An iterative differential block demodulation algorithm for fading channels

This paper presents an iterative algorithm for differential block demodulation of amplitude-phase-shift keying in channels whose characteristics change within a block. The algorithm has some features in common with both the expectation-maximization algorithm and the K-means clustering algorithm. The algorithm also provides symbol reliability information and block reliability information that can be used for iterative soft-decision decoding, errors-and-erasures decoding, adaptive modulation algorithms, and retransmission algorithms. The reliability information has the additional benefit that it can be determined even if amplitude scaling (due to an AGC device) is unknown. A reduced complexity algorithm has also been investigated. Numerical results are presented for a variety of modulation formats with Reed-Solomon coding and errors-and-erasures decoding in a fading channel. Compared with other techniques, results show that these algorithms, as a function of performance and complexity, perform extremely well.