The threats just keep growing to a resource that hundreds of millions of people around the world have come to rely on for a myriad purposes.

GNSS is, after all, an RF technology, vulnerable in its own way to the kind of disruptive effects that turn an AM radio into a static-ridden howl as you drive under a powerline. And the radiated energy of signals arriving with from satellite sources tens of thousands of miles away are orders of magnitude weaker than those carrying the top 40 tunes broadcast by a local station.

Powerful terrestrial wireless broadband systems, such as the one proposed by LightSquared Inc., can overwhelm sensitive receiver elements without even transmitting signals directly into GNSS bands.

And now, intentional jamming is no longer a phenomenon limited to theaters of military operations where attacks on positioning and navigation systems accompany efforts to deny communications and electronic surveillance to the enemy. Truck drivers seeking to thwart monitoring by dispatch centers or avoid federal limits on hours behind the wheel, use low-power jammers to disable a receiver a few feet from them — with no idea that they may be interrupting GNSS-based systems miles away.

Even Mother Nature gets into the act with solar flares, scintillation, and electron-fueled ionospherics.

To help sort the signal out from the noise surrounding this subject, we turned to Phil Ward, an electrical engineer and president of Navward GPS Consulting who has worked on GPS receiver design since 1976. A senior technical staff member at Texas Instruments Defense Systems and Electronics Group for 31 years, Ward is a fellow and former president of the Institute of Navigation and a senior member of the Institute of Electrical and Electronic Engineers.