JPS59167160A - Measuring method and device of degree of margin of signal discrimination - Google Patents

Abstract

PURPOSE:To obtain a high-precision measurement even for an AGC-system digital transmission system by changing either one, at least, of the amplitude and the timing of a digital signal, which is given to an object to be measured, at the interval of a time sufficiently short for the control time constant of an AGC by the time shorter than the interval to eliminate the influence of the AGC. CONSTITUTION:The value of the amplitude of a signal shown in Fig. (A) is stored in a word pattern generator 21 by 8-bit information, and a code converter 23 converts this signal to a ternary digital signal to generate the signals having various amplitudes. This output is inputted to an object 14 to be measured through a transmission medium 12. The object 14 to be measured has a signal discriminating circuit. By this constitution, the transmission pulse amplitude is reduced or increased by the code converter 23 to observe the limit of the amplitude generating a pulse loss error or insertion error by an error detector 15 with respect to the measurement of the degree of a margin of discrimination in an amplitude axial direction. Since the operation of the transmission pulse amplitude is executed in such low frequency that AGC does not respond, it has no influence upon the operation of a normal AGC amplifying system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method and apparatus for measuring a device including a digital signal code identification circuit. In particular, the present invention relates to a method of inputting a digital signal whose waveform has deteriorated due to passing through a communication transmission path, and measuring the discrimination ability for correctly identifying codes from the signal as a discrimination margin. Furthermore, the present invention relates to a method and apparatus for testing discrimination margin without being influenced by an AGC (automatic gain control) circuit when the device under test includes an AGC (automatic gain control) circuit.

[Description of prior art]

The conventional method for measuring digital signal identification margin is as follows:
A sinusoidal crosstalk tolerance measurement method (hereinafter referred to as rS/X measurement method) has been widely used. The principle of this measurement method is explained first.
To explain using a diagram, 11 is a pulse pattern generator;
12 is a transmission medium, 13 is a coupler, 14 is a device under test having a function of identifying digital signals (for example, a digital regenerator), 15 is an error rate measuring device, ] 6 is an attenuator, 17
is a sine wave oscillator. In this S/X measurement method, a sine wave is superimposed on the incoming signal at the input end of the device under test, so that the eye opening is equalized at the output of the amplifier that equalizes the transmission path loss, that is, at the input of the discriminator. This method estimates the digital signal identification margin in a steady state of operation from the relative relationship between the amount of superimposition of the sinusoidal signal and the deterioration of the error rate due to the reduction in the eye opening.

This method is widely used as a method for evaluating the discrimination margin of PCM repeaters and the like because the measurement system can be easily configured and the measurement reproducibility is relatively good.

However, this S/X measurement method has the following drawbacks.

■ If non-stationary noise such as impulsive noise is the dominant cause of error occurrence, using a sine wave, which is a stationary signal, as pseudo-noise will cause the peak value detection AGC amplifier to respond, so it will not be in actual operation. Since the margins of different states are evaluated, the evaluation accuracy becomes low.

■ Initial calibration of the S/X measurement method must be performed by extracting the equalization amplifier output level, but since it is generally impossible to open the product to be measured, it is necessary to estimate this and perform measurements. , and the evaluation accuracy decreases.

That is, in the conventional S/X measurement method, the frequency-gain characteristics of an amplifier for equalizing transmission line loss are fixed, and the discrimination level is automatically set at the center of the equalization eye pattern. This method is A
This was proposed for the TC (automatic identification level control) system. On the other hand, in recent digital transmission systems, an AGC (automatic gain control) method has been adopted in which the discrimination level is fixed and the gain characteristics of the equalizing amplifier are automatically controlled.

When a sine wave is superimposed on the transmission signal at the input end of such a system, the eye pattern at the input point of the discriminator becomes as shown in FIG. FIG. 2A shows an equalized eye pattern at the input point of the discriminator during steady operation. FIG. 2B shows an eye pattern when a sine wave is superimposed when the ATC method is adopted, and in this case, the desired measurement can also be performed by the above-mentioned S/X measurement method. FIG. 2C shows an eye pattern when a sine wave is superimposed in a method in which the AGC method is adopted, and shows that the eye pattern deteriorates and normal measurements cannot be performed.

