Re:Starlink Maritime
by lxgr on Friday July 08, 2022 @07:18PM
(#32029156)
5G and Wi-Fi don't use MIMO for terminal side spatial multiplexing though, as far as I know.
In MU-MIMO (available in newer versions of 802.11, for example), the base station transmits to and receives from multiple mobile devices that are located at different spatial angles. But in the mobile devices themselves, the gain from that steering is not high/fast enough to allow for multiple (relatively) fixed base stations in the same space.
In other words, a stationary/slowly moving antenna array on one side of the channel can target individual moving users due to angles changing slowly over time and the antenna array being quite sophisticated, but moving users with smaller antennas and angles varying over a much shorter period of time can't do the same.
Think about it: From a satellite's point of view, your angle varies much more slowly and predictably than the other way around, e.g. when taking a turn in a car or on a rocking boat (that's why high-gain antennas usually have to be gimbal-stabilized).
Starlink's orders of magnitude higher bandwidth, as far as I can tell, stems from requiring slowly and predictably changing angles on both sides, giving it m:n (relatively) independent spatial channels rather than just 1:n as is common for a one-sided omnidirectional approach. (That's also why Iridium and Globalstar wouldn't be able to scale significantly better in low-gain mobile-client applications by just launching more satellites.)
In MU-MIMO (available in newer versions of 802.11, for example), the base station transmits to and receives from multiple mobile devices that are located at different spatial angles. But in the mobile devices themselves, the gain from that steering is not high/fast enough to allow for multiple (relatively) fixed base stations in the same space.
In other words, a stationary/slowly moving antenna array on one side of the channel can target individual moving users due to angles changing slowly over time and the antenna array being quite sophisticated, but moving users with smaller antennas and angles varying over a much shorter period of time can't do the same.
Think about it: From a satellite's point of view, your angle varies much more slowly and predictably than the other way around, e.g. when taking a turn in a car or on a rocking boat (that's why high-gain antennas usually have to be gimbal-stabilized).
Starlink's orders of magnitude higher bandwidth, as far as I can tell, stems from requiring slowly and predictably changing angles on both sides, giving it m:n (relatively) independent spatial channels rather than just 1:n as is common for a one-sided omnidirectional approach. (That's also why Iridium and Globalstar wouldn't be able to scale significantly better in low-gain mobile-client applications by just launching more satellites.)