TDD LTE gaining momentum in 4G push, says ZTE
Some carriers could move from FDD
The Frequency Division Duplex (FDD) flavour of LTE will face increasing competition in favour of Time Division Duplexing (TDD), according to Chinese telecoms infrastructure giant ZTE.
Far more operators currently have FDD networks either in operation or trialing than TDD, as can be seen on this handy interactive map.
FDD's benefits are that it handles interference well and fits more neatly with the way many legacy networks were architected, ZTE’s VP of Wireless Sean Cai. That's all well and good, but TDD is more cost effective and efficient in the way it handles traffic, he says.
"TDD is gaining momentum," Cai told The Reg on a visi to HK this week. "TDD is becoming the trend."
“It’s not all about the technology but also the politics and regulations of individual countries.”
FDD LTE has been the natural choice for many operators in Europe and beyond who previously ran FDD 2G and 3G networks. However, by requiring paired spectrum the standard has been criticised for being inefficient, with downlinks becoming swamped while uplinks are wasted, Cai explained.
TDD transmits the up- and downlink traffic in the same unpaired frequency band, maximising available bandwidth, and incurs lower power costs. Another trump card is that an FDD set-up can be converted to TDD but not the other way around, said Cai.
"We're not able to predict when and how [some companies redeploy fdd spectrum to tdd] but we know it's going to be a long time," said Cai, stressing political and regulatory issues play a big role in operator strategy.
However, it could be 10 or 20 years before the LTE standards shake out and in the meantime ZTE has been promoting their co-existence in base stations by building the first dual-mode LTE network in the world for operator 3 in Sweden.
Cai was less willing to predict the end of the 3G TD-SCDMA which, despite technically being an international standard, is virtually unheard of outside of China.
The standard has caused China Mobile some headaches – Apple has never released an iPhone which supports it, for one – yet Cai feels the firm will have the edge when it comes to upgrading to TD-LTE as the process requires very little work.
In this context, far from backing the Betamax of 3G standards, China Mobile – the largest operator in the world with over 700 million subscribers – may have played a canny long game.
Cai was speaking ahead of Mobile World Congress, which opens later this month, when he said ZTE would be making some announcements on Radio Access Network technology. The firm has apparently worked hard in this area, with the goal of making the network more efficient by ensuring it can adapt dynamically to user behaviour.
Spectrum sharing, carrier aggregation, small cells and white space technology will also become vital in the coming years to coping with the flood of data and diminishing bandwidth, argued Cai. ®
Chicken and the egg?
"What do the Apples and Samsungs say about this?"
I don't care what Apple has to say; surprisingly I found my (CDMA/EVDO/LTE) Samsung Stratosphere actually has no Qualcomm hardware in it (the LTE chip is Samsung, and the CDMA/EVDO chip is Via Technologies.). But, Qualcomm in fact makes loads of chips, if they support TDD in 900/1800/2100 (Europe) and 700/850/1900/AWS (US) then so many phone makers just drop in a Qualcomm solution that phone makers could naturally follow, it'd be essentially a zero-cost option to support both FDD and TDD compared to now.
Anyway, any take off of TDD would necessitate changes of regulations on these bands so the cell co can use the band how they wish, as opposed to the current situation of having particular uplink and downlink bands. If that happens, indeed TDD should help use upstream spectrum that is likely rather wasted at present. At that point, the big question is, will carriers (outside China) actually decide to use TDD instead of FDD? That I do not know.
What about power?
Having more radio resource blocks available means you can use more. So you could use simpler modulation schemes which can worse signal- to noise ratios enabling you to use less signal meaning less power.
TDD on the other hand has serious problems as you need to manage the timing very accurately and you'll always have dead times when you need between sending and receiving.
lack of paired spectrum
Its a fair comment considering how much demand for spectrum there is forecast to be for mobile use and the lack of paired spectrum that seems to be available for international harmonisation in the near future. Maybe TDD will win just because of this (lack of) availability.
My uneducated feeling wonders if that killing off FDD now by ZTE becomes a self fulfilling prophecy. What do the Apples and Samsungs say about this? Though if the asymmetrical demands of mobile data consumption eg Lolcats galore on youtube continue, FDD will be a waste of good spectrum.
Sad face as my boss didn't send me the world mobile congress in Barcelona