JP4689456B2 - Radio base station apparatus and radio communication control method - Google Patents

Description

  The present invention relates to a spatial division multiple access (SDMA) type radio base station apparatus and a radio communication control method.

  As is well known, SDMA is a technique for multiplex connection by sharing the same frequency among a plurality of terminals by irradiating a narrow beam with high directivity toward a specific user terminal (hereinafter referred to as a terminal). . The SDMA wireless communication system is equipped with an adaptive array antenna in order to form the above highly directional beam, and forms a beam with a radiation pattern having a different directivity for each terminal. Communication is performed with a plurality of terminals simultaneously by adjusting the phase and amplitude of each beam. As a result, the same channel is allocated to a plurality of terminals at the same time, thereby increasing the channel utilization efficiency.

Also, in recent wireless communication systems, adaptive modulation that mutually monitors the quality of radio waves transmitted and received between a radio base station apparatus and a terminal and automatically selects the best modulation method according to the quality fluctuation The method is used. Specifically, when the quality is good, a modulation method capable of high-speed communication (for example, 16QAM (16 Quadrature Amplitude Modulation)) is selected, and when the quality is bad, a low-speed modulation method (for example, QPSK (Quadrature Phase Shift Keying) is selected. In addition to the selection of the modulation scheme according to the communication environment, the transmission power of each other is also controlled. For details of the SDMA communication system, see, for example, Patent Document 1 below.
Special table 2001-50789 gazette

  By the way, in the radio base station apparatus provided in the above-described SDMA radio communication system, a correlation value or a phase difference is calculated from a received signal received and a reference signal (a known signal such as a training signal or a pilot signal). Based on the calculation result, a weight value (reception weight) for weighting the received signal is obtained. High autocorrelation in signals within one channel (eg, correlation between training signals at multiple locations within a channel) or cross correlation between multiple channels (eg, correlation between training signals at different channels) If it is low, it is possible to almost completely separate signals received from a plurality of terminals using the same channel using the above reception weight.

  However, the situation of the radio wave propagation path may change due to the movement of the terminal, and even if the terminal is stationary, the situation of the radio wave propagation path will also change due to the movement of a moving body such as a car around the terminal. There is. When fading (a phenomenon in which the signal strength or the like changes greatly in time and space in wireless communication) due to such a cause or other causes, signal separation using the reception weight becomes difficult. When signal separation cannot be performed, a transmission error occurs, for example, a retransmission request is transmitted from the radio base station apparatus to the terminal, and resources of the radio communication system are wasted.

  In the SDMA wireless communication system, when it becomes difficult to separate a signal transmitted / received between a specific terminal and a wireless base station apparatus, the signal is transmitted / received to / from another terminal using the same channel as that terminal. Since it is difficult to separate the signals, there is a possibility that communication between a plurality of terminals may be adversely affected, and it is considered that resources are wasted. Here, when the above fading occurs, the signal separation problem can be avoided to some extent by increasing the transmission power. However, when the transmission power is increased, interference with other terminals increases, and an increase in transmission power may affect the wireless communication system.

  The present invention has been made in view of the above circumstances, and a radio base station apparatus and a radio communication control method capable of reducing transmission errors and suppressing resource consumption such as retransmission when a situation of a propagation path deteriorates The purpose is to provide.

