JP2007295627A - Wireless base station apparatus and antenna directivity control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless base station apparatus, capable of ensuring a proper CIR for a switch-back terminal when the terminal moves from a wireless base station during communication to other wireless base station by means of handover, and switches back to the original wireless base station in an SDMA communication system. <P>SOLUTION: Each of the wireless base station apparatuses controls the directivity of an array antenna and forms a transmission beam with individual radiation patterns by each terminal to conduct wireless communication with each terminal in the SDMA wireless communication system detect reception errors of a signal transmitted from each terminal. When detecting errors consecutively from all the terminals for a prescribed period, each wireless base station apparatus carries out the control of omnibus transmission, wherein a transmission beam of a call channel of each terminal is switched alternately, and no directivity is provided in the particular direction of the radiation pattern. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a spatial division multiplexing (SDMA) type radio base station apparatus and an antenna directivity control method.

  A conventional SDMA wireless communication system includes an adaptive array antenna in a wireless base station, and forms a transmission beam having a radiation pattern with a different directivity for each user terminal (hereinafter simply referred to as a terminal), and is used for a plurality of terminals at the same time. (For example, refer to Patent Document 1).

When a radio base station forms a radiation pattern of a certain terminal, the radio base station gives directionality to the terminal of the transmission partner by adaptive beam forming, and other than that by adaptive null steering. A null is formed in the direction of the terminal.
As a result, the same call channel (TCH) is allocated to a plurality of terminals while maintaining the call quality by maintaining the CIR (Carrier to Interference Ratio) of the terminal at a certain value (for example, 15 dB) or more, and the channel utilization efficiency is improved. Yes.

  In addition, as a wireless base station equipped with a conventional adaptive array antenna, there is a wireless base station that transmits a plurality of types of radio waves with different radiation patterns for a control channel (CCH) in order when broadcasting to an unspecified terminal (for example, , See Patent Document 2).

As a result, in omni transmission without directivity in a specific direction, the radiation pattern is dynamically changed so that the radio waves uniformly reach all directions due to the diversity effect.
JP 2002-58061 A JP 2001-127681 A

  However, in the conventional SDMA wireless communication system, when the CIR deteriorates and the terminal performs a handover to another radio base station and fails in the handover and tries to switch back to the original radio base station, the original radio base station Since the station does not know where the terminal is, it is difficult to secure an appropriate CIR for the terminal. For this reason, there is a problem that communication synchronization cannot be established with the terminal, and the call of the terminal is disconnected.

  The present invention has been made in view of such circumstances, and the object of the present invention is to move a terminal from a communicating wireless base station to another wireless base station by handover in an SDMA wireless communication system, Another object of the present invention is to provide a radio base station apparatus and an antenna directivity control method capable of ensuring an appropriate CIR for the terminal to be switched back when switching back to the original radio base station.

In order to solve the above problem, a radio base station apparatus according to claim 1 is provided for each terminal by an array antenna including a plurality of antennas, adaptive beamforming and adaptive null steering for controlling directivity of the array antenna. A radio base station apparatus that performs radio communication with each terminal by the SDMA method when receiving a signal transmitted from the terminal. Error detection means for detecting a reception error, and when the error is continuously detected for a certain period for all terminals, the transmission control means alternately transmits the transmission beam of the communication channel of each terminal, and The radiation pattern is controlled so as to perform omni transmission without directivity in a specific direction.
According to the present invention, when all terminals communicating with a radio base station switch back after moving to another radio base station, the terminal to be switched back can access (communication) from any direction. Therefore, it is possible to secure an appropriate CIR of the call channel for the terminal to be switched back. Thereby, it is possible to prevent the call of the terminal to be switched off from being disconnected.

The radio base station apparatus according to claim 2, wherein the transmission control unit performs control so that a transmission beam of a communication channel of each terminal is formed with different types of radiation patterns in the omni transmission. It is characterized by that.
According to the present invention, since the intensity of the transmission beam can be controlled uniformly in all directions, the same CIR can be ensured for a terminal accessing (communication) from any direction.

4. The radio base station apparatus according to claim 3, wherein the transmission control means forms the radiation pattern so that the phase and amplitude are the same and the maximum output is obtained by the plurality of antennas in the omni transmission. It is characterized in that a weighting coefficient for performing is calculated.
According to this invention, the transmission power of the omni transmission can be increased.

