  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.
