110 transfers the received information to the control unit 130.

[0070] The control unit 130 executes the processes of S403 to S405 in FIG. 4 to determine whether there is precoding information 141 corresponding to the received information (step S602).

[0071] If there is precoding information 141 corresponding to the received information (YES in step S602), the control unit 130 instructs the communication unit 110 to perform beamforming using the precoding matrix 307 indicated by the identified precoding information 141 as the precoding matrix for the terminal 200 that has performed handover, and to perform communication with the terminal. The communication unit 110 performs beamforming using the precoding matrix specified by the control unit 130, performs communication with the terminal that has performed handover (step S603), and ends the process.

[0072] If there is no precoding information 141 corresponding to the received information (NO in step S602), the communication unit 110 performs channel estimation with the terminal that has been handed over, calculates a precoding matrix, performs beamforming using the calculated precoding matrix, and executes communication (step S604), and ends the process. By performing the process of Fig. 6, the base station 100 can perform early beamforming and communicate with the terminal that has been handed over to the base station.

[0073] The above is an example of the operation of the base station 100 according to the embodiment.

[0074] <Summary> As described above, base station 100 estimates the movement of terminal 200, i.e., the location after a predetermined time, and applies a precoding matrix that was used for a terminal that was previously at that location, thereby making it possible to identify a precoding matrix without performing processing to calculate a precoding matrix to be used for terminal 200. If a precoding matrix has been used for a terminal that has previously been at the same location, there is a high possibility that communication can be performed even if it is similarly applied. As a result, a precoding matrix can be identified and communication can be performed earlier than if a precoding matrix is ​​calculated, and the processing load of control unit 130 for calculating a precoding matrix can be reduced.

[0075] <Modifications> It goes without saying that the base station 100 according to the above embodiment is not limited to the above embodiment, and may be realized by other methods. Various modifications will be described below.

[0076] (1) In the above embodiment, an example was shown in which the base station 100 estimates the position of the terminal 200 after a predetermined time, determines whether a terminal 200 previously existed at that position, and, if so, applies the precoding matrix used for the terminal 200 previously present. However, the base station 100 may acquire the position of the terminal 20 at the current time, rather than after a predetermined time, and determine the precoding matrix based on that position, as in the above embodiment. This configuration eliminates the need to perform processing to estimate the position of the terminal 200 after a predetermined time, thereby reducing the processing load on the control unit 130 of the base station 100. However, compared to the aspect shown in the above embodiment, there is a possibility that delays may occur in terms of beamforming tracking of the terminal 200.

[0077] (2) In the above embodiment, an example has been shown in which the precoding information 141 is identified based on the location information, moving speed, and moving direction of the terminal 200. However, as long as the precoding information 141 can be identified, identification based on the moving speed or moving direction may be omitted. In other words, the control unit 130 may omit one or both of the processes of steps S404 and S405 in FIG. 4 .

[0078] (3) In the above embodiment, the processing of steps S403 to S405 may fail to narrow down the information to one precoding information 141. In that case, the control unit 130 may randomly select one of the multiple pieces of precoding information 141, or may further narrow down the information to one using the following method. That is, if multiple pieces of precoding information 141 can be identified, the control unit 130 may identify the precoding information 141 that is closest overall in terms of the transmitted position, moving speed, and moving direction. The identification unit 133 may, for example, generate a vector A indicating the transmitted position, moving speed, and moving direction, and a vector B indicating the position, moving speed, and moving direction indicated by the precoding information 141, and identify the precoding information 141 with the shortest distance between vector A and vector B.

[0079] (4) In the above embodiment, the other terminal identified by the identification unit 133 may be a target terminal that was previously present at that location.

[0080] (5) In the above embodiment, the control unit 130 executes the process of Fig. 4 at predetermined time intervals for all terminals 200 communicating with the base station 100. However, this is not limited to this. The frequency with which the process of Fig. 4 is executed may be changed for each terminal 200 depending on the status of the terminal 200.

[0081] (6) In the above embodiment, if the precoding information 141 cannot be identified as a result of performing the processing of steps S403 to S405, the precoding matrix to be applied to the terminal 200 may be calculated as usual. Alternatively, the control unit 130 may use the precoding matrix that was used for the terminal 200 immediately before for the terminal 200 after a predetermined time (returning to the previous precoding matrix). Alternatively, if the control unit 130 cannot identify the precoding information 141, the control unit 130 may expand the range of conditions by expanding the range of the location, the range of the movement speed, or the movement direction, or by deleting any of the conditions, so that the precoding information 141 can be identified. This prevents the terminal 200 from being unable to communicate with the base station 100.

[0082] (7) A program for the base station 100 of the present disclosure to estimate the position of the terminal 200 and identify the precoding matrix to be applied based on past cases may be provided in a state stored in a computer-readable storage medium. The storage medium can store the program in a "non-transitory tangible medium." The storage medium can include any appropriate storage medium such as an HDD or an SSD, or an appropriate combination of two or more thereof. The storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile. Note that the storage medium is not limited to these examples and may be any device or medium capable of storing the program.

