JP2555114B2 - Line switching device for digital communication system - Google Patents

Description

The present invention relates to a line switching device of a digital communication system configured to be able to switch between an active system and a standby system, and an equalizer for disconnecting a transmission signal at the time of line switching is unnecessary. Digital communication that has a working system and a standby system and is configured to be capable of switching between the working system and the standby system for the purpose of preventing a response and facilitating the line switching and shortening the line switching time. The system further comprises an equalizer having a delay element for inputting a transmission signal from the changeover switch circuit of the active system to the transmission end side of the standby system and performing gain control using the output thereof. An input signal disconnection detection circuit for detecting disconnection of an input signal input to the equalizer, and a disconnection detection signal output from the input signal disconnection detection circuit when the disconnection of the input signal is detected. Maintain the output of the equalizer immediately before the disconnection detection signal is generated. The holding circuit that keeps operating and the output of the holding circuit is applied to the equalizer as a control signal for controlling the gain of the equalizer during the generation of the disconnection detection signal. It is configured to include a signal disconnection detection holding circuit having a switch circuit configured to apply the output of the equalizer as it is to the equalizer.

[Industrial applications]

The present invention relates to a digital communication system having a plurality of working systems and one protection system and capable of switching lines with each other, and more specifically, occurs when switching from the working system to the protection system in a digital radio transmission system. The present invention relates to a line switching device that eliminates the lengthening of the line switching time caused by an unnecessary response of an equalizer due to a momentary signal loss.

FIG. 4 shows a block diagram of a digital communication system to which the line switching device of the present invention is applied. One standby system 100 and a plurality of active systems, but only one active system 200 is shown in the figure, are provided in parallel. The active system 200 has a hybrid circuit 201 and a changeover switch 20 on the transmission side (transmission end side).
2, bipolar / unipolar converter 203, modulator 204
And an antenna 205. The active system 200 also includes an antenna 251, a demodulator 252, a unipolar / bipolar converter 253, and a changeover switch 254 on the receiving side (receiving side) connected to the transmitting side via the aerial line. Other active systems not shown also have the same configuration as above. The standby system 100 has a bipolar / unipolar converter 103 and a modulator 104 on the sending end side.
And an antenna 105. Further, the backup system 100 has an antenna 151, an antenna 151, on the receiving end side connected to the transmitting end side via an aerial line.
Demodulator 152 and unipolar / bipolar converter 153
Have.

The plurality of active systems and the standby system 100 are connected via a line 911 on the sending end side, and one of the active systems and the standby system is switched by a changeover switch, for example, 202. A test pattern signal generator 901 is connected to the line 911. The transmission end side is switched depending on the signal reception state of the reception end side, for example, deterioration of the received signal quality due to fading. That is, for example, when the receiving end detects the deterioration of the quality of the received signal due to fading, it instructs the transmitting end to switch the line to the protection system. Along with this, the changeover switch 254 on the receiving end side of itself is also changed over to the standby system. When the received signal has recovered to a quality equal to or higher than a predetermined quality, the backup system is switched back to the active system.

FIG. 4 describes the case where data is transmitted in one direction with one side as the sending end side and the other as the receiving side, but normally bidirectional data transmission is possible, and both the standby system and the working system are available. Also, a transmission / reception system is provided on one side and a transmission / reception system on the other side.

It is desirable that line switching from the active system to the standby system or vice versa be performed without interruption. Therefore, means for adjusting the changeover switch speed, the phase shift at the time of switching, and the data pattern shift are adopted. Although these various measures are taken on both the sending end side and the receiving end side, the present invention mainly provides switching from the sending end side to the instantaneous interruption or the receiving end side with little influence.