  In order to solve the above-described problem, an antenna directivity control method according to claim 4 includes an array antenna including a plurality of antennas, and performs adaptive beamforming and adaptive null steering for controlling the directivity of the array antenna. An antenna directivity control method in a radio base station apparatus that forms a transmission beam of an individual radiation pattern for each terminal and wirelessly communicates with each terminal by the SDMA method when receiving a signal transmitted from the terminal In addition, in the process of detecting a reception error and when the error is detected continuously for a certain period for all terminals, the transmission beam of the communication channel of each terminal is alternately directed and the radiation pattern is directed in a specific direction. And a process of controlling to perform an omni transmission without giving a characteristic.

  6. The antenna directivity control method according to claim 5, wherein, in the omni transmission, control is performed such that a transmission beam of a communication channel of each terminal is formed with different types of radiation patterns and transmitted. Yes.

  7. The antenna directivity control method according to claim 6, wherein a weighting factor for forming the radiation pattern so that a phase and an amplitude are the same and a maximum output is obtained in the plurality of antennas in the omni transmission. It is characterized by calculating.

  According to the present invention, when all terminals communicating with a radio base station switch back after moving to another radio base station, the terminal to be switched back can access (communication) from any direction. An appropriate CIR of the call channel can be secured for the returning terminal. Thereby, it is possible to prevent the call of the terminal to be switched off from being disconnected.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a radio base station apparatus (hereinafter simply referred to as a radio base station) 100 according to an embodiment of the present invention.

A radio base station 100 shown in FIG. 1 is a PHS (registered trademark) base station that performs digital radio communication with a terminal.
In this embodiment, for convenience of explanation, a case where four antennas perform multiplex communication with two terminals using the SDMA method will be described as an example. However, when three or more terminals are multiplexed using the SDMA method, The same applies to the above.

  In FIG. 1, the radio base station 100 includes an array antenna including four antennas ANT <b> 1 to ANT <b> 4, and these antennas ANT <b> 1 to 4 are connected to the transmission / reception changeover switch 2. The transmission / reception changeover switch 2 controls these antennas ANT1 to ANT4 in a time-sharing manner to perform switching control between transmission and reception. The transmission / reception changeover switch 2 is connected to four reception units 6 and four transmission units 8 of the radio unit 4. The first to fourth receiving units 6 are provided corresponding to the antennas ANT1 to ANT4, respectively, and are connected to each other via the transmission / reception changeover switch 2. The first to fourth transmitters 8 are provided corresponding to the antennas ANT1 to ANT4, respectively, and are connected via the transmission / reception changeover switch 2, respectively.

  The receiving unit 6 includes a low noise amplifier, a down converter, and an A / D converter (this configuration is not shown). The receiving unit 6 is also connected to the modem unit 12. In the receiving unit 6, the signal received by the antenna corresponding to itself is input to the down converter via the low noise amplifier, and the output of the down converter 18 is digitized by the A / D converter and output to the modem unit 12. .

  The transmission unit 8 includes two multipliers # 1_10 and # 2_10, a D / A converter, an upper converter, and a power amplifier (not shown). The transmission unit 8 is also connected to the modem unit 12. In the transmission unit 8, two weighting coefficients (complex numbers) input from the modem unit 12 are set in the multipliers # 1_10 and # 2_10, respectively. Multiplier # 1_10 is set with a weighting factor for forming a radiation pattern for one of the two terminals that perform multiplex communication using the SDMA scheme. Multiplier # 1_10 performs complex multiplication of the set weight coefficient and data to be transmitted to the terminal and outputs the result. Similarly, the multiplier # 2_10 is set with a weighting factor for forming a radiation pattern for the other terminal, and the multiplier # 2_10 performs complex multiplication of the set weighting factor and data to be transmitted to the terminal. And output. The outputs of the multipliers # 1_10 and # 2_10 are combined, converted into an analog signal by a D / A converter, and transmitted from an antenna corresponding to itself through an upper converter and a power amplifier.

  The modem unit 12 includes a plurality of CPUs, and performs phase control by modulation / demodulation of transmission / reception data and digital signal processing. Specifically, the following five controls are performed.

