Research On Vector-based Tracking Algorithms For GNSS Signals

Traditional tracking algorithm uses Costas loops and Delay Locked Loops(DLL) to track the carrier and Pseudo-Random Noise(PRN) signals broadcast bythe satellites, respective ly. The tracking loops in each channel operate independentof each other. In addition, the flow of information from tracking loops to positiondetermination is strictly left to right. The estimates of the tracking loops are thenfed forward to the navigation processor. The PVT estimates of the navigationprocessor are then formed using the estimates of the tracking loops. The signa ls ofdifferent satellites are processed collective ly and information is shared betweenthe different channels in the vector-based tracking algorithms. The task of signaltracking and navigation state estimation are no longer separate processes. TheExtended Kalman Filter (EKF) simultaneously tracks the received signa ls andestimates the receiver’s position, velocity and time.A major advantage of vector-based tracking algorithms is that once a good position, velocity and time solutionis available, all signa ls are continuous ly tracked even under weak (or no) signalconditions. Vector-based tracking algorithms are analyzed deeply as well astraditiona l tracking algorithm in this thesis.At first, the key techno logies of signals reception, inc luding the captureprocess, the tracking process, as well as the position determination process areanalyzed in detail based on the elaboration of the satellite navigation s ignalstructure represented by the GPS signal. The structure and working process ofcarrier tracking loop and code tracking loop are studied, and their characteristicsand measurement error performace have been analyzed using simulations in thisthesis.Then the princ iple of the Kalman filter was introduced, an Adaptive Kalmanfilter algorithm for carrier tracking loop was proposed in this thesis, the design ofthe carrier tracking algorithm has been completed by creating the system modeland measurement model. Then the principles of the extend Kalman filter algorithmwas studied, a method for designing vector delay lock loop (VDLL) using theextended Kalman filter was proposed, the design of the vector delay lock loop hasbeen completed, the system model and measurement model have been created bythis method in this thesis. Tracking process for different satellites is dealed withcollectively in this method, which makes that the singa l can be tracked when it isweak. The signal also can be tracked even when the signal of a satellite appearsagain after temporary disappearance. Finally, the thesis have analyzed the performance in the signal recaptureaspects by compared the vector-based tracking algorithms with traditiona l trackingalgorithm us ing the simulation, and the vector-based tracking a lgorithms wasshown to outperform the traditional methods.