This is microwave based. Those lines are well known by now and there are known routes within Europe (most notable Frankfurt<->London) and the US (NYC<->Chicago). However, microwave only works over short distances (FRA<->LON has multiple towers to cover the distance). Crossing the atlantic isn't possible. Shortwave could deliver a similar speedup over long distances.
I'm a bit sceptical though. Don't the waves have to bounce several times to get to the target? I'm not sure how much of the ~30% potential speed up vs. fibre you still get.
Yes, it has to bounce, but the number of times it bounces is dictated by the takeoff angle, as is the path length of each bounce relative to ground traversed. You aim for takeoff angles around 12 degrees. Since cos(12 degrees) ~= 0.98, there's not much path length added by the bouncing. So you still end up WAY ahead of fiber. I'll detail a stacked-curtain, log-periodic antenna used at another Chicago-area site in a forthcoming post.
I'd suspect the latency improvement is control over the entire path and not specifically about the propagation speed/delay.
Getting your data across a long haul undersea fiber requires aggregating it with everyone else's data at a central point before it gets sent out optically. This adds latency.
Even with the propagation variability of the wireless path you might be saving hundreds of nanoseconds.
There is some latency savings because the radio path is far straighter than the fiber path, even considering the ricochetting off the ionosphere and the earth. But the bulk of the latency savings comes from the fact that radio waves move at the full speed of light while photons through fiber only move at about 2/3 of that speed. So yeah, it works out to about a 10 ms savings on shortwave compared to fiber.
I doubt that this is a major factor. The extra delay (light speed vs. fibre speed) for signals across the Atlantic is at least 10ms each way, a few hundred nanoseconds for aggregation shouldn't make a difference there.
