JPS63206054A - Method and device for supervising transmission line - Google Patents

Abstract

PURPOSE:To supervise various kinds of abnormal quality of a transmission signal by supervising a signal power in a line spectrum appearing at the same frequency corresponding to the transmission speed. CONSTITUTION:An optical signal 10 sent via an optical transmission line is converted into an electric signal by a photodetector 2. The electric signal output is given to a discrimination circuit 4 via an amplifier 3. The circuit 4 processes the inputted electric signal at a prescribed threshold level and outputs a binary digital signal whose amplitude is constant. The digital signal output is outputted externally via a terminal 5 and given also to a tuning amplifier 6, which is a narrow band amplifier and its output is inputted to a transmission line supervision comparator 7. The comparator 7 compares the input with a reference voltage from a terminal 8 and outputs a supervisory signal to a terminal 9.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a transmission line monitoring method and a device therefor, and is used to monitor quality abnormalities of digital signals transmitted through transmission lines such as optical fiber cables. be done.

(Conventional technology) Even if optical transmission lines are designed with sufficient reliability in mind,
There is a possibility that you will suffer some kind of damage. In the event of faults and breakdowns, it is necessary to switch to a backup line or repair the fault. For this reason, the optical transmission line is constantly monitored.

The following two methods are known as typical optical transmission path monitoring methods.

The first method is a method for monitoring the level of light received by an optical receiver, and is widely known as, for example, a link monitor method. In other words, by photoelectrically converting an optical signal sent through an optical transmission line such as an optical fiber cable using an optical receiver, and comparing the level of the electrical signal obtained by this with a predetermined level, This monitors the deterioration of optical signals. This method has the advantage that the monitoring device can have a simple configuration.

The second method is a method in which a digital signal code rule is checked for a digital signal obtained from an identification circuit provided in an optical receiver. That is, an electrical signal obtained by photoelectrically converting an optical signal from an optical fiber cable is converted into, for example, a binary digital signal, and code errors and the like are monitored by checking the code rule. This method has the advantage that errors can be detected extremely accurately with respect to a specific code rule.

[Problem that the invention seeks to solve]

However, the conventional method described above has the following drawbacks.

According to the first method, it is difficult to detect an increase in pulse width distortion or an increase in error rate in the optical transmission line. This is because only the optical power is monitored, even though there are variations in the relationship between the optical signal power and the error rate. Therefore, it has not been possible to deal with a wide variety of abnormalities that occur in optical transmission lines.

According to the second method, only a specific code rule can be monitored, and the logic circuit for monitoring becomes large-scale. Therefore, the optical transmission systems to which this method can be applied are limited. Note that these circumstances are not limited to optical transmission lines using optical cable fibers, but also apply to electrical signal transmission lines using coaxial cables and the like.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a transmission path monitoring method that can monitor various quality abnormalities of a transmission signal, including an increase in pulse width distortion and an increase in error rate.

Furthermore, the present invention not only makes it possible to monitor various quality abnormalities in transmission signals, including increases in pulse width distortion and error rates, but also provides transmission line monitoring that allows devices to be made simple and compact. The purpose is to provide equipment.

(Means for Solving the Problems) The transmission path monitoring method according to the present invention is based on the power spectrum of a transmission code after converting an optical or electrical digital signal into a binary digital electrical signal with constant amplitude. It is characterized in that the transmission path is monitored by monitoring the signal power in the line spectrum that appears at the same frequency as the speed.

The transmission line monitoring device according to the present invention also includes an identification means for receiving an optical or electrical digital signal transmitted through the transmission line and converting it into a binary digital electrical signal with a constant amplitude; Tuned amplification means tunes and amplifies the output at the same frequency as the signal transmission speed on the transmission path and detects the power peak value of the line spectrum; The transmission line monitoring method according to the present invention is configured as described above, and is characterized in that the transmission line is monitored based on the output of the comparison means. The power spectrum of a transmission code such as an RZ code or a CMI code has a line spectrum that is standardized at the same frequency as the transmission rate, and this line spectrum has a predetermined value unless there is an abnormality in the quality of the transmission signal. By maintaining and monitoring this, the optical transmission path can be monitored.

