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GPS接收机输入信号的功率随时间而变化,如果采用固定门限判决是否完成捕获会出现检测概率降低或虚警概率提高的问题。鉴于此,提出了采用自适应捕获门限判决策略完成信号捕获。采用最大似然估计原理,根据判决统计量的样本值得到了噪声方差的最大似然估计,进而求得恒虚警率下的自适应捕获门限。同时,信号的平均捕获时间是GPS接收机性能的重要指标之一,研究了载波频率与伪码相位均为不确定值时的平均捕获时间的计算方法,推导了平均捕获时间与信噪比及门限值之间的约束关系。分析结果表明,自适应门限捕获方法能减小平均捕获时间,实现信号的快速捕获。
The power of the GPS receiver input signal varies with time. If the fixed threshold is used to determine whether the acquisition is completed or not, the detection probability decreases or the false alarm probability increases. In view of this, it is proposed to accomplish the signal acquisition by adopting the adaptive capture threshold decision strategy. Based on the maximum likelihood estimation principle, the maximum likelihood estimation of noise variance is obtained based on the sample values of the decision statistic, and the adaptive capture threshold under constant false alarm rate is obtained. At the same time, the average signal acquisition time is an important index of GPS receiver performance. The calculation method of the average acquisition time when the carrier frequency and the pseudo-code phase are both uncertain values is studied. The average acquisition time and signal-to- Constraints between thresholds. The analysis results show that the adaptive threshold capture method can reduce the average acquisition time and achieve fast signal acquisition.