GPS信号捕获与跟踪策略确定及实现

为了检测GPS(Global Positioning System)信号,设计了码环及载波环捕获与跟踪数字系统.序贯搜索与窄间隔超前-滞后型数字延迟锁相环的采用,保证了码相位的可靠捕获与精确跟踪,四相鉴频器、叉积自动频率跟踪算法及科思塔环载波相位跟踪算法的结合,既保证了载波频率(多普勒频移)的捕获速度,又使环路能有效地跟踪频率/相位变化,获得较好的动态性能与噪声性能.控制算法及参数确定的软化实现使系统具有较好的灵活性.基于扩频相关器与数字信号处理器的数字系统验证了上述方案的正确性及有效性. 

Control Strategy and Implementation for Acquiring and Tracking GPS Signal

A control strategy of acquisition and tracking for code loop and carrier loop is designed to detect GPS signal. Sequential searching scheme and narrow space non coherent digital delay locked loop assure reliable acquisition and precise tracking for code phase. Integrated algorithms of 4 quadrant frequency, cross product automatic frequency control and Costa phase locked loop are adopted to speed up frequency acquisition and effectively track carrier frequency/phase changing, and therefore obtain better dynamic and noise performance. The control algorithms and loop parameters determination are implemented by software with inflexibility. Digital system based on spread spectrum correlator and digital signal processor proved above scheme be correct and efficient.