Bit-Flipping Equalizer and ML Search-Space Analysis in Ultra-Wideband MIMO Channels

In this paper, we propose a low-complexity equalizer whose performance approaches that of the optimum maximum-likelihood (ML) estimator, in ultra-wideband (UWB) multiple- input multiple-output (MIMO) channels. Although the ML estimation offers the excellent performance, it is generally of high complexity due to the large size of searching space. Through a theoretical search-space analysis, we reveal that local searching algorithms may approximate the ML estimator when a large number of diversity branches is available. Based on the analysis, we develop a novel equalizer with simple bit-flipping for severely frequency-selective fading in UWB-MIMO channels.