JP2993097B2 - Automatic gain control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control system, and more particularly to an automatic gain control system used for demodulating a received burst signal in digital satellite communication transmitting a digitally modulated burst signal. About.

[Prior art] As a multiple access satellite communication method for performing communication on a common channel via a communication satellite, for example, a TDMA (time division multiple access) communication method, a pure Aloha communication method, a slotted Aloha communication method, and the like are known. Have been. In these communication methods,
It is necessary to reproduce a digitally modulated burst signal from each earth station scattered in various places participating in the communication system. As shown in FIG. 3, the burst signal usually has a head portion composed of a carrier recovery sequence for reproducing carrier and bit timing and a bit timing recovery sequence, and a unique word and data following the head portion. Consists of In order to faithfully reproduce the unique word and the data, it is necessary for each burst signal transmitted from each station to establish a quick synchronization between the leading carrier wave reproducing sequence and the bit timing reproducing sequence. Therefore, it is desirable to control the received power to be constant.

In the communication method described above, transmission power control may be performed to keep the received power of the burst signal constant. However, in order to reduce the size and cost of the earth station, such complicated devices are reduced as much as possible. Tend to. In this case, a large error occurs in the received power of the burst signal due to variations in the transmission output of earth stations scattered in various places and differences in weather conditions in each place.

FIG. 4 is a block diagram of a conventional automatic gain control method, and a received power is calculated by a power calculating circuit 43 from an output of the demodulator. The subtraction circuit 44 calculates a difference between the calculated received power and the reference value, and outputs a signal representing the difference to the filter circuit 45. The output of the filter circuit 45 is supplied to the variable attenuator 41. As described above, a method is employed in which a closed loop is configured so that the received power at the input of the demodulator becomes a predetermined level in accordance with the difference in received power, and the automatic gain control always functions regardless of the presence or absence of a burst signal. Have been.

[Problems to be Solved by the Invention] In the conventional automatic gain control method described above, if the control circuit is configured by a closed loop of the primary system, the response speed until the desired output power is obtained when the received power changes is a closed loop. Is inversely proportional to the noise bandwidth of Therefore, if the noise bandwidth is reduced in order to operate the demodulator under the condition that the carrier power to noise bandwidth is low (low C / N), such as in satellite communication, the response speed becomes slow.

On the other hand, the receiving side must wait for a burst signal to be transmitted and respond to a different reception power for the burst signal transmitted from the earth station in each place. That is, it is necessary to control different reception power to a predetermined power depending on a burst signal arriving from a standby no-signal state. However, the slow response speed means that the burst signal is received from the idle no-signal state and the gain control is completed between the carrier recovery sequence and the bit timing reproduction sequence at the beginning of the burst signal described above. In some cases, it may be difficult to establish synchronization. As a result, there is a disadvantage that the reception error of the burst signal or the bit error rate (BER) is deteriorated because the predetermined power is not obtained in the data portion even if the signal can be received.

 FIG. 5 shows an operation transition of the conventional automatic gain control.

[Means for Solving the Problems] The present invention relates to an automatic gain control system used for demodulating a received burst signal in digital communication for transmitting a digitally modulated burst signal. A demodulator for demodulating a digitally modulated wave, and a burst for outputting a detection signal when receiving the output of the demodulator and detecting the burst signal, and for outputting a control signal indicating the end of reception of the burst signal. A signal detection unit; and gain control means for controlling the variable attenuator based on the output of the demodulator, the detection signal, and the control signal. Set the variable attenuator to the average attenuation during reception of the burst signal, and open the automatic gain control from the set attenuation when the burst signal is received. Starting, the input signal to the demodulator is quickly controlled to a predetermined level.

The gain control means includes: a power calculation circuit that calculates power from the output of the demodulator; a subtraction circuit that calculates a difference between the power calculated by the power calculation circuit and a predetermined reference value; The circuit comprises a filter circuit for filtering the output of the subtraction circuit, and a gain control circuit for controlling the variable attenuator based on the detection signal from the burst signal detection section and the control signal.

The gain control circuit performs a switching control operation of outputting the output of the filter circuit as a gain control voltage or outputting a fixed value control voltage in accordance with the detection signal and the control signal. .

