If there were a standout among the various technologies displayed at this week's Mobile World Congress Shanghai, it would be LTE-TDD. In the steady stream of TDD-themed news, the tradeshow also featured enough prominent announcements from service providers about the lesser-known 4G standard to suggest it is ready for prime time.
The headline news undoubtedly concerned China Mobile Ltd. (NYSE: CHL)'s ultra-fast TDD rollout. The operator has managed to sign up more than 200 million subscribers in just 19 months, making it the fastest-growing operator in the world today. China Mobile has now deployed 900,000 basestations in more than 300 cities at a cost of 138 billion yuan (US$22.2 billion).
From next year, it is also planning to upgrade to TDD+, a solution it has developed with Huawei Technologies Co. Ltd. , Qualcomm Inc. (Nasdaq: QCOM) and SoftBank Corp. . Huawei this week unveiled details of the TDD+ offering, which combines carrier aggregation and MIMO to deliver download speeds of up to 5 Gbit/s and a fivefold improvement in spectrum efficiency.
TDD+ will be commercially available next year and while it is not an industry standard executives say several elements have been accepted by 3GPP.
Meanwhile, SoftBank Japan has revealed plans to trial LTE-TDD Massive MIMO, a likely 5G technology as well as an important 4G enhancement, from the end of the year. It is in talks with Alcatel-Lucent (NYSE: ALU) and Nokia Corp. (NYSE: NOK) as well as existing TDD vendors Huawei and ZTE Corp. (Shenzhen: 000063; Hong Kong: 0763).
Yet the signpost to a bigger LTE-TDD future is the planned launch of TDD-based services next year by established FDD operators NTT DoCoMo Inc. (NYSE: DCM) and KDDI Corp. It was the subject of a number of presentations at the event.
The Japanese government has auctioned off 3.5GHz spectrum to bring more capacity into what is, along with South Korea, the world's most saturated 4G market. The three operators have around 100 million 4G customers, representing 79% of all mobile subscribers.
SoftBank, one of the world's first operators to go live with LTE-TDD, has until now focused mainly on its LTE-FDD network. It has rolled out 70,000 FDD basestations, compared with 50,000 TDD units, according to Hidebumi Kitahara, senior director in the technology planning division of SoftBank's TDD offshoot WCP. (See Softbank Preps Pseudo-LTE TDD Service.)
But TDD is playing a sharply increasing role, Kitahara says. The operator expects to add another 10,000 TDD basestations this year to deliver additional capacity to Japan's data-hungry consumers. By 2019 Kitahara expects at least half of SoftBank's traffic to run over the TDD network.
When NTT DoCoMo and KDDI deploy LTE-TDD in mid-2016, Japan will be the first country where all operators have introduced the technology.
Currently, TDD accounts for 54 of the world's 393 commercial LTE networks, according to statistics from the Global Mobile Suppliers Association (GSA) . Thanks to the China Mobile effect, however, half of all LTE basestations in operation are TDD.
The ability to do carrier aggregation across TDD and FDD networks could also spur the adoption of TDD.
NTT DoCoMo CTO Seizo Onoe says that when the operator launches with LTE-TDD in 12 months it will be able to achieve peak speeds of 370 Mbit/s by using three-band carrier aggregation techniques.
Over time he expects carrier aggregation to eliminate the distinctions between the two LTE variants. "There will be no more TDD, no more FDD," he says.
Onoe and senior executives from other established FDD players SK Telecom (Nasdaq: SKM) and KDDI all gave keynote speeches at the GTI Summit, run by the LTE-TDD global industry body. KDDI has just become the newest board member of GTI.
In related news, Huawei has also announced a demonstration of FDD-TDD carrier aggregation with 3 Hong Kong , while Nokia and China Mobile say they have achieved speeds of 220 Mbit/s using carrier aggregation across multiple TDD bands.
— Robert Clark, contributing editor, special to Light Reading