In order to solve the above problems, a radio base station apparatus according to the present invention, a radio base station apparatus for allocating available communication the same channel at the same time to a plurality of user terminals using a plurality of antenna elements, the received signal a correlation calculation unit for calculating a correlation, on the basis of the the correlation calculated by the correlation calculating section, and a control unit for controlling the switch Yaneru to the user terminal, the correlation calculation unit, from the user terminal From a plurality of user terminals including an autocorrelation calculation unit that calculates an autocorrelation that is a correlation between known signals at a plurality of locations in a channel assigned to the user terminal using a received signal received, and the user terminal A cross-correlation calculating unit that calculates a cross-correlation between signals of channels assigned to each of the plurality of user terminals using each received signal. It is characterized in.
The control unit may change a channel modulation method.
The control unit includes an empty channel management unit that manages the availability of the channel, and changes the channel assigned to the user terminal when the empty channel management unit determines that the channel is available It is characterized by performing control.
The control unit transmits a control signal for instructing a modulation scheme to the user terminal to which the channel is allocated when the empty channel management unit determines that there is no free channel. It is characterized by that.
The control unit refers to a first threshold for the cross-correlation calculated by the cross-correlation calculation unit and a second threshold for the auto-correlation calculated by the auto-correlation calculation unit when performing the control. It is characterized by.
The control unit performs the control when the cross-correlation calculated by the cross-correlation calculation unit is higher than the first threshold and the auto-correlation calculated by the auto-correlation calculation unit is lower than the second threshold. It is characterized by performing.
In order to solve the above-described problem, a wireless communication control method according to the present invention is a wireless communication control method for controlling communication capable of simultaneously assigning the same channel to a plurality of user terminals using a plurality of antenna elements. An autocorrelation calculating step of calculating an autocorrelation that is a correlation between known signals at a plurality of locations in a channel assigned to the user terminal using a received signal received from the user terminal; a correlation calculation step of calculating the cross-correlations between signals of channels assigned to each of the plurality of user terminals with each of the signal received from the user terminal, and the autocorrelation issued before hexane based on said correlation, characterized in that it comprises a control step of performing control of the channel assigned to the user terminal.
The control step is characterized by changing a channel modulation method.
A determination step for determining whether or not there is a vacancy in the channel, wherein the control step has a predetermined relationship with respect to a preset threshold and the vacancy in the channel is determined in the determination step. If it is determined that there is, control is performed to change the channel assigned to the user terminal.
The control step includes transmitting a control signal for instructing a modulation scheme to the user terminal to which the channel is allocated when it is determined in the determination step that there is no available channel. Features.
As the threshold, a first threshold for the cross-correlation calculated in the cross-correlation calculating step and a second threshold for the auto-correlation calculated in the auto-correlation calculating step are set.
The control step determines whether or not the correlation calculated in the correlation calculation step has a predetermined relationship with a preset threshold value, and the cross-correlation calculated in the cross-correlation calculation step indicates the first threshold value. And whether the autocorrelation calculated in the autocorrelation calculating step is lower than the second threshold value.

  According to the present invention, the correlation of the received signal received from the user terminal is calculated, and when this correlation has a predetermined relationship with a preset threshold, the channel assigned to the user terminal is changed. Therefore, when the propagation path condition deteriorates, there is an effect that transmission errors can be reduced and resource consumption such as retransmission can be suppressed.

  Hereinafter, a radio base station apparatus and a radio communication control method according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a radio communication system including a radio base station apparatus according to an embodiment of the present invention. As shown in FIG. 1, the radio communication system includes a plurality of user terminals (hereinafter referred to as terminals) 1 and 2 and a radio base station apparatus 3. For example, only one radio base station apparatus 3 is shown in FIG. 1 for the sake of simplicity. By transmitting and receiving radio signals between the terminals 1 and 2 and the radio base station apparatus 3, for example, a call is performed between the user of the terminal 1 and the user of the one terminal 2.

  The radio base station apparatus 3 includes an adaptive array antenna composed of a plurality of antenna elements 11a, 11b, and 11b, and forms a beam having a radiation pattern with different directivity for each of the terminals 1 and 2. By adjusting the phase and amplitude of each beam, the same channel is assigned to the terminals 1 and 2 at the same time to communicate with the terminals 1 and 2. That is, the wireless communication system of the present embodiment is an SDMA wireless communication system. Next, the internal configuration of the radio base station apparatus 3 will be described.

