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Comment by gregschlom | Hacker News Reader

I know nothing about RF, can anyone comment on the technical challenges in making this possible? I always thought that you needed special antennas to communicate with satellites, how can a phone do it with no special hardware?

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In SATCOM, the link budget determines everything. In the link budget equation is the gain of both the receive and transmit antenna. If your phone antenna has a small gain (for a cell phone, you can consider it 0dB gain), then it has to be made up somewhere, and in this case it's on the satellite. The newer Starlink satellites have higher gain antennas for this use case. Despite this, the throughput is still quite low. The link budget equation results typically in a CNR value which provides you a budget for actual bandwidth/throughput. With a 0 gain ground antenna, there is only so much a small form factor satellite antenna can make up for. The satellite antennas also are phased array antennas which allow for beam steering which is another key technology here. As the satellite rapidly moves over the land it has to be able to maintain high gain in the direction it needs. A fixed antenna would either have a high gain in a single direction requiring lots more satellites for full coverage or wide beamwidths resulting in lower antenna gains and overall lower bandwidth/throughput, potentially to the point of uselessness.

TLDR: Bigger antennas on satellite.

And if you look at AST SpaceMobile plans. Its exactly that, much bigger sats with bigger antennas.

A traditional geosynchronous satellite is 22,000 miles above you. A starlink satellite is only 340 miles above you. And when you are outside you have a great line of sight with nothing in the way.

And your regular cell tower is within a few miles of your mobile at most. A few hundred meters in most cases. The phone is transmitting a few watts tops. I am very skeptical of them promising anything other than very-very low bandwith data, but I would love to hear from someone who actually knows about this stuff.

I make voice contacts with folks via the ISS repeater using a 5W radio and an omnidirectional antenna. It's much easier if you have an antenna with better directional gain, but it's definitely possible.

I'm assuming the Starlink satellites have higher gain antennas than the ISS's amateur radio setup, and they definitely have better coverage than the single space station. :)

At first I was skeptical that other satellite phone companies would use geosynchronous satellites but I looked up https://www.inmarsat.com/en/about/technology/satellites.html and sure enough they do

Still, you're going to require a bit of energy to push your radio signal even 340 miles through the atmosphere...

Since the announcement mentions "existing LTE phones" it seems to be no problem, power wise.

So, it all depends on the satellites antenna.

(power)

It is always a tradeoff between speed and necessary transmitting power. If you only need to transmit a small amount of data and don’t care if it takes very long, there are ways to spread out the data for it to be still receivable by the satellite. This is called channel coding.

This, combined with improvements in antenna design makes it possible to send data to satellites from phones (receiving data is pretty easy, see gps receivers). That said, it will take a long time for you to be able to have high speed satellite internet on your phone.

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