TD-LTE edges towards the mainstream

The TDD flavor of LTE is finally being regarded as a mainstream technology, which may still lag behind its FDD stable mate by about three years, but has a strong chance of gaining wide adoption outside the Chinese market where it originated.
China remains the key driver of the ecosystem, but new TDD spectrum will be allocated in most regions of the world during the current wave of 4G auctions, and carriers everywhere are considering how it could be harnessed to augment their capacity. For instance, some European operators expect to deploy TD-LTE as a second wave when their FDD capacity starts to get strained, or to use the TDD band for a separate layer of small cells, within a HetNet, or for a specific function such as machine-to-machine services.
Other operators, like Orange and AT&T, plan to use unpaired frequencies to add to their initial LTE network capacity, using supplemental downlink techniques. Then there are carriers which already have access to TDD bands, often because they have Wimax businesses, Clearwire being a famous example.
Most of this spectrum is in 2.3-GHz or 2.5-GHz, but some players, like UK Broadband, are even harnessing the 3.5-GHz band. This gained new prominence recently when the FCC talked about releasing 100MHz of spectrum here, possibly targeted at small cell networks with global roaming potential. The band is suited to small cells because it supports base stations with limited range, and so is generally uneconomic for macrocell rollouts.
Doug Pulley, chief technology officer [for] wireless at chip provider Mindspeed, said in a recent interview with ThinkSmallCell: “This is really nice spectrum to use. Significantly, it is one of the few global bands – and it is TDD everywhere. While it's at the limit of what a macro cellular network could deploy, it's really good at short range/high bandwidth, it will go through walls a little better than the 5-GHz used by Wi-Fi 802.11ac. There's also plenty of bandwidth available.
“The rules about how this spectrum could be allocated and used aren't yet clear. It could be standalone or possibly use carrier aggregation with other bands which could be quite interesting to existing spectrum holders. Perhaps it will be positioned somewhere between the 'free for all' Wi-Fi and completely independent cellular networks.”
These are interesting options for the future, but the real focus today is on the major new TD-LTE roll-outs like those in China and India, and even a few cellcos looking to do dual-mode FDD/TDD from day one to maximize their data capabilities (such as 3 Scandinavia).
According to DigiTimes, the chronicler of the Taiwanese device business, local handset makers expect demand for TD-LTE devices to take off in the second half of 2013 or the first half of 2014, while the latest figures from the GSA says that 68 of the 417 LTE devices now available have TDD mode enabled (this figure includes fixed gadgets and modems, not just handsets, and enabling TD-LTE does not mean it is actively used).
The expected uptick in late 2013 will depend on China Mobile sticking to its schedule for deploying 4G services from later this year. The cellco‘s vice general manager, Li Zhengmao, said this week that the operator would launch more than 10 TD-LTE smartphones by mid-2013, rising to over 100 by 2014. It is currently testing TD-LTE in 13 cities, including Shanghai and Beijing.
Li Zhengmao told local reporters: “The TD-LTE industry chain has become mature and it will have enough models within one or two years”, though Mobile also needs to obtain new operating licenses for 4G to achieve full coverage, and the government may not grant these for another two years at least. However, it will upgrade existing TD-SCDMA base stations in the meantime. Its growing network continues to be described as a trial because of the lack of licenses, though with 200,000 base stations planned by next year, that “stretches the definition of what a trial is” as Ric Clark, an Asia-Pacific vice president at Alcatel-Lucent, put it. Most of the phase two “trials” are in 2.6-GHz rather than refarmed 3G spectrum.
With all this activity, TD-LTE will account for 25% of all LTE connections by 2016, according to new estimates from Ovum. Analyst Daryl Schoolar said that mobile broadband services will be the main application of TD-LTE, but it will also be deployed for fixed wireless and small cell backhaul. He said: “Thanks to multi-standard base stations, mobile operators will look to the same vendors that deployed their 2G/3G and LTE FDD networks to deploy their LTE TDD networks.”
He added: “Combining multiple standards will grow the overall network capacity and increase quality of service. This is just a small part of it; the bigger opportunities lie in operators deploying it as their primary 4G network, such as Bharti Airtel in India and Mobily in Saudi Arabia. Moreover, LTE TDD provides cost benefits due to the price of unpaired spectrum, which can be passed on to end users.”
In this multi-standard world, interworking will be crucial. Ericsson recently performed the first bidirectional handover between FDD and TDD flavors of LTE on a live network, demonstrated on an FD-LTE network run by China Mobile Hong Kong. "As the handover demonstrates, Ericsson can offer operators a fully integrated FDD/TDD network that, from a systems point of view, is as simple as handover between a system running two frequencies," said the firm.