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How Many Frequency Bands Are There?
FoxIVX asks: "What is the carrying capacity of earth's atmosphere, in terms of pure bandwith? With radio, TV, HAM, citizens band, cellular, and countless other radio frequencies, each of them taking up space on the proverbial 'dial' what is left for the 'Wireless Revolution'? I know that, for now, radio-based data is slow and isolated, but what about the future, when everyone goes with cell phones instead of land-lines, and people start carrying around next-gen PDAs with full screen video capabilities and gigabytes of magnetic RAM? Does the spectrum of radio frequencies give enough room for this kind of data transfer? I know that with factors like distance/wattage, and various kinds of multiplexing you can squeeze more out of a certain wireless band, but there has to be some sort of a ceiling to it all. This could be an important new field as more and more areas and people go wireless. And this doesn't even touch on the issue of who owns the airwaves and who is going to regulate it all." Would the International equivalent of the FCC need to be formed to handle these kinds of issues on a global basis?
Nevermind the fact that the military /government has by far the largest chunks of useful spectrum, but no one ever goes asking THEM to give up some...
You can see the latest news on these fronts at:
http://www.arrl.org/news/bandthreat/
I love it when someone mentions audible sound as part of the electromagnetic spectrum. Sound is a pressure wave in air - that's why there's no sound in a vacuum. RF propagates just fine in a vacuum, since it's an electromagnetic field, not a pressure wave.
Umm... Audible sound is part of a different spectrum than visible light. They have nothing to do with each other. And the EM spectrum does not stop at visible light, it keeps going up through X-Rays to Gamma rays to cosmic rays.
I was actually looking through a document concerning the issues with the ISM (2.4ghz) bands today, and noticed the UK RF agency is setting aside frequencies in the 20ghz and 40ghz band for broadband wireless, since there seems to be a lot of cohesion between the various radio agencies, I presume these are being allocated world wide. They probably wont come cheap though, the third generation cellular licences were auctioned off earlier this year and generated £40 billion ($60b) in revenue. They also have a useful frequency wheel which shows you all the various allocated frequncies.
A company Time Domain is presuing will likely near-completly change the way we use wireless communications. Several groups have been working on similiar technology over the years, but TD is the closest to a great implementation that I know of (though I know of them mostly because they are in my hometown, Huntsville, AL).
Ok, quick explanation:
Instead of sending out a constant signal technology like what is being worked on at TD transmits on a range of frequencies (say 700MHz through 1.3GHz just as an example) with sharp (non-sine wave), semi-randomly timed pulses (the timing is known at both the recv and trans ends) at levels under the level of noise in dB. Now both the trans and recv ends know when to open up and listen or send data, and then shut down very quickly (application for OGR here for those interested in dnet). This does several things for you: it is now *really* hard to "fox-hunt" transmissions. Why? Because the signal is so extremely low that its very difficult to try to watch for it. It looks like plain old noise at this threshold. Secondly, since the transmission is so short and random, you can't monitor it for any real period of time.
Through this method you also gain the ability to have large numbers of users all on the "same freq" (not really as I said before, but sort of) because of the differing times which each pair (doesn't have to be just one recv of course) knows to listen for.
Right now they are beginning to market their "PusleOn technology", which emphazies the lower powered nature of this technology ("Megabits at microwatts I believe is their quote).
Might want to check out http://www.time-domain.com/
There's a detailed one at http://www.ntia.doc.gov/osmh ome/alloctbl/alloctbl.html, and another at http://www.strongsignals.net/htm/band plan.htm.
Posted by 11223:
:) (these opinions are not that of my employer but surely match them anyway...)
Keep in mind that if you hold your cell phone at the proper angle, you reduce the risk of heating your brain tissue. (This is OT but too important to ingore). Your antenna should be pointing out, away from your head at no less than a 25 degree angle (estimated). And don't buy a Nokia phone if you can avoid it
Posted by 11223:
I believe (I'm not an RF junkie) that it uses 800 mHz. But it's not a walky-talky - that's just part of the features of the unit. The way the direct connect work is that it still goes through the cell system. The system is also fully digital, and handles other modes such as 'net surfing - think of it as 2.5G cellular.
Now don't get me wrong, I'm as much in favor of astronomy as the next man, but that is the equivelent of a data channel of 50GB per second
How else do you expect them to recieve the plans for the benzel device so we can make contact?
Posted by 11223:
Well, my phone has an external microphone - waitaminit - that's not a phone, it's an icom radio!
Posted by 11223:
I think you're a troll. I'll bite anyway - sure, your cell phone is accessing the network. It's looking for cells, telling cell sites that it exists, and doing other chatter. The system wouldn't work without that chatter.
Posted by 11223:
Just to nitpick, you missed Nextel.
Well, letsee, if you keep taking away our ham bands, there'll be enough for e-m-gizmo-hype-PDA-wireless-2000 devices. Letsee, removing 2 meters (where ham satellites communicate) was on the block recently. Maybe they'll get rid of 6 meters (where the new digital mode PSK31 is common!), or maybe even our HF bands.
Insert sound of ham bands being sucked away for large, multinational corporation.
Not nessicarly. Maybe dad drove the entire family. Maybe it is cheaper to have a personal rocket in your backyard then a car. Maybe public transportation works for a change.
The large majority of the world's population has never driven in a car. If they can use their horse to get to the launch pad, they might still do that.
Even if you have only a narrow band to use, communications can be either directional or local (or both).
Also, Slashdotters may remember previous Slashdot postings about increasing the data carried by a signal by using its "3-D" properties, at least when you're transmitting over a volume (like through the air) rather than through a wire.
Ooh, a sarcasm detector. Oh, that's a real useful invention.
I think there are two obvious limits:
;-)_ ________
1. Creativity, to create numerous ortogonal coding systems: only limited by math no, no's
2. System sensitivity: ultimately limited by the laws of quantum mechanics, and our understanding of that fenomena.
So I think, there is enought room to grow.
Also remember that all kinds of light, X-rays, etc. are also part of the spectrum.
____________________________________________
What, do you have ANY idea what you are talking about? Do you know what HZ is?
OK, here it is CYCLES PER SECOND. That is it.
You can't "divide" it by HZ, that makes no sense.
There is no "size" to a HZ. It is perfectly possible someday that 98500000.2 and 98500000.3
could both be meaningful.
Don't spout off about what you don't know. mis-information is worse than ignorance
--
$you = new YOU;
honk() if $you->love(perl)
Cellular techniques provide essentially what we want in terms om BW/unit area. This is a cost issue, just how close are we prepared to place base stations to each other. Actually, this can be made cost effective by using multiple beam antenas which then essentially create smaller cells. Add to that a some computing power and you can add interference reducing techniques (now problably mostly used in millitary systems), although such techniques can be used with simple antenas as well. This enables more efficient frequency reuse patterns in cellular networks as well. My quess that smart antenna (beamforming down link and interferance rejection up-link) will be the future. Systems like that are being employed today. /jarek
Currently, telecommunications WDM (wavelength-division multiplexing, i.e. sending multiple signals on multiple light frequencies) fiber-optics gear typically uses 50GHz channel spacing. New stuff that has 25GHz channel spacing is starting to get developed, and a lot of 100 and 200 GHz stuff is deployed. (These channels are defined by the ITU, and are in the range of 194 to 196 THz (~1520 - 1565 nm wavelength). This is the so-called C band. L band is longer wavelength, and S band is shorter wavelength.)
#define X(x,y) x##y
#define X(x,y) x##y
Peter Cordes ; e-mail: X(peter@cordes ,
Ummm, the 56k limit has *nothing* to do with Shannon's law. POTS lines go onto 56k digital channels when they get to the CO (actually 64k AMI where you lose one bit per byte to make sure you don't get eight zeros in a row.)
Shannon's law is C = W log2(1 + S/N) where C is the channel capacity in bps, W is the bandwidth of the channel in hertz, and S/N is the signal to noise ratio. This means that with an infinite amount of power, you can get an infinite amount of data into your channel. This works a bit differently for spread spectrum and ultra wide band, but the law stays the same, the "channel" is just defined differently.
There are also several ways to reuse the same part of the spectrum: with microwave, you can send two beans polarized at 90 degrees relative to each other in the same space, direction, etc. You could do the same things with laser beams and be able to have even better reuse because they're so directional. You'd just need line of sight.
The end result is the same. There is no "maximum capacity" of our atmosphere to carry signals. I suppose a better question would be how many bits we can practically send in a metropolitan area within the power constraints of the devices we'd be using, with buildings and various other sources of interference. Probably the best situation would be low power ultra wide band or optical transceivers on every floor of every building and on every light post. That would give you terabits of bandwidth for every few hundred feet of space. Hopefully that will be enough for your evil purposes.
...with those frequencies.
The human voice still takes at least 2.5KHz of bandwidth to be intelligible. You can get away with packing that down somewhat, but fractional-Hertz bandwidth is useful only for very slow radiotelegraphy (Morse).
And as it happens, Ethernet was developed following work done on Hawaii's wireless computer ALOHANet.
There probably is a certain upper limit of tolerable packet collision though. Anyone have numbers?
-- This and all my posts are in the public domain. I am a lawyer. I am not your lawyer, and this is not legal advice.
We are in the process of changing over from an infrastructure where short haul data went over wires and long haul data went through the air, to one where long haul data goes over wires and short haul data goes through the air.
That is, I want my PDA, computer, and cell phone to chat with each other while they are on my desk, and my cell phone talks to a tower a few miles away at the most. Meanwhile my desktop PC and that cell phone tower are connected to land lines that take the data on to the phone networks/internet (slowly becoming one) and thence around the world.
So unless I'm crossing Antarctica by dog sled, the idea of long haul radio communication becomes much less interesting. Which means the same frequency bands can be used over and over again as I move from area to area.
