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0 pointsRobotbeat3y ago0 comments

Actually in exactly the same way. The nice thing about phased arrays is they steer electronically, so you can aim them extremely fast and compensate for any movement. That's how 5G works and that's also how Starlink on moving vehicles works.

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walrus013y ago

a flat panel phased array still has considerably more gain in the direction it's aimed, vs a randomly oriented omnidirectional (physical) antenna in a phone. i can guarantee you starlink doesn't work well when the array elements aren't aimed correctly in the general direction of where the satellites are.

the path loss and need for more gain at LEO satellite distance is considerably greater than talking about terrestrial cellphone networks in bands <2500 MHz.

RobotbeatOP3y ago

5G phones already use a flat panel phased array, just with fewer elements (and less gain, but that can be compensated by using a lot more elements on the satellite side and by operating at much lower bandwidth). And yes, I understand the difference between lower frequencies and higher. 5G can also use lower frequencies but the main bandwidth advantage (over LTE/etc) is in the higher frequency, the mm-wave, roughly 25-50GHz, a frequency band that overlaps that used by the Starlink phased arrays.

lxgr3y ago

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.)

gsich3y ago

>the mm-wave, roughly 25-50GHz, a frequency band that overlaps that used by the Starlink phased arrays.

And those require line of sight or be very close to them to achieve high speeds. That's why there is little incentive to provide them.

ackbar033y ago

Sorry to interject between two people who clearly know what their talking about.

I've been reading books on satellite communications and have some idea of all the technical terms you guys mentioned as well as relationship between 5g and phase array etc.

Where do you get your knowledge from regarding these issues in such detail? Do you guys work in this area? Are there any reading materials you recommend in this field that are relevant and updated to keep track of these tech?

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