This paper compares the performance of a MIMO system applying a Mismatched Maximum Likelihood Detector (MMLD) with that applying a Generalized Likelihood Ratio Detector (GLRD) in the presence of channel estimation errors. Two sources of error are considered: errors due to noise and errors due to time variations induced by Doppler effects. The MMLD relies on the available channel estimate whereas the GLRD combines the channel estimate with a block of received data and uses a joint channel-symbol estimation approach to solve for the transmitted symbols. The GLRD is shown to outperform the MMLD whenever errors in channel estimation are incurred and the performance gap depends on the amount of error. Furthermore, the GLRD provides a unified receiver structure which can also be applied to differentially encoded MIMO systems and to situation where no channel estimate is available as in blind MIMO. The improved performance of the GLRD comes with increased computational complexity. This problem is addressed through search efficient algorithms based on the branch-estimate-bound optimization framework. We analyze the performance of the GLRD and provide a tight upper bound on the BER of the system at high SNR. Simulation results are shown for a 2 × 2 MIMO system. Index Terms-Multiple-input multiple-output, channel estimation error, correlated block fading, mismatched maximum likelihood detector, generalized likelihood ratio detector, orderedbranch-estimate-bound algorithm.
Differential Multiple Input Multiple Output (MIMO) enables communication without the need for channel estimation and the associated overhead due to the transmission of pilots. A number of differential MIMO techniques were proposed using unitary or orthogonal space-time codes. These codes provide full diversity but achieve a data rate of no more than one symbol per channel use. This paper presents a block differential MIMO technique which can use any non-orthogonal full-rate full-diversity space-time code. This approach has a decoding complexity comparable to that of coherent MIMO.
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