Police Tech & Gear
with Tim Dees
More alternatives to GPS
Ways to navigate even if GPS is jammed or inaccessible
This space has featured a couple of stories on navigational aids inside and outside of buildings, including finding the location of someone in a strictly-indoor environment , and the unexpected consequences of jamming GPS signals , and just how easy it is to do that.
We’ve come to depend on the GPS system in many ways, which is a little scary in the light of how fragile that network is. Fear not, there are new technologies on the horizon.
One of these is coming from the science that helps manage airborne military vehicles, commonly called “drones.” Drones use GPS signals to tell themselves and their operators where they are, and disruption of those signals can be catastrophic if there is no contingency measure. An enemy could just jam local GPS signals and confuse the drones, making their area both attack- and surveillance-proof.
Signals Of Opportunity
The fallback measure is called NAVSOP, short for NAVigation via Signals Of Opportunity.
NAVSOP is something of a takeoff on legacy direction finding equipment in aircraft. Before more modern VOR (VHF Omnidirectional Radio) and DME (Distance Measuring Equipment) was available, pilots used directional antennas to get the approximate bearing to a transmitter (such as a commercial radio station) at a known location. They could determine their approximate position by triangulating two signals. There are lots of static transmitters out there, and more sophisticated receivers can use the signal strength and direction of those transmitters to make an estimate of the receiver’s position. Capture and locate enough signals, and the refined location becomes very accurate.
NAVSOP starts with a GPS-generated location and plots the frequency, signal strength and direction of all transmitters in range as it or drives over an area. An enemy can throw off the system by moving a transmitter or shutting it down, but they can’t move all of them or turn them all off without crippling their own infrastructure. The NAVSOP system can identify an anomalous signal or two in the mix, and disregard it for location purposes. It is constantly learning and refining its transmitter database.
Public safety could use this same system via the transmitters that are in place all over the country. On a large scale, these would include commercial TV and radio stations, aircraft navigation aids, land-mobile radio transmitters, and all sorts of other “signals of opportunity.” In an urban environment, the signal sample might include Wi-Fi hotspots and pet invisible fence transmitters. Your navigation hardware would no longer be dependent on weak GPS signals, and would work as well inside a building as outside. The receivers are likely to be no larger than GPS units of today.
Since GPS doesn’t work all that well without a view of the sky, other measures are needed for indoor navigation within shopping malls or large industrial facilities. You aren’t all that likely to get lost in one of these, but operations centers need to know where their security people are, especially if one is in distress. This is also an issue for firefighters, who can get lost inside a building consumed in fire and smoke.
A system called Smartsense http://www.fraunhofer.de/en/press/research-news/2012/may/navigating-the-shopping-center.html , under development by German research organization Fraunhofer, uses a flash drive-size circuit containing an accelerometer and a magnetic field sensor. The accelerometer tracks speed through movement cues, while the magnetic field sensor tracks compass direction the same way a magnetic compass does. The combination yields a very accurate location finder that depends not at all on GPS.
The system isn’t much good if it doesn’t “know” the building, but this is easily remedied. Smartphones with the Smartsense device embedded can either store the building map or download it on the fly when the user approaches the structure. Private citizens could use this technology to locate themselves in malls and theme parks, while public safety personnel can track their people and coordinate a search or tactical operation with real-time “God’s eye view” mapping.
You won’t get Smartsense on your next iPhone, but it’s not far away. It wasn’t so long ago that you would have thought someone had lost their mind if they said they were going to make a video with their cell phone.