(1) The digital signals converted at the final stage of each of the first to fourth receiving units 6 are combined so that, for example, D / U (Desire / Undesiree), that is, a CIR value is maximized. Demodulate.

(2) The phase of each reception at the antennas ANT1 to ANT4 is calculated, and control is performed so that the phase is equivalent at the antenna end during transmission.

Accordingly, directivity can be given to both transmission / reception in the direction of the terminal that performs communication.

(3) Suppression is performed by creating a null point in the arrival direction of the interference wave and the delayed wave.

(4) By controlling the phases of the signals supplied to the four antennas ANT1 to ANT4, it is possible to transmit with the beam narrowed with directivity in an arbitrary direction.

This phase control is performed by setting weighting coefficients for the multipliers # 1_10 and # 2_10 of the first to fourth transmitters 8, respectively.
As described above, the multiplier # 1_10 is set with a weighting factor for forming a radiation pattern for one of the two terminals performing multiplex communication using the SDMA method, and the other is assigned to the multiplier # 2_10. A weighting factor for forming a radiation pattern for the terminal is set.
Thereby, data can be simultaneously transmitted to the two terminals by the transmission beams of the radiation patterns having different weights.
Further, by setting the weighting factor, nulls can be formed in any direction of the radiation pattern of each transmission beam.

(5) To reduce interference in the downlink direction to surrounding base stations and terminals other than terminals that are communicating or exchanging data (communications).
The modem unit 12 is connected to the control unit 14.

  The control unit 14 includes a plurality of CPUs, and controls the entire radio base station 100. The control unit 14 has a function of calculating a weighting factor for forming a radiation pattern at the time of transmission and a weighting factor for forming a radiation pattern at the time of reception, a function of allocating a channel for space division multiplexing, For example, a function for calculating a received signal coefficient vector (Spatial Signature), a function for calculating a rate of change of the received signal coefficient vector, and a function for statistically processing received intensity (RSSI) from each terminal. Specifically, the following five controls are performed. The reception signal coefficient vector represents reception information (amplitude and phase) of the terminal.

(1) The necessary parameters and timing are instructed to the modem unit 12, and the data received by the modem unit 12 is processed. In this data reception process, a reception error is detected.

Also, transmission data to be radiated in the air is created and passed to the modem unit 12.

(2) The rate of change of the received signal coefficient vector from the terminal is calculated.

(3) Statistical processing is performed on the correlation coefficient between the terminals with respect to the uplink reception strength from the terminals.

(4) Channels for space division multiplexing are allocated so that the QOS (Quality Of Service) of the call when space division multiplexing is performed is equivalent to the QOS of the call when space division multiplexing is not performed.

(5) When a call is established for two terminals using the same call channel by space division multiplexing, the CIR value of the terminal is a value necessary for maintaining a good QOS of the terminal (for example, 15 dB) As described above, the weighting coefficient corresponding to each terminal is calculated.
The control unit 14 is connected to the line interface unit 15.

  The line interface unit 16 is connected to a digital communication line such as an ISDN line and executes an interface process therewith. The modulation / demodulation unit 12 and the control unit 14 realize an adaptive beamforming function and an adaptive null steering function.

  Next, an operation related to antenna directivity control in the above-described radio base station 100 will be described. First, with reference to FIG. 2 and FIG. 4 to FIG. 7, a case will be described in which one of a plurality of terminals communicating with the radio base station 100 moves to another radio base station. FIG. 2 is a first flowchart showing a flow of antenna directivity control processing performed by the radio base station 100 shown in FIG. 4 to 7 are conceptual diagrams for explaining the operation of controlling the directivity of the antenna. FIG. 4 is a conceptual diagram of a radiation pattern W1 for the terminal 201 in communication with the radio base station 100. FIG. 5 is a conceptual diagram of a radiation pattern W2 for the terminal 202 communicating with the radio base station 100. FIG. 6 is a conceptual diagram of radiation patterns W1a and b for the terminal 201 that is still communicating with the radio base station 100 after the terminal 202 moves to another radio base station. FIG. 7 is a conceptual diagram of a radiation pattern W2a for the terminal 202 after the terminal 202 has moved to another radio base station. 6 and 7, the position of the terminal 202 when the radio base station 100 has finally received normal data from the terminal 202 is indicated by a broken line.

