JPH0787422B2 - Multi-channel frequency multiplexed signal power control system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel frequency-multiplexed signal power control system, and more particularly to a multi-channel satellite switching system having a group demodulation circuit for converting a multi-channel frequency-multiplexed signal into a digital signal and collectively demultiplexing and demodulating it. Frequency multiplex signal power control system

[0002]

2. Description of the Related Art In a satellite communication system in which an exchange is mounted on a communication satellite, an SC using one carrier per channel
PC (Single Channel Per Car
In the case of adopting the rier) system, a plurality of earth stations use different carriers (channels) for communication and transmit to the communication satellites. Therefore, the satellite exchange receives the multi-channel frequency multiplexed signal. FIG. 4 shows a block diagram of an example of the related art which receives the multi-channel frequency multiplexed signal and performs power control.

In the figure, an automatic gain control circuit (AGC
A circuit 1 receives the received multi-channel frequency multiplexed signal and performs power control. The A / D converter 2 converts the multi-channel frequency multiplexed signal output from the AGC circuit 1 into a digital signal and supplies it to the batch demultiplexing circuit 3. The batch demultiplexing circuit 3 is composed of a digital filter or the like, and demultiplexes the input digital signal in units of a predetermined number of channels and outputs it to the demodulation circuit 4.

The demodulation circuit 4 is, for example, a phase locked
It is composed of a loop (PLL) and the like, and demodulates these input signals in channel units. Based on the control signal from the control circuit 6, the switch circuit 5 switches the demodulated signal on a channel-by-channel basis, incorporates it into the transmission data format, and outputs it to the beam modulator (not shown) of the assigned channel.

Here, the AGC circuit 1 is composed of a variable amplifier 7 and a power detector 8 as shown in FIG. 5, for example. The variable amplifier 7 amplifies and outputs the received multi-channel frequency multiplexed signal, and at the same time, the power detector. Based on 8, it is determined whether the power (power) of the amplified signal is larger or smaller than the threshold value set at the time of system design.

Since the power detector 8 variably controls the gain of the variable amplifier 7 so that the power of the amplified signal becomes equal to the threshold value, the amplified signal whose power is constant is output from the variable amplifier 7. Will be taken out. The threshold value is uniquely determined by the input voltage range of the A / D converter 2 in the next stage.

[0007]

However, since the threshold value of the power detector 8 is fixed in the above conventional power control method, the following problems occur. That is, when the earth station is a mobile unit such as a car telephone, the number of mobile units in communication (the number of calls) changes, so the number of channels of the frequency multiplexed signal received by the satellite changes, As a result, the power of the multi-channel frequency multiplexed signal also changes.

However, as described above, in the conventional method, since the threshold value of the power detector 8 is fixed, a large difference occurs in the amplification factor of the AGC circuit 1 according to the number of channels of the frequency multiplexed signal, and the signal is When the number of inserted channels is small, the amplification factor is large because the power of the frequency-multiplexed signal is small, so that the noise of the unused channels is also greatly amplified at the same time as the signal, and this noise of the demodulation circuit 4 is generated. A signal may be erroneously detected as a signal when the carrier is detected, causing a system malfunction.

The present invention has been made in view of the above points,
An object of the present invention is to provide a multi-channel frequency-multiplexed signal power control system that solves the above-mentioned problems by performing power control with an amplification factor according to the number of channels used.

[0010]

In order to achieve the above object, the present invention controls the power of a multi-channel frequency multiplexed signal in which carriers of a plurality of channels are frequency-multiplexed by a gain control circuit so as to be equal to a threshold value. Output to the A / D converter, and the number of channels of the multi-channel frequency multiplexed signal is discriminated by the discriminating means, and the threshold value is changed by the level control circuit according to the discriminated channel number. Is.

[0011]

In the present invention, the power after amplifying the multi-channel frequency multiplexed signal in the gain control circuit is controlled so as to be equal to the threshold variable by the level control circuit, and the threshold is controlled by the level control circuit. Since the variable control is performed according to the number of discriminated channels, the power is also controlled according to the number of discriminated channels. Therefore, according to the present invention, the amplification factor (gain) of the gain control circuit can be made substantially constant regardless of the number of channels, and when the number of channels is small, the power of the multi-channel frequency-multiplexed signal is higher than that when the number of channels is large. Can be controlled to a small level.

