JPH01154660A - Testing method for communication system - Google Patents

Abstract

PURPOSE:To evaluate the aperture of an eye pattern with a simple means by measuring the error rate of a signal identified by an identification point moved in the amplitude and time directions of the eye pattern. CONSTITUTION:A reception signal equalized and amplified by an equalizing amplifier 11 is inputted to a timing recovery circuit 13, from which an identification phase signal (c) is generated, the signal (c) is subjected to amplitude modulation at an identification phase modulation circuit 15 by using a signal shifted by pi/2 by a phase shifter 17 from a sinusoidal wave signal (d) from a sinusoidal wave oscillation circuit 16. On the other hand, the identification level signal (f) is subjected to amplitude modulation by using said sinusoidal wave signal (d) by the identification level modulation circuit 14 and the outputs of the modulation circuits 15, 16 are fed to an identification device 12 to form an identification point moved circularly or in an elliptic form. The identification device 12 uses the identification point to identify said signal (b) and the error rate of the identification output signal is measured by an error rate measuring instrument 18.

Description

[Detailed Description of the Invention] [Summary] Regarding a communication system testing method that evaluates the eye pattern aperture based on error rate, the present invention aims to evaluate the eye pattern aperture using a simple method. The identification level for performing identification is modulated with a sine wave, and the identification phase is modulated with a sine wave having a phase difference of π/2 from the sine wave to form an identification point that moves in a circular or elliptical shape, and this identification point The configuration is configured to identify the received signal by using the method and measure the error rate of the identified output signal.

[Industrial application field]

The present invention relates to a communication system testing method that evaluates the aperture of an eye pattern based on an error rate.

BACKGROUND ART In digital communication systems, tests are performed to determine whether desired characteristics can be obtained for each device including a transmitting device, a receiving device, etc., and testing methods corresponding to various test items have been proposed. Testing of such communication systems is
There is a demand for simple operation and high reliability.

[Conventional technology]

Test items for communication systems include, for example, transmission output level, modulation characteristics, code error rate characteristics, and eye pattern aperture. For example, to determine the modulation characteristics of an optical transmitter in a digital optical communication system, the output optical signal is input to an eye pattern measuring device and tested using an eye mask to see if the desired eye pattern aperture is obtained. method is known.

Regarding the reception ability of optical receivers in digital optical communication systems, there are methods to test the optical signal level from the test equipment by changing the level of the optical signal using an attenuator, etc., or by superimposing interference optical signals and measuring the error rate. It has been known.

[Problem that the invention seeks to solve]

Among the conventional test methods mentioned above, for example, the method of testing modulation characteristics using an eye mask visually observes the eye pattern displayed on an eye pattern measuring device, so there is a relatively low probability that The problem was that the modulation characteristics, which deteriorated the eye pattern, were overlooked.

In addition, in testing the reception ability of optical reception signals, the error rate is measured by degrading the eye pattern by superimposing an interference optical signal, but this eye pattern is based on the extinction ratio of the optical signal and The amount of deterioration changes depending on the duty, and the eye opening in the time direction cannot be evaluated, so it is not easy to conduct an accurate test.

Furthermore, when measuring the error rate as a test of transmission characteristics, it is not related to the eye pattern, and the aperture of the eye pattern cannot be fully grasped.

An object of the present invention is to evaluate the aperture of an eye pattern using simple means.

[Means for solving problems]

The communication system testing method of the present invention evaluates the degree of aperture by automatically moving the identification position of the eye pattern in the amplitude direction and the time direction, and will be described with reference to FIG.

In the communication system test method that performs the eye pattern l aperture evaluation test, identification level 2 is used to identify received signals.
is modulated with a sine wave, and the identification phase 3 is modulated with a sine wave with a phase difference of π/2 from the sine wave to form an identification point 4 that moves in a circular or elliptical shape, and reception is performed by this identification point. The signal is identified and the identified output signal is applied to the error measuring device 5 to measure the error rate.

[Effect]

By modulating the discrimination level 2 with a sine wave, the discrimination level 2 changes within the range A according to the period of the sine wave,
Further, by modulating the identification phase 3 with a sine wave, the identification phase 3 changes within the range B according to the period of the sine wave.

