Abstract: Orthogonal frequency division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies and developed as a popular scheme for 4G mobile communications. Inter-carrier interference (ICI) is a big challenge for OFDM systems while trying to utilize the full spectrum with zero cyclic prefix. It has been investigated that the ICI in OFDM is almost like the co-channel interference in CDMA and the techniques used there to reduce the interference can be used in OFDM also .The techniques are frequency domain equalizers like Operator perturbation Techniques (OPT) and Serial interference cancellation (SIC) and Parallel interference cancellation technique (PIC) along with Gauss Seidel iterative reduction technique. The aim of this paper is to study the OFDM systems suffering from ICI, due to large Doppler shift associated with high velocity of receiver. The main impact of ICI in an OFDM system is to destroy the orthogonality between subcarrier leads to the introduction of off-diagonal element in the channel matrix, making the traditionally considered diagonal channel matrix inaccurate and increasing the complexity of channel estimation and equalization .In this paper iterative cancellation methods have been studied and compared as they require the inversion of only a small portion of original full matrix and thus the complexity is reduced

Keywords: OFDM, ICI, Gauss-Seidel, OPT, PIC and SIC