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On Call: Welcome to 4G

Confused about 4G technology? CNET tells you what it is and what it promises.

On Call runs every two weeks, alternating between answering reader questions and discussing hot topics in the cell phone world.

It wasn't so long ago that the cell phone world was just transitioning to 3G technology. But now, just as we're getting settled, the ever-restless industry is moving on again. Fourth-generation technology, or 4G, is gaining traction and carriers are promising even faster data speeds.

So what is 4G?
To start, think of wireless technology as a family that gets faster with each generation. Second-generation (2G) networks were faster than the original first-generation wireless technology; third-generation (3G) is faster than 2G; and 4G is faster than 3G. Speed is important for data transmission (not so much for voice) because a faster network lets you do more with your phone. The 3G networks that we use today allow us to stream video, download music tracks and other large files, and surf the Web on full HTML browsers. Think of it like moving from a dial-up Internet connection to cable or DSL--suddenly you could do more with your computer and do it faster.

That's why it's easiest to think of 4G not in terms of what it is, but rather in terms of what it can do. While 3G offers data speeds of about 1.5 to 2 megabits per second (Mbps), 4G will double that--and it could go even faster. It's important to remember, however, that promises are just that. As any iPhone user can tell you, 3G speeds can vary widely in everyday use, so 4G performance won't always be perfect.

Types of 4G
Just as there are different types of 3G (EV-DO, UMTS, and HSDPA) there are two main types of 4G. I'll tell you the basics, but before we start it's important to note that 4G more or less marks the end of the traditional CDMA/GSM divide. Carriers can choose which technology they're going to employ--they aren't limited by what they're using now. That's why you'll get Verizon Wireless and AT&T both choosing the same 4G solution. They won't necessarily be interoperable, but they will be similar.

LTE, aka long-term evolution, is the natural outgrowth of current 3G technologies. As it has an all-IP architecture, it treats everything it transmits, even voice, as data. Verizon Wireless and AT&T have chosen LTE, and it's expected that T-Mobile will go that way as well. At the time of this writing, no commercial LTE devices are available in the U.S. market, though we expect to see announcements later this month at the annual CTIA show in Las Vegas.

Verizon said Monday that LTE testing in Seattle and Boston has gone well and that it will bring the technology to 25 to 30 markets this year. According to the carrier, its network is capable of download speeds of 40Mbps to 50Mbps and upload speeds of 20Mbps to 25Mbps. Average speeds, however, will more likely range from 5Mbps to 12Mbps for downloads and 2Mbps to 5Mbps for uploads.

In contrast, AT&T is a bit further behind. The carrier announced in February that it will begin LTE testing later this year and will deploy commercial networks in 2011. So, at least for the time being, don't get your hopes up that a 4G-capable iPhone will arrive at AT&T this summer. T-Mobile will be playing catch up for some time, too. Last month at the Mobile World Congress, T-Mobile CTO Cole Brodman said the carrier will expand its HSPA+ network to more U.S. cities this year. Though Brodman billed it as 4G technology, HSPA+ is an advanced 3G technology.

In contrast to LTE, WiMax, which stands for Worldwide Interoperability for Microwave Access, isn't an evolution of current cellular systems. Rather, it's more related to current Wi-Fi technology. The initial version for mobile use is based on the 802.16e wireless standard (Wi-Fi is 802.110). It has potential for very long range transmission (up to 30 miles) and could offer speeds of about 10Mbps.

Sprint is the only U.S. carrier to adopt WiMax, but for now the carrier's network is more widely available than LTE. Sprint and Clearwire have a WiMax network in 27 cities with at least eight more slated for the first half of this year. Sprint is promising average speeds of 3Mbps to 6Mbps with peak speeds up to 10Mbps. The carrier also has no 4G phones for now, but it introduced a WiMax-capable router last January at CES. And we expect to see it roll out some real 4G phones at CTIA.