[Operation] When a burst signal transmitted from an earth station in each place is waiting, that is, in a no-signal state, a loop including a demodulator, a power calculation circuit, a subtraction circuit, a filter circuit, a gain control circuit, and a variable attenuator is gain-controlled. Open loop by circuit. Then, the control voltage from the gain control circuit to the variable attenuator is set so that the input of the demodulator has a predetermined power with respect to the input signal of the standard power (the average value of the received power). Detection of a burst signal in a burst signal detection circuit (for example,
(Detection of carrier recovery sequence at the beginning of burst signal) In other words, automatic gain control is performed during reception of the burst signal by the gain control circuit due to reception of the burst signal, and predetermined based on the detection of the burst signal by the burst signal detection circuit. After the elapse of the burst signal length, that is, after the end of the reception of the burst signal, the control voltage to the variable attenuator at which the input of the demodulator becomes a predetermined power with respect to the input signal of the standard power from the automatic gain control is set. , For the next transmitted burst signal.

As in the past, when the automatic gain control is always performed, the gain of the variable attenuator is always at the maximum in a no-signal state in which a burst signal is waiting, and a high-power signal arrives there. At this time, it takes a response time to attenuate the received signal power with a variable attenuator in order to obtain a predetermined power at the demodulator input.

According to the control method of the present invention, while the burst signal to be transmitted is on standby, the amount of attenuation in the variable attenuator is set so that the predetermined power is obtained at the demodulator input with respect to the standard input power in the burst signal reception state. Therefore, even when a large amount of power arrives, the automatic gain control is started from the set attenuation amount, so that a predetermined level gain can be controlled with a shorter response time with a smaller control amount than in the related art.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an automatic gain control system according to an embodiment of the present invention.

This automatic gain control system includes a demodulator 1 for demodulating a digitally modulated wave, a power calculation circuit 2 for calculating power from the output of the demodulator 1, and a power calculated by the power calculation circuit 2 and a reference value. A subtraction circuit 3 for outputting an error between the signals, a filter circuit 4 for filtering the output of the subtraction circuit 3, a detection signal for receiving the output of the demodulator 1 and detecting and detecting the burst signal, A burst signal detection circuit 5 for outputting a control signal for notifying the end of the reception of the burst signal from a predetermined burst signal length based on the detection of the burst signal, and the output of the filter circuit 4 as a gain control voltage based on the detection signal and the control signal. A gain control circuit 6 for controlling switching between output and a fixed control voltage designated by a fixed value, and a gain control circuit provided before the demodulator 1 And a variable attenuator 7 that controls the amount of attenuation of the input signal at the output control voltage of the road 6.
A demodulator 1, a power calculation circuit 2, a subtraction circuit 3, a filter circuit 4, a gain control circuit 6, and a variable attenuator 7 form an automatic gain control loop.

The variable attenuator 7 controls the amount of attenuation of the input digital modulation signal by the applied control voltage to make the signal level appropriate. The demodulator 1 demodulates the digital modulation signal whose gain has been controlled by the variable attenuator 7 and outputs demodulated data. The power calculation circuit 2 calculates the power of the demodulated signal from the demodulated data, and the subtraction circuit 3 calculates an error between the power of the demodulated signal and a reference value and outputs the error to the filter circuit 4. The filter circuit 4 is a reduction pass filter, and removes unnecessary high frequency components. The burst signal detection circuit 5 receives the output of the demodulator 1, detects the burst signal by receiving the burst signal, outputs a detection signal notifying the detection of the burst signal to the gain control circuit 6, and based on the detection of the burst signal. Similarly, a control signal for notifying the gain control circuit 6 of the end of the reception of the burst signal is output. Based on these detection signals and control signals, the gain control circuit 6 performs switching control to output the output of the filter circuit 4 as a gain control voltage or to output a fixed control voltage specified by a fixed value. The voltage is applied to the variable attenuator 7 to control the amount of attenuation of the input signal.

 FIG. 2 shows the transition of the automatic gain control operation.

