Could xMax change the world of broadband?

There are three big questions about xMax, the broadband wireless technology that creator XG Technology claims will give megabit access without needing any dedicated spectrum. What are the details of the claim; does it work; and what does it mean for the future of wireless?

The claims are extraordinary. By combining Ultrawideband (UWB) and more conventional technology, xMax's creator, Joe Bobier, says that the system can let anyone be a wireless ISP — covering thousands of square miles from one very affordable transmitter, and building in denser coverage as new users come online. It does this by using parts of the spectrum with much better long-range and in-building characteristics than the multi-gigahertz bands used by WiMax, 3G and UMTS-TDD — alternative spectrum below 1GHz that, while very desirable, is occupied by other users.

Yet XG says that this spectrum can be reused without upsetting the current allocations because xMax has an unmatched data carrying capacity per watt: it is potentially thousands of times more efficient than its competitors, according to Bobier. Its very weak signals won't interfere with existing users nor they with it, thanks to xMax's receiver design. That, frustratingly, remains secret — although Bobier says that the key component is being patented and the patent should become public some time this month. He also says that the receiver is very simple and cheap to produce.

There are other claims, such as one that the system can be configured in an ultra-low-power mode so that a 2Mbps signal can be transmitted across over 10m with a power of just over 3nW. That's around 300 times less than a quartz wristwatch consumes. There are a wide variety of trade-offs that can be made to make the system match particular needs: one mode has a powerful but very narrow band signal providing timing information to increase the efficiency of the wide band component. If there's no narrow-band spectrum available, that can be omitted at a loss of around 25 percent of the efficiency. And cognitive radio techniques can be used so that multiple transmitters run by independent entities will automatically configure themselves to prevent mutual interference and advertise their most efficient access modes.

Does it work? Nobody can say for sure — not even XG. No independent tests have been published of any of the technology. However, the company has demonstrated a very important part of its plans: it has covered an area of over a thousand square miles with a claimed 50mW signal, and shown nearly 4Mbps arriving at a point almost 18 miles from the transmitter. Even given the details of the test — some 14dB total gain in the antenna systems and a 260m-tall tower for the transmitter — this is an exceptional result.

There are a nearly infinite number of questions to be answered on the technical side: how will the system work with multiple stations, how will it cope with real-life interference, and will it be allowed to operate in the same frequencies as existing licensed users. The company says that although there are severe limitations to the number of stations a single basic transmitter — possibly only 200 at a reasonable speed &;mdash; the much greater area the transmitter's signal usefully covers compared to the alternatives means that it is much easier to get that initial user base from among the much greater potential market. As more users arrive, it is easy to add more coverage by directional antennas or more base stations.

Alternatives such as WiMax would have to establish many more base stations initially to cover the same number of potential customers. Furthermore, the company has mathematically modelled high densities of users, indicating that the technology will continue to work well if it becomes very popular. And the company has said that xMax's key advantages can be combined with the best bits of other standards in a mix-and-match way to produce a very wide variety of solutions. Some big-name companies very active in wireless broadband are starting to take xMax seriously, even if none is ready to go on the record yet.

There are massive regulatory and strategic problems to overcome. UWB, perhaps the closest technology to xMax in existence, has so far failed to turn into consumer products after more than five years of promises; regulators outside the US have been cool towards it, existing spectrum users have raised question after question about its claimed ability to operate across multiple bands without causing interference, and the industry itself has been locked in a damaging, confusing and exhausting battle over the details of the standard. It is not clear that xMax could escape a similar fate, even if the technology questions were to be universally agreed. On the other hand, the bruising and disappointing experience of UWB is instructive: nobody I've talked to who was involved in the process says they'd do it the same way all over again.

And increasingly, regulators are willing to consider radical changes in their approach to managing spectrum. In the UK, Ofcom has said that its "view is that the market is better placed than a regulator to judge the optimum commercial service and technology", which, ten years ago, would have been an unthinkable attitude for such a regulator to adopt.

But if the technology works and the regulators are amenable, does that mean xMax has success guaranteed? Hardly. Take WiMax, which like UWB has been promised for a number of years but unlike UWB has spectrum allocated for it or its similary featured competitors in territories around the world. Despite many millions of pounds in investment and heavy promotion from companies such as Intel, nobody can say for sure whether WiMax will be a success. Even 3G remains something less than a sure bet in many of its markets.

[? /*CMS poll(20003928) */ ?]The most frustrating aspect of all this is that new wireless technologies are very much needed, and that for all its remaining uncertainties xMax has earned the right for a sober and searching review of its potential. That potential is significant: the ideas within xMax can plausibly play a major role in creating the cheap, capable and ubiquitous wideband wireless networks that will mark the next generation of access. Those ideas are just part of a much bigger game XG will have to play if it is to achieve success in a market filled with existing players jealously guarding their space, regulators working with many conflicting interests and alternative systems shrilly proclaiming their suitability.

If all goes well, xMax will have its place as a major component of the wireless future, but that 'if' will figure as prominently in the technology's immediate future as that 850 foot tower did in its immediate past.