摘要
极弱信号、大多普勒动态变化条件下的接收机抗干扰、快速捕获同步技术是低轨卫星短报文数据通信的研究难点.本文首先分析了多普勒特性对低轨卫星扩频信号快捕的影响,讨论了现有各种捕获策略的优缺点.在此基础上提出双倍采样、补零的部分匹配滤波与快速傅里叶变换相结合的二维并行快速捕获优化设计方案,并进行了性能仿真分析,最后结合面向判决的同步技术,给出接收机原理样机捕获时间的实现结果.在给定前导码条件下,优化后的二维并行捕获平均时间为10ms,远低于常规扩频码并行捕获的秒量级捕获时间,可以较好地满足低轨卫星星座全球短报文数据突发通信及随遇接入需求.
Large Doppler shifts and extremely weak signal in the condition of short datagram burst LEO satellite communication are always the technical challenges for fast acquisition receiver.Firstly,the influence of Doppler characteristics on the fast acquisition of LEO satellite spread spectrum signal is analyzed,and the advantages and disadvantages of different acquisition strategies are discussed.Based on double-sampling zero-padding technology of partial matched filter and Fast Fourier Transform(FFT),Optimization and implementation of two-dimensional parallel fast acquiring Direct Sequence Spread Spectrum(DSSS)signal processing method is presented.Different from the single sampling scheme in which the input signal is sampled according to the chip rate,the double sampling scheme has two sampling signals reaching the correlator in each chip time.That is,the correlator works on a clock with twice than the chip rate.The correlator selects a sampling signal at each interval and inputs it to the PN code part correlator for correlation operation,and then outputs the maximum value after passing through the FFT module and energy accumulation module for judgment.Therefore,the maximum sampling signal-to-noise ratio loss is about 0.9 dB,which greatly improves the performance compared with the single sampling method.Finally,combined with the decision oriented carrier forward estimation and PN code feedback synchronization technology,the actual test shows that the average acquisition time of the receiver is 10 ms,which is much lower than the tradition parallel acquisition time of PN sequence code in seconds order.It can better meet the service requirements of short datagram burst communication system with random access for LEO satellite constellation.
作者
张军
郑立荣
林宝军
沈苑
龚文斌
帅涛
ZHANG Jun;ZHENG Lirong;LIN Baojun;SHEN Yuan;GONG Wenbing;SHUAI Tao(School of Information Science and Engineering,Fudan University,Shanghai 200433;Innovation Academy for Microsatellites,Chinese Academy of Sciences,Shanghai 201203;University of Chinese Academy of Sciences,Beijing 100049;Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030)
出处
《空间科学学报》
CAS
CSCD
北大核心
2021年第6期976-982,共7页
Chinese Journal of Space Science
基金
上海市科委课题项目资助(16511103000)。
关键词
低轨卫星星座
短报文通信
快速捕获
直接序列扩频
快速傅里叶变换
Low-Earth Orbit(LEO)satellite constellation
Short datagram burst communication
Fast acquisition
Direct-Sequence Spread Spectrum(DSSS)
Fast Fourier Transform(FFT)
