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TD-LTE goes mainstream with a new performance promise

China Mobile's budding network is helping to pique interest in a different way of using scarce spectrum

By , IDG News Service
February 28, 2013 06:36 AM ET

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China Mobile promotes this feature as one of the main things that will make its network better. The carrier could divide its spectrum differently in various areas depending on how the network might be used there, said Lei Cao, a China Mobile representative in the company's MWC booth.

Some said TD-LTE saves carriers money and is just a better way to use spectrum.

"This is hotly debated, but the TD-LTE advocates will tell you that it can be deployed in cheaper unpaired spectrum and is more efficient when the downlink/uplink is asymmetric," Tolaga Research analyst Phil Marshall said in an email interview. Dedicating the same amount of spectrum to uplinks as to downlinks leaves a lot of uplink spectrum unused, he said.

The biggest reason FDD is still used is tradition, according to Marshall. When cell phones were used mostly for voice, upstream and downstream traffic was equal.

"Most of the cellular spectrum is allocated in FDD and systems are deployed this way," Marshall said. "The advocates of FDD will tell you that you get better performance consistency with FDD and it is easier to implement -- particularly when coordinatedA with other FDD systems."

Without the need for pairing, it's also easier to cobble together various frequencies. In January, China Mobile and ZTE said they had demonstrated combining two separate TD-LTE spectrum blocks into one virtual block and assigned 75 percent of the whole to downstream traffic.

It's not especially challenging to implement TD-LTE, Schoolar said. Nor is it hard to hand off subscribers from those networks to LTE FDD systems, according to China Mobile and others. Despite the dominance of FDD, most existing LTE base stations can be set up for TD use with a software upgrade or a new line card, Schoolar said. Sprint plans to mix FDD and TD networks by using the Clearwire TD-LTE network for extra capacity in busy areas, shifting users from one to the other as needed.

China Mobile Hong Kong has already launched a combined TD and FDD network. It puts subscribers on TD-LTE where it's available, then shifts them onto FDD where possible, and puts them onto GSM when necessary. All these transitions are transparent to users, Lei said.

The pre-commercial network in mainland China is growing rapidly despite the fact that China Mobile can't offer commercial service yet. There are about 20,000 base stations there today and will be 200,000 in 100 cities by the end of this year, Lei said. And China Mobile is not expected to be the only Chinese carrier to deploy TD-LTE.

That bodes well for a high-volume market that should make TD-LTE devices cheap and plentiful in other parts of the world, with the help of big silicon vendors, analysts said. "It really depends on guys like Qualcomm to make it happen," Marshall said.

Stephen Lawson covers mobile, storage and networking technologies for The IDG News Service. Follow Stephen on Twitter at @sdlawsonmedia. Stephen's e-mail address is stephen_lawson@idg.com

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