In this case, since amplitude modulation is performed using a sine wave with a phase difference of π/2, the locus of the combined identification point 4 becomes circular or elliptical.

The moving direction of this identification point 4 can be the arrow direction or the opposite direction depending on the selection of the phase difference of the sine wave, and the moving speed corresponds to the frequency of the sine wave and is compared to the frequency of the received signal. A sufficiently low frequency is selected.

This identification point 4 is used to identify the received signal, and the identified output signal is applied to the error measuring device 5 to measure the error rate.If the error rate is less than the desired error rate, the It can be seen that the opening degree of the pattern is a desired size. Therefore, the locus (width A,
From B), the size of the aperture of eye pattern 1 can be determined, and from the error rate in the case of the standard trajectory of discrimination point 4, it can be determined whether the aperture of eye pattern l is sufficiently large or not. .

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 11 is an equalization amplifier, 12 is a discriminator, 13 is a timing recovery circuit,
14 is an identification level modulation circuit, 15 is an identification phase modulation circuit,
16 is a sine wave oscillator, 17 is a phase shifter, and 18 is an error measuring device.

The received signal a is equalized and amplified by an equalization amplifier 11, and the equalized amplified output signal is sent to a discriminator 12 and a timing recovery circuit 13.
added to. The bit timing signal is regenerated from the timing regeneration circuit 13 and applied as the identification phase signal C to the identification phase modulation circuit 15. Furthermore, in a digital optical communication system, an optical signal is converted into an electrical signal and becomes the above-mentioned received signal a.

Further, the sine wave signal d from the sine wave oscillator 16 is applied to the discrimination modulation circuit 14, and the discrimination level signal f is amplitude-modulated. Further, the sine wave signal e whose phase has been shifted by π/2 by the phase shifter 17 is applied to the identification phase modulation circuit 15, and the identification phase signal C is modulated. That is, the identification timing phase is the sine wave signal e
is changed periodically according to

The discriminator 12 receives a modulation identification level signal g and a modulation identification phase signal g.

Since h is in an orthogonal relationship, the combined identification points move in a circular or elliptical manner as shown in FIG. The equalized amplified output signal i is identified by a changing identification point, and the identified output signal i of logic "1", "O" is applied to an error meter 18 to measure the error rate.

By setting discrimination level 2 and discrimination phase 3 at the center of the aperture of eye pattern 1 and selecting the amplitudes of sine wave signals d and e, the width of change A of discrimination level 2 in FIG.
Since it is possible to determine the width B of the change in the identification phase 2, it is possible to set these widths A and B and test the aperture of the eye pattern 1 that is less than or equal to a desired error rate.

For example, if the desired error rate is obtained even if the amplitudes of the sinusoidal signals d and e are set large and the widths A and B are made large, then the aperture of eye pattern 1 will be large; , the amplitudes of the sine wave signals d and e are set small to create widths A and B.
If the desired error rate cannot be obtained without reducing
It can be seen that the aperture of eye pattern 1 is small.

It is also possible to perform the test by shifting the center of the locus of the identification point 4 with respect to the center of the aperture of the eye pattern l. That is, when the discrimination level 2 is set upward or downward, the center of the locus of the discrimination point 4 moves upward or downward correspondingly. Similarly, when the identification phase 3 is set to the right or left, the center of the locus of the identification point 4 moves to the right or left correspondingly. For example, it is also possible to shift the identification phase 3 to the left and test the limit of the identification phase delay that provides a desired error rate.

FIG. 3 is an explanatory diagram of the test connection of the embodiment of the present invention, (A
) shows a case where the modulation characteristics of the transmitting device 21 are tested, and the testing device 22 is connected to the transmitting device 21. This test device 2
2 has the configuration shown in FIG. 2, for example,
The output signal of the transmitting device 21 is input directly or through an attenuator to the testing device 22, and as described above, it is tested whether the desired eye pattern aperture is obtained.

