Wireless communication apparatus and wireless communication method

Abstract

A wireless communication apparatus is configured such that a wireless communication function is distributed between a first communication device and a second communication device. The first communication device controls the second communication device so that a beam sweep is executed over a partial beam sweep range among the entire beam sweep range in which the second communication device can perform the beam sweep. The second communication device executes the beam sweep over said partial beam sweep range in response to the control from the first communication device.　

Description

Wireless communication device and wireless communication method

[0001] The present invention relates to a wireless communication device and a wireless communication method.

[0002] Wireless communication using high-frequency bands such as the millimeter wave band allows for wider bandwidth compared to wireless communication using the microwave band. An example of a wireless communication method using high-frequency bands is IEEE 802.11ad. Wireless communication using high-frequency bands has advantages such as high directivity of wireless signals in the propagation path and less interference with other wireless communications. For this reason, studies are underway to promote the widespread use of wireless communication using high-frequency bands.

[0003] The distance attenuation of a radio signal in the propagation path increases with the frequency of the radio signal. Radio signals in wireless communications such as IEEE 802.11ad, which use the 60 GHz band, are easily absorbed by oxygen in the propagation path, resulting in high propagation attenuation. For this reason, in wireless communications using high frequency bands such as the millimeter wave band, it is common practice for wireless communication equipment to form a directional beam (beamforming) towards the wireless communication equipment it is communicating with to transmit the signal.

[0004] For example, in a wireless communication system comprising a terminal and a base station, using a phased array antenna capable of forming a directional beam as the antenna of the base station is suitable for high-frequency wireless communication to obtain high antenna gain. In this case, the base station needs to direct the directional beam formed by the phased array antenna towards the terminal. A directional beam is a beam that has directionality in a specific direction. Hereinafter, directional beams that the base station can form in different directions will be referred to as candidate beams. The base station performs a beam sweep to determine the beam direction of the directional beam to be used for communication from among the candidate beams. A beam sweep means that the radio station (in this case, the base station) uses multiple candidate beams to sequentially transmit beam search signals in each direction, staggering the transmission timing of the beam search signals.

[0005] Conventionally, base station equipment using analog RoF (Radio-over-Fiber) has been proposed. In such base station equipment, the functions are separated into a central station and one or more antenna stations, allowing for the economical deployment of many antenna stations. In such base station equipment, the central station performs beam sweeps at each antenna station to determine the beam direction at each antenna station.

[0006] In conventional beam sweeps, the beam direction is sequentially changed from the aggregation station to the extension station (for example, sequentially changing each direction from the leftmost candidate beam to the rightmost candidate beam), and the quality information of each candidate beam is measured at the terminal. This quality information includes, for example, the received signal strength indicator (RSSI). The terminal notifies the base station equipment of the measured quality information for each candidate beam. Based on the notified quality information for each candidate beam, the base station equipment selects the candidate beam direction with the best quality (for example, the beam direction with the highest RSSI). The base station equipment then uses the selected candidate beam to communicate wirelessly with the terminal.

[0007] K. Ito, M. Suga, Y. Shirato, N. Kita, and T. Onizawa, “Efficiently Accommodating Highfrequency-band Wireless Systems by Using Analog Radio-over-fiber”, NTT Technical Review, vol. 18, no. 5, pp. 19-23, May 2020.

[0008] When beam sweeping is performed using conventional methods, it may not be possible to properly associate quality information with the correct beam direction, resulting in the selection of an inappropriate beam direction. Specifically, beam switching at extension stations is performed based on instructions from the aggregation station. Therefore, if the distance between the aggregation station and the extension station is large, or due to processing delays at the extension station, a delay may occur between the instructions from the aggregation station and the beam switching at the extension station. As a result, a beam search signal may be transmitted using the candidate beam before the beam is switched at the extension station. In this case, a discrepancy occurs between the candidate beam and the corresponding quality information. Consequently, it becomes impossible to determine the optimal beam direction for the terminal direction.

[0009] Therefore, one possible approach is to delay the transmission of the beam search signal until the beam switching is complete. However, delaying the transmission of the beam search signal for each beam used in the beam sweep has the problem of increasing the processing time required for the beam sweep.

[0010] In view of the above circumstances, the present invention aims to provide a technology that can shorten the processing time required for beam sweeping in a wireless communication system having a configuration in which the functions of wireless communication devices are separated.

[0011] One aspect of the present invention is a wireless communication device configured by separating the wireless communication function into a first communication device and a second communication device, wherein the first communication device controls the second communication device to perform a beam sweep on a portion of the beam sweep range out of all beam sweep ranges that the second communication device can beam sweep, and the second communication device performs a beam sweep on a portion of the beam sweep range in response to the control from the first communication device.

[0012] One aspect of the present invention is a wireless communication method performed by a wireless communication device configured to separate the functions of wireless communication into a first communication device and a second communication device, wherein the first communication device controls the second communication device to perform a beam sweep on a portion of the beam sweep ranges out of all beam sweep ranges that the second communication device can beam sweep, and the second communication device performs a beam sweep on the portion of the beam sweep ranges in response to the control from the first communication device.

[0013] The present invention makes it possible to reduce the processing time required for beam sweeping in a wireless communication system that has a configuration in which the functions of wireless communication devices are separated.

[0014] This figure shows an example of the configuration of a conventional wireless communication system. This figure shows an example of the functional configuration of a conventional control unit. This figure shows an example of a conventional quality information table. This is a sequence diagram showing the processing flow of a beam sweep performed by a conventional wireless communication system. This is a flowchart showing the processing flow of a beam selection operation in a conventional wireless communication system. This figure shows an example of the configuration of a wireless communication system in the first embodiment. This figure shows an example of the functional configuration of a control unit in the first embodiment. This is a flowchart showing the processing flow of a beam selection operation in a wireless communication system in the first embodiment. This is a sequence diagram showing the processing flow of a beam sweep performed by a wireless communication system in the first embodiment. This figure shows an example of the functional configuration of a control unit in the second embodiment. This figure illustrates a first method for limiting the target range of a beam sweep in the second embodiment. This figure shows an example of a three-dimensional antenna pattern. This figure illustrates a third method for limiting the target range of a beam sweep in the second embodiment. This is a flowchart showing the processing flow of a beam selection operation in a wireless communication system in the second embodiment. This figure shows an example of the functional configuration of a control unit in the third embodiment. This figure illustrates a surface interpolation method. This is a flowchart showing the processing flow of a beam selection operation in a wireless communication system in the third embodiment. This is a diagram illustrating a method for limiting the target range of a beam sweep in the fourth embodiment. This is a flowchart showing the processing flow of beam selection operation in the wireless communication system in the fourth embodiment.

[0015] One embodiment of the present invention will be described below with reference to the drawings.

[0016] (Conventional Configuration) Before explaining the content of the present invention, the conventional configuration will be described. FIG. 1 is a diagram showing a configuration example of a conventional wireless communication system S. The wireless communication system S includes a base station device 1, a terminal 30, and a response unit 35. The base station device 1 is composed of a control unit 10, an aggregation station 15, and a remote station 20. The base station device 1 is configured by separating the functions of wireless communication into a plurality of devices. For example, the base station device 1 has a configuration in which the communication function is separated to the remote station 20, and the signal processing function is separated to the control unit 10 and the aggregation station 15. The aggregation station 15 and the remote station 20 are connected by an optical transmission line. The optical transmission line is, for example, an optical fiber. The length of the optical fiber connecting the aggregation station 15 and the remote station 20 is several tens of km. That is, the aggregation station 15 and the remote station 20 are separated by several tens of km. The control unit 10 may be provided in the aggregation station 15. The response unit 35 may be provided in the terminal 30.

[0017] In the wireless communication system S, analog RoF transmission is performed between the aggregation station 15 and the remote station 20. In FIG. 1, one remote station 20 is connected to the aggregation station 15, but it is also possible to branch the optical transmission line from one aggregation station 15 by an optical combiner / splitter and connect it to a plurality of remote stations 20. The optical combiner / splitter combines or branches the input optical signal. The optical combiner / splitter is, for example, an optical splitter.

[0018] The control unit 10 performs beam sweep control in the remote station 20 and beam selection used for communication with the terminal 30. The beam sweep control in the remote station 20 is to transmit an instruction such as the execution of beam sweep and the switching of candidate beams to the remote station 20 to execute the beam sweep. When performing beam sweep control, the control unit 10 instructs the switching of candidate beams for which the remote station 20 transmits a beam search signal. In the following description, a signal for instructing the switching of candidate beams for which the remote station 20 transmits a beam search signal is referred to as a beam direction change instruction. The beam direction change instruction includes a beam ID for specifying the candidate beam to be switched to. Note that the beam direction change instruction may include identification information for specifying the remote station 20 that executes the beam search.

[0019] Furthermore, after transmitting the beam direction change instruction, the control unit 10 causes the relay station 20 to transmit a quality information acquisition instruction. The quality information acquisition instruction is an instruction for causing the terminal 30 to acquire the quality information at the time of receiving the beam search signal. Based on the quality information of each candidate beam obtained by beam sweeping, the control unit 10 selects a beam to be used for wireless communication with the terminal 30 from the candidate beams possessed by the relay station 20. That is, the control unit 10 determines the beam in the direction of the terminal. The control unit 10 may be an information processing device such as a personal computer. When the control unit 10 is provided in the aggregation station 15, the control unit 10 may be a processor such as a CPU (Central Processing Unit) provided in the aggregation station 15. The control unit 10 is one aspect of the first communication device.

[0020] The aggregation station 15 converts the instruction output from the control unit 10 into an optical signal and outputs it to the relay station 20. The aggregation station 15 converts the optical signal output from the relay station 20 into an electrical signal and outputs it to the control unit 10. The aggregation station 15 and the control unit 10 are connected by, for example, an electric wire. The aggregation station 15 is one aspect of the first communication device.

[0021] The relay station 20 includes a phased array antenna and performs beam sweeping with candidate beams formed by the phased array antenna. At this time, the relay station 20 transmits a beam search signal and a quality information acquisition instruction to the terminal 30 using the candidate beams. In FIG. 1, the relay station 20 is shown with a configuration for forming candidate beams B1 to B5 in five different directions, but the number of candidate beams that can be formed by the relay station 20 is not particularly limited. The relay station 20 performs beam sweeping by switching the beams in order from candidate beam B1 to candidate beam B5 according to an instruction from the control unit 10. The relay station 20 performs wireless communication with the terminal 30 using the candidate beam selected by the control unit 10. The relay station 20 is one aspect of the second communication device.

