JPH04266233A - Digital signal transmission system - Google Patents

Abstract

PURPOSE:To utilize a standby line effectively and to improve sufficiently the line quality by means of changeover of the line in the digital signal transmission system. CONSTITUTION:Comparator circuits 8-0-8-n compare a digital signal corrected by equalizers 4-0-4-n and demodulated by demodulators 5-0-5-n with resulting from a reception signal by demodulators 6-0-6-n. A line changeover control circuit 9 decides whether or not a result of line quality detection from signal processing units 7-0-7-n is within the range of a predetermined bit error rate. When the error rate is within the range through the decision, the line changeover control circuit 9 controls the system such that an active line having a largest number of dissidence detected from the result of comparison of the comparator circuits 8-0-8-n is replaced with a standby circuit B.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a digital signal transmission system, and more particularly to a digital signal transmission system in which switching between a plurality of working lines and protection lines is performed by comparing the quality of each line. Regarding switching.

0002

[Prior Art] Conventionally, in this type of switching system, a parity pulse or a syndrome pulse is used as a line quality detection method to determine the bit error rate (BER).
ErrorRatio) is commonly used. In a switching method using this line quality detection method, if a bit error rate worse than a predetermined bit error rate is detected at a receiving terminal station of a particular working line, a line failure alarm is activated at that receiving terminal station. be done. At that time, when the protection line is not being used by another working line and the bit error rate is lower than a predetermined value, the working line on which the line fault alarm has been activated is switched to the protection line.

[0003] In the above-mentioned line quality detection method, these redundant bits are kept to a minimum due to transmission capacity limitations, so the ability to detect bit error rates decreases in the case of continuous errors or burst errors, and in reality It is detected as a value lower than the bit error rate that is occurring. In particular, when selective fading occurs in a wireless transmission section, continuous errors and burst errors are likely to occur, and this tendency is remarkable. Therefore, even if line quality deterioration due to selective fading occurs on the working line, it will be detected as a lower value than the bit error rate that actually occurs, so Unless the line quality deteriorates more than the value, the working line will not be switched to the protection line. If the notch caused by selective fading moves rapidly on the line, switching to the protection line cannot be done in time and the line will be momentarily interrupted. Therefore, depending on the state of occurrence of fading, sufficient improvement in line quality cannot be expected by line switching.

In order to compensate for this point, conventionally, when the waveform distortion equalization correction signal of the receiving circuit exceeds a preset value, a line failure alarm is sent to the line switching control circuit, and the bit error rate is set at a preset bit error rate. The system used was to switch the working line to the protection line before detecting the value of . At this time, the waveform distortion equalization correction signal is the first-order distortion (LAD:L) of the equalizer.
inear Amplitude Distortio
n ) and quadratic distortion (QAD)
Amplitude Distortion) is used.

That is, as shown in FIG. 2, when n digital signals are transmitted using n working lines, the line quality is constantly monitored by the bit error rate on the receiving side, and the bit error rate is When the quality of the line is worse than a predetermined value, in other words, when the line quality has deteriorated below a predetermined value, the working line is switched to the protection line. Further, even when the bit error rate does not become worse than a predetermined value, if the first-order distortion or second-order distortion exceeds a predetermined value on the receiving side, switching from the working line to the protection line is performed.

[0006] A working line A-1 consisting of a working transmitting circuit 3-1, an equalizer 4-1, a demodulator 5-1, and a signal processor 7-1.
When selective fading occurs and the line quality deteriorates, the receiving terminal station detects the bit error rate with the signal processor 7-1 and then converts the bit error rate value into a predetermined bit error rate value. If the comparison results confirm that the line quality has deteriorated, a line failure alarm is activated. The activated line fault alarm is sent to the line switching control circuit 11.

[0007]Even if no deterioration of the bit error rate is 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. The generated line failure alarm is sent to the line switching control circuit 11.

At this time, similarly to the above processing, the working transmitting circuits 3-2 to 3-n, equalizers 4-2 to 4-n, and demodulator 5
-2 to 5-n and signal processors 7-2 to 7-n to the respective working lines A-2 to A-n, the backup transmission circuit 2, the equalizer 4-0, the demodulator 5-0, and the signal The bit error rate value detected in the protection line B consisting of the processor 7-0 is also compared with a predetermined bit error rate value. After confirming that the line quality has not deteriorated based on the comparison results and confirming that the first-order distortion or second-order distortion does not exceed the preset value, the current line A-2~
A line failure alarm is not activated from A-n and protection line B.

