JP2817290B2 - Power control method for digital radio transmission amplifier. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Controlling the transmission power of a power amplifier HPA that amplifies a multi-level QAM signal obtained by converting a digital signal to be transmitted into an analog signal and then quadrature amplitude modulating a wireless carrier with an analog multi-level signal. In order to reduce the power consumption of the multi-level QAM modulation transmitter, the purpose of this method is to control the transmission power of the final-stage power amplifier and to control the transmission power of digital radio transmission amplifiers. A transmission signal point recognition circuit that determines each signal point of the converted analog multi-valued signal by its vector length, and controls a DC bias that determines an operating point of the power amplifier according to the vector length of each signal point. A vector of analog multilevel signal points after converting a saturated output of the power amplifier into a digital signal to be transmitted to an analog signal. It is configured to control by length.

[Industrial applications]

The present invention relates to a digital multiplex radio system using multi-level quadrature amplitude modulation QAM, and more particularly to a control system of transmission power of a power amplifier at the last stage of a transmission device.

[Conventional technology]

Multi-level QAM modulation is widely used from the viewpoint of effective use of the frequency band for transmission signals, for example, 16-level QA
The M, 64-level QAM, and 256-level QAM signals have frequency utilization efficiencies of 1/2, 1/3, and 1/4 as compared with the 4-phase PSK modulation scheme having the same quadrature phase. However, since amplitude information is used in addition to phase information for signal transmission, linearity of amplitude is required in each circuit of the wireless device in order to transmit amplitude information accurately. Therefore, in each circuit, a so-called Back Off operation is performed in which each circuit operates at an operating point lower than the saturation output level by a certain level.

[Problems to be solved by the invention]

If the Back Off is set to, for example, 10 dB and taken by circuits such as amplifiers and mixers, the saturation output level of each circuit must be set to a value about three times the average level of the actual operating point, resulting in low power consumption of the device. It was in a state where it was difficult to convert. In particular, as shown in FIG. 5, the conventional digital radio transmission apparatus has a problem that it is difficult to reduce the power consumption of the last 16 power amplifiers HPA having the highest power level. The present invention is a multi-value QA
An object of the present invention is to provide a power control method for a digital radio transmission amplifier that controls the transmission power of a final-stage power amplifier HPA in order to reduce the power consumption of an M-modulation transmission device.

[Means for solving the problem]

The problem is that the amplitude value of the multi-level QAM modulation signal is different at each signal point of the transmission signal to be transmitted. For example, in a 16-level QAM signal,
In the code arrangement diagram of FIG. 3A, the signal point A (1
As shown in the table of FIG. 2B, the vector length of 1) is the square root of 18, the vector length of the signal points B (01) and C (10) is the square root of 10, and the vector length of the signal point D (00) is Focusing on the fact that the vector length is the square root of 2, the HPA that controls the saturation output of the 16 power amplifiers HPA at the final stage of transmission according to the vector length of the signal points A, B, C, and D of the signal to be transmitted. A saturation output control circuit 10 is provided. The control circuit 10 converts the digital signal to be transmitted into an analog signal as shown in FIG. 1 in consideration of the fact that a high-speed response in accordance with the changing speed of the signal point of the transmission signal can be performed. A transmission signal point recognition circuit 1 for discriminating each signal point A, B, C, D of the converted analog multi-valued signal by each vector length, and according to the vector length of each signal point A, B, C, D The present invention solves the above problem by providing an HPA saturation output control circuit 10 including a bias control circuit 2 for controlling a DC bias for determining an operating point of the power amplifier HPA.

In the principle diagram of FIG. 1 showing a basic configuration of a power control method of a transmission amplifier of a digital radio according to the present invention, reference numeral 1 denotes a signal necessary for multi-level QAM modulation of a radio carrier after converting a digital signal to be transmitted into an analog signal. This is a transmission signal point recognition circuit that determines each signal point A, B, C, D of an analog multilevel signal based on a predetermined vector length.

2 is a transmission end stage corresponding to a predetermined vector length of each signal point A, B, C, D of the multilevel signal recognized by the transmission signal point recognition circuit 1.
6 is a bias control circuit for determining a working point of the power amplifier HPA 6 and transmitting a bias control signal c for controlling a DC bias for determining its saturation output.

Reference numeral 10 denotes an HPA saturation output control circuit which includes a transmission signal recognition circuit 1 and a bias control circuit 2 and outputs a bias control signal c for controlling the saturation output of the 16 power amplifiers HPA at the end of transmission.

[Action]

The transmission signal point recognition circuit 1 inputs an analog multilevel signal after converting a digital signal to be transmitted into an analog signal, and sets each signal point A, B, C, D of the multilevel signal to a predetermined vector length. And sends it to the bias control circuit 2. The bias control circuit 2 generates a bias control signal c corresponding to a predetermined vector length of each signal point A, B, C, D of the analog multilevel signal. The power is sent to the 16 power amplifiers HPA at the final stage of transmission, and the DC bias that determines the operating point of the power amplifier HPA is controlled to control the saturation output of the power amplifier HPA.

Therefore, the saturation output of the power amplifier HPA changes according to the predetermined vector length of each signal point A, B, C, D of the multi-level signal for input multi-level QAM modulation.
The average power consumption of A is reduced and the problem is solved.

