JP4167691B2 - Adaptive array base station - Google Patents

Description

  The present invention relates to an SDMA (Space Division Multiple Access) communication system, and to an adaptive array base station adopting the SDMA method.

  In an adaptive array base station, when a terminal connected to its own base station (own base station connecting terminal) attempts handover, the terminal may fail to perform handover and be returned to its own base station. On the side, it enters the transmission / reception mode of synchronous burst for a maximum of 15 seconds. Even if a burst other than the synchronous burst is received during the synchronous burst transmission / reception mode, it is simply discarded (prior art 1). In addition, if a terminal connected to another base station moves and the interference from the terminal increases, if the base station scramble seed (8-bit identification information) is the same, Since it becomes impossible to distinguish between the desired wave from the base station connection terminal and the interference wave from the other base station connection terminal, NULL has been formed in the interference wave direction until then, and the transmission weight can be locked. It becomes impossible to lock (Prior Art 2).

  However, just by discarding other bursts without using the spatial multiplexing technique as in the prior art 1, a TCH burst of the communication channel is received from a terminal connected to another base station (for example, terminal A). In this case, since NULL is not formed in that direction, the terminal A is interfered. Further, when the transmission weight cannot be locked as in the prior art 2, time division multiplexing is impaired, which causes interference to terminals connected to other base stations. An object of the present invention is to provide an adaptive array base station that can guarantee the call quality of another base station connection terminal and its own base station connection terminal in view of the above-described problems of the prior art.

In order to solve the above-described problem, the adaptive array base station according to the first aspect of the present invention provides transmission weight information in a base station that performs communication in a time-space division multiple access scheme to a mobile communication terminal to be transmitted. Of the transmission weight information that has been buffered for a predetermined period of time when adaptive beamforming to the mobile communication terminal to be transmitted or null transmission to another base station connection terminal cannot be performed. To the optimum transmission weight information based on the error information, before the occurrence of the case where adaptive beam forming for the mobile communication terminal to be transmitted or null transmission to another base station connection terminal cannot be performed and at the nearest time Means for selecting transmission weight information and the optimum transmission weight information; It means for determining a transmission weight Zui, characterized by comprising a means for transmitting to the mobile communication terminal to be transmitted by using the transmission weight. Further, the second invention of the present application is the adaptive array base station of the first invention of the present application, wherein the error information is a CRC error number or a total of the CRC error number and the UW error number.

Furthermore, a communication method according to a third aspect of the present invention is a method for performing communication in a time-space division multiple access scheme to a mobile communication terminal to be transmitted, the step of buffering transmission weight information, When adaptive beamforming to a mobile communication terminal to be transmitted or null transmission to another base station connected terminal cannot be performed, an optimum based on error information is selected from the buffered transmission weight information for a predetermined period. Selecting transmission weight information at the nearest time prior to the occurrence of transmission weight information before adaptive beam forming for the mobile communication terminal to be transmitted or null transmission to another base station connected terminal; and And determining the transmission weight based on the optimal transmission weight information. A step that, characterized in that it comprises the steps of transmitting to the mobile communication terminal to be transmitted by using the transmission weight. Furthermore, a fourth invention of the present application is characterized in that, in the communication method of the third invention of the present application, the error information is a CRC error number or a total of the CRC error number and the UW error number.

  According to the adaptive array base station of the present invention, it is possible to guarantee the call quality of the other base station connection terminal and the own base station connection terminal.

  Next, with reference to the attached drawings, an embodiment when the adaptive array base station according to the present invention is applied to a PHS base station which is an adaptive array base station for digital radio communication will be described in detail. The term “PHS base station” used here means a base station used in the personal handyphone system (ARIB STD-28).

  FIGS. 1 to 13 are attached drawings, FIG. 1 is a sequence chart at the time of handover, FIG. 2 is a diagram showing beam transmission and NULL transmission in an adaptive array base station, and FIG. 3R> 3 is a synchronous burst transmission after handover. FIG. 4 is a functional block diagram of an adaptive array base station according to an embodiment of the present invention, FIG. 5 is a TCH data format, FIG. 6 is a SYNC data format, and FIG. 7 is a synchronous burst beam transmission and a synchronous burst NULL. Example of transmission time slot, FIG. 8 is a diagram showing synchronous burst NULL transmission after handover, FIG. 9 is a diagram showing a transmission wait lock state of an adaptive array base station, and FIG. 10 is a diagram showing transitions of a desired wave and an interference wave, FIG. 11 illustrates a transmission weight unlock state of the adaptive array base station, and FIG. 12 illustrates a transmission weight information buffering method. FIG. 13 is a diagram illustrating an example of a time slot, in which a buffered transmission weight information is used.

