JPS6354261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly provides half-second communication between a fixed station and a plurality of mobile stations.
When transmitting and receiving digital codes using the multiplex communication method, dedicated lines are used to connect the transmitting and receiving stations located far away from the communication control room of the fixed station, respectively, and the communication control room. This method involves controlling the receiver gain by using a combination of external AGC (automatic gain control) that is added to the machine and internal AGC of the receiver, and is expected to have a significant effect on ensuring high-quality data transmission. be done.

Conventional receiver AGC uses the DC voltage level detected by the intermediate frequency stage inside the receiver, and the attack time (rise time) is determined by the CR time constant, which has the gain of each high frequency and intermediate frequency section set in advance.
and decay time. However, with this type of system, it is possible to properly adjust the reception gain against the fading phenomenon that occurs during continuous data reception, but in the half-duplex communication mode where transmission and reception are frequently switched, Although high-speed control is required, it is difficult to follow the AGC operation and the quality of data reception deteriorates.Also, with the hardware configuration that integrates the transmitter and receiver, it is difficult to switch from transmitting to receiving inside the receiver. Although it is necessary to perform gain adjustment immediately and simultaneously, this method has serious drawbacks such as impossibility in terms of cost and operation, especially when the transmitting station and receiving station are installed separately.

The present invention has been made to eliminate the above-mentioned drawbacks, and by implementing the present invention, it is possible to perform digital code transmission using the HF band between, for example, a fixed station and an aircraft or ship that moves over a wide range and at a relatively fast speed. When configured with a half-duplex communication system, the fixed station remotely controls transmitting stations and receiving stations located far away with good geographical conditions and radio wave propagation conditions to improve reception S/N.
High-quality data transmission can be achieved even on a wireless line where the data constantly fluctuates. The present invention will be explained in more detail below using Examples. Note that the first
The figure shows an example of the configuration of a communication system consisting of a fixed station and a plurality of mobile stations, FIG. 2 is a block diagram of an example of the configuration of a transmitter/receiver in a fixed station communication control room according to the present invention, and FIG. Fig. 4 is a block diagram of a configuration example of a receiving section consisting of a conventional receiver and a judgment control circuit.
The figure shows the receiver AGC (external) of the receiving station from the communications control room.
AGC) voltage control characteristic example diagram, Figure 6 is a block diagram of a configuration example of a conventional reception station receiver with additional functions of the present invention, and Figure 7 is a half-duplex communication between a fixed station and a mobile station. This is a time chart when transmitting and receiving digital codes using this method.

In the communication system shown in Figure 1, 1 is a fixed station communication control room that controls the fixed station's transmitting station 2 and receiving station 3 and performs data transmission with mobile stations 4, 5, and 6 using a half-duplex communication method. shall be. In this case, the transmitting station 2 is equipped with a transmitter and a transmitting antenna, and the receiving station 3 is equipped with a receiving antenna and a receiver. It is connected by wave line etc. Further, mobile stations such as No. 4, No. 5, and No. 6 are each equipped with a terminal device for data communication, a modem, a transmitter, a receiver, and an antenna. HF band lines are normally used for long-distance communication between mobile stations and fixed stations that move over a wide area, but in HF band lines, the received field strength changes from moment to moment depending on the location, season, time of day, etc. It is well known that it is particularly difficult to control receiver AGC to achieve high quality data communication. Figure 4 shows the reception of received signals used in conventional receivers.
In this figure, 41 is a received incoming signal, and 42 is an AGC voltage generated to change the receiver gain in response to fluctuations in the input signal strength.
It shows the change in receiver gain due to voltage level change or AGC voltage. In this figure, when the incoming signal 41 is attenuated as shown by, for example, due to fading, the AGC circuit inside the receiver operates,
It is well known to reduce the feedback (bias) voltage to the high frequency and intermediate frequency sections of the receiver in order to increase the receiver gain, as shown by the gain change characteristic of 2. FIG. 6 is a diagram showing an example of the configuration of the receiver in this case (excluding the part of the F control line indicated by a broken line), where 61 is a receiving antenna, 62 is a high frequency amplifying section, 63 is an intermediate frequency amplifying section, and 64 is a receiving antenna. The low frequency amplification sections 65 and 66 are detection amplifiers, which detect and amplify the inputs from the high frequency section 62 and intermediate frequency section 63, respectively, and feed back the AGC output to each section of the receiver to change the receiver gain. In other words, for example, when the level of the received signal decreases due to fading, etc., the AGC output also decreases and the receiver parts 62, 6
The operating principle is to increase the gain of the amplifier 64 and control the output level from the amplifier 64 to be always constant, but the following problems arise in data transmission.

