JP2953411B2 - Transmission power control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transmission power control system for a satellite communication earth station.

[0002]

2. Description of the Related Art Conventionally, this type of satellite communication earth station employs a technique for detecting a reception C / N which is a reference for transmission power control.
A transmission power control method using the bit error rate of data to be transmitted and converting the bit error rate into C / N has been considered. FIG. 3 shows the configuration, in which the IF signal 21 of the received BPSK is
2, and is output as a demodulated received data signal 24 after error correction in the error correction unit 23. The bit error rate of a part of the demodulated signal is measured by the error rate measuring unit 25. The bit error rate is converted to C / N in the conversion unit 26. C / N difference detector 27
Calculates the C / N difference between the obtained C / N and the reference C / N. The control signal creation unit 28 creates a control signal from the C / N difference and inputs the control signal to the transmission power control unit 29. Transmission power control unit 2
9 calculates the variable attenuation based on the input control signal, and calculates the transmission data signal 3 modulated by the BPSK modulator 30.
The amount of attenuation of the variable attenuator 32 that attenuates 1 is controlled. Such a technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-280424.
Is described in Japanese Patent Application Publication No.

[0003]

In such a conventional technique, there is a problem that it takes time to measure the bit error rate when the data transmission speed is low. That is,
Normally, the operation C / N is relatively high, so that there is little error in data transmission, and the frequency of occurrence of erroneous bits is small, so it takes a long time, and when the data transmission speed is low, it takes more time. . Since C / N is detected from this bit error rate, C / N
It takes a long time to detect, and a problem arises that transmission power cannot be controlled at high speed.

[0004] It is an object of the present invention to speed up the C / N measurement time at the terrestrial communication earth station, calculate the accurate C / N, check the line condition, and optimally control the transmission power. It is another object of the present invention to provide a transmission power control method that can perform the above.

[0005]

According to the present invention, there is provided a satellite communication earth station apparatus comprising a digital demodulator using a Costas loop type carrier recovery circuit in a reception system and a transmission power control unit in a transmission system. Means for measuring the S / N from the reproduction carrier reproduced by the device, means for obtaining the reception C / N from the S / N, and controlling the transmission power in the transmission power control unit based on the reception C / N. Means. In particular, in the present invention, a band-pass filter for band-limiting a reproduced carrier reproduced by a digital demodulator, an FM demodulator for FM demodulating the reproduced carrier, and a circuit for measuring S / N from an output signal of the FM demodulator are provided. A C / N processing unit for obtaining a reception C / N from the S / N, and a control signal generation unit for generating a control signal for performing optimal transmission power level control from the obtained C / N. The transmission power in the transmission power control unit is controlled based on the control signal from the control signal generation unit. Here, the circuit for measuring the S / N comprises a low-pass filter for filtering the output of the FM demodulator, and a level detector for detecting the output level of the low-pass filter. N processing unit,
Recovered carrier C / N is obtained from S / N by S / N-C / N conversion based on demodulation sensitivity of FM demodulator, and received C
/ N is preferably obtained.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, reference numeral 1 denotes a digital demodulator using a Costas loop type carrier recovery circuit,
A hybrid 11 for dividing the F signal, and a divided IF
A mixer 13 for mixing one of the signals with a reproduced carrier from a carrier reproducing oscillator 12 and a mixer 1 for mixing the other of the IF signals with a reproduced carrier that has been phase-shifted by a π / 2 phase shifter 14.
5, low-pass filters 16 and 17 for filtering the outputs of the mixers 13 and 15, and a phase detector 18 for detecting the phase of these output signals and synchronizing the carrier reproduction oscillator.
And a combiner 19 that combines the output signals and outputs a received data signal.

A band-pass filter 2 for limiting the band of the reproduced carrier output from the carrier reproducing oscillator 12 is connected to the carrier, and an FM demodulator 3 for FM-demodulating the band-limited reproduced carrier. A low-pass filter 4 for passing the output signal of the FM demodulator 3 in a low-pass to obtain a level signal, a level detector 5 for measuring a signal-to-noise power ratio (S / N) based on the level signal, From the demodulation sensitivity of the FM demodulator 3, the reproduction carrier C / N is calculated by S / NC-N / C conversion (carrier level versus noise power), and the reception C / N is calculated. The C / N processing unit 6 for calculating, and the C / N calculated here
A control signal generator 7 for generating information for performing optimum transmission power level control from N is cascaded. Then, based on the control signal generated by the control signal generator 7, the transmission power controller 9 is configured to control the transmission power from the digital modulator 8 that modulates the transmission data signal.

