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VMSK/2 Promises 5 Times More Bandwidth
ksan writes "Acording to
this article in EDN Magazine; VMSK/2, a new modulation technique may improve modem, FM, AM and other types of transmission. They say that its possible to transmit 100 channels of 128kbps MP3 over an FM channel. Anyone can say more about this?"Read below to find out the *major* problems with this article.
Cancel those DSL orders! I wonder how the new technology will compare to other technologies, pricewise and feasibility-wise. I hope it can give DSL a run for the money. DSL is a great technology, but this sounds pretty cool. Things just keep getting better. I guess it'll be awhile until the technology will reach consumerville, at least my neighborhood anyway.
This is a emf signal, not a sound wave. How fast do you drive?
Doppler happens with any motion. How do you think the nice traffic officer figures out how fast you're moving? With the precision of this modulation scheme, the little bit of doppler that happens will become significant.
I work at Alphacom and have talked with several folks working on VMSK/2 and yes it is true it is an improvement. But it's definately not as great of an increase as this article claims.
After reading this article my impression is the author decided to exaggerate the technology to make his article more exciting. From what I've heard so far, the maximum transfer rates VMSK/2 will achieve is around 256kbit/s in optimal conditions. Most users can expect better then dual channel ISDN, which I think is pretty good for wireless.
Note: These are my personal views and do not reflect the views of Alphacom Communications.
> No one really "owns" the airwaves
Do you really believe that? If you live in the US, then the airwaves are owned (licensed? bought? stolen?) by a few large media corporations. Infinity, Clear Channel, and AMFM come to mind. Learn more about the situation at http://www.mediademocracynow.org.
If you really want the airwaves to be free, join us in protest of the NAB (National Association of Broadcasters) on September 20-23 in San Francisco during their convention.
Ryan
I seem to recall that a large part of the secret is phase modulation. (erm. although that may be my star trek fixation talking.)
I have vague recollections of polar plots (phase and amplitude). Each pulse is a point in this graph. Depending on how good your circuitry is, you can discriminate finer and finer regions. Ig you have 8 regions, you send 3 bits per pulse.
So if you believe that as a very rough sketch, you can extrapolate that better phase/aplitude detection allows you to discrimnate 2^19 regions. Hrm that sounds like a lot. Maybe not; assume 8 bits amplitude, that leaves you 2^11 bits phase, which you can do at 2048 hz sample rate.
How they then go to 2^90 regions... that I leave up to the experts. or better bullshit artists.
Does that make sense to anyone?
My understanding of the tech is that it is very similar to HDSL. The basic theory (of DSL) is that the only part of a wave that really matters is the peak or trough. The rest of the wave is just wasted bandwidth. To increase the data rate the DSL modem will produce a wave up to the peak/trough then stop that wave and go right into the next wave. The effect it produces on an o-scope looks like high-speed chirps.
/. dislikes whitespace, i'll give you an example using amplitude/phase readouts
The next stratagey they use is to increace the combination of bianary digits that a wave can represent. Instead of letting a peak/trough represent a bianry 1/0, they use a "bullseye" to let the peak/trough send multiple bits.
Since
0 volts amplitude and 0 degrees of phase shift would be binary 0000
.1v and 0d is 0001b
.2v and 0d is 0010b
.1v and 1d is 0011b
to help visualize this think about each wave as a seperate entity and not part of the carrier and then place the voltages and phases on a sheet of graph paper.
By allowing each wave to represent a byte/word vice a single bit, you pump up the datarate. This is why we refer to modems in kb/s and not baud anymore.
If this is what they are doing, they are just modifying the current algorithms that everyone uses for standard modems.
I'd rather you do it wrong, than for me to have to do it at all.
I read the EDN article yesterday and it has a number of factual errors. For example, it mentions that a 56kbps modem can deliver 19 bits/Hz which is just not true. The author got that number by dividing 56kbps by the 3kHz "bandwidth" of a voice line. Of course, 56kbps modems only do analog on your local loop and use more than 3kHz of bandwidth. That pair going to the central office can support much more than voice bandwidth (which is why DSL works so well) and the 56kbps modems use that fact as well as a characterization of the D/A and A/D converters at the CO. The real number is closer to 14 bps/Hz. Beyond your local loop the signal is digital all the way.
The amount of information that you can transmit through a channel is dictated by the Shannon limit:
D B * log2(SNR + 1)
Where D is the data rate in bits per second, B is the bandwidth in Hz and SNR is the signal to noise ratio of the channel (assuming Gaussian noise). In order to get 90 bps/Hz, you would need a channel SNR of over 270 decibels! Exponentials are ugly that way. For those not in the know, that's HUGE.