  FIG. 2 is a block diagram showing an internal configuration of the radio base station apparatus 3 according to the embodiment of the present invention. As shown in FIG. 2, the radio base station apparatus 3 includes antenna elements 11a, 11b, and 11c, an RF unit 12, a signal processing unit 13, a demodulation unit 14, a decoding unit 15, a SINR value calculation unit 16, a control unit 17, and a code. And a modulation unit 19. The antenna elements 11a, 11b, and 11c constitute an adaptive array antenna as described above. The RF unit 12 includes transmission / reception units 12a, 12b, and 12c that perform processing such as frequency conversion on signals received by the antenna elements 11a, 11b, and 11c or signals to be transmitted from the antenna elements 11a, 11b, and 11c. . These transmission / reception units 12a, 12b, and 12c are provided corresponding to the antenna elements 11a, 11b, and 11c, respectively.

  The signal processing unit 13 performs predetermined signal processing on the signal output from the RF unit 12 and outputs the processed signal to the demodulation unit 14. Further, the signal output from the modulation unit 19 is subjected to predetermined processing, and the processed signal is output to the RF unit 12. The signal processing unit 13 includes a synthesis unit 21, a reception weight calculation unit 22, an autocorrelation calculation unit 23, and a cross correlation calculation unit 24. In FIG. 2, only the configuration for processing the signal output from the RF unit 12 in the configuration of the signal processing unit 13 is illustrated, and the signal output from the modulation unit 19 is illustrated. Since the configuration for performing the predetermined processing is not directly related to the present invention, the illustration is omitted.

  The synthesizer 21 weights and synthesizes the signals output from the transmitter / receivers 12 a, 12 b, and 12 c of the RF unit 12 using the reception weight (weighting) obtained by the reception weight calculator 22. The reception weight calculator 22 calculates reception weights (W1, W2, W3) corresponding to the antenna elements 11a, 11b, and 11c. Although not shown in FIG. 2, the signal processing unit 13 is also provided with a transmission weight calculation unit that obtains a transmission weight that is a weight for a signal to be transmitted.

  The autocorrelation calculation unit 23 calculates the autocorrelation using the reception weight obtained by the reception weight calculation unit 22. Specifically, for example, considering the case where a channel between the radio base station apparatus 3 and the terminal 1 is established, the correlation between training signals at a plurality of locations in this channel is calculated. The autocorrelation calculated by the autocorrelation calculation unit 23 is supplied to the control unit 17. The cross-correlation calculating unit 24 calculates the cross-correlation using the signals combined by the combining unit 21. Specifically, for example, considering a case where a channel (same channel) is established between the radio base station apparatus 3 and the terminals 1 and 2, the correlation between the training signals between the channels is calculated. The autocorrelation calculated by the cross correlation calculation unit 24 is supplied to the control unit 17.

  The demodulator 14 demodulates the signal output from the synthesizer 21 of the signal processor 13 and outputs the demodulated signal to the decoder 15 and the SINR value calculator 16. The decoding unit 15 decodes the demodulated signal from the demodulation unit 14. The SINR value calculation unit 16 uses the demodulated signal output from the demodulation unit 14 to calculate (estimate) an SINR value that is quality information indicating the quality of radio signals from the terminals 1 and 2 and the like. Here, the SINR value is a value indicating a signal-to-interference and noise ratio, and the quality of a radio signal transmitted / received between the radio base station apparatus 3 and the terminals 1, 2 and the like. Is the quality information. The SINR value calculated by the SINR value calculation unit 16 is supplied to the control unit 17.

  The control unit 17 comprehensively controls the operation of the radio base station apparatus 3. Specifically, control of a radiation pattern of a beam from an adaptive array antenna including antenna elements 11a, 11b, and 11b, control of channel assignment with terminals 1 and 2, etc., communication with terminals 1 and 2 Various controls such as modulation scheme and transmission power control according to the environment are performed. The control unit 17 includes a free channel management unit 17a for managing whether or not there is a free channel to be set for the terminals 1 and 2 and the like. Based on the management result of the free channel management unit 17a, the control unit 17 Control channel assignment. Details of the channel assignment control will be described later.

