Maximum Likelihood Estimation and Correction of Carrier Frequency Offset in OFCDM Systems

In this paper, a Carrier Frequency Offset (CFO) correction scheme is proposed for a downlink Variable Spreading Factor (VSF) OFCDM system based on the maximum likelihood principle. The authors first derive the likelihood function for VSFOFCDM system with CFO, and then propose to use a gradient algorithm to estimate and minimize the effect of CFO in a tracking mode. The maximal ratio combining receiver is considered for detection. Their results show that the BER performance in the low SNR environment can be improved significantly with few number of iterations.