Fixed-Complexity Soft MIMO Detection via Partial Marginalization

This paper presents a new approach to soft demodulationfor MIMO channels. The proposed method is an approximationto the exact a posteriori probability-per-bit computer. Themain idea is to marginalize the posterior density for the receiveddata exactly over the subset of the transmitted bits that are receivedwith the lower signal-to-noise-ratio (SNR), and marginalize thisdensity approximately over the remaining bits. Unlike the exact demodulator,whose complexity is huge due to the need for enumeratingall possible combinations of transmitted constellation points,the proposed method has very low complexity. The algorithm hasa fully parallel structure, suitable for implementation in parallelhardware. Additionally, its complexity is fixed, which makes it suitablefor pipelined implementation. We also show how the methodcan be extended to the situation when the receiver has only partialchannel state information, and how it can be modified to takesoft-input into account. Numerical examples illustrate its performanceon slowly fading 4x4 and 6x6 complex MIMO channels.©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Erik G. Larsson and Joakim Jaldén, Fixed-Complexity Soft MIMO Detection via Partial Marginalization, 2008, IEEE Transactions on Signal Processing, (56), 8(1), 3397-3407.http://dx.doi.org/10.1109/TSP.2008.92526