JPH02305010A - Agc device - Google Patents

Abstract

PURPOSE:To decrease the fluctuation of an AGC output signal level and to reduce an ACQ(acquisition) time by providing two automatic gain control(AGC) circuits for a communication line assignment (CSC) signal and a burst signal. CONSTITUTION:A 1st AGC circuit 47 compensating a cable loss of a CSC signal and a 2nd AGC circuit 50 compensating the cable loss of the burst signal with the gain voltage of the 1st AGC circuit 47 and compensating the loss between lines are provided. That is, the 1st AGC circuit 47 applies gain control of the CSC signal and acquires and holds the gain control at that time simultaneously and at the time of receiving a burst signal, the 1st AGC circuit 47 is operated at a fixed gain based on the gain control voltage acquired and held. Then the loss caused in a peripheral terminal station (mainly cable loss) is compensated and the level difference between lines is compensated by the 2nd AGC circuit 50, then the gain control range of the AGC circuit is made narrow. Thus, the AGC output with less level fluctuation and short ACQ time is supplied to a demodulator 49 at the time of receiving the burst signal.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to VSAT (Very Small Aper
The present invention relates to an AGC (automatic gain control) device for compensating for losses in a satellite communication system such as a tureTerminal system.

[Conventional technology]

The VSAT system in the satellite communication system is a system in which a HUB station (central earth station) and a number of VSAT stations (peripheral terminal stations) perform two-way communication via satellite lines.
When a VSAT station receives user data from a terminal device, it uses a common signal line (
Requests the HUB station to allocate a communication line via the HUB station (Common Signaling Channel), and
Data is transmitted through a communication line allocated by the BU station.

A VSAT station used in such a VSAT system is shown in FIG.

FIG. 2 is a block diagram of the VSAT station.

In FIG. 2, the VSAT station has an antenna 1° and an outdoor unit (ODU) 2. Cable 3. It is composed of an indoor unit (IDU) 4. 0DU2 is composed of a distributor 21.24, a high power frequency converter 22, and a low noise frequency converter 23.
DU4 includes a distributor 41, a down converter 42, and a demodulator 4
3, a baseband processor section 44, a modulation section 45, and an up-converter 46.

0DU2 and IDU4 are connected by a cable 3, and the frequency band of this cable 3 is usually the IGHz band.
The amount of variation in cable loss is proportional to the cable length, and is up to 20~
It reaches 30dB.

This cable length-dependent loss can be compensated with a cable loss equalizer using a fixed attenuator, etc., but VSA
In the case of the T system, an AGC device that focuses on received signals is usually used in consideration of ease of installation.

FIG. 3 shows a block diagram of the demodulation section 43 in FIG. 2 including this AGC circuit.

In the figure, the demodulator 43 includes a plurality of AGC circuits 56, a plurality of control circuits 48. It is composed of a plurality of demodulation circuits 49.

The control circuit 48 is connected to a branch circuit 51. Level detector 52, comparator 53. Reference level setter 54. It is composed of an amplifier 55.

Next, the operations shown in FIGS. 2 and 3 will be explained.

First, a communication line assignment signal (
A C8C signal (hereinafter referred to as a C8C signal) is received by an antenna 1 via a satellite (not shown) on a C8C line.

Next, the received signal from the antenna 1 is input to the low noise frequency converter 23 via the distributor 21, where it is amplified and frequency converted, and then sent to the distributor 24, the cable 31, the distributor 41... The signal is input to the demodulator 43 via the down converter 42.

In the demodulator 43 , the input signal (CSC signal) is amplified by each AGC circuit 56 and then branched into two by a branch circuit 51 . 2
A level detector 52 detects the level of one of the branched signals, and a comparator 53 detects the difference between the detected signal level and a reference level set by a reference level setter 54. The output signal of the comparator 53 is sent to the AGC via the amplifier 55.
It is input to circuit 56 and controls the AGC gain.

The other signal branched into two is demodulated by a demodulation circuit 49,
The demodulated signal 102 is input to the baseband processor section 44 . The baseband processor section 44 receives the C8C signal, which is an input signal from the demodulation circuit 49, to control the terminal equipment (
(not shown), and transmits the data via this communication line to the modulator 45, up converter 46, distributor 41, cable 3, distributor 24,
The signal is transmitted from the antenna l via the high power frequency converter 22 and the distributor 21.

The burst signal received by the antenna 1 via the satellite on the communication line according to the C10 signal from the HUB station is input to the low noise frequency converter 23 via the distributor 21.
Here it is amplified and frequency converted. The output signal of the low noise frequency converter 23 is sent to the distributor 24, the cable 3, and the distributor 41.
, are input to the demodulator 43 via the down converter 42, and then input to the AGC circuit 56 for each line.

The output signal of the AGC circuit 56 is sent to the control circuit 48 and the demodulation circuit 4.
The demodulated signal 102 of the h1 demodulation circuit 49 is processed in the same way as the C8C signal described above by the baseband processor section 4.
4 to the terminal device.

