Wireless communication device and wireless communication method

Abstract

This wireless communication device is configured by separating a wireless communication function into a first communication device and a second communication device. The first communication device causes a terminal to transmit, after a lapse of a delay time from a timing when the second communication device has been instructed to set a candidate beam to be used for a beam sweep to be performed in the second communication device until the completion of the setting of the candidate beam about which the second communication device has been instructed, an instruction to acquire quality information relating to a reference signal to be transmitted by the set candidate beam. The second communication device transmits the instruction to acquire quality information to the terminal using the candidate beam set in response to the instruction 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, by separating the functions between a central station and one or more antenna stations, many antenna stations can be deployed economically. 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 by a conventional method, it may not be possible to associate quality information with the correct beam direction, and an appropriate beam direction may not be selected. Specifically, beam switching in the remote station is executed based on an instruction from the central station. Therefore, when the distance between the central station and the remote station is large or there is a processing delay in the remote station, a delay occurs from the instruction of the central station to the beam switching in the remote station. As a result, before the beam is switched in the remote station, the beam search signal may be transmitted using the candidate beam before the beam switching. In this case, a deviation occurs between the candidate beam and the corresponding quality information. As a result, there is a problem that the beam direction of the optimal terminal direction cannot be determined.

[0009] In view of the above circumstances, an object of the present invention is to provide a technology capable of determining the beam direction of the optimal terminal direction in a wireless communication system having a configuration in which the functions of a wireless communication device are separated.

[0010] One aspect of the present invention is a wireless communication device configured by separating the functions of wireless communication into a first communication device and a second communication device. The first communication device is configured to transmit an instruction to the terminal to acquire quality information regarding a reference signal transmitted using the set candidate beam after a delay time has elapsed from the timing when the first communication device instructs the second communication device to set the candidate beam to be used for beam sweeping in the second communication device until the setting of the candidate beam instructed by the second communication device is completed. The second communication device transmits an instruction to the terminal to acquire the quality information using the candidate beam set in response to an instruction from the first communication device. The wireless communication device includes:

[0011] One aspect of the present invention is a wireless communication method performed by a wireless communication device configured by separating the wireless communication function between a first communication device and a second communication device. After a delay time has elapsed from the timing when the first communication device instructs the second communication device to set candidate beams to be used for beam sweeping performed by the second communication device until the setting of the candidate beams instructed by the second communication device is completed, the first communication device causes the terminal to transmit an acquisition instruction for quality information regarding a reference signal transmitted using the set candidate beams. The second communication device transmits the acquisition instruction for the quality information to the terminal using the candidate beams set in response to an instruction from the first communication device.

[0012] According to the present invention, in a wireless communication system having a configuration in which the functions of a wireless communication device are separated, it becomes possible to determine the beam direction in the optimal terminal direction.

[0013] 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 the first method for limiting the target range of a beam sweep in the second embodiment. This figure shows the projection range of a beam sweep whose range has been specified by the first method for limiting the target range of a beam sweep in the second embodiment. This figure illustrates the second method for limiting the target range of a beam sweep in the second embodiment. This figure shows the projection range of a beam sweep whose range has been specified by the second method for limiting the target range of a beam sweep in the second embodiment. This figure illustrates the operation process for creating the beam sweep range specified by the second method in the second embodiment. This figure illustrates a third method for limiting the target range of a beam sweep in the second embodiment. This flowchart shows the flow of the beam sweep specified range creation process performed by the beam range specification unit in the second embodiment. This flowchart shows the flow of the beam selection operation in the wireless communication system in the second embodiment. This figure illustrates the operation process for creating the beam sweep range in the third embodiment. This flowchart shows the flow of the beam sweep specified range creation process performed by the beam range specification unit in the third embodiment.

[0014] One embodiment of the present invention will be described below with reference to the drawings.

[0015] (Conventional Configuration) Before explaining the contents of the present invention, let's first describe the conventional configuration. Figure 1 is a diagram showing an example of the configuration of a conventional wireless communication system S. The wireless communication system S comprises a base station device 1, a terminal 30, and a response unit 35. The base station device 1 consists of a control unit 10, an aggregation station 15, and an extension station 20. The base station device 1 is configured by separating the wireless communication functions into multiple devices. For example, the base station device 1 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 10 and the aggregation station 15. The aggregation station 15 and the extension station 20 are connected by an optical transmission path. The optical transmission path is, for example, an optical fiber. The length of the optical fiber connecting the aggregation station 15 and the extension station 20 is several tens of kilometers. That is, the aggregation station 15 and the extension station 20 are several tens of kilometers apart. The control unit 10 may be provided in the aggregation station 15. The response unit 35 may be provided in the terminal 30.