According to this configuration, the output of the carrier reproducing oscillator 12 in the Costas loop type digital demodulator 1 is
The signal is demodulated by the FM demodulator 3 through the band-pass filter 2. Since the reproduced carrier is an unmodulated wave, the FM demodulator 3 FM-demodulates the carrier noise component so that the noise level equivalently represents the phase noise level of the reproduced carrier, and the S / N is detected based on this. Will be. That is, usually, the demodulation sensitivity of the FM demodulator 3 is an arbitrary fixed value, and the S level of the output of the FM demodulator 3 is an arbitrary fixed value. The output level when the reproduction carrier is input to the FM demodulator 3 is N
Calculated from the leveled measurements. Utilizing this measurement method, the output of the FM demodulator 3 is passed through a low-pass filter 4 and the N-level effective value is detected by a level detector 5.

Here, the phase noise level of the reproduced carrier is inversely proportional to the received C / N (S / N is proportional). That is, when the C / N is low, the reproduced carrier has a high phase noise near the carrier, and when this is FM-demodulated, the noise level is high (S / N is low). Conversely, when the C / N is high, the reproduced carrier is high. The carrier has a low phase noise level near the carrier (high S / N) and a low noise level after FM demodulation. As shown in FIG. 2, in FM theory, S / N vs. C / N
Are proportional to each other, it is possible to quantitatively determine the reception C / N from the measured reproduction carrier. This relationship is as follows. Reproduction carrier C / N∝Reproduction carrier S / N Reception C / N∝Reproduction carrier C / N Therefore, reception C / N∝Reproduction carrier S / N. The C / N processing unit 6 calculates the reception C / N from the conversion of S / N to C / N.

Then, the control signal generator 7 generates information for performing optimal transmission power level control from the calculated C / N, and uses this signal to transmit the information to the transmission power controller 8.
, The transmission power is controlled optimally, that is, in accordance with the reception C / N.

As described above, instead of directly measuring the bit error rate from the data signal, the reproduction carrier of the Costas loop type digital demodulator 1 is FM-demodulated, the S / N is obtained from the noise level, and the S / N- By calculating the theoretically accurate reception C / N from the reproduction carrier C / N obtained by the C / N conversion, the FM demodulator 3 hardly takes any time for the demodulation operation. The speed is increased as compared with the method of calculating C / N from the bit error rate of the signal. Thereby, high-speed control of transmission power can be realized. Further, since the C / N value is used as an element for generating control information, accurate transmission power control can be performed.

[0012]

As described above, according to the present invention, the C / N is not determined from the bit error rate, but the S / N is measured from the reproduced carrier of the Costas loop type digital demodulator.
Further, the reception C / N is calculated from this S / N, and this C / N
Since the transmission power is controlled on the basis of
There is an effect that the measurement of N does not take much time, and that accurate and optimal control of transmission power can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a transmission power control system according to the present invention.

FIG. 2 is an S / NC / N characteristic diagram.

FIG. 3 is a block diagram showing an example of a conventional transmission power control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Costas loop type digital modulator 2 Band pass filter 3 FM demodulator 4 Low pass filter 5 Level detector 6 S / N processing part 7 Control signal generation part 8 Digital modulator 9 Transmission power control part

Claims (4)

(57) [Claims] 1. A satellite communication earth station device comprising a digital demodulator using a Costas loop type carrier recovery circuit in a reception system and a transmission power control unit in a transmission system, wherein a reproduction carrier reproduced by the digital demodulator is used. Means for measuring a signal-to-noise power ratio (S / N); means for obtaining a received carrier level-to-noise power ratio (C / N) from the S / N; and transmission power control based on the received C / N. Means for controlling transmission power in the unit. 2. A satellite communication earth station device comprising a digital demodulator using a Costas loop type carrier reproducing circuit in a receiving system and a transmission power control unit in a transmitting system, wherein a reproduced carrier reproduced by the digital demodulator is used. A band-pass filter for band limitation, an FM demodulator for FM demodulating a reproduced carrier, a circuit for measuring S / N from an output signal of the FM demodulator, and a C / N process for obtaining a reception C / N from the S / N And a control signal generator for generating a control signal for performing optimal transmission power level control from the obtained C / N, and the transmission power controller based on a control signal from the control signal generator. A transmission power control method characterized by controlling transmission power in a transmission. 3. A circuit for measuring S / N comprises a low-pass filter for filtering an output of an FM demodulator, and a level detector for detecting an output level of the low-pass filter. 3. The transmission power control method according to claim 2, wherein the transmission power control method is obtained by calculating a demodulation sensitivity of the demodulator and a detected level value. 4. A configuration wherein the C / N processing section obtains a reproduction carrier C / N from the S / N by S / N−C / N conversion based on the demodulation sensitivity of the FM demodulator, and further obtains a reception C / N. 4. The transmission power control method according to claim 2, wherein