JP7590128B2 - Antenna control device and antenna control system - Google Patents

Description

The present invention relates to an antenna control device and an antenna control system.

In wireless communication systems that use high-frequency radio waves such as millimeter waves, such as fifth-generation mobile phones, which are expected to become more widespread in the future, propagation loss may be greater than with radio waves in the frequency bands that have been used up until now. Therefore, for example, in communications that pass through obstacles, such as communications from outdoors to indoors or communications from outside the vehicle to inside the vehicle, the radio waves may have difficulty reaching the inside of the obstacle. For this reason, it is envisioned that high-frequency radio waves such as millimeter waves are first received by an antenna on the outside of the obstacle, such as outdoors or outside the vehicle, and the received high-frequency signal is then taken into the inside of the obstacle, such as indoors or inside the vehicle, via a coaxial cable. However, since signal loss of the received high-frequency signal is large with a coaxial cable, a technology is known that uses optical fiber as a high-frequency signal path instead of a coaxial cable.

For example, the communication system described in Patent Document 1 discloses the following configuration. That is, the communication system includes an antenna provided outside the building that generates an electrical signal from a received radio wave or generates a radio wave to be transmitted from an electrical signal in order to transmit and receive radio waves to and from a communication target outside the building. The communication system also includes a converter connected to the antenna and converts an electrical signal input from the antenna into an optical signal or converts an optical signal into an electrical signal and outputs it to the antenna. Furthermore, the communication system also includes a multimode optical fiber that connects between the converter and equipment inside the building and has multiple propagation modes for propagating optical signals.

JP 2018-198383 A

For example, when radio wave attenuation between outdoors and indoors is large and an outdoor antenna is connected to an indoor antenna with RoF (Radio Over Fiber), the positional relationship between the base station and the outdoor antenna is often fixed. Therefore, it is often sufficient to point the radiation direction of the outdoor antenna toward the base station.

However, the indoor area that an indoor antenna should cover may be relatively large, such as inside a factory or a shopping mall. When the indoor area that the indoor antenna should cover is large, the indoor antenna may need to have a directivity control function so that the indoor antenna can properly communicate with wireless terminals moving through the large area that should be covered. However, as described above, conventional technology does not assume that indoor antennas will have a directivity control function, and therefore, when the indoor area is large, it may be difficult to secure a wide communication area capable of performing stable communication corresponding to the large indoor area.

In other words, when applying RoF to existing communication standards that use radio waves in high frequency bands, such as those for fifth generation mobile phones, it may not be possible to provide a directivity control function to the indoor antenna connected to the RoF, making it impossible to achieve stable communication with wireless terminals moving around in a wide indoor area.

The present invention has been made in consideration of the problems inherent in such conventional technology. The object of the present invention is to provide an antenna control device etc. that can provide a directivity control function to an indoor antenna and can provide stable communication with wireless terminals moving in a wide indoor area, even when RoF is applied to existing communication standards that use radio waves in the high-frequency band.

An antenna control device according to an aspect of the present invention preferably includes: a communication status analysis unit that is electrically connected to a first antenna that directly communicates with a base station, calculates the difference between the number of times that the directivity of a second antenna that wirelessly communicates with the base station via the first antenna is switched and the number of times that a wireless terminal that directly communicates with the second antenna transmits an uplink control signal before data communication with the base station, and analyzes the communication status between the second antenna and the first antenna; a link control unit that, when the number of times that the uplink control signal is transmitted before the data communication is less than the number of times that the directivity of the second antenna is switched, causes the wireless terminal to retransmit the uplink control signal to the second antenna before the data communication by the difference number of times; and a directivity control unit that controls the directivity of the second antenna in a different direction each time the uplink control signal is received, and controls the directivity of the second antenna in a direction with the maximum reception level when the uplink control signal is received after retransmission of all the uplink control signals that should be retransmitted.

In another aspect of the present invention, the communication status analyzed by the communication status analysis unit of the antenna control device is preferably an uplink communication sequence of the communication sequence determined by the 5G communication standard.

In yet another aspect of the present invention, the communication status analyzed by the communication status analysis unit of the antenna control device is preferably an uplink communication sequence and a downlink communication sequence determined by the 5G communication standard.

In an antenna control device according to yet another aspect of the present invention, it is preferable that the uplink control signal counted as the number of times the uplink control signal is transmitted before data communication between the second antenna and the wireless terminal is performed is a random access preamble signal and an RRC (Radio Resource Control) setup request signal.

In yet another aspect of the present invention, the link control unit of the antenna control device preferably retransmits only the random access preamble signal, retransmits only the RRC setup request signal, or retransmits both the random access preamble signal and the RRC setup request signal.

In yet another aspect of the present invention, the link control unit of the antenna control device further includes a downlink control unit that generates a reception blocking signal to prevent the wireless terminal from receiving a downlink response signal, which is a response signal to the uplink control signal, in order to retransmit the uplink control signal, and receives the reception blocking signal from the link control unit, and upon receiving the reception blocking signal, the downlink control unit preferably blocks the communication path using a switch arranged in the downlink communication path at a timing before the downlink response signal is emitted to the wireless terminal, or increases the attenuation of the communication path using a variable attenuator arranged in the downlink path.

In yet another aspect of the present invention, the link control unit of the antenna control device preferably outputs a delay signal for delaying the uplink control signal to the uplink control unit by an uplink control unit disposed in the communication path between the second antenna and the first antenna.

In yet another aspect of the present invention, the antenna control device preferably changes the directivity of the second antenna by a swing smaller than the swing in the different direction before receiving a second or subsequent uplink signal transmitted from the wireless terminal to the second antenna after the directivity of the second antenna is controlled by the directivity control unit in the direction in which the reception level is maximum, measures the reception strength of the uplink signal for the changed directivity of the second antenna by a reception strength measurement unit, and controls the directivity of the second antenna by the directivity control unit in the direction in which the averaged reception strength for each changed directivity of the second antenna is maximum.

An antenna control system according to yet another aspect of the present invention includes an antenna control device, the first antenna, the second antenna, a transmission path electrically connecting the first antenna and the second antenna, an O/E (Optical/Electronic signal) converter disposed at the connection between the transmission path and the first antenna, and an E/O (Electronic/Optical signal) converter disposed at the connection between the second antenna and the transmission path, and the transmission path is preferably an optical fiber.

