New Technology Could Kill WiMax? 263
GolygyddMax writes "Techworld reports that a Florida-based start-up, xG, has developed a technology that's a 1000 times more efficient than WiMax and which could, in theory, lead to wireless LANs being powered by watch batteries. It is still in early development, but this technology could allow anyone to set up as an ISP. This could kill WiMax before it even gets off the ground." From the article: "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. The system carried 7.4 Mbit/s per MHz per Watt, said Professor Schwartz. By comparison, GSM would have around 0.0058, and CDMA/EV-DO about 0.0085 Mbit/s per MHz per Watt. "
How can they DO that? (Score:5, Informative)
How does that work?
The real issue: interference (Score:5, Informative)
Yeah, an immersive internet would be awesome... but this thing still has some issues to be resolved.
More details here (Score:5, Informative)
Nope, WiMax will come first (Score:5, Informative)
The reality of the situation is that if the new solution is exactly what it's sold to be (unlikely) then it probably will eventually break into the market, but even if it's made into a useable product immediately its use will be overshadowed by the well advertised and enthusiastically sold solution that the vendors are pushing instead. Vendors really don't care what's superior unless they're picking technologies from a menu and they have no interest in any of them (positive or negative). Vendors care about money, and if they've already spent some on one technology, they won't switch unless it's obvious that another technology will immediately dominate the market (VERY, VERY rarely does this happen).
Take off the rose colored glasses, people. Technically superior solutions MAY eventually win out over poorer ones if all else is equal, but all else NEVER is equal.
Plus, it's unlikely that this "breakthrough" is anything but some ambitious people trying to sell something inferior as if it's the solution to All Our Problems (tm).
Erik
Re:How can they DO that? (Score:1, Informative)
Re:Abort, Retry, Fail? (Score:2, Informative)
FAIL
Re:It is still in early development (Score:2, Informative)
"At the demonstration with other reporters, we were able to verify that the signals were being sent wirelessly, and checked the distance by GPS....."
Was the demo mention in the summary fictional?
How am I supposed to know without details??? (Score:2, Informative)
For example... your cable modem will most likely use QAM (Quadrature Amplitude
Modulation) because it doesn't have to expect a lot of interference on the
media. Your digital satellite feed and 802.16 Wimax use QPSK (Quadrature Phase Shift Keying)
because noise does not nearly affect carrier phase as much as the amplitude. None of
the modulation schemes today transmit information on the basis of a single cycle. A QPSK
transmitter will transmit thousands of cycles on one phase and then shift (if need be)
for the next symbol and send out thousands of cycles with that phase. Most textbooks
show just a handful of cycles in example graphs, which gives people the wrong impression.
In all cases this is done simply to reduce the error rate. As far as I can see a hell of a lot of math and thus computing power has to go into their receiver to get a decent rate unless you are just a few feet away from the transmitter.
Will this kill IEEE 802.16 ("WiMAX")...? No... not really. If really viable (and not the
usual crap hype) it will probably in a couple of years end up as an additional PHY.
More likely however, even though there is still a lot we could squeeze out of 1MHz of spectrum: it is hype but hey... surprise me...
Re:The real issue: interference (Score:3, Informative)
What does change are advancements in modulation, DSP's, antennas, equipment cost etc.
The real truth is (Score:5, Informative)
1 - is owned by a single vendor,
2 - has yet to be approved by the FCC,
3 - still needs to pass more testing stages before anyone will dare use it.
Even though it is a sound technology, it does something that other tech has not been allowed to do: use adjacent spectrum that is not licensed to the operator. There are significant hurdles to this technology being used.
Its not math, its advertising. (Score:3, Informative)
-Ruck
Reading assignment for today (Score:5, Informative)
Also, consider the black-box demo - so typical of snake oil these days. If it was an actual, novel system, you'd probably have a custom board with a pile of FPGAs and such in there. No amount of staring at it would tell you anything significant about how it works. On the other hand, if it's a commercial WiFi board with 'Netgear' plastered all over it, it's going to be pretty obvious. So what are they hiding?
