A fast algorithm for maximum likelihood detection of QPSK or pi /4-QPSK sequences with unknown phase

Maximum likelihood sequence detection (MLSD) of differentially encoded MPSK uses a joint decision on N symbols to achieve a performance gain over conventional 2 symbol differential detection. This paper gives a fast (optimum) algorithm to implement MLSD; the number of operations per N symbol block is of order N log/sub 2/ N. Thus, it is practical to implement MLSD for any reasonable N for moderate symbol rates; this is useful for the land mobile satellite and digital cellular channels.<
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