Efficient Equalization of Time-Varying Channels in MIMO OFDM Systems

The orthogonality of the cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) modulation is ensured as long as the channel can be assumed constant across the duration of one CP-OFDM symbol period. Unfortunately, this assumption may not hold anymore for a large variety of emerging scenarios with mobility, high carrier frequency and multiple carrier frequency offsets. To tackle this issue, we propose a novel equalization structure. In contrast to existing works in the literature, the equalizer is obtained by considering a Taylor approximation of the ideal time-varying channel equalizer function. This results in an extremely simple implementation only consisting of per-subcarrier multiplications and FFT/IFFT operations. The general form of the equalizer is particularized to two specific cases: zero forcing and linear minimum mean squared error. Furthermore, the implementation complexity of the equalizers is computed and an analytical formula is proposed to efficiently evaluate their performance. Finally, numerical results demonstrate the efficiency of the proposed receivers as compared to the ideal one and previous works.