Research And Implementation On The Tracking Algorithm Of GNSS Signal

Global Navigation Satellite System (GNSS) has been widely used in civilian fieldand military field, because of its advantage which include multi-system, multi-level andmulti-mode. Therefore, GNSS receiver has attracted more and more attention. The mainwork of receiver is demodulating and calculating navigation data, however the key todemodulation precise is tracking the signal of GNSS correctly. Therefore researching ontracking algorithm became an integral part of GNSS receiver.Researching on design and implementation of tracking algorithm is the main contentin this thesis. The paper describes the composition of GNSS system, introduces thecharacteristic of GPS signal and the basic structure of GNSS receiver. The focal point isthe basic principle of the key section in tracking signal of GPS. Studied the algorithmincluding carrier tracking and code tracking, and compared discriminator algorithm intraditional tracking loop. This paper according to the problems of large frequency errorand long adjustment time in traditional tracking algorithm, this paper suggests a trackingloop with kalman algorithm. Simulated GPS signal with Matlab tool and compared thetracking error. The mean error is35Hz with traditional algorithm, however the mean erroris closed to0Hz with kalman algorithm when the signal to noise ratio is-20dBHz. At thesame time, the time is reduced10ms when tracking is approaching stable. So the trackingalgorithm with kalman can reduce error and time.In hardware design, advanced a kind of carrier loop discriminator based on CORDICalgorithm. The discriminator use simple addition and subtraction and shift operationinstead of division and multiplication. It can save logical resource and cost. but alsoimprove the working efficiency. The paper has finished core module using FPGA andfunctional simulation of tracking unit in GPS receiver baseband processing.