JPH11261653A - Signal quality monitor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a simple signal quality monitor circuit capable of checking the deterioration of transmission characteristics, independently of the signal format. SOLUTION: This circuit is provided with a threshold voltage generating means, that applies a threshold voltage 6 which changes at a prescribed interval to a comparator 7, the comparator 7 that compares a multi-value electric signal with the threshold voltage 6 changing at a prescribed interval, a counter 8 that counts an output of the comparator 7, and an arithmetic circuit 10, that obtains the intensity distribution of the electric signal, based on the threshold voltage 6 and an output of the counter 8 for measuring noise distribution in the electric signal. In place of changing a threshold, the circuit may be provided with a threshold voltage generating means that applies different threshold voltages 6 to the plural comparators 7 respectively and the plural counters 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal quality monitoring circuit for examining deterioration of transmission characteristics in a telecommunication network.

[0002]

2. Description of the Related Art A code error rate or a Q value is used as a factor for specifying the transmission quality of a telecommunication network. One of the methods for measuring the bit error rate is a monitoring method called BIP-8 in the SDH transmission method. BIP-8
Does not estimate the bit error rate from all the bits, but extracts only a specific bit every certain period and estimates the bit error rate from that bit. But this BIP-8
Is limited to the SDH transmission method, other signal systems,
For example, in the case of PHD, another method must be used, so that the SDH code error monitoring circuit cannot be applied to PHD.

[0003] As another conventional Q value measuring method, there is a method in which a threshold value for judging a mark or a space is changed and a Q value is calculated from a result of measuring a code error rate for each value. NSBergano et al., IEEE Photon.Techno
l. Lett., Vol. 5, No. 3, pp. 304-306, 1993). But,
This method has a problem that the scale of the circuit is large, a long time is required for measurement, and the method is expensive.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple signal quality monitoring circuit which does not depend on a signal format in view of the above-mentioned problems.

[0005]

In order to achieve the above object, a signal quality monitoring circuit according to the present invention comprises: a threshold voltage generating means for supplying a threshold voltage which changes at a constant interval to a comparator; That compares the threshold voltage with the threshold voltage that changes at regular intervals, a counter that counts the output of the comparator, a memory that records the threshold voltage and the counter output, and an operation that reads the data in the memory and calculates the intensity distribution of the electric signal And a circuit configured to measure a noise distribution in the electric signal.

Another signal quality monitoring circuit according to the present invention comprises a threshold voltage generating means for supplying different threshold voltages to a plurality of comparators, and a plurality of comparators each for comparing an electric signal branched from a multi-valued electric signal with a threshold voltage. A comparator, a plurality of counters paired with the comparator, and an arithmetic circuit for calculating the intensity distribution of the electric signal from the threshold voltage and the counter output,
The apparatus is characterized in that it is configured to measure a noise distribution in an electric signal.

In optical multi-repeater transmission, an optical amplifier is used at each relay point in order to compensate for the intensity loss of an optical signal propagated through a fiber and keep the intensity of the optical signal constant. However, the optical amplifier has a problem of amplified spontaneou noise.
s emission noise (ASE noise)
The E noise propagates through the optical fiber together with the optical signal and is amplified at the relay point. Therefore, as the number of repeaters increases, ASE
The noise increases and becomes dominant compared to other noises.

When an optical signal on which ASE noise is superimposed is received and demodulated, the distribution of output voltages corresponding to spaces and marks can be approximated by a normal distribution (Gaussian distribution). FIG. 1 (a) shows the time waveform and intensity distribution of a signal without ASE noise, and FIG. 1 (b) shows the time waveform and intensity distribution of the signal with ASE noise superimposed. Fig. 1 (b)
, Σ ₀ and σ ₁ are the standard deviations of the output voltages corresponding to the space and the mark, respectively, and μ ₀ and μ ₁ are the average values of the output voltages corresponding to the space and the mark, respectively. When the output voltage corresponding to the space and the mark is represented by a normal distribution, the Q value and the bit error rate are represented by the following equations.

[0009]

(Equation 1) As described above, the bit error rate BER is calculated from the binary electric signal by Q
The value is obtained by directly measuring the value, and the signal quality can be monitored independently of the type of the signal system. The present invention is based on this principle.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. [Embodiment 1] FIG. 2 is a diagram showing the configuration of a first embodiment of the signal quality monitoring circuit of the present invention. In the figure, 1 is an input optical signal, 2
Is a photodetector that performs O / E conversion and clock extraction, 3 is a clock signal, 4 is an amplifier for an output voltage, 5 is an output voltage, 6 is a threshold voltage generated by threshold voltage generating means (not shown), 7 is A comparator, 8 is a counter, 9 is an output signal (count number) of the counter 8, 10 is an arithmetic circuit, 11 is a memory, and 12 is data in the memory 11.

The optical receiver 2 performs O / E conversion and clock extraction of the input optical signal 1. The extracted clock signal 3 is input to the comparator 7 and the counter 8. O /
The E-converted input optical signal 1 is amplified by the amplifier 4 to become an electric signal having an output voltage 5 (= v). Threshold voltage 6 (= v
_{i: i = 0,1, ...,} n) changes in the interval _{Δv = v i -v i-1} ,
The comparator 7 outputs a signal when compared to the threshold voltage 6 the output voltage 5 of the amplifier 4 for each bit v of <v _i. In counter 8 counts the output of the comparator 7 is once reset each time the threshold voltage 6 is changed to v _{i + 1} from the v _i, and inputs the counted number 9 in the memory 11. Memory 11
Count number 9 at that time of the threshold voltage _{6 (= F (v i)} )
Record The arithmetic circuit 10 obtains a Q value from the data 12 in the memory 11.

