Adaptive unequal error protection for subband image coding

An adaptive subband image coding system is proposed to investigate the perf ormance offered by implementing unequal error protection among the subbands and within the subbands, The proposed system uses DPCM and PCM codecs for source encoding the individual subbands, and a family of variable rate chan nel codes for forward error correction. A low resolution family of trellis coded modulation codes and a high resolution family of punctured convolutio nal codes are considered. Under the constraints of a fixed information rate , and a fixed transmission bandwidth, for any given image, the proposed sys tem adaptively selects the best combination of channel source coding rates according to the current channel condition. Simulations are performed on th e AWGN channel, and comparisons are made with corresponding systems where t he source coder is optimized for a noiseless transmission (classical optimi zation) and a single channel code is selected. Our proposed joint source-ch annel systems greatly outperform any of the nonadaptive conventional nonjoi nt systems that use only a single channel code at ail channel SNR's, extend ing the useful channel SNR range by an amount that depends on the code fami ly. A nonjoint adaptive equal error protection system is considered which u ses the classically optimized source codec, but chooses the best single cha nnel code for the whole transmission according to the channel SNR, Our syst ems outperform the corresponding adaptive equal error protection system by at most 2 dB in PSNR; and more importantly, show a greater robustness to ch annel mismatch. It is found that most of the performance gain of the propos ed systems is obtained from implementation of unequal error protection amon g the subbands, with at most 0.7 dB in PSNR additional gain achieved by als o applying unequal error protection within the subbands, We use and improve a known modeling technique which enables the system to configure itself op timally for the transmission of an arbitrary image, by only measuring the m ean of lowest frequency subband and variances of all the subbands.