[0022] Terminal 30 communicates wirelessly with the extension station 20. For example, terminal 30 communicates wirelessly with the extension station 20 using the beam formed by the phased array antenna provided by the extension station 20. Terminal 30 measures quality information when it receives a beam search signal transmitted from the extension station 20. In response to instructions from the response unit 35, terminal 30 transmits the measured quality information to the extension station 20.

[0023] Quality information refers to information relating to the quality of wireless communication, and may be, for example, the received signal strength (RSSI) of the beam search signal transmitted from the extension station 20, or the signal-to-noise ratio (SNR) obtained by estimating the received signal power and noise. In the following explanation, the quality information will be assumed to be the received signal strength (RSSI).

[0024] The response unit 35, in response to the quality information acquisition instruction transmitted from the outgoing station 20, causes the terminal 30 to acquire quality information. After acquiring the quality information, the response unit 35 also causes the terminal 30 to transmit the acquired quality information to the outgoing station 20, which was the source of the quality information acquisition instruction.

[0025] In the example shown in Figure 1, the terminal 30 is located in the direction of candidate beam B4 among the candidate beams formed by the extension station 20. In this case, the quality information of the beam search signal transmitted by candidate beam B4 is the highest among the candidate beams formed by the extension station 20. Therefore, the control unit 10 selects candidate beam B4 as the beam to be used for communication with the terminal 30.

[0026] Figure 2 shows an example of the functional configuration of a conventional control unit 10. The control unit 10 is composed of one or more processors such as a CPU and one or more memories. The control unit 10 realizes the functions of the beam sweep instruction unit 110, the quality information acquisition instruction unit 120, the information acquisition unit 130, and the beam selection unit 140 by having one or more processors execute a program.

[0027] The beam sweep instruction unit 110 generates a beam direction change instruction during a beam sweep. The beam sweep instruction unit 110 transmits the generated beam direction change instruction to the aggregation station 15. The beam sweep instruction unit 110 also transmits beam direction change instructions, including beam IDs indicating candidate beams in order, to the extension station 20 via the aggregation station 15 at predetermined timings.

[0028] The quality information acquisition instruction unit 120 generates a quality information acquisition instruction during beam sweeping. The quality information acquisition instruction unit 120 transmits the generated quality information acquisition instruction to the extension station 20 via the aggregation station 15. The quality information acquisition instruction unit 120 transmits the quality information acquisition instruction to the extension station 20 via the aggregation station 15 after the beam sweep instruction unit 110 has transmitted a beam direction change instruction. For example, the quality information acquisition instruction unit 120 transmits the quality information acquisition instruction to the extension station 20 via the aggregation station 15 immediately after the beam sweep instruction unit 110 has transmitted a beam direction change instruction.

[0029] The information acquisition unit 130 acquires quality information transmitted from the terminal 30. The information acquisition unit 130 records the acquired quality information in association with the beam ID notified by the transmission station 20.

[0030] The beam selection unit 140 selects a beam to be used for wireless communication with the terminal 30 based on the quality information for each beam ID recorded by the information acquisition unit 130. For example, the beam selection unit 140 selects the beam with the highest quality information.

[0031] Figure 3 shows an example of a conventional quality information table. The quality information table has multiple records representing quality information for each beam ID. Each record has a beam ID and a value for quality information. The beam ID represents identification information for identifying a candidate beam. The quality information represents quality information corresponding to the candidate beam identified by the beam ID. Here, the quality information table may also register information indicating the radiation direction in association with the beam ID. The radiation direction represents the radiation direction of the candidate beam. The radiation direction of a candidate beam is defined by the horizontal and vertical directions.

[0032] In conventional beam sweeps, the beam ID and quality information associated with the quality information table may not be the correct match. This is because, when the distance between the aggregation station 15 and the extension station 20 is large, or due to processing delays by the extension station 20, a delay occurs between the instruction from the aggregation station 15 and the beam switching at the extension station 20, resulting in quality information that does not accurately correspond to the candidate beam. The quality information table is maintained, for example, by the information acquisition unit 130.

[0033] (Conventional Beam Sweep Processing) Figure 4 is a sequence diagram showing the processing flow of a beam sweep performed by a conventional wireless communication system S. Figure 4 shows the processing flow when the beam sweep function is applied to a base station device 1 with an analog RoF configuration. Although beam sweeping is basically performed using all candidate beams, the processing is the same for all candidate beams, so Figure 4 explains using candidate beam B1 as an example.

[0034] The control unit 10 starts a beam sweep by the extension station 20 (step S11). The control unit 10 generates a beam direction change instruction including a beam ID to identify candidate beam B1 in order to perform a beam search toward the direction of candidate beam B1 (step S12). The control unit 10 transmits the generated beam direction change instruction to the aggregation station 15 (step S13). Subsequently, the control unit 10 generates a quality information acquisition instruction (step S14). The control unit 10 transmits the generated quality information acquisition instruction to the aggregation station 15 (step S15).

[0035] The aggregation station 15 receives the beam direction change instruction and the quality information acquisition instruction transmitted from the control unit 10. The aggregation station 15 transmits the received quality information acquisition instruction to the extension station 20 (step S16). In addition to a simple one-to-one connection, various connection configurations are envisioned between the aggregation station 15 and the extension station 20, such as when one aggregation station 15 accommodates multiple extension stations 20. Therefore, compared to the transmission of control instructions for terminal 30, such as the quality information acquisition instruction, instructions that require processing by the extension station 20, such as the beam direction change instruction, take time to transmit. For example, before the aggregation station 15 performs control in response to the beam direction change instruction, the aggregation station 15 may identify the target extension station 20, or if it has not been identified, it may determine the order in which to send instructions to multiple target extension stations 20. Therefore, there is a time interval between the aggregation station 15 receiving the beam direction change instruction in step S13 and transmitting the beam direction change control to the extension station 20 in step S21. Furthermore, calculation processing is required to form a candidate beam in a specific direction at the identified extension station 20. Processing to determine the beam direction of the extension station 20 based on the beam ID, as described later, is necessary to appropriately form candidate beams for the various antennas of the extension station 20. As a result, it takes time for the extension station 20 to receive the beam direction change control in step S21, as described later, and until the beam direction change setting is completed in step S29. Figure 4 exaggerates the time difference in which both the beam direction change control and the quality information acquisition instruction are processed, but the problem is that the order of these (originally, the quality information acquisition in step S22 occurs after the completion of the beam direction change setting in step S29) is reversed even slightly. After these processes are completed, the aggregation station 15 performs the beam direction change control on the target extension station 20.

[0036] The outbound station 20 receives a quality information acquisition instruction transmitted from the aggregation station 15. The outbound station 20 transmits the received quality information acquisition instruction wirelessly using the candidate beam set at the start of the beam sweep (step S17). The terminal 30 receives the quality information acquisition instruction transmitted from the outbound station 20. The terminal 30 outputs the received quality information acquisition instruction to the response unit 35 (step S18). The response unit 35 transmits a quality information acquisition execution instruction to the terminal 30 in response to the quality information acquisition instruction (step S19). The quality information acquisition execution instruction is an instruction to cause the terminal 30 to measure quality information.

[0037] The extension station 20 transmits a beam search signal in the direction of the candidate beam (the candidate beam before the change) that was set at the start of the beam sweep (step S20). The aggregation station 15, upon completion of the processing necessary for the beam direction change, controls the extension station 20 for the beam direction change (step S21). For example, the aggregation station 15 controls the rotation of the phase of the phased array antenna at the extension station 20 in order to form a candidate beam in the target beam direction. Here, the aggregation station 15 controls the rotation of the phase of the phased array antenna at the extension station 20 in order to form a directional beam in the direction of candidate beam B1 as the target beam direction. As a result, the extension station 20 starts setting the beam direction change in response to instructions from the aggregation station 15.

[0038] Terminal 30 receives a beam search signal transmitted from the extension station 20 using the candidate beam (the candidate beam before the change) that was set at the start of the beam sweep. Terminal 30 measures the quality information of the received beam search signal (step S22). Terminal 30 outputs the measured quality information to the response unit 35 (step S23). In response to the notification of quality information from Terminal 30, the response unit 35 instructs the base station device 1 to respond with the quality information (step S24).

[0039] Terminal 30 transmits the measured quality information to the base station device 1 in response to instructions from the response unit 35 (step S25). The extension station 20 of the base station device 1 receives the quality information transmitted from terminal 30. The extension station 20 converts the received quality information into an optical signal and transmits it to the aggregation station 15 (step S26). At this time, the extension station 20 also transmits the beam ID, which indicates the candidate beam used to transmit the beam search signal, to the aggregation station 15 along with the quality information. The aggregation station 15 transmits the beam ID and quality information transmitted from the extension station 20 to the control unit 10 (step S27).

[0040] The control unit 10 acquires the beam ID and quality information transmitted from the aggregation station 15, and registers the acquired beam ID and quality information in the quality information table (step S28). The extension station 20 completes the beam direction change setting (step S29). As a result, the extension station 20 can transmit a beam search signal in the direction of the candidate beam B1.

[0041] The control unit 10 generates a beam direction change instruction, including a beam ID to identify candidate beam B2, at a predetermined timing to perform a beam search toward the direction of candidate beam B2 (step S30). Subsequently, the processes from steps S13 to S28 described above are carried out until a beam search is performed toward the direction of the remaining candidate beams.

[0042] As described above, the beam direction change instruction and the quality information acquisition instruction are transmitted sequentially without any waiting time (delay considerations). As explained in Figure 4, in the beam sweep situation using candidate beam B1, the acquisition of quality information is performed at terminal 30 before the beam direction change setting at extension station 20 is completed. Ideally, when a beam direction change instruction including a beam ID to identify candidate beam B1 is given, it is desirable for terminal 30 to acquire quality information of the beam search signal transmitted by candidate beam B1.

[0043] However, in the process shown in Figure 4, quality information is measured at the terminal 30 before the setting change to candidate beam B1 is completed at the extension station 20. In other words, the timing of the completion of the beam direction change setting (step S29 in Figure 4) and the transmission by the extension station 20 in the beam direction at the time of quality information measurement (step S20 in Figure 4) are reversed. As a result, in conventional beam sweeps, quality information of beam search signals transmitted in a direction different from the original designated candidate beam direction is acquired and collected by the control unit 10. Consequently, a situation arises where the beam in the appropriate terminal direction does not have the maximum reception level, resulting in the problem that an appropriate candidate beam cannot be selected.

