均值分组块补零P码直捕算法原理及实现

Principle and implement of P-code direct acquisition based on average block zero padding

P码是长周期精密测距码,主要用于提供精确定位服务。提出了基于FFT的均值分组块补零P码直捕算法,通过直接平均法来降低运算量,用分段重叠补零法将连续的相干积分分解成普通的循环相关,对接收码和本地码的FFT结果缓存,用FFT结果的圆周移位代替多普勒频移搜索。硬件实现时采用双DDR2SDRAM缓存,32K点FFT单核复用的架构,详细描述了算法在FPGA上实现时的逻辑功能划分、核心子模块功能及具体实现方案。通过ModelSim仿真验证,算法提高了数据利用率,减少了捕获时间。

The long period precise ranging code （Pcode） is mainly applied to precise positioning service. A new Pcode direct acquisition method based on average block zero padding and FFT is provided to reduce the amount of calculation by direct aver age method. Using piecewise overlapping zero to make continuous coherent integration decomposed into a common cyclic corre lation and cache the FFT result of the received code and local codes, and FFT results circumference shift replaces the Doppler shift search. The hardware adopts double DDR2 cache and reuse of one 32 K Point FFT_IP core. Logic algorithm is implemen ted on the PPGA, and the function partitioning, and the core submodule functions and specific implementation plan are de scribed in details. ModelSim simulation shows that it can improve the use ratio of data and decrease the acquisition time.