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I can see a satellite transmitting powerfully to reach a phone on the ground. But how are they going to pick up the transmission from a phone, which is incredi

I can see a satellite transmitting powerfully to reach a phone on the ground. But how are they going to pick up the transmission from a phone, which is incredibly low power and designed to be picked up from a maximum range of 70km. The Wikipedia article also says that timing considerations give a maximum range of 35km. Which is a lot lower than the 2,000km of Low Earth Orbit.

pinkfoot 7y ago
No, the same Wikipedia says GSM in extended range can support calls up to 120km.
- lb1lf 7y ago
  That it can, but IIRC it does so by relaxing the timing constraints and halving the number of slots in each channel. Still leaves them with the interesting problem of the satellite necessarily seeing a lot of handsets at the same time; methinks even if all other engineering issues were magically resolved, they'd run out of bandwidth real fast. (Not to mention the regulatory hurdles.)
ellisv 7y ago
> I can see a satellite transmitting powerfully to reach a phone on the ground. Yes, wouldn’t this just be like GPS? I’m also not convinced the phone->satellite is practical/feasible.
- alienalp 7y ago
  For GPS, satellites just broadcast same signal for everybody. It won't be feasible to send that powerful signal for just a costumer cell phone and it is about signal strength. They transmit tiny amount of data and it is not required your phone to able to receive all the data.
bluesign 7y ago
‘Calls only’ maybe possible, as we have huge bandwidth to base station and calls require really small bandwidth. Also afaik 2g doesnt have strict timing requirements.
101404 7y ago
Low Earth Orbit has an altitude UP TO 2000 km. The ISS for example is at about 400 km. If they placed their sat at 100 km (right at the limits of "space") maybe it would be possible to be in range of a cell phone.
- bucket2015 7y ago
  I don't think it's feasible to have a satellite orbit at 100 km and not fall out of the sky in a few days due to atmospheric drag. Even ISS at 300-400 km orbit has to be regularly reboosted because it's continuously losing altitude.

pinkfoot 7y ago

No, the same Wikipedia says GSM in extended range can support calls up to 120km.

lb1lf 7y ago
That it can, but IIRC it does so by relaxing the timing constraints and halving the number of slots in each channel. Still leaves them with the interesting problem of the satellite necessarily seeing a lot of handsets at the same time; methinks even if all other engineering issues were magically resolved, they'd run out of bandwidth real fast. (Not to mention the regulatory hurdles.)

ellisv 7y ago

> I can see a satellite transmitting powerfully to reach a phone on the ground. Yes, wouldn’t this just be like GPS? I’m also not convinced the phone->satellite is practical/feasible.

alienalp 7y ago
For GPS, satellites just broadcast same signal for everybody. It won't be feasible to send that powerful signal for just a costumer cell phone and it is about signal strength. They transmit tiny amount of data and it is not required your phone to able to receive all the data.

bluesign 7y ago

‘Calls only’ maybe possible, as we have huge bandwidth to base station and calls require really small bandwidth. Also afaik 2g doesnt have strict timing requirements.

101404 7y ago

Low Earth Orbit has an altitude UP TO 2000 km. The ISS for example is at about 400 km. If they placed their sat at 100 km (right at the limits of "space") maybe it would be possible to be in range of a cell phone.

bucket2015 7y ago
I don't think it's feasible to have a satellite orbit at 100 km and not fall out of the sky in a few days due to atmospheric drag. Even ISS at 300-400 km orbit has to be regularly reboosted because it's continuously losing altitude.