JPS593898B2 - Communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a communication system, and particularly to a system for transmitting information between a master station and one or more slave stations, which compensates for loss in the transmission path and receives signals at a constant level. This is related to the communication method used.

When pulses are sent to a transmission line, waveform distortion occurs due to transmission loss (distortion).

This transmission loss is proportional to the square root of the frequency. Generally, in order to deal with this transmission loss, a circuit network with characteristics opposite to that of the transmission loss is provided on the receiving side to compensate for this. However, this loss changes as the distance changes, so the characteristics of the receiving circuit must be changed.

Therefore, conventionally, so-called automatic equalization circuits, automatic gain control circuits, etc. have been used. Now, this automatic equalization circuit,
An automatic gain circuit (AGC) can be effectively used in one-to-one communication, but cannot be used effectively in one-to-n multi-head knob type communication.

The reason for this will be explained below with reference to FIG. In the multi-drop data highway system shown in Figure 1, 1
1 is a master device (master station) including a computer, 1
2-1, 12-2, . . . are slave devices (slave stations) each including various terminals, and each slave station is connected to the transmission line 13.
It is connected to the multi-head knob type.

Information from the master station 11 is transmitted to each slave station (12-1, 12-2, . . .) via the downlink transmission path 13-1, while information from each slave station is transmitted through the uplink transmission path 13-1. -2 to the master station. In such multi-drop type communication, in order to compensate for the levels by providing automatic equalizers, AGC, etc. in each of the master station and slave stations, it is necessary for these circuits to operate stably, so signals are constantly transmitted. The receiving side must receive this and compensate the received signal level based on the received amount. In other words, the master station and slave stations must constantly send signals to each other.

However, in multi-drop type communication, although it is possible to constantly send signals from the master station to the slave station side, each slave station always sends signals to the master station at the same time, and this causes the master station to cannot compensate for the received signal level. That is, from all slave stations to only one master station,
This is because even if the signals are sent out at the same time, the master station cannot identify from which slave station the signals are being sent. From the above, level compensation cannot be achieved by simply applying an automatic equalizer, AGC, etc. in 1:n multi-drop type communication.

However, the present invention provides a new communication method that can automatically compensate levels in the directions of 1→n (master station→slave station) and n→1 (slave station→master station) in one-to-n communication. To summarize, the purpose is to provide the slave transmitter with the same loss compensation characteristics as the receiver on the slave station, thereby ensuring that the transmission from the master station to the slave station is This is achieved by a communication method that makes the transmission characteristics of the mobile station and the transmission characteristics from the slave station to the master station almost the same.

Hereinafter, the present invention will be explained in detail with reference to the drawings. As mentioned above, transmission loss is proportional to the square root of frequency, but as shown in Figure 2, the frequency characteristics of this transmission line are divided into a constant loss portion and a single pole that determines attenuation for a given cable length. It can be approximated by a combination of and a part that attenuates at 6 dB/0 ct. That is, for low frequencies, the line is considered to be a lumped constant within a certain distance, and simply considering the attenuation of the direct current resistance of the line will result in a flat frequency characteristic.

Also, in the high frequency range, the loss is proportional to V, so it is 6 dB/0.
It shows the attenuation characteristics of ct. Now, in 1-to-n communication,
In the direction from the master station to the slave station, the transmitter of the master station transmits a signal with flat characteristics as shown in Figure 3, while the receiver of the slave station transmits a signal with flat characteristics to compensate for transmission loss. It is sufficient to provide an approximation characteristic opposite to the approximation of the transmission line, that is, a constant gain portion and a single zero point as shown in FIG.

In FIG. 4, the 6 dB/0 ct curve is a portion for compensating transmission loss, and the 12 dB/0 ct curve is a portion for waveform equalization. In addition, the transfer characteristics of the transmitter on the master station side shown in Figure 3 are attenuated in high frequencies to reduce the influence of crosstalk caused by signals on the uplink, that is, the transmission path from the slave station to the master station. It's for a reason. The frequency characteristics of the slave station receiving section described above can be realized by the circuit shown in FIG.

That is, FIG. 5 is a circuit block diagram of the receiving section on the slave station side. 1 is an amplitude control circuit, which controls the amplitude by changing the variable impedance of a built-in diode (not shown) using the AGC voltage described below. An equalizer that approximates the high frequency loss of the transmission line to 6 dB/0 ct, amplifies it to compensate for it, and has a built-in variable capacitance diode (not shown) that is controlled by the AGC voltage in order to obtain a variable zero point: 3 is an input signal An amplifier that performs waveform equalization and amplification: 4 is a peak detector that detects the peak value of the input signal; 5 is a differential amplifier that compares the peak value with the reference voltage E, and amplifies the difference with direct current and performs AGC Generates voltage and this AGC
The impedance value and capacitance value of the variable impedance and variable capacitance diode are respectively controlled by voltage.

Note that 1 and 2 form a variable circuit.

According to this circuit, its gain and zero point change depending on the level of the received signal, and the input signal can be converted into a signal at a constant level and input to the rear identification circuit. Specific techniques for gain control of the amplitude control circuit 1 and equalizer 2 in this variable circuit are disclosed, for example, in Japanese Patent Publication No. 46-39770 or "High Speed PCM" (Electronic Engineering Progress Series 7; published by Corona Publishing Co., Ltd.) This is achieved by using equalizer or amplifier gain control techniques. Furthermore, the present invention is not characterized by the technique of gain control of these variable circuits, and further details will be omitted. FIG. 6 illustrates the frequency characteristics of the master station transmitter, the downlink transmission path, and the slave station receiver in downlink communication, where 101 is the frequency characteristic of the slave station receiver, and 102 is the frequency characteristic 103 of the transmission path. 104 is the frequency characteristic of the master station transmitter, and 104 is the overall characteristic.

