The Global Positioning System (GPS) receivers often encounter problems of code Doppler and navigation bit sign transitions which decrease output SNR of acquisition stage. The traditional methods of code phase search acquisition with post-correlation detections for weak signal acquisition fail to enhance the number of integrations between the received GPS signal and local Coarse/Acquisition (C/A) code; especially, when the code Doppler and navigation bit sign transitions occur. We propose an improved two-step time-parallel semi-bit acquisition method to overcome the navigation bit sign transition and the code Doppler limitations. This proposed method compensates the navigation bit sign transitions and code Doppler in the first and second step, respectively. Also, Fast Fourier Transform (FFT) is applied to increase the speed of code delay search. Experimental results demonstrate that the proposed method outperforms compared to the conventional methods such as coherent, non-coherent, differential coherent detection, coherent time parallel, non-coherent time parallel, differential time parallel, and improved semi-bit compensation. In contrary to the other conventional methods, the presented method can detect at least four satellites with 40.8% less SNR.

全球定位系统（GPS）接收器经常遇到码多普勒和导航位符号过渡的问题，这会降低采集级的输出SNR。具有弱相关信号采集后相关检测的码相位搜索采集的传统方法无法提高接收到的GPS信号与本地粗/采集（C / A）码之间的积分数量；特别是在发生代码多普勒和导航位符号转换时。我们提出了一种改进的两步时间并行半位捕获方法，以克服导航位符号过渡和代码多普勒限制。所提出的方法分别在第一步和第二步中补偿了导航位符号过渡和代码多普勒。另外，应用快速傅立叶变换（FFT）以提高代码延迟搜索的速度。实验结果表明，与传统方法相比，该方法的性能优于相干，非相干，差分相干检测，相干时间并行，非相干时间并行，差分时间并行和改进的半比特补偿。与其他传统方法相反，本方法可以检测到至少四颗SNR降低40.8％的卫星。