JP2658605B2 - Digital signal transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal transmission system, and more particularly, to a working line and a protection line when a selective fading occurs in a digital signal transmission system in which a plurality of working lines and a protection line are switched by comparing respective line qualities. Switching.

[0002]

2. Description of the Related Art Conventionally, in this type of switching system, a bit error rate (BER: Bit Err) using a parity pulse or a syndrome pulse as a line quality detection method.
rorRatio) is generally used. In the switching method using this line quality detection method, when a bit error rate worse than a predetermined bit error rate is detected at a receiving terminal station of a specific working line, a line failure alarm is activated at the receiving terminal station. Is done. At this time, when the protection line is not used for another working line and the bit error rate is lower than a predetermined value, the working line for which the line failure alarm has been activated is switched to the protection line.

In the above-described line quality detection method, since these redundant bits are kept to a minimum due to the limitation of the transmission capacity, the ability to detect the bit error rate with respect to a continuous error or a burst error is reduced. It is detected as a value lower than the occurring bit error rate. In particular, when selective fading occurs in a wireless transmission section, a continuous error or a burst error is likely to occur, and this tendency is remarkable. For this reason, even if the line quality degradation due to the selective fading occurs on the working line, it is detected as a value lower than the actually occurring bit error rate, and the bit error rate of a preset bit error rate is detected. If the line quality does not deteriorate below the value, the working line is not switched to the protection line. If the notch generated by the selective fading moves rapidly on the line, the line is momentarily interrupted because switching to the protection line is not in time. Therefore, depending on the fading occurrence state, it is not possible to expect sufficient line quality improvement by line switching.

In order to compensate for this, conventionally, when a waveform distortion equalization correction signal of a receiving circuit exceeds a preset value, a line failure alarm is transmitted to a line switching control circuit, and a preset bit error rate is transmitted. Before detecting the value of, the working line is switched to the protection line. At this time, the waveform distortion equalization correction signal includes a primary distortion (LAD: Li
near Amplitude Distortion) and second-order distortion (QA)
D: Quadratic Amplitude Distortion).

That is, as shown in FIG. 2, when n digital signals are transmitted using n working lines, the line quality is constantly monitored on the receiving side based on the bit error rate. When the line quality is lower than the predetermined value, in other words, when the line quality is lower than the specified value, switching from the working line to the protection line is performed. Also,
Even when the bit error rate does not become worse than the predetermined value, if the primary distortion or the secondary distortion exceeds the preset value on the receiving side, switching from the working line to the protection line is performed.

[0006] Working transmission circuit 3-1, equalizer 4-1 and demodulator 5
When selective fading occurs in the working line A-1 consisting of -1 and the signal processor 7-1 and the line quality is deteriorated, the receiving end station detects the bit error rate by the signal processor 7-1.
The value of the bit error rate is compared with a predetermined value of the bit error rate, and when the result of the comparison indicates that the line quality is degraded, a line fault alarm is activated. The activated line fault alarm is sent to the line switching control circuit 11.

[0007] Even if the deterioration of the bit error rate is not confirmed, if it is confirmed that the first-order distortion or the second-order distortion exceeds a preset value, the equalizer 4-1 activates a line failure alarm and activates. The sent line failure alarm is sent to the line switching control circuit 11.

At this time, similarly to the above processing, the working transmission circuits 3-2 to 3-n, equalizers 4-2 to 4-n, and demodulators 5-2 to 5-n
And the signal processors 7-2 to 7-n.
A-n and the value of the detected bit error rate in the protection line B including the protection transmission circuit 2, the equalizer 4-0, the demodulator 5-0, and the signal processor 7-0. Compare with rate value. The result of the comparison confirms that the line quality has not deteriorated, and confirms that the primary distortion or the secondary distortion has not exceeded a preset value. Then, the working lines A-2 to An and the protection line B does not activate the line fault alarm.

In the line switching control circuit 11, the equalizers 4-2 to 4
-n and the signal processors 7-2 to 7-n and the equalizer 4-0 and the signal processor 7-0 do not receive the line failure alarm, so that the working lines A-2 to An become the protection lines. Confirm that B is not occupied, and confirm that no line failure has occurred in the protection line B. At this time, if there is no line failure alarm on the protection line B, the line switching control circuit 11 sends a control signal to the transmission line switching circuit 1 to switch the transmission line switching circuit 1 and transmit the transmission line A-1. The transmitted digital signal is also transmitted to the protection line B.

