JP2008017517A - Radio device and antenna directivity control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio device and an antenna directivity control method maximizing the transmission power from an antenna up to a transmission capability. <P>SOLUTION: A control section 14 scales each normalized transmission weighting vector so that transmission output power of any of N antennas reaches the maximum transmission power value P[mW]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio apparatus and an antenna directivity control method.

Conventionally, in an AAA (Adaptive Array Antenna) base station for digital mobile communication composed of N antennas, a transmission output signal Y (t) for each antenna is obtained by multiplying an input signal vector X (t) by a transmission weight vector W. Y (t) = X (t) × W can be expressed. Here, the transmission weight vector W is a vector having weighting factors wj (j = 1, 2, 3,..., N) as elements. In general, each weighting factor of N antennas is normalized by Expression (1) in the algorithm in AAA.
W12 + W22 + W32 + ... + Wn2 = 1 (1)
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.

The scaling is performed according to 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 is a problem in terms of optimizing the transmission power from each antenna. Conventionally, scaling has been performed based on Equation (2) so that the total output from each antenna is always constant. For example, in the equation (2), when the ratio of transmission weight vectors for four antennas is W (1/5, 2/5, 2/5, 4/5), and scaling this, (1 / 9, 2/9, 2/9, 4/9).

  In general, the transmission power of each antenna is proportional to the square of the W component. Therefore, in the above example, the transmission power of the fourth antenna having the largest weight coefficient (component) is the maximum ((4/9) 2). Usually, the value obtained by multiplying the square of the component by the maximum transmission power Pmax is used as the transmission power. This means that the fourth antenna transmits with power of Pmax × (16/81), and this does not use the transmission output capability of the antenna 100%. As described above, the conventional scaling does not make maximum use of the transmission capability of the antenna.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radio apparatus and an antenna directivity control method capable of maximizing until the transmission power from the antenna becomes equal to the transmission capability.

The radio apparatus according to claim 1, wherein an array antenna including a plurality of antennas, and transmission control for forming a transmission beam having a predetermined radiation pattern to a terminal by adaptive beam forming and adaptive null steering for controlling directivity of the array antenna. In the wireless apparatus that performs wireless communication with the terminal, the transmission control means includes an absolute value of a maximum weight coefficient among weight coefficients set for each of the plurality of antennas. In this way, the transmission weight vector having the weighting factor as a component is scaled. Thus, among the weighting factors set for a plurality of antennas, the maximum weighting factor is represented by the weighting factor. By scaling the transmission weight vector, the largest weighting factor among the N antennas The transmission power can be maximized from the antenna to the full transmission capability. By maximizing the transmission power and transmitting, the power reaching the terminal can be increased, the downlink interference suppression capability can be maintained to the maximum, and the call quality of the terminal can be kept better.

  The antenna directivity control method according to claim 2, comprising an array antenna composed of a plurality of antennas, and performing control of power transmitted to the terminal by adaptive beamforming and adaptive null steering for controlling the directivity of the array antenna, A method for controlling antenna directivity in a wireless device that performs wireless communication with a terminal, wherein the weight is determined by an absolute value of a maximum weighting factor among weighting factors set for each of the plurality of antennas. Control is performed so that a transmission weight vector having coefficients as components is scaled.

  Since the radio apparatus and the antenna directivity control method of the present invention scale the transmission weight vector represented by the weighting factor with the largest weighting factor among the weighting factors set for a plurality of antennas, Among the antennas, the transmission power from the antenna having the largest weight coefficient can be maximized, and optimization can be performed so that the power reaching the terminal is 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 100 (radio apparatus) 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 communication is performed with a terminal using four antennas will be described as an example.

  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 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 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 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, the weighting coefficient (complex number) input from the modem unit 12 is set. The set weight coefficient and data to be transmitted to the terminal are converted to analog by the D / A converter, and transmitted from the antenna corresponding to itself through the upper converter and the 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 signal converted in the final stage of each of the first to fourth receiving units 6 has a maximum D / U (Desire / Undesire; desired wave / interference wave), that is, a CIR (Carrier to Interference Ratio) value, for example. Is synthesized and demodulated.

