JPH04323947A - Automatic gain adjustment system - Google Patents

Abstract

PURPOSE:To receive a signal at an optimum level momentarily from the start of a receiver at a subscriber side by taking notice of the presence of any signal input in a station and a subscriber device with respect to the automatic gain adjustment system in the burst transmission system. CONSTITUTION:An input level of a reception signal is compared with a reference level set by a reception level detection means 2 to detect the level of the reception signal in advance. The result of level detection is stored in a reception level storage means 3 while being sequentially revised. When a line interconnecting a station and each subscriber device is active and a receiver reaches the talking state, level information is read from the reception level storage means 3 and a reception section 4 adjusts the gain of the reception signal immediately.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain adjustment system in a burst transmission system. More specifically, the present invention relates to an automatic gain adjustment system that can set the signal level reaching a station from a plurality of subscriber transmission devices to a constant value.

[0002]In recent years, information and communication systems in the ISDN (Integrated Service Digital Network) are using 64Kb/s PCM for non-telephone services such as data, facsimile, and video.
It becomes possible to transmit data using a digital communication method based on signals. In the subscriber line transmission method in such transmission systems, the line terminating unit (OCU) at the central office is connected to the digital line terminating unit (DSU) installed at the subscriber's home via the subscriber line serving as the transmission path. Ru.

[0003] Nowadays, due to the need to reduce the cost of such digital transmission systems, it is considered that a transmission line extended from one station is branched to provide services to a plurality of subscribers. In this case, the signal from the station is broadcast to all subscribers, but the signal from the subscriber to the station is transmitted using Time Division Multiple Access (TDMA).
Multiple Access).

[0004] In this system, each subscriber's receiving device extracts and reproduces only the data of the number specified in advance from the station-side signal. Similarly, in the receiving device at the station, signals sent to the station from multiple subscriber-side DSUs installed at unspecified locations are synchronously reproduced by one OCU and transmitted to the switching circuit (MPX). Ru.

[0005] In order to reduce transmission errors during calls, it is necessary to set the signal level from each subscriber to a constant value. In automatic gain adjustment for this purpose, a preamble part other than data is prepared at the beginning of the digital data, and the carrier detection bit (CD), level setting bit, etc. contained therein are used.

[0006]

[Prior Art] Various cables have been used as transmission media in wired transmission systems. For example, optical transmission cables, which have been attracting attention in recent years, are capable of transmitting large amounts of data at high speed. Can be handled efficiently. However, even in the case of a transmission line using an optical transmission cable, a repeater is required to compensate for fluctuations in transmission loss and fluctuations in signal level.

[0007] An automatic gain control circuit (AGC) suppresses such irregular level fluctuations of an input signal in a relay station or a terminal device, and automatically adjusts the gain so as to amplify the received signal level to a constant level. For this reason, the AGC is composed of a control section that detects level fluctuation control information and a gain variable section that actually performs level adjustment. For example, in peak value detection √fAGC used in digital transmission systems, AG
It is operated so that the pulse peak value of the C circuit output is constant. As a result, a constant amplitude input is always provided to the pulse discrimination circuit, and discrimination characteristics that are not affected by variations in transmission loss in the cable are obtained.

[0008] In order to perform level adjustment using such AGC, first, the level of the received signal is extracted, and the difference signal between this level and a predetermined reference signal is fed back to the control section to adjust the amplification degree of the variable gain section. do. Then, the level of the amplified received signal is compared with the reference signal again, the gain is gradually controlled, and the signal is pulled to a predetermined input level. Gain adjustment in conventional subscriber transmission equipment is
This kind of feedback control type adjustment method was the mainstream.

[0009]

[Problems to be Solved by the Invention] However, when time division multiple access is made between a station and a plurality of subscriber equipment via branching and merging transmission lines, differences in the length of each transmission line, etc. Accordingly, the received signals transmitted in bursts from the subscriber equipment to the station are provided at various reception levels. Therefore, in a conventional automatic gain adjustment system that performs gain adjustment using AGC, the pull-in time for converging the reception level to a constant value varies depending on the dynamic range of each signal transmitted in bursts. In particular, when the dynamic range of the signal is large, it takes a long time to complete the pull-in. This requires a long training sequence prior to transmission, reducing the time span for actual data transmission.