  The channels provided in the radio section basically include a communication channel (TCH) for transferring user information and a control channel (CCH) for transferring control signals. Then, at the time of transition from the CCH to the TCH or when the terminal is handed over, synchronization is established between the base station and the terminal using a synchronization burst, and then a call is made on the TCH. In the case of the personal handyphone system, 32 bits of uplink synchronization word UW are prepared in the format of synchronization burst, and 16 bits of uplink UW are prepared in the format of TCH.

  In a PHS base station, if a terminal connected to the base station tries to perform a handover, the base station may fail to perform the handover and switch back to the base station. The synchronous burst transmission / reception mode of the synchronous burst is entered. Even if a burst other than the synchronization burst is received during this mode, the burst is simply discarded, and no change is made to the transmission of the next synchronization burst.

  FIG. 1 is a sequence chart when a conventional handover succeeds. There are two types of handover: switching when an instruction is issued from the base station and switching when an instruction is issued from the terminal. Here, the former sequence chart is shown. As shown in the figure, after issuing the handover instruction 105 from the handover source base station 103a, a call setup process (handover process 109 in FIG. 1) is performed between the terminal 101 and the handover destination base station 103b. In the former base station 103a, since there is a possibility that the terminal 101 fails to perform handover and switches back, a synchronization burst (107a to 107d) is transmitted for 15 seconds. If the handover is successful, the handover source base station 103a performs a disconnection process after transmitting a synchronous burst for 15 seconds. 2 and 3 are views showing a state when processing is performed according to the conventional sequence chart.

  FIG. 2 shows a conventional example in which a terminal PS2 (hereinafter referred to as PS2) is connected to a PHS base station 202 (hereinafter referred to as base station 202) and a terminal PS1 (hereinafter referred to as PS1) is connected to the base station 201. The state is represented graphically. The base station 202 transmits an adaptive beam to the PS2 connected to the base station (adaptive beamforming), and gives interference to the PS1 connected to the base station 201 (another base station). Form NULL (adaptive null steering) so that there is no. Further, the base station 202 in a communication state with PS2 receives a burst signal (hereinafter referred to as TCH burst) from PS2 in the TCH reception mode and transmits an adaptive beam in that direction. Further, when the base station 202 receives a TCH burst from PS1 in a communication state with the base station 201, the base station 202 regards the burst as an interference wave and forms NULL in the direction.

  FIG. 3 is a diagram showing a state when PS2 connected to the base station 202 in the conventional example is handed over to another base station. In the base station 202, there is a possibility that the PS2 may fail to perform handover and switch back, so that it enters the transmission / reception mode of synchronous burst for a maximum of 15 seconds. At this time, when the base station 202 receives the TCH burst from PS1, the base station 202 is in the synchronous burst transmission / reception mode, so only discarding the TCH burst has no effect on the transmission of the next synchronous burst. . Therefore, a synchronization burst is transmitted without forming NULL in the direction of PS1, which becomes an interference wave for PS1.

  In the form of Embodiment 1 of the present invention, when a TCH burst is received during the synchronous burst transmission / reception mode at the handover source base station after the terminal is handed over, it is regarded as an interference wave and the TCH burst is transmitted. A synchronous burst is transmitted so that a null is formed in the other direction. Thereby, it is possible to avoid the interference wave in the synchronization burst for the terminal unrelated to the handover.

  Referring to FIG. 4, there is shown a functional block diagram showing an embodiment when the adaptive array base station according to the present invention is applied to a PHS base station which is an adaptive array base station for digital radio communication. In FIG. 4, the adaptive array base station 202 according to the present embodiment includes four antennas ANT1 to ANT4, and these antennas ANT are connected to the transmission / reception changeover switch 12. The transmission / reception selector switch 12 controls these antennas ANT1 to ANT4 in a time-sharing manner to perform switching control between transmission and reception. A reception system module 14 and a transmission system module 22 are connected to the transmission / reception selector switch 12.