There's no avoiding noise in commuications channels: thermal noise abounds and in a radio link is not going to go below the 3 Kelvin cosmic microwave background radiation (in completely empty space). In order to get the 270dB signal to noise ratio with a 3 Kelvin noise floor, you would have to transmit with 42 kilowatts of power per Hertz of bandwidth. The whole thing doesn't seem very efficient to me. To compare, at 14 bps/Hz you can get away with an SNR of about 42dB, which would only require you to transmit about 10^-17 watts of power per Hz to compete with the cosmic microwave background.
Of course in a real application, your noise floor will be much more than the 3 Kelvin CMBR...
Here's an interesting page which describes VMSK technology in a semi-technical manner.
I understand that nudging the duty-cycle would cause spreading in the frequency domain (at least, I think I do) but didn't the article say that the signal is then run through some narrow bandpass filters or something? So then wouldn't the nudging sort of degrade to a phase shift or something?
My point was that this filtering would lose information. Your available bandwidth influences how fine and how fast a phase shift you can detect.
Good question, though.
I understand that nudging the duty-cycle would cause spreading in the frequency domain (at least, I think I do) but didn't the article say that the signal is then run through some narrow bandpass filters or something? So then wouldn't the nudging sort of degrade to a phase shift or something? Oh, man...freakin' electronical things, hurtin' my brainez.
jeb.
And then there are those people who live in areas with no other bandwidth alternitive except $600/month 128k ISDN..
This is probably a really really dumb question (to someone) but every time I hear about some new advance in wireless networking (which assumes 2-way communications) I start wondering about this:
How much wireless stuff can be crammed into a given volume of physical space before the crosstalk and interference disrupts everything?
I visualize the problem as this: radio is really just another form of light, so each wireless device is the electromagnetic equivelent of a 3-watt light bulb. The color of the light is its frequency (or "channel", if you prefer.)
Imagine the average suburban neighborhood, but where all the houses are made of glass (to allow the light metaphor to work - radio passes through walls) Each house now has a couple of thousand of these colored lights stuck in it (all my appliences, etc. are networked), shining all over the place. The neighbourhood is awash in light! How are these devices supposed to function in this kind of environment?
How well does the aether scale?
Want to learn about race cars? Read my Book
We can write the modulated signal as
v(t) = A * exp(j * m * (d(t) - 0.5))
where d(t) is a binary data signal. If m=Pi/2 then we have a BPSK style modulation. Make m small and we get a VMSK signal. This small value of m is what gives them a proportionally smaller occupation of the spectrum for the bit rate.
NoW consider the constellation of this modulation in the complex plane, we have two points representing the bits 0 and 1. For BPSK they are seperated by Pi radians, while with VMSK they are much closer together. VMSK is therefore clearly more vunerable to noise than a BPSK scheme. At the above website they clearly state that the noise resistance (C/I) is significantly better with VMSK!!!
It seems clear that there is a basic fault in their reasoning, and they can't beat Shannon in this manner. D.
Unfortunately, you're forgetting that FM is broadcast, and you don't have the power to broadcast the signal from your laptop (receive only)
Sure you do. Cellphones broadcast relatively strong FM signals, so why can't laptops? Of course it would require a complex network of antennas (perhaps use existing cell towers?).
=================================
I pledge allegiance to the flag...
of the Corporate States of America...
FM radio has a 200 kHz bandwidth. You need some seperation between channels so assume that each FM channel has a useable bandwidth of 150 kHz (as per the article). As for FM audio it only uses about 56 kHz. There is a subband of about 20 kHz that most FM stations lease out to transmit things like shopping mail music. There is a whole lot more bandwidth, but today's FM stations are not equipped to use it.
FM stereo uses 0 to 18 kHz for Left+Right, has a stereo pilot signal at 19 kHz, and has Left-Right centered around 38 kHz (20 to 56 kHz). I believe the Left-Right audio is double sideband modulated and the stereo pilot signal is frequency doubled to be used as its carrier. I can't remember where the subband is, but it somewhere above 56 kHz. I believe that the subband is either AM or double side band modulated (ie AM carrier surpressed). Yes the FM radio spec wastes a lot of bandwidth.
This is all from memory. Please correct me if I am wrong.
Could it be deployed in a cellular-like fashion, so when I drive cross-country, I could access my mp3s on my machine back home?
:\
:P
Great idea, but due to the possibility of someone intercepting the data, you'd have the RIAA on your ass
Could this be deployed in a car-to-car fashion?
Again, an interesting idea to most (including myself), but probably not to the RIAA. Incidentally, will this be a "tune-in-and-listen-to-what-I'm-listening-to" sort of thing or will it be a "listen-to-whatever-I-have-that-you-want" sort of thing? The second one could get rather complicated, especially with the driver trying to simultaneously drive and page through a list of MP3s trying to decide which one to listen to. It's hard enough trying to find a radio station to listen to
=================================
I pledge allegiance to the flag...
of the Corporate States of America...