The line switching control circuit 11 includes equalizers 4-2 to 4-2.
4-n and signal processors 7-2 to 7-n and equalizer 4-0
By not receiving a line failure alarm from the signal processor 7-0 and signal processor 7-0, it is confirmed that the working lines A-2 to A-n do not occupy the protection line B, and if a line failure occurs on the protection line B. Make sure you haven't. At this time, if there is no line failure alarm on backup line B,
The line switching control circuit 11 sends a control signal to the sending end line switching circuit 1, switches the sending end line switching circuit 1, and switches the working line A-1 to
The digital signal that was being transmitted by the line B is also transmitted to the protection line B.

Next, the line switching control circuit 11 sends a control signal to the receiving end line switching circuit 10, and switches the receiving end line switching circuit 10 to generate a signal in place of the digital signal output from the signal processor 7-1. The digital signal output from the processor 7-0 is output from the receiving end line switching circuit 10. By 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 setting the threshold value of the waveform distortion equalization correction signal, it is difficult to establish a relationship with the actual bit error rate depending on the state of occurrence of fading, and when the line quality is sufficiently good and switching is not necessary. However, if the first-order distortion and second-order distortion exceed preset values, the working line may be switched to the protection line. In this state, if line quality deterioration occurs in the working line A-n that requires switching to the protection line B, the protection line B will be used for the digital signal that was already being transmitted by the working line A-1. Therefore, the digital signal transmitted by the working line A-n cannot be switched to the protection line B.
Even if the line quality of the working line A-n further deteriorates, the line will not be switched to the protection line B.

[0012] In such a conventional switching method, when setting the threshold value of the waveform distortion equalization correction signal, it is difficult to establish a relationship with the actual bit error rate depending on the state of fading occurrence, and it is difficult to establish a relationship with the actual bit error rate when the line quality is sufficiently good. Even if switching is not required, if the primary distortion and secondary distortion exceed preset values, the working line A-1 is switched to the protection line B, so the other working lines A-2 to A-n are Backup line B
Even if it is necessary to switch to the protection line B, the other working lines A-2 to A-n cannot be switched to the protection line B because the protection line B is not available, and the effective use of the protection line B cannot be achieved. There are drawbacks. Furthermore, this also has the disadvantage that it is not possible to improve the line quality.

[0013]

[Object of the Invention] The present invention has been made to eliminate the above-mentioned drawbacks of the conventional system, and makes it possible to effectively utilize backup lines and to sufficiently improve line quality by switching lines. The purpose is to provide a digital signal transmission system.

[0014]

[Structure of the Invention] The digital signal transmission system according to the present invention performs
A digital signal transmission system for switching between one of the plurality of lines and a protection line, the digital signal transmission system comprising: equalizing means for equalizing and correcting waveform distortion of signals to each of the plurality of lines and the protection line; and the equalization unit. a first demodulating means for demodulating the signal equalized by the means into a digital signal; a second demodulating means for demodulating the signal to each of the plurality of lines and the protection line into a digital signal; The second demodulation means includes a comparison means for comparing demodulation results of each of the 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. shall be.

[0015]

[Embodiment] 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 an embodiment of the present invention. In the figure, the sending end line switching circuit 1 is controlled by a control signal from the line switching control circuit 9 of the receiving end station, and transmission is performed using n working lines A-1 to A-n at the sending end station. Among the n digital signals, the digital signal causing the line failure is also sent to the protection line B.

The protection transmission circuit 2 is connected to the protection line output of the sending end line switching circuit 1, and has a function of modulating the 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 sending end line switching circuit 1, and have a function of modulating digital signals and information for detecting line quality at the receiving end station. It has additional functions.

The equalizer 4-0 is connected to the preliminary transmitting circuit 2 through a communication line at the receiving end station, and equalizes and corrects the waveform distortion of the signal sent from the preliminary transmitting 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 preliminary transmitting circuit 2 through a communication line at the receiving end station, and directly inputs the waveform distortion of the signal sent from the preliminary transmitting circuit 2 without equalization correction, and converts the signal into its original form. It has the function of demodulating into 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 has a function of successively comparing the output signals of the demodulators 5-0 and 6-0, counting the number of data signals that do not match, and sending the number 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.
Consists of 0.

