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GPS (2022)

ciechanow.ski

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Re: GPS (2022)

#31

Post by 7373737373 »

londons_explore wrote: post #22

By the way... Gold codes (this article calls them chipping codes) can be used to solve a lot of engineering problems where you need to synchronise two things. Eg. "I want to transmit an infrared signal and receive it somewhere else, but the signal isn't bright enough to detect! - no worries, use a 1023 bit gold code, and suddenly you get a 30x effective brightness increase, and perfect time sync, with no hardware cha…

There is a nice series of posts about them here: https://natronics.github.io/blag/2014/gps-prn/

Re: GPS (2022)

#32

Post by nixpulvis »

Can someone help me understand why, in the last two interactive figures, the "Difference of Summed Areas" signal leads the "Actual Satellite X Source Data" signal?

It seems as though the receiver signal is almost predicting the source data bit changes, which should not be the case.

Re: GPS (2022)

#33

Post by MichaelZuo »

> One of those additional complexities worth mentioning is the velocity of a satellite relative to the observer on Earth. Due to Doppler effect this changes the frequency of the signal as seen by the receiver. To correctly acquire the signal the device has to tune in on both the time offset and the appropriate frequency.

Does anyone know of a diagram that shows this?

Re: GPS (2022)

#34

Post by User23 »

sillysaurusx wrote: post #12
User23 wrote: post #10

GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…

If you do run across the paper, please post it. It sounds quite interesting.

Found it![1]

[1] https://apps.dtic.mil/sti/pdfs/ADA516975.pdf

Re: GPS (2022)

#35

Post by User23 »

User23 wrote: post #10

GPS satellites don’t correct for relativistic effects. They just set the Earth as the preferred frame, which is a great choice for a terrestrial positioning system. I’ll see if I can find the paper it’s quite interesting. Edit: I can't find the specific paper I'm thinking of. It's one that discusses how when other orbiting bodies want to use GPS they have to make a bunch of complex corrections that terrestrial users…

Too late to edit, but here is the paper that I meant: https://apps.dtic.mil/sti/pdfs/ADA516975.pdf. At a mere 12 pages it's an easy read. Needless to say, the military is almost certainly the highest quality source for info on the actual engineering practicalities of GPS.

First sentence of the introduction:

  The Operational Control System (OCS) of the Global Positioning System (GPS) does not include the rigorous transformations between coordinate systems that Einstein's general theory of relativity would seem to require
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