Timing and Frequency Synchronization and Doubly Selective Channel Estimation for OFDMA Uplink

In this brief, a novel algorithm is proposed for timing and frequency synchronization and doubly selective channel (DSC) estimation in the uplink of orthogonal frequency division multiple access systems. By using a basis expansion model (BEM) to represent a DSC, a maximum likelihood approach is proposed to jointly estimate the timing and carrier frequency offsets of different users as well as the BEM coefficients of the time-varying channels. A space-alternating generalized expectation-maximization algorithm is then employed to transform the maximization problem for all users into several simpler maximization problems for a single user. Implementation issues are investigated and, the computational complexity and mean square error of the proposed scheme are evaluated. Performance assessment of the new scheme shows a significant improvement as compared with previous methods.