What the Heck is 3G?

The technology behind the new iPhone.

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Apple unveiled its new version of the iPhone with characteristic fanfare Monday, demonstrating download speeds several times as fast as the old version. Unlike its predecessor, the new iPhone uses the “3G” technology already offered by several other carriers. What, exactly, is 3G?

It means “third generation” and refers to a family of technologies that deliver much faster download and upload speeds for handheld devices and laptops. They work by allowing many cell phones or other wireless devices to communicate on the same frequency without getting confused. Compared with older systems, this allows for the transfer of a larger amount of data by eliminating the need to keep each signal separate.

The U.S. cell phone industry was born in 1983 with the introduction of the Advanced Mobile Phone Service, the first generation of mobile technology. This was an analog system; the wave signals between towers and mobile devices directly represented the audio waves they were transferring. To support as many callers as possible, the portion of the airwaves devoted to mobile communication was divided up into many small slices. (Carriers just recently stopped supporting the last remnants of this technology.) The first-generation system was gradually replaced by digital signals—2G—in which mobile signals were converted into zeros and ones before being transferred across the airwaves. This allowed for a much more accurate transfer of information. (Similarly, the use of digital encoding is why CDs tend to have a higher sound quality than records, as they are less prone to corruption.) * To cram more of this digital data into a given set of frequencies, many second-generation systems used a “time division” technology. * In addition to dividing up the bandwidth into many small slices, the carriers divided them up in time, switching very rapidly between different signals. In other words, your call might be broadcast on the same exact frequency as someone else using a cell phone on the same network—but your data and his would be alternating over the airwaves in little bursts lasting a tiny fraction of a second. That’s how the original 2G iPhone works.

In general, the third generation improves on the time-divided system by adding unique codes to each signal. Rather than alternate signals like many 2G systems, it lets several signals use a broader set of frequencies simultaneously and relies on the codes to sort out which is which. (There are other types of coverage classified under the “3G” umbrella, but the two principal third-generation systems in the United States use code division, which is considered the dominant 3G technology.) * Now you’ve got less to worry about from your neighbor: Your cell phone gets its own continuous, coded signal. That means it can transfer a lot more data in a given period of time. By way of analogy, experts like to compare this to a series of conversations all taking place in a room. Under a time-division system, everyone has to take turns speaking; under a code-divided system, everyone speaks a unique language to his or her conversation partner, and ignores the other conversations taking place in foreign tongues.

In the United States, Sprint and Verizon have used an early version of this technology for several years. (Some argue that these systems are technically a primitive sort of “3G,” while others classify them as “2.5G” or even “2.75G.”) Bona fide 3G systems, which first appeared in the United States in early 2002, generally refer to an alphabet soup of technologies that are faster and more standardized than the old Sprint and Verizon networks.

Carriers have generally overlaid third-generation technologies atop their existing networks and introduced devices that are capable of seamlessly switching between the older and newer systems, depending where the caller is and what he or she is doing with the device. Most major carriers offer 3G networks in urban areas, and still use 2G technology to cover less populated regions. Additionally, many 3G-capable devices are able to choose which technology is most appropriate for a situation, since high-speed connections aren’t necessary for every activity and usually drain more battery power.

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Explainer thanks Charles S. Golvin of Forrester Research and Philip Solis of ABI Research.

Correction, June 13, 2008: This piece originally stated that third-generation mobile systems use code-divided technology and implied that all second-generation systems use time-divided technology. While the dominant 3G systems in the United States both are both code-divided, there are a variety of technologies classified as 3G. (Return  to the corrected sentence.) Additionally, the piece stated that CDs have a higher sound quality than records. Many argue that high-quality records can be of superior quality to digital recordings. (Return  to the corrected sentence.)