  The reception module 14 includes four low noise amplifiers (LNA) 16, a down converter (D / C) 18, and an A / D converter (A / D) 20 provided for each antenna ANT. The reception system module 14 is also connected to the modem unit 30, and the low noise amplifier 16, the down converter 18, and the A / D converter (A / D) 20 are connected to the modem unit 30 from the transmission / reception changeover switch 12 that is a signal path. Connected in order.

  Similarly, the transmission system module 22 includes four D / A converters (D / A) 24, an upper converter (U / C) 26, and multiplier circuits (MP) 28a and b provided for each antenna ANT. ing. The transmission system module 22 is also connected to the modem unit 30. The D / A converter 24, the upper converter 26, and the multiplication circuits 28a and 28b are arranged in this order from the modem unit 30 serving as a signal path toward the transmission / reception system changeover switch 12. It is connected. In the case of spatial multiplexing for two calls, transmission can be made with different weights to each call using the multiplication circuit 28a and the multiplication circuit 28b.

  The modem unit 30 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. For example, D / U (Desire / Undesire) of the digital signal converted at the final stage of the reception system module 14 is synthesized and demodulated so as to be maximized.

2. The phase of reception at the antenna ANT 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 forming a null point in the arrival direction of the interference wave and the delayed wave.

4). By controlling the phase of the signals supplied to the n antennas, it is possible to transmit with the beam narrowed with directivity in an arbitrary direction.

5. Interference in the downlink direction is reduced with respect to terminals other than the user terminal that is exchanging data (communications) during communication with surrounding base stations.

  The modem unit 30 is connected to the control unit 32. The control unit 32 includes a plurality of CPUs and controls the entire base station 202. Specifically, the following six controls are performed.

1. Necessary parameters and timings are instructed to the modem unit 30, and the data received by the modem unit 30 is processed. Further, data to be radiated in the air is created and passed to the modem unit 30. Further, the control of the transmission output by weighting calculated by the calibration is instructed.

2. The rate of change of the spatial signature (reception response vector) from the user terminal (user terminal, hereinafter simply referred to as user) is calculated.

3. Statistical processing of the uplink received signal level RSSI from the user is performed.

4). Spatial multiplexing physical slot allocation is performed with logic such that the GOS (Grade Of Service: call quality) of spatially multiplexed calls is as similar as possible to that of normal calls that are not spatially multiplexed.

5. When establishing a spatially multiplexed call for multiple users, each user has a C / I (Carrier / Interference) for each user that is greater than or equal to the value required to maintain the user's GOS. Calculate the weight to.

6). It is connected to the ISDN line and executes processing of an interface with the ISDN line.

  The power supply unit 34 is a power supply unit that receives a power supply of 100 V and supplies power to the adaptive array base station 202. The modem unit 30 and the control unit 32 form a digital signal processing unit. The base station 202 performs adaptive array transmission that transmits each antenna with a predetermined weight based on reception information (amplitude and phase) received from N (N is a natural number of 2 or more) antennas. .

  As described above, in the present embodiment, after the terminal is handed over, the processes a and b can be performed during the synchronous burst transmission / reception mode in the adaptive array base station 202.

a. When a sync burst is received: A sync burst beam is transmitted in the direction in which the sync burst is received.

b. When a TCH burst is received: It is regarded as an interference wave, and a synchronous burst is transmitted so as to form a NULL in the direction in which the TCH burst is sent.

  FIG. 5 shows a signal format of TCH (TCH burst). Ramp time R for transient response (assuming the rise time of each slot) is 4 bits, start symbol SS (indicating signal start) is 2 bits, preamble PR (for bit synchronization establishment) is 6 bits, channel type CI Is composed of 4 bits, SA (SACCH) is composed of 16 bits, and the error detection code CRC is composed of 16 bits, and the information bit I on which the voice is actually carried is composed of 160 bits. In the case of TCH, the synchronization word UW is 16 bits.

  FIG. 6 shows a signal format of SYNC (synchronous burst). The ramp time R for transient response (assuming the rise time of each slot) is 4 bits, the start symbol SS (indicating signal start) is 2 bits, the preamble PR (for bit synchronization establishment) is 62 bits, and the channel type CI Is 4 bits, the destination identification code (including the call code of the partner station to be connected) is 42 bits, the calling identification code (including the call code of the local station) is 28 bits, the idle bit is 34 bits, and the error detection code CRC is It consists of 16 bits. In the case of SYNC, the synchronization word UW is 32 bits.