In an antenna control system according to yet another aspect of the present invention, it is preferable that the first antenna is arranged outside a building or a mobile object, the second antenna is arranged inside the building or the mobile object, and the building or the mobile object experiences a greater propagation loss for the beam-shaped radio waves radiated from the base station than in the air.

According to the present invention, even if RoF is applied to existing communication standards that use radio waves in the high frequency band, it is possible to provide an indoor antenna with a directivity control function, thereby making it possible to provide an antenna control device or the like that can perform stable communication with wireless terminals moving in a wide indoor area.

1 is a schematic diagram showing an example of the configuration of a wireless communication system using 5G wireless communication including an antenna control system according to this embodiment. FIG. 2 is a schematic diagram showing a state in which a communication channel is established between a wireless terminal and an indoor antenna in the antenna control system using RoF shown in FIG. 1 . A schematic diagram showing an example of a portion of a simplified 5G communication sequence according to this embodiment. 1 is a block diagram showing an example of an antenna control system according to an embodiment of the present invention. 5 is a flowchart showing an example of the operation of the antenna control system according to the present embodiment. 1 is a schematic diagram showing an example of beam operation in preparation for movement of a wireless terminal of the antenna control system according to the present embodiment. FIG. 6 is a flowchart showing an example of a beam operation in preparation for movement of a wireless terminal of the antenna control system according to the present embodiment.

(Outline of the Antenna Control System)
The antenna control system of this embodiment has a configuration in which, when RoF is applied to a communication standard such as an existing fifth generation mobile phone, the directivity of an indoor antenna is controlled in a simple manner in the direction of a mobile wireless terminal placed indoors by utilizing the initial communication sequence of the communication standard.

Specifically, the random access preamble or RRC setup request in the uplink of the 5th generation mobile phone communication sequence is retransmitted if necessary, and the signal strength and other information is measured for all directions in which the indoor antenna's directivity can be switched. Using parameters such as the measured signal strength, the antenna control device on the indoor antenna and the mobile wireless terminal share the optimal directivity direction for the mobile wireless terminal, enabling stable communication.

In addition, in order to accommodate the movement of a wireless terminal communicating with the indoor antenna, when receiving an uplink signal after the indoor antenna beam has been initially set, the beam may be adjusted to be smaller than at the initial setting, and the indoor antenna beam may be controlled to point in the direction of movement of the wireless terminal.

The antenna control system according to the present embodiment described above can be mounted on a moving object such as a vehicle. In this case, the wireless terminal is installed inside the vehicle and may not move. However, entertainment electronic devices and navigation devices may be installed in any position, and the installation location may be changed at any time.

(Antenna control system operation example)
An example of the operation of the antenna control system 1000 according to this embodiment will be described with reference to FIGS.

Figure 1 is a diagram showing an overview of the devices included in the antenna control system 1000 according to this embodiment. High-frequency radio waves such as millimeter waves have a short range, but it is possible to extend the range by narrowing the direction in which the radio waves travel and concentrating the energy. Prior to 4G, radio waves were transmitted from base stations over a wide area, but with 5G, as shown in Figure 1, radio waves are emitted in the form of beams toward each wireless terminal. This technology is also called "beamforming" because it forms beams. Furthermore, because radio waves have a hard time reaching the periphery of the beam, it is possible to reduce interference between base stations.

Furthermore, in order to narrow down the direction of radio waves to the direction of a specific wireless terminal, it is necessary to find where the wireless terminal is located. This mechanism is sometimes called "beam sweeping." In 4G and earlier, radio waves were transmitted from a base station over a relatively wide area to identify the location of the wireless terminal, but in 5G, a beam is emitted from the base station while rotating at a constant period like a lighthouse to identify the location of the wireless terminal. In other words, a "beam sweeping" function is executed between an array antenna (not shown) installed in base station 11 and wireless terminal 21, wireless terminal 23, and wireless terminal 24. Note that if outdoor antenna 200a2 is mounted on a moving object, the "beam sweeping" function may be executed between the array antenna and outdoor antenna 200a2.

By using the "beam sweeping" function, beamformed radio waves are radiated from the array antenna installed in the base station 11 as beam b1 toward the wireless terminal 21, beam b3 toward the wireless terminal 23, and beam b4 toward the wireless terminal 24. In addition, beam b2 is radiated toward the outdoor antenna 200a2. Each beam represents the distribution of the radio waves radiated from the array antenna, and is also an area indicating the range in which the array antenna can properly receive radio waves from wireless terminals, etc.

In addition, when the wireless terminal 21 moves, the base station 11 can control the array antenna to switch the radiation direction of the beam b1 to the direction of movement of the wireless terminal 21. Furthermore, when the wireless terminal 23 moves, the base station 11 can control the array antenna to switch the radiation direction of the beam b3 to the direction of movement of the wireless terminal 23. Similarly, when the wireless terminal 24 moves, the base station 11 can control the array antenna to switch the radiation direction of the beam b4 to the direction of movement of the wireless terminal 24. In addition, when the outdoor antenna 200a2 moves, the base station 11 can control the array antenna to switch the radiation direction of the beam b2 to the direction of movement. Before 4G, radio waves were transmitted over a fairly wide range, so if the wireless terminal moved within the base station area, the radio waves reached the wireless terminal. However, in the case of 5G, radio waves are emitted in a beam form, so if the wireless terminal moves, a "beam tracking" function that tracks the wireless terminal is required as described above.

Therefore, as shown in FIG. 1, directivity control technology that complies with the 5G communication standard is required between the indoor antenna 200b2 and wireless terminals such as wireless terminal 31, wireless terminal 32, and wireless terminal 33.