[0083] The base station 100 can realize the functions of the multiple functional units shown in each embodiment by, for example, reading a program stored in a storage medium and executing the read program. The program may also be provided to the base station 100 via any transmission medium (such as a communication network or broadcast waves). The base station 100 realizes the functions of the multiple functional units shown in each embodiment by executing a program downloaded via the Internet, for example. This program may be executed by the base station 100, etc.

[0084] The program can be implemented using, for example, a scripting language such as ActionScript or JavaScript (registered trademark), an object-oriented programming language such as Objective-C or Java (registered trademark), or a markup language such as HTML5, but is not limited to these.

[0085] At least a part of the processing in the base station 100 may be realized by cloud computing consisting of one or more computers. Furthermore, each functional unit of the base station 100 may be realized by one or more circuits that realize the functions described in the above embodiments, or the functions of multiple functional units may be realized by one circuit.

[0086] (8) The various techniques and processes described in the above-described embodiment and modifications may be combined as appropriate within the scope of achieving the purpose of identifying a precoding matrix to be applied to the position of terminal 200 after a predetermined time.

[0087] (9) According to each aspect of the present disclosure described above, fast and accurate communication between base stations and terminals, and ultimately between terminals, can be achieved, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs), which is to “build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation and resilience.”

[0088] REFERENCE SIGNS LIST 100 Base station 110 Communication unit 120 Input unit 130 Control unit 131 Acquisition unit 132 Estimation unit 133 Identification unit 140 Storage unit 141 Precoding information 150 Output unit

Claims

1. A base station that relays wireless communication between multiple terminals using MIMO (Multiple Input Multiple Output) transmission, comprising: an acquisition unit that acquires location information of a first terminal; an estimation unit that estimates the location of the first terminal after a predetermined time based on the location information; an identification unit that identifies a second terminal different from the first terminal that previously existed within a predetermined range from the location estimated by the estimation unit; and a communication unit that performs beamforming on the first terminal, using a precoding matrix that was used for the second terminal identified by the identification unit as a precoding matrix for the first terminal estimated to be located at the location estimated by the estimation unit, and communicates with the first terminal.

2. The base station according to claim 1, further comprising a storage unit that stores correspondence information that associates a precoding matrix used for the second terminal with location information of the second terminal when that precoding matrix was being used, and the identification unit identifies the second terminal based on the correspondence information.

3. The base station according to claim 2, characterized in that the correspondence information is further associated with speed information indicating the moving speed of the second terminal, the estimation unit further estimates the moving speed of the first terminal at a position of the first terminal after a predetermined time, and the identification unit further identifies the second terminal based on the moving speed.

4. The base station described in claim 3, characterized in that the correspondence information is further associated with directional information indicating the moving direction of the second terminal, the estimation unit further estimates the moving direction of the second terminal at the position of the first terminal after a predetermined time, and the identification unit further identifies the second terminal based on the moving direction.

5. The base station according to claim 1, characterized in that, when the communication unit cannot communicate with the first terminal estimated to be located at the position estimated by the estimation unit using the precoding matrix used for the second terminal, the communication unit returns to the precoding matrix most recently used for the first terminal and performs beamforming to communicate.

6. The base station according to claim 1, further comprising a transmitting unit that transmits location information indicating the location of the first terminal to another base station that covers the location when the location of the first terminal after a predetermined time determined by the estimation unit is outside the communication range of the base station.

7. A base station as claimed in claim 1 or 6, characterized in that it comprises: a receiving unit that receives, from another base station, location information indicating an estimated location of a third terminal after a predetermined time; said identifying unit identifying a second terminal that is present within a predetermined range from the location information; and said communication unit performing beamforming for said third terminal by using the precoding matrix used for the second terminal identified by said identifying unit as the precoding matrix for said third terminal that is estimated to be present at the location estimated by said estimating unit, and communicating with said third terminal.

8. A communications method in which a computer of a base station that relays wireless communications between multiple terminals by MIMO (Multiple Input Multiple Output) transmission executes the following steps: an acquisition step of acquiring location information of a first terminal; an estimation step of estimating the location of the first terminal after a predetermined time based on the location information; an identification step of identifying a second terminal different from the first terminal that previously existed within a predetermined range from the location estimated in the estimation step; and a communications step of performing beamforming on the first terminal using the precoding matrix used for the second terminal identified in the identification step as the precoding matrix for the first terminal estimated to be located at the location estimated in the estimation step.

9. A communications program that implements, in a computer of a base station that relays wireless communications between multiple terminals using MIMO (Multiple Input Multiple Output) transmission, the following functions: an acquisition function that acquires location information of a first terminal; an estimation function that estimates the location of the first terminal after a predetermined time based on the location information; a specification function that identifies a second terminal different from the first terminal that previously existed within a predetermined range from the location estimated by the estimation function; and a communications function that performs beamforming on the first terminal, using the precoding matrix used for the second terminal identified by the specification function as the precoding matrix for the first terminal estimated to be located at the location estimated by the estimation function, and communicates with the first terminal.

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