Soft MIMO Detection at Fixed Complexity

This paper presents a new approach to soft demodulation for MIMO channels. The proposed method is an approximation to the exact a posteriori probability-per-bit computer. The main idea is to marginalize the posterior density for the received data exactly over the subset of the transmitted bits that are received with the lowest signal-to-noise-ratio, and then marginalize this density approximately over the remaining bits. Unlike the exact demodulator, whose complexity is huge due to the need for enumerating all possible combinations of transmitted constellation points, the proposed method has very low complexity. Additionally, its complexity is fixed, which makes it suitable for pipelined implementation. Numerical examples illustrate its performance on slow fading 4times4 and 6times6 complex MIMO channels.