The uplink system using RoF in FIG. 1 further includes an O/E (Optical/Electronic signal) converter 300a2 and an E/O (Electronic/Optical signal) converter 300b2. As described above, the uplink system using RoF also includes an outdoor antenna 200a2, a transmission path 400a2, and an indoor antenna 200b2. The system using RoF also includes wireless terminals such as wireless terminal 31, wireless terminal 32, wireless terminal 33, and wireless terminal 34. In detail, as shown in FIG. 4, the uplink side may include an indoor antenna 200b2, an E/O converter 300b2, a transmission path 400a2, an O/E converter 300a2, and an outdoor antenna 200a2. Also, on the downlink side, an outdoor antenna 200a1, an E/O converter 300b1, a transmission path 400a1, an O/E converter 300a1, and an indoor antenna 200b1 may be provided. Also, the outdoor antenna 200a1 and the outdoor antenna 200a2 may be collectively referred to as the outdoor antenna 200a. Furthermore, the indoor antenna 200b1 and the indoor antenna 200b2 may be collectively referred to as the indoor antenna 200b. Furthermore, the O/E converter 300a1 and the O/E converter 300a2 may be collectively referred to as the O/E converter 300a. Furthermore, the E/O converter 300b1 and the E/O converter 300b2 may be collectively referred to as the E/O converter 300b. Furthermore, the transmission path 400a1 and the transmission path 400a2 may be collectively referred to as the transmission path 400a.

The indoor antenna 200 b 2 has a function of receiving a beam b5 from the wireless terminal 31 and generating an electrical signal from the received beam b5. The E/O converter 300b2 is connected to the indoor antenna 200b2 and has a function of converting an electrical signal input from the indoor antenna 200 b 2 into an optical signal. A transmission path 400a2 is provided between the E/O converter 300b2 and the O/E converter 300a2. An example of the transmission path 400a2 is an optical fiber. The optical fiber has a frequency characteristic with good flatness in the communication band of the optical signal, and it is preferable that the attenuation of the optical signal in the communication band is within a practically usable range. Note that the optical fiber may be capable of correcting the flatness and attenuation of the optical signal in the communication band by a component outside the optical fiber. Furthermore, it becomes possible to use any optical fiber that satisfies the above characteristics within the correctable range. The O/E converter 300a2 is connected to the outdoor antenna 200a2 and has a function of converting the optical signal transmitted through the transmission path 400a2 into an electrical signal and outputting it to the outdoor antenna 200a2. The outdoor antenna 200a2 has a function of generating radio waves to be transmitted from the electrical signal output from the O/E converter 300a2.

Antennas (not shown) included in wireless terminals such as wireless terminal 31, wireless terminal 32, wireless terminal 33, and wireless terminal 34 may be directional or omnidirectional. The antenna (not shown) of wireless terminal 31 in FIG. 1 is directional and can switch beams in three directions as shown in FIG. 1.

Figure 2 is a schematic diagram showing how the indoor antenna 200b2 in Figure 1 performs uplink wireless communication with the wireless terminal 35 using beam b21 when the indoor antenna 200b2 is configured to be able to switch between beams b21, b22, and b23 in three directions. Note that beam b21 is an area indicating the range in which the indoor antenna 200b2 can effectively receive radio waves from the wireless terminal 35.

In FIG. 2, using the communication sequence of the 5G communication standard, the indoor antenna 200b switches between beams b21, b22, and b23 in three directions in sequence. The order in which beams b21, b22, and b23 are switched may be any order without overlap.

The antenna control device (not shown in FIG. 2) controls the directivity of the beam of the indoor antenna 200b, and measures the reception strength by switching the direction of the indoor antenna 200b2 to one of three directions during one uplink transmission from the wireless terminal 35. That is, the reception strength in one direction of the indoor antenna 200b2 is measured for each uplink transmission from the wireless terminal 35. If the switchable direction of the indoor antenna 200b2 is three directions as described above, the uplink transmission of the wireless terminal 35 will be performed three times. Note that the number of switchable directions of the indoor antenna 200b2 can be any positive integer value. When the direction of the indoor antenna 200b2 is switched to the direction of the beam b21, the reception strength of the uplink transmission radio wave of the wireless terminal 35 may be strong. In this case, the direction of the indoor antenna 200b2 is selected to the direction of the beam b21, and wireless communication between the indoor antenna 200b2 and the wireless terminal 35 can be appropriately performed.

Figure 3 is a schematic diagram of the 5G wireless communication sequence executed in Figures 1 and 2.

First, in step S301, the base station constantly emits a beam formed from a beam, a synchronization signal, and an MIB (Master Information Block). The SSB (Synchronization Signal Block) indicates that the PBCH (Physical broadcast channel) that constantly emits the synchronization signal and the MIB is grouped as a block. The base station uses the SSB to provide important functions for initial access and mobility, such as establishing frame synchronization to the wireless terminal, measuring downstream reception quality, and notifying the wireless terminal of system parameters required for receiving other notification information. The communication carrier can set the transmission timing and transmission cycle of the SSB for each base station and notify the wireless terminal. In addition, if the wireless terminal detects the SSB, it selects the base station and the SSB and establishes timing synchronization and frequency synchronization.

Next, in step S302, the base station radiates a beam formed in the direction of the beam with system information included. The system information is information required to start random access, and includes information such as uplink carrier information and random access signal configuration information. From the received system information, the wireless terminal identifies the resources of the random access channel (PRACH: Physical Random Access CHannel) associated with the selected SSB.

Next, in step S303, the wireless terminal transmits a random access preamble signal with a preamble ID and PRACH timing determined from the PRACH resource. The wireless terminal transmits the random access preamble signal to establish random access with the base station. Then, the wireless terminal waits for a RAR (Random Access Response), which is a response to receiving the preamble signal, within a certain window.

In step S304, the base station that has received the random access preamble signal transmits an RAR containing control information regarding random access to the wireless terminal.

In step S305, when the wireless terminal receives the RAR, it transmits an RRC (Radio Resource Control) setup request to the base station at the transmission timing specified in the RAR, which serves as a link between the wireless terminal and the base station.

In step S306, the base station that has received the RRC setup request signal transmits an RRC setup signal to the wireless terminal, the RRC setup signal including control information related to RRC for linking with the wireless terminal.

In step S307, the base station transmits communication data and control messages to the wireless terminal based on the link information.

Details of the 5G wireless communication sequence from step S307 onwards are omitted in this specification.

As described above, in the 5G communication standard, there are only two uplinks before communication data is transmitted, so if the beam switching direction of the indoor antenna 200b2 is three or more directions, the beam of the indoor antenna 200b2 cannot be switched to three or more directions.

