Modelling and Comparison of Tracking Loops for GPS Signal

Anotace: Nowadays, Global Positioning System (GPS) applications are widely spread and affect all aspects of our modern lives. They can be found in many different fields, such as aviation, environment, marine, space, surveying, mapping, and military operations. In military, the GPS is employed in missile guidance, vessels and aircraft navigation, location, communication network timing, etc. The GPS receiver is required to be more and more robust to withstand harsh condition, for example losing signal or jamming. This paper demonstrates the implementation and simulation of an advanced tracking technique that is used in modern GPS receivers – a vector tracking loop. Brief related principles of a GPS receiver are introduced. The principle of traditional tracking loop is shown and compared to the vector tracking loop. An extended Kalman filter is employed as a vector tracking algorithm. The extended Kalman filter uses pseudo range rate, which is computed from both the code and the carrier to constrain the receiver velocity. The acquired results are compared and advantages of the vector tracking algorithm against the traditional tracking loop are presented in this paper, including characteristics of the vector tracking loop.