Research On Key Technologies Of GPS Software Receivers

The GPS software receiver achieves a great improvement compared with the conventional GPS receiver which is implemented in hardware. The software approach is very flexible. It can not only be used to develop new navigating and positioning algorithms with the advantages of software, but can also test common algorithms without changing the design of the hardware. Moreover, GPS software receiver can process data collected from various types of hardware and sampled with different frequencies, and it is easy to update. Hence, the development and maturity of GPS software receivers will guarantee the modernization of GPS.The paper analyzes the similarities and differences between conventional GPS receivers and GPS software receivers, expounds the key technologies of the software implementation,and study the techniques of acquisition of GPS signals, tracking GPS signals and obtaining navigation data based on experiments. Details are discussed on signal acquisition and tracking.Firstly, the paper compares the architecture of conventional GPS receivers with that of GPS software receivers, and introduces the signal process in the convetional receivers and the sampling frequency used to design software receivers. Furthermore, the key technologies to implement software receivers are analyzed.Secondly, using the experimental results, the paper investigates the technologies of signal acquisition and tracking, which is the emphasis. The investigation includes the design of the number of satellites to search, the data length for acquisition, the rang of code phase and frequency needed to be searched, frequency steps and code phase steps in acquisition and parameters of the signal detector, three kinds of acquisition algorithms and the transition from anqusition to tracking. Then, based on the principles of basic phase-locked loops, the tracking loops of software receivers are designed and realized, and the pricision problem of code locked loops. and the updata frequency of carrier locked loops are investigated.Finally, the process of obtaining navigation data is studied. The algorithms of bit synchronization and sub-frame synchronization are provided and the and experimental results of bit synchronization are shown.