The information-carrying capacity (C) of a channel is a function of its bandwidth B and signal (S) to noise (N) ratio. The formula (this is elementary information theory) is
C=B log2(1+S/N)
We can plug in the given values for B (200 KHz) and C (12.8M bit/sec) and determine the required signal to noise ratio:
12.8e6=2e5 log2(1+S/N)
log2(1+S/N)=64
S/N=2^64 - 1
Each bit of signal-to-noise ratio corresponds to 3 decibels (6 dB if you're talking about power, which I won't, just to be charitable), so the required S/N ratio is around 190 dB.
Is this achievable? In a word, no. It's not even close. They're off by more than 100 dB.
When these guys claim that `when properly implemented and used under the right conditions, the digital modulation scheme reportedly delivers 90 bps/Hz-over the air' they're blowing smoke. They're saying they need a 270 dB S/N ratio. (That's larger than my number because I gave them some extra slack.) If they could get it, their scheme would work, but they can't, so it won't.
-Tom Duff
I doubt it will take off.
Malike Bamiyi wanted my assistance.
I've looked for any decent links on this and most of the pages read like alien abduction sites, all fluff and hype. I found only one university with info on it and it was in China. Anyone care to translate? http://www.chinainfo.gov.cn/periodical/shjtdxxb/sh jt2000/0002/000225.htm
-d
dr. dopler's strange effect works for waves in general, not just the audio band.
"There's no secret. You just press the accelerator to the floor and keep turning left." -- Bill Vukovich
70 dBm is 70 dB (=10000000 times) above 1 mW = 10 W.
...
70 dBW is 70dB above 1 W = 10kW.
I think the math is OK
RFC1925
There's clearly something wrong here (see amusing calculations below). So, we go look at their web page. Wait a minute! Their pictures use square waves, not sine waves. They're actually broadcasting on all frequencies, and are misrepresenting their bandwidth. Problem solved. The real data rates may be what they claim -- they just use way more bandwidth than they claim.
The critical test, which they do not report, is to send and receive data through a narrow bandpass filter that eliminates the high-frequency components of the square-wave signal.
Amusing calculations:
The photon shot noise of a 1W, 100 MHz signal implies a maximum SNR of about 10^12.
SNR = Sqrt[Power/h*BW], h=6*10^-34 SI
A more reasonable microwatt radio signal has a maximum SNR of 10^9 and, with 100 MHz bandwidth, a throughput limit of 6 Mbps.
To get the SNR of 10^27 they claim as maximum (see below) you'd need a star-powered transmitter. And our sun probably isn't big enough.
To get a SNR of 10^19 you need something like 10^13 watts of receiver power. A nuclear plant wouldn't work. So, clearly either we've misinterpreted the research, they're full of crap, or they're on to something new.
See for yourself. My opinion? If it sounds too god to be true....
as an executive member of my college radio station, I'd argue the fact that there isn't any good music. If anything, there is MORE good music now than ever before. Thanks to technology and decreasing costs of really good equipment, almost everyone can make an album that sounds as good as one produced by WB or the other major labels.
Therefor, the question isn't that there isn't good music, just that no commerical top 20(which all commercial radio stations are now, by the way...) radio station is willing to play them. They are only willing to play something "safe," something that falls clearly within the genre, something that sounds similiar to another band that has proven sucessful.
If you want to hear the good music, now you have to turn to college radio. One I would suggest is the U of Minnesota's Radio K--they broadcast via realaudio, and you can check them out here
mike kohout
> 70 dBm is 70 dB (=10000000 times) above 1 mW = 10 W.
> 70 dBW is 70dB above 1 W = 10kW.
Gee, where was I when I wrote that ?
Yes, 70dBm is 10kW, but it only makes the case more clear. By using VMSK/2 modulation you use a lot of power to conserve bandwidth. This can be advantageous in some situations, but clearly *not* when you need high baud rates
RFC1925
Yeah, I didn't count that, since it's not actually carrying data. In fact, the FCC doesn't like to license stations less than 500kHz apart. 'Course, New York and L.A. are big markets...
Stereo pilot is at 19khz if i'm not terribly mistaken.Yeah... I've been thinking more of MTS stereo on TV, which is basically just the same thing as FM stereo with a different pilot frequency.
All frequencies higher than 18khz or so are filtered out(so that they don't mess with stereo carrier). 40khz bandwidth is a good estimate..Well, remember, they're not filtered out, they're modulated into the additive and difference signals. The (L+R) signal that you hear on a mono FM radio, then the pilot which turns on the FM stereo circuits, then the (L-R) difference signal which is used to create the stereo image. All that space is available under such a scheme.
Increased bandwidth does have a bigger impact, however. Would probably want to use frequency bands over 1ghz where a bandwidth of 500khz-1mhz is obtainable..Why, when you can basically run a dozen 56k modems slingshotted through the same given bandwidth? Use the bandwidth efficiently, and you don't actually need the 500-1,000kHz bandwidth.
