Pulse or digital communications – Testing
Patent
1994-02-14
1996-05-14
Chin, Stephen
Pulse or digital communications
Testing
375209, 375340, 371 51, 370 17, 364554, H04B 346
Patent
active
055175228
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In modern transmission systems, such as the ISDN (Integrated Services Digital Network) system or the wide-band ISDN (B-ISDN), to transmit data streams, the transmission properties of established transmission path must be checked for the occurrence of bit errors. Bit errors caused by external interference effects acting on the transmission path corrupt the digital data stream originally sent out and, thus, interfere with information transmission.
The object of the present invention is to provide a process for determining the nature of an interference that causes bit errors with regard to its stochastic or deterministic character. When the bit-error type is known, the origin and/or the cause of the bit errors can be searched for efficiently.
SUMMARY OF THE INVENTION
This objective is solved by the present invention which sets forth a process for determining the nature of a data-corrupting interference that causes bit errors in a data stream which is sent from a data source and which is fed via at least one transmission path to a data receiver. In this process, test data are sent out from the data source, and a bit-error function is derived from the bit errors that are recognized in the received test data. To check the periodicity of the bit-error function, the received data stream is subjected, section by section, to an autocorrelation. The length of the autocorrelated section, at any one time, is rated to contain a plurality, preferably at least 100 bit errors, that have occurred. Whether a stochastic or deterministic interference exists is determined from the configuration and number of the maxima of the thus derived autocorrelation function. In particular, if the autocorrelation function exhibits a significant maximum without further pronounced maxima, a stochastic interference is inferred while if the autocorrelation function exhibits several maxima distributed equidistant, a deterministic interference is inferred.
By comparing the received test data and the test data that, in some instances, has been corrupted by bit errors to the original test data, a bit-error function is derived that is autocorrelated section by section. The length of the evaluated section is rated to contain a plurality of bit errors when bit errors occur, so that the autocorrelation function gives a clear indication of periodically or stochastically occurring bit errors. Thus, the method of the present invention is based on the realization that when a long enough section of the bit-error function is considered, a reliable statement can be made about the stochastic or deterministic character of the bit errors and, thus, of the interference.
Stochastic bit errors indicate noise effects, for example. Therefore, when stochastic bit errors occur, transmitters contained in the transmission path, receivers, amplifiers, etc. will be suspected as causing interference and can be checked accordingly. A deterministic character of the bit errors indicates, for example, periodic influences (such as system hum). An important advantage of the process according to the present invention is that very distinct and, thus, clear measuring results are obtained with relatively little expenditure. Further, these measuring results can be evaluated quite easily.
A process in which the transmission properties are monitored by means of correlation functions in the broad-band network B-ISDN in the case of the ATM (asynchronous transfer mode) is described in the periodical "Telcom Report" 14 (1991) issue 2, pp 104-107. However, in this process, test data coded on the transmission side with the aid of 2.sup.5 -m-sequences are transformed on the receiving side in that the cross-correlation function is applied in the decoder, while information about the applied coding method is used. Conclusions about the number of bit errors can be drawn from the level of the main maximum of the particular cross-correlation function. However, details of the character (stochastic or deterministic) of the interference causing the bit errors cannot be
REFERENCES:
patent: 5048015 (1991-09-01), Zilberfarb
patent: 5144642 (1992-09-01), Weinberg et al.
patent: 5260972 (1993-11-01), Wang
NTZ, vol. 44, No. 8, Aug. 1991, Berlin, DE; pp. 548-557; Wolf et al.: "Bitfehler-strukturanalyse in der Breitband-ISDN-Messtechnik".
Telcom Report, vol. 14, No. 2, Mar. 1991, Munchen, DE; pp. 104-107: Wolf; "Messprazision Auf Breitem Band".
Electronics Letters, vol. 26, No. 6 Mar. 1990, Stevenage, GB; pp. 363-363; Butler et al: "Correlation of Interference and Bit Error Activity in a Digital Transmission System".
U.S. Ser. No. 07/941,090 based on International Application PCT/DE91/00323.
Arweiler Hans-Werner
Wolf Andreas
Chin Stephen
Le Amanda T.
Siemens Aktiengesellschaft
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