In this case, even in the case of modulation characteristics that cause eye pattern deterioration with a relatively low probability, it can be detected by error rate measurement, so it is possible to detect abnormalities in the modulator of the transmitter 21. In the case of an optical transmitter that sends out optical signals, it is sufficient to provide a light-receiving element or the like on the test bag [22 side] for converting optical signals into electrical signals.

In addition, (B) shows the case of testing the transmission characteristics, and the transmitter f
The output signal of 21 is input to the test device 22 via the transmission line 23, and it is tested whether or not the eye pattern aperture that is less than or equal to the desired error rate can be obtained, and is similar to the error rate characteristic test described above. Then, a test signal of a pseudo-random pattern is sent from the transmitting device 21, and the test device 22 performs discrimination using a moving discrimination point in the discriminator 12 in FIG. The error rate will be determined by comparison. And a predetermined width A.

If the error rate when identifying at the identification point 4, which is the locus of B, is less than or equal to a desired value, it is determined that the eye pattern opening degree is the desired size.

Further, (C) shows a case where a test including the repeater 24 is performed, in which the test device 22A is connected to the receiving section 24A of the repeater 24, and the test signal from the transmitter 21 is transmitted to the repeater 24 via the transmission path 23A. The input signal of the discriminator for performing identification reproduction of the receiving section 24A is input to the receiving section 24A, and the error rate measurement as described above is performed, and the aperture of the eye pattern is determined to be as large as desired. The error rate is used to evaluate whether the error rate is accurate or not.

In addition, the test signal received by the receiving section 24A of the repeater 24 is transmitted from the transmitting section 24B to the test device 22B via the transmission path 23B, and the test device 22B measures the error rate in the same manner as described above to determine the eye pattern. This is to evaluate whether the opening degree is a desired size or not based on the error rate.

Further, (D) shows a case where the receiving device 26 is tested, and the level of the test signal from the testing device 25 is adjusted and the receiving device 26 is tested.
6, and the input signal of the discriminator of the receiving device 26 is used to evaluate the eye pattern aperture by the above-mentioned error rate measurement in the testing device 25. In addition to the error measuring instrument, the error rate is also measured and tested. The test device 25 in this case has a configuration in which a configuration for outputting a test signal is added to the test device 22.

〔Effect of the invention〕

As explained above, the present invention modulates the discrimination level 2 and the discrimination phase 3 with a sine wave with a phase difference of π/2,
A discrimination point 4 that moves in a circle or an ellipse is formed, and the error rate of the discrimination output signal that identifies the received signal using the discrimination point 4 is measured.The range of change between discrimination level 2 and discrimination phase 3 is measured. If the desired error rate is obtained even if the value is increased, it is determined that the opening degree of eye pattern 1 is large.
The degree of aperture of the eye pattern 1 can be evaluated based on the error rate. Therefore, using this eye pattern 1 aperture evaluation test, each part of the communication system can be tested with simple operations.

Further, it is possible to independently test the amplitude direction and the time direction of the aperture of the eye pattern 1. That is, the aperture evaluation in the amplitude direction is performed by setting the discrimination level 2 and the sine wave that modulates it, and independently from this, the discrimination phase 3 is set.
It is possible to evaluate the degree of aperture in the time direction by setting the sine wave and the sine wave that modulates it. Therefore, it is possible to test not only changes in characteristics due to signal levels but also changes in characteristics due to delay characteristics and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIGS. 3(A) to 3(D) are diagrams illustrating test connections of the embodiment of the present invention. 1 is the eye pattern, 2 is the discrimination level, 3 is the discrimination phase, 4
is a discrimination point, 5 is an error measuring device, 11 is an equalization amplifier, 12 is a discriminator, 13 is a timing recovery circuit, 14 is a discrimination level modulation circuit, 15 is a discrimination phase modulation circuit, 16 is a sine wave oscillator, and 17 is a shifter. Phase device 18 is an error measuring device.

Claims (1)

[Claims] In a communication system testing method that performs an eye pattern (1) aperture evaluation test, an identification level (2) for identifying received signals is modulated with a sine wave, and an identification phase (3) is modulated with a sine wave. ) has a phase difference of π/2 from the sine wave.
Discrimination point (
4), identifying the received signal using the identification point (4), and measuring an error rate of the identification output signal.