Does anyone have a good physical intuitive explanation for why laser and radar data bandwidth to space are such huge pipes?
I have always been amazed at how satellites quote bandwidths on the order of Tb/s, when I don't fundamentally see how they're so different from gigabit fiber, copper, etc. You've still got some oscillation going on and a receiver that has to "decode" it just the same.
Is there a physically intuitive way to understand why the bandwidth of these methods is so great?
Shannon limit says nothing about frequency. It's about bandwidth. You can have just as much sodium available at lower frequencies than higher, and in fact, it's usually preferable.
The point being that people are discussing very high microwave frequencies Here. There is still a ton of spectrum available around 10-25GHz. You don't need 40+ to get that.
I don't think it is quite that high. Maybe on the order of 20 Gb/s.
> Each satellite in the SpaceX System provides aggregate downlink capacity to users ranging from 17 to 23 Gbps, depending on the gain of the user terminal involved. Assuming an average of 20 Gbps, the 1600 satellites in the Initial Deployment would have a total aggregate capacity of 32 Tbps.
They have a couple of GHz of bandwidth on the satellites for each of the user downlinks/ground station uplinks, and maybe a GHz for the user uplinks/ground station downlinks, operating in the Ku (12-18 GHz) and Ku (27-40 GHz) bands (requested frequencies on page 8 of the linked paper.)
It's usually a straight dead shot. With optical fiber and any land based radio, there is always obstructions to bend around, physical loses, ground clutter. Basically signal to noise is way higher with line of sight.
Higher SNR means lower bit error rate means deeper modulation (cutting edge is like 65536-QAM and maybe higher). Noisy channel coding theorem and all that.
I have always been amazed at how satellites quote bandwidths on the order of Tb/s, when I don't fundamentally see how they're so different from gigabit fiber, copper, etc. You've still got some oscillation going on and a receiver that has to "decode" it just the same.
Is there a physically intuitive way to understand why the bandwidth of these methods is so great?