[0044] (Conventional Beam Selection Operation) Figure 5 is a flowchart showing the processing flow of beam selection operation in a conventional wireless communication system S. The control unit 10 generates a beam direction change instruction for the extension station 20. For example, the control unit 10 generates a beam direction change instruction that includes a beam ID for identifying candidate beam B1. The control unit 10 transmits the generated beam direction change instruction to the aggregation station 15 (step S31). The control unit 10 also generates a quality information acquisition instruction. The control unit 10 transmits the generated quality information acquisition instruction to the aggregation station 15 (step S32). The aggregation station 15 receives the beam direction change instruction and the quality information acquisition instruction transmitted from the control unit 10. The aggregation station 15 transmits the received quality information acquisition instruction to the terminal 30 via the extension station 20.

[0045] Terminal 30 receives a quality information acquisition instruction transmitted from the outgoing station 20. Terminal 30 outputs the received quality information acquisition instruction to the response unit 35. The response unit 35 transmits a quality information acquisition execution instruction to terminal 30 in response to the quality information acquisition instruction. Terminal 30 receives a beam search signal transmitted from the outgoing station 20. Terminal 30 measures the quality information of the received beam search signal (step S33).

[0046] Terminal 30 transmits the measured quality information to the base station device 1 in response to instructions from the response unit 35 (step S34). The extension station 20 of the base station device 1 receives the quality information transmitted from terminal 30. The extension station 20 converts the received quality information into an optical signal and transmits it to the aggregation station 15. At this time, the extension station 20 also transmits the beam ID, which indicates the candidate beam used to transmit the beam search signal, to the aggregation station 15 along with the quality information. The aggregation station 15 transmits the beam ID and quality information transmitted from the extension station 20 to the control unit 10. The control unit 10 acquires the beam ID and quality information transmitted from the aggregation station 15 and registers the acquired beam ID and quality information in the quality information table in association (step S35).

[0047] Subsequently, the control unit 10 determines whether or not the beam sweep has been completed for all candidate beams (step S36). If the control unit 10 determines that the beam sweep has not been completed for all candidate beams (step S36-NO), the base station device 1 repeats the process from step S31 onwards. In this case, the base station device 1 performs the beam sweep on the candidate beams that have not yet been swept. For example, the base station device 1 performs the beam sweep on candidate beams other than candidate beam B1.

[0048] In this manner, the base station device 1 repeatedly executes the processes from step S31 to step S35 until a beam sweep is performed on all candidate beams. The steps described above include the process of acquiring quality information at the terminal 30 (for example, step S33), the process of notifying the terminal 30 of the quality information (for example, step S34), and the process of recording the quality information (for example, step S35). However, depending on the direction of the candidate beam, the terminal 30 may not be able to acquire the quality information. In this case, the base station device 1 cannot acquire the quality information from the terminal 30. Therefore, the base station device 1 does not need to associate quality information with candidate beams from which quality information could not be acquired.

[0049] If the control unit 10 determines that beam sweeping has been completed for all candidate beams (step S36-YES), the control unit 10 selects a beam direction to be used for communication with the terminal 30 (step S37). Specifically, the control unit 10 refers to the quality information table and selects a beam direction corresponding to the beam ID with the highest quality information. As a result, the base station device 1 sets the beamforming of the phased array antenna of the extension station 20 toward the selected beam direction and performs wireless communication with the terminal 30.

[0050] However, as mentioned above, a situation arises where the beam in the appropriate terminal direction does not have the maximum reception level, resulting in the problem that a suitable candidate beam cannot be selected. Therefore, as a method to solve this problem, in the first embodiment, after an appropriate delay (time) has been set and the beam direction change in the base station device 1 has been completed, quality information measured at the terminal 30 is acquired, and the acquired quality information is recorded in association with the beam direction of the extension station 20 at that time. This configuration solves the above problem. The configuration for realizing this process will be described below.

[0051] (First Embodiment) Figure 6 shows an example of the configuration of the wireless communication system 100a in the first embodiment. The wireless communication system 100a comprises a base station device 1a, a terminal 30, and a response unit 35. The wireless communication system 100a differs from the conventional wireless communication system S in that it includes a base station device 1a instead of a base station device 1. The terminal 30 and response unit 35 of the wireless communication system 100a are the same as in the conventional system, so the following explanation will focus on the differences from the conventional system.

[0052] The base station device 1a consists of a control unit 10a, a central station 15, and an extension station 20. The base station device 1a is configured by separating the wireless communication functions into multiple devices. For example, the base station device 1a has a configuration in which the communication function is separated into the extension station 20, and the signal processing function is separated into the control unit 10a and the central station 15. The central station 15 and the extension station 20 are connected by an optical transmission path. The control unit 10a may be provided in the central station 15.

[0053] In the wireless communication system 100a, analog RoF transmission is performed between the aggregation station 15 and the branch stations 20. In Figure 6, one branch station 20 is connected to the aggregation station 15, but it is also possible to branch the optical transmission path from one aggregation station 15 using an optical splitter and connect to multiple branch stations 20.

[0054] The control unit 10a performs the same processing as the control unit 10. However, the control unit 10a inserts a delay time after transmitting the beam direction change instruction and does not transmit the quality information acquisition instruction until the inserted delay time has elapsed. The delay time is a margin of time until the beam direction of the phased array antenna of the extension station 20 using analog RoF is set according to the instruction from the control unit 10a. In other words, the delay time is the time until the extension station 20 is set to the beam instructed by the beam direction change instruction transmitted from the control unit 10a.

[0055] Thus, the control unit 10a transmits a quality information acquisition instruction to the aggregation station 15 after a delay time has elapsed from the time the beam direction change instruction was transmitted. The control unit 10a performs this process for each candidate beam used in the beam sweep. By waiting for the delay time before transmitting the quality information acquisition instruction, the timing of acquiring the quality information at the terminal 30 can be delayed. Therefore, the extension station 20 can acquire the quality information after the setting to the candidate beam specified by the beam direction change instruction has been completed.

[0056] Figure 7 shows an example of the functional configuration of the control unit 10a in the first embodiment. The control unit 10a is configured using one or more processors such as a CPU and one or more memories. The control unit 10a realizes the functions of the beam sweep instruction unit 110, the quality information acquisition instruction unit 120a, the information acquisition unit 130, the beam selection unit 140, and the delay time insertion unit 150a by having one or more processors execute a program.

[0057] The control unit 10a differs from the control unit 10 in that it has a quality information acquisition instruction unit 120a instead of the quality information acquisition instruction unit 120, and it newly includes a delay time insertion unit 150a. The differences from the control unit 10 will be explained below.

[0058] The delay time insertion unit 150a inserts a delay time into the quality information acquisition instruction unit 120a after the beam sweep instruction unit 110 has transmitted a beam direction change instruction to the extension station 20.

[0059] The quality information acquisition instruction unit 120a generates a quality information acquisition instruction when the delay time inserted by the delay time insertion unit 150a has elapsed. The quality information acquisition instruction unit 120a transmits the generated quality information acquisition instruction to the extension station 20 via the aggregation station 15. In this way, the quality information acquisition instruction unit 120a does not transmit the quality information acquisition instruction immediately after the beam direction change instruction is transmitted by the beam sweep instruction unit 110, as in the conventional quality information acquisition instruction unit 120, but transmits the quality information acquisition instruction when the delay time has elapsed.

[0060] (Beam Selection Operation in the First Embodiment) Figure 8 is a flowchart showing the processing flow of the beam selection operation in the wireless communication system 100a in the first embodiment. In Figure 8, processes similar to those in Figure 5 are denoted by the same reference numerals as in Figure 5 and their explanations are omitted. The flowchart shown in Figure 8 describes the process for obtaining the original quality information corresponding to the candidate beam by considering delay.

[0061] After the processing in step S31 is performed, the delay time insertion unit 150a inserts a delay time into the quality information acquisition instruction unit 120a (step S101). The delay time inserted by the delay time insertion unit 150a is a waiting time to wait for the start of the execution of the operation. Therefore, it can also be said that the delay time insertion unit 150a inserts a waiting time into the quality information acquisition instruction unit 120a. The quality information acquisition instruction unit 120a generates a quality information acquisition instruction when the delay time inserted by the delay time insertion unit 150a has elapsed. The quality information acquisition instruction unit 120a transmits the generated quality information acquisition instruction to the aggregation station 15 (step S102). After that, the processing from step S33 onwards is executed.

[0062] (Beam Sweep Processing in the First Embodiment) Figure 9 is a sequence diagram showing the processing flow of beam sweep performed by the wireless communication system 100a in the first embodiment. In Figure 9, the processing flow is shown when the beam sweep function is applied to the base station device 1a with an analog RoF configuration. Although beam sweeping is basically performed using all candidate beams, the processing is the same for all candidate beams, so in Figure 9, candidate beam B1 is used as an example for explanation. In Figure 9, the same reference numerals as in Figure 4 are used for processing similar to that in Figure 4, and the explanation is omitted.

[0063] After the processes from step S11 to step S13 are executed, the delay time insertion unit 150a inserts a delay time into the quality information acquisition instruction unit 120a. As a result, the quality information acquisition instruction unit 120a waits for the amount of the inserted delay time before processing (step S201). While the control unit 10a waits for the amount of the delay time before processing, the aggregation station 15 receives the beam direction change instruction transmitted from the control unit 10a. The aggregation station 15 performs control for beam direction change to the extension station 20 in accordance with the received beam direction change instruction (step S202).

[0064] As explained in Figure 4, before the aggregation station 15 performs control in response to the beam direction change instruction, the aggregation station 15 identifies the target extension station 20, or, if not identified, determines the order in which to issue instructions to multiple target extension stations 20. Therefore, time is required from the beam direction change instruction (step S13) to the beam direction change control (step S21). In addition, calculation processing is required at the identified extension station 20 to form a candidate beam in a specific direction. In order to appropriately form candidate beams for the various antennas of the extension station 20, there is an antenna operation setting process that determines the beam direction of the extension station 20 based on the beam ID. As a result, it takes time from when the extension station 20 receives the beam direction change control in step S21 until the beam direction change setting is completed in step S29. Figure 4 shows the difference in processing time between the beam direction change control and the quality information acquisition instruction. The challenge is to reverse the original order, which is to acquire quality information in step S22 after the completion of the beam direction change setting in step S29. After completing these processes, the aggregation station 15 controls the beam direction change for the target extension station 20. The aggregation station 15 controls the beam direction change for the extension station 20 as soon as it has completed the necessary processes for the beam direction change. As a result, the extension station 20 starts setting the beam direction change in response to the instructions from the aggregation station 15.