  The encoding unit 18 encodes transmission data to be transmitted to the terminals 1, 2 and the like and outputs the transmission data to the modulation unit 19. The modulation unit 19 performs processing such as modulation of input data and outputs the processed data to the signal processing unit 13. The modulation unit 19 modulates input data using a modulation method such as 16QAM or QPSK. For the sake of simplicity, 16QAM and QPSK are given as examples of the modulation method in this specification, but the modulation method is not limited to this modulation.

  Next, a wireless communication control method according to an embodiment of the present invention will be described in detail. FIG. 3 is a flowchart illustrating an example of a wireless communication control method according to an embodiment of the present invention. In the following description, a case where radio signals are transmitted and received between the radio base station apparatus 3 and the terminal 1 will be described as an example. When a call request from the terminal 1 to the radio base station apparatus 3 is made or an incoming call response is made at the terminal 1 after notification of the incoming call from the radio base station apparatus 3 to the terminal 1, the terminal 1 and the radio base station apparatus 3 Session connection is made between the two (step S11). As a result, a channel is assigned to the terminal 1.

  When the session between the radio base station apparatus 3 and the terminal 1 is established, the control unit 17 of the radio base station apparatus 3 executes power control (step S12). Specifically, the modulation scheme and transmission power are dynamically controlled using the SINR value calculated by the SINR value calculation unit 16. This power control is also performed on the terminal 1 side. This control is a closed loop power control.

  When the power control is finished, the autocorrelation calculation unit 23 of the radio base station apparatus 3 calculates the autocorrelation using the reception weight obtained by the reception weight calculation unit 22 (step S13). Specifically, for example, the correlation between training signals at a plurality of locations in the channel assigned to the terminal 1 is calculated. The autocorrelation calculated by the autocorrelation calculation unit 23 is supplied to the control unit 17. When the autocorrelation is input from the autocorrelation calculation unit 23, the control unit 17 determines the communication environment with the terminal 1 (step S14).

  Next, the cross-correlation calculating unit 24 of the radio base station apparatus 3 calculates the cross-correlation using the signal output from the combining unit 21 of the signal processing unit 13 (step S15). This process is omitted if there is no other terminal (for example, terminal 2) connected to the radio base station apparatus 3 other than the terminal 1. Here, it is assumed that the terminal 2 is connected to the radio base station apparatus 3. In this process, specifically, the training signal of the channel assigned to the terminal 1 and the channel assigned to the terminal 2 (the same channel as the channel assigned to the terminal 1) The correlation between the training signal and the training signal is calculated. The cross-correlation calculated by the cross-correlation calculating unit 24 is supplied to the control unit 17.

  When the auto-correlation and the cross-correlation are input, the control unit 17 determines whether or not the cross-correlation is higher than a predetermined threshold and the auto-correlation is lower than the predetermined threshold (step S16). Here, the threshold value is set in the control unit 17 in advance, and the threshold value compared with the cross-correlation may be different from the threshold value compared with the auto-correlation. That is, a threshold for cross-correlation (first threshold) and a threshold for auto-correlation (second threshold) may be set. If the cross-correlation is not calculated in step S15, the control unit 17 determines only whether the autocorrelation is lower than a predetermined threshold.

  Here, when the autocorrelation is higher than the threshold value (second threshold value) and the cross-correlation is lower than the threshold value (first threshold value), between the radio base station apparatus 3 and the terminal 1 It is thought that there is little influence of fading. For this reason, for example, it is possible to separate a signal received from the terminal 1 from a signal received from another terminal to which the same channel as that assigned to the terminal 1 is assigned, using the reception weight. On the other hand, if the autocorrelation is lower than the above threshold (second threshold), or if the cross correlation is higher than the above threshold (first threshold), the influence of fading is considered large, and each terminal It will be difficult to separate signals received from

  If the determination result in step S16 is “NO”, since the signals received from the terminals can be separated, the process returns to step S13, and the autocorrelation calculation unit 23 calculates the autocorrelation. On the other hand, if the determination result in step S16 is “YES”, it is difficult to separate the signals received from the terminals, so that the control unit 17 has free space in other channels based on the management result of the free channel management unit 17a. It is determined whether or not there is (step S17). The other channels here are channels having different frequencies.

