JP4203529B2 - Radio apparatus and antenna directivity control method - Google Patents

Description

  The present invention relates to a spatial division multiple access (SDMA) wireless device and an antenna directivity control method.

  A conventional SDMA wireless communication system includes an adaptive array antenna (hereinafter referred to as AAA (Adaptive Array Antenna)) in a wireless base station, and forms a transmission beam having a radiation pattern having a different directivity for each user terminal (hereinafter referred to as a terminal). Then, radio waves for multiple terminals are transmitted at the same time. When a radio base station forms a radiation pattern of a certain terminal, it directs the direction of the terminal of the transmission partner by adaptive beam forming (Adaptive Beam Forming), and by adaptive null steering (Adaptive Null Steering). A null is formed in the direction of the other terminal. As a result, the same call channel (TCH) is allocated to a plurality of terminals while maintaining the call quality by keeping the CIR (Carrier to Interference Ratio) of the terminal at a certain value (for example, 15 dB) or more, thereby improving the channel utilization efficiency. Yes.

In general, in a radio base station, a transmission output signal Y (t) for each antenna to a plurality of terminals is obtained by multiplying an input signal vector X (t) and a transmission weight vector Wij by Y (t) = X (t) × Wij can be expressed. The transmission weight vector W is a vector having weighting factors Wij (j = 1, 2, 3,..., N) as elements.
Here, consider a case where two user terminals (hereinafter referred to as terminals) are spatially multiplexed by an SDMA communication method in a radio base station including four antennas. It is assumed that transmission weight vector W1 (w11, w12, w13, w14) for one terminal and transmission weight vector W2 (w21, w22, w23, w24) for the other terminal.
The weighting factor for each terminal is normalized by equation (1) in the AAA algorithm.

Then, by scaling the transmission weight vector, power to be transmitted from each antenna to a user terminal (hereinafter referred to as a terminal) is determined. Scaling is performed by equation (2).

While performing such scaling, as a directivity control of a plurality of antennas, a technique for controlling the transmission strength in addition to the directivity of the transmission signal according to the received signal strength from each terminal has been reported (for example, Patent Document 1).
Japanese Patent No. 3167682

  However, in the case of the above prior art, the directivity for each antenna is controlled, but there are problems in improving the transmission power efficiency and CIR stabilization for each terminal. Further, in Expression (2), the ratio of the transmission weight vectors for the four antennas for the two terminals is W1 (1/5, 2/5, 2/5, 4/5), W2 (5/6, 3 / 6, 1/6, 1/6), and scaling this, (1/9, 2/9, 2/9, 4/9), (5/10, 3/10, 1/10) , 1/10). Since the transmission power to each terminal is proportional to the sum of the squares of the components of W, the transmission power to each terminal varies considerably from terminal to terminal. This is due to the fact that the scaling value is different for each terminal. When scaling is performed with different scaling factors in this way, the balance of transmission weight vectors is lost between terminals multiplexed by SDMA. As a result, there is a problem that the CIR fluctuates for each terminal, and the overall call quality of the terminal deteriorates.

  Therefore, the present invention has been made in view of the above circumstances, and in the SDMA communication system, the transmission weight vector of each terminal is scaled by the same value, CIR fluctuation for each terminal is eliminated, and the signal is supplied to each terminal. An object of the present invention is to provide a radio apparatus and an antenna directivity control method capable of maximizing power to be transmitted.

The radio apparatus according to claim 1, wherein an array antenna including a plurality of antennas, and an adaptive beam forming and adaptive null steering for controlling directivity of the array antenna are used to transmit a transmission beam having an individual radiation pattern for each of a plurality of terminals. Control means for performing control, and in a wireless device that performs wireless communication with each terminal by the SDMA method, the control means has a CIR (Carrier to Interference Ratio) value of each terminal. A terminal-specific transmission weight vector composed of a weighting factor corresponding to each antenna is calculated so as to be equal to or greater than a value necessary for maintaining a good quality of service (QOS), and the calculated value is calculated for each terminal. multiplied by the same value to the transmission weight vector (scaled transmit weight vectors the calculated with the same value), Value serial multiplication, the out of the sum of the absolute value obtained by adding to each of the antenna of the weighting factor of each terminal, a maximum value, characterized in that.