[0065] The extension station 20 completes the setting for changing the beam direction (step S203). The quality information acquisition instruction unit 120a generates a quality information acquisition instruction when the delay time has elapsed (step S204). The quality information acquisition instruction unit 120a transmits the generated quality information acquisition instruction to the aggregation station 15 (step S205).

[0066] The aggregation station 15 receives a quality information acquisition instruction transmitted from the control unit 10a. The aggregation station 15 transmits the received quality information acquisition instruction to the extension station 20 (step S206). The extension station 20 receives the quality information acquisition instruction transmitted from the aggregation station 15. The extension station 20 transmits the received quality information acquisition instruction wirelessly using the candidate beam B1 after the setting change is complete (step S207). The terminal 30 receives the quality information acquisition instruction transmitted from the extension station 20. The terminal 30 outputs the received quality information acquisition instruction to the response unit 35 (step S208). The response unit 35 transmits a quality information acquisition execution instruction to the terminal 30 in response to the quality information acquisition instruction (step S209).

[0067] The outgoing station 20 transmits a beam search signal in the beam direction of candidate beam B1 after the setting change is complete (step S210). The terminal 30 receives the beam search signal transmitted from the outgoing station 20 via candidate beam B1. Subsequently, the processing from step S22 onwards is executed. In step S26, the outgoing station 20 transmits the beam ID indicating the candidate beam B1 used to transmit the beam search signal, along with quality information, to the aggregation station 15.

[0068] In this way, by inserting a delay time, the terminal 30 acquires quality information after the beam direction change setting of the extension station 20 is completed. As a result, in the first embodiment, the beam ID and quality information after the beam direction of the extension station 20 has been changed can be associated with and notified to the aggregation station 15. Consequently, the control unit 10a can acquire quality information corresponding to the direction of the specified candidate beam. Therefore, the beam in the appropriate terminal direction will have the maximum reception level, enabling optimal beam setting.

[0069] According to the wireless communication system 100a configured as described above, the control unit 10a transmits a quality information acquisition instruction to the aggregation station 15 after a delay time has elapsed from the time the beam direction change instruction is transmitted. That is, after a delay time has elapsed from the time the aggregation station 15 instructs the extension station 20 to set candidate beams to be used for beam sweeping performed at the extension station 20, the extension station 20 transmits a quality information acquisition instruction to the terminal 30 to be transmitted using the set candidate beams. The extension station 20 transmits a quality information acquisition instruction to the terminal 30 using the set candidate beams in response to the instruction from the aggregation station 15.

[0070] This prevents the acquisition of quality information for beam search signals transmitted in a direction different from the originally designated candidate beam direction. Therefore, the beam direction of the extension station 20 and the quality information corresponding to that beam direction can be associated across the entire beam sweep range. As a result, it becomes possible to determine the optimal beam direction for the terminal in a wireless communication system 100a that has a configuration in which the functions of wireless communication devices are separated.

[0071] (Modification 1) In the above-described embodiment, the case where the delay time is fixed was explained as an example. Depending on the analog RoF configuration, it is expected that the length of the optical transmission path connecting the aggregation station 15 and the extension station 20 may change. Also, there may be multiple extension stations 20 connected to the aggregation station 15, and the number of these extension stations 20 may differ. Therefore, the delay time may not be fixed, but may be configured to be specified by the operator. For example, the operator may specify a delay time that takes the analog RoF configuration into account and input it to the control unit 10a. In this configuration, the input specification of the delay time is executed before the processing of step S31 in Figure 8 (at the start of processing in Figure 8). For example, the input specification of the delay time is inserted before the processing of step S36 becomes "NO" and merges with the processing of step S31.

[0072] The delay time insertion unit 150a sets the input-specified delay time to the quality information acquisition instruction unit 120a. The timing at which the delay time insertion unit 150a inserts the input-specified delay time to the quality information acquisition instruction unit 120a may be after each sweep of candidate beams (however, for the first time, the target beam to be swept is set) (after the process in step S36 in Figure 8 becomes "NO" and merges to step S31), or it may be at the timing of step S101. If there is a timing to set the specified input delay time to the quality information acquisition instruction unit 120a after each sweep of candidate beams, the position of the waiting time insertion (step S101) in Figure 8 moves to a position before step S31. However, the waiting time insertion in step S101 only affects the transmission of the quality information acquisition instruction (step S102) and does not affect the transmission of the beam direction change instruction (step S31).

[0073] (Modification 2) In the above-described embodiment, a configuration was described in which the beam selection unit 140 selects the beam direction with the best quality information as the terminal direction (for example, step S37 in Figure 8). In contrast, the beam selection unit 140 may select the beam direction based on the quality information of multiple beams. In this configuration, the beam selection unit 140 refers to the quality information table and calculates statistical values ​​(e.g., mean and median) of the quality information for each of the three adjacent beams (e.g., candidate beams B1, B2, B3). The beam selection unit 140 performs this process for all beam IDs registered in the quality information table. Then, the beam selection unit 140 selects the direction with the highest calculated statistical value as the terminal direction. For example, the beam selection unit 140 may select the beam located in the center of the combination of beams with the highest statistical value (e.g., a combination of three beams) as the terminal direction beam, or it may select the beam with the highest quality information as the terminal direction beam.

[0074] However, the beam selection unit 140 compares the beam directions at both the leftmost and rightmost ends with the quality information of the adjacent beam direction (one to the right if it's the leftmost end, and conversely, one to the left if it's the rightmost end). This allows for the appropriate selection of a beam direction that is direct from the extension station 20 to the terminal 30, rather than using reflected waves, etc.

[0075] (Second Embodiment) In the first embodiment, a configuration was described in which a delay time is inserted and the beam sweep is performed on all candidate beams in order to ensure time for setting up the candidate beams to be used in the beam sweep at the extension station. However, in such a configuration, the time required for processing one candidate beam becomes long, and it takes an even longer time to complete the beam sweep on all candidate beams. Therefore, in the second embodiment, a configuration is described in which the time required for beam sweep processing is reduced by limiting the number of candidate beams.

[0076] Figure 10 shows an example of the functional configuration of the control unit 10b in the second embodiment. The control unit 10b is configured using one or more processors such as a CPU and one or more memories. The control unit 10b realizes the functions of the beam sweep instruction unit 110b, the quality information acquisition instruction unit 120a, the information acquisition unit 130, the beam selection unit 140, the delay time insertion unit 150a, and the beam range specification unit 160b by having one or more processors execute a program.

[0077] The control unit 10b differs from the control unit 10a in that it has a beam sweep instruction unit 110b instead of a beam sweep instruction unit 110, and it newly includes a beam range specification unit 160b. The differences from the control unit 10a will be explained below.

[0078] The beam range designation unit 160b designates the range of the beam sweep to be performed by the extension station 20. At this time, the beam range designation unit 160b determines the beam ID corresponding to the candidate beam for sweeping the designated range and notifies the beam sweep instruction unit 110b of information indicating the determined beam ID.

[0079] The beam sweep instruction unit 110b generates a beam direction change instruction to sweep the beam sweep range specified by the beam range specification unit 160b during a beam sweep. In this case, the beam sweep instruction unit 110b uses information indicating the beam ID notified by the beam range specification unit 160b. The beam sweep instruction unit 110b transmits the generated beam direction change instruction to the aggregation station 15. The beam sweep instruction unit 110b transmits the beam direction change instruction, including the beam ID notified by the beam range specification unit 160b, to the extension station 20 via the aggregation station 15 in order at predetermined timings.

[0080] One method for limiting the number of candidate beams is to limit the beam sweep range. Limiting the beam sweep range means that the extension station 20 does not perform a beam sweep on a portion of the total beam sweep range (i.e., a portion of the beam directions). The following describes a method for limiting the beam sweep range using Figures 11 to 13, but this is not the only method for limiting the beam sweep range.

[0081] (Method 1 for limiting the beam sweep range) Figure 11 is a diagram illustrating a first method for limiting the beam sweep range in the second embodiment. Figure 11 shows the beam sweep range in the first method within the beam sweep range. Here, the beam sweep range represents the range in which the extension station 20 can perform a beam sweep. The first method is a method of thinning out the horizontal direction more than the beam sweep range, as shown in Figure 11. In Figure 11, region R1 (white-painted area) represents the area where beam sweeping is not performed (the range that is not swept), region R2 (area painted with a pattern of small dots) represents the area where beam sweeping is performed (the range that is swept), and region R3 (area painted with a pattern of large dots) represents the estimated beam direction in which the terminal 30 is located.

[0082] The beam sweep range shown in FIG. 11 represents the angles of the beams formed by the phased array antenna of the outrigger 20 with respect to the front direction in the horizontal and vertical directions. As the beam sweep range shown in FIG. 11, the horizontal axis represents the horizontal direction θ [deg], and the vertical axis represents the vertical direction φ [deg]. In FIG. 11, as an example, the horizontal range is set to -30° ≤ θ ≤ 30°, and the vertical range is set to -15° ≤ φ ≤ 15°.

[0083] As the first prerequisite, the beam IDs for identifying the candidate beams formed by the phased array antenna of the outrigger 20 are sequentially assigned in the horizontal and vertical directions. For example, when the beam ID is set to 0000 to 0f1f (hexadecimal), the lower 2 digits of the beam ID distinguish 32 divisions in the horizontal direction (at approximately 2° intervals, from -30° to 30°), and the upper 2 digits distinguish 16 divisions in the vertical direction (at 2° intervals, from -15° to 15°). In the case of the example shown in FIG. 11, as a specific example of the beam ID, the beam direction at the upper left (θ ０ , φ １５ ) = (-30°, 15°) is (beam ID: 0000), and the beam direction at the lower left (θ ０ , φ ０ ) = (-30°, -15°) is (beam ID: 0f00).

