卫星导航中XFAST捕获的降计算量去模糊处理算法

卫星导航系统中,采用扩展复制重叠法(Extended Replica Folding Acquisition Search Tech-nique,XFAST)对长PN码进行直接捕获时,粗捕后得到的对齐码相位存在重叠模糊度.为减少去模糊处理的计算量,提高捕获速度,提出了一种新的去模糊处理算法.新算法在得到粗捕对齐码相位结果后,先对本地码序列重新按照对齐相位进行排列、分段、段内循环移位等操作,然后进行段间叠加,再与接收码序列通过FFT-IFFT运算实现循环相关运算,从而确定对齐码相位所在的子码段,得到无模糊度的捕获结果.理论分析与仿真结果证明,该算法可以在分段叠加段数和子段长满足一定关系的条件下,在检测性能满足系统要求下,大大降低去模糊处理的计算量和操作时间,从而提高捕获速度.

An ambiguity resolving algorithm for XFAST acquisition with less computational amount in satellite navigation

In satellite navigation system,extended replica folding acquisition search technique ( XFAST) is used to capture long PN-code directly,but the aligned code phase obtained after coarse acquisition has o-verlapped ambiguity. In order to reduce the computational amount of resolving ambiguity and to speed up acquisition process, a new method is proposed. Firstly, local code chips are arranged according to the coarsely captured aligned code phase,segmented and shifted circularly within separate segments,and then all new local code sub-segments are folded together. Further,the received code and the new local folded code are performing circular correlation operations through FFT-IFFT,and the precise code sub-segment of the aligned code phase can be determined. Thus the ambiguity of coarse acquisition can be solved. Theo-retical analysis and simulation results demonstrate that, under the condition that the number of sub-seg-ments and the length of the sub-segment satisfy certain relations,the proposed algorithm can reduce the computational amount of resolving ambiguity and operating time to speed up acquisition process greatly with the detection performance meeting the system requirements.