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UMTS: The 3G upgrade path to GSM

UMTS (Universal Mobile Telecommunications Service) is a 3G broadband, packet-based transmission of text, digitized voice, video, and multimedia.

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Some assume that 3G is not yet widely available, but nothing could be further from the truth. UMTS is essentially the 3G upgrade path to GSM, and it uses 5 MHz channels in place of the narrowband (but still digital) approach used in GSM. As you may know, more spectrum is the best way to improve both overall network capacity and data throughput, two key goals of 3G.

3G was actually defined with fundamental improvements to both voice and data in mind. With respect to data, three design points were specified by the International Telecommunications Union (ITU) -- 144 Kbps when moving rapidly, 384 Kbps when moving relatively slowly, and up to 2 Mbps when stationary or indoors. The ITU actually recognized a number of standards as meeting this definition of 3G, but UMTS -- having been developed by the European Telecommunications Standards Institute (ETSI), the people who invented GSM -- had a built-in advantage in the market and has now been deployed in many parts of the world.

UMTS has been the source of numerous improvements in data capabilities over the past few years. GSM's proponents realized early on that packet data based on IP would be the future. This led to the introduction of the General Packet Radio Service (GPRS) [http://www.gsmworld.com/technology/gprs/index.shtml], which in theory meets the definition of 3G when fully deployed. An upgrade to GPRS, known as Enhanced Data rates for Global Evolution (EDGE), is essentially GPRS on steroids – it uses much-improved modulation to yield peak speeds of up to 473.6 Kbps. I should probably mention here that peak speeds are just that, and you should expect throughput of no more than 30-50% of these numbers.

Although the UMTS specification does define data speeds as high as 2 Mbps, just as the ITU notes, wireless data on UMTS systems has taken a bit of a turn in recent years. Specifically, the UMTS community has introduced High-Speed Downlink Packet Access (HSDPA) and High-Speed Uplink Packet Access (HSUPA), which have peak throughputs of up to 14.4 and 5.8 Mbps, respectively. Most deployments will offer much less than these speeds -- Cingular, for example, states that its current implementation of HSDPA will offer about 400-700 Kbps, with "bursts" to 1 Mbps. Nonetheless, performance like that would have been unthinkable just a few years ago, and it seems likely that even higher speeds will be offered when more spectrum becomes available (via the upcoming and future auctions) and carriers begin to emphasize data services as the voice market saturates.

UMTS uses a technology known as Wideband Code Division Multiple Access (WCDMA), which allocates 5 MHz of spectrum to each channel. We'd have to devote the entire channel to a single user to offer 14.4 Mbps to any given customer; instead, carriers will typically provision multiple voice and data connections simultaneously. The carriers will attempt to get the best return on their investment in spectrum and equipment by optimizing the traffic mix at any given moment, but the good news is that UMTS offers a lot more capability than GSM and a very nice upgrade path for carriers and users alike.

In my next column, I'll discuss UMTS' key competitor in 3G – CDMA 2000.

About the author: Craig Mathias is a principal with Farpoint Group, an advisory firm based in Ashland, Mass., specializing in wireless networking and mobile computing. The firm works with manufacturers, enterprises, carriers, government, and the financial community on all aspects of wireless and mobile. He can be reached at craig@farpointgroup.com.
This was last published in June 2006

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