[0084] Also, the beam direction at the upper right (θ ３１ , φ １５ ) = (30°, 15°) in FIG. 11 is (beam ID: 001f), and the direction at the lower right (θ ３１ , φ ０ ) = (30°, -15°) is (beam ID: 0f1f). Furthermore, the beam direction at the center left (θ ０ , φ ７ ) = (-30°, 0°) is (beam ID: 0800), the beam direction at the center right (θ ３１ , φ ７ ) = (30°, 0°) is (beam ID: 081f), the beam direction at the center top (θ １５ , φ １５ ) = (0°, 15°) is (beam ID: 0010), and the beam direction at the center bottom (θ １５ , φ ０The direction of (0°, -15°) is (Beam ID: 0f10). And the center (θ １５ , φ ７ The beam direction that is directly in front of the antenna at (0°, 0°) will be (Beam ID: 0810).

[0085] The second prerequisite is to deal with cases using a vertically elongated (wide vertically and sharp horizontally) beam. The rationale for using this vertically elongated beam is a phased array antenna that allows for a wide sweep range in the horizontal direction and fine directional spacing. In order to ensure fine directional spacing within this wide horizontal sweep range, the phased array antenna of the extension station 20 needs to have a larger number of elements in the horizontal direction compared to the vertical direction. The antenna beam formed by beamforming with such an array antenna will have the shape described above.

[0086] As described above, the beam range specification unit 160b specifies the range in which a beam sweep is performed in which horizontal sweeps are thinned out from the beam sweep range. That is, in the specific example shown in Figure 11, the entire beam (θ ｈ , φ ｉ Assuming that the intervals are 2° in both the horizontal and vertical directions within the range of (-30° to 30°, -15° to 15°) (for example, h = 1, 2, ..., 31, i = 1, 2, ..., 7), the total count for all beams is 512 (= 32 × 16).

[0087] In addition, assuming a waiting time of approximately 700 msec per beam (including delay), the time required to sweep all beams would be approximately 6 minutes (5.97 min ≈ 358.4 sec (= 32 × 16 × 700 msec)) if calculated by simple multiplication. Therefore, sweeping all beams directly is not practical. Thus, as shown in the second embodiment, we consider reducing the processing time to a usable level by thinning out the beams targeted for the beam sweep.

[0088] One example of thinning the beam is to define region R1 (the white-painted area) as the area not to be swept and region R2 (the area painted with a pattern of small dots) as the area to be swept, as shown in Figure 11. Focusing on a certain horizontal row in Figure 11, the ratio of region R2 to region R1 is approximately 3 to 2. Therefore, by using the first method, the reduction rate of the beam to be swept is about 40%, and the sweep time can be shortened from about 6 minutes, which is the time required to sweep the entire beam range, to 3 minutes and 35 seconds (3.584 [min] ≈ 215.04 [sec] (= 32 × 16 × (100 - 40) / 100 × 700 [msec])). The target beam is a candidate beam used to sweep a limited sweep range.

[0089] Therefore, when considering the selection of a specific beam direction (the beam of the extension station 20 pointed toward the terminal 30), even if the horizontal beam is thinned to some extent, it is easier to obtain a received power greater than the noise for the received level (RSSI) of the beam of the extension station 20 pointed toward the terminal 30 (even if it is slightly misaligned vertically) at vertically adjacent points in the beam direction. As a result, even if the terminal 30 is located in the reduced beam direction, there are received levels for two beams vertically adjacent to it, one above and one below, and in this case, it can be identified as the reduced beam direction. Therefore, even if the number of beams to be swept is reduced to some extent, the beam toward the terminal can be identified.

[0090] (Method 2 for limiting the beam sweep range) As a second method for limiting the beam sweep range, in order to further increase the reduction in processing time compared to the first method, one can consider limiting the beam sweep range so that the ratio of the area to be swept to the area not to be swept is 1:1. One possible method for this is to create a checkerboard pattern. By doing so, the ratio of area R1 to area R2 becomes exactly 1:1, and the reduction in processing time can be increased to 50%. In this case, the time required for a full sweep can be reduced from approximately 6 minutes to 2 minutes and 59 seconds (2.987 [min] ≈ 179.2 [sec] (= 32 × 16 × (100 - 50) / 100 × 700 [msec])).

[0091] Furthermore, when using the first method described in Figure 11 above, the three-dimensional antenna pattern was only applicable to vertically elongated beams. However, when using the second method (where the beam thinning is in a checkerboard pattern), it can be applied to both vertically elongated beams and horizontally elongated beams.

[0092] Here, we will describe a beam pattern characteristic: a (three-dimensional) antenna pattern combining a horizontal plane and a vertical plane. Figure 12 shows an example of a three-dimensional antenna pattern. The example of the three-dimensional antenna pattern shown in Figure 12 is a beam in a certain direction formed by the phased array antenna of the extension station 20 in analog RoF. Note that beams in a different direction will have similar characteristics, which will be described later. The control unit 10a can use these characteristics to select an appropriate beam in the terminal direction even when sweeping with thinned beams using the first method described above.

[0093] Figure 12 allows us to examine the combination of elevation angle (vertical plane) and azimuth direction (horizontal plane) in more detail. The three-dimensional antenna pattern consists of a pattern on the vertical plane (V plane) at the elevation angle shown on the upper right, and a pattern on the horizontal plane (H plane) at the azimuth direction shown on the lower right. The example shown in Figure 12 is a beam in the forward direction. As can be seen from the comparison of the vertical plane pattern and the horizontal plane pattern, even in this three-dimensional antenna pattern, the width of the antenna pattern at the elevation angle (vertical plane) is wider than that in the azimuth direction (horizontal plane). Therefore, when the beam of this three-dimensional antenna pattern is viewed from a viewpoint in the opposite direction, the higher level portion appears to be a vertically elongated ellipse.

[0094] In the example shown in Figure 12, the beam was facing forward, but even with antenna patterns for beams changed to other directions, the shape of the high level in the vertical and horizontal planes of the main beam relative to the beam direction is substantially the same. Also, the appearance of the high-level portion as a vertically elongated ellipse when viewed from the opposite direction of the beam is substantially the same. That is, if the pattern in the vertical plane of the elevation angle (V plane) is about twice as wide as the horizontal plane in the azimuth direction (H plane), the shape of the three-dimensional antenna pattern beam can be confirmed as a vertically elongated ellipse when viewed from the opposite direction. Furthermore, in addition to the narrow region in which the reception level of the terminal is particularly high, it is also conceivable to utilize a slightly wider region in which the reception level of terminal 30 is moderately high.

[0095] (Method 3 for limiting the beam sweep range) Figure 13 is a diagram illustrating a third method for limiting the beam sweep range in the second embodiment. The third method is a method of further thinning the beam sweep than the first method. As shown in Figure 13, the third method thins the beam sweep range vertically more than in the first method, and thins the beam sweep range horizontally even more than in the first method. In Figure 13, region R1 (white-painted region) represents the region where beam sweeping is not performed (the range that is not swept), region R2 (region painted with a pattern of small dots) represents the region where beam sweeping is performed (the range that is swept), and region R3 (region painted with a pattern of large dots) represents the estimated beam direction in which terminal 30 is located. This region R3 corresponds to the narrow region in the antenna pattern shown in Figure 12 above where the reception level of terminal 30 is high. Furthermore, region R4 in Figure 13 (the area surrounding region R3) is a relatively wide region where the reception level of the antenna pattern in Figure 12 is moderately high. Note that in the detailed antenna pattern in Figure 12, the region with a high reception level and the region with a moderately high reception level and the relatively wide region are represented by ellipses, but in Figure 13, for simplicity, they are represented by vertically elongated rectangles.

[0096] The difference between this method and the first method shown in Figure 11 is that the horizontal sweep range is thinned out from the beam sweep range (region R1 in Figure 11 is about 40% of the beam sweep range), and then further thinned out (the number of beam directions excluded is increased). As can be seen at a glance in Figure 13, region R2 is significantly reduced compared to Figure 11. This means that the range in which beam sweeping is performed is significantly reduced compared to Figure 11. In Figure 13, the ratio of beams excluded from sweeping is 70.20%, and the ratio of beams included in sweeping is 29.80%. In Figure 11, the ratio of beams excluded from sweeping is 41.61%, and the ratio of beams included in sweeping is 58.39%. Compared to Figure 11, the number of beams outside the reduced sweep range in Figure 13 is approximately 1.7 times (≒ approximately 1.687 times).

[0097] As shown in Figure 13, where the target beam is thinned out more significantly than in Figure 11, the beam sweep of the present invention can still identify the directional beam of terminal 30. First, when sweeping, if the target beam at the extension station 20 is not present in the selection of the directional beam of terminal 30, a region R4 slightly wider than region R3 (the range in which a sufficiently high reception level can be obtained depending on the antenna beam shape in the beam direction in which terminal 30 is estimated to be present) is considered. This region R4 is the area surrounding region R3, where the reception level when radio waves transmitted by terminal 30 are received at the extension station 20 is moderately high. The beam direction to be swept in this region R4 is also considered together with the beam direction of region R3. In the example shown in Figure 13, the target beam includes a portion that spans left and right at the top of region R3 and a portion that spans from left to center at the bottom of region R4. From the collected information, which combines the received levels of the target beam directions in these two separate locations, the beam direction corresponding to the middle of region R4 (i.e., the central part of region R3) is selected as the beam from the extension station 20 to the terminal 30.

[0098] (Beam selection operation in the second embodiment) Figure 14 is a flowchart showing the processing flow of the beam selection operation in the wireless communication system 100a in the second embodiment. In Figure 14, the same processes as in Figure 8 are denoted by the same reference numerals as in Figure 8 and their explanation is omitted.

[0099] The beam range selection unit 160b presents and inputs the target beam determined by any of the first to third methods to the beam sweep instruction unit 110b (step S301). Subsequently, the processing from step S31 onwards is executed.

[0100] In step S31, the beam sweep instruction unit 110b generates a beam direction change instruction for the extension station 20. For example, the beam sweep instruction unit 110b generates a beam direction change instruction that includes a beam ID to identify one candidate beam from among a set of multiple candidate beams. The beam sweep instruction unit 110b transmits the generated beam direction change instruction to the aggregation station 15.

[0101] According to the wireless communication system 100a in the second embodiment configured as described above, the same effects as in the first embodiment can be obtained.

[0102] Furthermore, in the wireless communication system 100a of the second embodiment, the control unit 10b limits the range over which the beam sweep is performed at the extension station 20 in order to reduce the processing time required for beam sweeping. To this end, the control unit 10b identifies a beam ID for beam sweeping within the beam sweep range and notifies the aggregation station 15 of the identified beam ID. The aggregation station 15 then instructs the extension station 20 to perform a beam sweep using the candidate beam identified by the notified beam ID. In this way, the aggregation station 15 limits beam sweeping in a portion of the beam sweep range that the extension station 20 can beam sweep. This reduces the range over which the beam sweep is performed at the extension station 20. As a result, it becomes possible to reduce the processing time required for beam sweeping.

