Optical communications – Diagnostic testing
Reexamination Certificate
2000-06-13
2004-04-06
Pascal, Leslie (Department: 2633)
Optical communications
Diagnostic testing
C398S026000, C398S027000, C398S029000, C398S033000, C398S141000, C398S147000, C398S079000, C398S202000, C398S214000, C375S224000, C375S317000
Reexamination Certificate
active
06718138
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-167550, filed Jun. 14, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a digital-signal quality monitoring method which is used in a digital transmission system such as an optical transmission system and can easily monitor the quality of transmission signals; and a communications apparatus which uses this method.
In the field of recent digital transmission systems, as improvements are being made on the wave-length multiplexing technology and optical switching technology, there is an expectation for realization of large-capacity and highly-flexible optical networks. A great attention is paid particularly to a WDM (Wavelength Division Multiplexing) network which is characterized by its capability of employing different transmission speeds, transmission frame formats and modulation systems for different wavelength channels.
This type of network needs such control as to always monitor the quality of signals to transfer in an optical fiber and switch that optical fiber to a redundant system when some failure occurs in the optical fiber. Possible factors for the degradation of the quality of signals in an optical fiber are the deterioration of the S/N ratio caused by an increase in spontaneous emission (ASE) noise that is generated in an optical amplifier, the deterioration of waveforms originated by the wavelength dispersion and the non-linear characteristic of a transmission fiber and crosstalk to another wavelength channel due to a variation in signal wavelength.
A Q value has often been used as a parameter for monitoring the quality of binary digital signals that travel through an optical fiber. The Q value is a parameter which represents the S/N ratio that is defined by the following equation.
Q
=
&LeftBracketingBar;
μ
1
-
μ
0
&RightBracketingBar;
σ
1
+
σ
0
where &mgr;
1
and &mgr;
0
are arverage values of the mark level and space level respectively and &sgr;
1
and &sgr;
0
are dispersion values of the mark level and space level respectively.
Available methods for the acquisition of a Q value are a method of acquiring a Q value by measuring the reception error ratio while scanning a discrimination threshold value, as proposed in IEEE Photonics Tecnol. Lett., Vol. 5, No. 3, pp. 304-306, 1993, “Margin measurements in optical amplifier system” by N. S. Bargano et al., and a method of acquiring a Q value from the amplitude histogram of an eye pattern obtained by using the sampling technique, as proposed in ECOC '98, pp. 707-709, “Application of amplitude histograms for quality of service measurements of optical channels and fault identification” by K. Muller et al.
But, the first quality monitoring method which evaluates the quality by acquiring a Q value from a measured error ratio needs to generate a reference data pattern from a signal to be measured in order to detect an error, and also needs to count error bits. The second quality monitoring method which evaluates the quality by acquiring a Q value from the amplitude histogram of an eye pattern obtained by sampling requires a sampling circuit like a sampling oscillo-scope and a data processing circuit. The use of those quality monitoring methods results in an increased number of constituting components and enlarges the apparatus. Those methods also complicate the measuring algorithm.
While an error in a received signal can be measured by using error monitoring bytes B
1
and B
2
in an STM-n (Synchronous Transport Module-n) frame, this method not only requires a frame process but also a long time measure the signal quality when the error ratio is very small.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a digital-signal quality monitoring method which can easily and accurately monitor the quality of received digital signals, and a communications apparatus which uses this method.
To achieve the above object, a digital-signal quality monitoring method according to this invention is designed as follows.
(1) A digital-signal quality monitoring method comprising the steps of scanning a discrimination level while discriminating a value of an input n-value digital signal (n being a natural number equal to or larger than 2) by comparing that value with the discrimination level; detecting an average value of the discriminated signal; and computing a quality parameter from the average value.
(2) A digital-signal quality monitoring method comprising the steps of scanning a discrimination level and discrimination timings while discriminating a value of an input n-value digital signal (n being a natural number equal to or larger than 2) by comparing that value with the discrimination level; detecting an average value of the discriminated signal; and computing a quality parameter from the average value.
(3) In the digital-signal quality monitoring method (1), a probability density function along an amplitude axis of the input signal is acquired by differentiating the average value of the discriminated signal with respect to the discrimination levels and the quality parameter is computed from the probability density function.
(4) In the digital-signal quality monitoring method (2), a probability density function along an amplitude axis of the input signal at individual discrimination timing is acquired by differentiating the average value of the discriminated signal with respect to the discrimination levels and the quality parameter is computed from the probability density function.
(5) In the digital-signal quality monitoring method (1), a probability density function along an amplitude axis of the input signal is acquired by scanning the discrimination levels in such a way as to be proportional to time and differentiating the average value of the discriminated signal with respect to time and the quality parameter is computed from the probability density function.
(6) In the digital-signal quality monitoring method (2), a probability density function along an amplitude axis of the input signal at individual discrimination timing is acquired by scanning the discrimination levels in such a way as to be proportional to time and differentiating the average value of the discriminated signal with respect to time and the quality parameter is computed from the probability density function.
(7) In any one of the digital-signal quality monitoring methods (3) to (6), a probability density function along an amplitude axis with no input made has been acquired in advance, and the probability density function acquired at a time a signal is input is corrected based on that former probability density function.
(8) In any one of the digital-signal quality monitoring methods (3) to (6), an n number of average values and n number of dispersion values of the discriminated signal are acquired from the probability density function and the quality parameter is computed from the probability density function.
(9) In the digital-signal quality monitoring method (4) or (6), an eye opening is computed from the probability density function along the amplitude axis of the input signal at individual discrimination timing.
The following are feasible communications apparatuses which use the digital-signal quality monitoring method of this invention.
(10) A regular-system/reserved-system switching apparatus comprising switching means for selectively outputting an n-value digital signal (n being a natural number equal to or larger than 2) of a regular system or an n-value digital signal of a reserved system; quality monitoring means for monitoring the n-value digital signal output by the switching means, thereby acquiring a quality parameter; switching control means for controlling a switching action of the switching means based on the quality parameter obtained by the quality monitoring means, whereby the quality monitoring means scans a discrimination level whi
Kabushiki Kaisha Toshiba
Pascal Leslie
Phan Hanh
LandOfFree
Digital-signal quality monitoring method and communications... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital-signal quality monitoring method and communications..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital-signal quality monitoring method and communications... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3186833