ICI mitigation in MIMO-OFDM by iterative equalization using OPT in time varying channels

Time variation of channel in orthogonal frequency division multiplexing (OFDM) system destroys the orthogonality between subcarriers, and introduces inter carrier interference (ICI). Different methods have been used to combat ICI, but the computational complexity of some methods is high. In multiple-input multiple-output (MIMO) system the complexity is even higher. This paper proposes a low complexity iterative method called operator perturbation technique (OPT) is used for MIMO-OFDM system to reduce ICI under the assumption of linear time-varying channels. It requires channel estimation based on linear time-varying channel model. Time-domain synchronous-OFDM suits for this proposed iterative technique because its receiver can easily estimate linear time-varying channels. Simulation with QPSK modulation demonstrates the performance of the proposed method. Here we compare LTI and LTV performance for QPSK modulation. Result shows that the iterative method has nearly similar performance for both LTV and LTI channel irrespective of their channel condition. Also better BER and MSE performance for both LTV and LTI algorithm is achieved when the Doppler frequency is 10Hz.