Blind Frequency Synchronization for OFDM Systems with I/Q Imbalance

The presence of carrier frequency offset (CFO) and in-phase/quadrature-phase (I/Q) imbalance results in inter-carrier interference and thus greatly degrades the performance of orthogonal frequency division multiplexing (OFDM) systems. In this paper, we propose a new blind frequency synchronization scheme for OFDM systems with frequency-independent I/Q imbalance. A blind and joint estimator of CFO and I/Q imbalance parameter is first proposed by exploiting the multi-antenna redundancy at the receiver. Estimation computational complexity is reduced by expressing the cost function as a superposition of very few harmonically related cosine waves. The compensation for CFO and I/Q imbalance can be further carried out, which generates an equivalent received signal model without CFO and I/Q imbalance distortion. In this way, the conventional channel estimation and data detection can be performed. The Cramer-Rao bound of the CFO estimation is derived as a benchmark. The CFO estimation with frequency-dependent I/Q imbalance is further addressed. We also provide extensive simulations to demonstrate the superiority of the proposed method over existing competitors.