Design and simulation of MIMO-OFDM receiver employing turbo equalization.

Saif Salahuddin Qaddoori
Dr. Ra'ad S. Fyath

Abstract:Orthogonal frequency division multiplexing (OFDM) is a promising technique for high data rate wireless communications because it can combat intersymbol interference (ISI) caused by the dispersive fading channel. This is achieved by inserting a guard interval, whose length is at least equal to the maximum channel delay, which reduces the transmission efficiency. Applying multiple-input multiple-output (MIMO) scheme, by adopting multiple transmitting and receiving antennas, can enhance the transmission efficiency and link reliability. Further, incorporating an equalization stage in the MIMO-OFDM system will reduce the effect of ISI at high data rates. This thesis investigates the performance of a MIMO-OFDM system incorporating turbo equalization-based receiver. The aim of the investigation is to assess the key role played by turbo equalization in enhancing the performance of this advanced system under various operating conditions and to compare the results with those related to an OFDM counterpart. A software package is written in MATLAB version 7.3 (R2006b) environment to simulate both OFDM and MIMO-OFDM systems incorporating turbo equalization. Simulation results are presented to assess the effect of number of iterations, employed in the turbo equalization, on the performance of a 2×2 MIMO system operating over Rayleigh fading channel having different values of Doppler frequency shifts fd. The results indicate clearly that the unequalized MIMO-OFDM system outperforms the OFDM counterpart by 2.4dB signal-to-noise ratio (SNR) gain at bit error rate (BER)=10-4 and fd=30Hz when QPSK signaling and 1024 subcarriers are used. Employing an 8-iteration turbo equalizer will enhance the performance of both OFDM and MIMO-OFDM systems by 5.8dB and 6.4dB, respectively, at the same operating conditions.