[0010] As described above, in the conventional automatic gain adjustment system, the number of subscriber devices that can be connected to one station is limited, and at the same time, the number of circuit elements for realizing AGC on the station side and the subscriber side is limited. However, strict characteristics requirements are imposed and the circuit configuration becomes complex. As a result, there is a problem in that overhead occurs in the transmitted data, making it impossible to efficiently handle a large amount of subscriber data.

The present invention has been made in view of these points, and focuses on the fact that in a burst transmission system, there is always some kind of signal input to the station and subscriber equipment, thereby shortening the reception level adjustment time. In particular, it is an object of the present invention to provide an automatic gain adjustment system that can instantly receive a signal at an optimal level from the activation of a receiving device on the subscriber side.

[0012] Another object of the present invention is that when a signal is sent from the subscriber side to the station at an optimal transmission level according to the received signal level, gain adjustment can be made more easily on the station side. An object of the present invention is to provide an automatic gain adjustment system.

Furthermore, another object of the present invention is to provide an automatic gain adjustment system in which the station side obtains information on the received signal level at the subscriber side and can instantly and automatically adjust the reception level at the station side to the optimum level. The purpose is to

[0014]

SUMMARY OF THE INVENTION FIG. 1 is a block diagram illustrating the principle of the present invention that achieves the above object. In FIG. 1, received signals are transmitted in bursts between a time-division multiple accessed station and a plurality of subscriber devices via branching and merging transmission lines.

The burst-transmitted received signal undergoes automatic gain adjustment by the signal amplifying means 1 for gain adjustment provided in the receiving device of each subscriber device, is sent to the receiving section 4, and is output from the synchronization regeneration circuit 5. Reception processing is performed using a clock that is phase-synchronized with the received signal. At the receiver in such a burst transmission system, there is always some signal input to the station and subscriber equipment. Therefore, the level of the received signal is detected in advance by comparing the input level of the received signal input from the transmission path with a reference level set by the received level detection means 2.

This level detection result is sequentially updated and stored by the reception level storage means 3. Then, when the line between the station and each subscriber device becomes active and the receiving device enters a talking state, level information is read from the receiving level storage means 3 and gain adjustment of the received signal is immediately performed.

FIG. 3 shows an automatic gain adjustment system on the station side that adjusts the gain of the burst-transmitted received signal.
is shown in more detail. The reception level detector 22 is
It corresponds to the reception level detection means 2, and compares the input level of the reception signal with a set reference level,
Detect the level. Based on the level detection result of the received level detector 22, the amplification circuit 21 controls the degree of amplification so as to keep the signal level of the received signal constant. In the amplitude data reproducing circuit 23, this amplifier circuit 2
The above level information is reproduced for each received data received via 1.

Since the reproduced level information is a digital signal, it is transmitted from the amplitude data reproduction circuit 23 to the DA converter 24.
The gain of the amplifier circuit 21 is feedback-controlled based on the level information converted into an analog signal via the analog signal.

Note that if level information is not sent, the reception level detector 22 alone is sufficient, or if the level information is reliably reproduced for each received data, the reception level detector 22 is unnecessary. Sometimes it happens.

[0020]

According to the present invention, the level of the received signal transmitted in bursts is stored digitally, and when the line becomes active, it can be given to the receiver as a control signal for gain adjustment. In addition, if the subscriber side uses this stored digital data to set the signal level sent out when transmitting, the reception level at the station side that is simultaneously transmitted from multiple subscribers will be as uniform as possible. become. This makes it possible to easily control the gain of the receiving amplifier.

[0021] In a station-side device that receives signals from a plurality of subscribers, the reception level can be measured by monitoring the level of the reception signal and comparing it with a plurality of preset levels. The amplifier gain can be controlled with high precision by applying feedforward control to the

[0022] Furthermore, even if the above level information is simply sent from the transmitting side to the receiving side as part of the transmitted data without setting the level of the transmitted signal, the receiving side can decode this level information. , automatic gain adjustment of the receiving amplifier is immediately performed.

[0023]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 2 is a block diagram showing an example of a subscriber transmission device. A plurality of subscriber transmission devices are connected to the transmission medium 10, and data is transmitted to the station-side device via one transmission medium 10. The signal from the station is sent out to all subscribers at all times, and each subscriber device is always able to monitor the signal level from the station. It is assumed here that the level of the received signal is already known when the subscriber wishes to initiate communication with this subscriber equipment.

