The competition between LTE and mobile WiMax is getting pretty intense, considering LTE doesn't exist and mobile WiMax is not yet delivered.

But that is precisely why the technologies are at each other's throats. LTE is the anointed successor of the mobile operators' 3G systems, but the upstart WiMax has a lot of backers. And the hype has to start now, because it takes a long while to build a mobile network, and a lot of decisions will be made now, in this pre-delivery phase.

There's a very serious and refined hype war going on. And if the WiMax pitch is right, everyone benefits, because operators can choose between two essentially similar networks, driving down the prices of both. And users can choose between data-centric and voice-centric networks - and maybe get the best of both worlds.

At least, that's the view of Paul Senior, chief technology officer of Airspan. We spoke to him because he inadvertently started a storm last week, with reported comments about an FDD version of WiMax, which could release WiMax from its current spectrum ghetto - comments which the WiMax Forum clarified, saying it had no immediate FDD plans.

FDD is vitally important to create a mobile WiMax that can compete effectively with LTE, said Senior. But first, we asked him, who is right? Is there an FDD version of mobile Wimax on the way, or is the Forum right when it says it hasn't decided yet?

FDD WiMax is real enough to plan for

"Both of us are right, but we are talking about different aspects of the same thing," explained Senior. "It's complicated."

To build a mobile WiMax system, there has to be a standard, further refined with "profiles" that make sure implementations will interoperate. The more mature fixed WiMax standard already has both FDD and TDD options, certified by the Forum.

For mobile WiMax a standard was created that could support both options, and the next step is to refine this with profiles. "If you didn't have a profile the chances of two vendors interoperating would be zero," explained Senior. "The Forum asked, and everyone agreed that it was better to do the TDD profile first."

It's more complicated than that though, as there are two elements to the profile: a system profile, and a certification profile. "The system profile is a generic way in which FDD mobile WiMax would work," said Senior. By contrast, the certification profile defines the behaviour in particular frequency bands, and includes tests. "Ultimately, if the Forum wants a certified profile, it has to create a system profile and then a certification profile."

Senior and the Forum appeared to disagree, he says, because: "My comments were about system profiles. The Forum's comments were all about certification profiles. That's where the confusion comes."

The work on a system profile is well underway, he says, but certification profiles aren't begun yet, and the Forum can't talk about things before a decision is made.

The work on system profiles, after around 17 meetings over eight months, is solid enough to allow vendors like Airspan to get started on research and development, says Senior: "My belief as CTO of Airspan is that we have most of what we need. All that work might be for nothing, but as a vendor we take notice of that."

At this stage, vendors can do system architecture work, but they need a firm commitment from the Forum before they announce products development. "I need to know before I waste my time that the forum is going to do a certification profile," he says, "and in the next six months we will know for sure whether this is happening."

If it all happens as he hopes, "the Forum has it within its capability to build products before the end of 2009."

WiMax versus LTE - getting the hype phase right

Why is FDD mobile WiMax important? "We need to compete with another technology called LTE," says Senior, speaking as CTO of Airspan networks.

Is the end of 2009 a deadline, I ask? If FDD mobile WiMax misses, does LTE win? "Of course not," says Senior. "There is a hype phase in this stuff. We're much more into the hype phase in 2009 than we are in the reality." And the mobile operators' LTE will be just as much of a hype in 2009, he says. "There is a long lead time in all of this stuff."

But hype is important, in making sure the potential customers kick the tyres of a new technology while they are deciding what to adopt. "You must set expectations correctly," says Senior. "It is critical that if mobile WiMax wants to compete with LTE or fourth generation, we've got to get busy on doing things now to be in good shape in the relevant time frames. Now is the time to explain what we are doing."

By contrast, almost all of the work on LTE has focussed on the air interface, and there's been quite a lot more work on how you architect networks on LTE, he says: "But I don't believe any vendor has an LTE product that can be rolled out."

"It is a case of having the appropriate credibility at the right point in time, and having attractive plans for carriers," he explains.

How important is FDD?