Besides, UHF/microwave sucks. It's way too position dependant. I don't want a Walkman that has to be moved three feet to the left before I'm able to receive the Howard Stern show again. Since UHF/microwave tend to bounce off lots of things, reflections and self-cancelling signals are going to be a constant pain in the ass.
Fire and Meat. Yummy.
Hemos wrote:
VMSK/2 Promisses 5 Times More Bandwidth
...And 50% more "s"s.
A second thing that I was concerned with is how much would interference affect these signals. The article mentions interference should be low since it is such a narrow channel. I was thinking of a weak signal and how would it affect the data. Would the loss of data make the signal unusable. Plus in areas where overlapping stations on the same frequency, how would the data react.
It seems like they are testing this cellular communications and given the authors thoughts on the problems of FM and AM interference, it looks like they plan to use this with cellular service. Maybe radio from your cell phone? It looks this will be a pay service to subscribe, like radio cable. I wonder if it will catch on any faster than that?
-- Wolfpup
"A man whose circumstances went beyond his control." -- Styx
MTV stopped playing music years ago because there simply isn't enough good music to fill the airwaves. Britney Spears, N'Sync, and everyone else that will be on the FOX Teen Choice Awards tonight are proof that there is something wrong. Regardless of what percentage they make up in the general population, teenage girls seem to have a HUGE influence on the music that is chosen to be "popular". Popular music hasn't appealed to the masses in decades.
You can have all the bandwidth in the world -- if nobody's interested in what's on, it's all a big waste of time.
--
--
There's an interesting article in this week's New Scientist about actually making use of multipath reflections to enable more bandwidth to be squeezed out of a given transmission band by simply increasing the number of transmitters and receivers (well, OK, not simply, but you get the gist). Combined with an advanced modulation technique like this...
Well, the bandwidth of an ordinary PSTN telephone line (not DSL!) is only from about 300Hz to about 3kHz. And in that bandwidth, the practical transmission limit, the current state of the art, seems to be stuck at 56k.
You can't stream a 128kbps MP3 at 56kbps. Not in real time, as radio implies.
What's the bandwidth of a conventional FM radio station? 20kHz or so carrier deviation for mono. To light up the stereo light, the stereo pilot must be found, and that runs at about 21kHz carrier deviation, if I recall. A full FM stereo signal takes a carrier wave an modulates it about 44kHz either way, so 40kHz bandwidth is probably a practical conservative estimate and has easy enough numbers to work around.
Since a 56k modem uses quadrature amplitude modulation on ?4? simultaneous carriers in a total bandwidth of 2.7kHz (3000Hz top end - 300 Hz bottom end), then how many carriers could you stuff into a 40kHz wide data channel?
I think it's exponentially more.
This sounds very exciting.
Fire and Meat. Yummy.
For the benefit of us poor slobs who had the unutterably bad taste to attend college 20 years ago, when the best modulation methods going were things like Huffman codes and trellis codes, the notion of sending 19 bps/Hz (much less 90 bps/Hz) is a bit mysterious. Can one of you folks with a modern education post a few URLs where I could see how they are managing to accomplish this? Thanks, from the annoying old fart in the next cube.
WWJD for a Klondike Bar?
We need more scientists like Moore, who ensured that chips would continue to get faster and cheaper, and they have. That's progress. That's a good guy.
All Shannon, Nyquist, and Einstein have done is limit the rates of communication we can attain and bloat our harddrives with 2F-sampled signals (Mp3z, pr0n). What jerks. Much worse than Gates.
jeb
Instead of broadcasting just MP3's or any other form of digital media over the airwaves would it be feesable to get rid of them all together and use the internet for everything? If this kind of bandwidth is possible could we not change the FM/UHF/VHF bands to internet only communication, and the broadcasters would use the internet instead to broadcast their media. Because the broadcasters would use the internet they would be able to reach everyone in the whole world and not just the people in thier area. Of course this would allow anyone to be a broadcaster which the current broadcasters would likely be against.
With the broadband that is starting to roll out, houses with fibre or other broadband technologies would be able to use it as the connection, or for people out in the middle of nowhere they could use the wireless technology. Car radios would be internet clients that connect to all the radio stations, TV's would also do the same thing for TV broadcasts, etc.
I don't know if the bandwidth would be able to handle all of this, but if you could have 100 streams over each frequency I think we'd be okay, especially if they were low power which would allow the frequencies to be used over and over again within a certain distance. I'm sure someone out there will be able to figure it out.