The reason why the eye pattern deteriorates as shown in Figure 2C is that the gain-frequency characteristic of the equalizing amplifier operates to compensate for the loss proportional to the square root of the cable frequency, so a sine wave signal is superimposed on the input. As the equalizing amplifier output amplitude increases, its maximum value is detected and the high-frequency gain is significantly reduced to keep it at a constant value. In this case, an equalized waveform deviation as shown in the center of the hatched portion of the eye pattern in FIG. 2C occurs, and this becomes a waveform on which a sine wave is superimposed.

FIG. 3 shows a diagram focusing on the identification point portion of this waveform. The figure shows the case where peak value AGC control is applied to the equalized waveform on which a sine wave signal is superimposed.If the eye opening after control is M', then M'=Vp-3・D where δi sine wave peak The value of D, which is M′ −0, is D = V p /3. This is significantly different from 0.5Vp. The normal discrimination level is set to 0.5Vp, but in this case, the optimum sine wave superimposition resistance characteristic cannot be obtained, and rather 0.5Vp is set.
A value smaller than 5Vp shows apparently better characteristics.

In this way, the conventional S/X measurement method is suitable for evaluating digital repeaters where stationary noise such as crosstalk noise is the dominant factor in error occurrence, but it is suitable for evaluating digital repeaters where stationary noise such as crosstalk noise is the dominant factor in error occurrence. was not appropriate and had the disadvantage of decreasing evaluation accuracy.

[Purpose of the invention]

SUMMARY OF THE INVENTION The present invention aims to solve these drawbacks and to provide a measuring method and apparatus that enable highly accurate identification margin measurement even in digital transmission systems employing the AGC method.

[Features of the invention]

The present invention is characterized in that the discrimination margin on the receiving side is measured by applying deterioration corresponding to various disturbances or deterioration factors to the digital transmission signal at a low frequency to which the AGC feedback system cannot respond.

More specifically, at least one of the amplitude and timing of the digital signal applied to the object under test is changed at sufficiently short time intervals relative to the AGC control time constant, and for a time even shorter than this time, thereby eliminating the influence of the AGC. The present invention is characterized in that the code identification error of the signal appearing at the output of the device under test is measured while ensuring that no errors occur.

[Explanation based on examples]

FIG. 4 is a configuration diagram of a measurement system according to an embodiment of the present invention.

Reference numeral 14 denotes an object to be measured (for example, a digital regenerator), which includes a digital signal identification circuit. 12 is a transmission medium. An error detector 15 is connected to the output of the device under test 14 . 21 is a word pattern generator, the output of which is sent to a transmission medium via a code converter. The word pattern generator 21 is controlled by a controller 22 to which the output of the error detector 15 is connected.

Here, we will use a three-level digital transmission system (bipolar transmission system).
will be explained as an example.

A word string for measurement is stored in the word pattern generator 21, and when this word string is added to the code converter command, a bipolar code string as shown in FIG. 5A is obtained as the converted output. The word pattern generator 21 stores the amplitude value of the signal of one time slot shown in FIG. 5A using 8-bit information, and the code converter 23 converts this 8-bit signal into the It is configured to be able to convert into a ternary digital signal such as , and generate signals of various amplitudes for each time slot. The code converter 23 can be realized by an 8-bit AD converter.

The output of the code converter 23 is input to the device under test 14 via the transmission medium 12. In the device under test 14, after equalizing and amplifying the transmission path loss of the input signal and extracting the timing component,
The code string shown in FIG. 5B is obtained by identifying how the equalized amplified signal is output. This code string is applied to an error detector 15 to detect errors occurring in this transmission system.

Using such a measurement system, it is possible to measure (a) discrimination margin in the amplitude axis direction, (b) discrimination margin in the time axis direction, and (c) discrimination margin in both amplitude and time directions. can.

