A transceiver scheme for localized DFT spread OFDM (DFT-SOFDM) in time-selective channel

The transmission of Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-SOFDM) [4] through a time-selective fading channel with a significant amount of Doppler spread suffers from severe performance degradation. A shift in frequency caused by such channel leads to a loss of orthogonality between users. In this paper, we propose a DFT-SOFDM scheme augmented by MIMO and a new technique to overcome the adverse effects caused by Doppler shift. Repeated Alamouti orthogonal space time block codes are used for transmission of localized MIMO DFT-SOFDM signal. We derive the Minimum Mean-Squared Error (MMSE) combining and estimation scheme that ensures superior BER performance compared to the conventional Maximal-Ratio Receive Combining (MRRC) scheme. The proposed receiver provides a performance gain of 8.6 dB for a 4 users system at BER= 10^-3. This gain improves with increased number of users. MRRC gives an error floor due to multiple access interference, which increases with system load.