The Turbo Principle in Joint Source-Channel Coding

The turbo principle (iterative decoding between component decoders) is a general scheme, which we apply to joint source-channel decoding. As a realistic (e.g. speech parameter coding) example we discuss joint source-channel decoding for auto-correlated continuousamplitude source samples. At the transmitter the source samples are quantized and their indexes are appropriately mapped onto bitvectors. Afterwards the bits are interleaved and channel-encoded; an AWGN channel is assumed for transmission. The auto-correlations of the source samples act as implicit outer channel codes that are serially concatenated with the inner explicit channel code. Thus, by applying the turbo principle, we can perform iterative decoding at the receiver. As an example, we will show that with a proper bit mapping for a 5-bit quantizer iterative source-channel decoding saves up to 2 dB in channel SNR or 8 dB in source SNR for an auto-correlated Gaussian source.