A Master of Science thesis in Electrical Engineering by Nour Ali Kousa entitled, "A Double Dwell Frequency Synchronization Scheme For OFDM Systems," submitted in January 2015. Thesis advisor is Dr. Mohamed El-Tarhuni. Available are both soft and hard copies of the thesis.
Orthogonal Frequency Division Multiplexing (OFDM) is being used in many recent communication systems to cope with the demand for high data rate applications. It provides a significant improvement in the bandwidth efficiency with simple equalization at the receiver. ODFM systems provide high immunity against multipath fading and inter symbol interference (ISI) since the high data rate stream is divided among narrow overlapping but orthogonal subcarriers. However, OFDM requires accurate timing and frequency synchronization to preserve the orthogonality between subcarriers and maintain acceptable performance. Achieving accurate synchronization is a challenging task in multicarrier systems such as OFDM. It is noticed that frequency synchronization is more critical in OFDM than timing synchronization since a small frequency offset can destroy the orthogonality among the subcarriers causing inter-carrier interference (ICI), which results in serious performance degradation. In this thesis, the effect of frequency offset on OFDM system performance is investigated and a new synchronization scheme based on the Double Dwell System (DDS) is proposed. In DDS, the frequency offset estimation is carried over two stages: a coarse estimate is obtained over the first stage followed by a fine estimate in the second stage. The system performance is evaluated in terms of the mean square error (MSE) and symbol error rate (SER) and is compared to the conventional Single Dwell System (SDS). Simulation results show a significant performance improvement in the proposed method over SDS. Other results are presented in this thesis such as interference impact, pilot symbol design, optimization of search window and step size, and mitigation of fading effects.