  The synchronization word UW in both TCH (FIG. 5) and SYNC (FIG. 6) is a signal having a unique code string for each burst, and is normally used for establishing frame synchronization. This code is searched for from other people's signals and noise, and a selective filter is applied to this code to create a synchronization state. In this embodiment, this synchronization word UW is used to distinguish whether the received burst is a synchronization burst or a TCH burst. The process at this time is shown in steps 1-4.

  Step 1: A burst received during the synchronous burst transmission / reception mode is first confirmed by only the number of UW errors whether or not it is a synchronous burst. Specifically, the code sequence originally included in the UW signal of SYNC (FIG. 6) is compared with the code sequence of the received UW signal of the burst, and the number of mismatch bits (UW error count) is counted.

Step 2: If the number of UW errors is within an allowable range (4 bits or less in Japan, 1 bit or less outside of Japan), the burst is processed as a synchronization burst. That is, at the next transmission, adaptive beam transmission is performed in the direction in which the synchronization burst is transmitted.

Step 3: If the number of UW errors exceeds the allowable range, it is determined that the burst is not a synchronous burst, and then whether or not it is a TCH burst is confirmed only by the number of UW errors. Specifically, the code sequence originally included in the UW signal of the TCH (FIG. 5) is compared with the code sequence of the received UW signal of the burst, and the number of mismatch bits (UW error count) is counted.

Step 4: If the number of UW errors is within the allowable range (4 bits or less in Japan, 1 bit or less outside of Japan), the burst is processed as a TCH burst. That is, at the next transmission, adaptive null steering is performed by synchronous burst transmission in the direction in which the TCH burst is transmitted.

  FIG. 7 and FIG. 8 are diagrams for explaining an embodiment in which the synchronization burst / TCH burst is distinguished using steps 1 to 4. FIG. 7 is a time slot example of synchronous burst beam transmission and synchronous burst NULL transmission by the adaptive array base station 202. In the figure, the base station 202 receives a synchronization burst from the terminal in the third slot of one frame (S701). The adaptive array base station 202 performs synchronous burst beam transmission to the terminal in the direction in which the synchronous burst is received in the seventh slot (S703) of one frame. Subsequently, the adaptive array base station 202 receives the TCH burst from the terminal in the third slot of two frames (S705). Adaptive array base station 202 performs synchronous burst NULL transmission in the direction in which the TCH burst was received in the seventh slot (S707) of the second frame to the terminal.

  FIG. 8 is a diagram illustrating a state when PS2 connected to the base station 202 is handed over to another base station. When PS2 in communication with the base station 202 is handed over, the PS2 may switch back at the base station 202, so the synchronous burst transmission / reception mode is entered for a maximum of 15 seconds. At that time, when the base station 202 receives the TCH burst of PS1 in a communication state with the base station 201, the next synchronization burst is transmitted so as to form NULL in the direction. Thereby, the interference wave in the synchronous burst with respect to PS1 from the base station 202 can be avoided.

  FIG. 9 shows that there are three terminals (PS2, PS3, PS4) connected to the base station 202 (adaptive array base station), which transmit adaptive beams to these terminals, and are connected to the base station 201. It is a figure showing the state which has formed NULL so that interference may not be given with respect to PS1. The base station 202 in a communication state with three devices (PS2 to PS4) receives TCH bursts from three devices (PS2 to PS4) in the TCH reception mode, and transmits an adaptive beam in that direction. Further, when the base station 202 receives a TCH burst from PS1 in a communication state with the base station 201, the base station 202 regards it as an interference wave and forms NULL in that direction. The state in which the adaptive beam and the NULL direction are determined and the transmission weight is fixed is referred to as “the transmission weight is locked”.

  In the base station 202, since three machines (PS2 to PS4) are already in a call state, PS1 cannot be handed over to the base station 202. Therefore, the base station 202 tries to continue forming NULL for PS1. Normally, each base station is provided with a scramble seed (8-bit identification information) so that it can distinguish its own terminal, and that terminal connects to its own station based on the scramble seed attached to the burst from the terminal. The terminal is identified as a terminal connected to another station.