This refers to the channel capacity. This is the data rate supported by 1 Hz. of channel b/w. Remember that you can "violate" the nyquist rate for a digital signal if you use more than one "symbol," ala QAM, QPSK, etc. Therefore, it's possible to send more than 0.5 hz of informational b/w for every 1 hz. of channel b/w. btw: This is most likely a scam -- as a graduate degreed electrical engineer, with emphasis in information theory (which, strangely enough, is not mentioned in any of the sites claiming the miracle of this "new" modulation technique), I find many of the claims to be without substance. First off, eliminating redundancy from information to be transmitted is nothing new -- most non-lossy compression algorithms operate on this principle (for example, LZW compression used extensively on computers). The problem with eliminating redundancy is that you need to add some "controlled" redundancy back in to the information stream, in order to be able to detect and correct errors (hence convolutional, ECC, CRC-types of coding techniques for instance). I hear no discussion of the error performance of "VMSK" modulation. I also hear claims of "no drop in SNR as bandwidth is reduced." Sorry, guys, but if you're sending any "useful" information on the channel, this is going to require exponentially increasing power. This sounds an awful lot like "perpetual motion machine defeats bulk entropy. Film at 11." --- tjc
From my reading of this, this modulation scheme relies heavily on timing- which would really get screwed up if you happened to be moving, because of doppler shifts. Keeping accurate track of timing is very, very hard when moving. Also, they don't really address interference (intentional or incidental) which will make it that much harder to reach those bandwidths.
VMSK/2 seems to be mostly an academic modulation right now- they need to send it through much more rigorous testing in the real world, with real world components.
I'm skeptical when people talk about overturning Shannon's limit- people would love to disprove it, but it holds up time and time again.
Well actually since it's per Hz and Hz is per second, it would be 90 bits per second * second, or just 90 bits. But it's more informative to leave it at 90 bits per second per Hz.
With this technology, boasting that they could deliver 100 128Kbps MP3 channels probably means that they are probably planning on doing such a thing, maybe even squeezing the compression a little more to get a few more channels out of it.
While this is all great from a technological standpoint (and probably a business one at that), I see a trend of lower quality broadcasting coming about. While I understand that radio transmission is typically less than perfect (static, power wires, etc), digital artifacts of compression come through even on the clearest of signals. And on a side note, with digital cable, sometimes it almost looks like I'm watching a video screen with an 8-bit color depth.
I guess my rant is that the people on the delivery side of television and radio are letting their quality standards decrease. They can pack more content into the wires/airwaves by using compression, and this leads to lower quality decoded signals. For the average person, this is not an issue (and you're probably smirking right now). For the audiophile, this is quite a disturbing trend.
My two cents; no refunds.
--
Never hit your grandmother with a shovel, for it leaves a bad impression on her mind...
I guess that's how the whole dang human comedy keeps perpetuating itself. ok bye.
Axel
Axel
mhm23x3, alt.fan.karl-malden.nose
Multilevel Marketing Organisation.
Typically ML organisations are more interested
in building a network of "sales" agents and
taking their money than in delivering anything
like they promise.
Be skeptical.
See Alphacom Corporate page
for their spin.
Ethics II Axiom 2. "Man thinks." B. Spinoza
Nice theory, but this is impossible to implement:
....
Do the math:
Shannon's channel capacity theorem:
C= B * log2 ( 1 + SNR )
C = capacity in bps
B = bandwidth
SNR = signal to noise ratio
Solving for SNR in dB ( = 10*log10(SNR) ) gives:
SNR_db = 10 * log10 (( 2 ^ (C/B)) - 1)
With C = 12.8 Mbit/s and B = 200 kHz you get SNR = 192 dB !
To have a SNR = 192 dB, the signal has to be 1.8 * 10^19 times stronger than the noise ! A receiver with 200kHz bandwidth will typically have a noise floor at -120 dBm, so you need more than 70 dBm received signal strength. 70 dBm is 10 W !! And that is the signal strength at the receiving antenna, so the transmitter would have to be in the gigawatt range, to reach short distances.
This means that VMSK/2 can be used, but you can't reach 12.8 Mbit/s without a nuclear powered transmitter. You can get a decent bit rate with VMSK/2 on battery powered equipment, but you have to design for a few kbit/s, not 12.8 Mbit/s. Nice theory, but
RFC1925
maybe starting something similiar to a shoutcast/icecast server and recieving that, then you can listen to your mp3's and so can anyone else that may want to!
What? Not a single Asian among the authors? :)
It can't possibly be true, they got their math wrong for sure.
-- What you do today will cost you a day of your life.
Physicists are showing it may be possible to send some information faster than the speed of light, which is impossible, mathematically proven I believe.
An old "law" of physics says that it's impossible to set up magnets passively, with no outside supports, that levitate. Recently, scientists unveiled a magnetic bearing that does just this.
Didn't engineers say it was physically impossible to have a feature size of less than something like twice what we are using now? Granted, that wasn't a mathematical proof, but they seemed pretty confident about it.
