[time-nuts] GPS 18 behavior

[Tom Van Baak]

> For what it's worth, the application is a radar that detects buried 
> victims in disaster rubble, so the data we are collecting is basically 
> heartbeats and breathing.  the "when was the data taken" is a "where 
> were we when the data was collected" need.  The "sync" requirement comes 
> from being able to find the same heartbeat in multiple data streams.

Jim,

That's a fascinating application. Ok, one last comment then. As much as GPS is an obvious solution, did you consider the use of multiple homebrew timing pulse pseudolites instead? If one placed a couple of them around the vicinity of the disaster area you could triangulate for your ranging and timing information. Since the transmitters would then be less than 1 km away instead of more than 20,000 km away, you avoid all the limitations of GPS. Moreover, the solution would work if GPS were functional or not, something perhaps important for a disaster situation. Using some clever waveform (like what Loran-C did) you could better penetrate into all sorts of rubble and overcome multi-path at the same time.

I'm pretty sure there are a number of papers on local ranging and navigation based on these technique (e.g., UAV, robotics). The advantage is that it's a local solution, it can work indoors, underground, underwater, even on the moon; in general, it doesn't rely on a functioning GPS constellation with its inherently weak or jammable signals.

Of course all this from the guy who once tried to use seismic sensors and GPSDO to triangulate moles in his backyard...

/tvb