9 ms·

> The mosaic-X5 module is an ultra-low power, multi-band, multi-constellation GNSS receiver capable of delivering centimeter-level precision at high update rate

> The mosaic-X5 module is an ultra-low power, multi-band, multi-constellation GNSS receiver capable of delivering centimeter-level precision at high update rates. Dang. I was under the impression that GPS receivers this precise were available to the public. I participated in a rocketry project in 2015 and that's what we were told anyway.

defrost 3y ago
They've been available "to the public" (ie. non military) for 30 odd years .. it's just the components have been expensive and have required "some technical expertise" to glue it all together. The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcasts the "drift" in its fixed position as reported by the satellites - that's the error signal - deduct that and you've got improved position. We did this as part of geophysical surveying from aircraft and other moving platforms in the early 90s - recording the base station signal and merging that with other postfix error correction procedures in post processing. The military had that for mobile battlefield units to improve accuracy, fixed ground base stations broadcasting fixes to missiles. No real time updates in geophysics as the first priority was to minimise magnetic, electromagnetic, radiometric, gravitational, etc "noise" as much as possible - keep generation sources to a minimum and shield them as much as possible within the craft.
- dilyevsky 3y ago
  > They've been available "to the public" (ie. non military) for 30 odd years .. it's just the components have been expensive and have required "some technical expertise" to glue it all together. That is not what gps.gov says - only since 2014 https://www.gps.gov/systems/gps/modernization/civilsignals/#L2C https://www.gps.gov/systems/gps/modernization/civilsignals/#...
  - defrost 3y ago
    This: https://learn.sparkfun.com/tutorials/what-is-gps-rtk https://learn.sparkfun.com/tutorials/what-is-gps-rtk base + roving receiver pairs, has always been an option for 30 odd years - it's what gives the increased accuracy. L2C achieves ionospheric (and other) correction by another "dual" approach - dual frequencies, this has only recently been available. All the same, as I stated, non US military, non US companies have been using twin receivers to improve US GPS accuracy for 30 odd years. It was used here: https://www.mrd.gov.fj/index.php/31-products/58-regional-airborne-magnetic-and-radiometric-data https://www.mrd.gov.fj/index.php/31-products/58-regional-air... for example, 26 years ago.
- tivert 3y ago
  > The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcasts the "drift" in its fixed position as reported by the satellites - that's the error signal - deduct that and you've got improved position. https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS > The military had that for mobile battlefield units to improve accuracy, fixed ground base stations broadcasting fixes to missiles. Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. My understanding is the military has always had access to multiple GPS frequencies, which allow it to significantly reduce certain sources of error that single-frequency civilian units are subject to.
  - defrost 3y ago
    > Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. It doesn't require the cooperation of "the enemy" - one side alone can have a mobile firing control station which parks up (assumes a fixed position) and broadcasts a DGPS signal in addition to other CnC comms to missiles that it fires and controls. > My understanding is the military has always had access to multiple GPS frequencies, They've also planned for continued functioning as best possible in case of full and|or partial loss of GPS frequencies. To recap, there's always been a coarse L1 GPS signal - that was delibrately made worse until 2000 by the addition of a keyed random clock error that required a daily key to revert (Differential GPS could fix that for anybody, the US Coast Guard broadcast a DGPS signal to "fix" that), there's always been a second L2 frequency that dual frequency users with both the coarse L1 daily key and the additional L2 key could use to improve accuracy with dual frequency tricks .. and, again, Differential GPS could improve that even more (by eliminating ionospheric errors, etc) - by the magic of Kalman Filters. There's a history of DGPS use here: https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS It's mainly focused on civilian (and US Coast Guard who apparently weren't "military enough" or something <shrug>) efforts to get military grade GPS via their own DGPS adventures ... but it was also the case that even the US military with dual channels and all the keys to enable real time reversal of broadcast errors could also benefit from increased accuracy via local theatre broadcast DGPS. Do I have sources for the US military use of DGPS in the late 1980s and 1990s? As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work.
dilyevsky 3y ago
In 2014 they started broadcasting L2C signal which improved civilian precision to basically military level[0] There is also preproduction L5 now which gives you cm level precision [0] - https://www.gps.gov/systems/gps/modernization/civilsignals/#L2C https://www.gps.gov/systems/gps/modernization/civilsignals/#...
- londons_explore 3y ago
  Notable that the military encrypted code was also usable by civilians if you were happy to do 'codeless decoding'. Basically, you might not be able to decrypt the signal but it still contains useful timing information.
vikramkr 3y ago
Is this one that you quoted not available? That looks like a link to buy that recieiver in the parent comment, don't see anything about needing to be military or something else that would block it from being used for civilian use?
ddejohn 3y ago
weren't*