In Figure 4, the time it takes from when the incoming received signal becomes small to when the gain of the receiver is increased to return to the previous normal output level state (this is the decay time) is t ₂ , and the delay time is t2. After the aging phenomenon continues for T ₂ hours, the received signal begins to return to its original level, and in response to this, the AGC voltage is controlled in the direction of lowering the receiver gain.
In this way, the time it takes for the AGC voltage to increase and the receiver gain to remain constant (this is the attack
time) is t ₁ . In case of data communication
attack time t ₁ is about 20ms, decay time t ₂ is
This time is set to about 30 ms, but this time is determined by the CR of the circuit that provides the time constant of the detection amplifiers 65 and 66, and is set to 10 to 20 times more for normal voice communication than for data communication. be done. Also, if t ₁ and t ₂ are set too small during data communication,
Depending on the level of the incoming received signal from moment to moment.
The AGC voltage changes immediately, and it takes more time to restore the receiver to its proper gain, resulting in a deterioration in reception quality. On the other hand, t ₁ and
If t ₂ is set too large, it will not be possible to quickly follow fluctuations in the level of the incoming received signal, and the reception quality will deteriorate on the contrary, which is undesirable. In this way, the AGC of the receiving device in digital data transmission
Control characteristics are very important in obtaining good transmission quality.

In the present invention, the AGC control of the receiver is performed using an internal AGC that detects and returns the output obtained from a part of the receiver.
In addition to control, it is characterized by high-quality data transmission by using control using external AGC voltage, and the results are particularly remarkable for communication systems that perform polling-type transmission and reception. Next, a communication method and an AGC voltage generation and control method when using the method of the present invention will be explained.

Figure 2 shows the details of the reception station receiver in the communication control room.
FIG. 2 is a block diagram showing an example of the configuration of a circuit portion for controlling an AGC voltage. Transmission data for communication is a digital signal inputted from a terminal device such as a keyboard, reader, or computer of a printing telegraph machine to the interface section 11 shown in FIG. is modulated into a modulated signal for transmission at radio frequency,
It is sent from A to a transmitting station located far away using a dedicated line such as a microwave line, and is generally radiated with high power from the transmitting station. On the other hand, the incoming signal is received by the receiving antenna and receiver of the receiving station, passes through a dedicated line, and is input to the demodulator 22 from the line C in Figure 2, where it is detected as a digital signal. The interface unit 24 outputs the data to the terminal device. Note that the output of the interface section 11 on the transmitting side is also supplied to the data monitoring section 14, so that the transmitted data is constantly monitored. First, when starting data transmission, it is necessary to lower the receiver gain of the receiving station, especially if the transmitting station and receiving station are relatively close to each other and the transmission power is large, such as several hundred kilowatts. Therefore, if a transmission/reception switching signal is input from the (a) line connected to the transmission/reception switching device in the fixed station communication control room, the control section 18 operates, and the control signal generation section 15
A control signal is output to the oscillation signal comparator 16 from the oscillation signal comparator 16 . The oscillation signal comparison unit 16 selects one of the two audio frequency signals from the frequency dividers 19 and 20, which are two different frequency-divided outputs of the oscillator 21, which will be explained later, and selects one of the two audio frequency signals from the frequency dividers 19 and 20, which are two different frequency-divided outputs of the oscillator 21, which will be described later. It is sent from B through a band pass filter (LPF) 17 to a receiving station via a dedicated line. Next, the control operation of the receiving station using this signal will be explained using the time chart shown in FIG.

