Robust carrier frequency offset and channel estimation for orthogonal frequency division multiple access downlink systems in the presence of severe adjacent-cell interference

This study investigates joint estimation carrier frequency offset (CFO) and channel impulse response (CIR) in the problematic orthogonal frequency division multiple access (OFDMA) downlink scenario at the cell boundary, where a maximum supposition of three adjacent base stations preambles can be received. A novel scheme is proposed for estimating the CFOs and CIRs of different cells. First, the highly efficient joint maximum-likelihood (JML) algorithm is used to enable robust CFO estimation by exploiting the idempotent property of the projection matrix. Next, in order to estimate the precise CIR, the composite CFO-based and circularly shifted preamble signatures are proposed by applying the constrained minimum variance (CMV) algorithm to suppress adjacent-cell interference. Finally, the CFO and CIR estimations are enhanced by an iterative cancellation scheme. To the best of the authors research, there is no publication study proposed joint JML-CFO and CMV-CIR estimators for OFDMA downlink systems with adjacent-cell interference. Simulation results show that the proposed algorithms provide better performance than the conventional estimators and approach the theoretical Cramer-Rao lower bound at the cell boundary over frequency-selective fading channels.