2 ms·
For non-assisted GPS, the GPS device needs to download orbital information from the satellite directly when first powered on - with only ~50 bits/s of bandwidth
by drivebycomment 7y ago
For non-assisted GPS, the GPS device needs to download orbital information from the satellite directly when first powered on - with only ~50 bits/s of bandwidth, it can take a while - minutes to tens of minutes. With Assisted GPS, the GPS device can download the satellite orbital information and almanac directly from AGPS server (e.g. cell phone tower), usually at much higher bandwidth - as those local, always-running servers can constantly download and cache all satellite information.
- lucb1e 7y agoThe sats don't change orbit every few hours though, also without AGPS you usually can use the ephemerides from last time you used it. This is fun to observe when you buy a new phone and don't connect network yet, it takes a good while to find any satellites and finally find a fix. Then after cycling GPS, it finds it almost instantly.
- j1elo 7y agoThen how do the classic driving GPS devices work? I'm thinking here good old TomTom models, mine must have like what, 10 years? It typically claimed (not using it much lately) to have GPS reception after maybe 20 or 30 seconds since power up. I believe it cached the position of the GPS satellites, or something similar... could that be it?