The requirement an FDD version of mobile WiMax is more political than technical, but it will be critical when new spectrum is awarded, or re-allocated from GSM bands, he says: "99 percent of that spectrum is FDD."

Regulators might want to be technology-neutral and allow TDD or FDD on all spectrum, but it's a practical issue. Different bands will get turned off at separate times, and paired FDD channels butt up against each other, so it may be that only FDD will fit. "If you put TDD in, you increase the level of complexity. FDD makes the sharing a lot easier."

Also some operators have a permanent FDD licence within a particular band. If they want to re-use it, they need an FDD technology.

FDD is a natural technology for voice-centric networks, he says, "it's natural to have a radio scheme that can handle full duplex communications." With more sophisticated handsets, full-duplex can be produced with time slots, he says. "FDD mobile WiMax handsets could operate in either mode," he says. "Already, fixed WiMax devices can handle both."

"When we created mobile WiMax our philosophy was very data-centric," he admits, while the mobile operators' plans, even for 4G/LTE, start out from voice, and are evolving to handle data better.

"As we start to converge towards 4G, both voice and data become almost equal in importance," he says. "As WiMax emerges from 802.16e to 802.16m, we are interested to improving voice capability and mobility," he says. "802.16e was a fixed technology, tweaked to handle mobility, but 802.16m is a full blown mobile technology."

Why is LTE a challenge?

"We know that mobile WiMax can seriously outperform HSPA," he says, but admits that LTE will be more of a challenge when it arrives. "It's no longer session-centric, it is OFDMA based. In fact, it's a lot like mobile WiMax."

The biggest difference between the two is the choice of uplink modulation technique, he says (Wimax' OFDMA waveform has 10-12 subchannels, while LTE uses a single carrier technique, SC-FDMA). The main reason for the LTE's different choice is to get a higher output power from the handset, he says: "Battery life and range might be better, but you trade that for bit rate," he says. "In a voice centric technology, those choices make sense."

"There are different choices, around different mindsets," he says. "Consumer devices might have Wi-Fi and WiMax, while a voice device might have LTE."

But overall, LTE and mobile WiMax, are "so similar it is incredible," he says. "They could be software difference on the base station side."

Switching horses?

Despite this similarity, the LTE can't adopt WiMax, even if it were politically possible, he said: "They've gone way past that point."

What about going the other way? "It's not too late for WiMax vendors to offer LTE products." It might be even be pragmatic. "Although we've built mobile WiMax, we could easily do an LTE system - it depends on the market and importantly on the intellectual property situation around LTE and WiMax."

Intellectual property is key, he says - and WiMax has always looked good on this front, but it's early days, he points out, and IPR claimants might yet come out of the woodwork. "You could never say for sure, but there is a risk. As of today, we do not pay anybody. 802.16 is an IEEE technology, but there has never been an IEEE technology that has attracted huge IPR licensing issues.

3G, on the other hand has a public mass licensing scheme, and it's highly likely that LTE, coming out of the 3GPP group, is not going to be different, he says, although the existence of mobile WiMax might actually do the operators a favour and persuade the vendors to keep their claims moderate.

FDD WiMax is good for everyone

"It would be a good situation for the mobile operators, having two separate camps reducing their IPR claims in order to get market share," he says. "If I was a mobile operator I would be very happy with that. 3G has suffered from lack of competition."

A healthy mobile WiMax will create "an incredible fight, that the mobile industry should want to see happen - to promote innovation, and drive down pricing," he said. Both WiMax and LTE are supported by large groups.

The latest signs, obviously, will be the Mobile World Congress this month. "You will be seeing mobile WiMax on the show floor from twenty-plus companies - it's a massive step forward from last year."

But won't two technologies be wasteful, like past competitions, say between TDMA and CDMA? "From a hardware perspective it makes no bloody difference," says Senior. "It's all about what software you run on the base station. Even handsets could be soft in that fashion - you could just flash a handset with LTE, or mobile WiMax.

Intel and others are keen to drive this competition with an FDD option, he says. The only people who might object to it would be vendors who have a foot in both camps, and who would prefer WiMax to and LTE to remain distinct technologies.