In the figure, 11, 12, and 13 are transmission distances, and there is a relationship of 1, 12, 13. As described above, the level of the signal from the master station to the slave station is compensated by the overall characteristic 104.

On the other hand, in communication from the slave station side to the master station, a method is required that has low crosstalk and does not deteriorate the S/N at the receiving end. This is achieved by compensating the level of the transmitted signal.

That is, as shown in FIG. 7, the characteristics of the receiving section of the master station include a constant gain part a and a fixed zero point c to compensate for the maximum transmission loss.
As shown in Fig. 8, the transmitter characteristics of the slave station include a variable portion a with constant gain, and a fixed pole b that cancels each other out at the same frequency as the fixed zero point of the receiver on the master station side. A portion having the above variable zero points C1 to C2 is provided.

The frequency characteristics of the above-mentioned master station receiving section are similar to those of the slave station receiving section shown in Fig. 4, and the frequency characteristics of the slave station receiving section when the slave station receiving section compensates for maximum transmission loss Matches the frequency characteristics.

In other words, the frequency characteristics of the receiving section on the master station side are set such that when the maximum loss occurs in the transmission path, it can compensate for it alone. Now, as shown in FIG. 9, the slave station transmitting section is composed of a unipolar/bipolar converter 51, a 6 dB/0 ct attenuator 52 that attenuates the input signal at 6 dB/0 ct, an amplitude control circuit 53, an equalizer 54, and an amplifier 55. There is.

The amplitude control circuit 53 and the equalizer 54 constitute a variable circuit, and have exactly the same configuration as the amplitude control circuit 1 and equalizer 2 of the slave station receiving section described above, and the impedance and capacitance are adjusted by the AGC voltage in the slave station receiving section. change. Therefore, the frequency characteristics of the variable circuits of the slave station receiving section and the transmitting section change in exactly the same manner depending on the transmission distance, that is, the transmission loss, and the transmission loss from the slave station to the master station is sufficiently compensated.

Figure 10 illustrates the frequency characteristics of the upstream transmission line and the receiving section of the master station, respectively.
01 is the frequency characteristic of the slave station transmitter, 202 is the frequency characteristic of the uplink transmission path, 203 is the frequency characteristic of the master station receiver, 204
is a comprehensive property.

In the figure, 11 to 13 are the distances between the master station and slave stations, and 11<1
There are 23 relationships. Note that the characteristic 20111 is the frequency characteristic of the slave station transmitter when there is no loss in the line.
From the above, in uplink communication, the frequency characteristics of the master station receiving section are fixed to those that can compensate for the maximum line loss, and the frequency characteristics of the slave station transmitting section are changed according to the transmission distance, that is, the transmission line characteristics. This is to perform level compensation. If the characteristics of the slave station transmitting section are changed in exactly the same way as the characteristics of the slave station receiving section, it is possible to compensate for the loss in the uplink line. As described above, the signal from the slave station to the master station and the signal from the master station to the slave station are sufficiently compensated, and digital signals can be correctly identified in both the master station and the slave station.

Moreover, according to the present invention (1) Due to automation, on-site inspection and maintenance are easy.

(2) Since the AGC voltage is stable, stable uplink/downlink communication is possible. (3) Changes (temperature) in the transmission path can be absorbed by AGC on both the upstream and downstream sides.

The effects are remarkable.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the multi-drop communication system, Figure 2
The figure shows the frequency characteristics of the transmission line, Figure 3 shows the frequency characteristics of the master station transmitter, Figure 4 shows the frequency characteristics of the slave station receiver, Figure 5 shows the circuit block diagram of the slave station receiver, and Figure 6 shows the downlink. Figure 7 shows the frequency characteristics of each part and overall characteristics in communication. Figure 8 shows the frequency characteristics of the slave station transmitter. Figure 9 shows the circuit block diagram of the slave station transmitter. Figure 10 shows the frequency characteristics of each part and overall characteristics in uplink communication. 1, 53... Amplitude control circuit: 2, 54...
・・Equalizer, 3・・・Amplifier: 4・・・・
・Peak detector: 5...Differential amplifier.

Claims (1)

[Claims] 1 In a system in which a master station and one or more slave stations transmit information via a transmission path, the transmitter of the master station transmits signals with flat frequency characteristics, while the receiver of the slave stations a variable equalization circuit having a variable transfer characteristic that is flat at a low frequency level and having at least one variable zero point;
an equalizing amplifier that equalizes and amplifies the waveform of the output of the variable equalizing circuit; and a peak detector that detects the output peak value of the equalizing amplifier; without changing the transfer characteristics and variable zero point,
The signal level from the master station sent through the transmission path is compensated for and received, and the receiving section of the master station receives transmission with constant gain at a low frequency level to compensate for the maximum transmission loss on the transmission path. The transmitting section of the slave station has a fixed pole that matches the frequency of the fixed zero of the receiving section of the master station, and at least one variable zero point, and has a variable transfer characteristic that is flat at the low frequency level. A variable equalization circuit is provided, which changes the transfer characteristics of the slave station transmitter and the frequency of the variable zero point based on the peak value of the peak detector of the slave station receiver, and adjusts the level of the signal sent from the slave station to the slave station. A communication system characterized in that the transmitting section of the station compensates and transmits the data to the master station.