JPH09261147A - Reception c/n detection system, detector and transmission power control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the system in which accurate transmission power control is realized to improve the quality of a communication line based on accurate C/N detected when the C/N of a received pilot signal is decreased. SOLUTION: A received pilot signal is FM-demodulated by an FM demodulator 12 and an S/N processing section 15 obtains an S/N from an obtained noise level and a signal level based on a demodulation sensitivity of the FM demodulator. Furthermore, a C/N processing section 16 uses an S/N-C/N correlation characteristic based on the demodulation sensitivity to convert the S/N into the C/N. Thus, even when the C/N is low, the C/N is accurately measured and transmission output power is controlled optimizingly depending on a line state by using the accurate C/N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission power control system in a communication station, and particularly, it is applied to a satellite communication earth station device to detect a suitable reception C / N and control the transmission power based on the detected value. The present invention relates to a transmission power control method for performing.

[0002]

When configuring a communication line between a central station and a large number of small earth stations, such as a satellite communication system, it is necessary to control the transmission power of each station in order to cope with various obstacles in the communication line. Is required. In this case, since it is not economically effective to equip each of the small earth stations with a transmission power control device, a transmission power control device is installed in the central station to monitor the state of the communication line with the small earth stations and A method of controlling the transmission power of the central station to the station may be taken. For example, in the technique described in Japanese Patent Laid-Open No. 2-280424, C / N (carrier level / noise power ratio) is calculated from a received pilot signal from a small earth station, as shown in the partial structure of FIG. C in the measurement unit 31
/ N is detected, and the received C
/ N and the reference C / N 33 are calculated, and the transmission power control is performed based on the control unit 34 controlling the attenuator 35 provided in the transmission system so that the difference becomes zero or less than a predetermined value. .

To detect such a received C / N, a level detection system has been used conventionally. That is, the received pilot signal level is subjected to peak detection, and the received C / N is obtained from the ratio of the carrier level and the noise level obtained by this detection. When the C / N is low, the transmission power is increased, and when the C / N is high, the transmission power is suppressed to ensure the quality of the communication line.

[0004]

In such a conventional reception C / N detection method, an accurate C / N is detected when the C / N is low.
There is a problem that the value cannot be detected. The reason is that C
Since the peak of the pilot signal level is detected to detect / N, all signals input to the detector are detected, and when C / N is high, the input signal component is almost the carrier component. Therefore, the carrier level can be taken as C / N. However, when the ratio of the carrier component and the noise component is close to each other, that is, when the C / N is low, the carrier level and the noise level cannot be distinguished, and it becomes difficult to accurately detect the C / N. Therefore, the reliability of the transmission power control when the C / N is low is also lowered, and it is difficult to improve the quality of the communication line.

An object of the present invention is to realize accurate transmission power control for detecting an accurate C / N even when the C / N becomes low and improving the quality of a communication line based on the detected C / N. It is to provide a method capable of doing so.

[0006]

A received C / N detection method of the present invention detects an S / N by FM demodulating a received pilot signal and based on the S / N-C / N correlation characteristic of FM demodulation sensitivity. The C / N is detected by converting the S / N to C / N. Further, the reception C / N detection device of the present invention calculates the S / N from the FM demodulation means for FM demodulating the reception pilot signal and the signal level obtained from the demodulation sensitivity of this FM demodulation means and the FM demodulated noise level. A means for calculating and a means for converting this S / N into C / N based on the S / NC-C / N correlation characteristic of the FM demodulation sensitivity and detecting C / N are provided.

Further, the transmission power control method of the present invention detects the S / N by FM demodulating the received pilot signal, and based on the S / N-C / N correlation characteristic of the FM demodulation sensitivity, the S / N is detected.
Is converted into C / N, C / N is detected, and the transmission power is controlled based on this C / N.

According to the present invention, the received pilot signal level is not directly peak-detected, but FM demodulation is performed using the received pilot signal as a carrier, and the S / N is calculated from the noise level.
And theoretically correct C by S / N-C / N conversion.
Since / N is calculated, there is no case where the noise level and the signal level cannot be clearly distinguished as in the case of low C / N, an accurate C / N is required, and transmission power control is possible. .

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the reception C / N of the present invention.
1 shows a satellite communication system to which a transmission power control system equipped with a detection system is applied, in which a central station C and a small earth station T1,
T2, ... Are wirelessly connected to each other via a satellite S. The central station C detects the C / N in the received signal during communication with each small earth station, and controls the transmission power of the own station to the small earth station based on this C / N. .

FIG. 2 is a block diagram of a main part including a C / N detection system of the central office C and a transmission power control system including the C / N detection part. The C / N detection system 1 includes a bandpass filter 11 that band-limits a received pilot signal that is an unmodulated wave.
And FM for demodulating the band-limited pilot signal by FM
A demodulator 12, a low-pass filter 13 for low-passing the demodulated signal, a level detector 14 for detecting the level of the low-pass signal, and S based on the detected level.
S / N processing unit 15 for calculating the S / N and the calculated S / N
And a C / N processing unit 16 for obtaining C / N from
Then, the transmission power control system 2 controls the transmission power by the control unit 21 controlling the attenuator 22 inserted in the transmission system based on the C / N detected by the C / N detection system 1. .

