A Framework for Iterative Frequency Domain EP-Based Receiver Design

An original expectation propagation-based message passing framework is introduced, wherein transmitted symbols are considered to belong to the multivariate white Gaussian distribution family. This approach allows deriving a novel class of single-tap frequency domain (FD) receivers with a quasi-linear computational complexity in block length, thanks to fast-Fourier transform-based implementation. This framework is exposed in detail, through the design of a novel double-loop single-carrier FD equalizer (FDE), where self-iterations of the equalizer with the demapper and turbo iterations with the decoder provide numerous combinations for the performance and complexity tradeoff. Furthermore, the flexibility of this framework is illustrated with the derivation of an overlap FDE, used for time-varying channel equalization, among others, and with the design of an FD multiple-input multiple-output detector, used for spatial multiplexing. Through these different receiver design problems, this framework is shown to improve the mitigation of inter-symbol, inter-block, and multi-antenna interferences, compared to alternative single-tap FD structures of previous works. Thanks to finite-length and asymptotic analysis, supported by numerical results, the improvement brought by the proposed structures is assessed and then completed by also accounting for computational costs.