  First, as shown in FIGS. 4 and 5, two terminals 201 and 202 are communicating with the radio base station 100. The radio base station 100 is in a call state with each of the terminals 201 and 202 by space division multiplexing using one call channel. At this time, the radiation pattern W1 of the transmission beam from the radio base station 100 to the terminal 201 (see FIG. 4) has directivity in the direction of the terminal 201 and forms a null in the direction of the terminal 202. Similarly, the radiation pattern W2 of the transmission beam to the terminal 202 (see FIG. 5) has directivity in the direction of the terminal 202 and forms a null in the direction of the terminal 201.

  Further, the CIR value for the terminal 201 (the transmission beam (desired wave) of the terminal 201 / the transmission beam (interference wave) of the terminal 202) is equal to or higher than a certain value (for example, 15 dB), and the CIR value (terminal of the terminal 202) The weighting coefficients for the terminals 201 and 202 are calculated so that the transmission beam 202 (desired wave) / transmission beam (interference wave) of the terminal 201 is equal to or greater than a certain value (for example, 15 dB).

  In FIG. 2, the radio base station 100 receives data of the communication channel (TCH) from the terminals 201 and 202 (step S1), and when detecting an error related to reception from one of the terminals, the radio base station 100 proceeds to step S3. If there is no error, the process proceeds to step S6 (step S2).

Here, it is assumed that an error related to reception from the terminal 202 is detected. In step S6, a weighting factor for each terminal is calculated by the SDMA algorithm. A case where an error related to reception is detected for all terminals (in this example, both of the two terminals 201 and 202) will be described later.

  Next, in step S3, it is considered that the error corresponding terminal 202 has moved, the terminal 202 is excluded from the null forming target, and a weight coefficient for the normally received terminal 201 is calculated (step S3). In this example, since there is one terminal that is still communicating with the radio base station 100 due to normal reception, the terminal 201 uses a known AAA (Adaptive Array Antenna) algorithm to provide the terminal 201 with the maximum CIR. The weight coefficient is calculated based on the received signal coefficient vector. On the other hand, when there are three or more multiplexable units by SDMA and there are a plurality of terminals that are still communicating with the radio base station 100, terminals other than the terminal that calculates the weighting coefficient among these terminals that are still communicating The weighting coefficient is calculated based on the received signal coefficient vector of each terminal that is still in communication by the SDMA algorithm so that a null is formed in the direction of, and a CIR of a certain value (for example, 15 dB) or more is secured.

As a result of the process in step S3, no null is formed for the terminal corresponding to the error. Therefore, the transmission beam to the terminal 201 that is still communicating with the radio base station 100 has enhanced directivity to the transmission partner, and the transmission power is reduced. Increased compared to when nulls were formed. FIG. 6 shows this radiation pattern W1a. As shown in FIG. 6, no null is formed in the direction of the error corresponding terminal 202.

  Next, in step S4, a weighting coefficient for the error corresponding terminal 202 considered to have moved to another radio base station is calculated (step S4). In the calculation of the weighting factor, the weighting factor is calculated for the error corresponding terminal 202 based on the received signal coefficient vector at the time of normal reception immediately before the error detection. Further, priority is given to forming the maximum null in the direction of the terminal 201 that is continuously communicating with the radio base station 100 by normal reception, and control is performed so that the transmission power to the error-corresponding terminal 202 is maximized.

  In this embodiment, since the radiation patterns are formed by the four antennas ANT1 to ANT4, the weighting coefficient is calculated in the four-dimensional vector space. First, in the direction of the normal reception terminal 201 in the four-dimensional vector space. The weighting factor is calculated so as to form the maximum null. As a result, the number of degrees of freedom for calculating the weighting coefficient is changed from four to three. Next, a weighting factor is obtained so that the power transmitted to the error corresponding terminal 202 is maximized in the remaining three-dimensional vector space. FIG. 7 shows this radiation pattern W2a. As shown in FIG. 7, control is performed such that the maximum null is formed in the direction of the normally received terminal 201 and the transmission power to the error-corresponding terminal 202 is maximized.