  In this way, by scaling the transmission weight vector of each terminal composed of the weight coefficient of each terminal by the same value, the CIR of each terminal can be stabilized as a whole, and the variation of CIR for each terminal can be eliminated. Thereby, the call quality of a plurality of terminals spatially multiplexed by the SDMA communication method can be stabilized.

In addition, the absolute value of the weighting factor of each terminal is added for each antenna, and the transmission weight vector of each terminal is scaled by the maximum value among these added values, thereby further stabilizing the CIR of each terminal as a whole. Can do.

The antenna directivity control method according to claim 2, comprising: an array antenna including a plurality of antennas; and an individual radiation pattern for each of a plurality of terminals by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna. Is an antenna directivity control method in a radio apparatus that performs radio communication with each terminal using the SDMA method, and the CIR (Carrier to Interference Ratio) value of each terminal is QOS of each terminal. A process of calculating a transmission weight vector for each terminal composed of a weighting factor corresponding to each antenna so as to be equal to or greater than a value necessary for maintaining a good (Quality Of Service), and the calculation for each terminal. and a step of multiplying the same value for transmit weight vector, only contains the values for the multiplication, the each terminal Of the addition value of the absolute value obtained by adding to each of the antenna Kiomomi coefficients, a maximum value, characterized in that.

  According to the present invention, a terminal-specific transmission weight vector composed of a weighting factor corresponding to each antenna is calculated, the absolute value of the weighting factor of each terminal is added for each antenna, and By scaling the transmission weight vector of the terminal, fluctuations in CIR can be eliminated and stabilized. In addition, the power supplied to the terminal can be maximized.

Hereinafter, a preferred embodiment of a wireless device and an antenna directivity control method of the present invention will be described in detail with reference to FIG.
FIG. 1 is a block diagram showing a configuration of radio base station apparatus (radio apparatus) 100 according to the present embodiment. A radio base station apparatus (hereinafter, simply referred to as a radio base station) 100 illustrated 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 are used for multiplex communication with two terminals by the SDMA method will be described as an example. However, three or more terminals are multiplexed by the SDMA method. The same applies to the case.

  In FIG. 1, the radio base station 100 includes an array antenna including four antennas ANT1 to ANT4, and these antennas ANT1 to ANT4 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 radio unit 4 includes first to fourth receiving units 6 and first to fourth transmitting units 8, and the first to fourth receiving units 6 are provided corresponding to the antennas ANT1 to ANT4, respectively. The first to fourth transmitters 8 are provided corresponding to the antennas ANT1 to ANT4, respectively. The first to fourth reception units 6 and the first to fourth transmission units 8 are connected to the antennas ANT1 to ANT4 via the transmission / reception changeover switch 2, respectively.

  The receiving unit 6 includes a low noise amplifier (not shown), a down converter, and an A / D converter. The receiving unit 6 is 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 (not shown), an upper converter, and a power amplifier. The transmission unit 8 is 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 last stage of each of the first to fourth receiving units 6 are combined so that, for example, a D / U (Desire / Undesire), 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. Thereby, directivity can be given to 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 a weighting factor for each of the multipliers # 1_10 and # 2_10 of the first to fourth transmitters 8. 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, The function to calculate the received signal coefficient vector (Spatial Signature), the function to calculate the rate of change of the received signal coefficient vector, the function to statistically process the received intensity (RSSI) from each terminal, the function to scale, etc. Have. 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) Allocation of channels for space division multiplexing is performed so that the quality of service (QOS) of a call when space division multiplexing is performed corresponds to the QOS of a 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, the scaling of the transmission weight vector by the control unit 14 will be described. Here, consider a case where two terminals are spatially multiplexed by an SDMA communication system in a radio base station having four antennas.

