TD-LTE has entered the mainstream

Caroline Gabriel/Wireless Watch

Rethink

Part 1: LTE map to be very different from 3G's
Part 2: BRIC taking leading role in 4G 

The influence of China Mobile has promoted TD-LTE from sideline technology to mainstream contender. This trend will only accelerate as operators run short of spectrum and start to look at the neglected, and web-suitable, TDD frequencies. Also, TD-LTE provides a migration path for Wimax operators who want to tap into the broader device ecosystem and economies of scale promised by LTE.

The TDD flavor will allow some non-traditional players, such as TV operators and rural providers, to enter the mobile space, but its main function is likely to be as a second wave technology for cellcos whose FDD spectrum starts to get overstretched.

At this stage, they will either deploy or buy their own TDD licences, or offload traffic to a TDD-based partner. The biggest example is Clearwire in the US, which will migrate much of its Wimax network to TD-LTE. The resulting system will be able to provide wholesale and offload services to key customer Sprint, to complement its own FD-LTE build-outs in its 800MHz and PCS bands.

A similar approach is seen in Japan, where KDDI has a Wimax/TD-LTE subsidiary in the shape of the UQ Communications joint venture, and Softbank is planning a secondary network in the TDD spectrum it acquired from Willcom. And in Europe, some major operators like Orange are already testing TD-LTE with a view to activating their TDD holdings when they see their initial 4G net-works coming under strain. Some carriers will also look to use TDD bands for separate purposes to the FDD frequencies – perhaps to run a dense mesh of femtocells, offloading traffic from and FDD-based macro network to ease congestion; or to support specific services such as M2M.

The second dual-mode FDD/TDD network in the world went live last week, at Hutchison's Hi3G unit in Sweden. While many operators will wait until their current capacity is exhausted before adding TDD, Hi3G has taken this view at a far earlier stage than most of its peers and invested in both types of frequencies right at the beginning, seeking to steal a march on larger and more established rivals in the Nordic regions. It bought both types of licences in Sweden's 4G auctions and is now deploying services in Stockholm, Gothenburg and Malmo, using equipment from ZTE.

Its plan – like the other dual-mode projects at Aero2 and the Australian NBN broadband initiative – shows TD-LTE moving beyond its first customer bases, among Wimax carriers looking to migrate to the newer standard, to the future when it will also be part of the network mix for mainstream, traditionally FDD-focused cellcos.  The key to TDD success will be a broad device ecosystem, and China Mobile, with key ally Vodafone, has worked hard to persuade chipmakers and OEMs to support both modes as a default in their designs. They have not quite achieved that, but most silicon suppliers at least have TDD and dual-mode on their roadmaps, and the operator strategies outlined above will make affordable dual-mode devices essential from 2013. 

According to the GSA industry association, as of August there were 31 trial TD-LTE networks and one live. As well as the Wimax/LTE developments going on in the US, Japan, Korea and elsewhere, there is already a commercial TD-LTE carrier (Mobily in Saudi Arabia) plus the dual-mode rollouts. These deployments are proving a major boost for the Chinese vendors, whose Wimax activities and closeness to China Mobile have created a headstart in TDD technologies – Huawei (with Samsung) provides the kit for Mobily and Aero2, while ZTE is the partner for Hi3G. Samsung is also well placed for TDD because of its Wimax leadership.

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