The WiMax Forum wants operators to consider using Mobile WiMax – perhaps even using it instead of LTE, the mobile operators' officially anointed successor to 3G and HSPA networks. But can it really expect operators to change direction like that?

“LTE and WiMax are both overlays to cellular networks,” said Mo Shakouri, the WiMax Forum chairman “Operators need something for mobile data and LTE is a fork lift upgrade. If we can get enough deployments of Mobile WiMax. We have a shot at establishing ourselves.”

The point he is making is that operators need to add new capacity specifically for data, and their next steps for that are to use LTE or WiMax. Both of these use the same modulation technique (OFDM) as well as MIMO beam-forming. The addition has to be an overlay to the new network, and it has to be in new spectrum.

So operators can choose which to use. LTE has emerged from the 3GPP standards group, but is a data-oriented protocol, and interfaces to a new all-IP core network. WiMax also connects to that core. Both handle data, and operators are expected to move voice onto data.

“All roads lead to OFDM & MIMO,” is how a short white paper (PDF) from the WiMax Forum puts it. “Mobile WiMax (802;.16e) is already there.” WiMax has already used OFDM and MIMO for fixed networks, and wireless LAN is just adopting them for 802.11n.

Mobile WiMax could be preferable, the Forum says. It will have a vast array of devices, including dongles, smartphones and laptops, already on the market on Korea's WiBro. “A global industrial complex is in process of delivering the economies of scale of the PC industry to the mobile broadband area via WiMax,” says the white paper.

It's also going to be cheaper for operators, says the Forum, as they won't have to pay so much in licence fees for the IPR that is embodied in the radio equipment.

The message the Forum gives is that LTE doesn't have any inherently better upgrade path from today's 3G networks. It's simply come from the same people. The move to LTE doesn't have to be automatic.

So, I asked them, are you saying that LTE could be the Windows Vista of the 3GPP? The upgrade that's supposedly automatic, but which causes users to jib, and consider alternatives? The Forum doesn't tend to speak in quite such dramatic terms, but they liked the analogy.

Is FDD an issue?

It's been said recently, however, that WiMax needs an FDD option to position itself as the alternative for LTE – the WiMax Forum is keen to defuse any anxiety on that issue. There was a clear preference among Forum members to start with TDD, and is ready to create FDD profiles when there is demand, says Shakouri: “If the operators tell us tomorrow that they need it, we'll do it.”

He also dismisses the “Trojan Horse” idea - that having got IMT-2000 approval for TDD WiMax, an wiMaX FDD profile would automatically be approved for IMT-2000's agreed FDD spectrum. That's a separate approval process – but one Shakouri is confident will be successful. “The reason we got the TDD profile through the ITU is because the operators wanted it,” he says.

Vodafone's Arun Sarin made a plea for WiMax to be included in the 3GPP programme, in his MWC keynote, which was reported in some places as a request for the technologies to merge. In fact, it's been pointed out, that multiple technologies could be a benefit to operators, as competition will drive down the cost of both.

So which will win?

Silicon vendors are the ones working hardest to understand which direction things will go. After all, they will have to provide whichever base stations and handset chips the operators require.

To some extent, however, they can hedge their bets. The same silicon can support LTE or Mobile WiMax – the air interface is the same, and it's more or less just a software load that makes the difference .

In the traditional handset space, silicon vendors are backing LTE. Klaus Muller of NXP, the silicon company spun out of Philips, was demonstrating software defined handset silicon, and reckoned that the operators would stick with brand they know.

On the base station side, vendors have a bit more leeway. Rupert Baines of PicoChip – which launched a base station that can do either WiMax or LTE depending on softwar - had some sympathy for the Windows Vista analogy.

However, he believes in cellular networks the division will be 80-percent in favour of LTE, with the 20-percent going to vendors – like Sprint - moving on from CDMA. This will happen even if LTE is later than Mobile WiMax.

“It might be a slow and painful process, but operators are likely to go that way,” he said. “In that sense, it could be a good analogy.”

However, he pointed out that his 80-20 split is for cellular networks. In networks as a whole, WiMax could have the edge – boosted by deployments for fixed broadband in emerging markets such as Mexico, where due to a shortage of copper networks, WiMax is simply the only option.