基于FFT的高数据率低信噪比下的长码直捕算法

Long Code Direct Acquisition Algorithm of DSSS Signals Based on FFT in High Rate and Low SNR Condition

在伪码测距系统中,高信息速率的长码直扩技术可提高通信性能、改善测距精度,但与此同时弱信号的长码捕获存在巨大挑战.为此,提出一种基于FFT技术的长码直捕改进算法,主要包括非连续式码相位搜索和并行载波多普勒搜索策略、基于位同步的全比特相干积累算法和基于频率补偿的时频二维约束Tong判决算法.理论分析和仿真结果均表明,该直捕算法不仅能降低资源消耗、缩短捕获时间、大幅度降低虚警概率,还能消除能量累加时由于比特翻转所带来的影响.所提出的算法可实现虚警概率低于10-6,检测概率大于99.5%,捕获时间小于5s的盲捕性能.

In pseudo-code ranging systems, the high rate and long code direct sequence spread spectrum （DSSS） can improve not only the communication performance but also the ranging accuracy. However, long code DSSS acquisition of weak signals is still faced with lots of challenges. Hence, an improved DSSS acquisition algorithm based on FFT was proposed, including the discontinuous search of code phase and parallel search of Doppler, the whole-bit coherent accumulation based on bit synchronization and the Tong judgment based on the frequency compensation of the time-frequency two-dimensional constraint. Both theoretical analysis and simulation results show that the proposed algorithm can substantially reduce the resource consumption and the probability of false alarm, shorten the acquisition time and eliminate the effects of data modulation under conditions of long time accumulation. In this paper such performance can be realized that the false alarm probability is less than 10-6 , the detecting probability is over 99.5% and the acquisition time is less than 5 s.