[0012]

1 is a block diagram of an embodiment of a multi-channel frequency-multiplexed signal power control system according to the present invention. In the figure, the same components as those in FIG. 4 are designated by the same reference numerals. The embodiment shown in FIG. 1 is an example applied to a satellite switch of the mobile satellite communication system of the SCPC system. When the mobile station, which is an earth station, accesses the satellite switch at the time of calling, a packet control signal is supplied to the control circuit 12. To be done. Since this packet control signal includes the ID number of the sender and the ID number of the sender, the satellite exchange switches the switch circuit 5 based on this to allocate the satellite channel of the sender and the destination. To do.

After receiving the assignment of this channel, the calling mobile transmits a modulated wave obtained by modulating a predetermined carrier of the assigned channel with a voice signal to the satellite exchange. In the same manner, the other mobiles receive the assignment of another channel and transmit a modulated wave in which a predetermined carrier of the assigned channel is modulated with a voice signal to the satellite exchange. A multi-channel frequency multiplexed signal, which is a frequency division multiplexed signal of waves, is received.

This received multi-channel frequency multiplexed signal is
It is supplied to the AGC circuit 11 described later, where the power is A
After being controlled to be equal to a predetermined threshold value so as to fall within the input voltage range of the A / D converter 2, it is supplied to the A / D converter 2 and converted into a digital signal. As in the conventional case, this digital signal is collectively demultiplexed by the demultiplexing circuit 3 in units of a predetermined number of channels and then demodulated by the demodulation circuit 4.
After the switching circuit 5 performs switching on a channel-by-channel basis and incorporates it into the transmission data format,
The signal is transmitted from the antenna to the destination or source mobile unit via a modulator in the subsequent stage.

Here, in this embodiment, the AGC circuit 11 for performing power control is supplied with a level control circuit 13 to which a digital signal having a value corresponding to the number of channels obtained by the control circuit 12 based on the packet control signal is supplied. From this, a control signal of a level according to the number of used channels is supplied, and the threshold value for power control is changed. This AGC circuit 11 has a variable amplifier 2 as shown in FIG.
0 and a power detector 30. The power of the output frequency multiplexed signal of the variable amplifier 20 is detected by the power detector 30, and the level is compared with a threshold value to generate a control signal of a level corresponding to the difference between them. Then, the amplification factor (gain) of the variable amplifier 20 is controlled. As a result, the output signal of the variable amplifier 20 is controlled to be substantially equal to the threshold value of the power detector 30.

The threshold value of the power detector 30 is controlled by the output control signal of the level control circuit 13. The level control circuit 13 is composed of, for example, a D / A converter and generates a level control signal of a level proportional to the number of used channels. Here, the variable amplifier 20 and the power detector 30 are configured, for example, as shown in FIG.
In the figure, the variable amplifier 20 is configured to output the frequency-multiplexed signal amplified by the first amplifier 21 through the first variable attenuator 22 and the second amplifier 23.

On the other hand, the power detector 30 is a variable amplifier 20.
The low-pass filter (LPF) 31 that selects the low-frequency component of the output frequency-multiplexed signal, the second variable attenuator 32 that attenuates the output signal of the LPF 31, and the output signal of the second variable attenuator 32 It comprises an amplifier 33 for amplifying. L
The PF 31 is provided so that the threshold value does not follow high-speed fluctuations of the input signal. Further, the output signal of the amplifier 33 is input to the first variable attenuator 22 as a control voltage, that is, a threshold value. The first and second variable attenuators 22 and 32 described above have a configuration in which the amount of attenuation increases as the input control voltage increases.