[0016] In the wireless communication system S, analog RoF transmission is performed between the aggregation station 15 and the branch stations 20. In Figure 1, one branch station 20 is connected to the aggregation station 15, but it is also possible to connect multiple branch stations 20 by branching the optical transmission path from one aggregation station 15 using an optical combiner / splitter. An optical combiner / splitter combines or splits the input optical signal. An optical combiner / splitter is, for example, an optical splitter.

[0017] The control unit 10 performs beam sweep control at the extension station 20 and selects beams to be used for communication with the terminal 30. Beam sweep control at the extension station 20 involves sending instructions to the extension station 20, such as instructions to execute a beam sweep or switch candidate beams, to cause the beam sweep to be performed. During beam sweep control, the control unit 10 instructs the extension station 20 to switch candidate beams to which it will transmit beam search signals. In the following description, the signal used to instruct the extension station 20 to switch candidate beams to which it will transmit beam search signals will be referred to as a beam direction change instruction. The beam direction change instruction includes a beam ID to identify the candidate beam to which it will switch. The beam direction change instruction may also include identification information to identify the extension station 20 to which the beam search will be performed.

[0018] Furthermore, after transmitting the beam direction change instruction, the control unit 10 instructs the extension station 20 to transmit a quality information acquisition instruction. The quality information acquisition instruction is an instruction for the terminal 30 to acquire quality information when it receives the beam search signal. Based on the quality information of each candidate beam obtained by beam sweep, the control unit 10 selects a beam from among the candidate beams held by the extension station 20 to be used for wireless communication with the terminal 30. In other words, the control unit 10 determines the beam that will be directed towards the terminal. The control unit 10 may be an information processing device such as a personal computer. If 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.

[0019] The aggregation station 15 converts the instructions output from the control unit 10 into optical signals and outputs them to the extension station 20. The aggregation station 15 converts the optical signals output from the extension station 20 into electrical signals and outputs them to the control unit 10. The aggregation station 15 and the control unit 10 are connected, for example, by electrical wires. The aggregation station 15 is one embodiment of the first communication device.

[0020] The extension station 20 is equipped with a phased array antenna and performs a beam sweep using candidate beams formed by the phased array antenna. During this process, the extension station 20 transmits beam search signals and quality information acquisition instructions to the terminal 30 using the candidate beams. Figure 1 shows a configuration in which the extension station 20 forms candidate beams B1 to B5 in five different directions, but the number of candidate beams that the extension station 20 can form is not particularly limited. The extension station 20 performs a beam sweep by sequentially switching the beams from candidate beam B1 to candidate beam B5 in response to instructions from the control unit 10. The extension station 20 performs wireless communication with the terminal 30 using the candidate beam selected by the control unit 10. The extension station 20 is one embodiment of the second communication device.

[0021] 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.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] (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.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] 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).

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] (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.

[0044] 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).

[0045] 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).

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] (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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] (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.

[0060] 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.

[0061] (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.

[0062] 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).

[0063] 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.

[0064] 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).

[0065] 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).

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] (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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 16, but this is not the only method for limiting the beam sweep range.

[0076] (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 along with the beam sweep range in the first method. Here, the beam sweep range represents the range in which the extension station 20 can perform a beam sweep. The first method, as shown in Figure 11, is a method in which the beam sweep range is limited in the vertical direction but not in the horizontal direction. In Figure 11, region R1 (white-painted area) represents the area where beam sweeping is not performed (range not to be swept), region R2 (area painted with a pattern of small dots) represents the area where beam sweeping is performed (range to be swept), and region R3 (area painted with a pattern of large dots) represents the estimated beam direction in which the terminal 30 is located.

[0077] The beam sweep range shown in Figure 11 represents the angle of the beam of the phased array antenna of the extension station 20 in the left / right and up / down directions relative to the front direction. In the beam sweep range shown in Figure 11, the horizontal axis represents the horizontal direction θ [deg], and the vertical axis represents the vertical direction φ [deg]. In Figure 11, as an example, the horizontal range is set to -30° ≤ θ ≤ 30°, and the vertical range is set to -15° ≤ φ ≤ 15°.

[0078] As shown in the first embodiment, if the phased array antenna of the extension station 20 is swept across the entire sweepable range, the extension station 20 will beam sweep the horizontal range "-30°≦θ≦30°" and the vertical range "-15°≦φ≦15°". In contrast, the first method sweeps a range that is wide horizontally and irregularly shaped (mostly a rectangle with a full angle horizontally, with the top and bottom vertically protruding separately to the left and right), as shown in region R2. This makes it possible to limit the range of beam sweeping compared to sweeping the entire beam sweep range as in the first embodiment. As a result, the time required for beam sweeping can also be reduced.

