3G phone network standards vary by carrier

If you’re among the growing number of Americans using the Web or e-mail on your phone, the quality of that experience depends on your cell phone company's data network. Wireless carriers all make similar promises of blazingly fast mobile Internet, even more so now with 3G, or third-generation, wireless.

A speedy network with a strong signal brings faster-loading Web pages, quick e-mail delivery and smoother video streams on the go. Of course, sluggish data speeds and lousy network coverage means you'll likely wait until you get to work or home before jumping online via computer.

So what are the differences between the mobile Internet technologies and networks of AT&T, Verizon Wireless, Sprint and T-Mobile, the four major carriers in the United States?

T-Mobile and AT&T both use the GSM, or Global System for Mobile communications, standard, and the most popular form of cellular technology in the world by a wide margin. The GSM Association estimates more than 80 percent of cell phones worldwide are GSM.

In the other corner are Sprint and Verizon Wireless. Both carriers use CDMA-based cellular technology, short for Code Division Multiple Access.

Both GSM and CDMA are 2G, or second-generation, wireless technologies that use digital radio signals to transmit data. First-generation systems were based on analog radio and, compared to digital, were plagued by audio interference and high power requirements on cell phones.

To answer the growing demand for data services like multimedia messaging, e-mail and Web browsing, the GSM and CDMA carriers came up with their own solutions.

3G, as in iPhone 3G, is an abbreviation used for the third generation of cellular phones and networks. Starting in late 2006, Verizon Wireless and Sprint made a transition to 3G EV-DO (Evolution Data Optimized) directly, while AT&T and T-Mobile both followed a more complicated route.

Before AT&T and T-Mobile began rolling out 3G network services (AT&T is currently expanding its nationwide 3G coverage, while T-Mobile has only just started), both carriers introduced interim standards to handle voice and data transmission.

GPRS (Global Packet Radio Service) and later EDGE (Enhanced Data rates for GSM Evolution) allowed for data speeds ranging from a pokey 32 kilobits per second to near-3G speeds.

3G speeds vary
Minimum 3G data download speeds aren't clearly defined, but are often pegged at between 128 and 384 kilobits per second. That’s still slow compared to a household 802.11g Wi-Fi network, which has a maximum data rate of 54 megabits per second.

For those who use the iPhone, a Web page loads about twice as fast on Apple’s new iPhone with the 3G radio turned on, compared to the original phone’s 2G EDGE speeds. (Since the iPhone 3G went on sale July 11, some owners have complained that the 3G network is not working as fast as was promised.)

Universal Mobile Telecommunications Service (UMTS) is the standard that AT&T and T-Mobile are employing for their 3G services, although AT&T is using a faster variant called High-Speed Downlink Packet Access (HSDPA).

Marin Perez, InformationWeek.com’s associate editor and mobile industry expert, said Sprint's EV-DO 3G network, in its updated Rev. A form, transmits data at speeds up to 3.1 megabits per second. The company’s iPhone competitor, the Samsung Instinct, is the flagship of Sprint’s 3G phone lineup.

“Sprint has a wide, if not (the) widest 3G network of the carriers,” he said.

Verizon Wireless also uses a “fast” 3G, EV-DO Rev. A network “that's taking longer than expected to roll out,” he said. “Devices like the LG Venus, Rumor, and Dare, and even the Samsung Glyde, are helping the carrier attract data-heavy users.”

AT&T, exclusive carrier of the iPhone in the United States, uses UMTS/HSDPA, with peak data speeds of 3.6 megabits per second. By the end of the year, AT&T plans to have 3G coverage in 350 U.S. markets, including the 100 largest U.S. cities.

“AT&T has the handset everyone wants, but their 3G network is still smaller than Sprint’s,” Perez said.

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