# How is the GPS signal transmission time encoded in the GPS signal?

I am trying to really understand how GPS works, to be able to "explain it to my grandma" level of understanding.

One key aspect that I can't find an answer to is: how is the GPS signal transmission time, as registered by the on-board atomic clock, encoded in the GPS signal?

I would not imagine it is in the Navigation Message which has only a rate of 50bit/s which is surely not enough to achieve any type of spatial resolution.

• Welcome to Stack Exchange! You've added the gps tag, click it to see related questions and answers that may be helpful.
– uhoh
Commented Aug 14, 2022 at 5:42
• There is no easy and short description of this theme. A book about GPS needs 7 pages and 5 complex figures. Unfortunately there is no Wikipedia entry about this theme.
– Uwe
Commented Aug 14, 2022 at 9:29
• You can probably find the relevant info on Navipedia. gssc.esa.int/navipedia/index.php/GPS_Navigation_Message Commented Aug 14, 2022 at 10:22
• When comparing 50bit/s to the required timing precision, you miss one important fact: It doesn't matter how long a 'beep' is - the import thing is, how precisely can you detect when it starts? Commented Aug 14, 2022 at 16:27
• Not an expert here (hence, not an "answer") but aren't the PRN codes and even the carrier waves synchronized to the satellite's atomic clocks? I.E., if you are decoding the signal at all, then your local clock already is ticking in sync with the satellite's clock. If that's true, then in theory you should only need to hear the "clock offset" one time, and you should be able to know the value of the satellite's clock from that point onward. Commented Aug 15, 2022 at 0:20