Stability Criteria for GNSS Receiver Tracking Loops

Abstract

This paper analyzes the stability criteria for closed loop tracking in a GNSS receiver using Bode analysis techniques. This defines the stable limits of predetection integration time (T) for a given loop filter design, including its order and noise bandwidth (Bn) in combination with all of the other components involved in the closed receiver tracking loop. The loop filter design used in this paper is based on a traditional analog design converted to digital using the bilinear transform. The shortcomings of this traditional design are briefly described, but the traditional design suffices for small T and ample phase margin. Clearly, a pilot channel in modern GNSS signals permits much longer T than allowed by the original GPS data channels, but the stability assurance must be considered in either case. The methodology applies to both data (Costas) and data-less (pilot) tracking loops. Additional insight is provided using the results of this analysis. Copyright © 2014 Institute of Navigation.