  If the scramble seeds of the base station 201 and the base station 202 are different, the base station 202 recognizes that the scramble seed of the PS1 TCH burst is different from its own, so that the PS1 is the other station connection terminal. it can. Therefore, PS1 can be regarded as an interference wave, and NULL can be formed in that direction. However, when the scramble seeds of the base station 201 and the base station 202 are the same, under the situation A as shown below, the TCH burst from the PS1 that is originally an interference wave and the TCH burst from the PS2 that is the desired wave May become indistinguishable.

  Situation A: FIG. 10 shows a transition between a desired wave and an interference wave in the base station 202. The vertical axis represents the reception level, and the horizontal axis represents time. In the figure, the level of the disturbing wave 1003 from PS1 increases with the passage of time, and the level of the desired wave 1001 from PS2 decreases. In such a case, the base station 202 cannot distinguish between the desired wave and the disturbing wave. In FIG. 11, there are three terminals (PS2, PS3, PS4) connected to the base station 202, and when the terminal PS1 connected to the base station 201 moves, interference from the terminal increases. FIG. In the case as shown in FIG. 11, the reception level of the signal from each terminal is changed to a state as shown in FIG.

  As a result, a NULL is formed in the direction of the other base station connection terminal so far, and it can no longer be locked because it cannot be locked. As a result, interference is given to a terminal connected to another base station. In addition, since the terminal connected to the base station has been transmitted at a sufficient level until then, the transmission weight cannot be locked, so that a sufficient level for the terminal cannot be secured. The state shown in FIG. 11 is referred to as “transmission wait unlock”.

  Transmission wait unlock occurs when both of the following conditions are met.

Condition A: The interference wave RSSI value is higher than the desired wave RSSI value by a certain value or more.

Condition A: CRC error count is a certain value or more.

The unlocking of the transmission weight is released when both of the following conditions are satisfied.

Condition a: The desired wave RSSI value is sufficiently higher than the interference wave RSSI value.

Condition A: When the number of CRC errors is below a certain value, or when a call that is a disturbing wave is disconnected.

  The base station 202 according to the present invention buffers information related to transmission weights (amplitude, phase, number of UW errors, number of CRC errors, etc.) at a predetermined timing (for example, every 5 msec). In both the following periods, the optimum information is selected from the buffered transmission weight information (hereinafter referred to as “transmission weight information”), and the transmission weight is determined.

Period A: The transmission wait is unlocked to unlocked.

Period B: Unlocking transmission weight to disconnecting a call that is an interference wave.

  The selection of transmission weight information is performed by selecting the optimum transmission weight information buffered immediately before, calculating the transmission weight from “the optimum amplitude and phase of transmission weight information”, and using it. It shall be transmitted to the terminal connected to its own station. An example of a method for selecting optimal transmission weight information is shown below.

Selection method I: CRC error count is 1 bit or less. If there are multiple CRC errors that are 1 bit or less, the buffering is performed at the nearest time before the occurrence of unlocking.

Selection method II: When the number of CRC errors is 2 bits or more, the sum of the number of UW errors and the number of CRC errors is the smallest. If there are multiple items with the same total value, the one buffered at the nearest time before the unlock occurred.

FIG. 12 shows a time slot example of the transmission weight information buffering method. In this embodiment, the frame length is 5 msec, and the buffering timing is also 5 msec. In this embodiment, transmission weight information is buffered every 8 slots, such as the 3rd slot, the 11th slot, the 19th slot, and so on (S1201), but it is obvious that the present invention is not limited to this. . Here, a simple example of the buffering method is shown in Table 1.

In this embodiment, buffering is performed for 100 msec, and buffering is performed once every 5 msec. Therefore, it is assumed that there are a total of 20 pieces of information. Transmission weight information to be buffered is amplitude, phase, CRC error, and UW error. In this example, it is assumed that when the interference wave RSSI value is 15 dB or more higher than the desired wave RSSI value and the CRC error count at that time becomes 2 bits or more, the transmission weight is unlocked. The unlocking is canceled when the difference between the interference wave RSSI value and the desired wave RSSI value is smaller than 15 dB and the number of CRC errors is 1 bit or less.

  In the case of Table 1, since the interference wave RSSI value is 16 dB higher than the desired wave RSSI value in item 8 and the number of CRC errors at that time is 9 bits, the transmission weight is unlocked at this time (S1203 in FIG. 12). The base station 202 calculates the transmission weight using the phase and amplitude at the time of item4 in the case of Table 1 that satisfies the above-mentioned predetermined condition among the 20 transmission weight information up to immediately before item8. Transmission is performed (S1205 in FIG. 12R> 2).

