Iterative Decision Feedback Equalization and Decoding for Rotated Multidimensional Constellations in Block Fading Channels

It is known that rotated multidimensional constellations can be used effectively to achieve full-rate and full-diversity transmission in block fading channels. However, the optimal decoding complexity is exponential with the number of fading blocks (or degrees of freedom). In this paper, the authors propose a reduced-complexity iterative receiver structure operating on a block basis for coded modulation schemes with rotated constellations. The proposed detector is based on iterative forward and backward filtering followed by a channel decoder that uses a priori Log-Likelihood Ratios (LLR) of coded symbols. Forward and feedback filters are jointly optimized according to the Minimum Mean Square Error (MMSE) criterion to minimize the spatial interference induced by rotation.