Therefore, in this embodiment, the random access preamble signal and/or the RRC setup request signal are retransmitted to match the number of directions in which the beam of the indoor antenna 200b2 can be switched.

For example, if the number of beam switching directions of the indoor antenna 200b2 is four, the random access preamble signal may be retransmitted twice. In this case, there is no need to retransmit the RRC setup request signal.

Also, for example, if the number of directions in which the beam of the indoor antenna 200b2 can be switched is four, the RRC setup request signal may be retransmitted twice. In this case, there is no need to retransmit the random access preamble signal.

Furthermore, for example, if the number of directions in which the beam of the indoor antenna 200b2 can be switched is four, the random access preamble signal may be retransmitted once, and the RRC setup request signal may be retransmitted once.

As described above, the uplink signal to be retransmitted may be either a random access preamble signal or an RRC setup request signal.

In order to retransmit the random access preamble signal, it is necessary to prevent the wireless terminal from receiving the preamble signal reception response signal. For example, at the timing when the wireless terminal should receive the preamble signal reception response signal, the communication path of the indoor antenna 200b1 on the downlink side can be switched off with a switch, or the attenuation of the variable attenuator of the communication path can be increased. Similarly, to retransmit the RRC setup request signal, it is necessary to prevent the wireless terminal from receiving the RRC setup signal. For example, at the timing when the wireless terminal should receive the RRC setup signal, the communication path of the indoor antenna 200b1 can be switched off with a switch, or the attenuation of the variable attenuator of the communication path can be increased. Details will be described later.

(Example of configuration of antenna control system)
FIG. 4 is a block diagram showing an example of the configuration of the antenna control system 1000.

The antenna control system 1000 preferably includes the antenna control device 100, indoor antennas 200b1, 200b2, E/O converters 300b1, 300b2, O/E converters 300a1, 300a2, and outdoor antennas 200a1, 200a2. Furthermore, the antenna control system 1000 preferably includes transmission paths 400a1, 400a2 as transmission paths. Note that the uplink side preferably includes the indoor antenna 200b2, the E/O converter 300b2, the transmission path 400a2, the O/E converter 300a2, and the outdoor antenna 200a2. Furthermore, the uplink side preferably includes an uplink control unit 170 including a delay element. Furthermore, the downlink side preferably includes the outdoor antenna 200a1, the E/O converter 300b1, the transmission path 400a1, the O/E converter 300a1, and the indoor antenna 200b1. Additionally, the downlink side preferably includes a downlink control unit 160 that includes a switch or a variable attenuator.

The antenna control device 100 preferably includes a communication status analysis unit 110, a reception strength measurement unit 120, a link control unit 130, a reception strength storage unit 140, and a directivity control unit 150. The antenna control device 100 may also include an uplink control unit 170 including a delay element placed in the RoF communication path. Furthermore, the antenna control device 100 may also include a downlink control unit 160 including a switch or an attenuator.

The communication status analysis unit 110 has a function of analyzing whether or not the radio wave received by the indoor antenna 200b2 is an uplink control signal. For this purpose, the communication status analysis unit 110 is directly or indirectly connected to the communication path between the indoor antenna 200b2 and the E/O converter 300b2, and has a function of monitoring the signal propagating through the communication path. The communication status analysis unit 110 also has a function of determining whether or not the number of measurements of the uplink control signal measured by the reception strength measurement unit 120 matches the number of switchable directional directions of the indoor antenna 200b2. When the number of measurements of the control signal matches the number of switchable directional directions of the indoor antenna 200b2, the communication status analysis unit 110 selects from the reception strength storage unit 140 the directional direction information of the indoor antenna 200b2 that maximizes the reception strength level. Then, the communication status analysis unit 110 outputs the directional direction information to the directional control unit 150. If the number of times the control signal is measured is smaller than the number of switchable directional directions of the indoor antenna 200b2, the communication status analysis unit 110 outputs a retransmission control signal to the link control unit 130 to retransmit the uplink control signal. The communication status analysis unit 110 can also have a function of analyzing whether the radio wave received at the outdoor antenna 200a1 is a downlink control signal or a communication data signal. The communication status analysis unit 110 can also analyze the downlink communication sequence of the radio wave received at the outdoor antenna 200a1. In this case, the communication status analysis unit 110 is directly or indirectly connected to the communication path between the indoor antenna 200b1 and the outdoor antenna 200a1, and has a function of monitoring the signal propagating through the communication path.

The reception strength measurement unit 120 has a function of measuring the reception strength level of an uplink signal that is determined to be a control signal by the communication status analysis unit 110. The reception strength measurement unit 120 also has a function of storing the reception strength level in the reception strength memory unit 140 in association with the directivity direction of the indoor antenna 200b2 at the time the reception strength level was measured. The reception strength measurement unit 120 also has a function of measuring the reception strength levels of other uplink signals in order to detect the moving direction of the wireless terminal.

When the link control unit 130 receives a retransmission control signal from the communication status analysis unit 110, it generates a reception blocking signal to prevent wireless terminals located in the area of the indoor antenna 200b from receiving the downlink response signal, which is a response signal to the uplink control signal. The link control unit 130 outputs the reception blocking signal to the downlink control unit 160, which includes a SW or a variable attenuator. The link control unit 130 can also output a delay signal for delaying the uplink control signal to the uplink control unit 170 when it functions as a delay device located between the indoor antenna 200b2 and the outdoor antenna 200a2.

The reception strength memory unit 140 has the function of storing the number of switchable directional directions of the indoor antenna 200b2, the number of uplinks, and the reception strength level of the uplink signal measured by the reception strength measurement unit 120 in association with the directional direction.

The directivity control unit 150 has the function of controlling the directivity of the indoor antenna 200b1 and the indoor antenna 200b2 so as to correspond to the directivity direction information received from the communication status analysis unit 110.

