Abstract
In orthogonal frequency division multiplexing (OFDM) systems, the property of spectrum overlapping in an orthogonal way makes the system very sensitive to the frequency offset, which is usually introduced by the mismatch of oscillators in the transmitter and receiver or the Doppler effect. It is well known that the intercarrier interference (ICI) caused by the frequency offset may significantly degrade the system performance. Conventional ICI self-cancellation schemes can mitigate the ICI effect dramatically without doing frequency offset compensation, but the expense of halving spectral efficiency makes them less valuable. On the other hand, ICI can be suppressed by performing correlative coding in the frequency domain without halving spectral efficiency; however, this scheme usually cannot provide satisfactory performance in terms of the carrier-to-interference ratio (CIR) and the detection errors generated in the receiver would be propagated through OFDM symbols. In this thesis, we propose a new ICI suppression scheme that can be regarded as an improved version of the approach based on correlative coding; the main difference is that, for the proposed scheme, the data of the last subcarrier in an OFDM symbol is encoded with that of the first subcarrier in the same OFDM symbol, instead of the data of the first subcarrier in the subsequent OFDM symbol used for the original approach. Due to the cyclic nature, the modified correlative encoding procedure in the frequency domain can be easily realized by a specific time-domain windowing process. As compared to the original correlative coding scheme, the modified approach achieves better performance for ICI suppression and prevents error propagation through OFDM symbols, with a slight increase in the computational complexity at the transmitter but no increase at the receiver. To verify the effectiveness of the proposed scheme, we not only derive the theoretical CIR, but also present a number of computer simulation results, where both of them match pretty well.