Optimized source coding and coded modulation for digital transmission of still images on a noisy channel

In this paper, we propose a complete transmission system for still images which minimizes the distortion introduced by residual transmission errors. This system comprises a source encoder combining DCT (discrete cosine transform) and VQ (vector quantization). The compression rate is equal to 16.7 for an average PSNR (peak signal to noise ratio) of 29.2 dB. The data are then encoded by a BCH (63,57,3) block code and mapped on a 64-QAM constellation. The parameters of the code book and channel encoder have been optimized for 64-QAM. For channel decoding, we use maximum likelihood sequence decoding. The PSNR of the reconstructed image in the receiver is equal to 28.6 dB for a channel SNR of 11 dB. This represents a very small degradation of the PSNR (0.6 dB) in presence of a SER (symbol error rate) of 10% at the input of the receiver