改进的双块补零P码直接捕获算法

针对低信噪比和高动态环境下的P码直接捕获问题,本文对传统双块补零算法进行改进,提出一种分段旋转双块补零算法.算法通过分段FFT得到各数据段的频谱;通过频谱的循环移位进行频率斜升和初始频偏补偿,再求出频率补偿后的各段数据与本地伪码的相关值并进行非相干累加;对相关峰峰值进行恒虚警检测和抛物插值.仿真结果表明,本文所提算法与传统双块补零算法相比,检测概率和参数估计精度大致相当,捕获时间降低80%,逻辑运算单元和存储单元分别减少64%和99%.同时给出了不同系统要求下的关键参数选取方法,使算法具有较高的实用性. 

Improved Double Block Zero Padding Algorithm for P Code Direct Acquisition

A segmented rotation double block zero padding (DBZP) algorithm was proposed based on the improved traditional DBZP algorithm for direct acquisition of P code in the environment of heavy noise and large frequency dynamics. The input complex-valued baseband signal was first segmented into finite-length records, and then transformed into frequency coefficients by fast fourier transform (FFT). By estimating the initial value of the frequency offset and its slew, the center frequency offset was determined for each temporal record, which was then compensated by cyclically shifting the corresponding Fourier coefficient record. Once the compensation was done, the correlation between the input signal and the local PN code was performed in frequency domain, and the correlation output was non-coherently accumulated over a number of records. For the last step, the constant false alarm rate (CFAR) detection and parabola interpolation were utilized with the maximum value of the accumulated correlation output. It is found for typical acquisition scenario that the presented algorithm may cut down computational overhead, memory consumption and the mean acquisition time by 64%, 99% and 80%, respectively, in comparison with traditional DBZP algorithm, without noticeable SNR penalty. The principles for choosing key parameters of the algorithm are discussed to meet various practical requirements.