The downlink control unit 160 has a function of not radiating the downlink response signal, which is a response signal to the uplink control signal, from the indoor antenna 200b when the reception blocking signal is input, or radiating it at an extremely weak level. For example, the downlink control unit 160 that functions as a switch is provided between the O/E converter 300a1 and the indoor antenna 200b1, and the downlink control unit 160 turns off the switch at the timing when the downlink response signal is radiated from the indoor antenna 200b1. In this way, it is also possible for the downlink control unit 160 to prevent the downlink response signal from being radiated from the indoor antenna 200b1. Also, the downlink control unit 160 that functions as a variable attenuator is provided between the O/E converter 300a1 and the indoor antenna 200b1, and the downlink control unit 160 increases the attenuation of the variable attenuator at the timing when the downlink response signal is radiated from the indoor antenna 200b1. In this way, the downlink control unit 160 can treat the downlink response signal emitted from the indoor antenna 200b1 as a weak radio wave so that it is not received by the wireless terminal.

The uplink control unit 170 can be an electronic device such as a delay element. The uplink control unit 170 can be located anywhere between the outdoor antenna 200a2 and the indoor antenna 200b2. In FIG. 4, the uplink control unit 170 is located between the outdoor antenna 200a2 and the O/E converter 300a2. When the link control unit 130 outputs to the uplink control unit 170, which functions as a delay element, it is possible to delay the uplink control signal. By delaying the uplink control signal, it is also possible to secure processing time for the downlink control signal in the antenna control device 100.

E/O converter 300b, transmission path 400a, O/E converter 300a, and outdoor antenna 200a have already been described, so to avoid duplication, their explanations will be omitted. However, outdoor antenna 200a1 and outdoor antenna 200a2 may be configured to be able to switch directivity in order to appropriately continue communication with the array antenna of base station 11.

(Antenna control system operation example)
FIG. 5 is a flowchart showing an example of the operation of the antenna control system 1000.

In step S501, the communication status analysis unit 110 calculates the number of retransmissions required and sets the number of retransmissions required. The communication status analysis unit 110 can determine the number of retransmissions from the difference between the number of uplinks of the control signal before data communication, which is specified by the 5G communication standard, and the number of switchable directional directions of the indoor antenna 200b2. The communication status analysis unit 110 can also store the determined number of retransmissions in the retransmission count register. Note that the number of uplinks of the control signal before data communication and the number of switchable directional directions of the indoor antenna 200b2 may be stored in advance in the reception strength storage unit 140. Next, the antenna control device 100 proceeds to step S502.

In step S502, the communication status analysis unit 110 determines whether it is time to receive an uplink control signal. If it is time to receive an uplink control signal (step S502: YES), the antenna control device 100 proceeds to step S503. If it is not time to receive an uplink control signal (step S502: NO), the antenna control device 100 repeats step S502.

In step S503, the reception strength measurement unit 120 measures the reception strength level of the uplink signal that has been determined to be a control signal by the communication status analysis unit 110. The reception strength measurement unit 120 associates the reception strength level with the directivity direction of the indoor antenna 200b2 at the time the reception strength level was measured, and stores the association in the reception strength storage unit 140. The reception strength measurement unit 120 also increments a reception strength measurement counter for counting the number of measurements. Next, the antenna control device 100 proceeds to step S504.

In step S504, the communication status analysis unit 110 determines whether the reception strength measurement counter in which the reception strength measurement number is stored matches the number of orientation directions of the indoor antenna 200b2. If the reception strength measurement counter in which the reception strength measurement number is stored matches the number of orientation directions of the indoor antenna 200b2 (step S504: YES), the antenna control device 100 proceeds to step S505. If the reception strength measurement counter in which the reception strength measurement number is stored does not match the number of orientation directions of the indoor antenna 200b2 (step S504: NO), the antenna control device 100 proceeds to step S507.

In step S505, since the number of times the control signal is measured matches the number of switchable directional directions of the indoor antenna 200b2, the communication status analysis unit 110 selects from the reception strength storage unit 140 the directional direction information of the indoor antenna 200b2 that maximizes the reception strength level. The communication status analysis unit 110 then outputs the directional direction information to the directivity control unit 150. The directivity control unit 150 controls the directivity of the indoor antenna 200b2 so that it corresponds to the directional direction information received from the communication status analysis unit 110. Note that the directivity control unit 150 can also control the indoor antenna 200b1 so that it has the same directivity as the directivity of the indoor antenna 200b2. Next, the antenna control device 100 proceeds to step S506.

In step S506, the antenna control device 100 resets the values of the reception intensity measurement counter and the retransmission count register. For example, the values of the reception intensity measurement counter and the retransmission count register are set to zero. Next, the antenna control device 100 returns to step S501.

In step S507, the antenna control device 100 determines whether the value of the retransmission count register is zero. If the value of the retransmission count register is zero (step S507: YES), the antenna control device 100 returns to step S502. If the value of the retransmission count register is not zero (step S507: NO), the antenna control device 100 proceeds to step S508.

In step S508, the communication status analysis unit 110 outputs a retransmission control signal to the link control unit 130 because the value of the retransmission count register is not zero. When the link control unit 130 inputs the retransmission control signal, it generates a reception blocking signal to prevent a wireless terminal located in the area of the indoor antenna 200b from receiving a downlink response signal, which is a response signal to the uplink control signal. The link control unit 130 outputs the reception blocking signal to the downlink control unit 160. When the reception blocking signal is input from the link control unit 130, the downlink control unit 160 does not radiate the downlink response signal, which is a response signal to the uplink control signal, from the indoor antenna 200b2, or radiates it at an extremely weak level. Therefore, a wireless terminal located in the area of the indoor antenna 200b2 cannot receive the downlink response signal, so it retransmits the uplink control signal. The directivity of the indoor antenna 200b2 that receives the uplink control signal has switched to the next directivity direction. The value of the retransmission count register is decremented. The uplink control signal to be retransmitted may be either a random access preamble signal or an RRC setup request signal. Next, the antenna control device 100 returns to step S502.

As explained above, even if RoF is applied to existing communication standards that use radio waves in the high-frequency band, it is possible to provide indoor antennas with a directivity control function, making it possible to provide antenna control devices and the like that can provide stable communication with wireless terminals moving through a wide indoor area.

