A key challenge for Google’s Project Loon, which intends to use high-flying balloons to bring Internet connectivity to parts of the world that remain largely disconnected, is figuring out how to get the balloons to communicate with each other.

Speaking at MIT Technology Review’s EmTech Digital conference in San Francisco on Monday, Loon’s project lead, Mike Cassidy, gave some details about how this works, saying that the balloons use high-frequency radio waves to link up. Gimbals mounted to the balloons must be pointed precisely at each other—to within a tenth of a degree, he said—to enable one balloon to send data to another that’s 80 kilometers away.

Project Loon, which was named to MIT Technology Review’s 2015 10 Breakthrough Technologies list (see “How Google’s Crazy Stratospheric Internet Balloons Matured Into a Technology That Could Bring Billions More People Online”), works by having stations on land transmit an LTE wireless signal that is picked up by the balloons and transmitted from one balloon to the other. The balloons, which consist of a large outer balloon filled with helium and a smaller inner balloon filled with air, add or lose air in order to move up or down in the stratosphere; this lets them travel, since the wind that carries them moves in different directions at different altitudes.

Having a reliable way for the balloons to interact is important for Project Loon because it will allow the balloons to do things like spreading out to blanket a larger area with Internet access. Eventually, it could also enable the balloons to be more autonomous, communicating with each other about where one is or should go without needing to be told individually where to move.

Cassidy also said that the project will conduct tests in both the Northern and Southern hemispheres later this year; previously, plans for just a Southern Hemisphere test were known.

In the Southern Hemisphere test, Project Loon plans to run several balloons for two to three days, which will let the team test the whole Loon system—from ground stations that deliver LTE to the balloons, to the balloons communicating with each other.

Beyond South America, Cassidy sees Africa, where only about 10 percent of the continent has access to the Internet, as a big potential market for Loon, and he thinks it could be useful in India as well.

As for bringing Loon to places like the U.S. that are already largely connected but could still use improved Internet connectivity, Cassidy says that will also happen.

“Even in my house, I don’t have a cell signal,” he said. “We’re going to come to the United States, too.”