When Einstein was working on relativity, I'm sure people thought of all this dilation of time as being mathematically impossible, though I don't know what proof that would be violating.
Quantum physics is chock-full of logical impossibilities.
The point is, sometimes there are non-obvious ways to circumvent "laws" of nature. I'm not saying Alphacom has done this or anything, I'm just saying that we shouldn't brush off the possibility by saying that it would violate Shannon's law if they did.
jeb
Even if this is technologically sound, how easy would it be to implement something like this? Digital radio was supposed to be the "next best thing" and for some reason has failed miserably. Why? Because everyone has the same kind of radio, and not everyone can upgrade on a moment's notice. There won't be any people on the new system, so stations will stay on the old system (ratings, remember?). Since there won't be any stations on the new system, everyone will stay on the old and have no reason to upgrade.
icqqm [ICQ:11952102]
I like! Now, how stable can we make an FM signal to a computer? This could damn well be another method of providing high-bandwidth internet access, and a good one at that.
Because No one really "owns" the airwaves, like one does a cable, you could get a lot of competition amongst providers for customers.
I can see the Laptop/Handheld owners screaming now. I have a palm, and the thought of cheap high bandwidth wireless access for it amuses me.
-i
Nice to see this "confession" from someone in the know. It's still not enough, though. He says that the increase is not as big as the article claims when in fact there *cannot* be any increase in performance compared to state-of-the-art techniques like QAM.
The implementation of VMSK/2, however, is significantly simpler. VMSK/2 can be implemented with an extremely low gate count without quadrature A/D converters, complex digital signal processing and equalization. So if its performance is not too suboptimal it might still be interesting. It would have been much more interesting 10 years ago, though. Today you can put half a million transistors on a chip without blinking.
----
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
Match this with that power-line broadband, and just think of the potential... heck, we could stream MP3s faster than the speed of light - they could even be ripped and distributed before the artist records them!
--
"It's tough to be bilingual when you get hit in the head."
I wonder how this will affect the coming of Digital Radio, as well as the FCC's new standards to ease the starting of small community oriented radio stations...
credo quia absurdum
Sounds like a breakthrough
Higher bandwidth radio
Shortwave Pirates Smile
--
"It's tough to be bilingual when you get hit in the head."
Founder's Camp
Founder's Camp
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Am I the only one that read that as "VMS 2K?" Now there's a scary thought...
Very Minimal Shift Key
Heres the link to the "technical information." I still don't think it's anything but a scam. It reeks of it, just look at the ads and scrolling text.
My shift key is small enough. :P
Skreech
I Think the operative word here is *may*
I bet this is vapor ware and nothing will ever come of it.
___________________
___________________
He who laughs last... Thinks slowest
This really sounds like a good idea, like getting standard phone lines to have like 256kbit/s as standard, but would it work in practice with a lot of users on same telephone central??
-Stskeeps, http://unrealircd.com
I'm HIGHLY doubtful, to say the least, and the article does nothing to give any credence to the claims. A quick search of Compendex yields this article by the research report authors. Our library doesn't carry the publication so I can't check it out. If anybody else has access, I'd really be interested in a review. What is Applied Microwave and Wireless? Is it peer-reviewed?
Author(s):
Koukourlis, C.S.
Pliatsikas, J.C.
Sahalos, J.N.
Walker, H.R.
Title:
Spectrally efficient biphase modulation FOUND IN:
Applied Microwave and Wireless v 10 n 4 May 1998. p 74, 76-81
Publ. year:
1998
Abstract:
Phase modulated biphase codes which are transmitted single sideband-suppressed carrier at RF frequencies require much less bandwidth without any significant increase in circuit complexity. These codes have an important advantage over other bandwidth efficient modulation methods in that they do not lose bit energy with increasing bandwidth efficiency (compression). Actual measurements confirm this characteristic. 10 Refs.
Must be marketing,
Only a certain bit rate,
My pr0n remains slow.
Ceci n'est pas une sig.
From the article:
You can think of VMSK/2 as a form of duty-cycle modulation (Figure 1). Think of a "square" wave whose total period does not vary but which, depending on whether a given bit interval contains a 1 or a 0, spends slightly more or slightly less than half the period in the high state.
Problem - this kind of nudging of the duty cycle causes spreading in the frequency domain. In fact, it is these additional frequencies that encode the change in the duty cycle.
If you try to transmit a signal modulated using this technique through a very narrow channel centered about the carrier frequency, you will lose a lot of the duty cycle information, and your data signal will degrade a *lot*.
I am skeptical of this getting much more effective use of bandwidth than conventional encoding schemes. The best I can see them getting is a modest gain if this technique is less sensitive to common types of noise (which has yet to be demonstrated).
I agree, although I felt the journal article was just about right for my two years rusted EMC and Communications stuff.