[0103] In the third method of the second embodiment, if there is a reception level in the beams at vertically adjacent locations and their surroundings, the beam direction that should be selected can be estimated. Therefore, even if a corresponding percentage is reduced in the number of beams to be swept, the beam in the terminal direction can be determined.

[0104] (Modification) In the embodiment described above, the beam selection unit 140 is configured to select the beam direction with the highest quality information. In contrast, the beam selection unit 140 may be configured to select a beam direction by taking into account the quality information of adjacent beam directions in the direction corresponding to the antenna pattern. In this configuration, as the process in step S37 of Figure 14, the beam selection unit 140 uses the quality information for each beam ID recorded by the information acquisition unit 130 to check the quality information (for example, RSSI) of adjacent beam directions in the direction corresponding to the antenna pattern.

[0105] The beam selection unit 140 determines, based on the results of the check, whether multiple adjacent quality information (e.g., RSSI) values ​​are above a threshold. This determination does not necessarily require that the adjacent quality information (e.g., RSSI) values ​​be exactly the same, but it is a process to confirm whether a certain adjacent quality information (e.g., RSSI) is at a reasonably equivalent level compared to other beam directions. In other words, the threshold is the quality information of the beam direction at the center of the adjacent beam directions. If the beam selection unit 140 determines that multiple adjacent quality information (e.g., RSSI) values ​​are below the threshold, the beam selection unit 140 selects the beam direction corresponding to the beam ID with the highest quality information among the quality information for each beam ID recorded by the information acquisition unit 130.

[0106] On the other hand, if the beam selection unit 140 determines that multiple adjacent quality information (e.g., RSSI) is above a threshold, the beam selection unit 140 selects the beam direction of the center of the multiple adjacent beam directions.

[0107] (Third Embodiment) In the second embodiment, the processing time required for beam sweeping was reduced by reducing the number of beams to be swept. Therefore, the processing time can be reduced as the number of beams to be swept is reduced. However, the proportion of terminals located in beam directions that are excluded from the sweep also increases. In other words, in the second embodiment, it is conceivable that the original beam direction used for wireless communication between the extension station and the terminal may be excluded from the sweep. Therefore, in the third embodiment, a configuration will be described in which the quality information of the reduced beam directions is interpolated with quality information obtained from other beam directions.

[0108] Figure 15 shows an example of the functional configuration of the control unit 10c in the third embodiment. The control unit 10c is configured using one or more processors such as a CPU and one or more memories. The control unit 10c realizes the functions of the beam sweep instruction unit 110b, the quality information acquisition instruction unit 120a, the information acquisition unit 130, the beam selection unit 140c, the delay time insertion unit 150a, the beam range specification unit 160b, and the interpolation unit 170c by having one or more processors execute a program.

[0109] The control unit 10c differs in configuration from the control unit 10b in that it includes a beam selection unit 140c instead of the beam selection unit 140, and newly includes an interpolation unit 170c. The following explanation will focus on the differences from the control unit 10b.

[0110] The interpolation unit 170c interpolates the reduced quality information in one beam direction with quality information obtained in another beam direction by performing surface interpolation based on the quality information for each beam ID recorded by the information acquisition unit 130. There are several methods for surface interpolation, and any of them may be used. For example, examples of surface interpolation include spline surfaces (interpolation), B-spline surfaces, Betsey surfaces, NURBS (Non-Uniform Rational B-spline) surfaces, Coons patches, or Gregory patches.

[0111] The beam selection unit 140c selects a beam to be used for wireless communication with the terminal 30 based on the interpolation result from the interpolation unit 170c. For example, the beam selection unit 140c selects the beam with the highest quality information.

[0112] Here, the specific details of the third embodiment will be described. The interpolation unit 170c interpolates the reduced beam direction quality information by constructing a curved surface consisting of other obtained beam directions and quality information. This curved surface contains multiple beam directions (θ) for which measurements are available. ｈ , φ ｉ ) and the beam direction (θ) where no measurement was taken after reduction. ｊ , φ ｋ This includes the range ±30° in the horizontal direction and ±15° in the vertical direction, and if both the horizontal and vertical directions can be changed in 2° increments, then the horizontal direction is "-30°≦(θ ｈ , θ ｊ )≦30° and in the vertical direction "-15°≦(φ ｉ , φ ｋ This can be expressed as "θ ≤ 15°". ｈ ≠θ ｊ And h, j = 0, 1, 2, ..., 31. Also, φ ｉ ≠φ ｋ, and i, k = 0, 1, 2, ..., 15.

[0113] The beam direction (θ) is one of a number of fewer than the 512 (= 16 × 32) combinations of both horizontal and vertical directions. ｈ , φ ｉ Consider a curved surface formed from the quality information (e.g., RSSI) obtained at terminal 30 when sweeping with a portion of the beam. The interpolation unit 170c performs surface interpolation on such a curved surface. Then, the beam selection unit 140c selects the direction (θ) that yields the highest quality information on the interpolated curved surface. ｍａｘ＿ｒｓｓｉ , φ ｍａｘ＿ｒｓｓｉ The beam of ) is selected as the beam to be used for wireless communication with terminal 30.

[0114] Figure 16 is a diagram illustrating surface interpolation techniques. Figure 16 explains the approximation of a smooth surface using surface interpolation techniques. As mentioned above, there are various surface interpolation techniques in different fields, such as B-spline surfaces, NURBS surfaces, and Betsey surfaces. Fields where these surface interpolations are applied include machining and graphic design.

[0115] We will consider applying various surface interpolation methods to a three-dimensional graph of quality information obtained from a beam sweep of the extension station 20. Figure 16 shows an image of applying surface interpolation to quality information in the beam direction of the extension station 20. The beam direction of the extension station 20 is determined by the horizontal direction θ [deg] and the vertical direction φ [deg]. In the example of the three-dimensional graph shown as an image in Figure 16, the horizontal direction θ = -40° to 40° and the vertical direction φ = -15° to 15° are given. Also, in Figure 16, the RSSI, which is quality information, is represented as a surface with values ​​from -80 to -40 [dBm].

[0116] The effect of applying surface interpolation is that it can limit and reduce the number of beams to be swept. In other words, it reduces the number of combinations of the horizontal direction θ and the vertical direction φ of the beam. For example, in Figure 16, if the beam sweep range is horizontal θ = -40 to 40° and vertical φ = -15° to 15°, and all beams are swept every 2° in both directions (θ, φ), the total number of beams would be as many as [{40 - (-40)} / 2] × [{15 - (-15)} / 2] = 40 × 15 = 600.

[0117] By limiting the number of beams, interpolation is performed using a curved surface as shown in Figure 16, based on the reduced target beams of the sweep and the quality information of the terminal 30 obtained from those target beams. This allows for the determination of the appropriate beam direction.

[0118] (Beam Selection Operation in the Third Embodiment) Figure 17 is a flowchart showing the processing flow of the beam selection operation in the wireless communication system 100a in the third embodiment. In Figure 17, the same processes as in Figure 5 are denoted by the same reference numerals as in Figure 5 and their explanations are omitted. The beam range designation unit 160b presents and inputs the target beam determined by any of the first to third methods to the beam sweep instruction unit 110b (step S401). Alternatively, the beam range designation unit 160b may determine the overall proportion of beams to be swept and randomly select a beam direction from all beam sweep ranges to determine the target beam, which is then presented and inputted to the beam sweep instruction unit 110b. After that, the processes from step S31 to step S36 are executed.

[0119] In step S36, if the control unit 10c determines that beam sweeping has been completed for all candidate beams (step S36-YES), the interpolation unit 170c performs surface interpolation based on the quality information for each beam ID recorded by the information acquisition unit 130, interpolating the reduced quality information for each beam direction with the quality information obtained for other beam directions (step S402). Subsequently, the beam selection unit 140c selects a beam direction to be used for communication with the terminal 30 based on the results of the surface interpolation by the interpolation unit 170c (step S403). Specifically, the beam selection unit 140c selects the beam direction corresponding to the beam ID with the highest quality information in the surface obtained as a result of surface interpolation.

[0120] When the interpolation unit 170c uses a spline surface (interpolation) as the surface interpolation in the process of step S402, the interpolation unit 170c receives quality information for each beam ID (for example, beam direction (θ)) recorded by the information acquisition unit 130. ｈ , φ ｉ ), RSSI) are used as control points on the spline surface (interpolation). The beam direction (θ) for which there are no reduced measurements is used as an excluded beam that is not swept. ｊ , φ ｋ ) Regarding the Spline surface (interpolation), the surrounding control points (beam direction (θ) ｈ , φ ｉ Interpolated by ), RSSI)

[0121] The above quality information (for example, beam direction (θ) ｈ , φ ｉ Even if surface interpolation is performed using the control points (RSSI), in the case of a spline surface (interpolation), the quality information (for example, beam direction (θ)) is lost. ｈ , φ ｉ The measurement points are included in the surface interpolation for (RSSI). Therefore, if quality information measured by sweeping all directional beams is compared to a surface, the Spline surface (interpolation) is assumed to be closer than other surface interpolations. For this reason, the maximum quality information in the Spline surface (interpolation) is considered to best match the same value for a surface that could have been swept with all beams.

[0122] In the surface interpolation process of step S402, when the interpolation unit 170c uses a NURBS surface, the measurement point is not included in the surface interpolation with the measured RSSI as the control point. However, it is thought that the magnitude relationship (high and low levels of RSSI) on the surface interpolation is appropriately reflected, and an accurate beam direction (θ, φ) can be obtained. A NURBS surface is a type of representation method for freeform surfaces. While B-Spline surfaces cannot represent quadratic surfaces such as cones, NURBS surfaces are an improvement over B-Spline surfaces that can also represent two-dimensional surfaces.

[0123] NURBS surfaces are characterized by their flexibility and accuracy, making them convenient for computer programs and suitable for human editing. Based on these characteristics of NURBS surfaces, similar to the Spline surfaces (interpolation) described above, quality information (beam direction (θ) ｈ , φ ｉ The RSI (Ratio of Ratio 1) and RSI (Ratio of Ratio 2) are used as control points in interpolation using NURBS surfaces. This allows us to leverage the flexibility and accuracy of NURBS surface interpolation when determining the optimal beam from measurements obtained by sweeping only a limited target beam.

