Abstract
There are two major synchronization problems of an orthogonal frequency division multiplexing (OFDM) system. One is known as frame synchronization, and the other is the estimation of the carrier frequency offset. Before an OFDM receiver can successfully demodulate the received signal, the boundary of the frame should be found and the frequency offset should be estimated and compensated. Although the frame synchronization requirement of an OFDM system is eased by the usage of the cyclic prefix, the estimation error of the carrier frequency offset should be kept as small as possible since any amount of the carrier frequency offset will destroy the orthogonality between the subcarriers and introduce intercarrier interference. In this thesis, we propose a complete synchronization scheme, including detection of the physical layer convergence procedure (PLCP) preamble, frame synchronization, and frequency acquisition, based on the PLCP preamble field that is especially designed for synchronization in the IEEE 802.11a wireless local area network. In the proposed scheme, detection of the PLCP preamble is done by continuously monitoring the timing metrics with a correlation length that is equal to the length of each short symbol in the beginning of the PLCP preamble. Simulation results show that the probabilities of miss detection and false detection of the PLCP preamble are both under . Frame synchronization is achieved by searching the rapid degradation region of the timing metrics, which is caused by the transition from the short-symbol region to the long-symbol region of the PLCP preamble. Simulation results show that the proposed method leads to a smaller mean-squared error than the modified maximum likelihood estimator. Frequency acquisition is accomplished by the unused subcarriers specified in the PLCP preamble. The proposed acquisition scheme can combat the multipath effect and the residual time offset with significantly lower complexity than a previously described scheme.