The Design And Implementation Of Capture And Tracking Module In GNSS Software Receiver

With fast development of the communication industry, satellite navigation andpositioning technologies are improving. GNSS obtains people’s favour because of theadvantages of all weather, high precision, fast response. It is not only extensive used infields of military affairs, but also has important applications in communications,navigations, monitors and so on. The capture and tracking of satellite signals decideperformance of the receivers, playing the major role in software receivers. Quality ofcapture and tracking algorithms decide the receiver sensitivity and high or low positioningaccuracy directly, besides the speed of navigation and positioning will be effected byamount of computations of capture and tracking.The object of study of this text is COMPASS of GNSS. Firstly, composition,modulation mode and character of pseudo random code of COMPASS signals areresearched and the structure and principle of GNSS software receiver are found outdetailedly. Secondly, three capture methods which are common used in current are focusedon. By their good or bad are compared, code phase in parallel capture is drawn to be themost fast among three capture methods, in order to improve the speed of capture further,this text makes an improvement basing on code phase in parallel capture. In the case ofwithout affecting accuracy, code phase in parallel capture algorithm using code phase inparallel and carrier frequency in serial search is improved for code phase in parallel andcarrier frequency in four road parallel search, the more, Matlab is used to simulate andverify the improved capture algorithm. By simulation result of improved capture iscompared with simulation result of code phase in parallel capture, it can be seen thatimproved capture can improve the speed of signal capture effectively. Thirdly, codetracking loop, carrier tracking loop and loop filter which constitute tracking loop arereseached and analysised basing on understangding the working principle of phase lockloop. In the design of tracking loop, DLL is adopted as code tracking loop. FLL and CostasPLL is adopted separately as carrier tracking loop to track carrier frequency and code phase.Carrier tracking loop assisting code tracking loop is adopted to overcome dopplerfrequency which influence the pseudo random code. Two orders FLL assisting three ordersCostas PLL is adopted to enhance the performance of tracking loop and implement a moresteady tracking and Matlab is used to simulate and verify the designed tracking loop, theresult of simulation indicates this designed tracking loop can obtain the tracking purpose. Last, the designed capture and tracking loop are verified in FPGA+DSP hardware platform.