CN1481084A - Method for testing performances of optic transmission system and device - Google Patents

Abstract

The method includes following steps. Code flow is recovered by using a selected reference electrical level as decision electrical level so as to obtain reference code flow. Comparing the code flow with other code flows recovered under variant decision electrical levels obtains 'U' type relation curve between first error rate and decision electrical level, and the error rate at lowest point of 'U' type relation curve is deduced. Continuing to change reference electrical level obtains multiple error rates at lowest point of 'U' type relation curve, and the lowest error rate is found out from these error rates. Value of Q factor is deduced from the lowest error rate. Since recovered data as reference code flow from reference electrical level, thus, it is not needed to prepare a standard signal as reference code flow. In this way, difficulty of monitoring on site is solved, making test more convenient.

Description

A kind of method and device of measuring light transmission system performance

Technical field:

The present invention relates to a kind of method and device of measuring light transmission system performance.

Background technology:

The error rate (BER) and Optical Signal To Noise Ratio (OSNR) are the important parameters of monitoring fiber optic transmission system.The error rate is not the parameter of physical layer, and when the error rate hour, need considerable time to measure error code.Adopting measurement OSNR to come the transmission characteristic of monitoring system is a kind of alternative method, and it is bigger that this method is fit to dispersion tolerance, based on the system of noise limited, such as the system of 2.5Gbit/s.For the transmission system of higher speed, OSNR can not describe actual transmission performance well.A better way is the transmission performance that adopts the Q factor to come descriptive system.

The key of measuring the Q factor is to find optimum decision level, and the error rate BER of optimum decision level place correspondence and the Q factor have a simple relation, $\mathrm{BER}\≈\frac{\exp ({-Q}^2/2)}{Q\sqrt{2\mathrm{\π}}},$ By detecting the error rate that optimizing level goes out, just can obtain the Q factor.But the error rate at optimum decision level place is less usually, measures error rate inconvenience.Bergano has proposed to measure under a kind of suitable Gaussian Profile noise conditions the straightforward procedure of the Q factor.The principle of this method provides in Fig. 1, by the amplitude of continuous adjustment decision level, obtains the ber value of respective series.If decision level is decided to be the x axle, the error rate is the y axle, can obtain " U " font curve.Bergano has proposed to determine indirectly the method for lowest bit error rate point, and common way is to measure decision level to depart from the error rate of optimum decision level (generally 10 ^-4To 10 ^-10Between), simulate whole " U " font error rate with the decision level curve by the method for data fitting, thereby obtain the minimum error rate and best decision level.So just can calculate the Q factor.

But a problem of this method of measurement is to need one to come the error code of actual generations of comparison with reference to code stream when measuring error code in the line, be standard signal with reference to code stream in the general measure, thereby the use of this method is very inconvenient, especially is not suitable for on-site supervision.

Summary of the invention:

Purpose of the present invention is exactly in order to overcome the above problems, and a kind of method and device of measuring light transmission system performance is provided, and need not with reference to code stream, is convenient to on-the-spot the use.

For achieving the above object, the present invention proposes a kind of method and device of measuring light transmission system performance.

Described method comprises the steps: 1) choose first reference level, be that decision level is recovered code stream with this reference level, obtain with reference to code stream; The code stream that recovers under this decision level with reference to code stream and variation is compared, thereby obtain " U " font relation curve of article one error rate and decision level, and extrapolate the error rate at the minimum point place of " U " font relation curve; 2) choose second reference level, repeat said process, obtain the error rate at the minimum point place of another " U " font relation curve; 3) constantly change reference level, obtain the error rate at the minimum point place of a plurality of " U " font relation curve, and find out lowest bit error rate wherein, the reference level of this moment is optimum reference level; 4) with above-mentioned optimum reference level as optimum decision level, extrapolate the value of the Q factor from this lowest bit error rate.

The device of described measuring light transmission system performance comprises two data recovery module, links to each other respectively with measured data; The decision level of one of them data recovery module adopts reference level, and the decision level of another data recovery module adopts adjustable decision level; Also comprise two d type flip flops and one or, described d type flip flop input connects two data recovered streams respectively, output termination or door compare; Also comprise error counter, its input with or the door output link to each other, be used to write down last Different Results; Wherein the data recovery module of reference level also comprises a clock recovery circuitry, the clock that is produced is behind the process delay circuit, enter into above-mentioned d type flip flop and a clock counter respectively, d type flip flop makes the code stream of comparison synchronous, the clock counter record produces the data number, the output of it and error counter together is input to be carried out the error rate (BER) and calculates on the error rate (BER) calculation element, and and then utilizes fitting process to obtain " U " font relation curve of the error rate (BER) and decision level (Uth).

