I dont know if I'd call it direct line of site, but low bandwidth directional microwave communication is definitely used over-the-horizon from say Chicago to London. This [1] Bloomberg article has a great rundown on microwave in finance.
Bandwidth is low, but latency beats fibre, and you can bounce microwave off the ionosphere between London and Chicago (and various other routes). This article doesn't mention the cross Atlantic transmissions, but it is possible, and does happen.
Disclosure: I have worked at several of the Chicago based firms mentioned in the linked Bloomberg article.
Edit: grammar, formatting.
I wasnt directly involved in any of the microwave networking, but ask me what you want and I'll answer to the best of my ability.
Bandwidth is low, but latency beats fibre, and you can bounce microwave off the ionosphere between London and Chicago (and various other routes). This article doesn't mention the cross Atlantic transmissions, but it is possible, and does happen.
Disclosure: I have worked at several of the Chicago based firms mentioned in the linked Bloomberg article.
Edit: grammar, formatting.
I wasnt directly involved in any of the microwave networking, but ask me what you want and I'll answer to the best of my ability.
[1] https://www.bloomberg.com/news/features/2019-03-08/the-gazil...