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xMax - is it real?
We took investigative journalism to our personal limits
By Peter Judge, Techworld
Published: 10:00 GMT, 04 November 05
Along with one or two other journalists, I'm in Florida to see, a demonstration of xMax, and you can also see stuff at
With a new technology you do have to be careful whether you are actually seeing what they claim. In this case, we saw a demo that appeared to send data from a 50mW base station, using an omnidirectional antenna, to a receiver 18 miles away. Even given the fact that there was 6.5dBi of gain on the sending antenna, and 8dBi on the directional receiving antenna, that is still impressive - consider how small a signal that is, when you reach that radius!
As we discuss elsewhere, if this is true, the implications of this could be very impressive - although it is possible that the early promise might run up against barriers in the real world. There are two possible barriers - regulation, and interference.
Can regulation allow it?
Regulators might get cold feet about it - although the fact that it runs at low power means it could be allowed under current regulations.
The demonstration we saw used the unlicensed 900MHz band, where devices are allowed to radiate up to 1W of power. The regulators never envisaged that this would be enough for long-distance signals, that could deliver wireless broadband services but, we understand, there is nothing in the regulations to prevent it.
xG wants to use xMax modulation over a wider band, at tiny amount of power, less than the power which unintentional radio sources are allowed to leak (under the so-called "noise floor"). One implementation of this, which we described in July, uses a beacon signal, at a higher power level, that can be sent using a narrow-band licence, with broadband data carried under the noise floor, but now we are told, the beacon is optional, and can be replaced by synchronisation signals in the low-power signal itself.
What about interference?
The other possible bugbear is the fact that it won't be out there on its own. What if multiple xMax signals are using the same beacon frequency? What if multipath reflections produce something like an xMax modulated signal? Will it work for moving receivers, where Doppler effects will shift the radio signal cycles?
xG tells us all these have been considered, and will not produce unsurmountable problems. The demo we saw certainly appeared to work, although this was across 18 miles of swamp land with, we presume, not too many interfering sources, even in the crowded 900MHz band.
But is it real?
In the end, at this stage, whether this is a revolution hinges on whether the technology actually works in the scenario we have seen. And we have to wonder whether the demo could have been faked.
The technology is not published and has not been peer-reviewed. xG backer Rick Mooers says this is to keep it safe from competitors, and inventor Joe Bobier says he has a patent coming out in a month's time.
Till then, this technology rests on the status of the people who have seen and been convinced by it. This one has been checked over by Princeton professor of electrical engineering Stuart Schwartz, and that is the most important badge it has. Schwartz has effectively staked his reputation on it. Initially sceptical, he came round to the conclusion that it is clever, but not magic, and certainly not snake oil.
My colleague checks the antenna connections
In our turn, the journalists on the trip still did our best to check things out. Here is radio wizard Rupert Goodwins of ZDNet checking the antenna connections to the black box and the oscilloscope, while the inventor, Joe Bobier, talked to the rest of us.
The connections went where they should be, and when the receiving antenna we twisted out of alignment, the signal faded on the oscilloscrope - showing the signal came from an external source.
Another colleague, Adrian Mars, checked the distance using a GPS receiver - although fact that we spent half an hour in a bus driving along straight roads with names like Alligator Alley, did give us a general feel that we had gone something like the distance claimed.
But what about the base station? Was it really only a 50mW signal? Was the antenna really omnidirectional (a crucial point, since a directional antenna would have given a far better power level at the receiving station)?
So - is there a base station up there?
In the end, investigative journalism could only take us so far, and we had to take the word of Bobier and Schwartz. The transmitting station is at the top of an 850 foot tower, in the middle of the hurricane-battered Everglades.
Our American colleagues will be seeing the demo next Thursday. Perhaps one of them will go up there - or maybe xG could hold send a lucky employee up there for a video conference.
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