;-)
The main thing that I picked up on was the sheer lack of spacing between the transitions of the final data and the original clock. As I read it, this means that the clock recovery circuitry is going to have to be spot on every single cycle.
Admittedly things may well have changed since I last saw them, but PLLs were notoriously unstable when I played with them. I wonder how they're going to make the receivers sufficiently portable to make this worthwhile in a mobile situation.
What we probably need is the original StrongARM design crew from DEC and give them something like a DSP32 to play with
PS: I daren't imagine what the constellation diagram would look like for such a creation.
Correct me if I'm wrong but doesn't Hz mean "per second". Does this mean that we now have 90 bits per second per second? After 1 second, 90 bits transferred, after 2 seconds 360 bits... Wow, this could be big.
q='echo "q=$s$q$s;s=$b$s;b=$b$b;$q"';s=\';b=\\;echo "q=$s$q$s;s=$b$s;b=$b$b;$q"
Where have all the 20 channel 128kbit mp3 stream FM channels been?
Most of the article explained how different this transmission mode was from the standard we use now. Electromagnetics is a really complex and interesting field...
I can't get to the article (where I'm working this week has a weird proxy set up) but I'm curious -- are they proposing moving closer to what Shannon says the link is capable of, or are they trying to break it?
The first time I saw this on TV I did not know whether I should burst in laugh about their stupidity or start to cry about what happened to Germany. However, there is one thing for sure: If I was in the recruitment section of a big company I would hire these guys at once. I suspect the value of such people for marketing purposes is vitally unlimited.
Alpha Communications is such a scam!1 0710
1 0710
Notice how on the page they don't even mention what VMSK means? They do on their business scam site: http://www.alphacomopportunity.com/cgi-bin/d.cgi/
If you go to their page you see they avoid discussing their technology and talk all about their business plans.
I'm surprised these guys aren't advertising snake oil or $4000 a month work at home jobs in the newspapers. Don't be fooled they are scam artists.
I also saw on www.indexdirect.com/classifieds this advertisement:
Business Opportunities
FOR SALE Increase your current internet connection
Posted on: 2000-08-11 .
Details:
Increase your current internet connection by thirty times it's current speed! FREE for 5 days Become a distributor (under 10 bucks) Check out the VMSK technology!! Have a GREAT day
Email : carters@polbox.com
Contact: Shelby Carter
Website: http://www.alphacomopportunity.com/cgi-bin/d.cgi/
Listen to 128k mp3s with headphones especially when you hear a cymbal playing, it sounds distorted as hell. The minimum would have to be 192k to even be close to FM quality.
Only the State obtains its revenue by coercion. - Murray Rothbard
No, they are actually doing the opposite from that: instead of multiple bits/symbol, they are using one bit/symbol. The bit is initially encoded by a change in duty cycle of a square(-ish) wave. They then modulate a carrier with this signal, remove the carrier and a sideband, finally filtering the resulting sideband with extremely sharp, patented-technology filters.
I'm real suspicious... the initial square wave would have to be several MHz, and it seems that the subsequent processing would either wind up stripping out the information or result in a multi-MHz bandwidth in the resulting signal. I could be all wrong, but until I saw the math that shows exactly how the bits are encoded and extracted, I'd be skeptical.
Correct in respect to Doppler but wrong in its application. A radar gun actually does not measure anything but Delta D over Delta T (change of distance over change of time). Granted it does this quickly but it does not use the doppler effect to measure the speed. For doppler to really become an issue I would think that you would really need to be traveling around 1/10000th the speed of light or even 1/100000th for something like this.
Sorry, *absolutely* correct in its application. The only sort of police "radar" that uses timing to determine distance is a laser radar gun. The traditional RF police speed radar (known as Doppler radar) mixes a sample of the outgoing signal with a received signal and makes a beat between the two. Generally this beat is in the audio frequency range. By beating the outgoing with the incoming it doesn't really matter how much your main oscillator drifts, because over the microsecond or so that the signal takes to make a round trip it won't have drifted far. This sort of radar (as I have described it) can't distinguish between incoming and outgoing targets, but there are DSP based police doppler radars that have this ability, with a different downconversion technique.
Time to go back to basic physics- for a speed much less than c the doppler shift of a signal will be a factor of 1/(1 +/- (v/c)) where v is the radial velocity to or from the observer (- when approaching the observer, + when going away).
For example, with a radar operating at 18GHz, the doppler shift of a car moving at 100 ft/s is about 1.85 kHz. Check out this page for more information on doppler. Things do change as you approach the speed of light, but doppler still does matter, and I think it matters in this situation because of the extreme timing accuracy that this modulation requires. If the timing accuracy goes down, so will the bit-rate.
As an RF engineer and a broadcaster, I'm used to dealing with similar transmission system in satellites and cable distribution.
Increasing the symbol rate is not hard to understand. The ideas aren't crazy, it's just a tough idea to implement.
