4 ms·

Seconded. The article and these comments leave me wanting more!

jandrese 8y ago
What I know about this comes from some training I took for my job. The training came from the equipment vendor, but the instructor was also an operator so he knew the ins and outs of the system. There is a lot to cover, from calculating link budgets, scramble codes (related to anti-jam), waveforms, pointing a dish, calculating frequencies, reading channel allocation docs, tradeoffs of different frequency bands, etc... However, the basics are pretty basic. You modulate a series of bits onto a carrier at a specific frequency and radiate it at a specific point in the sky. The transponder on the satellite amplifies the signal, shifts it a fixed number of Mhz, and retransmits it back towards the Earth. There are some satellites that act like flying routers and actually decode the packet back into bits before re-encoding it for transport, but generally the added complexity has made this approach unpopular. One constellation that does this is Iridium, because it then forwards packets between satellites until it can be downlinked to the ground.
- wglb 8y ago
  Routing satellite to satellite sounds like a complex routing problem, no? Or are such routes computed before signal goes up?
  - 420codebro 8y ago
    One can build orbital models to predict link fade and anticipate when a given point to point link will die.
  - rtkwe 8y ago
    Not particularly. They're all in fixed known orbits so each satellite would know at any given time where all the other satellites in it's constellation will be so it can know what satellites will have the best signal between it and the downlink. With that all you really need is for the phones to ping the satellites every couple minutes while on to update the what satellites are over head of phone X. (You could even be clever and cheat a little by figuring out the rough coordinates of each handset and then figure out roughly what satellites would be near overhead too since handsets generally don't move very quickly.)

What I know about this comes from some training I took for my job. The training came from the equipment vendor, but the instructor was also an operator so he knew the ins and outs of the system. There is a lot to cover, from calculating link budgets, scramble codes (related to anti-jam), waveforms, pointing a dish, calculating frequencies, reading channel allocation docs, tradeoffs of different frequency bands, etc... However, the basics are pretty basic. You modulate a series of bits onto a carrier at a specific frequency and radiate it at a specific point in the sky. The transponder on the satellite amplifies the signal, shifts it a fixed number of Mhz, and retransmits it back towards the Earth. There are some satellites that act like flying routers and actually decode the packet back into bits before re-encoding it for transport, but generally the added complexity has made this approach unpopular. One constellation that does this is Iridium, because it then forwards packets between satellites until it can be downlinked to the ground.

wglb 8y ago
Routing satellite to satellite sounds like a complex routing problem, no? Or are such routes computed before signal goes up?
- 420codebro 8y ago
  One can build orbital models to predict link fade and anticipate when a given point to point link will die.
- rtkwe 8y ago
  Not particularly. They're all in fixed known orbits so each satellite would know at any given time where all the other satellites in it's constellation will be so it can know what satellites will have the best signal between it and the downlink. With that all you really need is for the phones to ping the satellites every couple minutes while on to update the what satellites are over head of phone X. (You could even be clever and cheat a little by figuring out the rough coordinates of each handset and then figure out roughly what satellites would be near overhead too since handsets generally don't move very quickly.)