(Overview of operation of antenna control system when wireless terminal moves)
Figure 6 is a schematic diagram showing the principle of changing the beam direction of indoor antenna 200b2 in the direction of movement of a wireless terminal even when the wireless terminal moves after the initial beam direction of indoor antenna 200b2 in Figure 5 has been determined.

At the time of initial connection with the wireless terminal communicating with the indoor antenna 200b2, the indoor antenna 200b2 changes the beam significantly to determine the approximate direction of the beam. For example, in FIG. 5, the indoor antenna 200b2 changes the beam significantly. Then, at the time of receiving the uplink signal after the transmission and reception of the RRC setup signal shown in FIG. 3, the indoor antenna 200b2 changes the beam slightly as shown in FIG. 6. For example, the change in the beam direction of the indoor antenna 200b2 when receiving the uplink signal after the RRC setup signal may change by an angle of 1/2 or less of the change in the beam direction of the indoor antenna 200b2 at the time of initial connection. As an example, if the change in the beam direction of the indoor antenna 200b2 at the time of initial connection changes every 30 degrees, the change in the beam direction of the indoor antenna 200b2 when receiving the uplink signal after the RRC setup signal may be 15 degrees or less. In addition, there may be cases where the beam swing width of the indoor antenna 200b2 when receiving the uplink signal after the RRC setup signal is smaller than the beam swing width of the indoor antenna 200b2 at the time of initial connection.

As an example, if the beam b24 of the indoor antenna 200b2 shown in FIG. 6 is the beam direction of the indoor antenna 200b2 at the time of initial connection, the angle change between the beam b24 and the beam b25 may be 15 degrees or less. Also, the angle change between the beam b24 and the beam b26 may be 15 degrees or less. Also, as an example, if the beam direction change of the indoor antenna 200b2 at the time of initial connection changes by 30 degrees or more, the angle change between the beam b24 and the beam b25 and the angle change between the beam b24 and the beam b26 may be 15 degrees or more. The angle change between the beam b24 and the beam b25 and the angle change between the beam b24 and the beam b26 may be the same or different. For example, the angle change between the beam b24 and the beam b25 and the angle change between the beam b24 and the beam b26 immediately after the initial connection may be the same. For example, if the reception strength of the beam b26 is the largest, in the next beam sweep, a beam can be generated left and right or front and rear around the beam b26. Thereafter, if it becomes possible to determine the direction of movement of the wireless terminal, the angle change of the left/right or front/back beams may be set to be large if the speed of movement of the wireless terminal increases. Furthermore, if it becomes possible to determine that the direction of movement of the wireless terminal is direction D1 shown in FIG. 6, it becomes possible to more appropriately point the beam in the direction of movement of the wireless terminal by arranging another beam in direction D1 during the next beam sweep from the beam direction with the maximum reception strength the previous time.

(Example of operation of antenna control system when wireless terminal moves)
FIG. 7 is a flowchart showing an example of an operation for changing the beam direction of the indoor antenna 200b2 to the direction of movement of the wireless terminal even when the wireless terminal is moving.

In step S701, the antenna control device 100 performs an operation to determine the initial beam direction of the indoor antenna 200b2 shown in FIG. 5. Next, the antenna control device 100 proceeds to step S702.

In step S702, the antenna control device 100 determines whether or not communication after the RRC setup signal has ended. If communication after the RRC setup signal has ended (step S702: YES), the antenna control device 100 returns to step S701. If communication after the RRC setup signal has not ended (step S702: NO), the antenna control device 100 proceeds to step S703.

In step S703, the antenna control device 100 determines whether it is time to receive an uplink signal. If it is time to receive an uplink signal (step S703: YES), the antenna control device 100 proceeds to step S704. If it is not time to receive an uplink signal (step S703: NO), the antenna control device 100 repeats step S703.

In step S704, the antenna control device 100 measures the received signal strength of the received uplink signal, associates the measured received signal strength with the beam direction of the indoor antenna 200b2, and stores it in the received signal strength memory unit 140. Furthermore, if the received signal strength with the same beam direction of the indoor antenna 200b2 is stored in the received signal strength memory unit 140, the antenna control device 100 calculates an averaged received signal strength by averaging the received signal strengths with the same beam direction. The averaged received signal strength can be calculated by the communication status analysis unit 110. Note that any known method can be used as the averaging method.

In step S705, the antenna control device 100 changes the beam direction of the indoor antenna 200b2 to the next beam direction. Next, the antenna control device 100 proceeds to step S706.

In step S706, the antenna control device 100 stores the change history of the beam direction of the indoor antenna 200b2 in the communication after the RRC setup signal. The storage location may be a register, a storage unit, etc. (not shown). For example, the beam change direction of the indoor antenna 200b2 in the communication after the RRC setup signal is set to three directions, with the beam b25 in FIG. 6 being the left beam, the beam b24 being the middle beam, and the beam b26 being the right beam. In this case, as an example, the storage unit for the beam direction change history is set to storage areas for the left beam, the middle beam, and the right beam, and information is set in the storage area for the beam direction set in step S705. For example, the numerical information "1" may be set. Note that there is no limit to the number of beam change directions of the indoor antenna 200b2 in the communication after the RRC setup signal, and the antenna control device 100 or the antenna control system 1000 can set any number as the number of beam change directions. Next, the antenna control device 100 proceeds to step S707.

In step S707, the antenna control device 100 reads the beam direction change history of the indoor antenna 200b2 and determines whether all beam change directions have been changed. For example, if the numerical information "1" is stored in all memory areas for the changeable beam directions, the antenna control device 100 determines that all beam change directions have been changed. If all beam change directions have been changed (step S707: YES), the antenna control device 100 proceeds to step S708. If any beam change direction has not been changed (step S707: NO), the antenna control device 100 returns to step S702.

In step S708, the antenna control device 100 determines the beam direction in which the averaged received signal strength stored in the reception strength memory unit 140 is maximized, and sets the beam direction in which the averaged received signal strength is maximized as the medium beam. The storage area for the change history of the beam direction of the indoor antenna 200b is also reset. As an example, the storage area for the change history of the beam direction is set to the numerical information "0". Note that if the averaged received signal strength varies greatly and is not stable, it is possible to increase the number of averagings until the variation in the averaged received signal strength becomes small, and then set the beam direction in which the averaged received signal strength is maximized as the medium beam. Next, the antenna control device 100 returns to step S702.

