Space–Time-Coded MIMO ZP-OFDM Systems: Semiblind Channel Estimation and Equalization

The space-time-block-code (STBC) multiple-input-multiple-output (MIMO) zero-padding orthogonal frequency-division multiplexing (ZP-OFDM) has been widely investigated in recent years. It provides a good performance for the multiuser scenario with a small number of pilots. However, it would fail in the face of complex symmetric signals. In this paper, novel channel estimation and equalization for complex input signals are investigated. With the Alamouti-like STBC scheme, the channel impulse responses of the space-time-coded MIMO ZP-OFDM system are shown to be identifiable up to two ambiguity matrices by subspace channel estimation. The frequency domain minimum mean-square error (MMSE) equalizer is then employed to detect the OFDM symbols. Furthermore, we propose a forward-backward averaging technique to enhance the performances of blind channel estimation. The weight analysis for the MMSE equalizer is also conducted to reduce the complexity of system design. Computer simulations demonstrate the effectiveness and correctness of channel estimation and weight analysis for the space-time-coded MIMO ZP-OFDM systems.