A low-complexity ICI mitigation method for high-speed mobile OFDM systems

Orthogonal frequency division multiplexing (OFDM) is a promising technique for frequency-selective fading channels. However, in high-speed mobile environments, the channel may be time-variant in one OFDM symbol. This will incur the intercarrier interference (ICI) degrading seriously the performance of an OFDM system. A simple remedy is to apply the zero-forcing (ZF) equalization method. Unfortunately, the direct ZF method requires an inverse of a huge matrix requiring a prohibitively high complexity. In this paper, we propose a low-complexity ZF method for ICI mitigation. The main idea is to explore the special structure of the ICI matrix and apply the Newton´s iterative matrix inversion method. With our formulation, fast Fourier transforms (FFTs) can be used to reduce the complexity. The proposed method can reduce the complexity from the order of O(N_c ³) to that of O(N_clog₂N_c) where N_c is the number of subcarriers. Computer simulations show that the proposed method can cancel the ICI effectively and at the same time reduces the computational requirement dramatically