Tests have proved this week that a rival mobile technology to WiMax works as expected, but there are some question marks over the final speed it will achieve 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 this week 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 100Mbit/s downstream and 50Mbit/s 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 2Mbit/s and 10Mbit/s, or about as fast (or faster) than typical home broadband in the US today. Current 3G usually runs below 1Mbit/s.
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 US, 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 1.5Mbit/s 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 US next year. From the start, WiMax should deliver speeds at least at the low end of the 2Mbit/s to 10Mbit/s range, Marshall said. But it faces the same questions when it comes to real speed on the subscriber's phone or laptop.