The challenge then becomes one of making the little short range devices smart enough to work out how to share the locally available spectrum equitabily, and not stomp all over each other.
I though you all would know that?
pronoblem
Such a transmitter is usually called a flashlight, crt, desktop, etc. since everything is actually a wave, oh and just to mess with your mind a bit: your eyes are really just antennas to pick up light waves frequency signals.....ponder that....so no you don't see something you receive its signal. KG4DCG
Life is but a Beta test...
IIRC, the carrying capacity of our atmosphere is about 12.
For example: Fiberless optics (via a system of relayed lasers) and satellites (a la Globalstar). These technologies certainly aren't as well-developed as 100-year-old radio, but they're showing a lot of promise.
Full disclosure: I do P.R. for Globalstar. (Not that it's relevant to this post...)
--Tom
Tom Geller
why? well, let's face it, our lawmakers are for sale, and these corporations have money. Not that I necessarily blame the lawmakers for pimping themselves, because they need the money in order to get elected. The candidate that promises the most to corporate America will get the most money and therefore the most publicity and therefore will get elected. See? Our country is set up to promote the interests of corporations. Nobody is going to revoke (or refuse to renew) the lease on the airwaves owned by any part of AOL/Time-Warner. For more info, a good starting point is Selling the Air, by Thomas Streeter (Chicago UP, 1996). Or, if the information revolution has given you add and you haven't the attention span to read a book, watch the movie Bulworth. Then you'll want to read the book.
Nyquist said the opposite. The data rate is (at max) twice the bandwidth. Thus with 1 GHz bandwidth, you can transmit 2 Gbit/s.
This holds true for any form of encoding, being amplitude, frequency or phase modulation, or a combination of them.
GCS/MU d- s+: a- C++$ USH++$ P- L+> E W++$ N o-- K- W++@ O-- M- !V PS Y+ PGP- t+ 5(+) X- R tv? b++++ y++(+++)
why is this +2?
--
Insert Witty Sig Here
Assuming the ultimate user interface is interactive HDTV from any human being to a server
or another human being. That would be about two megabits a second cleverly compressed. Intelligent TVs or immersive systems compute and display only what the eye is looking at the moment, simulating infinite TV screens. A given user would not need an independent TV in every room of a house or office, but bandwidth that followed him or her. So we are talking about 20 quadrillion independent bits per second of bandwidth for GUIs for the entire human race, if cleverly compressed. The highest multi-plexed optical cable carries about 5 terabits these days, or 1/4000th of the entire need capacity.
As phone companies know, you don't need all this bandwidth in all places all the time, because humans are spread out. Therefore they have telephone exchanges for wires, and cells for wireless. You might get my with a hundred thousand simultaneous interactive TV channels in the densest urban environment, allowing everyone to be using the interactive TV at once. We are basically talking about a million bits times a million channels, or something already within current optical communication capacities.
A current unknown is the multiplier effect of robotic servants. Every American currently has about a hundred embedded CPUs in appliances and vehicles currently serving them. Extrapolate this to vehicles that see for you, automated household appliances with vision, etc. I suspect these could increase bandwidth needs by a factor of 5-10, but not beyond that.
There was some guy claiming that he had developed (and had stolen by LBL or LANL!) a wireless technology that involved (and forgive the poor description) broadcasting on all frequencies at once. It supposedly offered unreal bandwidth at ultralow power consumption.
He was having some kind of patent fight with LBL or LANL or one of those government labs, making the semi-substantiated claim that they had ripped him off.
Anyway, the guy had enough credibility to get some venture capital backing, and had the interest of some brand-name RF companies. His problem was getting FCC/FAA approval to actually field test his stuff outside of a 100% shielded building since it apparently really does blast out over all frequencies at once and the FCC/FAA are kind of touchy about TXing on the airplane frequencies.
I read about it both here and in a big article in USA Today of all places (I read it there *before* it showed up on Slashdot, natch) about a year ago.
No, multi-bit operations aren't the same thing as analog at all. I don't think that they buy you anything, but that doesn't make them analog. Analog signals have fuzzy values between value transitions (that's more like an 8 than a 3, to take an example from my handwriting). Digital signals have precise definitions (e.g., a 1 is .5 V and a 0 is -.5 V). This allows digital signals to be reconsitiuted precisely. And if errors are introduced, they are also copied precisely. Integer Numbers are a good example of digital signals. A variable resistor (an old radio's volume control) is a good example of an analog signal transformer.
I think we've pushed this "anyone can grow up to be president" thing too far.
First, VLF is not very useful for any kind of "modern" usage. Keep in mind that the BPS of a signal can't (without some tricks) exceed the hertz of the signal, and 30 BPS is a bit pokey (if you're sending telegraphy-style messages, it's probably OK, but a decent size picture would take hours). So most of the low bands are out. With respect to the higher bands, keep in mind that under normal atmospheric conditions, there's not adequate propagation for anything above about 30-40 MHz to go beyond line of site. Yeah, there are exceptions (meteor scatter, satellites, moonbounce, various types of tropospheric ducting, etc) but that's the general rule. All that said, the FCC and other countries already belong to a treaty organization that regulates the usage of frequency bands and divvys them up according to usage. The International Telecommunications Union handles almost all of that stuff and act as a pseudo-international FCC organization to an extent. I won't vouch for the goodness/badness of how the ITU works specifically, but the need for such an organization is pretty clear.
"That's 2 bits per Hz"
Err... I think that's 2 Hz per bit!
This is actually a pretty difficult problem. This has to be examined at each wavelength and you can get very different types of results. Some radio wavelengths will be unusable due to atmospheric effects (molecules in our atmosphere), some will be blocked, some might be harmful to humans, and some are useful to astronomers. ...
But the real motivator will always be interference (from a varity of different causes). Some are obvious, emit at a certain wavelength and at exactly twice that wavelength. What you detect will be the constructive/destructive interference of the two. So how do you get around this problem
This is a very hard question that will be mostly decided by politics.
You do realize that radio is light.
Lower frequences than visible are not a good idea (lower than visible). You get a LOT more absorption (why do you think most/all lower frequency instruments are in space and not ground based). Plus you have much more obvious health side effects (what do you think UV and xray will do in your cell phone). Also power requirements go up a lot.
First of all, CDMA is used in a lot more that cellphones. Most military applications use them because the security of jumping from this frequency to that frequency. DSL's Multiplexing is the same as any wideband CDMA multiplexing. And CDMA isn't truly frequency hopping because it only hops up and down by one channel at a time (not like from channel A to channel XXX, only A to B to C, etc). And then to make things worse, writing software for CDMA is quite complicated.
CDMA isn't necessarily the way to go either. In GSM, you use slots (ie, you only transmit 1/8th of the time because you share the channel with 7 other people). You know, like you are radiating your head 12.5% of the time instead of 100% of it. GSM's use of spectrum is *not* quite as good as CDMA or TDMA for that matter, but they give up the spectral efficiency for voice quality. There are lots of ways of communicating, and spread spectrum isn't the answer to everything.
There are lots of problems with wireless communications are there are no easy answers. Some guy (www.timedomain.com I think) supposedly has a way to transmit with unlimited bandwidth by making the signal appear as noise. That is, instead of a continuous signal, he uses discrete signals instead. I haven't gone over the math, but apparently its pretty crazy stuff.
There is an excellent list at http://www.wibble.co.uk/links /ukspectrum/spectrum.htm
And more specifically, the ITU holds a World Radiocommunication Conference quite frequently. The last such conference just ended on June 2. The web page for WRC 200 can be found here. The decisions made here will be used as a basis for many of the upcoming 3G systems that are being talked about all over the place these days, among other things.
---
At the cost of using more bandwidth. The trick with cell phones is to make the phones use a very narrow range of frequencies. It is the precision with which the frequency is known by teh cell site that allows it to pick up the siganl from teh noise.
From hunting around a bit it appears that the International Telecommunication Union is responsible for international issues on radio frequencies, they are part of the UN. The downer for their web site, is that you have to pay to access the publications!
Jumpstart the tartan drive.
In countries that have decided to use GSM exclusively, such in Europe and Asia, there is no such problem. Since there is only one standard for mobile phones, you don't have multiple bands being taken up by competing mobile phone standards.
I reckon it is about time that the USA standardised on GSM and freed up the other bands. It would help everybody - both consumer and corporate.
Jumpstart the tartan drive.
So, uhh, what if somebody made a radio transmitter that went so high into the spectrum (above EHF) that the frequency matched visible light. Could you see it?
I don't know CDMA spec inside and out, but to me it looks like you are wrong. Multiplexing doesn't increase effective use of bandwidth, it simply uses more bandwidth. Thats how DSL works, simply multiplexes data above 40 kHz (I think...I'm not quite sure what the freqs are...above 10 kHz for sure).
Not true- CDMA multiplexes by putting multiple people on the same frequency. This is why it is essential that nobody is transmitting with any more power (or rather the signals, when they reach the tower, must be of equal power). Basically imagine that you write ten messages and encrypt them with a bunch of different private keys and then somebody listens to all of them but only pays attention to the one which they can decrypt...
Or the more common analogy is imagine you're in a room with a bunch of people speaking a bunch of different languages- your brain is able to block out anything you don't recognize.
If you are strictly concerned about absolute bandwidth effeciency, Time Division Multiplexing is just as good if not better. But total bandwidth used, Code Division is the better way to go.
Code Division = CDMA. This is the best way to make efficient use of bandwidth. W-CDMA (the new GSM standard) uses both TDMA (Time Division) and CDMA (Code Division).
-- atomly
Therefore, CDMA must be doing time multiplexing to some extent also. You cannot have multiple people on a channel without it. But this is a good thing, less radiation to your head is a good thing (even if its only 29.5 dBm).
No- you can indeed have multiple people on a channel with CDMA, that's what the MA means! Multiple Access!