[0012] FIG. 3 (a) is a diagram showing an example of the relationship between the number of times the threshold voltage v _i and the output voltage v is determined to be less than the threshold voltage F (v _{i). Here, f (v i) = F} (v i) putting the _{-F (v i-1) (} 2), f (v i) , the output voltage v is v _i-1 ≦ v <v
_It represents the number of times that it can be determined that it is within the range of _i . That is,
FIG. 3B showing the distribution of the output voltage v shows that the output voltage v
_i-1 ≦ v indicates the number of times it is determined that a <v _i. Therefore,
Setting the threshold voltage v _i is will be seeking a frequency distribution of the output voltage v, it represents the distribution of the output voltage itself.

Here, as described above, the frequency distribution of the demodulated output voltage is represented by the sum of two normal distributions whose average is a value corresponding to a space or mark due to the influence of ASE noise. In FIG. 3B, v _m0 and v _m1 are:

(Equation 2) Is the threshold voltage when

General formula of normal distribution

(Equation 3) From the following, the distribution f ₀ (v _i ) of the output voltage corresponding to the space and the distribution f ₁ (v _i ) of the output voltage corresponding to the mark are:

(Equation 4) Becomes However, K ₀ and K ₁ depend on the total number of counts. σ ₀ and σ ₁ are standard deviations of output voltages corresponding to spaces and marks, respectively, and v _m0 and v _m1 are average values of output voltages corresponding to spaces and marks, respectively.

When obtaining the standard deviations σ ₀ and σ ₁ , v
In _{m0 <v i <v m1,} f 0 (v i) and f ₁ (v _i) and because the _{overlap, v 1 <v i <v} m0 ( Fig _{3 (c)), v m1} <
v _i <v _n using the values in the range (FIG. 3 (d)).

In general, a frequency distribution g (x) having an average μ
Is expressed by the following equation.

(Equation 5)

From equations (3) and (6)

(Equation 6) Becomes

If the average values v _m0 and v _m1 and the standard deviations σ ₀ and σ ₁ are known, the Q value and the bit error rate can be obtained from equation (1). In the arithmetic circuit 10, the above equations (1), (2),
The calculations of (3) and (7) are performed, and the frequency distribution f (v _i ) of the output voltage 5, the average values v _m0 and v _m1 , and the standard deviations σ ₀ and σ
Find _{1 and} Q value.

[Embodiment 2] FIG. 4 is a diagram showing the configuration of a signal quality monitoring circuit according to a second embodiment of the present invention. In the figure, 6-
0, ..., 6-n are threshold voltages generated by threshold voltage generating means (not shown), 7-0, ..., 7-n are comparators, 8-0, ..., 8 -n is the counter, 9-0, ..., 9-n are the output signals of the counters 8-0, ..., 8-n, that is, the count numbers. is there.

The output voltage 5 is branched to each of the comparators.
Input to 7-0, ..., 7-n. Threshold voltages 6-0, ..., 6-n is a fixed value _{v i = v 0 + i ·} Δv (i = 0,1, ..., n) is set to the comparator 7-0,. .., 7-n, the output voltage 5 (=
v) the threshold voltage 6-0, ..., 6-n ( = v i) and by comparing the v
And it outputs a signal in the case of <v _i. Counter 8-0, ..., 8-
n counts the outputs of the comparators 7-0,..., 7-n and inputs the count numbers 9-0,.

The count number 9-0, ..., 9-n is the output voltage 5 is the threshold voltage 6-0, ..., it is equal to the cumulative frequency F of less than 6-n (v _i), the arithmetic circuit in 10, wherein in the same manner as in example 1 (1), (2), (3) and performs the operation of (7), the output voltage 5 frequency distribution f (v _i), the average value v _m0 and v _m1 , Standard deviations σ ₀ and σ ₁ and the Q value.

[0022]

As described above, according to the signal quality monitoring circuit of the present invention, the signal quality can be monitored by directly measuring the Q value without depending on the signal system.

[Brief description of the drawings]

FIG. 1 is a diagram showing a time waveform and intensity distribution of a signal when there is no ASE noise (a) and when ASE noise is superimposed (b).

FIG. 2 is a diagram showing a configuration of a first embodiment of a signal quality monitoring circuit of the present invention.

FIG. 3 is a diagram illustrating a relationship between a threshold voltage, a count number of a counter, and a distribution of an output voltage.

FIG. 4 is a diagram showing a configuration of a second embodiment of the signal quality monitoring circuit of the present invention.

[Explanation of symbols]

 Reference Signs List 1 input optical signal 2 light receiver 3 clock signal 4 amplifier 5 output voltage 6 threshold voltage 7 comparator 8 counter 9 counter output signal (count number) 10 arithmetic circuit 11 memory 12 memory data

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Haruhiko Ichino 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A threshold voltage generating means for supplying a threshold voltage varying at a constant interval to a comparator, a comparator comparing a multi-valued electric signal with a threshold voltage varying at a constant interval, and counting an output of the comparator. A counter, a memory for recording a threshold voltage and a counter output, and an arithmetic circuit for reading data of the memory and obtaining an intensity distribution of the electric signal, and configured to measure a noise distribution in the electric signal. Characteristic signal quality monitoring circuit. 2. A threshold voltage generating means for supplying different threshold voltages to a plurality of comparators, a plurality of comparators each comparing an electric signal branched from a multi-valued electric signal with a threshold voltage, and a pair with the comparator. A signal quality monitoring circuit comprising: a plurality of counters; and an arithmetic circuit for determining an intensity distribution of the electric signal from the threshold voltage and the counter output, and configured to measure a noise distribution in the electric signal. .