  As a result, the transmission beam for the terminal that has moved to another radio base station reduces the adverse effect on the terminal that is still communicating with the original radio base station, and when the moved terminal switches back, A radiation pattern suitable for the terminal to be switched back can be formed to ensure an appropriate CIR.

  Next, in step S5, the transmission power of the normally receiving terminal 201 is reduced based on the number of normally receiving terminals that are still in communication with the radio base station 100. The value (XdB) of the reduction amount of the transmission power is parameterized in advance. FIG. 6 shows this radiation pattern W1b.

As a result, after the terminal 202 moves to another radio base station, it is prevented from becoming an interference wave of the terminal 202 that switches back by reducing the intensity of the transmission beam for the terminal 201 that is still communicating with the original radio base station 100. In addition, the CIR for the terminal 202 to be switched back can be improved.

  In terminal 201 that is still communicating with radio base station 100, the power that reaches itself increases in step S3, and the influence of interference waves on itself is reduced in step S4. As a result, since the CIR of the terminal 201 is greatly improved, even if the transmission power of the transmission beam for the terminal 201 is lowered, an appropriate CIR can be secured for the terminal 201, and the call quality is good. Kept.

  As shown in FIG. 6, the transmission beam of the terminal 201 that is still communicating with the radio base station 100 in step S3 is a radiation pattern W1a, the directivity is enhanced, and the transmission power is increased. On the other hand, as shown in FIG. 7, the transmission beam of the terminal 202 that has moved to another radio base station in the above step S4 has the radiation pattern W2a, and the null for the terminal 201 is the maximum. As a result, even if the transmission power of the transmission beam of the terminal 201 is lowered by the parameterized value (XdB), the CIR value of the terminal 201 can be maintained at a level where the call quality is kept good. Then, by reducing the transmission power of the terminal 201 by X dB, the transmission beam of the terminal 201 becomes a radiation pattern W1b, and the null for the terminal 202 becomes large. Furthermore, since the transmission beam of the terminal 202 is controlled so as to have the maximum transmission power with respect to the terminal 202 by the above step S4, the CIR of the terminal 202 is significantly increased compared to the CIR before the movement.

  As described above, according to the present embodiment, when a terminal moves from a wireless base station in communication to another wireless base station by handover, the call quality of the terminal that is still in communication with the original wireless base station is good. Can be kept in. Furthermore, when the moved terminal tries to switch back to the original radio base station, an appropriate CIR can be secured for the switching back terminal, and communication connection with the switching back terminal can be easily performed. it can.

  As described above, it is considered that the terminal has moved to another radio base station by detecting an error related to reception from the terminal. The reason for this is that if it waits until it detects that it has actually moved, this detection takes about 100 ms, and during this time it can provide good CIR to the terminal that is still communicating with the original radio base station. This is because there is a possibility that the call quality of the terminal that is still in communication may deteriorate.

  Next, with reference to FIG. 3 and FIG. 8, a case will be described in which all terminals communicating with the radio base station 100 move to other radio base stations. FIG. 3 is a second flowchart showing a flow of antenna directivity control processing performed by the radio base station 100 shown in FIG. FIG. 8 is a conceptual diagram for explaining the operation of controlling the directivity of the antenna. First, in FIG. 3, the radio base station 100 receives data of the communication channel (TCH) from the terminals 201 and 202 (step S1), and all the terminals (both the two terminals 201 and 202 in this example). If an error related to reception is detected continuously for a certain period, the process proceeds to steps S12 to S16 (step S11).

  In steps S12 to S16, the transmission beams of the communication channels of the terminals 201 and 202 are alternately transmitted and the radiation pattern is omni-transmitted without directivity in a specific direction. At the time of this omni transmission, the weighting coefficient is calculated so that the four antennas ANT1 to ANT4 have the same phase and amplitude and the maximum output. Then, this weighting coefficient is set in both of the two multipliers # 1_10 and # 2_10 of each transmission unit 8 in FIG. This increases the transmission power by 6 dB.

Omni transmission is performed in a continuous burst of a plurality of frames for a certain period for one terminal. This is a process in consideration of the fact that there is a terminal specification that does not transmit uplink synchronization establishment data unless downlink synchronization establishment data is received continuously a plurality of times.

