Google's Reverse-Engineered Mobile Network

Project Loon sails through the stratosphere on June 9 Courtesy Google Project Loon

Although Google may sidestep questions about Project Loon at its earnings call, the company has no problem fielding queries about its ambitious—and more than just a little whacky—balloon-powered wireless network on Google+.

Ever since Google announced the X project during the summer, the Project Loon Google+ page has been running a series of fascinating short videos addressing many of the technical and intellectual challenges in building an untethered network floating freely in the stratospheric winds. Those videos have dealt with everything from balloon spacing to parsing wind data, and on Friday, Google posted an interesting entry about the antenna design of the Loon network.

Many people have compared Loon to a satellite broadband network because, on the surface, that’s what it resembles: a fixed transmitter on the ground pointing at an orbiting receiver in the heavens. In truth, however, Loon resembles the terrestrial cellular networks run by Verizon Wireless and AT&T much more than they do any satellite constellation.

As Loon network engineering lead Cyrus Behroozi explains in the video, most communications satellites are geostationary, meaning they’re following the Earth’s rotation over the same fixed point on the planet’s surface. From the perspective of someone on the ground, the satellite seems to hover in space, allowing you to easily point a dish directly at the source of your broadband connection.

In Loon’s case, the balloons are floating in the stratosphere, following its east-west winds across the globe. While Google will be able to control to a limited extent their spacing, speed, and direction of travel by moving the balloons up and down into different air currents, the dirigibles will largely go where the winds take them.

You can think of Loon as a mobile network in reverse. Instead of having a fixed grid of towers among which millions of subscribers are moving, Loon will have a have fixed grid of subscribers while the ‘towers’ move from place to place overhead.

To get Loon to work, Google thus has to deal with many of the same problems faced by mobile operators. One of these is resilience. In the mobile network, speed, capacity, and network performance tend to suffer as you and your smartphone move further away from a tower. In the case of Loon, homes and businesses will stay put, but Loon transmitters will appear and disappear over the horizon, handing off signals to the next approaching balloon. That means your Loon connection will be in constant state of topological flux, continuously moving from cell center to cell edge.

“They’ll be further away when they’re not directly overhead, and as they glide overhead they’ll become closer and then move further away again,” Behroozi tells viewers. “The antenna actually has to have more sensitivity off to an angle than it does straight overhead.”

To solve that problem, Loon engineers have created a reflecting plate in its bulbous antenna design, which will capture signals even when the transmission path is at an extremely obtuse angle. According to Behroozi, the design results in uniform signal strength, whether a balloon is directly over your home or on the horizon.

The design is rather simple, which Behroozi says is the point. To get the project pilot launched, Google wanted to stick to the basics. Google would design much more sophisticated antennas for Loon in the future, he explains.

I’m betting Google won’t get too complex in its designs for reasons of maintenance and cost. These balloons will float in the stratosphere, where they won’t be easy to fix if they malfunction. Should Loon really take off, Google will launch tens—if not hundreds—of thousands of them into the heavens. At that scale, cheap hardy equipment will be a big priority.

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