Metric transformation for a turbo-coded DPSK waveform

The classical turbo-decoding algorithm is based on the assumption that the input sequence to the decoder has been disturbed by a noise process that has a Gaussian distribution. For a differentially coherent phase shift keying (DPSK) waveform, the output statistics of a differentially coherent demodulator is nonGaussian. When this sequence is fed directly into the turbo decoder, particularly under a fading environment, the mismatch between decoder algorithm assumptions and actual input statistics can result in significant decoder performance degradation. This paper investigates the bit error performance for such a mismatch for the DPSK waveform. Techniques for forming enhanced turbo-decoding metrics with biased channel side information (CSI) are proposed. Using these new metrics, error performance in fading conditions is shown to improve significantly. Copyright © 2003 John Wiley & Sons, Ltd.

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