Achieving Near MAP Performance with an Excited Markov Chain Monte Carlo MIMO Detector

TL;DR

This paper presents an improved MCMC-based MIMO detector that overcomes high SNR stalling, identifies slow convergence and pseudo-convergence, and achieves near-MAP performance in complex, realistic wireless channels.

Contribution

The paper introduces an excited MCMC (X-MCMC) detector with novel convergence and pseudo-convergence detection methods, enhancing performance without hybridization or heuristic scaling.

Findings

Achieves near-MAP performance in 8x8 MIMO 256 QAM channels.

Effectively detects and mitigates slow convergence and pseudo-convergence.

Removes error floors and improves BER performance in realistic scenarios.

Abstract

We introduce a revised derivation of the bitwise Markov Chain Monte Carlo (MCMC) multiple-input multiple-output (MIMO) detector. The new approach resolves the previously reported high SNR stalling problem of MCMC without the need for hybridization with another detector method or adding heuristic temperature scaling factors. Another common problem with MCMC algorithms is the unknown convergence time making predictable fixed-length implementations problematic. When an insufficient number of iterations is used on a slowly converging example, the output LLRs can be unstable and overconfident. Therefore, we develop a method to identify rare slowly converging runs and mitigate their degrading effects on the soft-output information. This improves forward-error-correcting code performance and removes a symptomatic error floor in BER plots. Next, pseudo-convergence is identified with a novel way to visualize the internal behavior of the Gibbs sampler. An effective and efficient pseudo-convergence detection and escape strategy is suggested. Finally, the new excited MCMC (X-MCMC) detector is shown to have near maximum-a-posteriori (MAP) performance even with challenging, realistic, highly-correlated channels at the maximum MIMO sizes and modulation rates supported by the 802.11ac WiFi specification, 8x8 MIMO 256 QAM.