Like the idea of a fusion powerplant, the idea is fine, but making it happen is another issue.
The hard tech will be needed in the receivers. Making extremely narrowband filters isn't easy and from what I read, the patents are all locked up. Operating at current FM & TV frequencies lead to all kinds of multipath issues that can be solved, but add more to the reciever to deal with.
Look for impressive demos where the receiver is the size of refrigerator. Sizing down the technology to fit in a dashboard and cost $20 bucks a unit will be a real challenge. Much money will be sunk in attempting to make these systems small and rugged.
A better use might be in high end transmission systems. One transponder on a satellite give me 36MHz of bandwidth. Split the bird between two sites for duplex operation and imagine the amount of data I can squirt around the world. Satellite costs are already less than fiber rates for the amount of data they can pass. If you do the rough math you are talking about 3.24GIGAbits of transfer. What OC- is that?
It's been a while since Linear Systems & Communincation Theory, but I don't doubt the Shannon limit can be adapted to this keying system. I'll leave it to a comm theory expert to comment.
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bm :)-~
US Democracy:The best person for the job (among These pre-selected choices...)
This whole topic is some combination of genuinely good technology, hype, exaggerations by imperfect journalists, and fraud. From where I'm sitting, I don't know which of the above causes is the true explanation. But I doubt Shannon's law has been repealed. Alas...
I'll believe it when I see it, and can buy it or use it.
Have a nice day.
The enemies of Democracy are
Hemos just a bit of a lissssssp.
IS
Wouldn't that be cool if it was used on the up-and-comming 2-way satellite connections... there is some serious speed.... Also, good multicast support. :-)
Peace Out.
Anybody have a translation of this?
It's 10 PM. Do you know if you're un-American?
You *cannot* break Information Theory and with a given bandwidth and Signal/Noise ratio you can only get a certain bit rate (and it gets more difficult to get there the closer you get to that point). This is just plain marketing hype... The only promising technique discovered so far is to use multiple antennas at the transmitter & receiver and its still far from a working _product_.
-- Nimrod.
Woohoo - I was worried about the exhaustion of the letter "s" in the current address space.
Yeah, the only problem is the immense headache the artist get's if he doesn't bother to record the track later... (My apologies to non Terry Pratchet fans)
not only is the universe stranger than you imagine,
it's stranger than you are capable of imagining
Um, maybe it's just me, but I thought that Shannon's law had been prove n within the bounds of mathematics.
Secondly, the article gives _no_ information that Shannons law has been broken.
In fact, it hasn't. All Shannons law says is the relationship between the signal to noise ration, and the size of the channel, to how much data you can put through it.
In this case, Shannons law allows this to happen. But requires powers of something like (quick mental sums) 280dB.
That's, like, stupidly high.
It's possible that EDN got this all wrong, and someone has actually found an end-run around a whole lot of difficult stuff in conventional signalling theory. But I wouldn't bet on it, and if you're smart, you won't either. This may be some scheme to get investment money out of a bunch of suckers, and it behooves you to not be one of them.
--
Time is Nature's way of keeping everything from happening at once... the bitch.
Actually, VMS 2K is a reality (unfortunately). The NT kernel at the core of Windows 2000 was originally designed by one of the VMS designers.
<O
( \
XGNOME vs. KDE: the game!
Will I retire or break 10K?
In all likelyhood, Ibiquity Digital will be bringing digital radio to the States in the near future. In response to the VMSK article...bandwidth is good, but one must also pay attention to minor issues like the existence of several thousand existing analog stations and coverage area (i.e., robustness)...
Your monitor is staring at you.
I wonder what kind of range this system would have? Like current radio? Could it be deployed in a cellular-like fashion, so when I drive cross-country, I could access my mp3s on my machine back home? This could be really cool - Not needing to burn MP3s to CD so I can have car mixes, just fire up a radio connection and network over it. What about using multiple channels for faster throughput? e.g. recieve on 101.3, 101.5, and transmit back on 101.7? Could this be deployed in a car-to-car fashion? Like people who have their HAM callsign on their vanity license plate....
Don't pick up the pho*(@)$*@&@!@ NO CARRIER
While the ratio of people using regular phone line modems to higher speed digital people decreases, there will still be a large chunk of people who only have a phone line and would never bother investing the time or money into getting anything faster. I think this group is large enough to keep the analog modem market on its toes. 56k, apparently, is not the point at which we can all relax..
If these people have a technology that can do what they say it can do, they're in for some good times. After all, a typical slashdot page at -1 threshold takes about 26 seconds to load on a 56k.
Calling out bogus battery capacity claims.
No, it is not okay to point out spelling mistakes.
Your post should be moderated as
-1, offtoppic
-1, trolle
-1, flambat
or, to save karma from meta-moderation, -1, undderrrattedd
Have a nice day. ^_^
The enemies of Democracy are