Project Members: Jahshan Bhatti, Daniel Shepard, Todd Humphreys

Outside Collaborators: Brady O’Hanlon, Paul Kintner, and Mark Psiaki, Cornell University; Geoff Crowley and Gary Bust, ASTRA LLC

Former Project Members: Zach Tschirhart

Summary: The University of  Texas at Austin, Cornell University, and ASTRA LLC are collaborating to develop the CASES (Connected Autonomous Space Environment Sensors) GPS receiver.  The CASES sensor, a specialized embodiment of the GRID software-defined GNSS receiver, is primarily a space weather instrument, although its dual-frequency signal path and advanced tracking loops support carrier phase differential operation, which is sufficient for Precipitable Water Vapor (PWV) recovery.  CASES has been successfully field tested in Brazil and is set for deployment in the Antarctic in December 2010.  It is one of two software receivers considered for future incorporation into the International GNSS Service network.

CASES offers several innovations relative to existing science-grade GPS receivers:

(1) The sensor’s software radio architecture, in which all signal processing downstream of analog-to-digital conversion in the RF ront-end is implemented in software, makes it flexible, remotely reconfigurable, and allows it to support innovative algorithms for Total Electron Content (TEC) recovery and sustained tracking through vigorous ionospheric scintillation. Full remote reconfigurability, whereby an entirely new receiver personality can be downloaded from a remote location, is an asset in research missions such as the proposed project because the instrument’s behavior can be adapted to unforeseen challenges after deployment. In addition, full transparency into and control over the instrument’s behavior, products, and cadences enables researchers to confidently separate receiver effects from geophysical phenomena.

(2) The instrument’s use of the new civil GPS signals on the L2 frequency (L2C) makes possible the creation of more robust, less complex, and yet more precise GPS Total Electron Content receivers and scintillation monitors.

(3) The incorporation of specialized tracking loops provides robust operation in weak signal and scintillating environments. The tracking loop design is informed by studies of the effects of ionospheric scintillation on GPS carrier tracking loops.

(4) The sensor’s low cost—a factor of five price reduction compared to currently available science-grade GPS receivers ($2K vs. ~$10K)—is a consequence of its software radio architecture, which permits an off-the-shelf digital signal processor to replace special-purpose GPS chips used by other manufacturers.

Related Publications:

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

CASES: A Smart, Compact GPS Software Receiver for Space Weather Monitoring

CASES: A Novel Low-Cost Ground-based Dual-Frequency GPS Software Receiver and Space Weather Monitor