[0079] Figure 12 is a diagram showing the projection range of a beam sweep specified by the first method for limiting the beam sweep range in the second embodiment. In Figure 12, only the extension station 20 is shown for the purpose of explaining the extension station 20, but the extension station 20 shown in Figure 12 is connected to the aggregation station 15 via an optical transmission path. When the search range in the first embodiment is projected onto the horizontal plane, the search area (beam sweep range) is as shown in area R. That is, in a full beam search, it spreads out in an arc-shaped band relative to the horizontal plane of the ground. As for the antenna installation conditions, it is installed above the support column on which the phased array antenna of the extension station 20 is located, at a certain height. In reality, locations such as utility poles, streetlights, dedicated poles for attaching the extension station 20, or the rooftops and walls of buildings are envisioned. Also, the front direction of the phased array antenna is pointed towards the ground with a slight downward angle.

[0080] As shown in Figure 12, when the vertical search range is limited as in the first method, the area projected onto the horizontal plane of the ground becomes wider in the shape of an arc with respect to the position of the target terminal 30, as shown by region R2, and becomes even more irregular in shape.

[0081] (Method 2 for Limiting the Beam Sweep Range) Figure 13 is a diagram illustrating a second method for limiting the beam sweep range in the second embodiment. Figure 12 shows the beam sweep range along with the beam sweep range in the second method. The second method, as shown in Figure 12, is a method of limiting the beam sweep range to the target terminal 30 and its surroundings. In Figure 13, region R1 (white-filled region) represents the region where beam sweeping is not performed (the range that is not swept), region R2 (region filled with a pattern of small dots) represents the region where beam sweeping is performed (the range that is swept), and region R3 (region filled 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 Figure 13 is similar to the range explained in Figure 11; for example, the horizontal range is set to -30° ≤ θ ≤ 30°, and the vertical range is set to -15° ≤ φ ≤ 15°. In the second method, the beam sweep range is defined as the area projected around the target terminal 30 (center) and its surroundings (the area indicated by region R2). The projection station 20 performs the beam sweep with the beam within the area indicated by region R2 in Figure 13. This makes it possible to more efficiently determine the beam that is directed towards the target terminal 30.

[0083] One point to note in Figure 13 is that it is not a circle centered on the beam direction (for example, θ = 18°, φ = -6°) where the target terminal 30, indicated by region R3, is presumed to be located. The reason for this shape (wider on the near side (φ: negative direction) and narrower on the far side (φ: positive direction)) will be explained in Figure 15.

[0084] Figure 14 is a diagram showing the projection range of a beam sweep, where the range is specified by the second method for limiting the target range of the beam sweep in the second embodiment. In Figure 14, only the extension station 20 is shown for the purpose of explaining the extension station 20, but the aggregation station 15 is connected to the extension station 20 shown in Figure 14 via an optical transmission path. When the search range in the first embodiment is projected onto the horizontal plane, the search area (target range of the beam sweep) is as shown in region R. On the other hand, when the search range indicated by the phased array antenna of the extension station 20 (same as in Figure 13) is projected onto the horizontal plane on the ground, the search area (target range of the beam sweep) is as shown in region R2. On the horizontal plane, it is around the terminal position of the target represented by region R3 and in a roughly circular shape (however, corners are formed depending on the number of beam directions). This point will be explained using Figure 15.

[0085] Figure 15 is a diagram illustrating the operation process for creating the beam sweep range specified by the second method described above. In Figure 15, only the extension station 20 is shown for the purpose of explaining the extension station 20, but the aggregation station 15 is connected to the extension station 20 shown in Figure 15 via an optical transmission path. This operation process can determine the beam ID corresponding to the candidate beam for sweeping the region that will result in the beam sweep range. This operation process is performed by the beam range specification unit 160b. The beam range specification unit 160b notifies the beam sweep instruction unit 110b of the beam ID obtained by this operation process, which helps to shorten the time required for the beam sweep.

[0086] The conditions for creating the target area for beam sweep in region R2 shown in Figure 15 are as follows: • Phased array antenna position of extension station 20: coordinate + height (x ｏ , y ｏ , h), where the antenna height is h [m]. • Antenna front direction of the phased array antenna of the projecting station 20: azimuth angle + depression angle (θ, φ) • The terminal position is assumed to be on the horizontal plane which is the ground surface, and the assumed terminal position of the target is: center coordinates (x, y) • The periphery of the assumed terminal position of the target (circular with radius): r [m]

[0087] Furthermore, the transformation process shown in Figure 15 is as follows: • Back projection: First, consider the range projected onto the ground surface when the phased array antenna of the extension station 20 is beam swept (directed in each direction of the curved surface). That is, the assumed target terminal is located within a certain range on the horizontal plane. From this assumed target terminal position and surrounding range, the curved surface on which the phased array antenna of the extension station 20 beams is determined by inverse transformation. • Curved surface: The phased array antenna of the extension station 20 is positioned at a height h [m] of the support column, etc., and is directed towards the ground surface in the horizontal and vertical directions (θ ｏ , φ ｏ) is installed with a downward angle. The shape of the phased array antenna of this extension station 20 that sweeps the beam is a curved surface. A part of this curved surface becomes the beam direction of a limited sweep range. Stretching (planarization): The curved shape of the phased array antenna of the extension station 20 described above that sweeps the beam in all directions is stretched out to a plane, corresponding to Figure 14 (planarization).

