Threshold setting method for GPS signal acquisition under cross-correlation effect
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摘要: 传统GPS卫星信号捕获门限设定方法在互相关干扰情况下存在较大虚警概率,所以无法捕获弱信号.针对该问题进行分析,在此基础上提出一种针对多颗能量不同卫星同时存在情况下的信号检测模型和概率模型.信号检测模型在相关积分非相干累加基础上引入双门限多次检测,由于在考虑噪声的同时也考虑了互相关干扰对弱信号捕获的影响,其概率模型为非中心χ2分布.在原有的恒虚警门限检测方法基础上,提出考虑强信号互相关干扰对微弱信号检测影响情况下的门限计算方法作为新的门限上限,而将原有的门限计算方法作为门限的下限.在此基础上提出强、弱卫星信号共存时的检测思路,即先用门限上限检测强信号并进行互相关干扰消除处理,再用门限下限判断是否有弱信号存在.采用仿真数据和实际数据针对考虑互相关干扰的门限上限进行实验,并和原有门限方法进行比较,证明在强、弱信号共存情况下原有门限无法检测出卫星信号,而新的门限设定方法可以正常工作,并具有较高的检测概率和较低的虚警概率.Abstract: Traditional global positioning system(GPS) signal acquisition threshold method suffers from large false alarm ratio in the condition of cross correlation interference, and thus influences weak signal acquisition. This problem was analyzed and signal acquisition detector was improved under the situation of more than one satellites existing with different signal power. Double threshold multiple detection algorithm was introduced based on the coherent correlation and non-coherent accumulation. The statistical model is non-central chi-square distributed due to cross correlation influence. A threshold calculation method was put up in the weak signal detection based on the original fixed false alarm criterion, and this threshold was considered to be the upper threshold. The original threshold was considered to be the lower threshold. An algorithm was put up considering both strong and weak signal coexistence, strong signals were acquired first and then cross correlation interference was eliminated, weak signals were acquired after that. Simulated and real data have been used to test the upper threshold, results were compared with the original method. It is proved that original method can-t detect satellite signals while new threshold works efficiently with high detection possibility and low false alarm ratio.
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