The equalizers 4-1 to 4-n are connected to the working transmitting circuits 3-1 to 3-n through communication lines at the receiving end stations, respectively, and receive signals sent from the working transmitting circuits 3-1 to 3-n, respectively. The waveform distortion of the received signal is equalized and corrected. Demodulators 5-1 to 5-
n has a function of demodulating the output signals of the equalizers 4-1 to 4-n into original digital signals. Demodulators 6-1 to 6-
n are connected to the working transmitting circuits 3-1 to 3-n through communication lines at the receiving end stations, respectively, and the working transmitting circuits 3-1 to 3-n, respectively,
It has a function of directly inputting the waveform distortion of the signal sent from 3-n without equalization correction, and demodulating the signal into the original digital signal. The signal processors 7-1 to 7-n have a function of detecting the line quality of the digital signals demodulated by the demodulators 5-1 to 5-n, respectively, and sending the detected line quality to the line switching control circuit 9. Comparison circuits 8-1 to 8-n are demodulators 5-1 to 5-n,
It has a function of successively comparing the output signals of 6-1 to 6-n, counting 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 A-n are connected to these working transmitting circuits 3-1 to 3-n, equalizers 4-1 to 4-n, and demodulator 5.
-1 to 5-n, 6-1 to 6-n and signal processors 7-1 to 7
-n and comparison circuits 8-1 to 8-n.

The line switching control circuit 9 includes signal processors 7-0 to 7-0.
If the line quality detection result from 7-n is within the predetermined bit error rate range, the working line with the largest number of discrepancies in the output signals from comparator circuits 8-0 to 8-n is selected as protection line B. Switch to. In addition, when the line quality detection results from the signal processors 7-0 to 7-n deteriorate beyond a predetermined bit error rate range, the line switching control circuit 9 lowers the bit error rate as in the conventional example. The worst working line is controlled to be switched to protection line B.

The receiving end line switching circuit 10 uses a control signal from the line switching control circuit 9 to convert a digital signal sent using the working line in which a line fault alarm has occurred among the n working receiving circuits to a line fault alarm. It has a function of switching to and outputting a digital signal from the backup line B where no line failure alarm has occurred, and a function of outputting a digital signal sent using the working line where no line failure alarm has occurred.

Therefore, if the line quality detection results from the signal processors 7-0 to 7-n are within the predetermined bit error rate range, the line switching control circuit 9 selects the comparison circuits 8-0 to 7-n.
Since the working line with the largest number of mismatches in the output signals from 8-n is switched to protection line B, selective fading can be detected early and switching to protection line B can be made. Furthermore, when the line quality detection results from the signal processors 7-0 to 7-n deteriorate beyond a predetermined bit error rate range, the line switching control circuit 9 selects the working line with the worst bit error rate. Since it controls switching to protection line B,
The protection line B can be used effectively, and the line quality can be sufficiently improved by line switching.

In this way, if the line quality detection results from the signal processors 7-0 to 7-n are within the predetermined bit error rate range, the received signal, which is largely affected by selective fading, can be processed as is. The digital signals demodulated by the demodulators 6-0 to 6-n and the received signals whose effects of selective fading have been reduced by equalization correction by the equalizers 4-0 to 4-n are transferred to the demodulators 5-0 to 6-n. The line switching control circuit 9 compares the digital signal demodulated by 5-n with the digital signal demodulated by comparing circuits 8-0 to 8-n, and switches the working line with the largest number of mismatches detected by the comparison to the protection line B. By controlling this, selective fading can be detected early and switched to protection line B, so protection line B can be used effectively, and line quality can be sufficiently improved by line switching. can be achieved.

[0024]

As explained above, according to the present invention, a digital signal is obtained by demodulating a signal that has been equalized by an equalizer, and a digital signal is obtained by demodulating a signal sent directly to each of a plurality of lines and a protection line. By comparing the data and switching between one of the multiple lines and the protection line according to the comparison result, the protection line can be used effectively, and the line quality can be sufficiently improved by line switching. This has the effect of being able to achieve this goal.

[Brief explanation of the drawing]

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

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

[Explanation of symbols]

1 Sending end line switching circuit 2 Preliminary transmitting circuit 3-1 to 3-n Working transmitting 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 to 8-n Comparison circuit 9 Line switching control circuit 10 Receiving end line switching circuit

Claims (1)

[Claims] 1. A digital signal transmission system that switches between one of the plurality of lines and a protection line according to a comparison result of line quality of each of the plurality of lines, wherein each of the plurality of lines and the protection line an equalizing means for equalizing and correcting the waveform distortion of the signal to the plurality of lines, and a first demodulating means for demodulating the signal equalized and corrected by the equalizing means into a digital signal, and to each of the plurality of lines and the protection line. a second demodulating means for demodulating the signal into a digital signal; a comparing means for comparing the demodulation results of each of the first and second demodulating means; 1. A digital signal transmission system comprising control means for controlling switching between one of the lines and a protection line.