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Comment by seamac3 | Hacker News Reader

Why don't the stock market traders just use satellite? Shouldn't those transmissions be faster than cable transmission? They are only gaining milliseconds right? I wonder who will be affected. It seems like a lot of wattage, but the stock traders antennas are located in the upper US.

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Satellites mean you are eating round trip delay times to orbit and back, encode and decode on both ends, signal strength competition, etc. It's a bad trade. Speed of light limits are a big limiting factor, which is another way of saying you want to minimize your total transmission distance.

Going into orbit increases your total transmission distance. If you can afford to put in the infrastructure, you never want to go into orbit.

It looks like, as the crow flies distance between Chicago and Frankfurt, would take a pulse around 23ms to arrive, at the speed of light. It looks like for a LEO satellite, the round trip time, is around 40ms.

They mention it uses the ionosphere, so curious exactly how long it takes the short-wave pulse to arrive.

HF radio reflects off the ionosphere's F-layer, located about 100-200 miles up. To get from Chicago to Frankfurt requires several hops between the ionosphere and the earth's surface. The hop length is one or two thousand miles.

Satellites such as Starlink operate in low earth orbit at about 350 miles, significantly above the F-layer. Also, they introduce repeater delay when they relay a data packet. To get from Chicago to Frankfurt would require relaying the packet thru multiple satellites. So, greater distance (even if passed by laser between satellites) plus repeater delays.

Also note that satellites in LEO are the only option. Geosynchronous satellites are completely out of the game due to the much greater distances involved.

Radio ham blog post discussing HF propagation:

    https://www.pa9x.com/long-path-or-short-path-propagation/

Microseconds matter to them; even with a satellite in low-earth orbit (~342 mile), you’re looking at a round-trip time of 3.68ms, on top of any packet latency introduced by the satellite itself.

It’s always going to be faster to go point-to-point than pay the light-speed cost of bouncing all the way out to orbit and back.

Speed of light.

They actually want to locate their servers inside the market buildings, to gain those precious nanoseconds.

I suspect reason we are seeing the HF proposal now is the coming Starlink laser links will offer similarly low latency. The HF proposal is to provide an alternative to potential Starlink monopoly. They don't want to get locked out if Starlink is exclusive.

Their latency requirements are such that they want as straight and short a line as possible because a larger round-trip eats up precious nanoseconds. The speed of light is not fast enough for these folks

On that note, Ryan North's book "How to Take Over the World" has a whole chapter about this. He proposes building a tunnel from New York to Chicago, to get the best possible straight-line distance between the two cities, thereby minimizing latency. Leasing this line for HFT is the funding source for most of the later supervillain schemes.

They measure performance in microseconds.

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