低轨卫星短突发通信具有多普勒频偏和多普勒变化率较大、突发符号较短和突发信号导频长度受限等特点,采用传统的时频同步算法在低信噪比条件下性能较差.为了提高时间同步和频偏估计性能,准确完成同步过程,基于时分多址(Time Division Multiple Access,TDMA)接入帧结构提出一种新的时频同步算法.该算法采用二维搜索算法进行整数倍的时延估计和粗频偏估计;在补偿大频偏和整数倍时延后,估计小数倍时延;采用结合低通滤波的快速傅里叶变换(Fast Fourier Transform,FFT)算法进行精频偏估计.仿真结果表明,每符号能量与噪声功率谱密度比值(Ratio of Symbol Energy to Noise Power Spectral Density,Es/N0)为4.5 dB时,时延检测概率准确率达到99.99％,整体解调性能相较于M&M等算法有2 dB以上的性能提升.
Time-Frequency Synchronization Algorithm for Short Burst Communication of LEO Satellite
Short burst communication of low earth orbit satellite is characterized by significant Doppler frequency offset and Doppler rate variation,short burst symbols,and limited burst signal pilot length.Traditional time-frequency synchronization algorithms perform poorly under low signal to noise ratio conditions.In order to improve the performance of time synchronization and frequency offset estimation,and to accurately complete the synchronization process,a new time-frequency synchronization algorithm based on Time Division Multiple Access(TDMA)frame structure is proposed.This algorithm first utilizes a two-dimensional search algorithm for integer multiple delay estimation and coarse frequency offset estimation.After compensating for large frequency offsets and integer multiple delays,it estimates fractional multiple delays.Finally,it employs an Fast Fourier Transform(FFT)algorithm combined with low-pass filtering for fine frequency offset estimation.Simulation results show that with Es/N0=4.5 dB,the probability accuracy of delay detection reaches 99.99％,and the overall demodulation performance is improved by more than 2 dB compared to algorithms like M&M.
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