I was looking for the kind of internet speeds that are possible via satellites. GEO satellites tend to have very high latency and LEO constellations like Iridium and Globalstar have lower latencies but their throughput is lesser than ground-based broadband internet. What are the technical reasons that make broadband internet user-speeds difficult to achieve via satellites?
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It’s mainly the frequency at which the signal travels. There are a limited number of frequency bands available and due to size and power requirements for faster speeds, it becomes a bit impractical, plus higher frequency bands are more susceptible to interference.
Let’s say right now that the satellite uses the Ka 26.5-40Ghz frequency band. Thay means theoretically it can spend a max of 26.5-40Gbps. But of course in practically you never get ideal rates because you need to maintain packet integrity (ie data correction). And this gets worse with interference since one side has to constantly repeat itself a lot. And of course you have to share the total bandwidth with all the other users in the same area too. So then your 40Gbps max is probably down to 500Mbps or less.
The distance the data has to travel from the satellite to your receiver is the main problem. It’s the same as being too far away from your wifi router or when there’s lots of blockage in the way like walls. For satellite internet the blockages are mostly atmospheric conditions such as weather.
Simplest Answer: They are very far up. Geostationary orbit is 22,236 mi. LEO is not as bad, but are much smaller in number and have higher fuel requirements.
Also consider that upgrading/replacing/repairing the hardware requires launching a new satellite. Not exactly like changing a device in a rack or utility shed.
Power, noise, and bandwidth. A communications satellite has multiple transponders, each with maybe 36MHz bandwidth. The transponders are radio receivers and transmitters. They use a lot of power. For an economic successful system, you’ll need to have thousands of satellites in LEO, and millions of users. Starlink is trying to build such a system, but you aren’t going to see fiber-like speed. For weak signals, noise is a big problem.
> [The Shannon-Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. ](https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem).
It’s not a technical problem it’s economic. It costs a fortune to put a satellite in orbit, and no one puts them up expecting to lose money on them. To attract customers, prices need to be competitive with ground internet, which means you need a huge number of customers sharing the satellite’s bandwidth to make that return. That many people sharing means everyone gets a small piece so the speeds tend to be lower.
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