Estimation and Mitigation of Intercarrier Interference for OFDM Systems in Multipath Fading Channels

Orthogonal frequency division multiplexing (OFDM) is a transmission technique which is robust in multipath channels. It is though sensitive to frequency errors that may be caused by several factors such as frequency offset at the local oscillator, phase noise and mobility of the receiver. These errors may destroy orthogonality among subcarriers and introduce intercarrier interference (ICI) that may be represented in the frequency domain by means of an ICI matrix. Estimation of this matrix is crucial to optimize performance. In this work we propose two iterative methods that use pilot tones in the frequency domain and converge very quickly. The first proposed method works in two steps. Initially, correlation between received signal and estimated transmitted one is used to recover the channel matrix, and then it estimates the actual transmitted data by means of MMSE. This method is shown to be very effective in AWGN channel with frequency offset at the local oscillator or in one time variant path channel. The second method represents an extension to more severe channel conditions such as multipath fading. In this case a different frequency domain OFDM channel representation is needed and a suitable scheme is implemented to recover channel and data. Simulation results show that the proposed algorithms look promising to be used in actual implementations.