First, the above (a) measurement of discrimination margin in the amplitude axis direction will be explained. To measure the discrimination margin in the amplitude axis direction, determine to what level the transmitted pulse amplitude is reduced or increased by successively reducing the transmitted pulse amplitude (inducing a pulse loss error) or increasing the transmitted pulse amplitude (inducing a pulse insertion error). Although this does not result in an error, it is observed by the error detector 15. Specifically, the fifth
By limiting the transmission pulse amplitude as shown by the broken line fa) in FIG. Also, broken line +b+'
b If the transmitted pulse amplitude is limited as shown, the discrimination margin can be measured for unipolar pulses.

A feature of the present invention is that the transmission pulse amplitude is manipulated at an extremely low frequency, such as once every 10 to 10 hints, when the AGC does not respond. Therefore, this does not affect the operation of the peak value detection AGC amplification system installed in Tsutomi's digital transmission equipment. The overall transfer function determined by the transmission line-equalizing amplifier does not change during the measurement.

In this way, in the measurement using the method of the present invention, the overall transmission system can be considered to be a linear system, and the occurrence of errors can be evaluated correctly.

Next, a method for measuring the discrimination margin in the amplitude axis direction described in (b) above will be described. For this measurement, it is necessary to find the code sequence exhibiting the worst code amount interference in the output of the equalizer, and to detect the minimum discrimination margin as seen from the transmitting side in the shortest possible time. A method for executing this in the minimum time will be explained using FIG.

In this case as well, the code operation is performed at a very low frequency when the AGC of the device under test does not respond.

FIG. 6A shows an AMI code string. The chain line fal in the figure and the identification level of the received signal with the positive polarity code are replaced with the transmitted signal level. In other words, for the three positive polarity codes shown in FIG.
If the value falls below the + discrimination level, the received pulse sequence becomes erroneous.

In reality, because of the equalization deviation of the equalization amplifier, the low-frequency cutoff characteristics, etc., errors may occur even if a signal is sent out with a pulse amplitude greater than this discrimination level.

6 - 7 show a method of searching for the minimum permissible limit of the transmission pulse amplitude. That is, a level search is performed to detect the identification level of the receiving section for code (1). First, for the maximum pulse amplitude Vp, a pulse of V p /2 is sent out as shown in ■. In this case, an error will occur in the receiving section. This error information is fed back from the error detector 15 to the controller 22 of the transmitting section, and in response to this, a pulse of Vp/2 (1+Vp 2) shown in (2) is sent out. In this case, no error occurs.

Feedhack this again and then send out the pulse as shown in ■. In this way, Vp is 172
If it can be quantized and varied by (M+1) operations, it is possible to detect the transmission amplitude level that does not cause the most recent error in the discrimination level (al). For the discrimination level detected in fl),
Furthermore, it is determined whether the transmission pulse amplitude needs to be increased, that is, whether there is negative code amount interference at the time of code (4). When it is necessary to increase the amplitude of the transmission pulse, the amplitude of the transmission pulse is increased until no errors occur, as shown in FIG. 6 (2). This operation is then executed for the code string period of the test signal (for example, in the case of a PN signal, 2'' - 4 bits 2N is the number of shift register stages). In this way, the allowable minimum pulse amplitude of the positive polarity transmission pulse can be measured. This is the discrimination margin of the positive pulse signal at .

Similarly, for the zero pulses of codes (3), (5), and (8), the pulse amplitudes are increased in both positive and negative polar directions, and the maximum allowable amplitude is determined. Furthermore, by determining the minimum allowable amplitude for the negative polarity pulses of signs (2) and (6), the AMI
The positive and negative pole discrimination margin of the entire code series is determined.

The measurement time T by the above method is extremely short. When the PN signal is used as a test signal, the measurement time T is expressed by the following equation using an N-stage shift register.

T=tm ・ (4(M+1)) where tm: Error measurement time per one time M: ■ Transmission amplitude is variable with a quantization step of ρ/2 γ: Maximum value of intersymbol interference (Vp = 1) Generally 2N >>
1. Although γ〈〈1, T=tm−(4(M+1
) +3 + 2 N-1). For example, if t m -50 m sec M-7N=8, then T#2j sec and the identification margin measurement by this measurement method is completed in an extremely short time.

