I/Q imbalance and CFO in OFDM/OQAM systems: Interference analysis and compensation

Offset-QAM (OQAM) based OFDM has been considered as a promising technique for future wireless networks due to its higher resilience to narrow-band interference and doubly dispersive channels. In this paper, we investigate the effects of the RX imperfections, namely the I/Q imbalance (IQI) and the carrier frequency offset (CFO), on OFDM/OQAM downlink performance coupled with the imperfect knowledge of the frequency-selective channel. The influence of each impairment is characterized by the interference analysis of the demodulated signal that reveals interesting insight into the distortion origination. Then, we analytically investigate the performance loss as a function of IQI, CFO and channel distortions in a realistic receiver with channel estimation error. To cope with impaired reception, a joint maximum-likelihood estimation method with repetitive training signals is employed. Simulation results demonstrate the relative sensitivity of OFDM/OQAM receivers to the impairments and that the performance loss due to the imperfections can be recovered by the compensation technique.