Furthermore, since the transmission path monitoring device according to the present invention is configured as described above, the identification means can detect the transmitted electrical signal (or the electrical signal obtained by photoelectrically converting the transmitted optical signal) by The tuning amplification means works to convert the digital signal into a fixed binary digital signal, and the tuning amplification means works to detect a line spectrum appearing at the same frequency as the transmission speed in the power spectrum of the binary digital signal output from the identification means.
The comparison means functions to compare the power peak values of the line spectra at predetermined levels, and therefore functions to monitor quality abnormalities in the transmission signal on the transmission path.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to FIGS. 1 to 4 of the accompanying drawings. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 is a configuration diagram of an embodiment of an optical transmission path monitoring device according to the present invention. Further, FIG. 2 is a waveform diagram showing an example of an RZ code and a CMI code, which are particularly problematic in the present invention.

FIG. 3 is a characteristic diagram showing the line spectrum in the power spectrum of the RZ code, and FIG. 4 is a characteristic diagram showing the line spectrum in the power spectrum of the CMI code.

Before explaining specific embodiments, first, RZ code, CMI
A transmission code such as a code will be briefly explained.

In general, in transmission using optical fiber cables, digital modulation such as binary modulation is used because the transmission path has a sufficiently wide band and there is nonlinearity in the current-optical output characteristics of semiconductor light sources. There are many things. This binary modulation is a binary code in which "1" and "O" correspond to the on and off states of light. Typical binary digital codes include the aforementioned RZ (Return to Zero) code and CM I code.
(Coded MarkInVerSiOn) code, etc.

Figure 2 shows R when the original code is rollololJ.
A Z code and a CMI code are shown. As shown in Figure 2 (a), the RZ code is suitable for optical fiber transmission because the timing information is limited. However, in the unipolar RZ code as shown in Figure 2 (a), the same code is etc., timing information may be lost or unbalanced DC components may occur.Therefore, in order to prevent these problems, the scrambled RZ It is common practice to use codes.

On the other hand, the CMI code shown in FIG. 2(b) actively utilizes the broadband characteristics of optical fibers, but it requires a transmission line band wider than the required bandwidth of the original code. However, there is no loss of timing information, good DC balance, and it is possible to monitor errors during transmission line operation.
It has several characteristics. Therefore, it is particularly suitable for medium- and small-capacity digital transmission systems.

Next, the optical transmission path monitoring method according to the present invention will be specifically explained.

In the method of the present invention, when a transmission code such as an RZ code or a CMI code has a transmission rate of B0 (b/S), the frequency is B. (H2
This was done by focusing on the fact that it has a line spectrum of ). That is, as shown in FIG. 3, the power spectrum of the RZ code after photoelectric conversion and identification has a line spectrum at frequency 80. Also, as shown in Figure 4, the power spectrum of the CMI code is
It has a line spectrum.

The power of the line spectrum of the digital signal binarized via a discriminator or the like is standardized, and maintains a constant value unless the pulse width is distorted. because,
If we look at rOJ and the appearance rate of "1" during a certain length of time, it is fixed, for example, 1 to 1 or 2 to 1. Therefore, when understood as a power spectrum, the peak value due to such duty ratio This is because a line spectrum with - appears. Note that in the RZ code, the power peak value of the line spectrum varies depending on the frequency of appearance of the binary information "O" and "1" to be transmitted. However, by performing scrambling as described above, it is easy to make the appearance probability of rOJ "1" 1:1, so it is easy to maintain the power peak of the line spectrum constant.

