Research On Synchronization Algorithms For OFDM

Orthogonal Frequency Division Multiplexing (OFDM) has become the key technique in broadband wireless access and the next generation B3G/4G mobile communication system. Extensive attentions have been paid to OFDM due to its high spectral efficiency, high data rate and well anti-multipath ability. But OFDM is very sensitive to synchronization errors. The timing synchronization error will introduce inter-symbol interference(ISI), while the carrier frequency error will introduce sub-channel interference(ICI). It is important for OFDM system to obtain accurate symbol timing and carrier frequency synchronization. This paper researchs some typical symbol synchronization algorithm and the carrier frequency synchronization algorithm in depth. It analys and compares these performances, and proposed a new carrier frequency synchronization algorithm. The main thesis is as follows:First, the decline of wireless channel and the channel models are discussed in brief. The model of wireless channel which used in the paper is introduced, and the basic principles, features, and technical advantages of OFDM technology is discussed in detail. In addition, a detailed theoretical analysis and simulation are employed to discuss the effect of timing offset and carrier offset on OFDM system.Secondly, algorithms of timing synchronization which includ the frame timing synchronization and symbol timing synchronizationare , are simulated by comparing the performance of various algorithms have been studied in depth. In the frame timing, synchronization algorithm based on training sequence is much better reduce received signal power which compared with synchronization algorithm based on idle symbol energy detection. In the time-domain rough timing, symbol timing synchronization algorithm based on time-domain 16 points training sequence has relatively good performance of timing synchronization which compared with Maximum Likelihood symbol timing synchronization algorithm based on cyclic prefix. In the frequency-domain fine timing, symbol timing synchronization algorithm based on frequency domain long training sequence is much better than symbol timing synchronization algorithm based on frequency domain pilot, which reduced hardware complexity.Finally, three algorithms of carrier frequency synchronization are studied and analyzed, which are Maximum Likelihood algorithm based on cyclic prefix, time-domain correlation algorithm based on training sequences, and frequency-domain correlation algorithm utilizing based on pilots, and on this basis, a combined estimation algorithm based on both training sequences and pilots is proposed in the paper. Simulation result shows that proposed algorithm outperforms the three classical algorithms in both the estimation range and performance, especiallt when the initial frequency offset is large, which is required in practice.