〔Example〕

FIG. 2 is a block diagram showing a configuration of a power control system of a digital radio transmission amplifier according to an embodiment of the present invention.
The figure is an explanatory view for explaining the operation, and FIG.
It is an arrangement diagram of each signal point of a 16-value QAM signal and (b) a relation table of each signal point and its vector length. FIG. 4 is an input / output characteristic diagram of the power amplifier HPA at the final stage of transmission.

FIG. 2 is a block diagram showing a configuration of a heterodyne transmission apparatus. A digital-to-analog converter D / A 12 that converts a digital quaternary signal output from the transmission logic conversion circuit 11 into an analog quaternary signal determines the spectrum of the 16-value QAM signal to be transmitted by the transmitting device. However, this spectrum information is also input to the HPA saturation output control circuit 10 to generate bias control signals c _{A to} c _D for controlling the saturation output of the final 16 power amplifiers HPA. The control circuit 10 includes a transmission signal point recognition circuit 1 and a bias control circuit 2. The transmission signal point recognition circuit 1 inputs Ich and Qch of analog quaternary signals for 16-level QAM modulation from the D / A 12, and outputs the signals. Code positions on the I and Q channels of the quadrature phase of the signal, for example, positions A (11), B (01), C (10), D in quadrant 11
(00) is detected based on the respective predetermined vector lengths, and the bias control circuit 2 generates bias control signals c _{A to} c _D for controlling the saturation output of the power amplifier HPA at the last stage based on the vector length of the signal.

FIG. 3A is a layout diagram of each signal point of the 16-value QAM signal, and FIG. 3B is a diagram showing each signal point A, B, C, D and its vector length (power of the signal). 6) is a relation table. FIG. 3 (b)
Each signal point A, B, of the transmission signal having the vector length shown in
The transmission signal point recognition circuit 1 recognizes C and D, and the bias control circuit 2 generates bias control signals c _{A to} c _D for controlling the saturation output of the final-stage power amplifier HPA based on the signal vector length. I have. The bias control circuit 2 has a ROM table 2
1 and a current limit or voltage limit circuit 22.
The table 21 sends information on current limitation or voltage limitation to the limiting circuit 22 according to the vector length corresponding to each of the code points A, B, C, D input from the transmission signal point recognition circuit 1,
Are converted into bias control signals c _{A to} c _D for controlling the saturation output of the power amplifier HPA at the final stage and output.

FIG. 4 shows the input / output characteristics of the power amplifier HPA at the final stage, and shows the actual state in which the saturation power of the power amplifier HPA is controlled in the direction of decreasing.

Therefore, the power control method of the transmission amplifier of the digital radio according to the present embodiment shown in FIG. 2 is based on the bias control signals c _{A to} c _D output from the HPA saturation output control circuit 10 and the power amplifier HP of the final stage.
Since the saturation output of A changes according to the predetermined vector length of each signal point A, B, C, D of the multilevel signal for input analog 16-level QAM modulation, the average consumption of the power amplifier HPA The power is reduced and there is no problem.

[Effects of the Invention] As described above, according to the present invention, the saturation output of the power amplifier HPA at the final stage is used for input multi-level QAM modulation by the bias control signal c output from the HPA saturation output control circuit. Since the average power consumption of the power amplifier HPA is reduced because it changes according to the predetermined vector length of each signal point of the analog multilevel signal, and the transmission power of the conventional power amplifier HPA is 0 dB, the 16-level QAM modulated signal In the case of, the transmission output of the power amplifier HPA is 10 log (1 × 4/16 + 0.55 × 8/16 + 0.11 × 4/16) = − 2.5
7dB, about half. Therefore the final stage power amplifier HPA
Power consumption is greatly reduced, and an effect that the power consumption of the transmitting device can be reduced is obtained.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a basic configuration of a power control system of a digital radio transmission amplifier according to the present invention. FIG. 2 is a block diagram showing a configuration of a power control system of a digital radio transmission amplifier according to an embodiment of the present invention. FIG. 3 is an explanatory diagram for explaining the operation of the embodiment of the present invention, FIG. 4 is an input / output characteristic diagram of a power amplifier at the final stage of transmission, and FIG. 5 is a block diagram of a conventional digital radio transmitting apparatus. is there. In the figure, 1 is a transmission signal point recognition circuit, 2 is a bias control circuit, 10 is an HPA saturation output control circuit, 13 is a multi-level QAM modulator, and 16 is a power amplifier HPA.

Claims (1)

(57) [Claims] 1. A system for controlling the transmission power of a power amplifier that amplifies a multi-level QAM signal obtained by quadrature amplitude-modulating a radio carrier with an analog multi-level signal after converting a digital signal to be transmitted into an analog signal, A transmitting signal point recognizing circuit (1) for discriminating each signal point (A, B, C, D) of the analog multi-level signal to be transmitted based on its vector length, and A bias control circuit (2) for controlling a direct current bias for determining an operating point of the power amplifier, wherein each signal point of an analog multilevel signal after converting a digital signal to be transmitted into an analog signal from a saturation output of the power amplifier; A power control method for a digital radio transmission amplifier, characterized in that control is performed with a vector length of (A, B, C, D).