In FIG. 2, the AGC 11 automatically adjusts the amplification gain of the input signal. This AGC11 is
After the subscriber transmission equipment is activated, it is controlled in a predetermined sequence and works to maintain the control voltage of the gain adjustment amplifier at a required potential. As a result, a signal of a constant magnitude is input to the identification circuit of each subscriber transmission device, regardless of the distance from the station. Here, the signal from the transmission medium 10 is applied to a level detector 12 of this subscriber transmission equipment. This level detector 12 compares the input level of the received signal that is constantly inputted with a reference level set there, and detects the level of the received signal that is inputted here in advance before making a call. There is. In this level detection of the received signal, different levels are used as reference levels,
It is compared with a plurality of reference signals at a predetermined timing, and one level signal among the plurality of divisions is output as a digital value.

Level information, which is the detection result of the level detector 12, is written into the digital memory 13 and stored there. The detection result of the level detector 12 is DA
The data is converted into analog data by the converter 14 and provided to the AGC 11. As a result, the AGC 11 adjusts the gain so that the signal is received at the optimum level instantly from the activation of the receiving device on the subscriber side. The detection result of the level detector 12 is also given to the transmission level adjustment circuit 15 via the DA converter 14, and the transmission level adjustment circuit 15 adjusts the subscriber transmission data sent from the subscriber transmission equipment to the station. Transmission level is adjusted.

A data addition circuit 16 is provided on the input side of the transmission level adjustment circuit 15 as a level information sending means. This data addition circuit 16 inserts the level information read from the digital memory 13 into a part of the subscriber transmission data. This level information is further sent from the transmission level adjustment circuit 15 to the transmission medium 10 together with the subscriber transmission data.

When the subscriber is not on a call, only the level detector 12 which monitors the level is active and the input level of the signal received via the transmission medium 10 is digitally written into the digital memory 13. When communication starts, level information is read from the memory 13 and
Set the gain of GC11. As a result, the feedback type A
Feedforward control is applied to the GC 11, and its amplifier gain can be controlled with high precision. Moreover, AG
At C11, feedforward control from the DA converter 14 is executed simultaneously with normal feedback control. Therefore, the dynamic range of the input to the AGC 11 is compressed, allowing rapid convergence to a constant amplification.

FIG. 3 is a block diagram showing an example of an automatic gain control device on the station side. This constitutes a part of the transmission equipment on the station side, and a plurality of subscriber transmission equipment similar to that shown in FIG. 2 are branched and connected to the transmission medium 10. A plurality of subscriber transmission data transmitted in bursts is sent to the AGC 21 of the station side device via one transmission medium 10.
is input. In this case, it is assumed that all of the plurality of subscriber transmission data have already been level-adjusted in each subscriber transmission device, or contain level information that is the result of input level detection in the subscriber device. However, in general, AGC2 in the automatic gain adjustment system of the present invention
The effect of No. 1 is also achieved for a plurality of subscriber transmission data received without such conditions regarding the subscriber transmission equipment.

That is, the reception level detector 22 corresponds to the reception level detection means 2, and is
The input level of the signal received via 0 is compared with a set reference level to detect the level. This reception level detector 22 may be simple and composed of at least one flip-flop. Based on the level detection result of the received level detector 22, the amplification circuit 21 controls the degree of amplification so as to keep the signal level of the received signal constant. In the amplitude data reproducing circuit 23,
The level information is reproduced for each received data received via this amplifier circuit 21. The reproduced level information is output to the processing section 25. Further, this level information is given to the amplifier circuit 21, but since this is a digital signal, the amplifier circuit 21 is supplied with the level information converted from the amplitude data reproducing circuit 23 to an analog signal via the DA converter 24. The gain is configured to be feedback controlled. Further, the transmitter 26 always outputs a transmission signal to the transmission medium 10.

Note that if level information is not sent, it is sufficient to provide the reception level detector 22, or if the level information is reliably reproduced for each received data, the reception level detector 22 may be installed. It may become unnecessary. On the other hand, if the signal transmission level is not adjusted on each subscriber side, it is effective to use a feedback loop including the received level detector 22 and the DA converter 24 in combination.

