A robust frequency synchronization method for non-contiguous OFDM-based cognitive radio systems

For non-contiguous OFDM (NC-OFDM) based cognitive radio systems, one of the significant challenges for a secondary receiver is to establish frequency synchronization without spectrum synchronization information (SSI). In this paper, we propose a robust carrier frequency offset (CFO) estimation method for NC-OFDM receiver when the interference from primary users is considered. The key idea of the proposed method is first to make a decision on which subchannels are active by employing two consecutive and identical training symbols, and then to estimate the CFO effectively by using a maximum likelihood algorithm based on the information on selected active subchannels. Simulation results show that the proposed method can provide a satisfactory estimation accuracy, which is close to the corresponding Cramér-Rao lower bound (CRB) with the ideal SSI over an additive white Gaussian noise (AWGN) channel.