As described above, when receiving an uplink signal from a wireless terminal in communication after the RRC setup signal, the beam direction of the indoor antenna 200b2 is changed and the average reception strength is calculated. Then, the beam direction with the largest average reception signal strength is set as the central beam direction, and the beam direction of the indoor antenna 200b2 is changed to the left or right or forward or backward from the central beam direction, so that wireless communication can be continued appropriately even when the wireless terminal moves. Also, by setting the beam direction with the largest average reception signal strength to the direction from which the wireless terminal moves and changing the beam direction of the indoor antenna 200b2 to the expected direction of movement of the wireless terminal, wireless communication can be continued appropriately even when the wireless terminal moves. Note that the beam direction of the indoor antenna 200b1 can be changed in conjunction with the beam direction of the indoor antenna 200b2.

(Modification)
In the above embodiment, the RoF system to which the antenna control system 1000 is applied is described as an example constructed inside and outside a structure such as a building. However, the embodiment is not limited to the inside and outside of a structure such as a building, and can be applied to a RoF system that connects the inside and outside of a moving body such as an automobile, a train, an airplane, or a ship. In addition, with regard to structures, the embodiment can be applied to all RoF systems that connect the inside and outside of structures such as houses, factories, and shopping malls.

The features of the antenna control device 100 and antenna control system 1000 of this embodiment are described below.

The antenna control device 100 according to the first aspect preferably includes a communication status analysis unit 110 that analyzes communication between the outdoor antenna 200a2, which is a first antenna that directly communicates with the base station, and the indoor antenna 200b2, which is a second antenna that is electrically connected. The communication status analysis unit 110 preferably calculates the difference between the number of times that the directivity of the second antenna that directly communicates with the base station is switched and the number of times that the second antenna and the wireless terminal transmit an uplink control signal before data communication. If the number of times that the uplink control signal is transmitted before data communication is less than the number of times that the directivity of the second antenna is switched, it is preferable to include a link control unit 130 that causes the wireless terminal to retransmit the uplink control signal to the second antenna before data communication by the difference number of times. The antenna control device 100 preferably further includes a directivity control unit 150 that controls the directivity of the second antenna in a different direction for each reception of the uplink control signal. It is preferable that the directivity control unit 150 controls the directivity of the second antenna in a direction in which the reception level is maximum when the uplink control signal is received after retransmission of all uplink control signals that should be retransmitted.

With the above configuration, even if RoF is applied to existing communication standards that use radio waves in the high-frequency band, it is possible to provide an antenna control device 100 that can provide a directivity control function to an indoor antenna and can provide stable communication with wireless terminals that move around in a wide indoor area.

It is preferable that the communication situation analyzed by the communication situation analysis unit 110 of the antenna control device 100 relating to the second aspect is an uplink communication sequence of the communication sequence determined by the 5G communication standard.

With the above configuration, even in RoF communications using the 5G communications standard, it is possible to provide an antenna control device 100 that can provide a directivity control function to an indoor antenna and can provide stable communications with wireless terminals moving in a wide indoor area.

It is preferable that the communication status analyzed by the communication status analysis unit 110 of the antenna control device 100 relating to the third aspect is an uplink communication sequence and a downlink communication sequence of the communication sequence determined by the 5G communication standard.

According to the above configuration, even in the case of RoF communication using the 5G communication standard, it is possible to more reliably provide the indoor antenna with a directivity control function by analyzing not only the uplink communication sequence but also the downlink communication sequence. In other words, by analyzing the uplink communication sequence and the downlink communication sequence, it is possible to more reliably grasp the communication sequence according to the 5G communication standard.

In the antenna control device 100 according to the fourth aspect, the uplink control signal counted as the number of times the uplink control signal is transmitted before data communication between the indoor antenna 200b, which is the second antenna, and the wireless terminal is performed is preferably the following signal. That is, examples of the uplink control signal include a random access preamble signal and an RRC setup request signal.

According to the above configuration, by using the random access preamble signal and the RRC setup request signal that are defined in the 5G communication standard and are used reliably, retransmission control that is suitable for the directionality of indoor antennas can be more appropriately performed.

The link control unit 130 of the antenna control device 100 according to the fifth aspect preferably retransmits only the random access preamble signal, or retransmits only the RRC setup request signal. Alternatively, the link control unit 130 preferably retransmits both the random access preamble signal and the RRC setup request signal.

According to the above configuration, by using the RRC setup request signal and/or random access preamble signal, which are defined in the 5G communication standard and are used reliably, retransmission control becomes possible in various patterns, and the scalability of retransmission control can be improved.

The link control unit 130 of the antenna control device 100 according to the sixth aspect preferably generates a reception blocking signal for preventing the wireless terminal from receiving the downlink response signal, which is a response signal to the uplink control signal, in order to retransmit the uplink control signal. The antenna control device 100 preferably further includes a downlink control unit 160 that receives the reception blocking signal from the link control unit 130. When the downlink control unit 160 receives the reception blocking signal, it is preferable that the downlink control unit 160 blocks the communication path by a switch arranged in the downlink side communication path at a timing before the downlink response signal is emitted to the wireless terminal. Alternatively, when the downlink control unit 160 receives the reception blocking signal, it is preferable that the downlink control unit 160 increases the attenuation of the communication path by a variable attenuator arranged in the downlink side path at a timing before the downlink response signal is emitted to the wireless terminal.

The above configuration makes it possible to have a wireless terminal that wirelessly communicates with the second antenna retransmit an uplink control signal with a simple configuration. In addition, the above-described simple configuration also makes it possible to freely set the number of retransmissions.

The link control unit 130 of the antenna control device 100 according to the seventh aspect preferably outputs a delay signal to the uplink control unit 170. The delay signal is preferably a signal for the uplink control unit 170, which is disposed on the communication path between the second antenna and the first antenna, to delay the uplink control signal.

According to the above configuration, by delaying the uplink control signal, there may be some cases where more time is available to generate signals such as reception blocking signals, and retransmission control may be possible more reliably.

