Banded equalizers for MIMO-OFDM in fast time-varying channels

We propose low-complexity equalizers for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems in frequency-selective time-varying channels, by extending the approach we formerly proposed for single-antenna OFDM systems. Specifically, by neglecting the intercarrier interference (ICI) coming from faraway subcarriers, we design minimum mean-squared error (MMSE) block linear equalizers (BLE) and MMSE block decision-feedback equalizers (BDFE) that employ a band LDL factorization algorithm. The complexity of the proposed banded equalizers is linear in the number of subcarriers, differently from conventional MMSE-BLE and MMSE-BDFE characterized by a cubic complexity. We also consider a receiver window designed to minimize the power of the undesired ICI. Simulation results show that windowing is beneficial in controlling the complexity of the proposed equalizers with acceptable performance loss with respect to the conventional MMSE-BLE and MMSE-BDFE.