An unequal error protection trellis coding scheme for still image communication

The source and channel coding functions of a communication system are usually designed independently of one another. This is justified by Shannon´s separation principle (1948), which indicates that no performance loss is suffered if the two functions are thus partitioned. However, Shannon´s theorem is an asymptotic result that permits unlimited delay and complexity; given a constraint on complexity/delay, joint source-channel coding may outperform separately designed pairs. In this work, we consider the problem of reliable communication of compressed still grey-level images over very noisy channels. An unequal error protection (UEP) joint source-channel coding scheme is proposed for transmitting discrete-cosine transform (DCT) encoded images over an additive white Gaussian noise (AWGN) channel used in conjunction with coherent M-ary phase shift keying (MPSK) modulation. More specifically, it consists of a sequence maximum a posteriori (MAP) detection scheme that exploits both the channel soft decision information and the statistical image characteristics