I guess another way to explain it is like a hashtable... You have a bunch of data but you only get the value corresponding to your key. A bunch of people are transmitting on the same channel with different codes (the C in CDMA) but they are parsed (the D) out according to these codes so that multiple people can be on one channel (the MA).
If CDMA is time multiplexing, then all W-CDMA most likely is just multi-slot. And its not the new GSM spec. The standards are going to be fought for a long time, but there is also EDGE (total estimated throughput of 384 kbps) and CDMA-1 (???). I'm not sure about the details of CDMA-1, but EDGE is just multi-slot GSM with GMSK, 8 DPQPSK (something like that), and TDMA voice.
GSM is currently multi-slot (TDMA)... But the new standards being worked on (and there are multiples, but W-CDMA shows the most promise for data) are CDMA + TDMA.
-- atomly
As a theoretical question, you're talking about electro-magnetic
radiation. The range of frequencies "available" range from 0 up
through radio (10^10 Hz), microwave, visible light (10^15 Hz), X rays
and gamma rays (10^22 Hz) I don't think there's an upper bound,
although generating them starts to take a LOT of energy.
As a term, "bandwidth" measures the rate at which you can communicate
information. It is a measure of the range of frequencies you use to
transmit the information (highest minus lowest). The bit rate is more
or less equivalent to the width (in Hertz) of that frequency band.
So using all of visible light, for instance, like fiber-optic DWDM is
heading towards, gives:
7.5 x 10^14 for violet
4.2 x 10^14 Hz for red
3.3 x 10^14 Hz of bandwidth, or in the hundreds-of-terabits/sec range.
(Let's ignore polarizing the light for now, shall we?)
But so what, that's theory. You care about how usable it is, with
issues like how much it disperses and how well it penetrates air,
clouds, trees and skyscrapers. The higher the frequency, the more it
behaves like photons and less like waves. Microwaves are pretty
"beamy", which makes them good for point-to-point links. Ozone
effectively blocks out everything above near-UV, so using x-rays to
communicate with satellites is out.
I'm sure others are pointing out the free-air EM-spectrum
transmissivity charts and such.
-dca
Here is the deal with GSM, PCS and all of those other acronyms. There are basically two types of cellular networks being built now. They are TDMA - time division something access and CDMA - code division whatever. GSM is TDMA as are a lot of other cellular networks. Qualcomm(sp) developed CDMA as a successor to TDMA and it truly is surperior. Instead being able to only put one call on a frequency at a time as with AMPS or 3 at a time with TDMA, CDMA allows 20 calls per frequency. This is one way to solve the wireless bandwidth shortage I guess but I have read that the limit for voice or data is 14.4k I think, could be wrong but its close.
As far as all of standards, most are just GSM or similiar modified to work with frequency allocations in the US. The only exception to this that I know of is Sprint PCS which is CDMA. I hear that many new cell networks are on hold waiting for new technology that is supposed to replace CDMA in 2 years. Expect this to have better data capability also. I just happened to hear this from an article on Chinese cell networks and why that huge deal with qualcomm fell through. The only drawback to CDMA that I know of is expensive equipment.
As far as how to regulate bandwidth, I have a feeling it will be a mix of low power towers and high power towers in rural areas with adjustable wattage on the phones themselves. Anyone know of the company that is installing those boxes in subways and airports to allow phones to work there? Same kind of concept. Anyway, I hope that clears some things up. Oh yea, and PCS is just a generic term in the US for digital networks.
I believe in the future that wireless will be a mix of both small bases on every telephone pole in congested areas and large power towers in rural area like parks. The phones themselves can adjust their own wattage after syncing with the tower. This also prolongs battery life in the congested areas but still allows communication in rural areas. This will happen almost for sure and is allready happening to an extent, small bases in airports and subways ect. Good enough solution?
I think what he was trying to say is that cars are going away. I hope cars go away, they have ruined city life. WTF was all of that about anyway?
The higher frequency you use, the quicker the signal dies out with distance (for a given power).
If a transmission on a high frequency can't be received more than a few miles, this can be a good thing - you can reuse that frequency at many other locations!
So within a given radius, a whole bunch of high frequencies can be used for various transmissions, and further away the same frequencies can be re-used for other transmissions. With relay equipment connecting the two areas, you can relay information point to point, across much larger distances (ala Packet Radio). So if you're trying to talk to someone in your same city, the transmission stays within that city (possibly relayed a few times). If its destination is across the country, more relaying must occur (or land-lines used for the major span of distance).
All you need is some kind of registrar to make sure no transmitter uses frequencies that will conflict with other nearby transmitters. Hmm, a central authority that organizes who uses what numbers, where have we seen that idea before? All it takes is an InterNIC for radio frequencies, which we already have... they're called the FCC in the United States; similar organizations in other countries.
Just wanted to make one thing clear about the relationship between bandwidth (as in the width of radio frequency bands), and bandwidth (the amount of data we can put through a channel). I don't think that this is what the original question was about, but it's in many ways more important, and I thought this might help clear it up for some readers...
The first (the original meaning) of bandwidth is simply the range of frequencies that we're talking about - for example, the bandwidth of a telephone line is fixed at about 4kHz, spanning from about say 100Hz (?) up to approx 4kHz. This is the thing that most of the posts have been talking about. How then did we get first 300, then 1200, then 2400, up to 56kbps (well, 40kbps) through the phone line, when the bandwidth hasn't ever increased?
Well, the second meaning of bandwidth, the one us net users are always complaining we don't have enough of, isn't actually really to do with frequency ranges, instead it just means how much information we can put through the "real" bandwidth we have. Obviously if we have more "real" bandwidth we can get more "data" bandwidth out of it (eg. if I have 2 phone lines I can do twice as much data (bad explanation, sorry)), but that's not the only way we can get more.
So how much "data" BW can we get out of "real" BW? This is governed by something called Shannon's Law, and it turns out that the key factor is the signal-to-noise ratio (SNR). To get a feel for how this works, imagine that you and I are talking at a really noisy party, so noisy we can hardly hear each other. Obviously we're going to have to go pretty slowly, repeat lots of words ('mmnrnrg!' 'what?' 'mnngvr mgnd!' 'WHAT!?' 'I said, NEVER MIND'), and we're going to be able to get a lot less data through our channel (even though the audio bandwidth is no different) to if we were chatting outside.
Now if you're asking, how much data can we get through the atmosphere, it comes down to how much radio frequency BW there is, secondly how much noise there is, and thirdly how good we are at getting towards the limits of Shannon's law. It's this last one that we've been improving with the successive generations of phone modems, and we're getting pretty close now (when it's worth the cost to do so, anyway), hence don't expect 115kbps analogue modems to appear anytime soon.
BTW IMHO the limits for upper frequencies we can use aren't just to do with electromagnetic propagation, but also to do with our ability to design circuits that will work - now that we're well into GHz & THz we're starting to really feel some of the physical limits (eg. things like electron & hole mobility in semiconductors (which governs how quickly our transistors work & so the upper frequencies they'll work at)).
Will Bryant, Core Development
Will Bryant, Core Development
http://www.core-dev.co.nz/will/
no, "binary" is having only two values, "digital" is having only _a finite number_ of values. in any case talking about it like this is an oversimplification, and it's kinda pointless..
Will Bryant, Core Development
Will Bryant, Core Development
http://www.core-dev.co.nz/will/
oops forgot to mention something, notice since it's signal-to-noise ratio, not just noise power, we can get more data through by increasing the power of our signal.
Hence the problem with "56kbps": the amount of power you're allowed to put through is limited by the FCC, and so is the capacity - so we only get 40-something kbps..
BTW there are lots of posts talking about the capacity theorem in more detail, for those interested in the maths.
Will Bryant, Core Development
Will Bryant, Core Development
http://www.core-dev.co.nz/will/
Damnit, I just can't remember where I've seen/heard this before! Where's it from again?
you're applying an old push media metaphor. think of hte problems. dead links all over the place. hypermedia, for the most part (that bowtie shit aside), relys on a complete, active information base. dont just mutter "corporations will take care of it". there's going to be branding, and definitely user fees -- for now. but even the logistic problem of selecting pages makes it infeasible.
I received an email from ARRL (The Ham radio advocacy organization) a few weeks ago indicating that this has already happened. A rather large chunk around 17GHz IIRC has been set aside by the ITU from the available pool for any country to use for transmitting.
Didn't Negroponte mention something about this in the book, The Media Lab? I definitely recall his mentioning something about wireless data capacities.
Mind you, I'm not sure if this takes into account such clever schemes as spread-spectrum (bless you, Hedy Lamarr, wherever you are).
-TBHiX-
There is an upper limit. When you are pumping so much energy through an area and you can't see through the glowing gas molecules in what used to be your atmosphere, you've reached your limit.
Sorry, but what kind of stupid question is this??
The "bandwidth" of the Earth, the atmosphere, the universe or whatever, is, for all intents and purposes, limitless.
The only problem we humans have is what frequency bands are already in use, and what are the limits of our technology.
There is no inherent limit. Yes, if you use exceedingly high frequencies, the attenuation tends to drop off very rapidly, in general, but that's not something that can't be worked around sooner or later.
Now this sort of question should've never been posted...
Thanks for correcting my errors. :-)
I'm not sure what I can talk about with my friend's gadgets, and what I can't. I will say that the ultimate use required a whole lotta transmitters, in proximity to one another, and not necessarily in proximity of the receiver (but it was really low power). Information was compressed into small packets, then broadcast at random intervals. The receiver only needed one good reception during [time period], and thus you could get around non-reports, crosstalk, and transmitters picking the same millisecond to broadcast. You really only wanted one report during the time period, and didn't care if you missed a few.