[Conventional technology]

Bipolar / unipolar converter 103 or 203 on the sending end side
Is a line length equalizer 1a and an amplitude detector as shown in FIG.
31, amplifier 32, clock recovery circuit 4a and bipolar /
The unipolar converter 5a is constructed as shown. The line length equalizer 1a receives the transmission bipolar signal SBI via the changeover switch 202 or the hybrid 201, and the amplitude detector 3
An AGC loop formed by 1 and the amplifier 32 is formed to equalize the input bipolar signal SBI. Clock recovery circuit 4a
Extracts the clock CLK from the output S1 'of the equalizer 1a and supplies this clock CLK to the bipolar / unipolar converter 5a. The bipolar / unipolar converter 5a converts the equalized bipolar signal S1 'into a unipolar signal for modulation device 10
It transmits via 4,204 and antennas 105,205.

[Problems to be solved by the invention]

The changeover switch 202 is speeded up in order to speed up the switching, but switching of the bipolar signal is performed by a mercury relay or the like.
A switching time of about several ms is used. Therefore, switching from the active system to the standby system requires a switching time τ as shown in FIG. 6 (a), during which the bipolar signal SB
I signal loss occurs.

On the other hand, since the equalizer 1a itself has a delay element, even if the input bipolar signal SBI is cut off, an unnecessary response is shown according to the time constant of the delay element, and its output is shown in FIG. 6 (b).
Changes as shown in FIG. Moreover, the time τ ′ until the stability is reached is considerably longer than the signal disconnection time τ. Since the fluctuating signal having an unnecessary response is sent out accordingly, there arises a problem that the receiving end side also makes an unnecessary response. Switching time τ
There is a problem that the unnecessary response time τ'is longer and the switching time is substantially longer.

From the above, even if the bipolar signal is disconnected during switching and the input to the equalizer is disconnected, unnecessary response can be substantially prevented.
It is desired that the switching time can be shortened.

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the line switching device of the digital communication system of the present invention. The line switching device is provided in the bipolar / unipolar switching device 103 on the sending end side of the standby system.

The line switching device of the present invention detects the disconnection of the bipolar signal input to the equalizer 1 to the equalizer 1, and in the case of the signal disconnection, outputs the output S1 of the equalizer 1 immediately before the signal disconnection. The detected voltage is retained and continuously applied as an AGC feedback signal to the equalizer 1. When the signal is restored, the voltage detected from the output S1 of the equalizer 1 is directly equalized as an AGC feedback signal as before. A signal disconnection detection holding circuit 2 provided to the container 1 is provided.

More specifically, the line switching device of the present invention is
In a digital communication system configured so that the active system and the standby system can be switched to each other, on the transmission side of the standby system,
A transmission signal (for example, a bipolar transmission signal) from a working changeover switch circuit is input, and an equalizer 1 having a delay element for performing gain control using the output is provided and the equalizer 1 is provided. An input signal disconnection detection circuit that detects disconnection of the input signal (for example, input bipolar signal) and disconnection in response to the disconnection detection signal output from the input signal disconnection detection circuit when the input signal disconnection is detected. A holding circuit that continues to hold the output S1 of the equalizer 1 immediately before the detection signal is generated, and a holding circuit as a control signal (for example, an AGC feedback signal) that controls the gain of the equalizer 1 during the generation of the disconnection detection signal. And a switch circuit configured to apply the output of the equalizer 1 to the equalizer 1 as it is in the case other than the above-described input signal disconnection. Has two

When switching back from the standby system to the active system, the hybrid circuit 201 directly connects the bipolar / unipolar converter 203.
Since a bipolar transmission signal or the like is applied to the input terminal and the input signal is not disconnected, it is not necessary to provide the above circuit in the working system.

[Work]

Even if the signal disconnection detection holding circuit 2 holds the input signal such as the input bipolar signal, by holding and giving the AGC feedback signal of the equalizer state immediately before the signal disconnection, the state of the equalizer is maintained immediately before the signal disconnection. Hold the state. Therefore, unnecessary operation does not occur, the equalization state is kept constant, and the switching disconnection state is virtually eliminated.

〔Example〕

A line switching device according to an embodiment of the present invention will be described with reference to FIG.