Therefore, the method of the present invention detects the power peak value of this line spectrum using, for example, a narrowband tuned amplifier, and compares it with a predetermined reference level. Then, when the detected peak value falls below a predetermined reference level, it is determined that there is an abnormality in the optical transmission path. That is, when pulse width distortion increases due to an abnormality in the optical transmission line, the bandwidth of the above-mentioned line spectrum widens and the peak value decreases, so that an abnormality in the optical transmission line is detected by the decrease in the peak value.

According to the method of the present invention, it is possible to accurately detect abnormalities in the optical transmission path without knowing the relationship between the received power (received power) of the optical receiving device and the error rate, and therefore it is possible to accurately detect the abnormality in the optical transmission path. It is possible to monitor signal quality abnormalities. Further, since the decrease in the peak value of the line spectrum has a large correlation with the error rate, there is an advantage that the error rate itself can be indirectly monitored.

The method of the present invention is not limited to the above method, and various modifications are possible.

For example, the format of the transmission code is not limited to RZ code and CMI code. That is, any transmission code may be used as long as a line spectrum appears in the received power spectrum.

Further, the frame structure of the signal in the optical transmission path may be of any type. Furthermore, the present invention is not limited to monitoring the signal and power based on the peak value of the line spectrum, but may also detect and monitor the spread of the band of the line spectrum at a predetermined level.

Furthermore, the method of the present invention is not limited to optical transmission lines using optical fiber cables or the like, but can also be applied to monitoring electrical signal transmission lines using coaxial cables or the like.

Next, the configuration and operation of an embodiment of the optical transmission path monitoring device according to the present invention will be specifically explained with reference to FIG.

As shown in the figure, the photoelectric transformer circuit 1 is composed of a light receiving element 2 such as a photodiode and an amplifier 3, and this output signal (electrical signal) is given to a digital signal discriminator 4. The digital signal output of the discriminator 4 is outputted to the outside via a terminal 5 and is also provided to a tuned amplifier 6. The tuned amplifier 6 may be, for example, a crystal filter, a ceramic filter, or an SA filter.
It is a narrow band amplifier composed of a W (surface acoustic wave) filter and the like, and its output is input to the first terminal of the transmission path monitoring comparator 7. Here, the reference voltage ref is applied from the terminal 8 to the second terminal of the comparator 7, and therefore, a monitoring signal as a comparison result is outputted from the comparator 7 to the terminal 9.

Next, the operation of the above embodiment will be explained.

First, an optical signal 10 sent through an optical transmission line such as an optical fiber cable (not shown) is input to the light receiving element 2 and converted into an electrical signal. This electrical signal output is then amplified by an amplifier 3 and given to a discriminator 4.

The discriminator 4 processes the input electrical signal at a predetermined threshold level and outputs a binary digital signal with constant amplitude. Therefore, even if there is variation or deterioration in the amplitude of the signal sent via the optical fiber cable, the electrical signal is adjusted to a constant amplitude. However, if there is pulse width distortion in the signal transmitted through the optical fiber cable, this will not be corrected by the discriminator 4, and the pulse width distortion will appear as is in the digital signal output after discrimination.

When pulse width distortion appears in the digital signal after identification in this way, the band of the line spectrum becomes wider when this is understood as a power spectrum. For this reason,
The power peak value of the line spectrum decreases. the result,
The output of the narrowband tuned amplifier 6 will be lower than when there is no pulse width distortion.

The output of the tuned amplifier 6 thus obtained is input to a comparator 7 and compared with a reference level V ref. Therefore, when there is no pulse width distortion, the tuned amplification output ≧V
ref, and when there is pulse width distortion, the tuning amplification power becomes <V ref , so that abnormalities in the optical transmission line can be monitored by outputting a monitoring signal at the terminal 9.

The device of the present invention is not limited to the above embodiments, and various modifications are possible.

For example, the transmission code is not limited to the RZ code or the CMI code, but may be any other code as long as a line spectrum appears in the power spectrum after photoelectric conversion and identification. Also,
The rOJ of the signal after identification and the appearance probability of "1" are not limited to 1:1 (duty ratio is 50%), but also 1/2:1.2
Any ratio may be used as long as it has a constant ratio such as /3 to 1.2 to 1 (the probability of appearance of "O" and "1" does not change over a certain period of time).