[0088] The beam sweep range specified by the second method can be created by following the procedure of the operation. Note that this method is also applicable to the first method. (Procedure 1) The beam range specification unit 160b specifies the center coordinates (x, y) indicating the position of the assumed target terminal 30 (hereinafter referred to as "terminal position") on a horizontal plane corresponding to the ground, and the radius r [m] of the circle around the terminal position.

[0089] (Procedure 2) The beam range designation unit 160b meshes the area around the designated terminal position (on the horizontal plane). That is, the beam range designation unit 160b meshes the area specified by a circular radius r [m]. Here, meshing means dividing the area into meshes of a predetermined size.

[0090] (Step 3) The beam range designation unit 160b back-projects each divided region separated by the mesh onto the beam sweep coordinates of the curved surface-shaped extension station 20. The back-projection (calculation) includes the antenna position (x ｏ , y ｏ , h) and its direction (θ ｏ , φ ｏ ) can be utilized.

[0091] (Procedure 4) The beam range designation unit 160b acquires beam IDs corresponding to the range projected onto the beam sweep coordinates at the extension station 20 as beam IDs for candidate beams to be swept. That is, the beam range designation unit 160b acquires beam IDs corresponding to candidate beams whose range projected onto the beam sweep coordinates at the extension station 20 can be swept as beam IDs for candidate beams to be swept. The beam range designation unit 160b notifies the beam sweep instruction unit 110b of information indicating the acquired beam IDs. The beam sweep instruction unit 110b completes the beam sweep by executing beam sweeps for all notified beam IDs.

[0092] Furthermore, the back projection (image coordinate transformation) mentioned above can be adapted from the image distortion correction technique used in around-view monitors, which correct camera images to display to the driver (on a monitor) the surroundings of the car (especially blind spots that cannot be directly seen from the driver's seat).

[0093] (Method 3 for limiting the beam sweep range) Figure 16 is a diagram illustrating a third method for limiting the beam sweep range in the second embodiment. Figure 16 shows the beam sweep range in the third method within the beam sweep range. The third method is a method of uniformly thinning the beam sweep range, as shown in Figure 16. In Figure 16, region R1 (white-filled 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 the terminal 30 is located.

[0094] Beam IDs for identifying candidate beams formed by the phased array antenna 20 of Zhang Out are sequentially assigned in the horizontal and vertical directions. For example, when the beam IDs are 0000 to 0f1f (hexadecimal), the lower two digits of the beam ID distinguish 32 divisions in the horizontal direction (at approximately 2° intervals, from -30° to 30°), and the upper two digits distinguish 16 divisions in the vertical direction (at 2° intervals, from -15° to 15°). In the case of the example shown in FIG. 16, as a specific example in terms of beam ID, the beam direction at the upper left (θ ０ , φ １５ ) = (-30°, 15°) has a beam ID of (beam ID: 0000), and the beam direction at the lower left (θ ０ , φ ０ ) = (-30°, -15°) has a beam ID of (beam ID: 0f00).

[0095] Therefore, in the case of the third method, the beam range specifying unit 160b acquires the beam ID specified in the region R2 as the beam ID of the candidate beam to be the target of the beam sweep. The beam range specifying unit 160b notifies the beam sweep instructing unit 110b of the information indicating the acquired beam ID. The beam sweep instructing unit 110b completes the beam sweep by executing the beam sweep for all the notified beam IDs.

[0096] Also, as shown in FIG. 16, instead of thinning out uniformly, the thinning ratio may be changed according to the terminal position (for example, not thinning out much in the vicinity of the direction where the target terminal is located, and thinning out in the direction where no target terminal is expected).

[0097] (Beam Sweep Specifying Range Creation Process of the Second Embodiment) FIG. 17 is a flowchart showing the flow of the beam sweep specifying range creation process performed by the beam range specifying unit 160b in the second embodiment. In the process shown in FIG. 17, the case of creating a range for specifying a beam sweep (beams to be the target of the sweep) around the position of the terminal 30 (the case of creating the range of the beam sweep specified by the second method) will be described.