  Then, when the communication channel data is normally received for any of the terminals and the communication channel is established (in the case of “YES” in step S14), the processing ends. Thereafter, the process of FIG. 2 is executed.

  Thus, by omni-transmitting the transmission beam of the speech channel, the radiation pattern W3 of the transmission beam does not have directivity in a specific direction and the transmission power increases as shown in FIG. The communication area expands compared to SDMA. Accordingly, when all terminals communicating with the radio base station 100 move to another radio base station and then switch back, the terminal to be switched back can access (communication) from any direction. Since the power received by the terminal to be switched back becomes larger by YdB (6 dB or more), it is possible to ensure an appropriate CIR of the call channel for the terminal to be switched back. As a result, it is possible to prevent the call of the terminal to be switched off from being disconnected.

  In addition, the radiation pattern of the transmission beam to be omni-transmitted may be dynamically changed using a different radiation pattern that provides a diversity effect. For example, different types of radiation patterns are used for a beam transmitted in a continuous burst for one terminal so as to obtain a diversity effect. According to this configuration, since the intensity of the transmission beam can be controlled uniformly in all directions, a similar CIR can be ensured for a terminal accessing (communication) from any direction.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.

It is a block diagram which shows the structure of the radio base station apparatus (radio base station) 100 by one Embodiment of this invention. 4 is a first flowchart showing a flow of antenna directivity control processing performed by the radio base station 100 shown in FIG. 1. 4 is a second flowchart showing a flow of antenna directivity control processing performed by the radio base station 100 shown in FIG. 1. It is a 1st conceptual diagram for demonstrating the operation | movement which controls the directivity of an antenna. It is a 2nd conceptual diagram for demonstrating the operation | movement which controls the directivity of an antenna. It is a 3rd conceptual diagram for demonstrating the operation | movement which controls the directivity of an antenna. It is a 4th conceptual diagram for demonstrating the operation | movement which controls the directivity of an antenna. It is a 5th conceptual diagram for demonstrating the operation | movement which controls the directivity of an antenna.

Explanation of symbols

  2: transmission / reception changeover switch, 4: wireless unit, 6: reception unit, 8: transmission unit, 10: multiplier, 12: modulation / demodulation unit, 14: control unit, 16: line interface unit, ANT1 to ANT4: antenna, 100: Radio base station apparatus (radio base station), 201, 202: terminal

Claims (6)

An array antenna comprising a plurality of antennas, and transmission control means for performing control to form a transmission beam of an individual radiation pattern for each terminal by adaptive beamforming and adaptive null steering for controlling the directivity of the array antenna, In a radio base station apparatus that performs radio communication with each terminal by the SDMA method,
When receiving a signal transmitted from the terminal, it comprises an error detection means for detecting a reception error,
When the error is continuously detected for a certain period of time for all terminals, the transmission control means alternately transmits the transmission beam of the communication channel of each terminal and directs the radiation pattern in a specific direction. Control to do no omni transmission,
A radio base station apparatus. In the omni transmission, the transmission control means controls the transmission beam of the communication channel of each terminal to be formed and transmitted with different types of radiation patterns.
The radio base station apparatus according to claim 1. The transmission control means calculates a weighting factor for forming the radiation pattern so that the phase and amplitude are the same and the maximum output in the plurality of antennas in the omni transmission.
The radio base station apparatus according to claim 1 or 2. An array antenna comprising a plurality of antennas is provided, and a transmission beam having an individual radiation pattern is formed for each terminal by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna. An antenna directivity control method in a radio base station apparatus that performs radio communication with
A process of detecting a reception error when receiving a signal transmitted from a terminal;
When the error is continuously detected for a certain period of time for all terminals, a process of alternately transmitting the transmission beam of the communication channel of each terminal and omni-transmitting the radiation pattern without directivity in a specific direction; ,
An antenna directivity control method comprising: In the omni transmission, the transmission beam of the communication channel of each terminal is controlled to be formed and transmitted with different types of radiation patterns.
The antenna directivity control method according to claim 4. In the omni transmission, a weighting factor for forming the radiation pattern is calculated so that the phase and amplitude are the same and the maximum output is obtained by the plurality of antennas.
6. The antenna directivity control method according to claim 4, wherein the antenna directivity is controlled.

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