TV and cellphone signals may provide GPS back-up

location based services

Soldiers may no longer need to rely on satellite navigation to pinpoint themselves or targets, if a new US military research project succeeds.
The Robust Surface Navigation programme, funded by the US government's Defense Advanced Research Projects Agency (DARPA), aims to extract accurate positioning information from "signals of opportunity". These may include television and cellphone transmissions, if satellite signals are unavailable.
Global Positioning System (GPS) receivers pinpoint their location by measuring precisely how long signals from several satellites take to reach them. But these signals can be difficult to receive in built-up urban areas, or inside buildings, and can also be jammed by an enemy.
To overcome this problem, the Robust Surface Navigation project is intended to replace missing GPS information by using other incidental signals to calculate location.
TV guide
"Television transmissions from terrestrial transmitters with relatively high power could be used like GPS," says Bart Ferrell, programme manager for precision navigation at the Boeing Phantom Works in Missouri, US. The company has been awarded one of two DARPA contracts to develop this technology.
Other potential sources include signals from cellphone towers, communication satellites, Russia's GLONASS navigation system and Europe's forthcoming Galileo navigation satellites.
Boeing has enlisted help from a Silicon Valley company called Rosom, which has already developed location systems based on television transmission. "With television, it's quite similar to GPS, if you know the location of the emitter and the time of emission," says Rosom's Jon Metzler.
Mixed signals
Rosom's system monitors periodic image-synchronisation elements of television signals to determine the transit time, allowing a receiver to calculate its position relative to the transmitter. The approach works with both digital and analogue television signals.
The first goal is to "assess what signals are available and which would be suitable for use in this system", Ferrell says. If the results are promising, the next stage will be to develop and test a prototype that would automatically choose from available local signals, select those most suitable for use, and calculate its position.
The long-term goal is to develop a new-generation of compact satellite receiver that can switch to local signals when needed.