A friend of mine is working for a company that uses spread spectrum technology, which provides for an infinite number of possibilities (as told by him). Errors that follow are my own ability, as a non-EE, to understand the whole thing. :-)
He said the transmitters they were using broadcast at signal strengths below the natural background radiation. That meant you couldn't detect it (neato), and that you didn't need a license or FCC approval to broadcast. Since it's not using one band, but various signal strengths between an upper and lower frequency limit, it didn't fall into the idea/trap of a band or bandwidth.
To visualize this, compare the light frequencies coming off a laser to those from a burning candle. The candle has various wavelenghts it uses, which can be distinct, and detectable as a signature. The laser, on the other hand, is a lot of energy on one wavelength. ___|___ compared with _-~-_~_
My friend said that the receiving station just looked for a signature of a certain profile between certain frequencies, then extracted what it wanted from there. One member of his team had some background in sonar with the military (as in writing the code and creating the equipment), so you can see that there's a pre-existing, proven method of recognizing something with digital filtering.
PCS phones are different from old-style cellular phones, but they're still cellular and they're still phones.
It's like saying cellular phones aren't telephones because you find a definition like:
cellular - used to describe a two-way radio system that is designed so the portable units work in a broader area than the operating radius of a single stationary unit. Cellular systems use radio waves rather than the wires used by telephones for transmission and reception.
I don't buy that. You can buy hand-held radios that are smaller than cell phones and are able to transmit two ways over a distance of a mile or more. Your argument doesn't make sense. It doesn't require more power to detect a signal and obviously a cell phone has enough power to get to a repeater.
-- Virtual Windows Project
The idea is not to save power but to get a phone with excellant reception with high reliability at very low cost. My cell phone has a broadcast life of 8 hours and a standby life of 30hrs. I've seen some that have more. Digital transmission requires a lot less power than analog. I think rebroadcast over 1sq mile is feasable - most radios have a 2-mile range.
And yes it's complex to figure out how to route calls. It's sort of like the internet except the nodes move all the time. It would be an interesting problem to work on...
-- Virtual Windows Project
Yay! Sterilize the yuppies =:-)
---
Play Six Pack Man. I
To sum up (in the US, anyways)
Each operator at a particular frequency gets access only to their frequency "block." They can basically run whatever standard they want to over that block, or even mix it up if they want to.
At the 800MHz level, there are two operators per region (the "cellular" operators) with 30MHz each. Originally they used only AMPS, but most have moved to D-AMPS (analog, but digital carrier signal for caller ID, etc.) or full fledged digital technology (in the US, TDMA or CDMA, but not GSM). These frequencies are definitely still in operation.
At the 1900MHz level ("PCS") there are 6 operators per region, with frequency blocks broken into 3 chunks of 30MHz and 3 chunks of 10MHz. Since these were auctioned in 1997 (and were specifically for digital technology), they all use one of the digital standards- TDMA, CDMA, or GSM. GSM is definitely the least common - I don't think there's more than 1 GSM player in any market (generally Voicestream, Powertel, BellSouth, or PacBell).
That's all the frequencies currently used for cellular/PCS phones in the US (except for Nextel, which got a bunch of old 2-way radio spectrum at the bottom of the 800MHz spectrum). The next auctions are going to be at 700MHz, in the region previously reserved for UHF channels 60-69. After that, they're going to auction off some spectrum at the 1.9GHz held by organizations that went bankrupt (greatly simplified). Sometime in 02 I think they'll finally sell the 2.5GHz spectrum.
As for Europe, my knowledge is hazier, but I'm pretty sure that they originally licensed at 900MHz (analog, later GSM) and then later at 1800MHz (pure GSM).
Your comment on the cellular infrastructure consolidation is beginning to come true- approximately 40% of the towers in the US are now held by large independent "tower consolidators" that rent space on the tower to anyone who wants to pay for it. You still need to provide your own radios and backbone, but the important part, the tower position, is becoming more of a commodity.
What does NexTel use? (Are you talking about their walky-talky feature?)
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Huh? You need to use more granualarity, which means more sensitive receivers and more transmission power to achieve the same range, but what's this analogue crap?
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It's interesting how quickly these go out of date... recent FCC spectrum auctions don't seem to be included
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I'm a leaf on the wind. Watch how I soar.
I forget who the quote's by, but it's that simple.
There is no theoretical capacity to the bandwidth of the air (or, really, even of wires) so long as newer, narrower protocols are being devised -- or even additions onto existing protocols that would provide distinguishment between multiple transmissions that otherwise interfere.
It doesn't seem to matter how much band width we have, what matters is how much data we can fit. For example, Color TV doesn't use anymore bandwidth then B&W TV, and Stereo TV is the same. The reason Color TV works is because of great Engineers making due with what the FCC would allow them to use. A lot of RF engineers will bad mouth the FCC, but they make good engineers, great engineers.
Most new cell phones now have an optional headset, so you don't have to worry about getting a brain tumor from holding a small but powerful radio transmitter next to your head. But most people will probably keep the phone in their lap while using the headset.
Ummm, I guess there would be a physical upper limit. I don't happen to know exactly where it is, but the radio part of the spectrum does have specific boundaries.
Shannon's formula _does_ exactly explain why 56K modems are the limit. Telco samples the phone line at 8 kHz and 8 bits per sample (64k bit rate). It's the fact that the analog line is quantized to 8 bits that determines the signal to noise ratio (about 6 dB per bit=48 dB). Given that amount of noise, no modem designer can invent a signaling structure that gets more bits per symbol. What you say is also true, given an optimum signaling structure...the digital trunks will only carry 64K less overhead.
The BLAST algorithm mentioned in the start of this thread does significantly better that dual polarized links. BLAST allows the transmitter power to drop in half when using two antennas (same _total_ power as number of antennas increase). Try this with separate dual polarized links, the S/N drops and the Shannon limit drops _exactly_ in half...resulting in the same net throughput. The magic of BLAST is that the data rate _grows_ linearly with number of antennas while keeping total power constant.
Claude Shannon develop a relationship between capacity and bandwidth ("the Shannon Limit") that has held for 40-50 years. That's (mostly) why modems topped out at 56K.
But here's some brilliant work that supports 10X better for wireless links http://www.bell-labs.com/project/blast/
"Spacial Reuse" says that capacity is effectively unlimited. In other words, if you need more capacity, make the cell sizes smaller.
Personally, I think we all should own a 12 GigaWatt EFH Handheld...
Some days I get the sinking feeling Orwell was an optimist.
It is obvious that you are talking DSCS here, but rememeber that Civ SATCOM (i.e. C and Ku bands) use higher freqs, and that higher freqs need less power. Also depends on what type of Mod/coding you use, an all digital system uses less power on a TDMA/CDMA system then one using FDMA. On the ground based side this is true as well, I just worked with a system that uses an 18" reflector and .25 Watts with a range of 30 miles. Lower freq systems have a 8-12' reflector and use about 200-500W for similar range. If they worked something like this in an omnidirectional T/CDMA format you could pass it to a repeater, and from there the possibilties are endless, SAT/LOS/Cable you name it. The problem is that the range would be decreased greatly, so it would only be available in large metro areas.
(To avoid some confusion, I'm going to use one definition of bandwidth: How many bits you can squeeze into a certain amount of time. The concept of a frequency band becomes somewhat moot...)
This technology could be used to create sort of an ultra-high-bandwidth wireless world wide web. There would really be no need for any other form of radio transmission, since other formats are less efficient by nature. Once fully developed, the bandwidth would be astonishing. (But then, when is anything really fully developed?) Think of it -- instead of hogging up one whole frequency band (or more), your transmitter only uses nanoseconds of time to transmit bits into a local area, only when it needs it. Transmitters share the space. This is a lot like how a LAN works, but with much more bandwidth.
Here's the kicker: Unlike a LAN, collisions become near impossible, because receivers use the transmitter's location to weed the signal out from the noise of other sources. Even if two transmitters send a pulse at the exact same time, the receiver only pays attention to the portion of the signal that is coming from the transmitter that it is listening to. Of course, sometimes another signal will overwhelm everything else, (like a lightning strike nearby) but these are rare.
This is like listening to a person talking on a subway. You can hear them clearly over the noise because your brain singles out not only the sound but the location of the speaker. You can selectively ignore other sounds coming from different locations, even if many people are talking.
This technology covers a local area -- one transmitter can't send a signal across the world. It's great for low-power transmissions between two nearby devices (feet or miles). To move data further, a repeater could pick up the signals and send them where necessary. Nobody will need to license anything, just get a box to hook up or a device with it built-in, and either join some local connections or pay a service provider for access to the global net. Heck, the devices themselves could act as repeaters, who needs ISP's?
This is scary technology to many because a lot of people will lose money if it becomes established. It has the potential to place wireless technology directly into the hands of the people, cutting out the middleman.
On a lighter note... This type of transmission is indistinguishable from noise, if you don't have the right receiver that "knows" the transmitter that it's listening to. I have a good idea why SETI hasn't been able to hear anything... :>8-)
My Nextel phone already receives more spam than my normal email systems...received a message yesterday on my phone (with HTML tags and other garbage that doesn't belong in email) from some moron selling satellite receiving systems, or something (didn't read it...saw the subject and "<HTML>" and hit Erase).
The really strange part is that I've never given anybody the email address for my phone. Where are the spammers getting it? Are they just hitting every phone in Nextel's exchanges? (The email address for a phone is (10-digitphone#)@page.nextel.com, so I'd imagine that a cross between a bulk mailer and a wardialer would allow you to spam phones.)
_/_
/ v \
(IIGS( Scott Alfter (remove Voyager's hull # to send mail)
\_^_/
20 January 2017: the End of an Error.
Actually we are currently working on embedding nano-silica particles in polymers because the particles are small enough that at 50% sand the plastic is transparent. This is because the silica particles are smaller than the wavelength of visable light, and hence there is no resonance. Resonant frequency is a function of the length and the speed of light in said medium.
Likewise the color of the sky is related to the size of the particles.
