Danish Duo – FDD & TDD

The LTE spectrum auction in Denmark concluded with four operators securing bands at 2.5GHz. Hutchinson-backed 3 Denmark led the charge followed by TDC, Telenor Denmark and Telia Denmark.

The interesting thing that jumps out of the auction is that most of the operators acquired unpaired spectrum in addition to the more common paired spectrum. 3 Denmark acquired 25MHz of unpaired spectrum while Telia Denmark & Telenor Denmark each acquired 10MHz of unpaired spectrum.

LTE supports both Frequency Division Duplexing (FDD) & Time Division Duplexing (TDD) modes of operation and while 3G too has a TDD standard (TD-SCDMA) it never gained much traction outside China.

This begs the question now: Why are operators are acquiring unpaired spectrum for LTE?

In my view the answer is rather obvious: network operators around the world are seeing exponential traffic growth and their next network needs to be built for capacity.

During the last two decades operator strategies were focused on coverage – providing the best possible coverage to the user. Marketing battles, spectrum acquisition and network build-outs were all influenced by this coverage-centric strategy. Going forward, however, I believe the battlefront with data is going to shift and in the next two decades it will be about capacity. Coverage will be taken for granted and consumers will pick and churn based on which operator provides higher data rates – and not peak data rates but rather speeds that users can realize in real life. Capacity, capacity, capacity will be the mantra of the next generation of wireless networks. The Danish auction clearly suggests that operators’ spectrum acquisition strategy was heavily influenced by a capacity-centric network rollout strategy…and next in line is the network build-out.

With LTE, networks will mutate. From traditional macro-based “outside in” rollouts the next generation of networks will employ hierarchical cell structures to put additional capacity in the network. Don’t get me wrong, LTE networks will have macro sites and macro networks will be deployed, but their role in the network will change to only provide outdoor coverage and ubiquitous mobility. On the other hand, picocells, metro-femtos and femtocells will form the second layer in the network providing capacity delivering dedicated, localized bandwidth to users.

During the last few years the industry has seen fierce debate and discussions on interference management as 3G femtocells arrived on the scene. Numerous interference management algorithms have been designed, but the reality is that algorithms can only go so far. It only takes yet one more use-case to be defined to break the algorithm as there is no getting around the laws of physics. However, at least the Danish operators now have a simple option to pursue – rolling out their LTE macro networks on FDD (paired) bands while deploying the small-cell second layer on TDD unpaired spectrum.

In other words, FDD for Macro, TDD for Femto.

No interference, a clean architecture and a network designed to deliver capacity. Cheaper and more readily available unpaired spectrum unlocks the potential to realize a multi-layer, non-interfering network rollout that is built for capacity and clearly the Danes have taken their first step in that direction. Now that’s the power of TD-LTE!

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