The control unit 14 scales the normalized transmission weight vector of each terminal by Expression (3).

  For example, in Expression (3), the ratio of the transmission weight vector for each terminal from the four antennas ANT1 to ANT4 is the transmission weight vector W1 (w11, w12, w13, w14) = (1/5, 2) for one terminal. / 5, 2/5, 4/5), W2 (w21, w22, w23, w24) = (5/6, 3/6, 1/6, 1/6), the scaling factor is “30”. / 31 ". With this scaling, the terminal with the transmission weight vector W1 ((30/31) · (1/5, 2/5, 2/5, 4/5)), and the terminal with the transmission weight vector W2 ((30/31) (5/6, 3/6, 1/6, 1/6)) In this way, since the transmission weight vector to each terminal is scaled by the same value by scaling with the same value (here, “30/31”) for each terminal, the CIR variation of each terminal as a result. Can be eliminated, and the power reaching each terminal can be maximized.

  Here, the fluctuation | variation of CIR by the simulation of this Embodiment is demonstrated. FIG. 2 shows the CIR difference between the terminals in the conventional scaling, and FIG. 3 shows the CIR difference between the terminals in the scaling of the present invention. In each figure, the vertical axis represents the frequency distribution probability, and the horizontal axis represents the CIR difference between terminals. As shown in FIG. 2, it can be seen that the conventional scaling has a variation of CIR of +/− 5 dB between terminals. On the other hand, when the scaling according to the present invention is performed, it corresponds to 0 dB as shown in FIG. 3, and it can be seen that there is no CIR variation between terminals.

  In this way, the transmission weight vector for each terminal consisting of the weighting coefficient corresponding to each antenna is calculated, the absolute value of the weighting coefficient for each terminal is added for each antenna, and the maximum value among these addition values is used for each terminal. By scaling the transmission weight vector, CIR fluctuations can be eliminated and stabilized. In addition, the power supplied to each terminal can be maximized. Thereby, the call quality of a plurality of terminals spatially multiplexed by the SDMA communication method can be stabilized.

  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 the block diagram which showed the structure of the radio base station apparatus which concerns on this Embodiment. It is the figure which showed the CIR difference between each terminal in the conventional scaling. It is the figure which showed the CIR difference between each terminal in the scaling of this invention.

Explanation of symbols

2: Transmission / reception selector switch, 4: Wireless unit,
6: reception unit, 8: transmission unit,
10: multiplier, 12: modem unit
14: Control unit, 16: Line interface unit,
ANT1 to ANT4: antenna, 100: radio base station apparatus (radio apparatus).

Claims (2)

An array antenna comprising a plurality of antennas, and a control means for performing control to form a transmission beam of an individual radiation pattern for each of a plurality of terminals by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna. In a wireless device that performs wireless communication with each of the terminals by the SDMA method,
The control means includes a weight corresponding to each antenna so that a CIR (Carrier to Interference Ratio) value of each terminal is equal to or greater than a value necessary for maintaining a good quality of service (QOS) of each terminal. Calculate the transmission weight vector for each terminal consisting of coefficients,
For each terminal , multiply the calculated transmission weight vector by the same value,
The wireless device , wherein the value to be multiplied is the maximum value among the added values obtained by adding the absolute value of the weighting factor of each terminal for each antenna . Each terminal includes an array antenna including a plurality of antennas, and forms a transmission beam having an individual radiation pattern for each of a plurality of terminals by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna. An antenna directivity control method in a wireless device that performs wireless communication with
Each terminal is composed of a weighting factor corresponding to each antenna so that a CIR (Carrier to Interference Ratio) value of each terminal is equal to or greater than a value necessary for maintaining a good quality of service (QOS) of each terminal. A process of calculating a transmission weight vector of
For each of the terminals, seen including a the steps of multiplying the same value for transmit weight vectors the calculated,
The antenna directivity control method characterized in that the value to be multiplied is the maximum value among the added values obtained by adding the absolute value of the weighting factor of each terminal for each antenna.

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