Design of ring convolutional trellis codes for MAP decoding of MPEG-4 imagery

Previously, we proposed a trellis coded modulation system using CPFSK and ring convolutional codes for transmitting the bits generated by an embedded zerotree wavelet encoder. Improved performance is achieved by using maximum a posteriori (MAP) decoding of the zerotree symbols. In this paper, the optimal ring convolutional trellis codes are determined for MAP decoding. The CPFSK transmitter is decomposed into a memoryless modulator and a continuous phase encoder over the ring of integers modulo 4; the latter is combined with a polynomial convolutional encoder over the same ring. In the code design process, a search is made of the combined trellis, where the branch metrics are modified to include the source transition matrix. Simulation results of image transmission are provided using the optimized system.