If atmospheric and obstruction effects cut off everything above, say, 30 GHz
It won't cut off everything above 30 Ghz. As a counter example consider X-rays. X-rays don't have any trouble penetrating. The question becomes, with frequencies high enough to not resonant with the atmosphere, how do we recieve them? Also note how directional we get as our frequency increases! Opps! Sorry Chief! Missed the satelight by that much.
There is also the information theoretical limit. The bandwidth used and the interfering noise can be combined to find the theoretical limit.
But you are presupposing a bandwidth, so you can't solve for the maximum bandwidth without getting your a priori value back.
The question is: is there a theoretical limit to how high the frequency can go?
Again, after getting past resonance with the atmosphere the problem is that (at least) by x-ray we are going to be way directional, and how do you "recieve" an x-ray transmission? Then ask: what about gamma-rays?
x-rays "lose coherence" and "degrade" in an atmosphere??? don't think so! :=)
I want my MHz (sorry...its an MTV commercial pun)
its all based on di-lithium crystals. Unfortunately all I seem able to order is plain old ordinary lithium...anybody know where I can buy di-lithium?
my department chair told me last semester there are no tachyons...*sigh*
then he asked me how i felt about easter bunnies and santa, so i quantum tunneled right out of his office
Ok, this is getting WAY offtopic, but I just had to thank you.
That's the funniest thing I've heard/read all day.
Thanks!
I'm still chuckling.
As for a "global FCC," well that's just a huge stinker of a solution. After all, look at the marvelous job they do here in the US...
At least you don't have a CRTC.
*shudders at the thought of Canadian Content laws.*
Well, yes. But for the long haul, it is perfect. You are in NYC with your Cell. You make a call, it goes into the network, to a laser transmission device, which beams it to Japan. There it off-loads back onto the cell network (bypassing thousands of miles of local cell traffic, keeping airwaves clear) and to your friend overseas.
It's only when we've lost everything, that we are free to do anything...
Wow, that was easily the most Americentric stat I've seen in a long time...so it's 1/4 billion drivers for the US and 1/4 billion for everywhere else? Assuming 6 billion people on earth, the US has (6 / 0.25) 1/24 of the world population. There is no way that the other 5.75 billion walk everywhere. Your assumption states 250 million drivers other than those in the US. That means one hell of a lot of people either walking or taking the busses.
I think I'm gonna go invest in Greyhound.
TheGeek
TheGeek
http://www.geekrights.org
Kill the monkey
There is no room in the FCC-regulated frequency band for my transciever.
I got this newly invented Star-Trek styled Transporter. It takes a 5000 GHz wide multi-spectral frequency band.
It takes somewhere from 20Mhz for the Transporter's ISDN D channel (for coordinate transport and other control channels).
And its enhanced Z^10K (Z channel x 10,000) needs to take up the entire 100Mhz to 10,000 GHz code and time-based divison/frequency hopping.
Who wants to be stuck in the transport buffer for eons waiting for a 19K mobile phone to transmit his entire Human Genome?
Dammit, FCC, we can't get no where with this agency.
Okay, so it's not infinite. But if you could get transmitters and recievers sensitive enough to deal in hertz, that would still open up huge amounts of the spectrum for use.
Don't forget that Friday is Hawaiian shirt day.
On the practical front, it's essential that two parties that wish to communicate be on the same frequency, and since the equipment necessarily has to be optimized for a specific range of frequencies, the "band" concept will be around for a long time.
For regulatory purposes, it's nice to be able to plan what type of signals are going to be in what frequency ranges, so that appropriate use is made of a finite resource. There are also restrictions as to the type of transmission, allowable power levels, and bandwidth used.
As we move forward into the future, there will still be a need for fixed frequency, single channel communications for a number of reasons, including local broadcasting, and other places where simple equipment is essential.
I believe that most other use of the spectrum will eventually go digitial, using technology such as CDMA to spread a signal out, and remove the dependence on a channel, in the traditional sense. The technology to make this happen is here, and it's getting cheaper much in accordance with Moore's law. I suspect we'll eventually see the single channel transmitters outlawed, just as spark-gap transmitters were outlawed with the advent of oscillator based transmitters.
The only remaining concern is simple, to quote Scotty: "I can not change the laws of physics". It's all a matter of increasing the ratio of signal to noise. Spreading a signal out decreases the effect of noise on any one frequency, and makes sharing possible. Using only the required amount of power helps as well. (Cell phones have done this since the beginning) Many of the new uses are short range in nature, which also helps, because a given frequency can be used in many different locations, with low power, at the same time. (The CELL in cell phone)
I rambled, but I hope it all makes sense, and answers the question somewhat.
--Mike--
It looks a bit out of date, but its comprehensive.
penguinicide... when jumping out a window just won't do.
The general upper end to the RF spectrum is usually given to be around 300 GHz, as you go higher the more the RF starts behaving as light, very much line of sight. In addition to that, you need to start thinking about the attenuation of the transmission medium. The atmosphere has certain bands that it has relatively high attenuation: There is a peak in attenuation at about 22GHz, 55GHz, 120GHz, 190GHz, and the next at about 400GHz. The gaps between are better in terms of attenuation, still not great compared to the frequencies we are used to using. Once you get into space, you are no longer limited by your atmosphere, so you only have to worry about line of sight and naturally occuring noise. (Galactic noise actually goes down as frequency goes up.)
The higher in frequency you go, the more line of sight you get to be. This can be used to your advantage, especially in terms of frequency reuse, the key to cellular, which employs spatial separation and frequency separation.
Also, as you go higher in frequency, the smaller your bandwidth gets in relation to your frequency, so you have some definite advantages there- 1GHz of bandwidth is much easier to get in the 90 GHz atmosphere "hole" (W Band) than at X band (5-11 GHz).
Is there a limit? Yes. Are we going to reach it? Maybe, but as time goes on we will get cleverer especially in terms of reuse over distance. Before we actually saturate the ether we have the potential for multi gigabit/s information bandwidths.
Yeah, but audible sound isn't electromagnetism, so they're not in the same frequency spectrum.
-CausticPuppy "Of all the people I know, you're certainly one of them." -Somebody I don't know
Whenever an expert has defined a telecommunications limit it has eventually been broken. Whatever the "limit" is right now it won't stand for long. Market pressure seems to drive physics, not science.
"Radio of conventional wavelengths will pass through rain, smog, and clouds with little difficulty. Higher frequencies, however,have problems."
Not 100% correct. Sometimes rain and clouds mean something else. Its called a tempeture inversion. Basically there are times where warm air gets smashed inbetween cold ones. Radio waves around the HAM Radio 2 meter band (144Mhz) can go thousands of miles in this inversion. There are confirmed reports of talk between L.A. and Hawaii with these inversions. Normally the 2 meter band is line of sight and I have only reached 150 miles with the help of a repeter on my 5 watt handheld. Clouds (which make rain) can be a sign of this happening.
Data can only be carried over a frequency at 1/2 the frequency. In other words, 2kb on a 4Khz band.
Another problem is the earth. Considering that the earth is now proven to be round, high frequencies can not go very far. This is because of the F layer in the ionosphere. Basically every frequency above 50Mhz goes right though this layer but anything below bounces right off. This is the reason that the HAM Radio 10 meter band is so popular. Its frequency is below the 50Mhz cutoff line and it bounces of the surface of the earth too giving worldwide reception. On rare occassions the E layer flares up and frequencys around the 50Mhz band (6 meter HAM band) gets bounced too.
Yet another problem is that even higher frequencies just want to go plain strait. This starts around the 1Ghz and up region.
Putting this all together means that if someone wants long range reception (500+ miles from the tower), the maximum data transfer is incredibly slow. Anything faster means a ton of repeaters or good radios for transmissions from space.
I should say that this is a very rough calculation. A lot of factors come into play when computing these rates. On one hand, the 3dB per bit/sample increase is only a estimate; it is actually a little less (i.e. the 21dB difference between what QPSK need and the 30dB available will get you more than just 7 bits). You can also use error correcting codes to increase a little bit more your rate. Lastly, the bandwidth may be a little higher than 3000Hz. On the other hand, it's really difficult to get 1 sample/Hz; it's more like 0.8 sample/Hz or even less.
IIRC, the 56kbs is achieved fiddling with the equipment interfacing with the local loop (i.e., the last mile) to get a higher bandwidth (but I may be wrong on this respect). This is done on the ISP side since it costs money to do that, and you'd have to do it for every phone line.
Note that you pay the price of a higher complexity to achieve this. To squeeze the 3000Hz bandwidth out of the telephone channel you need a good equalizer, and to achieve the 9 bits/sample you need complexity to implement the modulation (actually, most of the complexity is on the demodulator/decoder, i.e., on the receiver side). Old modems, e.g. the 9.6kbs, used a bandwidth of 2400Hz and a 16QAM modulation. The really old modems, i.e., the 300bps and 600bps used FSK, a modulation which is wasteful on bandwidth but yields simple receivers.
So, you are basically correct wrt the way to increase data rates, but your use of analog of analog is misleading.
The only cell system I'm intimately familiar with is GSM, but I can tell you that normal GSM cells can be up to 17km in diameter, or about 10 miles. Generally speaking, cell phones have to transmit farther than a simple two-way radio.
The also have to do other things such as a lot of signal processing, reporting received signal strength back to the tower (even when you're not in a call), and monitor the "pilot" transmissions from the tower for incoming calls, text messages, etc. And we expect them to do this in a tiny, lightweight package with long battery life.
While the idea of cell phones acting as repeaters has some merit (in crowded areas where the phone will only have to transmit a few hundred feet to the next phone), the task of orchestrating that is very complicated.. And even though you're transmitting over a shorter distance, you'll be rebroadcasting other people's calls, which means you won't end up saving any power overall.
