19 ms·

Another company that is doing 10Gbit/s. Considering a single Starlink satellite will have 4 laser links plus has a total radio bandwidth of about 20Gbit/s, this

Another company that is doing 10Gbit/s. Considering a single Starlink satellite will have 4 laser links plus has a total radio bandwidth of about 20Gbit/s, this is sufficient. https://www.reddit.com/r/Starlink/comments/en7dtx/comment/fdx379d?utm_source=share&utm_medium=web2x https://www.reddit.com/r/Starlink/comments/en7dtx/comment/fd... ...however, this is nowhere near any fundamental limit on optical transmission. SpaceX is operating around 20-40GHz radios, and let’s just say a bandwidth 1% of the frequency with a SNR of 1, giving them a bit rate per channel of 200-400Megabits/s. The same calculation with near IR optical (which is optimistic obviously) gives 3 Petahertz frequency, 30THz bandwidth, and 30terabits/s/channel. So optical is nowhere near any kind of fundamental limit, unlike radio which needs many channels (ie phased array, MIMO, spatial multiplexing generally, etc) to saturate the bandwidth of the satellite bus. (Also, note that broadband users have a capacity factor of like 1-2%, so on average 20Gbps can give service to like 10,000 subscribers per viewable satellite using 100Mbps peak service.)

grkvlt 6y ago
3 PHz is way into the UV part of EM, near IR is about 30 THz so 300 Gbps max on a NIR channel using your numbers?
- Robotbeat 6y ago
  Hah, oops. 3e-15s period, not 3e-16s. You’re right. What’s an order of magnitude between friends? (Won't let me edit the original post.)
- Robotbeat 6y ago
  So you are correct, of course. I meant to use 1000nm, not 100nm. However, the thing about being in space is you actually COULD use vacuum UV (including 100nm) which doesn’t propagate in fiber and is even blocked by air. Not only does that have the bandwidth advantage but also allows even smaller apertures (or greater gain for the same aperture). Of course, vacuum UV transceivers aren’t really available (you can get coherent UV lasers down to 126nm) but in the long term it is possible.

grkvlt 6y ago

3 PHz is way into the UV part of EM, near IR is about 30 THz so 300 Gbps max on a NIR channel using your numbers?

Robotbeat 6y ago
Hah, oops. 3e-15s period, not 3e-16s. You’re right. What’s an order of magnitude between friends? (Won't let me edit the original post.)
Robotbeat 6y ago
So you are correct, of course. I meant to use 1000nm, not 100nm. However, the thing about being in space is you actually COULD use vacuum UV (including 100nm) which doesn’t propagate in fiber and is even blocked by air. Not only does that have the bandwidth advantage but also allows even smaller apertures (or greater gain for the same aperture). Of course, vacuum UV transceivers aren’t really available (you can get coherent UV lasers down to 126nm) but in the long term it is possible.