TD-LTE catching fire, but challenges remain

The TLE 3000 evolved packet core from Datang Mobile supports TD-LTE.

Interest in TD-LTE, the version of LTE slated to run in the unpaired spectrum known as Time Division Duplex, has heated up rapidly--so much so that TD-LTE equipment maturity doesn't fall behind FDD (Frequency Division Duplex) equipment. But the technology still faces challenges thanks to a slow release of spectrum in some areas and the fragmentation of the global LTE market when it comes to the myriad of spectrum bands LTE technology in general will be operating in.

According to Erik Ekudden, vice president of technology strategies with Ericsson (NASDAQ:ERIC), several commercial TDD deployments are slated for next year, with China and India--the world's two fastest growing mobile markets--leading the way. But lack of spectrum in some areas will likely hold mass rollouts at bay.

"What we see is the tests and trials done in India and in China and elsewhere show a very stable and mature technology," Ekudden said. "Deployment plans are related to the release of licenses and spectrum, and that part is not there yet. We already have commercial-grade TD-LTE equipment with USB equipment and modules for these mainstream bands."

TD-LTE in China, the U.S. and elsewhere

China Mobile is the most aggressive operator when it comes to pushing the commercialization of TD-LTE technology. With the approval of the Chinese Ministry of Industry and Information Technology (MIIT) to conduct large-scale testing of TD-LTE technology, China Mobile has tapped vendors such as Ericsson, Alcatel-Lucent (NYSE:ALU) and Nokia Siemens Networks to deploy various pieces of the network in seven large Chinese cities.

And the world's largest mobile operator in terms of subscribers has been reaching out overseas to push the technology. Most recently, China Mobile and Clearwire announced they will collaborate to speed up the development of TD-LTE devices and develop system requirements.

Clearwire recently confirmed it will begin deploying "LTE-Advanced-ready" network technology in addition to maintaining its mobile WiMAX network and it will use TD-LTE technology--though the action is contingent on Clearwire getting an additional $600 million in funding. The LTE deployment will take advantage of Clearwire's all-IP network architecture and will involve upgrading base station radios and some core network elements. Clearwire said it will use multicarrier, or multichannel, wideband radios that will be carrier-aggregation capable.

It also appears that the majority of India's Broadband Wireless Access (BWA) licensees, which were contemplating WiMAX  for their 2.3 GHz licenses last year, will deploy TD-LTE technology. Some rather large licensees such as Aircel, Bharti Airtel and Reliance Industries will likely be among the first operators to deploy TD-LTE.

Meanwhile, operators in Europe are sitting on vacant TDD spectrum that was attached to 3G spectrum licenses they won more than a decade ago. Ekudden said these operators, however, have two schools of thought when it comes to TD-LTE deployments: use the spectrum to deploy a macro-cellular network or augment FDD LTE capacity with TD-LTE technology, incorporating it in small-cell form to augment network capacity and coverage.

"It all depends on an operator's spectrum situation," Ekudden said. "TD-LTE doesn't have to be a standalone technology."


TD-LTE is spreading across the globe, according to the Global TD-LTE Initiative trade association.

The benefits of a TDD approach

TDD technologies are better suited to accommodate asymmetric data traffic, which has a much heavier downlink load, increasingly driven by streaming video and audio applications. FDD interfaces have dominated in the cellular network because they are designed to carry the inherently symmetric voice traffic. A mixture of the two types of technologies means data-heavy services such as video could be carried over the TDD network, creating a more efficient use of the network.

As such, base-station and device chipsets capable of incorporating both TDD and FDD flavors of LTE are a requirement, even if an operator is deploying only a TD-LTE network because of the need to roam.

The inclusion of multiple flavors of LTE is a challenge given the fact that not only do TDD and FDD need to be supported but operators around the world will be launching LTE in more than 40 different frequencies around the world.


TD-LTE is set to grow, according to research firm Ovum.

Clearwire CTO John Saw said the main goal in Clearwire's partnership with China Mobile is to accelerate the TD-LTE ecosystem by accelerating the development of a global multi-band, multi-mode chipset that incorporates frequencies between 2.3 GHz and 2.7 GHz.

"If you look at the entire map for 4G, those frequencies are the closest thing to what I call a 4G world band since they are used in many countries," Saw said.

Moreover, the FDD mode of LTE is becoming a requirement among the large operators like China Mobile and Clearwire, said Eran Eshed, co-founder and vice president of marketing and business development with chipmaker Altair Semiconductor.

"There is a small market for TDD only, but FDD is the baseline and is needed for roaming," Eshed said.

TD-LTE devices coming online

The ZTE MF880 USB Modem supports TD-LTE in the 2.3 and 2.6 GHz bands.

2.5 GHz TD-LTE devices are available today in Europe and Asia, and Clearwire has been testing them, Saw said. But he said that Clearwire "wants to be the catalyst to further accelerate high-volume chipsets and devices that would give customers more choices in the future."

He said Clearwire won't come to market with a single-mode TDD device but is pushing heavily for  multi-mode chips that not only incorporate TDD and FDD flavors of LTE but also 3G technologies. The wholesale operator wants to be able to serve as an offload network for all 3G and 4G carriers in need of relieving heavy data traffic, Saw said.

Eshed said Clearwire's agreement with China Mobile is critical because the two, in conjunction with other operators, will hammer out device and chipset requirements and specifications.

"The LTE standard is huge standard with a gazillion different features," Eshed said. "Different carriers have different views. Being able to look at one or two sets of requirements will make it much easier to prioritize."

Altair and Qualcomm appear to be the furthest ahead when it comes to bringing a single TDD/FDD LTE chip to market. Altair's chipsets have already undergone extensive testing with six major infrastructure vendors in a variety of TDD/FDD bands. IPWireless rolled out a tri-band dongle more than eight months ago based on Altair chips. It supports the 800 MHz, 1800 MHz and 2.5 GHz bands.

Eshed predicted that at an FDD/TDD LTE smartphone will come to market within six months.

Qualcomm recently announced a collaboration with Huawei, ZTE, Quanta and BandRich that culminated into the launch of TD-LTE/3G devices based on Qualcomm's MDM9x00 chipsets for the Indian market.    

TD-LTE catching fire, but challenges remain
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