The simple solution for crowded cell airwaves is simply to make the cell smaller...
also very directional
First of all you can have a carrier frequency of 65856736.678 Hz if you so please. Second is not anything fundamental to nature!
Second of all... The real issue is bandwidth of transmission. When you're just transmitting this 65856736.678 frequency you're effectively transmitting with a zero bandwidth. Then again, you're not transmitting any information either. Once you start modulating this carrier frequency stuff begins to happen. You get sidebands and all that stuff. Some of these are required to reconstruct the signal in the receiving end(at least one sideband for FM-transmission, can suppress carrier and second sideband to conserve power). These sidebands are what use the bandwidth!
Whenever you modulate(FM) a carrier with a frequency you get sidebands for carrier + modulating frequency and carrier - modulating frequency. Only one of these is necessary as the other one can be reconstructed at receiving end and used for demodulation. Still, you're effectively transmitting with more than one frequency(thus using bandwidth).
There is a fundamental law of physics that defines the maximum information handling capacity for a bandwidth and it is as follows:
C = W x Log2[1 + (P/N)]
C is bits per second, W is bandwidth, P is power in watts of the signal through channel and N is the power in watts of the noise out of the channel.
This is the theoretical limit for transfer of information. Please note that this has nothing to do with dividing into parts of hertz but rather this is the fundamental limit. You give a bandwidth(that can include all those silly parts of hertz) amount of transmitting power and amount of noise and you get the limit.
The preceding law doesn't have anything to do with the modulation technique used. It just tells how much data you can fit into, say, the frequency area(also called bandwidth) between 65123456.7 and 65765432.1 Hz. This limit cannot be exceeded anymore than anything can travel faster than light in vacuum. In a real world situation you will end up with a transmission rate lower than given by this law.
And yes.. data compression can improve throughput..
The frequency spectrum starts at the low end, with audible sound and stretches all the way up to visible light. The higher in frequency you go, the more "directional" the signals have to be. This is why you have microwave dishes and not just microwave vertical antennae.
As to the number of frequencies available, it would all depend on the resolution. For instance, in the 2 meter ham band and VHF public safety band, narrow FM is generally used for communications. From 144.000 Mhz to 144.500 Mhz you could probably squeeze in 50 signals (using CTCSS or some other form of encoding).
Just my 2 cents..
Joseph KB7PPL
I know nothing about wireless communications.
As new technologies are accepted, the old technologies are often abandoned. The PS2 is a good example. The PS2 can do everything the PS1 can do, plus more. This is why not many people are heard saying things such as "Well, the hell with the PS2, I'm sticking with my PS1". With this in mind, don't you think we could and would use the standard radio bands of today for use with the technology which replaces it? And for that technology's descendants?
...for a given quantity of energy is given in this paper: http://xxx.lanl.gov/abs/cond-mat/9907500 I'm not sure we'll actually be hitting those limits within the next century or so but it's an interesting paper nonetheless.
--
-- SIGFPE
There is also the information theoretical limit. The bandwidth used and the interfering noise can be combined to find the theoretical limit. People used to approximate Shannon's law by saying the limit was 1 bit/sec per Hz. For typical S/N ratios over things like analog lines using old modems this was not too far off. But as you go to better signalling systems the S/N ratios start allowing you to do better than that. Hence the ability to transfer 50+ Kb/sec over a nominal 4 KHz analog channel.
The S/N term is logarithmic and better telemetry systems and coding systems eventually run up against quantum walls, thermal noise limits, etc. that impose some fundamental limits on available S/N. So you still cannot escape Shannon's law.
The present bandwidth allocations are a sometimes crude attempt to manage the co-existance of different imperfect hardware, signalling, and coding systems. To a certain degree some signalling and coding systems can co-exist, e.g. spread spectrum signals hiding underneath the noise threshold for SSB signals. This kind of co-existance is permitted in very few bands. Most bands are allocated to a single telemetry and coding system so that the necessary guard bands, emission quality, and other constraints can be described easily and enforced easily. Real world hardware is imperfect, so you do need some saftey margins as well as guard bands due to signalling technology.
Up in the millimeter bands the attenuation due to molecular absorbtion has interesting effects. You get line of sight transmission that is relatively unaffected by rain and fog, blocked completely by most structures, and attenuates at 20-100db/km. This leads to some inherent excellent re-usability when used for short distance point to point links. It originally (and still) was used for other interesting things like covert radars and covert links that deliberatly operated near the peaks of molecular absorbtion bands.
I would just like to point out that cellular systems provide spatial multiplexing so that frequencies can be reused over and over again. Rather than increasing the bandwidth that we require we can go so smaller and smaller cells in a cellular system - down to so called microcells and picocells with base stations on every street, home or even room. With these types of systems we want low power short range radio transmission to reduce co-channel interference and to enable efficient reuse of the frequencies. There are currently two main frequency ranges of interest for this - around 27GHz and around 60 GHZ. The advantage of such high frequencies as 60GHz is that they are absorbed easily by the water in air so their range is very small enable very small cells.
As for the transmission bandwidth of air - well lets say vacuum UV starts at a wavelength of 200nm - this corresponds to a frequency of 1500THz! However as we go to higher and higher frequencies the radiation will travel in more direct paths and suffer more from scattering and so in practice I expect the 60-70GHz type range is probably as far as is practical for broadcast systems. Point to point links can of course use optical wavelenegths.
A while back there was a /. story about Ultra Wideband radio technology. According to Time Domain's webpage, the FCC has recently (May 10, 2000) "adopted a proposal to consider permitting the operation of Ultra-wideband (UWB) technology." If the US government ever decides to stop strangling this technology, there wouldn't be nearly as much of a need to move into the higher gigahertz frequencies.
Yahoo's Ultra Wideband category..
Learn the rules so you know how to break them properly.
www.teslabox.com
No, his assumption does not state that.
He was responding to someone who claimed M > C, where M = number of people who walk on the moon and C = number of people driving cars.
He was pointing out that, given even a conservative estimate of C -- which, in this case, would be a low value -- that was unlikely to be the case.
You just jumped in, probably having been taught to look for any evidence of "Americentrism" and jump on it publically rather than actually think and comprehend for yourself, and attacked the facts he posted to support the notion that his conservative estimate for C was probably quite low.
In other words, you beat him up for setting to low a limit on C on the basis that he set too high a limit on one of its components (the portion of C represented by drivers outside the USA).
In fact, he set (and implied) no upper limit on the number of drivers of cars outside the USA. So he can't be accused of Americentrism on this basis. Just as someone who says "I think there are more than 500 computers in the world, because I know for a fact there are 250 here in my home town, so, assuming we have no more than half of the world's computers here..." is guilty of actually believing his town has half of the world's computers.
Thanks for the blast from the past, though -- it's USENET all over again, which is why I gave up reading (and posting) there -- too many people who'd rather smear others in public than carefully consider whether it's deserved -- the geek version of "shoot first, ask questions later".
Practice random senselessness and act kind of beautiful.
you will discover subspace communications. Take it from a well known space-time traveler.
--President of the High Council
To-do List: Receive telemarketing call during a tornado warning. Check.
It seems to me that the bandwidth capicity of the atmosphere could be almost endless. Technological advances happen every day that allow us to carry more data over less and less medium. Why shouldn't this apply to the atmosphere as well? It is one of the oldest researched parts of the earth. I'm somewhat surprised that scientists haven't been researching a way to transmit on more and more frequencies, not to mention pushing larger amounts of data.
Good idea signal, lets use wavelengths harmful to humans to transmit email from grandma. With good ideas like this one, why arent you out making millions instead of trolling
Infact, someone I know very well is planning on doing this soon - next summer.
Oh wonderful, not only does signal 11 troll on slashdot, but now he is involved in terrorism as well.
What a world
NightHawk
Tyranny =Gov. choosing how much power to give the People.
If you have noticed we seem to open up more bands to the general public whenever we get more applications that need them. Granted we will reach a ceiling eventually but I have a feeling for the international aspect of it it is going to fall like the 2.4ghz band does now. In case you havent tried it try using several 2.4 ghz devices nearby. Especially the phones they interfere with everything but sound fine. They have the highest power and cause the most interference so they win. As for companies getting together or some new body regulating it? I doubt it or else we will all end up losing our cool toys. LEts hope not, I like bluetooth, 2.4ghz phones, cell phones etc etc.
I am 31337 or something.
CDMA = Code division multiple access, which according to my understanding means that you can carry out multiple conversations on the same freq. but all encoded differently so that only the intended recipient can decode the conversation.
TDMA = Time division multiple access, which is essentially a round-robin protocol for fitting multiple conversations on the same freq. Your phone just gets a small time slice.
As for a global FCC? Forget it! Individual countries already have allocated most available bandwidth unilaterally. This means that the paging spectrum in Brazil may be used for something different in Argentina. Hardware is constructed accordingly, so it will be nearly impossible to migrate everybody over to a standard any time soon.
--Dan Boxwell
Remember, there was a time when the biggest concern in the field of computing was how to go about fitting all the necessary wires into your computer without having the whole thing overheat or be too complex to troubleshoot. Then we discovered the microchip. We're clever little buggers.
Remember, kids, it's only premarital if you plan on getting married.
well, there are as many frequency bands as the US Government's FCC says there are.
kick some CAD
1) Much of the EM nature of the atmosphere still eludes us. Data from every sunspot cycle still trashes some working model of what the heck is really going on. It's been a priority most of the last century and it ain't been an easy nut to crack. 2)The recent experiments that seemed to accelerate the speed of light again illustrated that quantum mechanics stand a strong likelihood of reconceiving the idea of information transmission. dentext Now, for extra credit, look up 'Science', 'Technology' and 'Engineering' in the OED. Impress your friends who didn't know there was difference.
I like the polarization idea, in that that shows that there are other "characteristics" available to be exploited to send information. Who know what else someone will find to exploit, which is my point.
