Dual-mode LTE ready for prime time

When the TDD thread of the LTE standard emerged, it was mainly regarded as a technology island inhabited by China Mobile alone, and/or a migration path for Mobile Wimax operators.
Now, as more carriers succumb to the charms of TDD spectrum – often plentiful and cheap, and highly suitable for data-heavy services – TD-LTE is becoming part of mainstream planning for many cellcos.
Established 3G providers will still stay with familiar FDD for the first wave of LTE build-out where they can, but many plan to add TDD later to boost capacity, while some firms have found TDD spectrum a useful alternative when they failed to secure more mainstream frequencies at a decent price.
3 Group was the first to deploy a dual-mode TD/FD-LTE network in Sweden, and China Mobile's Hong Kong unit followed suit last week. Against this backdrop, devices are starting to appear, but TD-LTE is no longer a standalone platform, but must be integrated into multimode roadmaps, making handover a critical issue.
This month, Korea's SK Telecom said it had developed technology to allow handover within a single device, working with Ericsson and 4G chipset specialist Altair. This is significant because it paves the way for dual-mode LTE devices based on a single modem chipset.
The partners demonstrated their breakthrough in a moving vehicle and have now presented the technology to the NGMN (Next Generation Mobile Network) Forum operating committee, with a view to offering it commercially to other operators round the world.
Such an approach could get a solution broadly adopted more quickly than a formal standards organization process, and reflects the strategy of cutting edge mobile carriers like SKT not only to leverage their R&D in their own networks but to gain influence and revenue by exporting them abroad.
Martin Wiktorin, president of the Ericsson-LG venture in Korea, said: “Ericsson is dedicated to ensuring the success of seamless data communications on converged LTE FDD/TDD for operators, so that they can make the most of their spectrum investments and provide the best quality service for their customers.”
Kang Jong-Ryeol, head of the network technology R&D center at SKT, added: “The bidirectional handover technology will allow users to experience seamless LTE service even while on international roaming.”
In Hong Kong, meanwhile, ZTE - one of the two vendors supplying dual-mode TD/FD-LTE infrastructure for China Mobile Hong Kong, says it has deployed the TDD components of the network, which was launched commercially in FDD-only mode in April.
In July, China Mobile Hong Kong awarded Ericsson and ZTE contracts to expand the capacity and coverage of its 4G network by deploying TD-LTE to augment its existing FDD platform. It aims for dual-mode coverage of over 70% of the territory, with commercial TDD/FDD services expected by the end of the year once devices supporting both modes are sufficiently available.

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