[0098] The beam range designation unit 160b obtains the estimated position coordinates (x, y) on the horizontal plane from an external source as the estimated position of the terminal 30 (step S301). Next, based on the obtained estimated position coordinates (x, y), the beam range designation unit 160b defines the position (x, y) where the terminal 30 is located and the area surrounding the position (x, y) where the terminal 30 is located (circular radius r [m]) (step S302). Next, the beam range designation unit 160b meshes the area within the defined area surrounding the position (x, y) where the terminal 30 is located (step S303). The area surrounding the defined position (x, y) where the terminal 30 is located is circular on the horizontal plane. Therefore, the beam range designation unit 160b divides the circular area into meshes and defines the coordinates (x) of the center of each mesh. １ , y １ ), (x ２ , y ２ ), …, (x Ｎ－１ , y Ｎ－１ ), (x Ｎ , y Ｎ ) Please request this.

[0099] Next, the beam range designation unit 160b performs a back projection transformation on each coordinate on the obtained horizontal plane to determine the beam sweep coordinates on the curved extension station 20 (step S304). The beam sweep coordinates represent the angle indicating the beam direction. The beam range designation unit 160b determines the beam direction (θ) through the back projection transformation. １ , φ １ ), (θ ２ , φ ２ ), …, (θ Ｎ－１ , φ Ｎ－１ ), (θ Ｎ , φ Ｎ ) obtain.

[0100] Here, for the back projection transformation, a projection transformation can be applied to the camera image affected by the distortion of the vehicle's around-view monitor, transforming it into an image from a bird's-eye view of the vehicle. The horizontal plane on which terminal 30 is located corresponds to the bird's-eye view image, which is processed by transforming the distorted image captured by the camera relative to the ground around the vehicle. In addition, the beam direction from the extension station 20 corresponds to the distorted image acquired by the camera around the car.

[0101] With these two correspondences, the vehicle's around-view monitor converts the distorted camera image into an overhead view image by projection transformation (holographic matrix). Therefore, by applying this back projection transformation, the horizontal plane coordinates (x ｉ , y ｉ ) from the beam direction (θ ｉ , φ ｉ ) can be determined. Note that the beam direction (θ) ｉ , φ ｉ The parameter suffixes i = 1, 2, ..., N are used for the angle of ).

[0102] Next, the beam range designation unit 160b selects and aggregates candidate beams to be used for beam sweeping based on the back-projected beam direction (step S305). The beam range designation unit 160b determines these candidate beams in the following order: (1) selection of candidate beams and (2) aggregation of candidate beams. First, in (1) selection of candidate beams, the beam range designation unit 160b determines each beam direction (θ) within the sweep range. ｉ , φ ｉ Based on (i=1 to N) and the beam width, candidate beams B1, B2, ..., Bn that include the back-projected beam direction are selected. Next, in (2) candidate beam aggregation, the beam range specification unit 160b aggregates candidate beams that are in the same direction in the above selection into one. Here, we assume that the result of the selection in (1) above is candidate beams B1, B2, ..., Bn (n≦N). Also, we assume that the result of aggregation in (2) is candidate beams B1, B2, ..., Bm (m≦n) that are to be swept. Then, in the results of (1) and (2), the number of beams decreases in order (N≧n≧m).

[0103] Then, the beam range designation unit 160b sets the range of candidate beam directions determined for the sweep as the target beam (step S306). The target beam is a candidate beam used to perform a beam sweep within a limited sweep range. Specifically, the beam range designation unit 160b sets information indicating the beam ID corresponding to the candidate beam determined for the sweep in the beam sweep instruction unit 110b.

[0104] There are two ways to specify the range of the target beam. The first is to set all of the aggregated candidate beams in the beam sweep instruction unit 110b (hereinafter referred to as (Method A)). In this (Method A), all candidate beams that make up the aforementioned region R2 (for example, Figures 12, 14, and 15) are beam swept. The second is a range condition that includes all candidate beams (hereinafter referred to as (Method B)). In this (Method B), candidate beams that satisfy a certain condition (for example, in the case of Figure 16, the direction is regularly sparse) are beam swept from region R (the entire area that can be beam swept by the array antenna). Either of these methods is sufficient for specifying the range, but each has its advantages and disadvantages. (Method A) is a method of setting all of the target candidate beams B1, B2, ..., Bm as a list. For example, a condition is needed to separate the candidate beams that make up region R2, as shown in Figures 11 and 12, from region R1. Therefore, in Figure 11, the vertical direction can be roughly defined as -13°≦φ≦3°, or, if the conditions in Figure 11 are to be more detailed, the boundary conditions can be specified by a combination of three rectangular regions: -30°≦θ≦30° = -10°≦φ≦0°, 8°≦θ≦30° = 2°≦φ≦3°, and -30°≦φ≦-10° = -13°≦θ≦-10°. On the other hand, in order to be more detailed for Figure 13, the boundary conditions of region R2 and region R1 need to be specified by combining a larger number of rectangular regions.

