UBC Theses and Dissertations
Effect of channel transmission errors on DPCM systems Palffy-Muhoray, Peter
Differential pulse code modulation (DPCM) is a practical encoding scheme f o r speech, television and telemetry signals. In this thesis, the mean square error [omitted] is minimized in situations where the noise contribution which results from channel transmission errors is significant. Expressions for the quantizer and channel noise were developed for both uniform and non-uniform quantization. These expressions were then used to obtain the mean square error as a function of the system parameters for binary symmetric channels, natural coding and previous sample feedback. Sampling was at the Nyquist rate, and the non-uniform quantization was logarithmic. Mean square error [omitted] was minimized, and the optimum system parameters were obtained using a computer search. Gaussian, television and speech were considered as message signals. DPCM was found, for a given channel capacity, to have a lower mean square error than PCM in all cases. Logarithmic quantization was found to yield better performance than uniform quantization for speech signals for the PCM case, and for speech and television signals for the DPCM case. In general, the ratio of the mean square errors of DPCM to PCM increases while the difference in performance decreases as channel noise increases.