Research On Baseband Signal Processing And Anti-jamming For Software GPS Receiver

GPS navigation system plays an importan role in military,national defense,people's livelihood in modern times.And the users capture and track the GPS signal and finally calculate the location information by GPS receiver.Whether or not the receiver is done well,will affect final positioning accuracy and reliability directly.The focus of this thesis was on GPS software receiver which develops rapidly in the present.To improve the performance of the GPS receiver,a FPGA-based baseband processor was designed.The processor can capture and track the GPS signal accurately based on adaptive antenna anti-jamming algorithm and baseband processing algorithm.Firstly,the rationale of GPS navigation system was discussed,and GPS signal structure was analyzed included fundametal of spread spectrum,C/A code method,the composition of navigation message and the modulation of C/A code and P code.For the antenna jamming problem,classical algorithm of anti-jamming was discussed.The LCMV method has been improved,and a new method for wideband interference has been developed to constrain sidelobe levels.The design of GPS baseband processor used the Spartan 3 FPGA of Xilinx company,and completed the NCO module in PRN code tracking loop and carrier tracking loop,the PRN code generator module,the loop phase detector module and the loop filter module by Verilog.The carrier tracking loop was complete by Costas loop,and the PRN code tracking used delay locked loop.Besides achieving fundamental functions,the baseband processor was optimized in the thesis,a CPU was designed to perform certain functions on baseband signal process.This method increase the number of channel of the baseband processor,and decrease hardware cost.Finally,the schematic of the whole system design and view RTL schematic of every module was given.With real GPS data sampling,the correct position information could be calculated by the output of the baseband processor.The experiments verify the performance of the baseband processor.The synthesis results of before and after optimizaiton indicate that the optimization plan can enhance the efficiency greatly.