[0105] Method B is a way of setting necessary and sufficient conditions for candidate beams B'1, B'2, ..., B'm (where the number of beams is not the same as Method A #Bm≠#B'm). For example, the necessary and sufficient conditions for identifying candidate beams corresponding to region R2 shown in Figure 16 are given by the following function. First, the beam direction (θ ｉ ､φ ｊ ), where i, j = 1, 2, ... Next, an appropriate function f(θ ｉ ､φ ｊ ) = a・θ ｉ + b・φ ｊ Check if the condition = c ± d・k (where a, b, c, and d are constants, and k is an integer including positive and negative values, and k = 0, ±1, ±2, ...) is satisfied. In the example shown in Figure 16, the beam direction (θ ｉ ､φｊ ) is a relatively simple function f(θ ｉ ､φ ｊ By confirming that ) = c ± d・k, it can be determined as a candidate beam included in region R2. Comparing the two, (Method B) is more desirable for the setup, but if the setup conditions are not simple, (Method A) can be used.

[0106] (Beam selection operation in the second embodiment) Figure 18 is a flowchart showing the processing flow of the beam selection operation in the wireless communication system 100a in the second embodiment. In Figure 18, the same reference numerals as in Figure 8 are used for the same processes, and their explanation is omitted. The beam range specification unit 160b sets the target beam determined in the process of Figure 17 to the beam sweep instruction unit 110b (step S401). The setting method may be either (method A) or (method B) described above. After that, the processes from step S31 onwards are executed.

[0107] 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 plurality of candidate beams corresponding to the set target beam. The beam sweep instruction unit 110b transmits the generated beam direction change instruction to the aggregation station 15.

[0108] 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.

[0109] 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.

[0110] (Third Embodiment) In the second embodiment, a configuration was described in which a beam sweep designation range is created on the premise that the terminal is not moving. In general, it is conceivable that the terminal may move and its position may change over time. Therefore, in the third embodiment, a configuration will be described in which the movement of the terminal is estimated and a beam sweep designation range is created around the estimated terminal position. In the third embodiment, the system configuration and device configuration are the same as in the second embodiment.

[0111] In the third embodiment, the processing performed by the beam range specification unit 160b of the control unit 10b differs from that in the second embodiment. The differences from the second embodiment will be explained below.

[0112] In the third embodiment, the extension station 20 performs a beam sweep only on the estimated destination position where the terminal 30 is estimated to move, and the area surrounding the estimated destination position. The following describes the process for creating the beam ID data used in this beam sweep.

[0113] Figure 19 is a diagram illustrating the operation process for creating the beam sweep range in the third embodiment. Figure 19 shows the estimated position of the destination of terminal 30 and an image of the surrounding area. In Figure 19, only the extension station 20 is shown for the purpose of explaining the extension station 20, but the aggregation station 15 is connected to the extension station 20 shown in Figure 19 via an optical transmission path. In Figure 19, region R3' represents the position of terminal 30 before movement. Also, similar to Figure 15, it is assumed that terminal 30 is located on the horizontal plane (on the ground) in Figure 19 as well. However, movement is considered for terminal 30 dealt with here, and the estimated position of the destination (region R3) of the target terminal 30 is given by the center coordinates (x', y'), and the radius of the surrounding area of ​​the estimated position is given by r' [m]. To find this estimated position of the destination, the center coordinates (x, y), which is the position of the target terminal 30 before movement, and the direction of movement θ are used. ｍ Let's assume we can use d [m] as the distance traveled.

[0114] Then, the terminal position (considering movement) and its surroundings can be back-projected onto the beam search area of ​​the phased array antenna of the extension station 20 (part of the curved surface in Figure 19). This back-projection transformation is the same as in Figure 15, and details of the transformations related to the projection are omitted. Also, the environmental conditions related to the inverse transformation are approximately the same as in Figure 15, and the position of the phased array antenna of the extension station 20 is coordinate + height (x ｏ , y ｏ In addition to , h), the direction of the antenna front of the phased array antenna of the extension station 20 is the azimuth angle + depression angle (θ) ０ , φ ０ )

[0115] The estimated destination position and its surrounding area (a circle with center coordinates (x', y') and radius r' [m]) on the target terminal 30 are back-projected, and the portion of the curved surface obtained represents the area where the phased array antenna of the extension station 20 will perform a beam sweep. Furthermore, by stretching (flattening) this curved surface, the limited area where the phased array antenna of the extension station 20 will perform a beam sweep can be determined.

[0116] The beam sweep range of the extension station 20 relative to the terminal 30, taking movement into consideration, can be created by the following procedure: (Procedure 1') The beam range specification unit 160b uses the center coordinates (x, y) indicating the terminal position on the horizontal plane to determine the movement direction θ ｍ Furthermore, the destination coordinates (x', y') indicating the position after moving a distance d [m] are identified.

