The orthogonal frequency division multiplexing (OFDM) is a modulation scheme which divides the available spectrum into several subchannels (subcarriers) and transmits digital signals through the subchannels. Synchronization is critical to the performance of the OFDM system because it is very sensitive to carrier frequency offset due to frequency difference between oscillators in the transmitter and the receiver.
In this thesis work, we propose a frequency offset estimation algorithm for synchronization of OFDM systems. The algorithm doesn't need any pilot symbol for synchronization of carrier frequency. The algorithm estimates frequency offset by using redundancies of OFDM symbols such as the cyclic prefix and the guard band. The algorithm consists of two stages. First, by using the correlation of cyclic prefix in the time domain, it estimates the frequency offset that is less than half the subcarrier spacing. Then it estimates the frequency offset of integer multiples of the subcarrier spacing by using the power of the guard band. A fast initial acquisition is possible since the algorithm uses the redundancies of data symbols instead of pilot symbols. We apply the proposed algorithm to the digital audio broadcasting (DAB) system in order to obtain the performance of it. The algorithm results in good estimation performance for the additive white Gaussian noise (AWGN) channel and the multipath fading channel. We also observe no comparable performance difference between the proposed algorithm and the system with pilot symbols in the practical range of interest.