Owing to adopted above scheme, utilize the reference level restore data as the reference code stream, realize error code testing, this recovers from measured data stream with reference to code stream, so just do not need to prepare in advance a standard signal as the reference code stream, greatly facilitate test, solved the difficult problem of on-site supervision.

Description of drawings:

Fig. 1 is the principle schematic of the prior art simplified measurement Q factor.

Fig. 2 is a measuring principle schematic diagram of the present invention.

Fig. 3 is the circuit diagram of a specific embodiment of the present invention.

Embodiment:

Also the present invention is described in further detail in conjunction with the accompanying drawings below by specific embodiment.The method of this patent obtains embodying in Fig. 2, and it is based on such fact: when reference level changed, the error rate that obtains and decision level relation curve be the U font always.Suppose a reference level, as the point of the A among Fig. 2.The code stream (being the code stream that decision level is recovered with this reference level promptly) that recovers down with this reference level is with reference to code stream, compare with the code stream that recovers under the decision level that changes, thereby obtain " U " font relation curve of error rate BER and decision level Uth, and extrapolate (using fitting process) relevant parameter, thereby calculate the minimum error rate, i.e. the error rate at curve minimum point place.The method data available fitting process of calculating, for example can adopt formula: $\mathrm{BER}(V,V_R)=\frac{1}{2}\mathrm{erfc}\left(\frac{|u_1-V|}{{\mathrm{\σ}}_1}\right)*(1-\frac{1}{2}\mathrm{erfc}\left(\frac{|u_1-V_R|}{\mathrm{\σ}1}\right))$ $+\frac{1}{2}\mathrm{erfc}\left(\frac{|V-u_0|}{{\mathrm{\σ}}_0}\right)*(1-\frac{1}{2}\mathrm{erfc}\left(\frac{|V_R-u_0|}{\mathrm{\σ}0}\right))$

U wherein ₁And u ₀Be " 0 " and " 1 " level average.σ ₁And σ ₀It is the variance of " 0 " and " 1 " noise.V and V _RBe decision level and reference level.This step is similar to the method for determining lowest bit error rate point indirectly that Bergano proposes, and just reference code stream wherein is not special standard code stream, but has made the code stream that recovers from measured data stream under the reference level into.Obviously, the latter is easy to obtain, but because it is not real standard code stream, what measured lowest bit error rate neither be real is minimum, also needs following steps further to measure.

Consider another reference Point C, repeat the process described in the previous step, obtain another minimum error rate.

Change reference level, the lowest bit error rate in finding all minimum error rates (B point in as figure), the lowest bit error rate that perhaps ought calculate changes less than 10 ^-15The time, just stop to change reference level.At this moment reference level is optimum reference level, and this level also is the optimum decision level simultaneously, in view of the above, can think the relational expression of the error rate BER and the Q factor $\mathrm{BER}\≈\frac{\exp (-Q^2/2)}{Q\sqrt{2\mathrm{\π}}}$ Set up, can extrapolate last Q value from the error rate at this moment like this.

The selection principle of reference level and decision level is to make the error rate that records 10 ^-4To 10 ^-10Between, this moment, decision level departed from the optimum decision level, and the error rate can record the result quickly than lowest bit error rate height.

What Fig. 3 provided is the schematic diagram of measuring the enforcement circuit of the Q factor.This circuit comprises two data recovery module, links to each other respectively with measured data; The decision level of one of them data recovery module adopts reference level, and the decision level of another data recovery module adopts adjustable decision level; Also comprise two d type flip flops and one or, described d type flip flop input connects two data recovered streams respectively, output termination or door compare; Also comprise error counter, its input with or the door output link to each other, be used to write down last Different Results; Wherein the data recovery module of reference level also comprises a clock recovery circuitry, the clock that is produced is behind the process delay circuit, enter into above-mentioned d type flip flop and a clock counter respectively, d type flip flop makes the code stream of comparison synchronous, the clock counter record produces the data number, the output of it and error counter together is input to the error rate (BER) calculation element---and carry out the error rate (BER) on the CPU and calculate, and and then utilize fitting process to obtain " U " font relation curve of the error rate (BER) and decision level (Uth).CPU also produces circuit with the reference decision level of one of them data recovery circuit and links to each other, the size of control reference level.