FIG. 4 is a diagram showing an example of a burst transmission system. In the line termination device 20 on the station side, a multiplexed signal with a number of channels corresponding to the number of connected subscribers is sent from a transmitter 26, and this multiplexed signal is sent to the automatic gain of each subscriber receiver via a branch circuit 101. It is input to the control device 18. Similarly, signals from a plurality of subscribers are combined by a combining circuit 102 and transmitted to the line termination device 20 on the station side via a single transmission medium. In this case, the signals sent to each subscriber in bursts from the transmission section 26 of the station are as follows:
It is assumed that which subscriber receives data at which time position, and at what time position thereafter, it is determined in advance.

Transmission signals are input to the subscriber receiving section at different signal levels depending on the distance from the station for each subscriber. However, in order for the reception processing unit 19 to quickly and accurately reproduce the transmitted data, the data must always be received at a constant and optimal level. In the present invention, in response to such requests, each subscriber receiving section
Based on the fact that the automatic gain control device 18 including GC is always connected to the station side and receiving signals, the reception level is stored digitally and the reception level is instantly adjusted when a communication state is established. It is configured so that it can be done. Regardless of how accurately this received level information is detected, received level information indicates the degree of signal attenuation depending on the distance between the station and the subscriber, or depending on the transmission conditions of the transmission medium. be. Therefore, by providing a level monitoring means that operates even when the subscriber is not talking, the level of the signal being transmitted is divided into at least two levels prior to data transmission and level detection is performed. If the level information corresponding to the level detected in this manner is stored on the receiving side, the reception level adjustment time can be shortened without requiring a long training sequence as in the prior art.

The same holds true for the automatic gain control device 27 of the line termination device 20 on the station side. However, the processing unit 25 on the station side does not necessarily need to monitor the reception level in order to reproduce the transmission data Xk from the received signals from each subscriber input in bursts. In that case, the level information detected by the automatic gain control device 18 on the subscriber side is given to the transmission level adjustment circuit 15, and the transmission level sent out from each subscriber is adjusted in advance according to the distance to the station. or send level information to processing unit 1.
This is because it is possible to control the reception level by transmitting the information along with the subscriber data at 7 and decoding it in the processing unit 25 on the station side that reproduces the data from each subscriber. The present invention can also be applied to an optical AGC circuit that transmits a signal in the form of light and performs photoelectric conversion on the receiving side, and then corrects amplitude fluctuations of the signal in a transmission path or the like.

FIG. 5 is a block diagram showing an example of an automatic gain adjustment circuit for optical communication used when the signal to be transmitted is an optical pulse. 31 is an avalanche photo diode (hereinafter referred to as APD) that converts optical input pulses into electrical pulses, and 32 is an AGC amplifier that inputs the electrical pulses of APD 31. Here, 32a and 32b are a preamplifier and a postamplifier of the AGC amplifier 2, respectively.

The pulse amplitude detection circuit 33 is the AGC amplifier 3
This pulse amplitude detection circuit 33 is connected to an AGC switching circuit 34. The AGC switching circuit 34 switches the control voltage of the APD 31 based on the above-mentioned level information, and the AGC switching circuit 34 switches the control voltage of the APD 31 based on the level information, and is within the normal application range where the DC voltage of the pulse amplitude detection circuit 33 is below a predetermined threshold, that is, within the appropriate dynamic range. , a constant gain control voltage for the AGC amplifier 32 and a variable control voltage for the APD 31 are generated, and if the input is in an inappropriate dynamic range exceeding a predetermined threshold, the AG
A variable gain control voltage for C amplifier 32 and APD 3
A constant control voltage relative to 1 is generated. 35 is APD
D/D (DC/
DC) converter circuit. And here AGC
The input voltage of the switching circuit 34 is controlled by level information, and is taken out as a received level monitor output and monitored.

In the embodiment of the present invention described above, automatic gain adjustment is performed at the leading time position of each signal. However, if the level information is sent from the subscriber side and the signal sending level on the subscriber side is not sufficiently adjusted, the level of the burst signal received at the station side will be large for each subscriber. It is expected that things will be different. In that case, a means is required on the station side to reset the reception level every time a burst ends.

