Study On The Technologies Of OFDM Synchornization In UWA Communication System

In recent years, as orthogonal frequency division multiplexing (OFDM) technology with high spectrum efficiency, strong ability of overcoming multi-path fading and narrowband interference, the ability of high-speed transmission in the case of efficient utilization of bandwidth and simple method, it becomes one of the focuses in high-speed UWA communication. But OFDM is very sensitive to time- domain synchronization and frequency-domain synchronization, especially about frequency-domain synchronization. Furthermore, because the signal used by Underwater Acoustic Communication is broad-band and with very low central frequency, communication performance is seriously degraded by Doppler shift. As a result, precise time and frequency synchronization, good performance of Doppler estimation and compensation are the foundation of the system based on OFDM working effectively. The main content of this paper are as follows:1. Two methods about time synchronization is are proposed. One is LFM correlation detection, the other is based on energy detection based on moving window.2. The synchronization of symbol and frequency are main technologies for OFDM system, some classic synchronization algorithm are proposed in this paper, such as data-aided and nodata-aided algorithm. Then a new fine timing synchronization algorithm which use pilot symbol is introduced, and a frequency synchronization algorithm is improved3. Aiming at the underwater communication system based on OFDM, a method is proposed which uses Doppler frequency shift estimation that takes advantage of the structure of OFDM symbol. And a technology is proposed which compensates the Doppler frequency shift with interpolation in frequency domain.4. Eventually, the performance of data frame detection algorithm, timed signal synchronization algorithm, frequency estimation algorithm is validated in laboratory tank experiment.