[0124] In the process of step S402, it is conceivable that one of the following methods may be used for surface interpolation: a Betsey curve, a B-spline surface, a Coons patch, or a Gregory patch. Unlike the spline surface (interpolation), with these surface interpolation and surface patching methods, the measurement points may not necessarily be included in the interpolated surface. Nevertheless, regardless of which surface interpolation or surface patching method is used, the interpolation unit 170c will sweep the beam direction (θ) of the limited target. ｈ , φ ｉ Surface interpolation is performed using the quality information obtained from the beam (θ) and its target beam. In these surface interpolations, the beam direction (θ) that is not subject to sweeping is used. ｊ , φ ｋ The missing portion of the beam is the surrounding measured beam direction (θ ｈ , φ ｉ It is supplemented smoothly and continuously to a reasonable extent based on the RSSI.

[0125] Among these surface interpolation methods, Betsey surfaces, for example, are a surface interpolation method with excellent features in various aspects and are widely used in the field of computer graphics. They are visually intuitive and mathematically convenient for many applications. Therefore, the beam direction (θ) when sweeping a Betsey surface... ｈ , φ ｉ Using the measured values, surface interpolation can be completed with a small number of points, or surface interpolation can be performed by adding measurements sequentially from the fewest values ​​to approximate the result of a full sweep.

[0126] Unlike other surface interpolation methods (such as B-Spline surfaces and NURBS surfaces), Spline surface interpolation interpolates using a surface that includes the measurement points (control points). For this reason, Spline surface interpolation is suitable for interpolating the surface formed by the quality information (e.g., RSSI) measured at terminal 30 with respect to the beam direction (θ, φ) of the phased array antenna of the extension station 20.

[0127] When applying NURBS surfaces to surface interpolation based on quality information (e.g., RSSI), even if the RSSI measurement points are used as control points, unlike spline surfaces (interpolation), these control points do not pass through the surface. However, NURBS surfaces have excellent characteristics (advantages) as surface interpolation tools. For example, they offer flexibility in changing the surface shape by editing the control points, and accuracy, such as the ability to define a quadratic Betsier surface in three-dimensional space and apply a projection transformation to obtain a conic section. Therefore, applying NURBS surfaces provides advantages such as flexibility and accuracy in surface interpolation.

[0128] Betsey surfaces, B-spline surfaces, Coons patches, and Gregory patches can also be used to leverage the unique characteristics of each surface interpolation method by applying other surface interpolation methods to RSSI only on the directional beam of the sweep target.

[0129] According to the wireless communication system 100a in the third embodiment configured as described above, the same effects as in the first embodiment can be obtained.

[0130] Furthermore, in the wireless communication system 100a of the third embodiment, the control unit 10c interpolates the quality information for some beam directions based on the quality information for other beam directions, even if quality information for some beam directions is insufficient. This suppresses the effects that occur when a portion of the beam sweep range is thinned out in order to reduce the processing time required for beam sweeping. As a result, it becomes possible to reduce the processing time required for beam sweeping and to determine the beam direction.

[0131] (Fourth Embodiment) In the third embodiment, a configuration was described in which missing beam direction quality information is interpolated using curved surface interpolation. In the fourth embodiment, assuming the use of curved surface interpolation, a configuration is described in which the beam sweeping the phased array antenna of the extension station is further thinned out. The system configuration and device configuration in the fourth embodiment are the same as in the third embodiment.

[0132] In the fourth embodiment, the processing performed by the control unit 10c differs from that in the third embodiment. The differences from the third embodiment will be explained below.

[0133] Figure 18 is a diagram illustrating a method for limiting the beam sweep range in the fourth embodiment. Figure 18 shows the sweep range of the phased array antenna of the extension station 20. As shown in the legend, the beam directions to be swept are region R2 (the region colored with a pattern of small dots) and region R5 (the region colored with a pattern of diagonal lines to the right). Region R1 (the white-colored region) is the region where beam sweeping is not performed (the range that is not swept).

[0134] Furthermore, Figure 18 shows two types of meshes. The first mesh is a coarse mesh, consisting of four squares and a dashed-dotted cross. The second mesh is a mesh in which the area enclosed by the dotted line is divided into a fine mesh. Additionally, for reference, it is assumed that there are narrow areas where the reception level of terminal 30 is high, and slightly wider areas where the reception level of terminal 30 is moderately high.

[0135] In the fourth embodiment, the beam direction of the phased array antenna of the extension station 20 is determined by following a two-step procedure as shown below. (Procedure 1) The control unit 10c first divides the entire sweep range of the phased array antenna of the extension station 20 into a coarse mesh (the first mesh described above) and generates multiple sub-regions. The control unit 10c selects some of the multiple sub-regions and performs a sweep on the beam in the direction of the center of each selected sub-region (cross of dashed lines). This corresponds to performing a beam sweep on the beam corresponding to the range shown in region R2 in Figure 18.

[0136] (Procedure 2) The control unit 10c forms a curved surface in three-dimensional space based on the quality information obtained from the beam direction sweep corresponding to each selected sub-region. The control unit 10c applies surface interpolation during this surface formation. Here, after surface interpolation, the control unit 10c checks the mesh in the beam direction with high quality information. In Figure 18, as shown in the areas with particularly high and moderately high reception levels, the second mesh in both the horizontal and vertical directions from the bottom right was not in the first beam direction, but it is highly likely that it will be confirmed as a good mesh through surface interpolation.

[0137] (Step 3) The control unit 10c divides the mesh in the beam direction and the surrounding mesh (in the dotted line area in Figure 18) that was confirmed to have a good reception level in the first surface interpolation into finer meshes and generates multiple sub-regions.

[0138] (Procedure 4) The control unit 10c selects some of the multiple subregions generated by dividing the area into a fine mesh the second time, and performs a sweep on the beam in the direction of the center of each selected subregion (cross of dashed lines). This is equivalent to performing a beam sweep on the beam corresponding to the area shown in region R5 in Figure 18.

[0139] (Procedure 5) The control unit 10c combines the results of the terminal reception level obtained in the second sweep with the results of the first sweep to form a curved surface in three-dimensional space. The control unit 10c applies surface interpolation when forming this curved surface.

[0140] (Procedure 6) The control unit 10c selects the beam direction that is in the center of the directional mesh where the reception level appears to be good in the second surface interpolation (the beam direction with the highest reception level, or the beam direction where the above reception level is high in surface interpolation even if it was not selected in the fine mesh of the second step) as the beam to be used for wireless communication with the terminal 30.

[0141] Following the above procedure, the control unit 10c determines the beam direction of the phased array antenna of the extension station 20. In short, in the fourth embodiment, the beam range of the fine mesh is narrowed down by surface interpolation from the results obtained with the coarser mesh (first time) partial beam candidates, and the beam direction is determined by surface interpolation of the second time results.

[0142] In the fourth embodiment, as can be easily seen in Figure 18, the number of beams to be swept can be significantly reduced. In the first mesh (coarse mesh), the number of beams is 1 / 10 of the original fine mesh. In the example in Figure 18, it is 1 / 9 of the original fine mesh. If we consider the total sweep processing time of approximately 6 minutes (≒358.4 [sec]) as described in the second embodiment, applying the method in the fourth embodiment reduces the sweep time by approximately 40 seconds (≒39.8222... [sec] ≒ 1 / 9 × 358.4 [sec]). Furthermore, the central direction of all coarse meshes is not used in the sweep; only a portion is selected. At this point, a reduction of more than an order of magnitude in the number of beams has been achieved. On the other hand, even if the beam reduction during sweeping is significant, surface formation and surface interpolation are performed on the received level of the terminal obtained by the sweep, and the same procedure is performed from the general direction (within the range of the coarsest mesh and its surrounding meshes) to the finer mesh, so the beam direction can be appropriately determined.

[0143] (Beam selection operation in the fourth embodiment) Figure 19 is a flowchart showing the processing flow of the beam selection operation in the wireless communication system 100a in the fourth embodiment. The beam range designation unit 160b determines the target beam (candidate beam) to sweep in a part of the coarse mesh (first mesh). The beam range designation unit 160b presents the determined target beam to the beam sweep instruction unit 110b (step S501). The beam sweep instruction unit 110b generates a beam direction change instruction for the extension station 20. For example, the beam sweep instruction unit 110b generates a beam direction change instruction that includes a beam ID to identify one candidate beam from among a set of multiple candidate beams. The beam sweep instruction unit 110b transmits the generated beam direction change instruction to the aggregation station 15 (step S502). The aggregation station 15 receives the beam direction change instruction transmitted from the control unit 10c. The aggregation station 15 starts beam direction change control for the extension station 20 in accordance with the received beam direction change instruction.

[0144] The delay time insertion unit 150a inserts a delay time into the quality information acquisition instruction unit 120a (step S503). The quality information acquisition instruction unit 120a generates a quality information acquisition instruction when the delay time inserted by the delay time insertion unit 150a has elapsed. At the time the delay time has elapsed, the beam direction change control instructed by the control unit 10c has been completed at the extension station 20. The quality information acquisition instruction unit 120a transmits the generated quality information acquisition instruction to the aggregation station 15 (step S504). The aggregation station 15 receives the quality information acquisition instruction transmitted from the control unit 10c. The aggregation station 15 transmits the received quality information acquisition instruction to the extension station 20. The extension station 20 transmits the quality information acquisition instruction transmitted from the aggregation station 15 to the terminal 30 with the set beam.

[0145] Terminal 30 receives a quality information acquisition instruction transmitted from the outgoing station 20. Terminal 30 outputs the received quality information acquisition instruction to the response unit 35. The response unit 35 transmits a quality information acquisition execution instruction to terminal 30 in response to the quality information acquisition instruction. Terminal 30 receives a beam search signal transmitted from the outgoing station 20. Terminal 30 measures the quality information of the received beam search signal (step S505).

[0146] Terminal 30 transmits the measured quality information to the base station device 1 in response to instructions from the response unit 35 (step S506). The extension station 20 of the base station device 1 receives the quality information transmitted from terminal 30. The extension station 20 converts the received quality information into an optical signal and transmits it to the aggregation station 15. At this time, the extension station 20 also transmits the beam ID, which indicates the candidate beam used to transmit the beam search signal, to the aggregation station 15 along with the quality information. The aggregation station 15 transmits the beam ID and quality information transmitted from the extension station 20 to the control unit 10c. The control unit 10c acquires the beam ID and quality information transmitted from the aggregation station 15 and registers the acquired beam ID and quality information in the quality information table in association (step S507).

