Source-channel optimized trellis codes for bi-tonal image transmission over AWGN channels

We consider the design of trellis codes for transmission of binary images over additive white Gaussian noise (AWGN) channels. We first model the image as a binary asymmetric Markov source (BAMS) and then design source-channel optimized (SCO) trellis codes for the BAMS and AWGN channel. The SCO codes are shown to be superior to Ungerboeck´s (1982) codes by approximately 1.1 dB (64-state code, 10^-5 bit error probability). Furthermore, we compare the proposed SCO system to a more traditional tandem system consisting of a Huffman code, a convolutional code, an interleaver and an Ungerboeck trellis code. Using a facsimile image, we compare the image quality of an SCO code, an Ungerboeck code, and the tandem code. The SCO code yields the best reconstructed image quality at 4-5 dB channel SNR