Next, the line switching control circuit 11 sends a control signal to the receiving line switching circuit 10 and switches the receiving line switching circuit 10 to replace the digital signal output from the signal processor 7-1 with a signal. The digital signal output from the processor 7-0 is output from the receiving-end line switching circuit 10. With the above processing, the switching of the digital signal transmitted by the working line A-1 to the protection line B is completed.

However, when the threshold value of the waveform distortion equalization correction signal is set, it is difficult to associate with the actual bit error rate depending on the fading occurrence state, the line quality is sufficiently good, and switching is not required. However, if the primary distortion and the secondary distortion exceed predetermined values, the working line may be switched to the protection line. In this state, if the working line An degrades in line quality requiring switching to the protection line B, the protection line B is used for a digital signal already transmitted by the working line A-1. Therefore, the digital signal transmitted by the working line An cannot be switched to the protection line B, and the switching to the protection line B is not performed even if the line quality of the working line An further deteriorates.

In such a conventional switching method, when the threshold value of the waveform distortion equalization correction signal is set, it is difficult to associate with the actual bit error rate depending on the fading occurrence state, and the line quality is sufficiently high. If the primary distortion and the secondary distortion exceed the preset values even when switching is not required, the working line A-1 is switched to the protection line B, so that the other working lines A-2 to An become inactive. Even if it is necessary to switch to the protection line B, since the protection line B is not vacant, the other working lines A-2 to An cannot be switched to the protection line B, and the protection line B should be used effectively. There is a drawback that you can not. In addition, there is a disadvantage that the line quality cannot be improved.

[0013]

SUMMARY OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, which makes it possible to make effective use of the protection line and to sufficiently improve the line quality by switching the line. The purpose is to provide a digital signal transmission system.

[0014]

According to the digital signal transmission system of the present invention, according to the result of comparing the line quality of each of a plurality of lines,
A digital signal transmission system for switching between one of the plurality of lines and a protection line, comprising: an equalizing unit configured to equalize and correct waveform distortion of a signal to each of the plurality of lines and the protection line; First demodulating means for demodulating the signal equalized and corrected by the means into a digital signal; second demodulating means for demodulating a signal to each of the plurality of lines and the protection line into a digital signal; A comparison means for comparing the demodulation results of each of the second demodulation means, and a control means for controlling switching between one of the plurality of lines and a protection line according to the comparison result of the comparison means. And

[0015]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In the figure, a transmitting end line switching circuit 1 is controlled by a control signal from a line switching control circuit 9 of a receiving end station, and is transmitted at the transmitting end station using n working lines A-1 to An. From the n digital signals, a digital signal having a line failure is also transmitted to the protection line B.

The standby transmission circuit 2 is connected to the standby line output of the transmission line switching circuit 1 and has a function of modulating a digital signal and a function of adding information for detecting the line quality at the receiving end station. The working transmitting circuits 3-1 to 3-n are respectively connected to the n working line outputs of the transmitting end line switching circuit 1 and function to modulate digital signals and information for detecting line quality at the receiving end station. Has the function of adding.

The equalizer 4-0 is connected to the auxiliary transmission circuit 2 at the receiving end station through a communication line, and equalizes and corrects the waveform distortion of the signal transmitted from the auxiliary transmission circuit 2. Demodulator 5-0
Has a function of demodulating the output signal of the equalizer 4-0 into the original digital signal. The demodulator 6-0 is connected to the auxiliary transmission circuit 2 at the receiving end station via a communication line, directly inputs the waveform distortion of the signal transmitted from the auxiliary transmission circuit 2 without performing equalization correction, and converts the signal into the original signal. It has the function of demodulating to digital signals. The signal processor 7-0 has a function of detecting the line quality of the digital signal demodulated by the demodulator 5-0 and sending it to the line switching control circuit 9. The comparison circuit 8-0 includes demodulators 5-0 and 6
It has a function of successively comparing the output signals of −0, measuring the number of data signals that do not match, and sending out to the line switching control circuit 9.
The protection line B includes the protection transmission circuit 2, the equalizer 4-0, the demodulators 5-0 and 6-0, the signal processor 7-0, and the comparison circuit 8-0.

