Fast mobile on track but faces curves

A new mobile technology offering several megabits per second is working as planned, but that doesn't guarantee that kind of speed at its launch date in 2010.

An emerging mobile technology that would give on-the-go users several megabits per second is working as planned so far, but that doesn't guarantee you'll get that kind of speed at its planned launch date of 2010.

The system, called LTE (Long Term Evolution) or SAE (System Architecture Evolution), is the next major evolution from the world's most common mobile technology, GSM (Global System for Mobile Communications). As such, it has the backing of the 3GPP (Third-Generation Partnership Project) and mobile giants including Ericsson, Nokia, Alcatel-Lucent, T-Mobile and Vodafone.

The initiative they are backing, called the LTE/SAE Trial Initiative (LSTI), said that in tests, the new technology met targets for physical-layer throughput to both stationary and moving users. It met expected peak data rates in tests with both single-antenna and multiple-antenna radios in lab and urban field settings, the group said. LSTI also announced some big new backers, including China Mobile, Huawei, LG Electronics, NTT DoCoMo and Samsung.

The peak data rate for LTE in initial deployments is 100M bps (bits per second) downstream and 50M bps upstream, according to LSTI. That speed is for one channel, which would be shared by many users in a given area, according to Yankee Group analyst Phil Marshall. But the news is still good: Marshall believes a real user would get anywhere between 2M bps and 10M bps, or about as fast or faster than typical home broadband in the U.S. today. Current 3G usually runs below 1M bps.

Between here and that 4G promised land are several hurdles, however. First, most carriers will need new radio spectrum to carry LTE services, Marshall said. Current 3G uses about 5MHz of spectrum for communication from the base station to the handset and 5MHz the other direction, he said, while LTE will need about twice that much to deliver the promised speeds. Auctions in Europe for "3G extension" bands that could be used for LTE will probably be done by 2010, but current users may still be vacating it, he said. In the U.S., parts of the 700MHz spectrum set to be auctioned early next year could be used for LTE.

Once networks get up and running, the speed you get will depend partly on how many base stations your carrier puts up for it, as well as how many other people are trying to use your local base station, Marshall said. Also, the wireless link between the handset and base station doesn't go all the way to the Internet. In between is the carrier's "backhaul" connection, which today often consists of one or more T-1 leased lines at 1.5M bps each. Without upgrades, backhaul could create a bottleneck.

LTE's rival, mobile WiMax, will be out sooner with large deployments such as Sprint Nextel and ClearWire's Xohm network in the U.S. next year. From the start, WiMax should deliver speeds at least at the low end of the 2M bps to 10M bps range, Marshall said. But it faces the same questions when it comes to real speed to the subscriber's phone or laptop.

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Stephen Lawson

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