G.-C. Zhu, F. Alajaji, J. Bajcsy, and P. Mitran (Canada)
Non-systematic Turbo codes, non-uniform memoryless sources, joint source-channel coding, Rayleigh fading channels, Shannon limit.
In this work, we investigate the joint source-channel coding problem of transmitting non-uniform memoryless sources over wireless Rayleigh fading channels via Turbo codes. The source redundancy in the form of non-uniformity is exploited in the Turbo decoder by incorporating the source statistics in the modified extrinsic information. In con trast to previous work, non-systematic recursive convolu tional encoders are proposed as the constituent encoders, as they produce almost uniform outputs irrespective of the degree of non-uniformity in the source. As a result, unlike the outputs of systematic encoders, they are suit ably matched to the channel input since a uniformly dis tributed input maximizes the channel mutual information and hence achieves capacity. Simulation results show sub stantial gains achieved over previously designed systematic Turbo codes, and the gaps to the optimal Shannon limit are therefore significantly reduced. In comparison with a tan dem scheme, our system offers robust and superior perfor mance at low BER levels (below £¥¤§¦©¨ ), while the complex ity is lower.
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