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GPS-Free Navigation! – Except it’s Not

October 18, 2016

Some really smart and clever people are figuring out how to navigate without GPS – or so their headlines claim. Take for example this recent post by the University of California, Riverside –

No GPS, No Problem: Next-Generation Navigation

UC Riverside Team is developing a navigation system that uses existing cellular signals, not GPS, and will support autonomous vehicle development

This is one of many efforts using signals of opportunity for navigation. It is particularly noteworthy since they are targeting the autonomous vehicle market.

Two problems here that we can see right off.

First – Most all the signals of opportunity they are using rely on GPS timing for proper operation. Network synchronization for WiFi, cell phones, digital broadcast, and so on is almost always traceable back to GPS.  And, when used, time-of-day information almost always from GPS also. So without GPS there would be no WiFi, cell networks, etc. True, backup clocks are often able to provide hold-over during transient GPS disruptions, but that doesn’t make these networks, or the navigation systems that use them, “GPS-free.”  And GPS doesn’t even have to fail to cause these networks to fail. GPS’s 13.7 microsecond timing “glitch” in January this year was enough to cause failure or degradation of unlucky digital broadcast, first responder radios, cell towers, and other systems across the globe.

Second – These folks are talking about navigation of autonomous vehicles. For us, that’s a safety-of-life application. Navigation signal integrity must be paramount. Signals of opportunity are just that – “of opportunity.”  There is no guarantee that, at any given moment, they will be there, that they will look like what they looked like before, or that they can be trusted. We are very much looking forward to having a self-driving car.  But we want to be assured that the car’s navigation is based on solid signals with high integrity.