I don't think those requirements are hard. You can build a system that works in three cases 1) GPS is available full time 2) GPS is available intermittently. 3) there is not GPS system, world war III has destroyed it.
I think what you want is a system that is failure tolerant and can make use of the best available source of timing and degrade performance gracefully. And you need this is be automatic with the only control maybe being a status LED that shows free/yellow/red Each system has a GPS receiver that disciplines a crystal oscillator. This oscillator is used for timing. I think it's clear that this handles cases #1 and #2. Then use you Blue Tooth or whatever other short distance communications system you have to support an IP network. TCP/IP over zBlueTooth works well and is a standard now. Using this you can configure a NTP based network of "peers". Each of the above systems, when they are close enough will share timing with the other peers. The system runs on a "consensus time". If one or more systems has access to GPS those system will supply timing to any other system in range of the blue tooth. If there is no GPS at all the systems will form what they call an "orphan network" and will remain synced to each other untill some outside source of time connects and puts them all back on GPS time. NTP is pretty good at handing the case where timing sources come on and off line and where network connects connect and then go away. It is very failure tolerant. What you'd have is a kind os graceful degradation. When GPS is visible to all units they are all "dead-on" and running well above you specs. If GPS is hidden (perhaps in an urban canyon or you happen to be inside a tunnel) the systems ail remain in spec for many hours or even days depending on how much money you spent on the crystal (or Rubidium) oscillators Finally if there is no GPS at all but several systems are within blue tooth range that can sync to each other at the few millisecond level. but because you did spend $$ on a god crystal will stay sync'd for hours even when out of bluetooth range with no GPS. The good thing is that you only need to integrate existing technology to make this happen. The software, hardware and all the parts are available. You'd not have to pay to advance the state of the art. You would have to balance things like crystal oscillator stability vs. power. Ovenized units suck up power. TCOXs use less power but maybe hours and not days of hold over time is enough. The LED's color depends on the estimated timing error, NTP is good at computing that based on if GPS is connected and working, the network status and so on. So it might be green for microsecond level, yellow for millisecond level error and red for "few seconds" level, flashing for no-sync On Tue, Jul 23, 2013 at 7:55 AM, Jim Lux <jim...@earthlink.net> wrote: > It *is* an interesting problem.. It's sort of weird, though, as I write the > requirements.. > > High frequency accuracy (1E-10, 1E-11) ideally.. or high stabiity over 1-100 > seconds, with a way to get "knowledge". > > But relatively low timing accuracy: 1-3 milliseconds over the same 100 > second interval (1E-5) > > Often you have a time requirement that is commensurate with the frequency > requirement. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.