  Since the transmission weight unlock state continues from item 9 to item 11, the transmission weight is calculated from the buffering data as in item 8. In item12, the difference between the desired wave RSSI value and the disturbing wave RSSI value is 8 dB, and the CRC error number at that time is 1 bit. Therefore, the desired wave and the disturbing wave can be distinguished, and beam transmission and NULL transmission can be performed. Therefore, at this time, the unlocking of the transmission weight is released and the transmission weight can be locked again.

  In FIG. 13, there are three terminals (PS2, PS3, PS4) connected to the base station 202, and when the adaptive beam is transmitted to them, the terminal PS1 (the connected terminal of the base station 201) is It is a figure showing the state which has approached. In the base station 202, even when PS1 forming NULL is approaching and the transmission weight is unlocked, the buffering data is used as in the example of Table 1 to lock the previous transmission weight. The best transmission weight at can be used. As a result, the interference that the base station 202 gives to PS1 can be kept to a minimum, and the desired wave (adaptive beam) for PS2 to PS4 can be kept to a minimum, and all four units (PS1 to PS4) can communicate. Quality is improved.

  As described above, according to the present invention, it is possible to minimize interference with a terminal connected to another base station, and it is possible to ensure a minimum level with respect to the terminal connected to the base station. Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this, and can be used in a communication system other than the personal handyphone system.

The sequence chart at the time of the conventional handover. The figure showing the beam transmission and NULL transmission in an adaptive array base station when processing is performed according to the sequence of FIG. The figure showing the synchronous burst transmission after a hand-over when processing is performed according to the sequence of FIG. The functional block diagram of the adaptive array base station which is embodiment of this invention. The data format of the call channel TCH which is embodiment of this invention. 4 is a data format of a synchronous burst SYNC according to an embodiment of the present invention. 4 is a time slot example of synchronous burst beam transmission and synchronous burst NULL transmission according to an embodiment of the present invention. The figure showing the synchronous burst NULL transmission after the handover which is an embodiment of the invention. The figure showing the transmission weight lock state of the adaptive array base station which is embodiment of this invention. The figure showing transition of the desired wave and interference wave which are the embodiments of the present invention. The figure showing the transmission weight unlocking state of the adaptive array base station which is embodiment of this invention. The time slot example explaining the buffering method of the transmission weight information which is embodiment of this invention. The figure showing the state which used the buffered transmission weight information which is embodiment of this invention.

Explanation of symbols

PS1, PS2, PS3, PS4 Terminal 201 Base station 202 Adaptive array base station

Claims (4)

In a base station that performs communication in a time-space division multiple access method for mobile communication terminals to be transmitted,
Means for buffering transmission weight information;
When adaptive beam forming for the mobile communication terminal to be transmitted or null transmission to other base station connected terminal is not possible,
Adaptive beamforming for the mobile communication terminal to be transmitted or other base station connection terminal, which is optimum transmission weight information based on error information out of the transmission weight information buffered for a predetermined period Means for selecting transmission weight information at the nearest time before the occurrence when null transmission cannot be performed ,
Means for determining a transmission weight based on the optimal transmission weight information;
Means for transmitting to the mobile communication terminal to be transmitted using the transmission weight;
A base station characterized by comprising: The base station according to claim 1, wherein the error information is a CRC error number or a total of a CRC error number and a UW error number. A method of performing communication in a time-space division multiple access method for a mobile communication terminal to be transmitted,
Buffering transmit weight information;
When adaptive beam forming for the mobile communication terminal to be transmitted or null transmission to other base station connected terminal is not possible,
Adaptive beamforming for the mobile communication terminal to be transmitted or other base station connection terminal, which is optimum transmission weight information based on error information out of the transmission weight information buffered for a predetermined period Selecting transmission weight information at the nearest time before the occurrence when null transmission is not possible for
Determining the transmission weight based on the optimal transmission weight information;
Transmitting to the mobile communication terminal to be transmitted using the transmission weight;
A communication method comprising: 4. The communication method according to claim 3, wherein the error information is a CRC error number or a total of a CRC error number and a UW error number.

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