Relevant Patent applications (Score:3, Informative)
The invention disclosed in this application uses a method of modulation named Tri-State Integer Cycle Modulation (TICM) wherein a carrier signal, comprised of a continuum of sine waves is modulated such that spectrum utilization is minimal. A modulation event is imposed upon the carrier signal by modifying the carrier frequency at precisely the zero crossing point or the zero degree angle. The method of imposing the modulation event is by increasing the frequency of the carrier for one or an integer number of wavelets then lowering the frequency of the carrier for one or the same integer number of wavelets then returning to the carrier frequency to derive the modulation event. The main carrier frequency is only modulated beginning at the zero degree phase angle and ending at the 360-degree phase angle.
20050007447 [tinyurl.com] Modulation compression method for the radio frequency transmission of high speed data
20040196910 [tinyurl.com] Integer cycle frequency hopping modulation for the radio frequency transmission of high speed data
Re:How can they DO that? (Score:4, Informative)
Patent? (Score:1, Informative)
Re:How can they DO that? (Score:3, Informative)
On their site, xG has a plot of bit error rate versus Eb/No [xgtechnology.com] (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.
Re:How can they DO that? (Score:3, Informative)
Not quite. It suggests they can cram 7.4 bits into a 1Hz wide channel.
For example in theory you could descide to represent data using a carrier which
at any instant in time can be at one of 256 different power levels. That gives
you eight bits per symbol. To keep the frequency components of the signal within
a 1HZ channel you have to change the power level slowly which liits the symbol rate. For this to work you need the signal to noise ratio to be high enough that you can tell the difference between the different carrier levels in the time available. If you make the symbols longer you have more time to average out the noise.
Shannon's law gives the maximum amount of data that can be sent through a channel with a paticular bandwidth and s/n ratio.
is xG VMSK (Score:3, Informative)
"XG technologies goes on the air with their method in November from an 800 foot tower..."
More info on VMSK here [uni-lj.si] and here [qualcomm.com]. The first paper states "no ultra narrowband modulation method, which includes VMSK and VPSK, can have substantially greater efficiency than conventional methods, such as QAM, in transmission in the same frequency band".
IAARE (Score:5, Informative)
well, not professionally but I know what it is about.
Digital transmission works as follows: you select a certain waveform out of a set and transmit it. At the receiver you try to figure out which one it was. Unfortunately the reception is distorted because of noise you pick up, such that the distinction is not perfect (e.g. in case you can reliably tell 8 possible waveforms apart three bits will be conveyed each time you do this). Using more power will lead to a better distinction and therefore higher bit rate. Using a larger (RF) band width allows you to send more waveforms per second hence also increasing the number of bits transferred (this is simplified somewhat).
Shannon left us a nice formula to calculate the capacity aka maximum possible throughput EVER, but first you need to calculate the signal and noise power you receive.
1) If we assume the waves travel in free space, the received signal power will be dependent on
- transmit power
- transmit antenna gain (dish is more focused than dipole etc.)
- free space loss (FSL, i.e. field strength getting weaker far from the source because the energy is spread out in all directions)
- receive antenna gain
This is an optimistic assumption because their setup takes place in suburban territory!
We can assume both the antenna gains are 0dB, being small and probably not perfectly matched.
The FSL is equal to: R^2*4pi^2/lambda^2 (R=distance, lambda=wavelength)
At 900 MHz lambda=0.33m, R=18 miles=29e3 m.
FSL= 3e11(in 'power') or 115dB.
The transmit power was 50mW, i.e.17dBm, the total received power will be 17-115=-98 dBm. The thermic background noise is equal to -173dBm/Hz (best case, due to ambient temparature - this is a bit optimistic too because other wireless devices are transmitting there too).
2) The channel capacity is given by Shannon as C=B*log2(1+S/N), where C=capacity (bits/sec), B=bandwidth (physical, in Hz), S=signal power (-98dBm), N=noise power (-173dBm/Hz*B).
You can now play with the bandwidth to influence the capacity. To a certain extent an increased bandwidth will increase the capacity but after a while you are just catching more noise while the signal will be spread out in frequency, so this saturates.
