Nonsymmetric sources and optimum signal selection

There are some applications where the information source is nonsymmetric. Here, it is shown that differential pulse code modulation (DPCM) of video signals results in a nonsymmetric source. Previous works on 2-D signal design have been focused around equally likely sources. In this paper, an iterative algorithm for minimum error signal design subject to average power (or peak power) constraint is presented. Then, design of minimum cost signal sets is addressed, and application to a DPCM system for picture transmission is developed. Comparisons are made between the nonsymmetric and symmetric signal design in one case and between minimum error signal design and minimum cost signal selection in the other case, for the transmission of DPCM-coded signals. It is seen that nonsymmetric signal design gains significant improvements over the equally likely signal selection when the channel is noisy. Minimum cost signal design also demonstrated some improvement relative to minimum error signal selection over noisy channels.