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Let me follow up on my own post (can I give myself mod points?).

Here, xG provides a brief description of their spectrum using tehnique: (basically, look for unused segments):

http://www.xgtechnology.com/Technology/technology.html

I was unable to find any reference to xG Flash, the modulation scheme debunked by Phil Karn. Here is xG's description of xMax, the modulation system currently used by xG:

http://www.xgtechnology.com/Technology/xmax-physical-layer.html

which is pretty mundane (for wireless nerds like me: it is BPSK with r=1/2 convo code). No revolutionary power-saving modulation here!
Phil Karn seems to apply the term xMax interchangeably with Flash however, so I am not sure what's up with that.

My guess is now that they've gotten their hand slapped, they "retired" the xG Flash modulation (though it is still mentioned in the press release archives with bogus statements about saving power).

For the record, I have no association whatsoever with xG or Phil Karn.

Let me follow up on my own post (can I give myself mod points?).

Here, xG provides a brief description of their spectrum using tehnique: (basically, look for unused segments):

http://www.xgtechnology.com/Technology/technology.html

I was unable to find any reference to xG Flash, the modulation scheme debunked by Phil Karn. Here is xG's description of xMax, the modulation system currently used by xG:

http://www.xgtechnology.com/Technology/xmax-physical-layer.html

which is pretty mundane (for wireless nerds like me: it is BPSK with r=1/2 convo code). No revolutionary power-saving modulation here!
Phil Karn seems to apply the term xMax interchangeably with Flash however, so I am not sure what's up with that.

My guess is now that they've gotten their hand slapped, they "retired" the xG Flash modulation (though it is still mentioned in the press release archives with bogus statements about saving power).

For the record, I have no association whatsoever with xG or Phil Karn.

but for god sake..there is allready better technology to do that..and even many times cheaper..thats XMAX, this only, will make a revolution on internet accesses.
http://www.xgtechnology.com/

http://www.codingheaven.net/

xmax will be the next wireless internet access technology to put the eyes on. Even wimax, will be put behind. no frequency band licence is needed, very low power, very cheap devices, any one could install an ISP, interesting signal range, what could we want more ? :)
please check it out!
http://www.engadget.com/2005/07/05/xmax-cheap-wire less-broadband/
http://www.xgtechnology.com/
http://www.techworld.com/mobility/news/index.cfm?N ewsID=4722
http://www.codingheaven.net/

I am not an engineer, but does this sufficiently address the potential problem the parent post brings up? (from http://www.xgtechnology.com/faqs.asp#q7)

Q: What is Shannon's Law?

A: Shannon's Law is the relationship between channel capacity C (bits/sec) or maximum data rate, bandwidth B (Hz) and Signal to Noise power ratio S/N, as summarized in the Shannon-Hartley Theorem: C = B log 2 (1+S/N). The narrowband channel allocation that xMax uses to coordinate reception of its wideband xG Flash Signal is not the system's information-bearing bandwidth. xMax does not violate Shannon's Law.

Phil Karn debunked the claims about VMSK here:
http://www.ka9q.net/vmsk/

I AM a radio engineer, and I am extremely dubious about some of the claims in the article/website/etc. The thin line on the spectrum analyzer looks alot more like a sine wave than a system that "modifies each cycle of the sine wave". Others have pointed out that this is another way of stating the essence of phase/frequency modulation, a very old modulation technique.

On the xG website there is a press release that has some tortured details:
http://www.xgtechnology.com/newsitem.asp?id=21

"xG's Flash Signal technology, which utilizes single-cycle waveforms to transmit information at a minimum effective rate of 1 MB/s for each megahertz of spectrum"

Well, to me, you take away the "megas" and you get 1 bit/sec/Hz for the spectral efficiency .. .the same as BPSK.

The only important technical point I can find in the article is this one:

"Moreover, because the receiver -- the design of which is xG's most-guarded intellectual property -- includes a passive wavelet path filter that acknowledges only single-cycle waveforms, all other RF signals are ignored."

My guess is that he has an antenna/feedline scheme that cancels signals that cross correlate with a 1 cycle delayed version of themselves. Most likely, he does this by using two antennas and a bit more coax (at a particular design frequency) on one antenna to cancel any signals that are coherent with themselves for some integration time. This is not a particularly new or cleaver idea, but I suppose you could use it with the modulation scheme to increase the SNR of the signal (assuming of course that most signals are not like yours).

Also, if this is the case, then the geometry of the antenna array relative to the transmitter will be important, because at the wavelength used (900 Mhz) the configuration of the antennas will yeild different phases depending on how they are aligned relative to the transmitter. I take further proof of this in the zdnet article which describes the signal as degrading when the antenna is pointed away from the transmitter. (near the end)

ZDNet UK saw that the bitstream vanished when the receiving antenna was moved out of alignment with the distant transmitter

http://news.zdnet.co.uk/communications/wireless/0, 39020348,39235645,00.htm

This scheme will yield better performance, that is.. until everyone is using it. If there are many signals that are not coherent with themselves over the integration time of the circuit, then the supposed advantages in terms of interference rejection will disappear.

