Abstract
Orthogonal frequency division multiplexing (OFDM) has become one of the promising techniques for future wireless communication systems to achieve high-speed and high-quality digital transmission and reception. However, this technique usually has high sensitivity to frequency offset which is often caused by the Doppler shift and/or the mismatch between oscillators in the transmitter and receiver. Such frequency offset distorts the orthogonality among the subcarriers and then introduces intercarrier interference (ICI) which lowers the overall system performance. To achieve better performance, a two-path parallel cancellation scheme known as conjugate cancellation (CC) was proposed recently. Although this scheme can effectively improve the carrier-to-interference ratio (CIR) performance at low frequency offset situations, it cannot provide satisfactory performance when the frequency offset is high. Furthermore, the CIR performance of the CC scheme is even worse than a regular OFDM system when the frequency offset is higher than 0.25. In this thesis, we propose a modified two-path conjugate transmission scheme along with an enhanced method for intercarrier interference cancellation in OFDM systems. Unlike conventional CC scheme where the second-path’s signal is formed by the conjugate of the first one, the proposed scheme employs the conjugate of the first-path signal multiplied by j as the second path’s signal. Simulation results show that the proposed scheme can achieve better CIR and bit error rate (BER) performance than the CC scheme at high frequency offset situations. Moreover, if coarse frequency offset information is available, the enhanced method can further improve the system performance.