Talk:Global Positioning System: Difference between revisions
Question about implementation detail: clock needed in receivers? |
a reply re implementation details |
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synchronously, with one digit coming every millisecond, and the receiver sees two sequences which have an offset of 3, then he knows that the signal from the one satellite travelled 3 (or 13, or 23...) milliseconds longer than from the other, without any need for a clock. |
synchronously, with one digit coming every millisecond, and the receiver sees two sequences which have an offset of 3, then he knows that the signal from the one satellite travelled 3 (or 13, or 23...) milliseconds longer than from the other, without any need for a clock. |
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But I don't know the implementation details. Do we have any experts here? [[user:AxelBoldt|AxelBoldt]] |
But I don't know the implementation details. Do we have any experts here? |
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[[user:AxelBoldt|AxelBoldt]] |
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Messages are typcally referenced against an on-board quartz crystal clock, which provided a timebase that all the others are compared to. The signal are individually weak, fading, full of interference -- comparing them directly with one another is harder than receiving them all independently, and comparing. Single channel receivers (now mostly obsolete) also had no other way of doing it. [[user:The Anome|The Anome]] |
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Revision as of 14:34, 7 April 2002
Was the "selective availability" actually turned off? when?
I don't know, that's what the article said :-) --AxelBoldt
May 2 2000
Yup, see http://www.ngs.noaa.gov/FGCS/info/sans_SA/
Should differential GPS be described here or on a separate page.
Anyone have a Code vs. Carrier Phase description?
I put some info about differential GPS (DGPS) here since it was just a little bit of stuff. If it grows larger we can later split it to a separate article. Right? --Tbackstr
Is it really necessary that the receivers have a clock with good short term accuracy? I thought that the signals from the satellites are such that by simply comparing them, the receiver can tell the time difference, without much of a clock. For instance, if all satellites send the sequence 12345678901234567890... synchronously, with one digit coming every millisecond, and the receiver sees two sequences which have an offset of 3, then he knows that the signal from the one satellite travelled 3 (or 13, or 23...) milliseconds longer than from the other, without any need for a clock.
But I don't know the implementation details. Do we have any experts here? AxelBoldt
Messages are typcally referenced against an on-board quartz crystal clock, which provided a timebase that all the others are compared to. The signal are individually weak, fading, full of interference -- comparing them directly with one another is harder than receiving them all independently, and comparing. Single channel receivers (now mostly obsolete) also had no other way of doing it. The Anome