In the antenna control device 100 according to the eighth aspect, it is preferable that the directivity of the second antenna is controlled by the directivity control unit 150 in the direction in which the reception level is maximum. Furthermore, after the directivity of the second antenna is controlled, it is preferable to change the directivity of the second antenna by an amplitude smaller than the amplitude in the different direction before receiving the second or subsequent uplink signal transmitted from the wireless terminal to the second antenna. It is also preferable that the reception strength measurement unit 120 measures the reception strength of the uplink signal for the changed directivity of the second antenna. Furthermore, it is preferable that the directivity control unit 150 controls the directivity of the second antenna in the direction in which the averaged reception strength for each changed directivity of the second antenna is maximum.

According to the above configuration, when receiving an uplink signal from a wireless terminal in communication after the RRC setup signal, the beam direction of the indoor antenna 200b2 is changed and the average reception strength is calculated. Then, the beam direction with the greatest average reception signal strength is set as the central beam direction, and the beam direction of the indoor antenna 200b2 is changed to the left or right or forward or backward from the central beam direction, so that wireless communication can be continued appropriately even if the wireless terminal moves. Also, by setting the beam direction with the greatest average reception signal strength in the direction from which the wireless terminal moves and changing the beam direction of the indoor antenna 200b2 in the expected direction of movement of the wireless terminal, wireless communication can be continued appropriately even if the wireless terminal moves.

The antenna control system 1000 according to the ninth aspect preferably includes an antenna control device 100 according to any one of the first to eighth aspects, an outdoor antenna 200a2 which is a first antenna, and an indoor antenna 200b2 which is a second antenna. The antenna control system 1000 also preferably includes a transmission path 400a2 which electrically connects the first antenna and the second antenna. The transmission path 400a2 is preferably an optical fiber. The antenna control system 1000 preferably further includes an O/E converter 300a2 which is disposed at the connection between the optical fiber and the first antenna, and an E/O converter 300b2 which is disposed at the connection between the second antenna and the optical fiber.

With the above configuration, even if RoF is applied to an existing communication standard that uses radio waves in the high-frequency band, it is possible to provide an antenna control system 1000 that can provide a directivity control function to an indoor antenna and can provide stable communication with wireless terminals that move around in a wide indoor area.

In the antenna control system 1000 according to the tenth aspect, it is preferable that the first antenna, the outdoor antenna 200a2, is placed outside the building or mobile body, and the second antenna, the indoor antenna 200b2, is placed inside the building or mobile body. It is preferable that the building or mobile body experience a larger propagation loss than air for the beam-shaped radio waves radiated from the base station.

The above configuration enables wireless communication between a wireless terminal placed inside an object such as a building or a moving object where high-frequency radio waves are attenuated more than air and a base station via RoF according to the 5G communication standard.

Although the embodiments have been described in detail with reference to the drawings, the present invention is not limited to the contents described in the above embodiments. Furthermore, the components described above include those that a person skilled in the art would easily imagine and those that are substantially the same. Furthermore, the configurations described above can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 100 Antenna control device 110 Communication status analysis unit 120 Reception strength measurement unit 130 Link control unit 140 Reception strength storage unit 150 Directivity control unit 160 Downlink control unit 170 Uplink control unit 200a Outdoor antenna 200b Indoor antenna 400a Transmission path 1000 Antenna control system

Claims (8)

An antenna control device, comprising: a second antenna electrically connected to a first antenna that directly communicates with a base station, the first antenna being configured to control a directivity of the second antenna that directly communicates with a wireless terminal that does not directly communicate with the base station, with respect to the wireless terminal;
a communication status analysis unit that calculates a difference between the number of times the directivity of the second antenna is switched and the number of times an uplink control signal is transmitted before the wireless terminal performs data communication with the base station, and analyzes a communication status between the wireless terminal and the base station;
a link control unit that, when the number of times of transmission of the uplink control signal before the data communication is performed is smaller than the number of times of switching of the directivity of the second antenna, retransmits the uplink control signal from the wireless terminal to the second antenna the difference number of times before the data communication;
a directivity control unit that controls the directivity of the second antenna in a different direction each time the uplink control signal is received, and controls the directivity of the second antenna in a direction in which a reception level is maximum when the uplink control signal is received after all the uplink control signals that should be retransmitted are retransmitted. The antenna control device according to claim 1, wherein the communication status analyzed by the communication status analysis unit is an uplink communication sequence of a communication sequence determined by a 5G communication standard. The antenna control device according to claim 1 or 2, wherein the uplink control signal counted as the number of times the uplink control signal is transmitted before the second antenna and the wireless terminal perform the data communication is a random access preamble signal and an RRC setup request signal. The antenna control device according to any one of claims 1 to 3, wherein the link control unit causes only the random access preamble signal to be retransmitted, causes only the RRC setup request signal to be retransmitted, or causes both the random access preamble signal and the RRC setup request signal to be retransmitted. the link control unit generates a reception blocking signal for preventing the wireless terminal from receiving a downlink response signal, which is a response signal to the uplink control signal, in order to retransmit the uplink control signal;
a downlink control unit that receives the reception blocking signal from the link control unit;
5. The antenna control device according to claim 1, wherein, when the downlink control unit receives the reception blocking signal, the downlink control unit blocks the communication path using a switch arranged in the communication path on the downlink side, or increases the attenuation of the communication path using a variable attenuator arranged in the path on the downlink side, at a timing before the downlink response signal is emitted to the wireless terminal. The antenna control device according to claim 5, wherein the link control unit outputs a delay signal for delaying the uplink control signal to the uplink control unit by an uplink control unit disposed in a communication path between the second antenna and the first antenna. An antenna control device according to any one of claims 1 to 6,
The first antenna;
The second antenna;
a transmission line electrically connecting the first antenna and the second antenna;
an O/E (Optical/Electronic signal) converter disposed at a connection portion between the transmission line and the first antenna;
An antenna control system including an E/O (Electronic/Optical signal) converter disposed at a connection between the second antenna and the transmission line, the transmission line being an optical fiber. The antenna control system according to claim 7, wherein the first antenna is arranged outside a building or a mobile body, the second antenna is arranged inside a building or a mobile body, and the building or the mobile body experiences a larger propagation loss for the beam-shaped radio waves radiated from a base station than in air.

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