Low-Complexity Semiblind Multi-CFO Estimation and ICA-Based Equalization for CoMP OFDM Systems

We propose a low-complexity semiblind structure with multiple-carrier-frequency-offset (CFO) estimation and independent component analysis (ICA)-based equalization for multiuser coordinated multipoint (CoMP) orthogonal frequency-division-multiplexing (OFDM) systems. A short pilot is carefully designed for each user and has a twofold advantage. On the one hand, using the pilot structure, a complex multidimensional search for multiple CFOs is divided into a number of low-complexity monodimensional searches. On the other hand, the cross correlations between the transmitted and the received pilots are explored to allow simultaneous elimination of permutation ambiguity and quadrant ambiguity in the ICA equalized signals. Simulation results show that with a low training overhead of 1.6%, the proposed semiblind system not only outperforms the existing multi-CFO estimation schemes in terms of bit error rate (BER) and mean square error (MSE) of multi-CFO estimation but achieves a BER performance close to the ideal case with perfect channel state information (CSI) and no CFO at the receiver as well.