  If the determination result in step S17 is “YES”, that is, if there is a vacancy in another channel, the control unit 17 has a pending (undecided) channel assigned to the terminal 1 for the encoding unit. A message (control signal) indicating this is output as transmission data. This transmission data is transmitted from the antennas 11a, 11b, and 11c to the terminal 1 via the encoding unit 18, the modulation unit 19, the signal processing unit 13, and the RF unit 12. Next, the control unit 17 assigns an empty channel to the terminal 1 and reconnects it (step S18). When the above connection is completed, the radio base station apparatus 3 performs communication as usual (step S19).

  On the other hand, when the determination result of step S17 is “NO”, that is, when there is no vacancy in another channel, the control unit 17 instructs to lower the rank of the modulation scheme by one in order to suppress the transmission power of the terminal 1. (Control signal) is output as transmission data. Here, the rank of the modulation scheme is defined by the communication speed. For example, 16QAM capable of performing high-speed communication than QPSK is higher than QPSK. The transmission data output from the control unit 17 is transmitted from the antennas 11a, 11b, and 11c to the terminal 1 via the encoding unit 18, the modulation unit 19, the signal processing unit 13, and the RF unit 12 (step S20).

  When this transmission data (control signal) is received, the terminal 1 sets the modulation scheme for transmitting one signal to the next lower rank. Here, the transmission power of the terminal 1 or the transmission power of the radio base station apparatus 3 varies depending on the modulation scheme. Specifically, the transmission power increases as the modulation scheme has a higher rank, and the transmission power decreases as the modulation scheme has a lower rank. For this reason, the transmission power of the terminal 1 is suppressed by setting the modulation scheme to the rank one lower in the terminal 1. When the above process ends, the process returns to step S13. Note that the processing shown in FIG. 3 ends when the connection with the terminal 1 is interrupted.

  As described above, in this embodiment, the correlation (autocorrelation and cross-correlation or only autocorrelation) of the received signal received from the terminal is calculated, and this correlation has a predetermined relationship with a preset threshold value. In this case, control is performed to change the channel assigned to the terminal. For this reason, it is difficult to separate a signal received from the terminal 1 and a signal received from the terminal 2 to which the same channel as that assigned to the terminal 1 is assigned due to fading or the like. In addition, resources of the wireless communication system are not wasted due to retransmission or the like.

  Further, in the present embodiment, when there is no empty channel, control is performed to instruct the terminal 1 to specify a modulation method and suppress transmission power. When the transmission power of the terminal 1 decreases, interference with other terminals decreases, so the signal received from the terminal 1 and the terminal 2 to which the same channel as the channel allocated to the terminal 1 is allocated. Separation from the received signal is not difficult. Therefore, it is possible to suppress wasteful resource consumption of the wireless communication system.

  Although the radio base station apparatus and the radio communication control method according to the embodiment of the present invention have been described above, the present invention is not limited to the above-described embodiment, and can be freely changed within the scope of the present invention. For example, in the above-described embodiment, the SINR value is used as the quality information indicating the quality of the radio signal. However, other than this, a CNR (Carrier to Noise Ratio) value, SNR (Signal to Noise) is used. Ratio: signal to noise ratio) value, CIR (Carrier to Interference Ratio) value, or SIR (Signal to Interference Ratio) value can also be used.

