Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-01-16
2001-01-30
Le, Vu (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S243000, C341S200000, C382S251000
Reexamination Certificate
active
06181745
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for monitoring a transmission quality of digitized signals that have been subjected to a quantizing operation.
BACKGROUND INFORMATION
Reference signals, for example the test lines in a television image, can be utilized to measure the signal-to-noise ratio of, for example, a digitized television image. This procedure requires, however, a complex and expensive test receiver with corresponding measurement technology. The monitoring of pilot signals requires a similar outlay.
A method for determining the quantization distortion of transmission devices is described in European Patent Application No. 0 030 383, where a certain frequency band is provided at the transmitter end and fed into a transmission device. At the receiver end, a level measurement is performed within a transmitter-end frequency band, along with a measurement outside that frequency band. The quantization noise ratio is determined from a difference between these two measurements.
A method for determining signal power and distortion power is described in European Patent Application No. 0 069 972. Two signals are generated; the first digital signal is transmitted directly to a receiver end; the second signal is initially conveyed to a codec. The distortion power is determined from samples of the received signals. German Patent Application No. 29 45 034 describes an arrangement for measuring a ratio of a signal distortion to a quantization distortion. Two level meters are used to determine the difference between a reference signal and a noise signal containing the quantization distortion.
SUMMARY OF THE INVENTION
According to a method of the present invention, digitized signals can be evaluated, in simple fashion and during transmission, in terms of their transmission quality. No interruption in service is required. It can be easily evaluated as to whether a D/A converter provided in the transmission path is operating properly.
The invention is based on the following realizations: The achievable transmission quality of a digitized signal, e.g. the signal-to-noise ratio, is directly proportional to the resolution of an associated D/A converter located in the transmission path, and the maintenance of its quality parameters. The present invention provides that in the uniform quantization of an analog signal during A/D conversion, given sufficient modulation (generally >6 bits for a sine carrier or for multi-tone signals such as those which occur with television distribution services), the finite number of quantization steps results in an error having a property of Gaussian white Gaussian noise. This white noise is uniformly distributed over the entire Nyquist spectrum, i.e. even in the frequency regions in which no useful signal is being transmitted. By measuring a mean of the quantization interference power in these regions, the quantization step for the associated D/A converter can be determined and compared with an expected value. If there is an impermissibly large difference between the determined quantization step and the expected value, an error signal is transmitted, for example via remote control devices, to a central display.
Thus, a plurality of D/A converters, for example in a television distribution network, can be monitored during operation in terms of their respective transmission quality. At the same time, data can be gathered regarding the long-term stability of the D/A converter.
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“Adaptive Quantizer”, IBM Technical Disclosure Bulletin, vol. 9, Iss. 6, Nov. 1, 1996, pp. 621-623.
Kenyon & Kenyon
Le Vu
Robert & Bosch GmbH
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