Robust image communication using subband coding and multilevel modulation
John M. Lervik, Tor Audun Ramstad · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
Visual communication systems can exploit the advantages of analog transmission and digital compression: Analog transmission allows the quality of the recovered data to vary gracefully as the channel conditions vary, whereas digital compression allows for powerful data reduction. In this paper, a system optimized for bandwidth- and power-limited channels which combines analog and digital communication principles is proposed. The system achieves a high bandwidth compression efficiency by combining subband signal decomposition and dynamic bandwidth allocation with 81-PAM transmission. Furthermore, graceful degradation is obtained by finding mappings from the subband samples to the channel space which minimize the impact of channel errors in the reconstructed signal. The optimized mapping system outperforms a conventional system using random mappings. In addition, it is shown that the proposed system performs better, in a rate-distortion sense for a given channel signal- to-noise ratio, than a similar subband system using conventional bit allocation, optimized mappings, and 64-PAM. A novel definition for measuring system efficiency, based on comparisons to pure analog PAM transmission, is used to evaluate the proposed system. The ideas presented in this paper can be used for future terrestrial TV broadcasting and mobile communication systems.