[lxgr]

They didn't circumvent phone antennas being largely omnidirectional (unlike VSAT or phased arrays, which are highly directional) and as a result having much lower gain, they just work with it, just like Iridium, Globalstar, Inmarsat, Thuraya, and all the other early players in what's now called "direct to device".

The market is as bimodal as ever on the device side: On one side, you have small, battery-powered, (mostly) omnidirectional device antenna, portable devices that mainly operate in the L-band, which works much better in these conditions; on the other side, you have highly sophisticated, steered, high power (dozens of watts) antenna arrays operating in the Ku or Ka band.

On the satellite side, both can be served by the same satellites, as has been the case for e.g. Inmarsat's I-6 series and Starlink's direct-to-cell capable satellites (I believe these all include Ku-band coverage as well).

[piltdownman]

Well they've circumvented the need for dedicated hardware to achieve NTN on unmodified UE, ahead of any such implementation in the 3GPP specs. The incumbents all rely on dedicated proprietary platforms - not an off-the-shelf Android SoC smartphone which represents the target-device in the developing world

Traditional 5G UEs are inherently size-bound in terms of supporting device-side beamforming at any performant level, so you're limiting the Starlink style Ku-band spectrum sharing through spatial multiplexing afforded by their directional arrays. No argument there.

ASTS are tricking a NTN connection by fooling an unmodified 5G UE into thinking it's connecting to a terrestrial gNodeB, and then handing it off using bent-pipe architecture to the various terrestrial serving gateways. They claim to have flipped the dependency to allow their proprietary phased array satellites to do the heavy Tx/Rx lifting, and have some Doppler Compensation secret sauce to fix the issues on the terrestrial side.

[amluto]

I suspect that the lack of ability to form nulls in the beam is as big or even a bigger limitation than the reduction in gain when going from a big array to a phone.

The SNR in Shannon’s Law has a log in front of it, but spectrum reuse is more or less linear. If there are five visible satellites and I can null out four of them, then I can receive from and transmit to the fifth without substantial interference. (I’m not saying this is easy! Contemplate how many WiFi generations have had MIMO and how limited it still is.)

So I believe that it’s comparatively straightforward to demonstrate a shiny new direct-to-cell system with a single phone on a stage, but achieving usefully large aggregate bandwidth in a dense area will be more challenging.

FWIW the problem with Iridium, historically anyway, was that available bandwidth was very low, so they had to charge a silly amount for usage of that bandwidth, so very few people used it. Iridium used low-ish frequencies, with narrow bandwidth, and (I think) no MIMO whatsoever, not even polarization diversity.

[lxgr]

Yes, for more than one satellite covering the same area on the ground with a spotbeam on the same frequency at the same time to make sense, you inherently need steering/beamforming.

That's why Iridium has the constellation planned out so that you never have more satellites in the sky than strictly necessary for full coverage on the equator (where satellite density is lowest), and outer spot beams get turned off progressively as the satellites approach the poles as they'd only create interference without increasing bandwidth due to the lack of terminal-side steering.

Now I wonder if they already changed that for the second generation sats, given that there are some steered terminals available that could probably make good use of the extra satellite density near the poles, which is also an area underserved by geostationary beams?

[NetMageSCW]

Dense areas get terrestrial towers as the do now. Non-dense areas fall back to satellite towers with no change in devices needed.

[lxgr]

Definitely, and I think GP raises a valid point: Without beamforming, there’s no point in having more than one station covering the same area, whether terrestrial tower or satellite-based spot beam.

And while 4G and beyond use some mild device-side beamforming, it’s a whole different ballpark than parabolic antennas or phased arrays in terms of gain.