Low Complexity Space-Frequency MIMO OFDM System for Double-Selective   Fading Channels
  This paper presents a highly robust space-frequency block coded (SFBC) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. The proposed system is based on applying a short block length Walsh Hadamard transform (WHT) after the SFBC encoder. The main advantage of the proposed system is that the channel frequency responses over every two adjacent subcarriers become equal. Such interesting result provides an exceptional operating conditions for SFBC-OFDM systems transmitting over time and frequencyselective fading channels. Monte Carlo simulation is used to evaluate the bit error rate (BER) performance of the proposed system using various wireless channels with different degrees of frequency selectivity and Doppler spreads. The simulation results demonstrated that the proposed scheme substantially outperforms the standard SFBC-OFDM and the space-time block coded (STBC) OFDM systems in severe time-varying frequency-selective fading channels. Moreover, the proposed system has very low complexity because it is based on short block length WHT. 
F. Kalbat and A. Al-Dweik
cs.IT math.IT