So Polygon has dug into the background behind the Wii-U gamepad's streaming technology. Goes into a fair bit of detail.
http://www.polygon.com/2012/11/16/3653294/wii-u-range-test-gamepad
There's a video and more details at the link.
http://www.polygon.com/2012/11/16/3653294/wii-u-range-test-gamepad
Second-screen gaming, the ability to view full maps, menus or even play an entire game on the 6-inch screen built into the WIi U's GamePad, is made possible by a special form of WiFi.
The technology, co-developed by Nintendo and wireless and broadband communication giant Broadcom, marries run-of-the-mill WiFi with a power bit of proprietary software to create a two-way stream of low-latency, high-definition video and controls between the WIi U and its innovative GamePad.
The technology is built on top of something called WiFi Miracast, which Broadcom first developed last summer. It's a system that is specifically designed to deal with interference issues while maintaining liquid fast two-way communication.
Broadcom and Nintendo then teamed up to create a more solid system for the Wii U to GamePad connection.
While the official specs for the Wii U's GamePad say that it will operate properly at a distance between 8 inches and a bit more than 26 feet from the console, Polygon found that we could get quite a bit more out of the connection. And set-ups in rural location could close to quadruple that distance.
There's a video and more details at the link.