[0117] (Procedure 2') The beam range specification unit 160b specifies the identified destination coordinates (x', y') and the area around the destination coordinates as the radius r' [m] of a circle.

[0118] (Step 3') The beam range specification unit 160b meshes the area around the specified destination coordinates (on the horizontal plane). That is, the beam range specification unit 160b meshes the area specified by the radius r' [m] of the circle.

[0119] (Step 4') The beam range designation unit 160b backprojects each divided region separated by the mesh onto the beam sweep coordinates of the curved surface-shaped extension station 20. That is, the beam range designation unit 160b backprojects the destination coordinates (x', y'), which are the position of the moving terminal on the horizontal plane, and the area surrounding the destination coordinates (a circle with radius r' [m] centered at coordinates (x', y')) onto the curved surface-shaped beam sweep coordinates.

[0120] (Procedure 5') The beam range designation unit 160b stretches (flattens) the inversely projected curved surface and acquires the beam ID (a pair of horizontal θ and vertical φ) corresponding to the range projected onto the beam sweep coordinates at the extension station 20, as the beam ID of the candidate beam to be targeted for beam sweep. The beam range designation unit 160b notifies the beam sweep instruction unit 110b of the information indicating the acquired beam ID. The beam sweep instruction unit 110b completes the beam sweep by executing a beam sweep for all the notified beam IDs.

[0121] (Beam sweep specification range creation process in the third embodiment) Figure 20 is a flowchart showing the flow of the beam sweep specification range creation process performed by the beam range specification unit 160b in the third embodiment. The process shown in Figure 17 describes the case in which a range for specifying a beam sweep (the beam to be swept) is created around the location of the destination terminal 30.

[0122] The beam range designation unit 160b acquires information related to the movement of the target terminal 30 (step S501). The information related to the movement of the terminal 30 includes the coordinates (x, y) of the current position of the terminal 30 on the horizontal plane and the direction θ in which the terminal 30 is moving. ｍ The information includes the angle between the predetermined reference direction and the direction of movement, and the distance d [m]. Next, the beam range designation unit 160b determines the predicted position of the destination terminal 30 based on the acquired information related to the movement of the terminal 30 (step S502). That is, the beam range designation unit 160b determines the current position coordinates (x, y) and the direction of movement θ of the terminal 30. ｍ Based on the distance d [m], the predicted position coordinates (x', y') of the terminal 30's destination, which can be calculated on the horizontal plane, are obtained.

[0123] Next, the beam range designation unit 160b defines the position (x', y') where the terminal 30 is located after relocation, and the area surrounding the position (x', y') where the terminal 30 is located (circular radius r [m]) based on the acquired position coordinates (x', y') (step S503). Next, the beam range designation unit 160b meshes the area within the defined area surrounding the position (x', y') where the terminal 30 is located (step S504). The area surrounding the defined position (x', y') where the terminal 30 is located is circular on the horizontal plane. Therefore, the beam range designation unit 160b divides the circular area into meshes and defines the coordinates (x') of the center of each mesh. １ , y' １ ), (x' ２ , y' ２ ), …, (x' Ｎ－１ , y' Ｎ－１ ), (x' Ｎ , y' Ｎ ) Please request this.

[0124] Next, the beam range designation unit 160b performs a back projection transformation on each coordinate on the obtained horizontal plane to determine the beam sweep coordinates on the curved extension station 20 (step S505). The beam range designation unit 160b determines the beam direction (θ') through the back projection transformation. １ , φ´ １ ), (θ´ ２ , φ´ ２ ),…, (θ´ Ｎ－１ , φ´ Ｎ－１ ), (θ´ Ｎ , φ´ Ｎ ) obtain.

[0125] Next, the beam range designation unit 160b selects candidate beams to be used for the beam sweep based on the back-projected beam direction (step S506). Here, unlike the second embodiment, candidate beams are not aggregated. A beam sweep targeting a moving terminal 30 is desirable to be performed faster than a beam sweep targeting a stationary terminal 30 where movement is not considered. Therefore, it is faster to set the candidate beams as the target beams (using unaggregated candidate beams) and perform the beam sweep at the time of selection. Furthermore, if appropriate meshing has been performed for the terminal position and surrounding area, aggregation of candidate beams is not particularly necessary.

[0126] The beam range designation unit 160b specifies each beam direction (θ') within the sweep range. ｉ , φ´ ｉ Based on (i=1 to N) and the beam width, candidate beams B1, B2, ..., Bn that include the back-projected beam direction are selected. Then, the beam range specification unit 160b sets the range of candidate beam directions determined for sweeping as the target beam (step S507). The beam range specification unit 160b sets the target beam determined in the process of Figure 20 to the beam sweep instruction unit 110b. After that, the processes from step S31 onwards in Figure 18 are executed.

