Alamouti Space-Time Coded OFDM Systems in Time- and Frequency-Selective Channels

We propose low-complexity equalizers for Alamouti space-time coded orthogonal frequency-division multiplexing (OFDM) systems in timeand frequency-selective channels, by extending the approach formerly proposed for single-antenna OFDM systems. The complexity of the proposed algorithm is linear in the number of subcarriers by exploiting the band structure of the frequency-domain channel matrix and a band LDL factorization. We design minimum mean squared error (MMSE) block linear equalizers (BLE) and block decisionfeedback equalizers (BDFE) with and without windowing. We also develop a low-complexity algorithm that adaptively selects the useful bandwidth of the channel matrix. Simulation results show that the proposed algorithm produces a correct estimate of the bandwidth parameter.