| More and more attention is paid to GPS software receiver recently. Researching groups all over the world set up their own software-based GPS receiver system. The main difference between the conventional receiver and software-based receiver is that the acquisition and tracking processes are achieved on PC using software. This arranging scheme provides the software receiver with flexibility, because it is convenient for researchers to develop or modify algorithms without the need to change the hardware. Then we can study the influence of the parameters to GPS performance.This paper introduces the GPS code structure and the theory of the software receiver firstly. Then, the methods for signal acquisition are expatiated. Acquisition is the first step of the software section for a GPS software receiver. For a receiver that receives L1 C/A code, the function of the acquisition is to detect the presence of certain GPS satellites and find the initial phase of the C/A code and the frequency of the carrier. This paper introduces three basic acquisition methods, including serial search acquisition, parallel frequency search acquisition and parallel code acquisition method. Based on the theory of acquisition methods, the processing steps are given respectively. After that, gives a method of finding the fine frequency of the carrier in order to initial the tracking loop successfully. Usually, 1ms length of data can complete the acquisition. It is difficult to acquire signal using 1ms data if the signal-to-noise is too low. So modified acquisition algorithm is needed to acquire weak signal. This paper gives the algorithm of detecting weak signal based on the parallel code search method by combining coherent integration and noncoherent integration.After that, the algorithms are verified including the normal signal and the weak signal acquisition using real GPS signal collected by front end, and the results show that these algorithms can acquire the GPS signal successfully.
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