Even a year ago, the TDD flavor of LTE was at least two years behind its FDD cousin and very much the junior partner.
But the eagerness of vendors to access the dollars of chief backer China Mobile, as well as others including Reliance Infotel in India and Clearwire in the US, has accelerated their R&D roadmaps and the technology is close to full commercial availability.
It is particularly being eyed as a standard which can be adapted more flexibly than FD-LTE to take advantage of underused spectrum, including unlicensed frequencies and the 3.5GHz band, and to support new business models, such as machine-to-machine and data-intensive services for business.
One way to extend LTE into bands where it does not sit comfortably in its current forms is to use license exempt spectrum. Deploying LTE in such bands is increasingly discussed as a way to maximize capacity and simplify data offload from licensed networks. As regulators in the US and Europe become friendly towards one of the (mainly) license exempt options, the white spaces in TV bands, Huawei has produced a TD-LTE system for the frequencies from deep in its laboratories.
The vendor said it had been working on the technology for two years but had not publicized it. However, supporters of the TDD version of LTE – which will underpin China Mobile's 4G roll-out in future, among others – see an opportunity to extend its influence by pushing it into unconventional bands, even if FD-LTE remains dominant in the “classic” mobile broadband frequencies such as 1.8GHz, where most spectrum is still being allocated on a paired basis.
Huawei's trial platform is called TVWS (TV White Space) LTE TDD and it is now embarking on field tests, particularly with an eye to interference problems with incumbent broadcasters or wireless microphone users. The trial is scheduled to be completed in mid-2012.
“The LTE TDD system can take full advantage of TVWS bandwidth and enhance spectrum efficiency,” Tan Zhu, director of Huawei's wireless strategy department, states. “This LTE TDD system will benefit network and service providers by offering a combination of strong operation and management capability, a mature industry chain, and variety of deployment scenarios.”
As with other sub-1GHz spectrum options, the key attraction is that fewer cell sites are needed, reducing the cost of covering sparsely populated areas, and low frequencies also deliver good indoor penetration. So far, most technologies tested in the white spaces have been akin to Wi-Fi, as pushed by backers like Microsoft and Google. Other pioneers like the UK's Neul are focusing on applications like machine-to-machine communications, which will not come up against the capacity limitations of the spectrum in the same way as mobile broadband.
Meanwhile, a new joint venture between VelaTel Global Communications (previously the Wimax operator Chinatel) and NGSN (Next Generation Special Network Communication Technology, is showcasing how TD-LTE can be adapted to innovative business models even when most mainstream consumer services are running in the paired FDD frequencies. The pair plan to build and operate a TD-LTE network to support business-to-business services, initially in China.
NGSN has a valued added services license to provide location-based and other information offerings in China, while VelaTel has spectrum and commercial broadband wireless networks in several regions, as well as in other emerging markets such as Peru. It already has a strong vendor partnership, including financing deals, with ZTE, which will supply the new TD-LTE plans, starting with the north eastern province of Heilongjiang.
The first focus will be on navigation and location services, but the companies plan later to expand into other applications as well as other Chinese regions. There will be no attempt to address retail consumers though, according to VelaTel’s CEO George Alvarez, because of the “attendant challenges of marketing budgets and competition with other carriers for subscribers.”
Instead, like other 4G start-ups such as LightSquared, the new venture will pursue a wholesale and B2N strategy, with NGSN acting as the first “anchor tenant.” As well as its own services for corporations, it will help enlist other customers among enterprises and vertical services suppliers.
The network could have potential in home automation, smart grid, environmental protection, industrial automation, healthcare, precision agriculture, public security and video surveillance, said NGSN’s general manager Lu Bin.