Multiple Frequency Offset Estimation and Mitigation for Cooperative OFDM System

In this paper, we propose a multiple CFOs(Carrier Frequency Offset) estimation and mitigation algorithm for the destination node in a cooperative OFDM(Orthogonal Frequency Division Multiplex) system. In a cooperative OFDM system, every relay node has a separate local oscillator, so that each relay-to-destination link has individual CFO parameter, so that the traditional estimation and mitigation algorithms are no longer applicable. In the proposed algorithm, based on the specially designed training sequences, the destination node can decouple the signal from different relay nodes by correlation and simplify the MD(Multi-Dimensional) nonlinear problem to an ID linear problem. Then, an mitigation matrix can be constructed, and the ICI(Inter-Carrier-Interference) caused by multiple CFOs can be perfectly compensated based on the over sampled OFDM symbol vectors. Theoretical analysis and simulation results prove that the proposed algorithm is effective in estimating the multiple CFOs and mitigating the performance degradation.