[0127] 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.

[0128] Furthermore, in the wireless communication system 100a of the third embodiment, the aggregation station 15 is notified of the position and a beam ID indicating a candidate beam for beam sweeping the destination terminal position. The aggregation station 15 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 instructs the extension station 20 to perform a beam sweep using the destination terminal position and a candidate beam for beam sweeping the area around the destination terminal position. As a result, even if the terminal 30 moves, a beam sweep can be performed in the surrounding area including the location of the terminal 30. Furthermore, since the extension station 20 performs a beam sweep in the surrounding area including the location of the terminal 30, it is possible to reduce the processing time required for the beam sweep.

[0129] (Modification 1 common to the first to third embodiments) In the embodiments described above, 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 cases where there are multiple extension stations 20 connected to the aggregation station 15, and the number of such 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 units 10, 10a, and 10b, or input a specified delay time.

[0130] In this configuration, in the first embodiment, the process of specifying the input delay time is executed before the process of step S31 in Figure 8 (at the start of the process in Figure 8). For example, the process of specifying the input delay time is inserted before the process of step S36 becomes "NO" and merges with the process of step S31. In the second and third embodiments, the process of specifying the input delay time is executed before the process of step S401 in Figure 18 (at the start of the process in Figure 18).

[0131] The delay time insertion unit 150a inserts the input delay time into the quality information acquisition instruction unit 120a. The timing at which the delay time insertion unit 150a inserts the input specified delay time into 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 or step S36 in Figure 18 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 in the quality information acquisition instruction unit 120a after each sweep of candidate beams, the position of the waiting time insertion (step S101) in Figures 8 and 18 will move 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).

[0132] (Modification 2 common to the first to third embodiments) In the embodiments described above, 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 Figures 8 and 18). 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, and B3). The beam selection unit 140 performs this process for all beam IDs registered in the quality information table. The beam selection unit 140 then 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.

[0133] However, at the left and right (or top and bottom) edges of the overall region R, it is not possible to select three adjacent beam directions. Therefore, the beam selection unit 140 may select two adjacent beams inside region R. In this case, when the beam selection unit 140 selects two adjacent beams, it is desirable to select the beam direction corresponding to the edge of region R. Furthermore, in the more exceptional case of dealing with the four corners of the overall region R, the beam selection unit 140 can change its method of selecting five beam directions (top, bottom, left, right, and in a cross shape including the center) instead of three adjacent beam directions. In this case, the beam selection unit 140 selects three adjacent beam directions at the four corners of the overall region R, including one side of the top and bottom and one side of the left and right. Also, at the left and right or top and bottom edges of region R, the beam selection unit 140 selects four beam directions because one beam direction is outside region R and cannot be selected. In any case, it is desirable for the beam selection unit 140 to select the beam direction corresponding to the missing cross intersection. The beam selection unit 140 selects five beam directions in a cross shape for most of the beam directions in the inner portion of region R using this modification method, and the beam direction at the intersection of the selected cross shape is desirable.

[0134] 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.

[0135] 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".

[0136] In each of the embodiments described above, the aggregation station 15 can be reinterpreted as "CS (Central Station)", "Base Station", "CU (Central Unit)", "DU (Distributed Unit)", "RU (Radio Unit)" (however, corresponding to the DA mentioned above), and "Master Unit".

[0137] In the embodiments described above, 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 outward 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)".

[0138] Some or all of the base station device 1a in the first to third 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.

[0139] 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).

[0140] 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.

[0141] The present invention can be applied to beam sweeping in base station equipment using analog RoF.

[0142] 1, 1a...Base station equipment, 10, 10a, 10b...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...Beam selection unit, 150a...Delay time insertion unit, 160b...Beam range specification 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 instructs the second communication device to set a candidate beam to be used for beam sweeping performed by the second communication device, and after a delay time has elapsed from the time the second communication device instructs the second communication device to set the instructed candidate beam, it instructs the terminal to obtain quality information relating to the reference signal to be transmitted with the set candidate beam; and the second communication device transmits the instruction to obtain the quality information to the terminal using the candidate beam set in response to the instruction from the first communication device.

2. The wireless communication device according to claim 1, wherein the first communication device restricts beam sweeps in a portion of the beam sweep ranges out of all beam sweep ranges that the second communication device can beam sweep.

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 using the destination location of the terminal and candidate beams for beam sweeping around the location.

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 instructs the second communication device to set candidate beams to be used for beam sweeping performed by the second communication device, and after a delay time has elapsed from the time the second communication device completes setting the instructed candidate beams, the first communication device instructs the terminal to obtain quality information relating to a reference signal to be transmitted with the set candidate beams, and the second communication device uses the candidate beams set in response to the instruction from the first communication device to transmit the instruction to obtain the quality information to the terminal.

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