JPS61274527A - Automatic gain control communication system - Google Patents

Abstract

PURPOSE:To avoid an overload state in a reception station and to stabilize a communication level by controlling the reception amplification gain and the transmission amplification gain of a fixed station based on a pilot signal sent from a mobile station being communication object. CONSTITUTION:A fixed station 2 is connected to one end of a guide line 1 installed in a tunnel, a pseudo load 3 is connected to the other to attain communication by moving mobile stations 41-4n along the guide line 1. A transmission or reception signal to transmission/reception sections 201-20n is brought into the optimum matching state by using an antenna coil 5 connected to the guide line 1 of the fixed station 2. A reception section R and a transmission section T are provided to the transmission/reception sections 201-20n, the reception section R is provided with a channel filter 25 and a pilot filter 26 and the filter 26 extracts from the mobile stations 41-4n by the filter 26. Then based on the pilot signal from the mobile stations 41-4n, the gains of a transmission amplifier 44 and a reception amplifier 22 are controlled to stabilize the communication level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic gain control communication system that is capable of stabilizing the communication level between a fixed station and a mobile station that communicate with each other via a guide line.

[Background technology]

For example, the automatic gain control communication system shown in FIG. 2 has been proposed. This automatic gain control communication system consists of a guide line 1 laid in an underground common trench or a tunnel,
A fixed station 2 on the ground connected to one end of the line 1; a pseudo load 3 connected to the other end of the guide line 1; It is composed of mobile stations 4, . . . The fixed station 2 is connected to the mobile station 4. It is equipped with a plurality of transmitting/receiving units having different frequencies so that each of ~4 fl can be individually called and communicated with.

In the above configuration, the mobile stations 4I to 41 usually move with only the receiving section in the operating state in order to save power consumption. For example, when the fixed station 2 makes a call to the mobile station 41, the fixed station 2 calls and communicates with the mobile station 41 using a transmitting/receiving section of a frequency set therein. In addition, mobile stations 41 to 47
In this case, by calling the fixed station 2, the transmitter/receiver on the same frequency responds and a telephone conversation can be made.

By the way, in the configuration as shown in FIG. 2, the mobile station 4. ~
As 4n moves away from the fixed station 2, the received electric field strength of the receiving section within the fixed station 2 becomes weaker. Therefore, the reception state of the fixed station 2 is made constant regardless of changes in the communication distance.
Conventionally, configurations that allow stable communication have been adopted. That is, the mobile station that receives a call from the fixed station 2 sends out a pilot signal in conjunction with turning on the transmission switch of the transmitter in order to respond, and the fixed station 2 that receives this pilot signal receives the signal. The section incorporates a so-called AGC circuit that controls the gain of the receiving amplifier according to the strength of the pilot signal.

[Problems to be solved by the invention]

However, in this automatic gain control communication system, only the AGC control is performed in the receiving circuit of the fixed station, and the transmission level is constant, so there is a problem that the receiving circuit of the mobile station with close communication distance may be overloaded. was there.

[Means and effects for solving the problem] The present invention has been made in view of the above, and in order to stabilize the communication level between a fixed station and a mobile station, a pilot signal transmitted from a mobile station is The present invention provides an automatic gain control communication system that controls not only the receiving amplification gain of a fixed station but also the gain of a transmitting amplifier based on the present invention.

〔Example〕

The automatic gain control communication system according to the present invention will be explained in detail below.

Figure 1 is an embodiment of the present invention (only the configuration of the fixed station is shown)
is connected to the guide line 1, and transmits/receives the transmitting/receiving section 20. with optimal matching of transmitting power and receiving signals. ~20. an antenna coil 5 for transmitting data to and from each of the antenna coils 5, and a transmitting/receiving section 20. whose transmitting terminals and receiving terminals are all connected in parallel to the antenna coil 5, and which communicates with a specific mobile station. ~
201.

Transmitting/receiving section 20. ~20fi has the same configuration except for the communication frequency, and is a receiving unit that receives a signal from a mobile station transmitted from the antenna coil 5, amplifies and demodulates it, amplifies the low frequency, and outputs audio from the speaker 23. The transmitter T modulates the audio signal of the microphone 24, amplifies its power, and then sends a modulated signal of a predetermined frequency to the antenna coil 5.

The receiving section R includes a branching filter 21 that passes only a specific frequency range of the signal from the antenna coil 5, and a receiving amplifier 22 that amplifies the signal that has passed through the filter 21.
A first demodulator 23 converts the signal from the amplifier 22 using a predetermined frequency; an oscillator 24 supplies a signal of a predetermined frequency to the demodulator 23; A channel filter 25 extracts only the signal component corresponding to the content, a pilot filter 26 extracts only the pilot signal component from the output signal of the demodulator 23, and a pilot signal is received according to the level of the pilot signal output from the filter 26. A G C (A
an automatic gain control circuit 27 that applies AGC to the transmission amplifier 44 of the transmission section T (described later), and a second demodulation circuit that demodulates the signal output from the channel filter 25 to an audio level. an oscillator 29 that oscillates a signal of a predetermined frequency to be supplied to the demodulator 28, and a demodulator 28.
a low-pass filter 30 that removes high frequencies from the signal output from the filter, an audio amplifier 31 that amplifies the voltage and power of the signal from the filter 30 to a predetermined level, and a speaker that is driven by the audio amplifier 31 to emit audio. It is composed of 32 pieces.

