Research On Synchronization Theory Of OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) technology is considered to be the core technology of the future4G networks. In an OFDM system, the performance is sensitive to the carrier frequency offset (CFO). The CFO will destroy the orthogonality of the subcarriers and cause intercarrier interference (ICI), which not only reduces the carrier to interference power ratio (CIR) but also leads to a phase rotation of the desired signal. Therefore, synchronization is critical for OFDM systems. In existing ICI cancellation schemes, the discussion is mainly about CIR improvement, leaving the equally important phase rotation error (PRE) not considered. In this paper, ICI mechanism and polynomial cancellation coding (PCC) scheme is studied. We proposed a simple ICI cancellation scheme which can improve both CIR and PRE. Simulations show the proposed algorithm considerably outperforms the PCC scheme in the presence of large CFO. Simulation results show that, when the carrier frequency offset(CFO) is greater than0.25, the OFDM system’s CIR using the proposed algorithm is greater than the conventional one by at least15dB; and the phase shift could be improved at least by π/8. When the carrier frequency offset equals to0.2and SNR is bigger than15dB, the system BER keeps lower than10-4.