With most American mobile data networks busy trying to deliver third-generation (3G) mobile wireless access to traveling businesspeople, Sprint's newly launched Xohm service takes a giant step forward by offering America's first 4G system.

Based on WiMax technology, it can deliver broadband data speeds to notebooks, Internet tablets and eventually smartphones. But at the moment, there aren't many devices to connect with, the network is struggling with reliability issues, and the high-speed service is limited to just one city -- Baltimore.

WiMax (Worldwide Interoperability for Microwave Access) is a wireless data system based on Orthogonal Frequency-Division Multiple Access (OFDMA) technology and the IEEE's 802.16e spec. That's a lot to swallow, but Xohm's basic facts are that it broadcasts on the 2.5-GHz portion of the radio frequency spectrum, a slightly higher frequency than the 2.4 GHz that the 802.11b/g/n standards, commonly used in Wi-Fi networks, operate on.

Because it has a longer range and can deliver higher data rates than 3G services, WiMax has the power to transform the way we think of wireless data delivery. Think about receiving the equivalent of a home DSL or cable broadband connection while you're mobile, and you get an idea of its potential to put data everywhere you'll be. In other words, WiMax can turn a city into a hot spot for wireless data.

"WiMax is Wi-Fi's big sister," says Sean Maloney, Intel's executive vice president. "It will have a big impact on mobility by covering a larger area. The future is here, now."

In the lab, WiMax can deliver a peak data speed of 40Mbit/sec. But in the real world, speed depends on things like how far you are from a transmitting tower, how many others are using the network and the general health of the Internet. Expect to see download speeds between 3Mbit/sec. and 5Mbit/sec., or about three times what the current 3G networks from AT&T, Sprint and Verizon can deliver.

The technology first went commercial in South Korea in 2006 under the name WiBro. Available in 407 locations in 133 countries, according to the WiMax Forum, the wireless system is prominently used in South Korea, Italy, Taiwan, Brazil and Japan every day for a variety of uses.

Enter Xohm

To see just what WiMax is, how it works and what it's actually capable of, I went to Baltimore, the first U.S. city to offer WiMax service commercially, to try it out. Called Xohm, the new network is a joint venture of Sprint and Clearwire.

So far, Xohm has spent about US$3.2 billion to develop, test and roll out WiMax in a few places, according to Sprint CEO Dan Hesse. "It's just the start. Another $5 billion will be required to create a national network," he explains. Google,

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