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How does the paid system work? Do they broadcast more precise data in an encrypted format?
by tinco 10y ago
How does the paid system work? Do they broadcast more precise data in an encrypted format?
- nraynaud 10y agoI guess the ephemerides have their numbers truncated or noised in the clear version and more decimals in the encrypted version?
- grandalf 10y agoThis how GPS worked when there was a reduced-quality version for civilian use, so I think it's a likely guess.
- Matthias247 10y agoIt should be the same as with GPS. I can't remember the exact details since my study is quite some time ago. But in principal GPS (and most likely also Galileo) works by correlating in the incoming signal with a locally generated one. The transmitted sequences and basically look like noise in the spectrum. You can only decode them with their counterparts. For professional (and military use) other sequences are generated and transmitted in parallel (could be on other frequencies). These are longer and therefore allow decoding with a higher precision. But you have to be aware of the code to be able to use those signals. There some info written on the web, but for details you need to be aware of lots of signal theory: https://en.wikipedia.org/wiki/GPS_signals https://en.wikipedia.org/wiki/GPS_signals http://www.navipedia.net/index.php/Correlators http://www.navipedia.net/index.php/Correlators
- rconti 10y agoI think the assistance provided by DGPS goes down as your distance from the correction-factor transmitter increases. Likely it's an encrypted message from the satellites themselves.
- Matthias247 10y agoI did not meant DGPS. The satellites themselfes transmit longer sequences for the "professional" users which allow for a higher precison through the correlation process.