Carrier Frequency Offset and I/Q Imbalances Compensation in OFDM Systems

Carrier frequency offset (CFO) and I/Q imbalances severely degrade the performance of direct-conversion OFDM receiver. In this paper, based on the subcarrier allocation (SCA) of OFDM signal, a novel approach for compensating CFO and I/Q imbalances is proposed. First, we derive a useful matrix representation of OFDM signal with CFO and I/Q imbalances. Then, maximum likelihood CFO estimation, as well as the associated SCA, are given. With the CFO estimate, a SCA-based algorithm which has a close-form solution, is proposed for the compensation of I/Q imbalances. Furthermore, due to the correspondence between the CFO estimate and the compensation of I/Q imbalances, the proposed approach can be extended to a blind compensation scheme, suitable for OFDM signals with asymmetric SCA. Finally, computer simulations demonstrate the validity of the proposed approach.