In this configuration, in the C / N detection system 1, the received pilot signal is band-limited through the band-pass filter 11, FM demodulated by the FM demodulator 12, and output from the low-pass filter 13. Usually, the demodulation sensitivity of the FM demodulator has an arbitrary known setting, so that the signal level (S level) of the FM demodulation output has an arbitrary known value. Therefore, the noise component is output by passing the noise component in the band pass filter 11, performing FM demodulation of this, and outputting it from the low pass filter 13.
Therefore, by detecting this noise component in the level detector 14, the value of the noise level (N level) (RMS
Value) is detected.

Then, in the S / N processing section 15, S / N is calculated from the ratio between the detected noise level and the known signal level.
Calculate N (Signal to Noise Ratio). Further, in the C / N processing unit 16, between the S / N and the C / N according to the FM theory, as shown in FIG.
The calculated S / N is converted to C / N by utilizing the mutual linearity characteristic as described above. Thereby, C
The C / N is calculated in the / N processing unit 16.

As described above, in the C / N detection system 1, the carrier level of the pilot signal is not measured by peak detection, but the S level is first calculated from the noise level obtained by FM demodulating the pilot signal and the known signal level. Since / N is obtained, the noise level can be clearly detected, and the S / N can be obtained accurately. And this S / N is S / N-
Since C / N is calculated by converting it into C / N based on the C / N correlation characteristic, even when the C / N is low, it is impossible to distinguish the noise level and the carrier level as in the level peak detection. The accuracy of C / N does not decrease.

Then, in the transmission power control system 2 of FIG. 2, the line status with the corresponding small earth station is calculated based on the C / N output from the C / N processing unit 16, and the line status is calculated. The control unit 21 controls the transmission system attenuator 22 of its own station on the basis of the data of 1 to set the transmission power optimally. In this case, in the control unit 21, for example, as in the prior art shown in FIG.
Then, a difference from the reference C / N is obtained, and control is performed so that the difference becomes zero or a predetermined value or less.

In the above embodiment, the station that detects the C / N from the received pilot signal controls the transmission power of its own station. However, the data of this C / N is sent to the opposite station. Then, the opposite station configures the system so as to control the transmission power based on this data, or calculates the transmission power control data based on C / N and then sends this control data to the opposite station. It goes without saying that it can be configured to control the transmission power of the station.

[0016]

As described above, according to the present invention, the S / N is obtained from the noise level obtained by FM demodulating the received pilot signal and the signal level based on the demodulation sensitivity.
Since C / N is calculated by converting S / N using the N-C / N correlation characteristic, accurate C is obtained even when C / N is low.
/ N can be measured. Also, this exact C / N
Can be used to control the optimum transmission output power according to the line status.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a satellite communication system to which the present invention is applied.

FIG. 2 is a configuration diagram of a main part of a central station including a C / N detection system and a transmission power control system of the present invention.

FIG. 3 is a diagram showing a correlation characteristic between S / N and C / N.

FIG. 4 is a block diagram for explaining a conventional transmission power control method.

[Explanation of symbols]

 1 C / N detection system 2 Transmission power control system 11 Band pass filter 12 FM demodulator 13 Low pass filter 14 Level detector 15 S / N processing unit 16 C / N processing unit 21 Control unit 22 Attenuator

Claims (4)

[Claims] 1. A S / signal obtained by FM demodulating a received pilot signal.
N (signal-to-noise power ratio) is detected and S / of FM demodulation sensitivity is detected.
A reception C / N detection method, wherein the S / N is converted into C / N and the C / N is detected based on an N-C / N (carrier level to noise power ratio) correlation characteristic. 2. An FM for FM demodulating a received pilot signal.
Demodulation means, means for calculating S / N from the signal level obtained from the demodulation sensitivity of the FM demodulation means and FM demodulated noise level, and this S / N is the S / N-of FM demodulation sensitivity.
A receiving C / N detection device, comprising means for converting the C / N to C / N based on the C / N correlation characteristic and detecting the C / N. 3. A bandpass filter for filtering the received pilot signal, an FM demodulator for FM demodulating the filtered pilot signal, a level detector for detecting the level of the demodulated signal, and a level detector. S / of a low-pass filter that low-passes the received signal, a noise level that is passed through the low-pass filter, and a signal level obtained from the sensitivity of the FM demodulator.
S / N processing unit for calculating N, and C / N processing for converting the calculated S / N into C / N based on S / N-S / N correlation characteristics obtained from the demodulation sensitivity of the FM demodulator. And a receiving C / N detection device. 4. The FM demodulation of the received pilot signal to S /
N is detected, the S / N is converted into C / N based on the S / N-C / N correlation characteristic of the FM demodulation sensitivity, C / N is detected, and the transmission power is calculated based on this C / N. A transmission power control method characterized by controlling.