[0147] Subsequently, the control unit 10c determines whether or not the beam sweep has been completed for all candidate beams (step S508). If the control unit 10c determines that the beam sweep has not been completed for all candidate beams (step S508-NO), the base station device 1 repeats the process from step S502 onwards. In this case, the base station device 1 performs the beam sweep on the candidate beams that have not yet been swept.

[0148] If the control unit 10c determines that beam sweeping has been completed for all candidate beams (step S508-YES), the interpolation unit 170c performs surface interpolation based on the quality information for each beam ID recorded by the information acquisition unit 130 (step S509). Subsequently, the beam range designation unit 160b identifies the coarsest mesh in the beam direction with the highest quality information (e.g., RSSI) in the surface interpolation, and its surrounding area (step S510).

[0149] The beam range designation unit 160b divides the identified coarse mesh and its surroundings into finer meshes, generating multiple sub-regions. The beam range designation unit 160b selects some of the sub-regions generated by the second division into finer meshes, and determines the target beam (candidate beam) to sweep in a portion of the coarse mesh (first mesh) in the beam towards the center of each selected sub-region.

[0150] The beam range selection unit 160b inputs the determined target beam to the beam sweep instruction unit 110b (step S511). The beam sweep instruction unit 110b generates a beam direction change instruction for the extension station 20. For example, the beam sweep instruction unit 110b generates a beam direction change instruction that includes a beam ID to identify one candidate beam from among the multiple candidate beams set in the process of step S511. The beam sweep instruction unit 110b transmits the generated beam direction change instruction to the aggregation station 15 (step S512). The aggregation station 15 receives the beam direction change instruction transmitted from the control unit 10c. The aggregation station 15 starts beam direction change control for the extension station 20 in accordance with the received beam direction change instruction.

[0151] The delay time insertion unit 150a inserts a delay time into the quality information acquisition instruction unit 120a (step S513). The quality information acquisition instruction unit 120a generates a quality information acquisition instruction when the delay time inserted by the delay time insertion unit 150a has elapsed. At the time the delay time has elapsed, the beam direction change control instructed by the control unit 10c has been completed at the extension station 20. The quality information acquisition instruction unit 120a transmits the generated quality information acquisition instruction to the aggregation station 15 (step S514). The aggregation station 15 receives the quality information acquisition instruction transmitted from the control unit 10c. The aggregation station 15 transmits the received quality information acquisition instruction to the extension station 20. The extension station 20 transmits the quality information acquisition instruction transmitted from the aggregation station 15 to the terminal 30 with the set beam.

[0152] Terminal 30 receives a quality information acquisition instruction transmitted from the outgoing station 20. Terminal 30 outputs the received quality information acquisition instruction to the response unit 35. The response unit 35 transmits a quality information acquisition execution instruction to terminal 30 in response to the quality information acquisition instruction. Terminal 30 receives a beam search signal transmitted from the outgoing station 20. Terminal 30 measures the quality information of the received beam search signal (step S515).

[0153] Terminal 30 transmits the measured quality information to base station device 1 in response to instructions from response unit 35 (step S516). The extension station 20 of base station device 1 receives the quality information transmitted from terminal 30. The extension station 20 converts the received quality information into an optical signal and transmits it to aggregation station 15. At this time, the extension station 20 also transmits the beam ID, which indicates the candidate beam used to transmit the beam search signal, to aggregation station 15 along with the quality information. Aggregation station 15 transmits the beam ID and quality information transmitted from extension station 20 to control unit 10c. The control unit 10c acquires the beam ID and quality information transmitted from aggregation station 15 and registers the acquired beam ID and quality information in the quality information table in association (step S517).

[0154] Subsequently, the control unit 10c determines whether or not the beam sweep has been completed for all candidate beams (step S518). If the control unit 10c determines that the beam sweep has not been completed for all candidate beams (step S518-NO), the base station device 1 repeats the process from step S502 onwards. In this case, the base station device 1 performs the beam sweep on the candidate beams that have not yet been swept.

[0155] If the control unit 10c determines that beam sweeping has been completed for all candidate beams (step S518-YES), the interpolation unit 170c performs surface interpolation based on the quality information for each beam ID recorded by the information acquisition unit 130 (step S519). Subsequently, the beam selection unit 140c selects the beam direction with the highest quality information (e.g., RSSI) in the surface interpolation as the beam to be used for wireless communication with the terminal 30 (step S520). As a result, the base station device 1 sets the beamforming of the phased array antenna of the extension station 20 toward the selected beam direction and performs wireless communication with the terminal 30.

[0156] According to the wireless communication system 100a in the fourth embodiment configured as described above, the same effects as in the first embodiment can be obtained.

[0157] Furthermore, in the wireless communication system 100a of the fourth embodiment, the control unit 10c determines the optimal beam direction in the terminal direction based on the results obtained by performing interpolation processing twice. Specifically, the control unit 10c first causes the extension station 20 to perform a beam sweep (first beam sweep) on a portion of the beam sweep range out of all beam sweep ranges that it can beam sweep. The control unit 10c uses the quality information obtained from the first beam sweep to perform surface interpolation to interpolate the quality information in the range where the beam sweep was not performed. Subsequently, the control unit 10c identifies the range to perform the second beam sweep based on the quality information obtained as a result of surface interpolation, and causes the beam sweep to be performed on the identified beam sweep range. The control unit 10c uses the quality information obtained from the second beam sweep and the quality information obtained from the first beam sweep to perform surface interpolation to interpolate the quality information in the range where the beam sweep was not performed. In this way, the control unit 10c performs surface interpolation twice. Then, the control unit 10c selects the optimal beam direction based on the results of the second surface interpolation. For example, the control unit 10c selects the beam direction with the highest quality information in the surface interpolation as the beam to be used for wireless communication with the terminal 30. Therefore, in a wireless communication system 100a with a configuration that separates the functions of wireless communication devices, it becomes possible to determine the optimal beam direction for the terminal.

[0158] In each of the embodiments described above, the extended station 20 can be interpreted as "RRU (Remote Radio Unit)", "RU (Radio Unit)" (corresponding to CU and DU described later), "Distributed Antenna (DA)", "Slave unit", and "Antenna".

[0159] In each of the embodiments described above, the aggregation station 15 can be reinterpreted as "CS (Central Station)", "Base Station (BS)", "CU (Central Unit)", "DU (Distributed Unit)", "RU (Radio Unit)" (however, corresponding to the DA mentioned above), and "Master Unit".

[0160] In the above-described embodiments, the base station devices 1 and 1a can be reinterpreted as "Base Station (BS)", "Wireless Base Station", "Fixed Base Station", "NodeB", "eNodeB", "gNodeB", "Access Point", "Transmission Point (TP)", "Reception Point (RP)", "Transmission / Reception Point (TRP)", "Distributed Antenna (DA)", "Cell", "Sector", "Macrocell", "Smallcell", "Femtocell", and "Picocell". However, to be more precise, the base station devices 1 and 1a are divided into an outpost station 20 (corresponding to "RRU", "RU", and "DA") and an aggregation station 15 ("CS", "CU", and "DU"). Therefore, the "base station (BS)", "access point (AP)", and "transmit / receive point (TRP)" are located at the same position as the extension station 20, and their functions are those of both stations combined. "Cell", "sector", and "microcell" indicate the range that is accommodated by these "base stations (BS)", "access points (AP)", and "transmit / receive points (TRP)".

[0161] Some or all of the base station device 1a in the first to fourth embodiments described above may be implemented using a computer. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. Here, "computer system" includes hardware such as an OS (Operating System) and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), CD-ROMs, and storage devices such as hard disks built into a computer system.

[0162] Furthermore, "computer-readable recording media" may include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, as well as those that hold programs for a certain period of time, such as volatile memory inside computer systems that act as servers or clients in such cases. In addition, the above-mentioned program may be for the purpose of realizing a part of the aforementioned functions, or it may be a program that can realize the aforementioned functions in combination with a program already recorded in the computer system, or it may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0163] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0164] The present invention can be applied to beam sweeping in base station equipment using analog RoF.

[0165] 1, 1a...Base station equipment, 10, 10a, 10b, 10c...Control unit, 15...Aggregation station, 20...Extended station, 30...Terminal, 35...Response unit, 110, 110b...Beam sweep instruction unit, 120, 120a...Quality information acquisition instruction unit, 130...Information acquisition unit, 140, 140c...Beam selection unit, 150a...Delay time insertion unit, 160b...Beam range specification unit, 170c...Interpolation unit, 100a...Wireless communication system

Claims

1. A wireless communication device configured by separating the wireless communication function into a first communication device and a second communication device, wherein the first communication device controls the second communication device to perform a beam sweep on a portion of the beam sweep ranges out of all beam sweep ranges that the second communication device can beam sweep, and the second communication device performs a beam sweep on a portion of the beam sweep ranges in response to the control from the first communication device.

2. The wireless communication device according to claim 1, wherein the first communication device interpolates quality information in a portion of the beam sweep range obtained by performing a beam sweep, in the portion of the entire beam sweep range in which a beam sweep has not been performed, and selects a beam direction to be used for communication with the terminal based on the interpolation result.

3. The wireless communication device according to claim 1 or 2, wherein the first communication device causes the second communication device to perform a beam sweep on a first beam sweep range out of all beam sweep ranges that the second communication device can beam sweep, interpolates quality information in the range of the beam sweep range in which a beam sweep has not been performed using first quality information obtained from performing a beam sweep on the first beam sweep range, determines a second beam sweep range based on the interpolation result, performs a beam sweep on the determined second beam sweep range, interpolates quality information in the range of the beam sweep range in which a beam sweep has not been performed using second quality information obtained from performing a beam sweep on the second beam sweep range and the first quality information, and selects a beam direction to be used for communication with a terminal based on the interpolation result.

4. A wireless communication method performed by a wireless communication device configured by separating the functions of wireless communication into a first communication device and a second communication device, wherein the first communication device controls the second communication device to perform a beam sweep on a portion of the beam sweep ranges out of all beam sweep ranges that the second communication device can beam sweep, and the second communication device performs a beam sweep on a portion of the beam sweep ranges in response to the control from the first communication device.

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