Re:WiFi: “beamforming” only begins to describe it (2014)
by Robotbeat on Sunday April 05, 2020 @12:05PM
(#22786354)
Your point is a good one, and I don’t think you should get down-voted. I’ve seen many people appeal to Shannon’s law for SINGLE channel as an argument to why things like MIMO or Starlink are limited to low amounts of bandwidth. More channels is absolutely an important way to get around the “but there’s only so much bandwidth” argument, and by increasing number of channels (and increasing size of reciever and transmitter), you absolutely can just keep increasing throughput for the same frequency bandwidth allocation.
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Re:WiFi: “beamforming” only begins to describe it (2014)
by namibj on Sunday April 05, 2020 @01:08PM
(#22786809)
Thank you for the support.
The case of StarLink (in difference to (indoor) 802.11n/ac) won't give you more than polarization duplex (capped at 2x, in practice you'd get up to (iirc) ~30dB isolation) for any individual point-to-point connection. Yes, including the satellite <=> ground-facility "backhaul".
Theoretically it _should_ be possible to get like 10x bandwidth via spatial MIMO when using <3μm (likely <1μm) wavelengths, but that might require optical heterodyne detection to get the MIMO streams separated from another in the speckle pattern the atmosphere caused.
I'd like to read that paper about optical heterodyne detection spatial MIMO for the link to/from a satellite in an 200~1000km orbit.
Re:WiFi: “beamforming” only begins to describe it (2014)
by Robotbeat on Sunday April 05, 2020 @02:50PM
(#22787541)
One terminal (which has beamforming capability on both ends with hundreds of elements) can connect to multiple satellites with the same frequency band.
Re:WiFi: “beamforming” only begins to describe it (2014)
by namibj on Sunday April 05, 2020 @03:46PM
(#22788038)
Oh sure, that's a massive effect. It's just that for a single p2p link, there'd be at most minimal benefit from MIMO. As soon as there are either multiple satellites or multiple user terminals (or dare both), i'd expect nothing worse than the bandwidth scaling with the square root of the antenna count.