Frequency Offset Estimation in I/Q Mismatched OFDM Receivers

The direct-conversion architecture is a promising solution for the design of low-cost mobile terminals. However, it introduces extra RF impairments that greatly complicate fundamental receiver functions, including the synchronization task. This work deals with pilot-aided carrier frequency offset (CFO) recovery in an OFDM direct-conversion receiver plagued by frequency-selective I/Q imbalance. Since the exact maximum likelihood (ML) solution of this problem requires a complete search over the frequency uncertainty range, we propose a simpler scheme that dispenses from any peak-search procedure. Numerical simulations and theoretical analysis indicate that the proposed scheme attains the relevant Cramer-Rao bound at all signal-to-noise ratios of practical interest.