The transmitter T also includes a microphone that converts audio into electrical signals.
an attenuator (ATT) 34 that sets the output of the microphone 33 to an optimal level; a filter 35 that passes only signals within the required bandwidth of the audio signal output from the attenuator 34;
a first modulator 36 that modulates the signal at a predetermined frequency;
, an oscillator 37 that outputs a signal of a predetermined frequency to the modulator 36, a channel filter 38 that passes only the frequency range output from the modulator 36, and mobile stations 41 to 4n.
a signal circuit 39 that sends a signal to designate one of them as a communication partner; a signal filter 40 that passes only the frequency range output from the circuit 39; and a signal filter 40 that modulates the audio component and the signal component to a predetermined frequency. a second modulator 41; an oscillator 42 that outputs a carrier signal to the modulator 41;
A low-pass filter 43 that passes only frequency components within a predetermined width centered on the carrier signal, and a gain of the signal output from the filter 43 is adjusted while being controlled by an AGC signal output from an automatic gain control circuit 27. It is composed of a transmission amplifier 44 that amplifies voltage and power to a predetermined level, and a branching filter 45 that passes only the frequency component output from the modulator 41.

In the above configuration, for example, the fixed station 2
．． The mobile station 4. operates the transmitter T of the mobile station 4. In response, the mobile station 4. turns on its transmitter circuit,
A pilot signal is sent to the guide line 1 together with the contents of the call. This transmission signal is received by the receiving unit R (other transmitting/receiving units 20
□～20. (blocked by a demultiplexing filter provided at the input stage), is amplified by an amplifier 22, and then subjected to two demodulation processes to amplify the sound, and output it to the speaker 3.
Audio is output from 2. At the same time, automatic gain control circuit 27
A GC signal is generated by the pilot signal transmitted from the mobile station 41, and is output to the reception amplifier 22 and the transmission amplifier 44. This AGC signal indicates a level corresponding to the received strength of the pilot signal, and functions to apply strong AGC to the amplifiers 22 and 44 when the signal is strong, and to apply weak AGC to the amplifiers 22 and 44 in the opposite case. The reception level of the pilot signal PL at the fixed station 2 is higher when the mobile station is located at a location with less transmission loss (i.e., closer to the fixed station 2), and the higher the transmission loss is (i.e., the farther away from the fixed station 2) the mobile station is located. Therefore, by varying the gain of the transmission amplifier 44 according to the reception level of this pilot signal PL, the transmission output level from the fixed station 2 is controlled, and the mobile station receiving it The optimum receiving level is always obtained in the receiving circuit, and no overload condition occurs, making it possible to make good calls.

The above is the transmission/reception unit 20. ~20. This is a case where the mobile stations 4□ to 4n correspond one-to-one, but it is also possible to configure a system in which the calling frequencies of the mobile stations 4° to 4n are the same and a single transmitter/receiver is used to make batch calls. be. In this case, mobile station 4. The reception level of the fixed station 2 is added to the number of pilot signals transmitted from each of 4n to 4n that have responded. Generally, there are about five mobile stations in one communication system, and the maximum level addition is about 7 dB, and this 7 dB pilot signal level addition exceeds the transmission level of fixed station 2. AGC is applied to increase the signal by 7 dB'). At this time, by specifying the person to call,
Except for the corresponding mobile station, the other mobile stations sequentially shift their modes to the standby state, so ultimately their transmission gains are controlled only by the pilot signal PL from the designated mobile station. , you can make normal calls.

Note that the present invention can also be applied to a configuration in which AGC is not applied on the receiving side.

〔Effect of the invention〕

As explained above, according to the automatic gain control communication system of the present invention, the receiving amplification gain and the transmitting amplification gain of the fixed station are controlled based on the pilot signal transmitted from the mobile station to be called, so that the receiving station The communication level can be stabilized by avoiding overload conditions.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an automatic gain control system. Code table 1----1 guiding line, 2--Fixed station, 4. ~47
−−−−−−Mobile station, 5−・−Antenna coil,
201~20n'---- Transmitting/receiving section, 21.45
----- Branching filter, 22---- One receiving amplifier,
23, 28--Demodulator, 24.29.37.42
-1--Oscillator, 25.38--Channel filter, 26--1--Pilot filter, 2
7----・Automatic gain control circuit, 30, 35.43--
---Low-pass filter, 31--Audio amplifier, 32--Speaker, 33--Microphone, 34--Antenna, 36.41--
--1 modulator, 39 ---1 signal circuit, 40 ---1 signal filter, 44 --- transmission amplifier.

Claims (1)

[Claims] A fixed station is connected to the terminal of a guide line laid inside a tunnel, etc.
In communication equipment that performs communication between a mobile station moving along the guide line and the fixed station, a transmission level of the fixed station is controlled according to a reception level at the fixed station of a pilot signal transmitted from the mobile station. An automatic gain control communication system characterized by providing gain control means.