Yes spread spectrum is an interesting technology, but one that spreads out on the spectrum like a butter in a hot pan raising the level of background noise. If more people used this the effective background noise would get so large that everyone would need to use this technology. A self fullfiling technology.
Maybe a way can be found to add a skewness factor, as sort of frequency shift within one half cycle. This might be measurable as well. We thought that no more information could be added to the current lines, but they keep finding more ways to pack and compress. Remember when they wanted to close the patent office?
Would that that were really true. There are laws now that make it a crime to listen in to certain frequencies, govt, mobile radio, cell. And radio receivers have to be limited to only listen in on acceptable bands (although easy fixes exist to change that). The ideal of the airwave belongs to the people has been eroded.
Note that some wireless providers, such as Nextel, want you to use Email to send an alphanumeric message. In the old days you'de use TAP, or TNPP if you were another provider, but now they want Email input from everyone. So, yes, a wardialer style program can spam Nextel users. There's also some TAP hubs that are great inputs, once you know their dial-in number. Once you're there you can just cycle through the set of 10 digits number, noting which get kicked back as "not in service" so you can build a database of how to hit the next time.
I was involved with starting a Wireless Internet Provider in a North Carolina Town. We provide 11mb Wireless Access to our customers. The Lucent WaveLan cards that we used to get everything going make use of the 2gig range. 2.4gig to be exact. We experienced very few problems with this setup (except for the line of site limitation). We did, however, get interference from an 800mhz Pager Tower. This being a third harmonic situation, the best we could hope to do was place some filters on the tower. That, or look for another location :-). For anyone that doesn't quite understand the 3rd Harmonic thing, let me know. A quick explaination is: 800mhz x 3 = 2,400mhz (2.4gig). Take care and Happy Giggin'
---
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Rob Flynn
Pidgin
I don't think we need any thing similar to the FCC - as they have show repeatedly in the past they give away frequency to massive corporations (who could pay) and deny the little gal any access. They trample on free speech and they are APPOINTED FOR LIFE! Please, no more FCC-like organizations.
e x p e c t d e l a y . c o m
Everything depends on the situation. As anyone involved with radio knows, each band has different advantages and disadvantages. Lower frequencies penetrate obstacles, but require huge amounts of power to work efficiently. Higher frequencies have smaller antennas, consume lower power, but don't go as far. When we're dealing with going through walls, really the barrier is in the single-GHz range. Having experimented with 10GHz radios myself, something as simple as a bush can severely degrade ths signal.
If, on the other hand, walls don't matter, why not use infrared? We already use it for remote controls, and the bandwidth is certainly there. Another advantage (or disadvantage, depending) at higher frequencies is more directionality. In the 2-digit GHz range and above, antennas aren't wires anymore, they're dishes. A signal is beamed in a direction. And even better between that and the IR band, directionality means you can have more users. Signals can cross each other without interfering. But then again, if this is for indoor use, the point becomes moot. Higher freq's are used for outdoor communication when line-of-sight transmission is possible.
The solution, therefore, really depends on the problem. If it's indoors, you can mount an IR transmitter to the wall and move your computer around as you wish. If we're talking about your car, that's not likely unless you can put a satellite transmitter on your roof.
So what most companies are doing, now that the range between 100 and 1000 MHz is just about used up, is they're going just above that to 2GHz, where we had the problems mentioned in a previous article. Everyone's trying to use it, and they're causing interference.
In short, this problem ain't gonna be solved soon, and in any case it all depends.
icqqm [ICQ:11952102]
Sure. Hams mostly know that if you take two frequencies, add a little bit of math, and a lot of power with a short distance, you get signal mixing. A high frequency and a low frequency comes out as a medium frequency. To most involved in radio this is considered a bad thing as it adds to unnecessary clutter on the airwaves.
icqqm [ICQ:11952102]
This seems to be like asking "How many numbers are there?" The limiting factor is going to be the bandwith resolution of the transmitters/recievers. An electrical engineer could probably intelligently comment on what limits that.
A lot of bandwith efficiency increases will probably come from the use of better data compression before transmission. If you go from 2:1 compression to a 4:1 compression algorithm for a particular application - you then have twice the effective bandwidth.
With very powerful processors becoming cheaper and smaller (and low powered i.e. Crusoe) I can see a time where voice conversations are mp3-like encoded in real time before being transmitted from our phones.
Data packets will have their own lossless compression, etc. - Just as analog modems used integrated compression to speed up landline communication, similiar technologies will allow better use of the same bandwidth.
--Aaron Greenberg
Define bandwidth.
:)
......
Are you talking about absolute carrying capacity
per Hz? That's 2 bits per Hz (there is some law
that proves it but I can't recall what's the name), IF you just do "up-down" as bit 1 and bit 0. of course there is such schemes such as using a step scheme such as to squeeze 2^n bits per Hz (with n = # steps) out but they run into s/n problems.
You can go higher and higher frequencies if you wanna more juice. You pay for higher frequencies with more power to increase s/n of your signal. So as long as you have power, you can go as high as you want. The ceiling? I bet it's the melting temperature of your transmitter
OTOH, if your "bandwidth" means the fuzzy idea of "data carried", used by internet talking heads and news anchor people, then
Mode (3) smart-aleck mode. Press * to return to main menu.
I'm not sure. In the Netherlands we've had multiple operators for years, and with the recent entrants we now have five operators sharing two frequency ranges (900MHz and 1800MHz). Of course, roaming requires multiband handsets.
However, we still have the situation that every farmhouse along the highway has five sets of three antennas (for a total of six 900MHz and nine 1800MHz antennas). This is totally insane, and it still doesn't dawn on the incumbents that sharing the base stations makes economic sense. We are starting to see shared base stations, for example in the Amsterdam subway tunnels, but those came about only because the subway system said "work it out among yourselves or go climb a tree".
The whole mobile telephony issue is just shouting out for intervention by some governing body (preferably not government :-) that forces the operators to work something out. The Dutch regulator even says upfront that their sole aim is to foster competition, and that they will bear higher consumer prices as a result. This has lead, among other weirdnesses, to a phone call from my home town of Leiden to Amsterdam (30 miles) being more expensive than a phone call from Leiden to Paris, TX (cross-atlantic).
Bert Driehuis -- All I asked was a friggin' rotatin' chair. Throw me a bone here, people.
We will never have a real problem because all we need to do is use spread spectrum. Today, the cost doesn't justify this approach. If there is a problem in the future, there will always be a way out.
Actually, the formula accounts for noise, so actual rate does not get worse when noise is PRESENT. Rather, it gets worse because the spectral and statistical characteristics of actual noise is different from noise models used during system design.
...invention.
Therefore we will never run out of bandwidth! If this ever becomes a concern, a new method of carrying wireless data will be developed.
Spiral antennas of this nature are often used in things like radar warning receivers for military aircraft where one needs to listen to a wide range of possible threat radar bands. A modern figher aircraft could easily have 10 spiral antennas on it. Next time you are at an airshow, see if you can spot them (hint: they are usualy under small dome shaped radomes about 5cm across).
Re: "A radio signal can be modulated within an
almost infinite range." You don't understand the
problem. Consider a radio signal.
For our purposes it is an Electric vector whose
strength and direction varies with time. If it
is a sinusoid, it is a "pure" frequency, and
occupies a single point on the spectrum. But
even if it is not a sinusoid it can be considered
as the superposition of (generally infinitely
many) sinusoids. This viewing of a time signal as a superposition of sinusoids is the Fourier transform. Now a lot of natural and technological constraints really depend on the frequency content of a signal rather than directly on its time content. If you make a rapid modulation of the signal, you are automatically using very high frequencies. Thus your signal gets the high fequencies' problems
Looked at the link you gave -- this just looks like regular spread spectrum stuff. Interesting, but is it a panacea? In the military applications for which this was originally developed, it made a lot of sense; but imagine thousands of spread-spectrum users operating at once. Each one of them is noise to all the others, noise that can only be surmounted by turning up the power. But if they all turn up the power, they get nowhere.
Another problem is range. Because of the differing attenuation of different frequencies and because the highest frequencies propagate pretty much along the line of site, you will get very bad distortion. Not enough to matter over the distances concerned on a typical battlefield, but I doubt you could call your mom cross-country with it.
This isn't to knock the technology, which is cool and which is nice to see in civilian uses, but just to suggest certain limitations. I'm sure someone more knowledgeable than me could make a better case, telling us how much use spread spectrum could get before it is saturated.
802.11 wireless ethernet uses the same frequency and
is nowhere near dead even if France doesn't like it.
C = 2Wlog^2M where C = data rate (bps) W = bandwidth M = number of levels per signal element Say your bandwidth is 3000 Hz and you have eight levels per signaling element. Your data rate is then 18,000 bps. This equation is an ideal one as it does not take effects into account such as noise, signal attenuation, etc. Whew... My first post on Slashdot! :)
A place for everything, everything in its place. - Ben Franklin
We're worried about frequency because our computers are going to have wireless connections to the internet instead of using the telephone. My Phone isn't going to use phone lines, it's going to be on the internet. My TV isn't going to be on cable anymore, it's going to be on phone lines. The appliances in my kitchen are all going to be part of a smart house and talk to my computer and it's hooked up to my cell phone (?) and where the hell am I now? Oh, talking to the internet. So now all the crap in my house can get random e-mails with .VBS script attachments.
I don't think there's enough bandwidth.
