Project Members: Todd Humphreys

Outside Collaborators: Joanna Hinks and Paul Kintner, Cornell University


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, much effort has been devoted to developing a realistic scintillation model that captures the features of scintillation relevant to carrier tracking. Dr. Humphreys's Ph.D. work at Cornell University was centered on this effort. By 2008, he and his Cornell collaborators developed the Cornell Scintillation Model for hardware-in-the-loop scintillation testing of GNSS receivers. In October, 2010, Spirent Communications adopted the Cornell Scintillation Model as an embedded part of their SimGEN software, enabling Spirent users wordlwide to test their receivers under realistic equatorial scintillation scenarios. The University of Nottingham carried out an evaluation of the Spirent-implemented Cornell Scintillation Model and verified that the model produces the advertised scintillation levels. Raytheon recently used the Cornell Scintillation Model to study the effects of ionospheric scintillation on service availability of the GPS augmentations sytems.

You can can download the toolkit directly from the GPS Laboratory at Cornell University that enables hardware-in-the-loop scintillation robustness testing of GNSS receivers.

Related Publications:

Simulating Ionosphere-Induced Scintillation for Testing GPS Receiver Phase Tracking Loops

GNSS and Ionospheric Scintillation: How to Survive the Next Solar Maximum

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

Modeling the effects of ionospheric scintillation on GPS carrier phase tracking

Evaluating GPS Receiver Robustness to Ionospheric Scintillation