In the automatic gain control system operating in this way, when waiting for a burst signal transmitted from each earth station, the automatic gain control loop is opened and the input signal of standard power (average of received power) is applied. On the other hand, a fixed control voltage is set from the gain control circuit 6 to the variable attenuator 7 so that the input of the demodulator 1 has a predetermined power. Then, in the burst signal detection circuit 5, the detection of the burst signal, for example, the detection of the carrier reproduction sequence at the head of the burst signal, notifies the reception of the burst signal by a detection signal.

Upon receiving the detection signal, the gain control circuit 6 closes the automatic gain control loop, and performs automatic gain control in the burst signal reception state. Subsequently, after the elapse of a predetermined burst signal length based on the detection of the burst signal by the burst signal detection circuit 5, that is, the gain control circuit 6 reopens the automatic gain control loop by the gain control circuit 6 with the control signal indicating the end of the burst signal reception. The same output control voltage as in the burst signal waiting state is applied to the variable attenuator 7 to prepare for the next transmitted burst signal.

According to such an automatic gain control method, when there is no signal waiting for a burst signal, the variable attenuator 7 has already set the average attenuation during reception of the burst signal. Even if a signal is transmitted, the control amount is small, and it is possible to quickly set a predetermined demodulator input level.

Therefore, when the automatic gain control is always performed as in the conventional case (FIG. 5), the variable attenuator 7 has the maximum gain when there is no signal during standby. When the burst signal arrives there, the variable attenuator 7 is controlled so that the power becomes a predetermined value at the demodulator input. Therefore, a response time is required (especially, as the power difference between the no-signal state and the burst signal reception state becomes larger, On the other hand, the present method is advantageous in establishing phase synchronization, and it is possible to prevent reception errors of burst signals due to synchronization delay and deterioration of error rate characteristics.

[Effect of the Invention] As described above, in the automatic gain control method of the present invention,
The variable attenuator is set to the average attenuation during reception of the burst signal in a no-signal state waiting for the transmitted burst signal, and the gain is switched to automatic gain control by receiving the burst signal. The input signal to the demodulator can be set to a predetermined level in time, which is advantageous for establishing phase synchronization and has an effect of preventing reception errors of burst signals due to delay of synchronization establishment and deterioration of error rate characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment according to the present invention, FIG. 2 is a diagram showing an operation transition of automatic gain control of the present invention, FIG. 3 is a diagram showing a typical burst signal configuration, and FIG. FIG. 5 is a diagram showing an automatic gain control circuit of FIG. 1 ... demodulator, 2 ... power calculation circuit, 3 ... subtraction circuit, 4 ...
Filter circuit 5, burst signal detection circuit 6, gain control circuit 7, variable attenuator 8, demodulator input signal 9, control signal 10, control voltage to variable attenuator.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 1/16 H04B 7/14

Claims (3)

(57) [Claims] 1. An automatic gain control system for demodulating a received burst signal in digital communication for transmitting a digitally modulated burst signal, comprising: a variable attenuator for controlling an attenuation of a received signal; A demodulator for demodulating a wave, a burst signal detecting unit for outputting a detection signal when receiving the output of the demodulator and detecting the burst signal, and outputting a control signal indicating the end of reception of the burst signal; And gain control means for controlling the variable attenuator based on the detection signal and the control signal. The variable attenuator receives the burst signal when there is no signal waiting for a transmitted burst signal. By setting the average attenuation to the average value and starting automatic gain control from the set attenuation when the burst signal is received, the demodulation is performed. Automatic gain control method being characterized in that so as to control quickly to a predetermined level an input signal to. 2. The automatic gain control method according to claim 1, wherein said gain control means includes a power calculation circuit for calculating power from an output of said demodulator, and a power calculated by said power calculation circuit. A subtraction circuit for calculating a difference from a predetermined reference value, a filter circuit for filtering an output of the subtraction circuit, and the variable attenuator based on the detection signal from the burst signal detection unit and the control signal. And a gain control circuit for controlling the gain. 3. The automatic gain control system according to claim 2, wherein said gain control circuit outputs an output of said filter circuit as a control voltage of gain or a fixed value according to said detection signal and said control signal. An automatic gain control method for performing a switching control operation of whether or not to output the control voltage.