Hi > On Mar 12, 2018, at 9:54 AM, Peter Reilley <preilley_...@comcast.net> wrote: > > Reading this paper makes one wonder if there are other improvements that > can be made to increase the robustness against jamming, software bugs, solar > events > or hostile attacks to the GPS system > > A suggestion: > > Create a parallel terrestrial GPS system. This would be a system of GPS > transmitters > mounted on cell phone towers. They would masquerade as GPS satellites (but > unusually low > and stationary). It would be ideal if they could have unique identifiers > and be integrated > into the GPS receivers timing and location calculations as any other > satellite. If there > is no room in the existing ID space then the terrestrial node would take over > the ID of > a satellite that is below the horizon. When the satellite reappeared the > terrestrial node > would simply take over a different below the horizon satellite's ID.
If it takes over the ID of an existing satellite, it also takes over the ephemeris and almanac information for that satellite. There is only a *very* finite amount of “data space” in the transmissions for that stuff. Simple answer - it would have to be an independent system. You need a unique almanac for it and unique ID numbers for the stations. > > Such a system could be built out as needed. It may not require any > alterations to existing > GPS receivers. It would not disrupt the operation of the existing satellite > constellation. > It would protect against attacks on the satellite system by either a human > enemy or a natural > one, the sun. > > Each node need not contain an accurate time source like a cesium standard. > They could > derive timing from a neighbor. If you do that, you make your backup system *very* open to attack. Spoof one and all the rest tracking it follow …. > Cesium reference nodes would be periodically placed around the > system. Timing derivations would be more accurate since the distances would > be much closer and > thereby encounter less environmental disturbance. Only if you distributed a *lot* of very good clocks *and* monitored them the same way as you monitor a GPS sat. Since they are all low to the ground, that would take a *very* different setup for monitoring. > > GPSDO units would prefer such close and stationary references vs distant > moving ones. Ummm …… errrrr ….. not so much. A GPSDO simply locks up to “all in view”. Unless you tell it to reject a sat, it uses it. To the degree that there is a rejection process (TRAIM), it looks at the group solution. If the “majority time” looks ok … off we go. ====== The idea of using cell tower signals for timing was at the heart of a couple of systems. The gotcha turned out to be that not all tower operators are created equal. Unless you have direct control over the gear ( = you own and operate it) there is no way to keep it “correct”. If you are going out to buy up a bunch of cell tower space, that is quite expensive. There are other *much* less expensive ways to create an independent system. In fact, we already have several alternate systems (Glonass and Galileo and BeiDou). They are already available (or will soon be available) in the data stream of a lot of GPS modules. Working out what to do with them is less complex than adding a “something else” system. Bob > > Pete. > > On 3/11/2018 5:26 PM, Magnus Danielson wrote: >> Hi Andy, >> >> On 03/11/2018 08:40 PM, Andy Backus wrote: >>> Thank you for your posting, Magnus. >>> >>> Your information is very interesting. >>> >>> Do you mind saying a little more about the "incident" on 26-JAN-2016? I >>> don't find reference to it in the link. And my own TE plot for then shows >>> no obvious disturbance. >>> >>> Thanks. >> Please read this: >> https://rubidium.dyndns.org/~magnus/papers/GPSincidentA6.pdf >> >> In short, the GPS to UTC time correction polynomial got screwed up. >> >> I got email from NASA, ended up having to call NASA HQ and got invited >> to Washington DC to present before the US PNT advisory board. >> >> Among the stranger things I've done in my life, but it was fun. >> >> Cheers, >> Magnus >> _______________________________________________ >> time-nuts mailing list -- firstname.lastname@example.org >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- email@example.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- firstname.lastname@example.org To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.