For these numbers the (theoretical) maximum capacity would be about 4.5e7 bits/sec or 45MB/sec. But even to achieve the 3.7Mb mentioned you already need a bandwidth of 700kHz (rough estimate, I made a plot in matlab).
At that point you transmit 3.7Mb/(50mW)/(0.7Mhz)=100Mb/s/W/MHz, so their figure of 7.4 MB/2/W/MHz is not impossible. However it will be difficult to achieve. We have made some assumptions (especially about the loss in the urban envorinment), and their bit rate only has a 'margin' of a factor 12 (45 to 3.7). There you have it.
WiMAX lives (Score:2, Informative)
WiMAX is simply a term used to denote appliances which have been certified by the WiMAX Forum [wimaxforum.org]
From their FAQ [wimaxforum.org]:
"The WiMAX Forum is an organization of leading operators and communications component and equipment companies. The WiMAX Forum's charter is to promote and certify the compatibility and interoperability of broadband wireless access equipment that conforms to the Institute for Electrical and Electronics Engineers (IEEE) 802.16 and ETSI HiperMAN standards"
They have started testing loads of equipment from various manufacturers, as part of their "certification" process. These products should have been certified before the end of the year. Here are some examples:
Siemens "WayMax" [siemens.com]
Alvarion BreezeMax [alvarion.com]
WiMAX is very much alive.
Re:How can they DO that? (Score:3, Informative)
The easiest way (to explain) to make it work is to assume that for each period you change the amplitude of the sine wave, e.g. you transmit a sine wave of 1V, 2V, 3V... or 128V. At the receiver you measure the amplitude (number from 1 to 128) and this would allow you to transmit 7 bits. At the same time you can transmit cosine waveforms and play the same trick (another 7 bits). This would be one way to transmit 14 bits/Hz, albeit not what these guys (pretend to) do.
Brings to mind VMSK (Score:3, Informative)
http://www.ka9q.net/vmsk/ [ka9q.net]
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 [xgtechnology.com]
"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 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
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
Re:IAARE (Score:3, Informative)
Yes, it's called "coding gain" and it can be measured in dB. If you want to get the results you would have had with twice as much signal to noise ratio, you need 10*log(2)=3dB coding gain. Unfortunately, putting in forward error correction reduces the data rate or increases the bandwidth, so you need to make sure you're coming out ahead.
If you're interested in experimenting with these topics, try reading about ham radio digital modes for HF (3-30Mhz). The cost of entry is low, and with open source software such as gMFSK [connect.fi] it's possible to do your own experimentation. You might start with this historic article [arrl.org] that started a new set of experimentation on a phase-shift keying modulation scheme called PSK31 [arrl.org], which packs all the power into a tiny 31Hz wide bandwidth. You can read a less technical description [wa5znu.org], or read about other modulation techniques using multiple carriers (MFSK [qsl.net], Olivia [sunrise.ch], which uses Walsh functions for FEC and can be copyable with low power in noisy conditions).
For a long overview of HF digital mode performance in practical circumstances, see this paper [rsgb.org.uk] from the Radio Society of Great Britain.
There's also plenty going on in UHF as this 900 Mhz work is doing, but it's a little harder to experiment there, but if you are already comfortable building 802.11 equipment and have the skills necessary there, there's plenty to do. Some hams recently conducted Earth-Moon-Earth bounce communcations using 47GHz (which I heard one of the 24GHz pioneers say would never happen!).
And at the other end of the spectrum, US, Australian, and European hams are experimenting with LF [arrl.org] in the 137KHz region (under special license in the US) and have made super-slow communications across the oceans. There are challenges here as well, and the data rates are extremely low, not unlike the 76KHz signal that we used to send to our nuclear submarines underwater, which I think is roughly one bit (a repeated "don't-blow-it-up don't-blow-it-up don't-blow-it-up...).
Some history of the principals... (Score:1, Informative)
Here's a Google cache link [google.com] to one of the stories.
Choicest quote:
They may have the real thing this time, but... (An account of the story much friendlier to Mooers appears on his website.)