4 ms·

Not the OP. We have to clarify what you mean by "support multiple simultaneous beams". The SL receiver is half-duplex, so it can only send or receive at any gi

Not the OP. We have to clarify what you mean by "support multiple simultaneous beams". The SL receiver is half-duplex, so it can only send or receive at any given time, and, in theory anyway, it uses beamforming to communicate with just one bird at a time (if it couldn't beamform to within sufficient tolerance, then that would be an FCC no-no.) There's no theoretical reason, AFAIK, that it couldn't rapidly switch between birds, but the actual feasibility of that depends on terminal firmware, the ground network being setup to handle that, the arc between two birds, and whether or not the antenna's scan angle can encompass that arc. The primary difference between the ground terminals and the antennas in space is the amount of power passing through them, but also their sophistication (primarily the beamforming capability.)

jcims 6y ago
Ah, was actually wondering about the duplex situation as well, thanks for answering a bonus question :) Re: multiple beams I'm thinking about the ability to split the array up into 'subarrays' with independent beamforming capability. Probably doesn't work for reasons above my head but I was just trying to think about the mechanics of the transition between satellites. Having a chameleon mode with one eye pointed at one satellite and another pointed at the next seems like one way to ensure a seamless transfer. But realistically the dish probably knows where to steer next within an approximation of its beamwidth, so it probably just flips like a channel. Thanks for the answers!
- matmatmatmat 6y ago
  Ah, OK, I understand better. Yes, in theory, a terminal with a phased array antenna can be built to emit more than one beam simultaneously and steer them independently. Doing so is currently still costly in terms of research, electronics, and power, so it's unlikely that the SL terminal can do it. It would also require there to be a second PHY chip somewhere in the terminal, which would also drive up cost. Also, it's not really necessary. Satcom already requires nanosecond-level timing accuracy, so I would think their terminal can probably steer its beams with at most ms lag.
mNovak 6y ago
Do you have a reference for the half-duplex note? That would seem a waste given that they already have FDMA. Also most satcom applications are full duplex.
- matmatmatmat 6y ago
  https://twitter.com/TMFAssociates/status/1300438995843776514 https://twitter.com/TMFAssociates/status/1300438995843776514

jcims 6y ago

Ah, was actually wondering about the duplex situation as well, thanks for answering a bonus question :) Re: multiple beams I'm thinking about the ability to split the array up into 'subarrays' with independent beamforming capability. Probably doesn't work for reasons above my head but I was just trying to think about the mechanics of the transition between satellites. Having a chameleon mode with one eye pointed at one satellite and another pointed at the next seems like one way to ensure a seamless transfer. But realistically the dish probably knows where to steer next within an approximation of its beamwidth, so it probably just flips like a channel. Thanks for the answers!

matmatmatmat 6y ago
Ah, OK, I understand better. Yes, in theory, a terminal with a phased array antenna can be built to emit more than one beam simultaneously and steer them independently. Doing so is currently still costly in terms of research, electronics, and power, so it's unlikely that the SL terminal can do it. It would also require there to be a second PHY chip somewhere in the terminal, which would also drive up cost. Also, it's not really necessary. Satcom already requires nanosecond-level timing accuracy, so I would think their terminal can probably steer its beams with at most ms lag.

mNovak 6y ago

Do you have a reference for the half-duplex note? That would seem a waste given that they already have FDMA. Also most satcom applications are full duplex.

matmatmatmat 6y ago
https://twitter.com/TMFAssociates/status/1300438995843776514 https://twitter.com/TMFAssociates/status/1300438995843776514