According to the present invention, the signal level sent to the station from a plurality of subscriber transmission devices installed at unknown locations, which are generally not fixed, can be controlled at a constant level. However, in the above description, burst transmission is performed between a fixed station and a subscriber. In this case, it is also possible to preset the reception level for each subscriber to a certain extent on the station side.

[0038]

As described above, in the present invention, level information necessary for adjusting the reception level is monitored prior to the start of a call, and the level can be adjusted in a short period of time. Therefore, improvement in transmission efficiency in burst transmission and stability in circuit operation are realized. When transmitting on the subscriber side, this stored digital data is used to set the signal level to be sent out, so that the receiving level on the station side, which is simultaneously transmitted from a plurality of subscribers, can be made as uniform as possible. Therefore, according to the present invention, it is also possible to easily control the gain of the receiving amplifier.

[0039] Furthermore, in a station-side device that receives signals from a plurality of subscribers, the reception level can be measured by monitoring the level of the reception signal and comparing it with a plurality of preset levels. Type AG
By applying feedforward control to C, the amplifier gain can be controlled accurately, the device can be made smaller, and the configuration can be simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention.

FIG. 2 is a block diagram showing an example of a subscriber transmission device.

FIG. 3 is a block diagram showing an example of an automatic gain control device on the station side.

FIG. 4 is a diagram showing an example of a burst transmission system.

FIG. 5 is a block diagram showing an example of an automatic gain adjustment circuit for optical communication.

[Explanation of symbols]

1 Signal amplification means 2 Reception level detection means 3 Reception level storage means 4 Receiving section 5 Synchronous playback circuit

Claims (7)

[Claims] Claim 1: Time division multiple access is made between a station and a plurality of subscriber equipment via branching and merging transmission lines, and gain adjustment of a received signal transmitted in bursts is performed by a signal amplifying means (1). In the automatic gain adjustment system, the receiving level detecting means (2) detects the level of the received signal by comparing the input level of the signal input from the transmission path with a set reference level, and the receiving level detecting means (2
), the receiving level storage means (3) sequentially updates and stores the level detection results of the above, and when the subscriber device enters a call state, the level information is read from the receiving level storage means (3). An automatic gain adjustment system characterized in that the gain adjustment of the received signal is performed immediately upon receiving the received signal. 2. The reception level storage means (3) is a digital memory (13) that stores the level detection result of the reception level detection means (2) as a digital value. Automatic gain adjustment system. 3. A transmission level adjustment circuit (15) for adjusting the transmission level of subscriber transmission data sent from the subscriber device to the station based on level information in the reception level storage means (3). The automatic gain adjustment system according to claim 1, characterized in that: 4. An automatic gain adjustment system in the station that simultaneously receives gain-adjusted subscriber transmission data from the plurality of subscriber devices, wherein the input level of the subscriber transmission data is set to a set reference level. Based on the level detection result of the reception level detection means (2) and the reception level detection means (2) that performs the level detection,
2. The automatic gain adjustment system according to claim 1, further comprising signal amplification means (1) whose amplification degree is controlled so as to keep the input level of the subscriber transmission data constant. 5. Level information transmitting means (16) for inserting the level information of the reception level storage means (3) into a part of the subscriber transmission data and transmitting the data from the subscriber device to the station.
The automatic gain adjustment system according to claim 1, further comprising the following. 6. An automatic gain adjustment system in the station that receives subscriber transmission data including the level information from each subscriber device, comprising: a reproducing means (23) for reproducing the level information for each received data; , the reproducing means (2
6. The automatic gain adjustment system according to claim 5, further comprising amplification means (21) for amplifying the received signal based on the level information reproduced by step 3). 7. Automatic gain adjustment that adjusts the gain of a received signal burst-transmitted to the station by time-division multiple access between the station and a plurality of subscriber devices via branching and merging transmission lines. The system includes a reception level detector (22) that compares the input level of the reception signal with a set reference level and detects the level; an amplifier circuit (21) in which the degree of amplification is controlled so as to keep the signal level of the signal constant; and an amplitude data reproducing circuit that reproduces the level information for each received data received via the amplifier circuit (21). (23); and a DA converter (24) that feedback controls the gain of the amplifier circuit (21) based on the level information reproduced by the amplitude data reproduction circuit (23). automatic gain adjustment system.