By changing the pulse transmission time position using a similar method, it is possible to measure the discrimination margin of the time axis method at the discrimination level of the equalized eye pattern. That is, by simultaneously executing the amplitude axis direction margin measurement method and the time axis direction discrimination margin measurement method, the above measurement (c) can be performed.

The discrimination margin of the equalized eye pattern shown in Fig. 7, ■,■
', ■' and ■, ■, ■', ■' are measured as a ratio to the amplitude Vp or time C.

By performing both of the above measurements simultaneously, it is also possible to measure the innermost edges (indicated by bold lines) of the equalized eye pattern waveform.

Next, a measuring device for measuring the amplitude axis discrimination margin will be described.

FIG. 8 is a configuration diagram of an apparatus according to an embodiment of the present invention. 30 is a clock generator, and 21 is a word pattern generator constituted by a ROM. 32 is a signal selection circuit, 23 is a code converter, and 34 is a driver amplifier. 14 is an object to be measured having a digital signal identification function, 15 is an error detector, and 22 is a controller.

38 is a shift register, and 39 is a display with an arithmetic function.

The test signal is obtained by driving the word pattern generator 21 with the output of the clock generator 30 and applying the output to the code converter 23 for signal conversion. The accuracy is selected so that the error detector 15 can detect code errors in this test signal. controller 2
2 is also preloaded with the stored contents of the word pattern generator 21. The controller 22 sets the MSB of the shift register 38 to "0" at the measurement start bit position (for example, reference numeral (1) in FIG. 6) and controls the selection circuit 32 to select the output of the shift register 38.

Hereinafter, according to the measurement procedure shown in FIG. 6, the output of the word pattern generator 21 is sequentially replaced with the output of the shift register 38, the identification level is searched, and when the measurement is completed for all of the child species codes, the arithmetic function is added. The value obtained by dividing the output of the shift register 38 by 2 is displayed on the display 39. Similarly, the discrimination margin for zero and negative polarity pulses can be measured with this measurement circuit.

The discrimination margin in the time axis direction can be measured by changing the drive timing from the controller 22 to the signal selection circuit 32.

[Explanation of application examples]

Although the above example shows the measurement of a three-value regenerative repeater, the present invention can be implemented to measure the discrimination margin of any device having a circuit for discriminating digital signals, including an AGC system.

[Explanation of effects]

