Project Members: Todd Humphreys

Outside Collaborators: Todd Moon, Utah State University

Summary: Increased dependence on the Global Positioning System and other satellite navigation systems makes users vulnerable to signal loss or degradation caused by ionospheric effects. Radio wave scintillation, the temporal fluctuation in phase and intensity caused by electron density irregularities along the propagation path, stresses a GPS receiver's carrier tracking loop, and, as severity increases, can lead to navigation bit errors, cycle slipping, and complete loss of carrier lock.

Increasingly, modern GPS applications are exploiting techniques that require carrier phase measurements. In view of this trend, and of their already widespread use, we focus on phase tracking loops, or phase lock loops (PLLs), as opposed to frequency tracking loops. We are interested in developing phase tracking strategies that are specially designed to maintain lock in the presence of severe scintillation. Design and testing of such receivers depends crucially on an accurate understanding of scintillation and its effects on receivers. Accordingly, in previous work we have devoted much effort to developing a realistic equatorial scintillation model which captures the features of scintillation that are relevant to carrier tracking. This model informs our design of scintillation-robust carrier tracking techniques.

Related Publications:

A data-driven testbed for evaluating GPS carrier tracking loops in ionospheric scintillation

Development and Field Testing of a DSP-Based Dual-Frequency Software GPS Receiver

Modeling the effects of ionospheric scintillation on GPS carrier phase tracking

The Semidiurnal Variation in GPS-derived Zenith Neutral Delay

Analysis of Ionospheric Scintillations using Wideband GPS L1 C/A Signal Data

Riding out the rough spots: Scintillation-robust GNSS carrier tracking