Further, the transmission line is not limited to an optical fiber cable, and may be a coaxial line or the like. However, in this case, the photoelectric conversion circuit itself becomes unnecessary. Furthermore, in the case of optical fiber cables, it is rare for code errors to suddenly occur in the signal transmission path, and pulse width distortion is usually caused by deterioration of the optical signal, resulting in violation of coding rules. occurs, resulting in a code error. Therefore, since there is a high correlation between an abnormality in an optical transmission line and a signal error rate, the apparatus of the present invention is particularly effective for monitoring optical transmission lines. On the other hand, when a copper coaxial cable or the like is used, code errors may suddenly appear due to the influence of electromagnetic waves, and in this case, there is little correlation between pulse width distortion and code errors.

Therefore, although it is not possible to monitor code errors in such a case, even a copper cable or the like is effective in dealing with code errors caused by pulse width distortion.

〔Effect of the invention〕

As explained above in detail, according to the transmission path monitoring method according to the present invention, the power spectrum of a transmission code such as an RZ code or a CMI code has a line spectrum normalized at the same frequency as the transmission rate. However, this line spectrum maintains a predetermined value unless there is an abnormality in the quality of the transmitted signal. Therefore, by monitoring this, we can monitor the increase in pulse width distortion and error rate in the optical transmission line.
Various quality abnormalities in transmission signals can be accurately monitored.

Further, according to the transmission path monitoring device according to the present invention, the transmitted electrical signal (or the electrical signal obtained by photoelectrically converting the transmitted optical signal) is converted into a binary digital signal with a constant amplitude by the identification means. In the power spectrum of the binary digital signal output from the identification means, a line spectrum appearing at the same frequency as the transmission speed is detected by the tuned amplification means, and the peak value of this line spectrum is compared at a predetermined level by the comparison means. Ru. Therefore, it is not only possible to accurately monitor various abnormalities in the quality of transmission signals, including increases in pulse width distortion and error rates in the transmission path, but also the effect of making the device simpler and more compact. There is.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a transmission path monitoring device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of an example of an RZ code and a CMI code, and FIG.
The figure is an explanatory diagram of the power spectrum of RZ code, and Figure 4 is C
FIG. 2 is an explanatory diagram of a power spectrum of an MI code. DESCRIPTION OF SYMBOLS 1... Photoelectric conversion circuit, 2... Light receiving element, 4... Digital signal identifier, 7... Transmission path monitoring comparator.

Claims (1)

[Scope of Claims] 1. In a transmission path monitoring method for monitoring a transmission path for transmitting a digital signal, the power spectrum of a transmission code after the digital signal is converted into a binary digital electric signal with constant amplitude. . A transmission path monitoring method, characterized in that the transmission path is monitored by monitoring signal power in a line spectrum that appears at the same frequency as the transmission speed. 2. The transmission path monitoring method according to claim 1, wherein the transmission code is an RZ code or a CMI code. 3. In a transmission line monitoring device for monitoring a transmission line for transmitting digital signals, an identification means receives a digital signal transmitted through the transmission line and converts it into a binary digital electric signal with a constant amplitude; a tuned amplification means that tunes and amplifies the output of the identification means at the same frequency as the signal transmission speed in the transmission path and detects the power peak value of the line spectrum; and a power peak of the line spectrum detected by the tuned amplification means. 1. A transmission path monitoring device comprising: comparing means for comparing values at predetermined levels, and monitoring the transmission path based on the output of the comparing means. 4. The transmission path monitoring device according to claim 3, wherein the transmission code is an RZ code or a CMI code. 5. The transmission line is an optical transmission line, and the identification means converts the signal obtained by photoelectrically converting the optical digital signal transmitted through the optical transmission line into a binary digital electric signal with a constant amplitude. A transmission path monitoring device according to claim 3, characterized in that: