Iterative MAP detection of coded M-DPSK signals in fading channels with application to IS-136 TDMA

Maximum a posteriori (MAP) detection of M-DPSK modulated signals is proposed for both time-nondispersive and time-dispersive fading channels. When the communication system comprises an inner convolutional encoder with a bit-interleaver, it is shown that an iterative receiver obtained from the concatenation of a MAP M-DPSK detector and a MAP convolutional decoder is capable of improving the performance in both channel environments. Such a receiver is based on the turbo decoding concept of refining the reliability information provided at the output of each soft-in/soft-out receiver stage, by running multiple detection/decoding iterations in a receiver with feedback from the outer stage to the inner stage. Furthermore, the general case of multiple receiving antennas is considered. Combining the received signals is addressed in both an environment characterized by thermal noise (i.e. AWGN) uncorrelated through the antenna elements, and an environment characterized by spatially correlated noise such that arising in the presence of cochannel interference in a TDMA system (e.g. IS-136).