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

Abstract

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(c)log(2)N(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.