Inter-Carrier Interference Mitigation in OFDM-based Cooperative Communication in Doubly Selective Channels

This paper investigates orthogonal frequency division multiplexing (OFDM) based cooperative communication system for frequency flat and selective channel conditions. Carrier frequency offset (CFO) that creates inter-carrier interference (ICI) is one known problem in OFDM-based systems. The CFO problem becomes worse when OFDM is integrated into the cooperative systems as identical OFDM signal suffers from several offsets at different uncorrelated channels. To minimize the multiple CFO effects, a two step technique is proposed in this work. Firstly, a time-domain windowing is used at the transmitter to reduce the effect of frequency offset due to Doppler shift. Secondly, Maximum Likelihood (ML)-based CFO estimation is used in each of the receiving nodes to reduces the effect of synchronization errors. The performance of the time-domain windowing and the ML-based CFO estimation is investigated, separately and jointly. Then, comparison of these systems with inter-carrier interference (ICI) self-cancellation and data conjugate techniques is performed. The combined technique has a signal to noise ratio (SNR) advantage of 7dB for a sample standard bit error rate (BER) value of 10(-3).