For example, the fixed station in the communication system shown in Figure 1 is the 7th station.
When configuring a polling type communication system using the time chart shown in the figure, AGC control is performed as shown below. 71 in Figure 7 _is the transmitter and transmitting antenna of the transmitting station from the communication control room of the fixed station.
72 indicates that the interrogation data is transmitted to the mobile station by operating only during each time period of T ₂₁ , and 72 is the first
Data 73 indicates that the mobile station in the figure, for example station 4, sent response data only during T ₁₂ , and data 73 indicates that station 5 sent response data only during T ₂₂ . When the fixed station and mobile station are continuously receiving incoming reception signals after starting data communication, the above internal
The AGC circuit operates to keep the receiver output level constant and ensure high quality data. At this time, for example, if the transmission signal ends at time a ₁ in FIG _.
(during this period, the receiver gain of the fixed station is lowered by the internal AGC voltage), data monitoring section 1 in Figure 2
4 determines and outputs a control signal indicating the end of the transmission data, and notifies the control signal generator 15 of the end of the transmission data. When the control signal generation section 15 receives this control signal, it operates the oscillation signal comparison section 16. As explained above, when switching from reception to transmission, it is necessary to quickly lower the receiver gain of the reception station. Furthermore, at the end of transmission, it is necessary to operate in the complete opposite manner so that response transmission data from the mobile station can be sufficiently captured and received no matter when it arrives. In particular, in order to receive response data correctly from the beginning, AGC control must be performed to quickly increase the receiver gain at the receiving station. In the method of the present invention, the gain of the reception station receiver is increased or _decreased by using two frequencies in the voice band sent from the communications control room via a dedicated line. ₂ , and ₁ to obtain two-frequency output.
It is sufficient to divide the frequency by providing an oscillator with a frequency _{of 0} equal to the least common multiple of ₂ , and FIG. 21 shows an oscillator with a frequency of ₀ . There is a relationship of ₀ = n ₁ = m ₂ , for example ₁ = 1200
Hz, ₂ = 1500Hz then n = 5, m = 4 and ₀ = 6000Hz
is chosen as. In Figure 2, 19 is 1/n
The frequency divider circuit outputs ₁ , and 20 is the 1/m frequency divider circuit.
Assume that it outputs ₂ .

First, increase the gain of the receiver at the receiving station.
The case where AGC control is performed will be explained. It is assumed that while the fixed station is transmitting, _one wave is selected through the LPF 17 and sent out from B. When the data transmission is finished, the control signal from the control signal generator 15 to the oscillation signal comparison unit 16 is switched to the _2- wave selection command as described above, and _{the 2-} wave signal is sent out from B after passing through the LPF 17, and is sent to the oscillation signal comparison unit 16 through the dedicated line. The signal is input from D to the judgment control circuit of the receiving station shown in FIG. 35 in Figure 3
and 37 are band pass filters (BPF) for extracting ₁ wave and ₂ waves, respectively, 34 and 36 are detectors for DC detection of the output of the BPF, and 33 is a comparison detection section that connects the detectors 34 and 3.
The magnitude of the level of the input from step 6 is determined. Also 3
1 is a receiving antenna, and 32 is a receiver. In order to prevent malfunctions due to noise etc. when the comparison detection unit 33 determines the level of _{the 1st} wave and _{the 2nd} wave as in this example, it is desirable to make the BPF 35 and BPF 37 have as narrow band characteristics as possible. Large absolute delays must be avoided. The time spent on actual transmission/reception determination is within 2 to 3 ms. If the comparison detection unit 33 determines that the input level of the _second wave has become higher than the input level of _{the first} wave, the receiver 32 is in a state where the AGC characteristics are released, that is, the receiver gain is at its maximum (actually B in the communication control room so that the
As shown in FIGS. 3 and 6, the output is input to the comparison detection section 33 through the dedicated line input terminal D and is controlled through the F line. In this case, AGC is inside the receiver.
Unlike AGC, it works as an external AGC and changes the AGC voltage as quickly as possible (within 1ms).

