An improved two-step time-parallel semi-bit method for GPS weak signal acquisition

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.