(2) The phase of each received wave 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 phase of the signal supplied to each of the 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 first to fourth transmitters 8. By setting the weighting factor, a null can be formed in an arbitrary 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, a weighting factor for forming a radiation pattern at the time of reception, a function of scaling, and the like. Specifically, 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. The reception signal coefficient vector represents reception information (amplitude and phase) of the terminal.

  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 modem 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. The control unit 14 determines the normalized transmission weight vector by using the expression (3) so that the transmission output power at any one of the N antennas is the same as the maximum transmission power value P [mW]. ) To scale. At this time, the transmission output power of each antenna from the radio base station 100 is expressed by Equation (4).

  For example, in Expression (3), when the ratio of the transmission weight vectors for the four antennas ANT1 to ANT4 is W (1/5, 2/5, 2/5, 4/5), the maximum component is “ Since it is 4/5 ", when this is scaled, it is represented by (1/4, 2/4, 2/4, 4/4).

Here, the transmission power of ANT4 having the largest weight coefficient is the maximum ((4/4) 2 = 1)). At this time, the maximum transmission power Pmax from the antenna ANT4 of the radio base station 100 becomes P [mW] from the equation (4), and it can be seen that the maximum output power can be output.

  In this way, by scaling the transmission weight vector represented by the weighting factor with the maximum weighting factor among the weighting factors set for the plurality of antennas, the weighting factor is equal to one among the N antennas. Transmission power can be maximized from the largest antenna to the same transmission capability as the hardware (power amplifier). As long as the ratio of the weighting factors of each antenna does not change, the downlink interference suppression capability does not change. Therefore, the radio base station 100 according to the present embodiment maintains the downlink interference suppression capability to the maximum and reaches the terminal. By increasing the power, the call quality of the terminal can be kept better.

  FIG. 2 is a table showing the results of the simulation of the present embodiment. In this simulation, the average downlink power was obtained as the power reaching the user by the four transmission methods of modes 1 to 4. The simulation conditions are shown below. The number of antennas is four, and a 125 mW power amplifier (PA) is mounted on one antenna. The number of desired users is 1, and the number of interfering users is 1. The wireless environment is 100% Rayleigh fading. The required upstream SNR is 20 dB and the required upstream CIR is 10 dB. Mode 1 transmits with one antenna equipped with 500mW PA. Mode 2 is selective diversity transmission with 4 antennas each equipped with 500mW PA. In mode 3, the total output of the four antennas is fixed at 125 mW (125 mW PA is installed in each transmission system). Mode 4 (corresponding to the present embodiment) is 500 mW Optimum Power Mode (125 mW PA is installed in each transmission system). The number of transmission bursts is 10,000.

  “Average Downlink Power” as a result of simulation for modes 1 to 4 under the above conditions is shown in FIG. The values of each mode are all shown as relative power with respect to the value of mode 1. Further, when calculating “Average Downlink Power”, the average power is calculated by adding the downstream powers of 10000 bursts with a linear scale, and then converted to the dB scale.

  As shown in FIG. 2, the result of mode 4 corresponding to this embodiment is excellent. The result of mode 2 is better than that of mode 4, but this is because each antenna requires 500 mW of PA, and there is a problem that the equipment cost is high.

It is a block diagram which shows the structure of the radio base station apparatus which concerns on embodiment of this invention. It is a table | surface which shows the simulation result of embodiment of this invention.

Explanation of symbols

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

Claims (2)

An array antenna comprising a plurality of antennas, and transmission control means for forming a transmission beam of a predetermined radiation pattern to the terminal by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna, and Wireless devices that communicate wirelessly between
The transmission control means scales a transmission weight vector having the weight coefficient as a component by an absolute value of a maximum weight coefficient among weight coefficients set for each of the plurality of antennas. A wireless device. An antenna in a radio apparatus that includes an array antenna including a plurality of antennas, performs power control to be transmitted to a terminal by adaptive beam forming and adaptive null steering for controlling the directivity of the array antenna, and performs radio communication with the terminal A directivity control method,
Control is performed so that a transmission weight vector having the weighting factor as a component is scaled according to an absolute value of a maximum weighting factor among weighting factors set for each of the plurality of antennas. Antenna directivity control method.

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