The equalizers 4-1 to 4-n are connected to the working transmission circuits 3-1 to 3-n at the receiving end station via communication lines, respectively, and sent from the working transmission circuits 3-1 to 3-n, respectively. Equalization correction of the waveform distortion of the received signal. The demodulators 5-1 to 5-n are equalizers 4 respectively.
It has a function of demodulating output signals of -1 to 4-n into original digital signals. The demodulators 6-1 to 6-n are connected to the working transmission circuits 3-1 to 3-n at the receiving end stations through communication lines, respectively, and receive the signals transmitted from the working transmission circuits 3-1 to 3-n, respectively. It has a function of directly inputting waveform distortion without performing equalization correction and demodulating the signal into an original digital signal. Signal processor 7-1 ~
7-n has a function of detecting the line quality of the digital signal demodulated by the demodulators 5-1 to 5-n and transmitting the same to the line switching control circuit 9. The comparison circuits 8-1 to 8-n are demodulators 5-1 to 5-
It has a function of sequentially comparing the output signals of n, 6-1 to 6-n, measuring the number of data signals that do not match, and sending it to the line switching control circuit 9. The working lines A-1 to An include these working transmission circuits 3-1 to 3-n, equalizers 4-1 to 4-n, and demodulators 5-1 to 5-n, 6.
-1 to 6-n, signal processors 7-1 to 7-n, and comparison circuits 8-1 to 8-n
Consists of

The line switching control circuit 9 includes signal processors 7-0 to 7
If the line quality detection result from the comparators -n is within the range of the predetermined bit error rate, the working line having the largest number of mismatches in the output signals from the comparison circuits 8-0 to 8-n is set to the protection line B.
Switch to Further, the line switching control circuit 9 includes a signal processor 7.
If the line quality detection result from -0 to 7-n becomes worse beyond the predetermined bit error rate range, control is performed so that the working line with the worst bit error rate is switched to the protection line B as in the conventional example. I do.

The receiving-end line switching circuit 10 converts a digital signal transmitted using a working line on which a line failure alarm has occurred among the n active receiving circuits by a control signal from the line switching control circuit 9 into a line failure alarm. A function of switching to a digital signal from the protection line B in which the line failure does not occur, and a function of outputting a digital signal transmitted using the working line in which the line failure alarm has not occurred.

Therefore, if the line quality detection results from the signal processors 7-0 to 7-n are within the range of a predetermined bit error rate, the line switching control circuit 9 causes the comparison circuits 8-0 to 8-n Since the working line having the largest number of mismatches in the output signal from n is switched to the protection line B, selectivity fading can be detected early and switched to the protection line B. When the line quality detection results from the signal processors 7-0 to 7-n deteriorate beyond the predetermined bit error rate range, the line switching control circuit 9 determines the working line having the worst bit error rate. Since control is performed so as to switch to the protection line B, the protection line B can be effectively used, and the line quality can be sufficiently improved by switching the line.

As described above, if the channel quality detection results from the signal processors 7-0 to 7-n are within the range of the predetermined bit error rate, the received signal which is greatly affected by the selective fading is left as it is. The demodulator 5 demodulates the digital signal demodulated by the demodulators 6-0 to 6-n and the received signal which has been equalized and corrected by the equalizers 4-0 to 4-n to reduce the influence of the selective fading.
-0 to 5-n and the comparison circuit 8-0 to
8-n, and the line switching control circuit 9 controls the working line having the largest number of mismatches detected by the comparison to be switched to the protection line B, thereby detecting the selective fading early. Thus, it is possible to switch to the protection line B, so that the protection line B can be effectively used, and the line switching can sufficiently improve the line quality.

[0024]

As described above, according to the present invention, a digital signal obtained by demodulating a signal subjected to equalization correction by an equalizer and a digital signal obtained by demodulating a signal to each of a plurality of lines and a protection line as they are are obtained. By controlling the switching between one of the plurality of lines and the protection line in accordance with the comparison result, the protection line can be used effectively, and the line switching can sufficiently improve the line quality. There is an effect that it can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sending-end line switching circuit 2 Preliminary transmission circuit 3-1 to 3-n Working transmission circuit 4-0 to 4-n Equalizer 5-0 to 5-n, 6-0 to 6-n Demodulator 7-0 ~ 7-n signal processor 8-0 ~ 8-n comparison circuit 9 line switching control circuit 10 receiving end line switching circuit

Claims (1)

(57) [Claims] 1. A digital signal transmission system for switching between one of a plurality of lines and a protection line in accordance with a comparison result of line quality of each of the plurality of lines, wherein each of the plurality of lines and the protection line Equalizing means for equalizing and correcting waveform distortion of a signal to the first channel; first demodulating means for demodulating a signal equalized and corrected by the equalizing means into a digital signal; A second demodulating means for demodulating the digital signal into a digital signal;
And comparing means for comparing the demodulation results of the respective second demodulation means, and control means for controlling switching between one of the plurality of lines and the protection line according to the comparison result of the comparison means. Characteristic digital signal transmission system.