The equalizer 1 is composed of a line length equalizer 1a, and the signal break detection holding circuit 2 is composed of an input signal break detection circuit 21, a holding circuit 22 and a switch circuit 23. Others are the same as the conventional one, and the amplitude detection circuit 3 is composed of an amplitude detector 31 and an amplifier 32.

The operation of the apparatus shown in FIG. 2 will be described with reference to FIGS.

The holding circuit 22 holds the voltage from the amplifier 32 by inputting the output of the amplifier 32 and detecting disconnection of the input. on the other hand,
In a normal state, the switch circuit 23 feeds back the output of the amplifier 32 to the equalizer 1a as shown by the solid line in the figure.

The input signal disconnection detection circuit 21 receives the bipolar input SBI, and when the signal level becomes zero, it immediately switches the circuit.
A switching signal S21a is output to 23 (FIG. 3 (b)), the switch circuit 23 is energized as shown by the broken line, and the holding circuit 22
The holding signal S21b is output to the holding circuit 22 and the holding circuit 22 holds the equalization state of the equalizer 1a immediately before the signal break. As a result, the switching period τ and the equalization state of the equalizer 1a are held in the state immediately before the interruption of the input signal (FIG. 3 (d)).

This is essentially the same as no switching occurs,
The unnecessary operation of the AGC loop of the equalizer does not occur.

When detecting the signal restoration, the input signal disconnection detection circuit 21 restores the normal state (after time t2).

〔The invention's effect〕

As described above, according to the present invention, even if a disconnection of the input signal due to the operation of the changeover switch actually exists, the input signal is not substantially disconnected and the equalizer has a relatively simple circuit configuration. A line switching device that does not cause unnecessary operation is provided. As a result, no unnecessary operation occurs due to disconnection of the line on the receiving end side.

[Brief description of drawings]

1 is a block diagram of the principle of a line switching device of a digital communication system according to the present invention, FIG. 2 is a circuit diagram of a line switching device according to an embodiment of the present invention, and FIGS. 3 (a) to 3 (d) are FIG. 4 is an operation timing chart of the line switching device of FIG. 4, FIG. 4 is a configuration diagram of a digital communication system to which the line switching device of the present invention is applied, FIG. 5 is a circuit configuration diagram of a conventional bipolar / unipolar conversion device, and FIG. 5A and 5B are operation timing charts of the apparatus shown in FIG. (Explanation of symbols) 1 ... Equalizer, 2 ... Signal loss detection holding circuit, 3 ... Amplitude detection circuit, 4,4a ... Clock recovery circuit, 5,5a ... Bipolar / unipolar conversion circuit, 1a ... … Line length equalizer, 21 …… Input signal disconnection detection circuit, 22 …… Holding circuit, 23 …… Switch circuit, 31 …… Amplitude detector, 32 …… Amplifier.

Claims (2)

(57) [Claims] 1. A digital communication system having an active system and a standby system, wherein the active system and the standby system can be switched to each other, and the digital communication system comprises: Input the transmission signal from the working switch circuit,
An equalizer (1) having a delay element for performing gain control using the output, and an input signal loss detection circuit (21) for detecting a loss of an input signal input to the equalizer (1), When the disconnection of the input signal is detected, the equalizer (1) immediately before the disconnection detection signal is generated in response to the disconnection detection signal output from the input signal disconnection detection circuit (21).
Holding circuit (22) for continuously holding the output of the equalizer (22), and while the disconnection detection signal is being generated, the output of the holding circuit (22) is used as a control signal for controlling the gain of the equalizer (1). 1) and a switch circuit (23) configured to apply the output of the equalizer (1) to the equalizer (1) as it is in the case other than the input signal disconnection. Detection and holding circuit (2)
And a line switching device of a digital communication system. 2. An amplitude detection circuit (3) is provided between the output of the equalizer (1) and the signal break detection circuit (21).
The line switching device according to claim 1, wherein the circuit is configured to provide an amplitude control voltage by the amplitude detection circuit (3).