To explain Fig. 6, which has added a control function using the F control line, input from the F line shorts the CR time constant circuits of the detection amplifiers 65 and 66, minimizing the AGC voltage and maximizing the gain of the receiver. do. FIG. 5 is a time chart explaining this external AGC characteristic. In FIG. 5, 51 is the transmission signal of the fixed station transmitter, and 52 is the comparison detection unit 3 of FIG.
3 is a time chart of the control signal on the control line F given to the receiver to determine the level and maximize the receiver gain when switching from ₁ wave to ₂ waves, 53 is the receiver gain due to this control signal This is a time chart of changes. When the emitted signal from the transmitter ends at point 51, the control signal 52 is given to the receiver with a delay of Δt (1ms), and after _t3 , the AGC voltage becomes the minimum and the receiver gain becomes the maximum. Become. In this case, Δt+t ₃ is approximately 2 to 3 ms, and the internal AGC decay explained in FIG.
Since the relationship Δt+t ₃ <<t ₂ is maintained with respect to time t ₂ , the counter-reply signal from the mobile station is awaited with the receiver gain at its maximum from the beginning. When a received signal actually arrives following such a standby state, the incoming signal causes internal damage to the receiver, as explained in Figure 4.
The AGC voltage level changes depending on the operation of the AGC circuit.
Since it increases at attack time t ₁ and lowers the receiver gain, data reception can always be performed with an appropriate gain. The received signal is sent from the receiver 32 of the receiving station to the input of the communication control room shown as C in FIG. 2 via a dedicated line shown as line E in FIG. 3. Also, when the fixed station switches from receiving to transmitting and the number of signals arriving at the receiver from the dedicated line (B-D) changes from ₂ waves to ₁ wave, the external AGC operates in the same way to suppress the receiver gain. be able to. However, in this case, since the only problem is the quality of the reception monitor of the own station, this function may be omitted in some cases. Although the case where gain control is performed using the received level difference between two control signals of two frequencies ₁ and ₂ has been described above, control may be performed using the received output of one control signal.

As explained in detail above, according to the method of the present invention, the fixed station automatically transmits signals from the communication control room to the receiving station receiver when the fixed station switches between transmitting and receiving.
Control voltage and internal AGC generated inside the receiver
Since AGC control of the reception station receiver is performed in combination with the control voltage, the receiver can always operate under good conditions and receive high quality data.
Note that the transmitter and receiver of a mobile station each use a half-duplex communication transceiver with integrated hardware, but unlike a fixed station, the transmitter and receiver of the mobile station can switch between transmitting and receiving. It is easy to make the gain of the receiver section zero or suppress it, and then quickly restore it after transmission is complete, as shown in FIG.

[Brief explanation of the drawing]

Figure 1 is an example of the configuration of a communication system between a fixed station and a mobile station, Figure 2 is an example of the configuration of a transmitter/receiver in a fixed station communication control room according to the present invention, and Figure 3 is a receiver installed at a fixed station reception station. FIG. 4 is an example of the AGC characteristics of a conventional receiver, FIG. 5 is an example of the AGC characteristics of the receiver according to the present invention, FIG. 6 is an example of the configuration of the receiver, and FIG. is a time chart of digital data transmission and reception using the half-duplex communication method between a fixed station and a mobile station. 1... fixed station, 2... transmitting station, 3... receiving station,
4, 5, 6... Mobile station, 11, 24... Interface section, 12, 23... Memory, 13... Modulator, 14... Data monitoring section, 15... Control signal generation section, 16... Oscillation signal comparison section, 17...Low frequency filter (LPF), 18...Control section, 19, 20...
...Frequency divider, 21... ₀ frequency oscillator, 22...Demodulator, 31...Receiving antenna, 32...Receiver, 3
3... Comparison detection section, 34, 36... Detector, 3
5, 37...Band frequency filter (BPF), 62...High frequency amplification section, 63...Intermediate frequency amplification section, 64...Low frequency amplification section, 65, 66...Detection amplification section.

Claims (1)

[Claims] 1 When transmitting and receiving digital code data using a half-duplex communication method between a fixed station and multiple mobile stations, each consisting of a communication control room and a transmitting station and a receiving station located far away, each connected via a dedicated line. To,
A control signal is sent from the communications control room to the receiving station in response to the switching operation from the end of transmission from the fixed station to data reception from the mobile station, and the receiver at the receiving station controls its gain based on the received output of the control signal. A reception AGC control method is characterized in that the response data can be received correctly from the beginning of the response data, and the gain is controlled according to the output of the receiver during subsequent continuous reception.