基于短时傅里叶变换的水声OFDM时间同步方法

正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术具有抗多径、频带利用充分、传输数据率高的优点,在水声通信中具有重要的发展前景。由于多普勒频移和多径时延的存在,需对OFDM信号进行时间同步。同步不准会引起OFDM水声通信中符号间干扰和子载波间干扰,提出了一种基于叠加单频序列的短时傅里叶变换(STFT)时间同步方法,该方案首先提取叠加在OFDM符号上的单频信号,对该信号进行短时傅里叶变换,随后对其时频幅度谱进行分析,利用平坦区域确定同步时刻。仿真和试验结果表明,该方案有效可行。

Research on underwater orthogonal frequency division multiplexing timing synchronization based on short time Fourier transform

Orthogonal Frequency Division Multiplexing (OFDM) is a method that can combat multipath, fully use the frequency band and have high data transmission rate. Consequently it has a promising future in underwater acoustic communication. Underwater channel is a Doppler-distorted, high noised and time-varying multipath channel. Due to the existence of multipath and Doppler shift, timing synchronization plays a key role in OFDM systems. In this paper, a timing synchronization method based on short time Fourier transform (STFT) is proposed. First, STFT is operated on the outcome of the received single frequency signal accompanying the OFDM symbol, and then the time-frequency spectrum is obtained for calculating the summation of the outcome after STFT and finding the edge which is the original point of the underwater acoustic OFDM symbol. The results of simulations show good performance of this method even under low ratio of signal to noise.