In summary, if everything is as I have guessed, this technology is about the same as using a better antenna for a regular wifi system ... it will get better performance, but at the cost of requiring knowledege of where the base station is located relative to the mobile unit. Also, if the technology is what I have guessed, it will be easily copied if the market finds it to have great value, of which I am dubious. I could be wrong about all of this, but it would be interesting to see more technical information rather than a few plots and a dog-and-pony show. Appeals to authority fail to be very convincing when you are talking about claims in a field with well-known laws limiting performance.

The per MHz refers to the bandwith of the signal. 900 MHz is not the bandwith but the center frequency. Whats got me all sorts of confused is looking at their Spec Anny plots. The damn thing looks like a CW spike and not a modulated carrier. Plus the second plot located here http://www.xgtechnology.com/plots.asp makes it look like it has a carrier plus noise over noise of like 60dB. WTF?? Untill they actually release something more specific about their modulation technique I claim smoke and mirrors.

7.4 Mbps per MHz per Watt is a silly way of saying things. The key is signal to noise at the receiver, which depends on signal loss and noise in the received spectrum where you are seeking the signal.

On their site, xG has a plot of bit error rate versus Eb/No (the energy in a bit over the spectral noise power, which is related to carrier-to-noise ratio as Eb/No=C/No - 10log(data rate)). It appears to perform as well as BPSK (binary phase shift keying). Although it doesn't make it clear how many bits per cycle (technically, bits per symbol) xMax is supposed to have.

You can transmit many bits per hertz. You can modulate between multiple amplitudes or multiple phases or a combination of both over a single sine wave phase. But the hit is that the more bits you send per hertz, the higher the bit error rate you get with the same amount of noise.

"At the demonstration with other reporters, we were able to verify that the signals were being sent wirelessly, and checked the distance by GPS, but had to take the 50mW base station - and its omnidirectional antenna - on trust, since it was at the top of an 850ft mast. The demonstration will be repeated for the US press next week.
Before any of this happens, more demonstrations are needed, to show the system is robust against interference and multipath, and can operate in an area more crowded than 18 miles of swamp. It will also need to be approved by the FCC and other regulators round the world."

It sounds like a great idea, power-efficient and cheap technology will be widely used. But will the FCC approve or will they somehow change the spectrum licensing?

From: http://www.xgtechnology.com/faqs.asp#q16
"Some of the uses their website proposes are: The initial market applications are expected to include, but are not limited to, the following:
Broadband Internet
Beyond 3G - Mobile Broadband
Cellular Telephones (800 MHz - Upgrade to Digital High-Speed Broadband)
Cable TV - Wireless
Cable TV - Wired
HDTV - Wireless
HDTV - Wired
Public Safety Communications (i.e. Police Cars, Fire Trucks, Ambulances, etc)
Satellite
Phones, TV, Radio
Broadband
Wireless LAN
Wireless ATM Circuit (622Mbs)
Ultra fast Bluetooth
Home Automation/Wireless Appliances
Ultra fast DSL
Video on Demand"

Pretty soon everyone will have a wireless network.

Well, the technology site does confirm that in their house they obey the law of Shannon, so they must be using a huge bandwidth.

Note the following: In the first is the statement that Shannon's theorem is not violated but no justification is given. In the second it says that most power is put in the carrier. Both of these statements should raise red flags. Be skeptical!

Your are correct. This is just another scheme to fleece investors. The technology cannot work as claimed.

A system with similar claims called VMSK has been around for years. Phil Karn, a very highly respected engineer, thoroughly discredited it. But they are still soaking investors.

Here is Phil's analysis that shows their claims cannot be true:

http://people.qualcomm.com/karn/papers/vmsk/critiq ue.html

The arguments with Walker, the inventor, went back and forth for a long time. Here is a summary page

http://people.qualcomm.com/karn/papers/vmsk/

Walker's site is still active:

"Ultra Narrow Band Modulation"

http://www.vmsk.org/


You can see much of the claims are similar to the XMax hype. Here is Joe Bobier's site, xG Technology:

http://www.xgtechnology.com/index.html

Since VMSK was debunked long ago and is still being used to soak investors, we can expect XMax to similarly enjoy a long life keeping the unscrupulous owners rich.

Mike Monett

The technical details are sparse but here are two links.

In the faq http://www.xgtechnology.com/faq.htm there is a brief description. Note that the spectrum plot shown is basically worthless because it does not show any signal details.

Here is a magazine article http://www.mwee.com/showArticle.jhtml?articleID=16 3700624 that has a little more information.

Note the following: In the first is the statement that Shannon's theorem is not violated but no justification is given. In the second it says that most power is put in the carrier. Both of these statements should raise red flags. Be skeptical!

The technology site seems to confirm this.