defrost 3y ago

They've been available "to the public" (ie. non military) for 30 odd years .. it's just the components have been expensive and have required "some technical expertise" to glue it all together. The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcasts the "drift" in its fixed position as reported by the satellites - that's the error signal - deduct that and you've got improved position. We did this as part of geophysical surveying from aircraft and other moving platforms in the early 90s - recording the base station signal and merging that with other postfix error correction procedures in post processing. The military had that for mobile battlefield units to improve accuracy, fixed ground base stations broadcasting fixes to missiles. No real time updates in geophysics as the first priority was to minimise magnetic, electromagnetic, radiometric, gravitational, etc "noise" as much as possible - keep generation sources to a minimum and shield them as much as possible within the craft.

dilyevsky 3y ago
> They've been available "to the public" (ie. non military) for 30 odd years .. it's just the components have been expensive and have required "some technical expertise" to glue it all together. That is not what gps.gov says - only since 2014 https://www.gps.gov/systems/gps/modernization/civilsignals/#L2C https://www.gps.gov/systems/gps/modernization/civilsignals/#...
- defrost 3y ago
  This: https://learn.sparkfun.com/tutorials/what-is-gps-rtk https://learn.sparkfun.com/tutorials/what-is-gps-rtk base + roving receiver pairs, has always been an option for 30 odd years - it's what gives the increased accuracy. L2C achieves ionospheric (and other) correction by another "dual" approach - dual frequencies, this has only recently been available. All the same, as I stated, non US military, non US companies have been using twin receivers to improve US GPS accuracy for 30 odd years. It was used here: https://www.mrd.gov.fj/index.php/31-products/58-regional-airborne-magnetic-and-radiometric-data https://www.mrd.gov.fj/index.php/31-products/58-regional-air... for example, 26 years ago.
tivert 3y ago
> The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcasts the "drift" in its fixed position as reported by the satellites - that's the error signal - deduct that and you've got improved position. https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS > The military had that for mobile battlefield units to improve accuracy, fixed ground base stations broadcasting fixes to missiles. Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. My understanding is the military has always had access to multiple GPS frequencies, which allow it to significantly reduce certain sources of error that single-frequency civilian units are subject to.
- defrost 3y ago
  > Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. It doesn't require the cooperation of "the enemy" - one side alone can have a mobile firing control station which parks up (assumes a fixed position) and broadcasts a DGPS signal in addition to other CnC comms to missiles that it fires and controls. > My understanding is the military has always had access to multiple GPS frequencies, They've also planned for continued functioning as best possible in case of full and|or partial loss of GPS frequencies. To recap, there's always been a coarse L1 GPS signal - that was delibrately made worse until 2000 by the addition of a keyed random clock error that required a daily key to revert (Differential GPS could fix that for anybody, the US Coast Guard broadcast a DGPS signal to "fix" that), there's always been a second L2 frequency that dual frequency users with both the coarse L1 daily key and the additional L2 key could use to improve accuracy with dual frequency tricks .. and, again, Differential GPS could improve that even more (by eliminating ionospheric errors, etc) - by the magic of Kalman Filters. There's a history of DGPS use here: https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS It's mainly focused on civilian (and US Coast Guard who apparently weren't "military enough" or something <shrug>) efforts to get military grade GPS via their own DGPS adventures ... but it was also the case that even the US military with dual channels and all the keys to enable real time reversal of broadcast errors could also benefit from increased accuracy via local theatre broadcast DGPS. Do I have sources for the US military use of DGPS in the late 1980s and 1990s? As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work.

dilyevsky 3y ago

In 2014 they started broadcasting L2C signal which improved civilian precision to basically military level[0] There is also preproduction L5 now which gives you cm level precision [0] - https://www.gps.gov/systems/gps/modernization/civilsignals/#L2C https://www.gps.gov/systems/gps/modernization/civilsignals/#...

londons_explore 3y ago
Notable that the military encrypted code was also usable by civilians if you were happy to do 'codeless decoding'. Basically, you might not be able to decrypt the signal but it still contains useful timing information.

vikramkr 3y ago

Is this one that you quoted not available? That looks like a link to buy that recieiver in the parent comment, don't see anything about needing to be military or something else that would block it from being used for civilian use?

ddejohn 3y ago

weren't*