Study On Acquisition And Tracking Algorithms Of GPS L2C Signal And The Software Implementation

In order to meet the growing requirement of civilian users for high-precision positioning in complex environment, the U.S. government announced a new GPS modernization initiative that called for the addition of two civil signals, one of which is denoted as L2C. Because of FEC (forward error correction) and TDM (time division multiplex), L2C lowers the data demodulation and carrier tracking threshold. As a result, L2C is likely to become the signal of choice for application like personal navigation in wooded areas and inside buildings. Besides, L2C will provide civilian users the ability to correct for ionospheric delays by making dual-frequency measurements, thereby significantly increasing accuracy. Currently, L2C is transmitted by eight modernized GPS IIR-M satellites. It's expected that it will be fully available in future years. This thesis deeply investigates L2C acquisition methods and tracking algorithms, as well as real-time processing for L2C on SDR (software defined receiver).L2C has unique features that make it different in signal acquisition. L2C can be acquired by CM code and CL code, respectively. In CM code acquisition, based on the ODA (overlap and discard) and folding algorithm, three improved algorithms are set forth. The performances of these algorithms are analyzed and compared by simulation. Three direct acquisition methods are described for CL code, namely the overlap and discard algorithm, the double length and zero padding algorithm, and the extended code folding algorithm. Simulation results demonstrate that the folding algorithm has the worst performance under the same acquisition condition in order to get the least computation burden.Three tracking algorithms for L2C are presented and compared, which are the algorithm using CM code only, the one using CL code only and data/pilot combined tracking algorithm. Simulation results show that data/pilot combined tracking algorithm has the best performance among the three both in carrier tracking and code tracking under the same tracking condition. Tracking algorithm using only CL code has better tracking performance than the one using CM code only.The architecture and key technologies of SDR are studied to realize L2C real-time processing in this thesis. The signal process creates three threads and manages various functional modules by class. In order to solve time-consuming problem when correlating and generating local signal, carrier and code stripping algorithms are studied. It's proposed that the segmented down-converting method should be used for carrier removal and local code fixed method for code removal. Currently, SDR can do signal processing of L2C in real-time and get correct navigation results.