Measured data flow is divided into two-way, enters two data recovery module respectively.The decision level of a data recovery module adopts reference level (being controlled the size of this reference level by CPU), and the decision level of another data recovery module adopts adjustable level.The data recovered flow point is through behind two d type flip flops, enters one or compare.Last Different Results is noted down by error counter.Wherein the data recovery module of reference level also produces a clock, and this clock enters into d type flip flop and clock counter respectively through behind the suitable time-delay.Wherein the purpose of d type flip flop is to make the code stream of comparison synchronous.The clock counter record produces the data number, just can calculate the error rate in conjunction with error counter.The calculating of the error rate is finished by CPU, after handling through CPU at last, exports last result.

Claims (8)

1, a kind of method of measuring light transmission system performance is characterized in that comprising the steps:

1) choosing first reference level, is that decision level is recovered code stream with this reference level, obtains with reference to code stream; The code stream that recovers under this decision level with reference to code stream and variation is compared, thereby obtain " U " font relation curve of article one error rate (BER) and decision level (Uth), and extrapolate the error rate at the curve minimum point place of " U " font relation curve;

2) choose second reference level, repeat said process, obtain the error rate that another " U " font relation curve minimum point place (B) locates;

3) constantly change reference level, obtain the error rate at the minimum point place of a plurality of " U " font relation curve, and find out lowest bit error rate wherein, the reference level of this moment is optimum reference level;

4) with above-mentioned optimum reference level as optimum decision level, extrapolate the value of the Q factor from this lowest bit error rate.

2, the method for a kind of measuring light transmission system performance as claimed in claim 1 is characterized in that: the selection principle of reference level and decision level is to make the error rate that records 10 ^-4To 10 ^-10Between.

3, the method for a kind of measuring light transmission system performance as claimed in claim 1 or 2 is characterized in that: when the lowest bit error rate of calculating changes less than set point, just stop to change reference level.

4, the method for a kind of measuring light transmission system performance as claimed in claim 1 or 2 is characterized in that: the error rate of optimum decision level place correspondence and the relation of the Q factor are: $\mathrm{BER}\≈\frac{\exp (-Q^2/2)}{Q\sqrt{2\mathrm{\π}}}.$

5, the method for a kind of measuring light transmission system performance as claimed in claim 1 or 2 is characterized in that in step 1) to 3) in, the method that obtains " U " font relation curve is: measured data flow is divided into two-way, enters two data recovery module respectively; The decision level of a data recovery module adopts reference level, and the decision level of another data recovery module adopts adjustable decision level; The data recovered flow point is through behind two d type flip flops, enters one or compare; Last Different Results is noted down by error counter; Wherein the data recovery module of reference level also produces a clock, this clock is after the process time-delay, enter into d type flip flop and clock counter respectively, d type flip flop makes the code stream of comparison synchronous, the clock counter record produces the data number, calculate the error rate (BER) in conjunction with error counter, and and then utilize fitting process to obtain " U " font relation curve of the error rate (BER) and decision level (Uth).

6, the method for a kind of measuring light transmission system performance as claimed in claim 3, it is characterized in that: the calculating of the error rate is finished by CPU, and by the size that CPU controls reference level, after handling through CPU at last, exports last result.

7, a kind of device of measuring light transmission system performance is characterized in that: comprise two data recovery module, link to each other respectively with measured data; The decision level of one of them data recovery module adopts reference level, and the decision level of another data recovery module adopts adjustable decision level; Also comprise two d type flip flops and one or, described d type flip flop input connects two data recovered streams respectively, output termination or door compare; Also comprise error counter, its input with or the door output link to each other, be used to write down last Different Results; Wherein the data recovery module of reference level also comprises a clock recovery circuitry, the clock that is produced is behind the process delay circuit, enter into above-mentioned d type flip flop and a clock counter respectively, d type flip flop makes the code stream of comparison synchronous, the clock counter record produces the data number, the output of it and error counter together is input to be carried out the error rate (BER) and calculates on the error rate (BER) calculation element, and and then utilizes fitting process to obtain " U " font relation curve of the error rate (BER) and decision level (Uth).

8, the device of a kind of measuring light transmission system performance as claimed in claim 7, it is characterized in that: the described error rate (BER) calculation element is CPU (CPU), it also produces circuit with the reference decision level of one of them data recovery circuit and links to each other the size of control reference level.