Here, since the output level control signal of the level control circuit 13 is set so that the signal level increases in proportion to the number of used channels, the second variable attenuator is used when the number of used channels is large. The input level control signal of 32 is large, and its attenuation amount is large.
Since the control voltage (threshold value) input to the variable attenuator 22 has a small level because it is greatly attenuated, the attenuation amount of the first variable attenuator 22 is small. On the other hand, when the number of used channels is small, the input level control signal of the second variable attenuator 32 is small and the amount of attenuation is small, so that the amount of attenuation is not so great.
The control voltage (threshold value) input to 2 becomes large, and the attenuation amount of the first variable attenuator 22 becomes large.

Therefore, according to the present embodiment, even if the power of the input frequency multiplexed signal increases substantially in proportion to the number of used channels, the attenuation amount of the first variable attenuator 22 is small when the number of used channels is large. Therefore, when the number of used channels is small, the amount of attenuation of the first variable attenuator 22 is large, and power control can be performed according to the number of used channels. Therefore, when the number of used channels is small, noise which is amplified by a large amplification factor and is set to an unnecessarily large level is detected as a signal when the carrier of the demodulation circuit 4 is detected. It is possible to prevent the system from malfunctioning, and it is possible to greatly improve the reliability of the system as compared with the conventional one.

The present invention is not limited to the above-described embodiment, but is, for example, the variable amplifier 20 and the power detector 3.
0 is considered to be various modifications other than the embodiment shown in FIG.

[0021]

As described above, according to the present invention,
Since the amplification factor (gain) of the gain control circuit can be made substantially constant regardless of the number of channels, the noise level of the unused channels received by the demodulator can be suppressed to a low level regardless of the number of used channels. Therefore, when the present invention is applied to a satellite exchange, the dynamic range of the AGC circuit in the demodulation circuit can be increased, and the dynamic range of the group demodulator as a whole can be increased.

Further, according to the present invention, when the number of channels used is small, the power of the multi-channel frequency multiplexed signal can be controlled to be smaller than that when the number of channels is large.
When the number of used channels is small as in the past, noise that was amplified by a large amplification factor and was set to an unnecessarily large level was detected as a signal when the carrier of the demodulation circuit was detected. It is possible to prevent the system from malfunctioning, and the reliability of the system can be greatly improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the system of the present invention.

FIG. 2 is a block diagram of an embodiment of a main part in FIG.

FIG. 3 is a detailed block diagram of the AGC circuit of FIG.

FIG. 4 is a block diagram of an example of a conventional method.

5 is a detailed block diagram of the AGC circuit in FIG.

[Explanation of symbols]

 2 A / D converter 3 batch demultiplexing circuit 4 demodulation circuit 5 switch circuit 11 automatic gain control circuit (AGC circuit) 12 control circuit 13 level control circuit 20 variable amplifiers 21, 23, 33 amplifier 22 first level attenuator 30 Power detector 31 Low-pass filter (LPF) 32 Second level attenuator

Claims (3)

[Claims] 1. A multi-channel frequency-multiplexed signal power control system for controlling the power of a multi-channel frequency-multiplexed signal in which carrier waves of a plurality of channels are frequency-multiplexed and then inputting to an A / D converter to convert into a digital signal. A gain control circuit for controlling the power of the multi-channel frequency multiplexed signal so as to be equal to a threshold value and outputting it to the A / D converter; a discriminating means for discriminating the number of channels of the multi-channel frequency multiplexed signal; And a level control circuit that varies the threshold value according to the number of channels determined by the means. 2. In the satellite exchange system having a group demodulation circuit for demodulating the output digital signal of the A / D converter after batch demultiplexing, the multi-channel frequency division multiplexed signal is one carrier per channel from a plurality of earth stations. 2. The multi-channel frequency-multiplexed signal power control system according to claim 1, wherein the multi-channel frequency-multiplexed signal power control method is a frequency-multiplexed signal of a transmission wave transmitted in step 1. 3. The gain control circuit compares a variable gain variable amplifier for amplifying the multi-channel frequency multiplexed signal with the threshold value varied by the level control circuit and the power of the output signal of the variable amplifier. The multi-channel frequency-multiplexed signal power control system according to claim 1, further comprising a power detector that controls the gain of the variable amplifier according to the difference between them.