4 ms·

Elon Musk has stated that until they have inter-satellite laser links deployed, they can get wide area low latency communications by relaying via ground station

Elon Musk has stated that until they have inter-satellite laser links deployed, they can get wide area low latency communications by relaying via ground stations at a high slant angle. I built a simulator and ran an analysis of this, and actually it works pretty well. My video analysing all this is here: https://youtu.be/m05abdGSOxY https://youtu.be/m05abdGSOxY

walrus01 7y ago
There's a variety of software packages you can use to simulate the ground footprint of a starlink satellite, from the TLEs (two line elements). Or Iridium or anything else. It's a circle many hundreds of km wide. Assuming that an earth station will have a minimum look angle of about 18 degrees above the horizon, one can calculate the serviceable area for customer and trunk link spot beams within the satellite's moving footprint. The scenario shown in your youtube video has uses for HFT and similar very latency sensitive applications. But because it's RF, there's no way that a chain of starlink satellites relaying through multiple ground stations will compete in raw throughput and capacity with fiber. Remember that a single IT standard 100GHz grid DWDM channel is a few terahertz wide, and 80 channels can easily fit in the conventional bands of a long haul DWDM system in just two strands of fiber.
- mhandley 7y ago
  Yes, that's correct, but the interesting part is not the footprint, but the latency and variability of the dynamically routed paths you can obtain. That's what I simulated. I also made some modifications to how you'd normally route such a network, because the conventional approach wasn't fast enough if you have a wide choice of groundstations and the topology is continuously changing. The animations in the video are doing the route calculations in realtime once per frame of video; I was pretty pleased with those optimizations. One surprise, for me at least, was that there are paths where you sometimes want to relay via ground stations, even when the satellites have inter-satellite laser links. That's in the video towards the end. Edit: in response to the point you added about bandwidth: that's correct - there's no way the ground relay path competes with fibre on bandwidth. There are, however, many potential uses that require low latency and are not high bandwidth.

walrus01 7y ago

There's a variety of software packages you can use to simulate the ground footprint of a starlink satellite, from the TLEs (two line elements). Or Iridium or anything else. It's a circle many hundreds of km wide. Assuming that an earth station will have a minimum look angle of about 18 degrees above the horizon, one can calculate the serviceable area for customer and trunk link spot beams within the satellite's moving footprint. The scenario shown in your youtube video has uses for HFT and similar very latency sensitive applications. But because it's RF, there's no way that a chain of starlink satellites relaying through multiple ground stations will compete in raw throughput and capacity with fiber. Remember that a single IT standard 100GHz grid DWDM channel is a few terahertz wide, and 80 channels can easily fit in the conventional bands of a long haul DWDM system in just two strands of fiber.

mhandley 7y ago
Yes, that's correct, but the interesting part is not the footprint, but the latency and variability of the dynamically routed paths you can obtain. That's what I simulated. I also made some modifications to how you'd normally route such a network, because the conventional approach wasn't fast enough if you have a wide choice of groundstations and the topology is continuously changing. The animations in the video are doing the route calculations in realtime once per frame of video; I was pretty pleased with those optimizations. One surprise, for me at least, was that there are paths where you sometimes want to relay via ground stations, even when the satellites have inter-satellite laser links. That's in the video towards the end. Edit: in response to the point you added about bandwidth: that's correct - there's no way the ground relay path competes with fibre on bandwidth. There are, however, many potential uses that require low latency and are not high bandwidth.