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UBC Theses and Dissertations

An adaptive subband-based joint source-channel coder for image transmission Alavi, Amin

Abstract

An adaptive subband image coding system is proposed that uses DPCM and PCM codecs for source encoding the individual subbands, and a family of variable rate channel codes for forward error correction. A low resolution family of trellis coded modulation codes and a high resolution family of punctured convolutional channel codes are implemented and investigated. Implementation of unequal error protection among the subbands, and within the subbands, is examined for the two separate versions of our system. Simulations are performed on the AWGN channel and comparisons are made with corresponding systems that use only a single channel code, or that use the same family of codes for an adaptive equal error protection scheme. Our proposed adaptive systems outperform any of the systems that use only a single channel code greatly, extending the useful SNR range by an amount that depends on the code family. As well, our systems outperform the corresponding adaptive equal error protection systems by as much as 2 dB PSNR. This is primarily due to the use of unequal error protection among the subbands, as surprisingly little additional gain is achieved by applying unequal error protection within the subbands. We use and improve a known modelling technique which enables the system to configure itself optimally for the transmission of an arbitrary image, by only measuring the mean of lowest frequency subband and variance of each of its subbands. Because our systems require an estimate of the channel SNR, we have investigated the sensitivity to poor channel SNR estimation, and have found negligible performance loss for channel mismatches up to 1.5 dB.

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