[Problem to be solved by the invention]

As described above, the amount of variation in cable loss due to the cable 3 reaches a maximum of about 30 dB, and in order to compensate for this, an AGC gain with a dynamic range of 30 dB or more is required. In this case, for example, there is no cable loss and VSA
If the reception level of the T earth station can be received at approximately the normal level, the AGC circuit output signal will become very large, and the difference in fluctuation when returning from the excessive level to the normal level is approximately 30 dB.
It becomes.

As described above, the AGC circuit waits for the input signal with a voltage gain that compensates for the maximum loss, so the smaller the cable loss, the greater the variation in the AGC output signal level, and the longer the ACQ (ACQUISITION) time. Become. If the input signal to the AGC circuit is in the continuous signal mode of the C8C line, the response time will not be much of a problem. However, in a discontinuous signal mode such as burst signals of a plurality of other communication lines, the burst signal is input from a no-signal state, and the fluctuation in the AGC circuit output signal level becomes excessive.

Therefore, each time a signal arrives, a long ACQ time occurs, resulting in a problem of system response time.

[Means to solve the problem]

In an AGC device of a peripheral station in a VSAT satellite communication system that performs satellite communication using burst signals of a plurality of communication lines, a first AGC circuit that compensates for cable loss of the communication line allocation signal; and a second AGC circuit that compensates for the loss between each line after compensating for the cable loss of the burst signal using the gain voltage of the circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, showing each device in the demodulation section 43 in FIG.

In FIG. 1, the output of the first AGC circuit 47 is branched into two branches, one being connected to a control circuit 48 and the other being connected to a plurality of second AGC circuits 50. The internal and other connections of the control circuit 48 are the same as those shown in FIG.
The entire configuration of the SAT station is also applicable to the present invention.

Next, this operation will be explained.

As described above, the input signal 101 to the second AGC circuit 47 is the C8C signal of the C8C line and the burst signal of the communication line, and the overall operation in FIG. 1 will be omitted here.

First, the input signal (C8C signal) 101 is input to the first AGC circuit 47 , where the cable loss caused by the cable 3 is compensated for, and then input to the branch circuit 51 in the control circuit 48 . One of the outputs of the branch circuit 51 is a level detector 52
The level is detected by the comparator 53, and the difference between the detected signal level and the reference level set by the reference level setter 54 is detected. The output signal of the comparator 53 is input to the first 〇〇 line 47 via the amplifier 55 as an AGC gain control signal 103. The C8C signal whose level has been corrected by the AGC loop formed by the first AGC circuit 47 and the control circuit 48 is sent to the demodulated signal 102a via the demodulator 49.
is output as

Next, the input signal (burst signal) 101 is sent to the first AGC.
In the circuit 45, the cable loss is compensated by the AGC gain corresponding to the above-mentioned C8C signal, and the signal having only the level difference between the lines is input to the second AGC circuit 50 for each line.

AG formed by the second AGC circuit 50 and the control circuit 48
The C loop compensates for level differences between each line. The control circuit 48 uses one branch signal of the branch circuit 51 as an AGC gain control signal 104 to the second AGC circuit 50 and outputs the other signal to the demodulation circuit 49 . The demodulation circuit 49 demodulates the input signal and outputs it as a demodulated signal 102b.

〔Effect of the invention〕

As explained above, the present invention provides two AGC circuits, one for the C8C signal and one for the burst signal.
The first AGC circuit performs gain control of the C8C signal, and at the same time obtains and holds the gain control voltage at that time, and when receiving a burst signal, operates with a fixed gain based on the gain control voltage held in the first AGC circuit. Since the loss (mainly cable loss) occurring within the VSAT station is compensated for by this, and the level difference between lines is compensated for by the second AGC circuit, the gain control range of the AGC circuit can be narrowed. Therefore, it is possible to supply an AGO output with small level fluctuation and short ACQ time to the demodulator when receiving a burst signal.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a VS
FIG. 3 is a block diagram of the demodulation section of a conventional VSAT station. ■・・・Antenna, 2・・・Outdoor equipment (O
DU), 3...Cable, 4...Indoor equipment% 21,24°41...Distributor, 22.
...High power frequency converter, 23...Low noise frequency converter, 42...Down converter,
43... Demodulation section, 44... Baseband processor section, 45... Modulation section, 46...
...up converter, 47.50...AG
C circuit, 48... Control circuit, 49...
Demodulation circuit, 51...Branch circuit, 52...
・Level detector, 53... Comparator, 54...
...Reference level setter, 55...Amplifier. Agent Patent Attorney Uchihara Oto 3V Tebu L2 Co

Claims (1)

[Claims] In a satellite communication system that has a central station and a plurality of peripheral stations and performs satellite communication using a communication line allocation request signal and a communication line allocation signal of a common channel signal line and a burst signal of a plurality of communication lines. In the AGC device of the peripheral station, a first AGC circuit that compensates for the cable loss of the communication line assignment signal; and a loss between each line after compensating for the cable loss of the burst signal with the gain voltage of the first AGC circuit. An AGC device comprising: a second AGC circuit that compensates for.