Most of Google's current balloons carry radios that operate in the 2.2GHz and 2.6GHz LTE bands -- chosen because those bands provide coverage across the U.S., Europe and Asia. The signal from each balloon covers an area with a radius of 40 kilometers, and Google is preparing to do tests in the 700MHz LTE band to cover an area four times as large.
The balloons Internet connection comes from access points on the ground, and because a balloon wont always be within range of one, the signal is passed from one balloon to the next until an access point is in range. This balloon-to-balloon network can run at speeds of up to 4Gbps while the downlink speed to handsets on the ground is around 30Mbps at best.
Keeping track of the balloons is perhaps one of the easiest challenges, because it involves sifting massive amounts of data and modeling wind patterns -- the kind of things Google's data scientists are adept at doing.
Balloons stay in communication with Google through the Iridium satellite network. They send out location and other data at intervals ranging from every second to every couple of hours. But the balloons actually log thousands of data points every second that are recorded and stored for later analysis, so any part of the flight of any balloon can be analyzed.
Flight tests are currently taking place in New Zealand, Argentina, Chile, and the state of New Mexico, and one of the most recent innovations has been an automatic balloon launch system.
For Loon to cover the world, tens of thousands of balloons will need to be in the sky at any one time, and with a 100-day life span per balloon, that means hundreds of launches each day to keep the network up and running. At that level of activity, a system that relies on humans would have trouble keeping up.
But for all that's known about the technology behind Loon, the biggest unanswered question is perhaps the most interesting: when will it be commercially available?
Google declined an interview request for this story. It has said it won't offer Loon service to consumers itself but rather is partnering with cellular operators around the globe, essentially leasing out the balloons as they pass over areas that need coverage. Under this business model, Google is freed from the hassle of dealing with individual subscribers and can operate under the carriers' existing wireless licenses.
Unfortunately, there's still no clear indication of when commercial service will be available. Google says it want's to bring the cost per balloon down to about $10,000, and it's not there yet, but it is getting close.
"We're well within 10X of that," said an engineer.
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