As described above, according to the present invention, for each digital signal equalization and timing discrimination unit, the measurement of the digital signal discrimination margin as a comprehensive characteristic is performed using extremely infrequent measurement of the waveform or time position of the transmitted pulse signal. to change from the specified state and observe any errors caused by this. For this reason,
It is possible to avoid changes in the operating point of the AGC equalization amplifier and timing circuit, which operate with a constant time constant, which occurs in conventional S/X measurement methods, and eliminates stationary noise systems (e.g. crosstalk noise) and non-stationary noise systems (impulse noise). This makes it possible to measure with extremely high precision and good reproducibility for any type of noise (like noise). Furthermore, the measurement circuit can be configured extremely simply.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a sine wave crosstalk resistance measurement system used as one of the conventional digital signal identification margin evaluation methods. FIG. 2 is an explanatory diagram of an equalized eye pattern when measuring sinusoidal crosstalk tolerance. Figure 3 shows the gain of the equalizer when measuring sinusoidal crosstalk resistance.
FIG. 3 is a diagram showing an example of frequency characteristics. FIG. 4 is a basic configuration diagram of a measurement system according to an embodiment of the present invention. FIG. 5 is a signal waveform diagram for explaining the operation of the basic measurement system. FIG. 6 is a diagram illustrating a method for speeding up measurement according to the present invention. FIG. 7 is a diagram showing each parameter of an equalized eye pattern that can be measured by the method or apparatus of the present invention. FIG. 8 is a block diagram of a measuring device according to an embodiment of the present invention. Patent Applicant Nippon Telegraph and Telephone Public Corporation Agent Patent Attorney Takashi Ide Naoji ¥11 Illustration helmet 2 times 1 Pl 4 Already B 11101001 Figure 5 (+) (2) D) (4) (5)
(6) (7) (8) Sale 6 Figures, ¥17 Figure 182 Part 8 Amendment to Figure Procedures April 20, 1980 1, Indication of Case Patent Application No. 198292 2
, Name of the invention Signal identification margin measurement method and device 3, Relationship with the case of the person making the amendment Patent applicant address 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name (422) Representative of Nippon Telegraph and Telephone Public Corporation Shin Fuji
4. Agent → 5. Date of amendment order (voluntary amendment) 6. Number of inventions increased by amendment None 7. Subject of amendment (1) The scope of claims will be amended as shown in the attached sheet. (2) "In this case, FIG. 2" on page 6, line 5 of the specification is amended to "In this case, FIG. 2." (3) On page 6, line 7 of the specification, "This is a sine wave" is corrected to "This is a sine wave." (4) Correct rlo-" to 10-'J on page 10, line 16 of the specification to "102 to 104." (5) On page 11, line 14 of the specification, "(a) and," is amended to "(a) is." (6) "Time C" on page 15, line 6 of the specification is corrected to "time τ." (7) "Output 2" on page 16, line 16 of the specification is corrected to "output 2'". (8) Specification, page 18, lines 11 to 12 [FIG. 3 is a diagram showing an example of the gain-frequency characteristics of the equalizer during measurement of sinusoidal crosstalk resistance. [Figure 3 is a detailed explanatory diagram of equalization eye pattern deterioration during sinusoidal crosstalk resistance measurement. ” he corrected. (9) Replace drawing Figure 7 with the attached drawing. 9. List of attached documents + 11 Drawings (Fig. 7) 1 copy [Attachment] [Claims] (1) Digital signal code identification means and a digital signal inserted into the input signal path of the code identification means. In a method of measuring the discrimination margin of a digital signal of a device under test by applying a digital signal to a device under test including an automatic gain control means, The interval is controlled and changes at least one of the amplitude and timing of the digital signal applied to the object to be measured for a short time of 2 minutes, and the change appears in the output of the object to be measured. A signal identification margin measuring method characterized by measuring a code identification error of a signal. (2) Identifying the digital signal of the device under test by applying a digital signal to the device under test, which includes a digital signal code identification device and an automatic gain control device inserted into the input signal path of the code identification device. An apparatus for measuring margin, comprising means for generating a digital signal that can be identified by the object to be measured, and means for connecting to the object to be measured and detecting a code identification error thereof, The means for generating Σ
A signal discrimination margin measurement device characterized in that it is configured to give a maximum change in at least one of the amplitude and timing of a digital signal that is generated for a short period of time. P)7 Figure

Claims (2)

[Claims] (1) Identifying the digital signal of the device under test by applying a digital signal to the device under test, which includes a digital signal code identification device and an automatic gain control device inserted into the input signal path of the code identification device. In the method of measuring the margin, at least one of the amplitude and timing of the digital signal applied to the device under test is controlled at a time interval that is sufficiently short with respect to the control time constant of the automatic gain control means, and for a time even shorter than the control time constant of the automatic gain control means. A method for measuring a signal discrimination margin, characterized in that the code discrimination error of a signal appearing in the output of the object to be measured is measured by applying a change. (2) Identifying the digital signal of the device under test by applying a digital signal to the device under test, which includes a digital signal code identification device and an automatic gain control device inserted into the input signal path of the code identification device. An apparatus for measuring margin, comprising means for generating a digital signal that can be identified by the object to be measured, and means for connecting to the object to be measured and detecting a code identification error thereof, The generating means is configured to change at least one of the amplitude and timing of the digital signal to be generated for a time period even shorter than the control time constant of the automatic gain control means at sufficiently short intervals. A signal identification margin measurement device characterized by: