Wimax-to-LTE conversion: not so simple

Adlane Fellah, Maravedis
Wireless Asia

The wireless broadband market has been divided into the two main groups of wireless operators: the established mobile operators with or without 3G spectrum, and the new entrants, mainly greenfield operators and other fixed line operators. The Wimax Forum and 3GPP have been pursuing two separate avenues to reach the same market.

All-IP Wimax, coming from the IT world, hoped to disrupt the established reign of the dominant mobile operators by providing new entrants with a technology that was not the evolution of past cellular technologies and spectrum characteristics, namely FDD. Wimax was for greenfield players or operators with TDD spectrum that did not need backward-compatibility with legacy cellular technologies supported by LTE. 

On the other hand, LTE was developed by mobile operators - along with their vendors - with little likelihood they would embrace a new disruptive standard. LTE had never been appealing to Wimax operators as an FDD-only technology... at least not until TD-LTE appeared from the ruins of China's TD-SCDMA efforts. There is plenty of TDD spectrum available, and in most cases it is cheaper and under-utilized. Even 3G licenses frequently have TDD allocations and upcoming 2.5 GHz auctions in most cases contemplate TDD bands.

Now that TD-LTE is on the horizon, the question of if and how Wimax operators should transition to LTE has become more relevant. Two years ago several Wimax vendors started to offer a roadmap from Wimax to LTE, thus breaking the taboo that Wimax was losing ground to LTE as a dominant mobile technology.

In response to these trends, the Wimax forum initiated the Wimax 2.0 upgrade that offers most of the same features as LTE-Advanced while providing backward compatibility to Wimax 1.0. Wimax 2.0 is purportedly set to become available towards the end of 2011, but there is little evidence of vendor investment support in the development, especially in these difficult times when resources are limited and vendors have to make a choice.

But what choices do operators have in terms of TD-LTE spectrum?

The Global Certification Forum (responsible for LTE equipment certification) is starting its work in the 2.3 and 2.6 GHz bands, giving a migration path to many mobile Wimax operators operating in those bands. However, due to high signal attenuation, 3.5 GHz band is not seen as suitable for mobile deployments, which is why it is being mostly used today for fixed or nomadic services.

Therefore, LTE has initially left 3.5 GHz band out of its target bands. 3.5 GHz spectrum holders represent the bulk of Wimax operators, and do not have the option of migrating to TD-LTE, at least for now - the Release 10 table has not been released and it is very possible that 3.5 GHz will be included in the profile bands as a way for LTE to enter the fixed/portable market. Other semi-licensed bands such as TV white spaces and 3.65 GHz in the US do not have yet an LTE roadmap.

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