Approximate ML Detection Based on MMSE for MIMO Systems

We derive two types of approximate maximum likelihood (ML) detection based on minimum mean squared error (MMSE), MMSE-CML (conditional ML) detection and MMSECLML (conditional local ML) detection, for MIMO communication system. A simple reliability judge rule to judge the estimate of the transmit symbols is also given. For the proposed MMSECML detection, received signals are first sent into MMSE detector to do linear equalization, then the estimate of transmit signals is judged in reliability judge module; If the estimate is judged to be reliable, we take the estimate as the final result; if not, the received signals are then sent into conditional ML (CML) detector to get the final result; Unlike conventional ML detector, the CML detector performs a tree search till the estimate satisfies the reliability judge rule or an entire tree search has been done. For the proposed MMSE-CLML detection, we use CLML search instead of CML search in MMSE-CML, which searches in the neighborhood of the output provided by the MMSE detector. Simulation results show that the MMSE-CML detector achieves near the same performance as optimal CML detector at reduced complexity, and MMSE-CLML detector achieves suboptimal performance at remarkably reduced complexity. DOI: 10.2529/PIERS070205100143