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Mobile WiMax & LTE: Collision or Convergence?

The specter at the impending WiMax feast is that it is not the only 4G mobile in the offing, and a lot of industry money is riding on the GSM/3GPP Long Term Evolution (LTE) as the technology that will result in (almost) a single global mobile system, with multiband handsets being usable anywhere and with ultrafast broadband capabilities. So it is being promoted by many in the mobile industry as the 4G successor to the current 3G technologies, split between W-CDMA, CDMA 2000, and (perhaps) the upcoming Chinese TD-SCDMA. The advantages and opportunities presented by a single global mobile technology are obvious and would represent a major break with the fragmentation that has bedeviled mobile since the plethora of 1G technologies in the 1970s and 80s.

Given that GSM/3GPP technologies hugely dominate current systems, the big mainstream mobile operators are looking closely at LTE, and some have been campaigning to speed up its standardization process. Vodafone Group plc (NYSE: VOD - message board), Verizon Wireless , and China Mobile Communications Corp. are running (or will run) LTE trials. Vodafone’s began in Europe in February 2008. NTT DoCoMo Inc. (NYSE: DCM - message board) has said it will start commercial deployment in 2009, Verizon in 2010/11, and Vodafone after 2010. KPN ran a trial in 2007 to compare 3G HSPA with WiMax to determine which would be the best technology to use for providing broadband access in rural Netherlands – a decision is due during 2008. And both AT&T and Verizon say they will use spectrum won in a recent FCC auction to build LTE 4G networks in that 700MHz band that will be able to deliver video and other advanced mobile services, with network rollout beginning around 2010.

LTE is acquiring heavyweight support from the mainstream mobile vendors, which are taking steps to boost the technology. In April 2008, Alcatel-Lucent, NextWave Wireless, Nokia, Sony Ericsson Mobile Communications , NEC Corp., and Nokia Siemens Networks created a framework for LTE IP licensing, intended to keep royalty payments low and hence encourage the takeup of their LTE technology.

Technically, two versions of LTE will coexist: Frequency Division Duplex (FDD) LTE and Time Division Duplex (TDD) LTE. These are a compromise technology hangover – FDD follows on from W-CDMA, and TDD from TD-SCDMA. A key issue for the industry is to produce chipsets that can handle both forms, so that a single handset can automatically switch between them and be used globally. In theory, LTE will support connections speeds of up to 50-100 Mbit/s (or even higher) eventually. In comparison, 3G is expected to approach 30 Mbit/s eventually, but is currently limited to about 4 to 7 Mbit/s.

Mobile WiMax versus LTE 4G looks like a sticky issue that could affect WiMax operators and the development of the WiMax market generally. Ericsson, for example, has given up on mobile WiMax to concentrate on LTE 4G. Some mobile operators have complained at the slow pace of 4G development, and have hinted that they will used WiMax instead. There are also some conflicts of interest among vendors and among operators over the two technologies.

However, technically, WiMax and LTE look as if they could converge pretty closely in the long term, as they share common features (such as MIMO antennas and beam forming), and both are OFDM based. Perhaps more to the point is the "natural" realm of application of the two technologies. LTE is being developed as the obvious 4G extension for the mainstream big mobile operators. In developed markets, where they already have good 3G coverage and a roadmap to increase 3G speeds over the short-to-medium term, the arrival of the first LTE rollouts in two or three years’ time means that they have little motive to scramble to introduce another new technology, such as WiMax. And these operators clearly want to generate as much revenue out of their current new HSDPA/HSDPA+ networks between now and, say, 2012/13 before they are forced into another upgrade by LTE.

WiMax supporters may, however, suggest that waiting for LTE to arrive could prove a false economy for these operators.

“They should be clear that there is no ‘evolution’ or ‘upgrade' to LTE from existing 2G or even 3G networks,” says Asas Inbar, Alvarion's senior manager of corporate marketing. “It's, at the very least, a radio access network fork-lift upgrade. In that respect, the question the operator should ask is whether the competitive landscape allows taking no action for the next three to four years while waiting for LTE to arrive. The alternative is to deploy WiMax now.”

Both LTE and WiMax 802.16m are proposing up to 20MHz bandwidth with 4x4 MIMO and beam-forming advanced radio techniques to increase spectral efficiencies. According to Telsima’s Mack, the main differences are evident in LTE’s SAE (Service Architecture Evolution) network topology, which is being designed to accommodate legacy 3GPP standards. He points out that this typically requires an expensive box with complex software to make the accommodation within a given network.

“However, the premises of both WiMax and LTE are sound: all-IP networks connected to base stations able to communicate to mobile subscriber devices over advanced OFDMA air interfaces,” he says. “The questions surrounding which technology are more those of – when is the deployment to take place? in what spectral band? for what targeted consumer applications? and with what legacy support requirements?”

Further, some vendors seem already to be preparing for WiMax/LTE coexistence (or, at least, are hedging their bets). For example, NextWave’s V5 TD-CDMA base-station platform (available later in 2008) will “support the installation of both WiMax and LTE radio shelves – all supported by a common digital baseband unit,” according to the company. Motorola has made a similar move by developing a common baseband control unit for both WiMax and LTE. And Telsima says that it will support both technologies, as it will require minimal changes to its base station and supporting ecosystem to accommodate LTE.

Extra impetus for WiMax/LTE convergence comes from the International Telecommunication Union, Radiocommunication Sector (ITU-R) ’s recent call for candidate technologies for IMT-Advanced, a new generation of mobile systems that go beyond the current IMT-2000 specifications. Neither LTE nor WiMax currently satisfy the needs of IMT-Advanced, but the organizations behind the two – the 3rd Generation Partnership Project (3GPP) and the Institute of Electrical and Electronics Engineers Inc. (IEEE) , respectively – are working on proposals for the necessary enhancements, such as the IEEE’s 802.16m. However, some in the industry see this a good opportunity to merge the two to avoid a fragmentation of effort and markets, and to stop standards running too far ahead of market realities.

Overall, the immediate outlook seems for WiMax and LTE to coexist, but with LTE focused largely on the established cellular operators and markets, and with WiMax focused more on alternative and emerging operators and markets. However, the two technologies are at different phases of development, with WiMax being at least two years ahead of LTE in terms of commercial deployablity. So there may well be some timing interactions between them: Should mobile WiMax prove obviously successful, there would be pressures on the cellular operators to speed up their LTE deployments.

And it shouldn’t be forgotten that both WiMax and LTE are but a means to a similar long-term end – bringing IP broadband access to myriad mobile and other widely distributed devices, many of which have never been able to communicate before. There could be a new business model building out there.

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