It is a block diagram which shows schematic structure of a radio | wireless communications system provided with the radio base station apparatus by one Embodiment of this invention. It is a block diagram which shows the internal structure of the radio base station apparatus 3 by one Embodiment of this invention. 5 is a flowchart illustrating an example of a wireless communication control method according to an embodiment of the present invention.

Explanation of symbols

1, 2 Terminal 3 Radio base station apparatus 11a, 11b, 11c Antenna element 17 Control unit 17a Free channel management unit 23 Autocorrelation calculation unit 24 Cross-correlation calculation unit

Claims (12)

In a radio base station apparatus that performs communication capable of simultaneously assigning the same channel to a plurality of user terminals using a plurality of antenna elements,
A correlation calculation unit for calculating the correlation of the received signal;
Wherein, based on the correlation calculated by the correlation calculating section, and a control unit for controlling the switch Yaneru to the user terminal,
Equipped with a,
The correlation calculation unit
An autocorrelation calculating unit that calculates an autocorrelation that is a correlation between known signals at a plurality of locations in a channel assigned to the user terminal using a received signal received from the user terminal;
A cross-correlation calculating unit that calculates cross-correlation between signals of channels assigned to each of the plurality of user terminals using each of reception signals received from a plurality of user terminals including the user terminal;
The radio base station apparatus characterized by comprising.   The radio base station apparatus according to claim 1, wherein the control unit changes a channel modulation scheme.   The control unit includes an empty channel management unit that manages the availability of the channel, and changes the channel assigned to the user terminal when the empty channel management unit determines that the channel is available The radio base station apparatus according to claim 1 or 2, wherein control is performed.   The control unit transmits a control signal for instructing a modulation scheme to the user terminal to which the channel is allocated when the empty channel management unit determines that there is no free channel. The radio base station apparatus according to claim 3. The control unit refers to a first threshold for the cross-correlation calculated by the cross-correlation calculation unit and a second threshold for the auto-correlation calculated by the auto-correlation calculation unit when performing the control. The radio base station apparatus according to any one of claims 1 to 4, wherein: The control unit performs the control when the cross-correlation calculated by the cross-correlation calculation unit is higher than the first threshold and the auto-correlation calculated by the auto-correlation calculation unit is lower than the second threshold. The radio base station apparatus according to claim 5, wherein: In a wireless communication control method for controlling communication capable of simultaneously assigning the same channel to a plurality of user terminals using a plurality of antenna elements,
An autocorrelation calculating step of calculating an autocorrelation that is a correlation between known signals at a plurality of locations in a channel assigned to the user terminal using a received signal received from the user terminal;
A cross-correlation calculating step of calculating a cross-correlation between signals of channels assigned to each of the plurality of user terminals using each of reception signals received from a plurality of user terminals including the user terminal;
Based on said correlation and said autocorrelation issued before hexane, a control step for controlling the channel assigned to the user terminal,
A wireless communication control method comprising: 8. The wireless communication control method according to claim 7 , wherein the control step changes a channel modulation method. Determining whether there is a free channel,
In the control step, the channel assigned to the user terminal is determined when the correlation has a predetermined relationship with a preset threshold value and the determination step determines that the channel is free. claim 7 or 8 radio communication control method, wherein by performing control to change. The control step includes transmitting a control signal for instructing a modulation scheme to the user terminal to which the channel is allocated when it is determined in the determination step that there is no available channel. The wireless communication control method according to claim 9, wherein: The threshold value, wherein, characterized in that a first threshold value for said cross-correlation calculated by said cross correlation calculation step, and a second threshold for said autocorrelation calculated by said autocorrelation calculating step is set The wireless communication control method according to any one of claims 7 to 10 . The control step determines whether or not the correlation calculated in the correlation calculation step has a predetermined relationship with a preset threshold value, and the cross-correlation calculated in the cross-correlation calculation step indicates the first threshold value. The wireless communication control method according to claim 11 , further comprising: determining whether or not the autocorrelation calculated in the autocorrelation calculating step is lower than the second threshold.

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