Depending on the country there may be different uses for the same frequencies. A good example of this is the overlap between some Ham Bands in the USA and Shortwave Radio bands in foreign countries. And there are many many unauthorized uses of frequencies from the illegal FM/AM radio stations in Berkeley, CA, to the encrypted number codes in Cuba and responding revolutionary armies in South America. The truth is that the FCC doesn't have the manpower nor the time to control the frequencies to the extent that they would like you to believe they can. And it is next to impossible to control these issues outside of the country. International agreements are fine. Just remember they are only as good as the compliance of those countries that sign them. One other point: Most of the charts listed here make ambigious the fact that the government owns MOST and controls ALL of the frequencies. That includes military, agencies, fire, police, etc. There is NO shortage of frequencies. What is happening is that government agencies are frequently using obsolete technologies that squander the bands allocated to them. They could work with much less if they used technologies developed since the vacuum tube was replaced by the transistor. But there is no incentive for them to upgrade their hardware.
Wovon man nicht sprechen kann, darueber muss man schweigen. Ludwig Wittgenstein
When most ppl think of the radio they think of frequencies higher than light. That is your UHF, VHF, Microwave, etc. If you use everything in the low end of the spectrum you will get more usable bandwidth. The bandwidth in the low end is alot smaller than at the GHz range but if we ever run out we can use it. Or we could plan ahead and use it for things that do not need much bandwidth.
-Grant
|grant.henninger.name|
I haven't bothered to read anyone elses posts on this topic. Why you ask? Because as knowledgeable as they might be they are all out of date and don't even know it. There is a new radio technology on the horizon called PulsON by the folks who invented it. You can read all about it at www.time-domain.com, it changes everything you thought you knew about wireless anything. It answers the questions of bandwidth, security, power requirements, interference from noise, penetration into buildings and much more. It's only a matter of time gang and I personally can hardly wait. Read up at www.time-domain.com
This may be semantics, but the earth's atmosphere doesn't have a bandwidth capacity per se. While the atmosphere certainly affects the propagation of certain frequency bands, the atmosphere doesn't provide the bandwidth and therefore can't be said to have a capacity. The proagation of electromagnetic radiation through space is, as far as we know, the same throughout the universe. It's not a function of the atmosphere. I hope you knew this already and I just misinterpreted your question!
Seriously... I don't know... but with all the talk of cell phones causing tumors, etc. what's the impact of having EVERYTHING wireless? I know that cell phones are really only a danger when they're right next to your head, being that the power decreases exponentially with distance, etc., but if EVERYTHING goes wireless, won't our bodies be constantly bombarded by these waves? Not that they aren't already...
I don't think that americans having cell phones does anything to deprive spectrum from a prospective vietnamese cell phone user -- I only wish my phone had that kind of range. Anyway, clean water and a safe home are vital things, but most people have higher aspirations than that. IMO Maslow's hierarchy of needs (the idea that people don't think/care about complex needs until their basic needs are met) is bullshit.
The standard telephone system is 8-bits per sample at a sampling rate of 8kHz. 8bits/sample*8000samples/s = 64kbps theoretical max. But with all the variables involved like noise, 56k is a big stretch at best. The "audio bandwidth" comes from the 8kHz sampling rate. At that rate, the ideal audio bandwidth is 4kHz, but practical filters limit it to lower than that.
As for the data rate/bandwidth ratio, it depends on the line coding (how ones and zeros are represented by the signal). Looking at baseband, each different method of coding was different frequency spectra for random data, and most of the information is held in the "first null bandwidth", which is from 0Hz to the first zero component. The lowest that the first null goes is the data rate, where 1Mbps takes 1MHz, but coding methods with that bandwidth generally make it harder to recover the clock (data) rate from the signal. Of course, the bandwidth taken by the transmitted signal after conversion to bandpass may vary depending on the modulation method (single/double/vestigal sideband, etc).
As far as I have been able to observe, humans have values, and lichens do not. Most humans I know place a high value on natural beauty, more so than reliable cell phone recption. Remember, your apparently narrow definition of progress is just a value, not a natural law, no matter what the lichen-voices in your head may say.
Am I the only one to notice the .int tld???
At first glance, I'm sure people would think, "Every person on earth can't be given an individual frequency".
As wireless technology becomes available to the general public, I think first of all the progression towards transmitters and receivers which operate on smaller frequency ranges is going to be apparent.
Second of all, it may not be necessary to put people on unique static frequencies for 2 reasons.
More than one person could handle receiving transmissions intended for other people. Through the use of public-key cryptography, networks could be set to act as LANS, and airwaves transmitting all packets with equal time to a small area of subscribers, rather than a large area.
Meaning, packets intended for you would have an ID header, a size, and a time of transmission publicly available, but only your device would know your ID and have the key to decode the packet.
Secondly, we may be looking towards instituting dynamic IP ranges for individuals. Since the lower frequencies travel shorter distances, it is only necessary to ensure unique frequencies for individuals within the areas they can transmit. Using GPS technology, or signals sent from server stations as the subscriber goes out of distance, devices can be set to transmit on a new assigned frequency for a different area.
I think the question in this case isn't what frequencies we can all use, but instead how are we going to share these frequencies among ourselves.
On that note: the frequency range doesn't say much, HAM radios very low frequencies bounce of the earths stratosphere as do the reserved AM radio frequencies - meaning worldwide transmission for some and not for others probably isn't too feasible.
TCP/IP will solve all! 8-)
Ace
someone I know very well is planning on doing this soon - next summer.
In that case, I suggest you leave town ASAP.
Dyolf Knip
--
Dyolf Knip
----
It's been a long time since I've done calculus, and I don't have the time to do the integration anyway, so here's a general estimation, probably accurate within a few orders of magnitude... : )
Let's say that we have a range from 100 Mhz to 20 GHz. Divide that into theoretical bands of 0.1 Mhz. That gives you about 200,000 bands.
Assume that it's all digital, that you get one bit per Hz. That means that the 20 GHz band can pump around 20 gigabits/second. That means that on *average*, each band would have about 10 gigabits of bandwidth, giving you an overall bandwidth of (200,000 * 10 gigabits) of around 200 terabits/second. Quite a bit.
Again, those are just estimates.
steve
Oh, you're not stuck, you're just unable to let go of the onion rings.
Bandwidth ceilings are always being broken. Or has everyone forgotten about the alleged 9600 bps limit on existing telephone lines we were told about back in the mid 80s? For a more recent example, take a look at the technology described at http://www.timedomain.org/applications/comparison. html and see why this is a pointless question.
Please! It's not like everyone needs a unique frequency to communicate. Think about the way tcp/ip works. All those ethernet cards all using the same frequency and I still get my email, and my streaming audio. Two PCS phones, in the same room can still use the same frequency to talk to the tower. They just use addressing to know to which phone a digital packet is directed.
As for how much bandwidth a single frequency can handle, that will depend more on technology than on the radio signal itself. A radio signal can be modulated within an almost infinite range. It's building the transmitters and receivers that can disern the minute modulations that is the problem.
This space for rent.
You might want to look up a guy named Fourier, I think he did some work in this area...
Uhh, you guys did realize that AM and FM are not spectra. AM and FM are modulation type -- ways of encoding information on a carrier frequency. While it is true that the US governemt set aside spectra for use of AM and FM radio there is no reason why one couldn't transmit an AM singal in the FM band.
In fact I beileve that when Armstrong invented FM the FCC gave him bandwidth at much lower frequencies. However Sarnoff and others had invested so much money in AM that they wanted to hurt FM (which was a much better way of sending music -- and not just because in the US FM stations mostly transmit in stereo.) They forced the FM to move their bandwidth. Those old AM stations remind me of M$. It is because of them that FM didn't take off until the 70's even though FM has been around since the 1930's or so.
The answer to this question is the use of spread spectrum (SS) technology. In about 10-20 years SS will be the very latest technology and band limits as we know them will be a thing of the past.
Once we begin to reach the saturation point, on land and in the air, the big players will begin dividing it all up (not just what's left - all of it) for themselves. It will be the same - I can only get to information which is posted, and to which I have access, but it's the corps who will choose that data for me.
Basically, the information will be like a television with 100,000 channels, which is not that different from the internet now, only it will be much more controled by big businesses who have bought out the government.
I'd rather have someone respond than be modded up.
Think of it. This is EXACTLY why SETI is destined to forver fail.
The future of communications is point-to-point wormhole transmission. Two points will be opened up between locations, connecting a pair of laser emitters/detectors. No possible interception of the signal, no battle with the speed of light (required for deep space transmission) or strength of signal. No battle over precious bandwidth.
We are very close to realizing this technology. Radio will survive for another 100 years, maximum on this planet, supplanted by supperior point-to-point technology, as it happens for all star-faring sentient species.
Virtually all countries send representatives to finalize plans for global RF allocation. This allows manufacturers worldwide to be able to design equipment that is more likely to work worldwide. For example, FM radio generally occupies the 88-108 MHz band, although there is some variation as to channel centers. This allows mfgs to design and build RF tuner ciruits optimized for just that band.
As an example of when happens when you DON'T adhere to the ITU WRC plans: Satellite C-band is set at 5.9-6.4 GHz up, 3.7-4.2 GHz down. India decided they didn't like that and went with their own C-band frequency plan -- 6.7-7.0 up and 4.5-4.8 down. Guess what? It's a real pain in the ass to find RF gear that works in India -- any vendor who want to do business in India has to re-engineer their RF cirucits to work at the the India bands.
Of course, India decided they were a big enough market that they could get away with it, and to some extent they have -- INSAT gear exists. But it's more expensive.
WHICH defeats the whole point -- global standards so manufacturers can design one set of RF circuits. Resulting in larger economies of scale and lower prices.
One simple rule for its versus it's
To really push this technology fast. If it is implemented correctly (securely, high-speed, long-range) out-of-the-box, it would probably be possible to convince radio/tv stations, and some other normal RF broadcasters to switch to wireless digital packets. This is sorta like how the phone systems are switching from analog lines to digital lines and trunks.
Course, that's probably wishful thinking, but some real foresight would really save us trouble down the road when freqs get overused and we have to make a change then. (think of IPV4...ouch)
I made a comparison between human infestation of earth and plant infestation of earth. It was funny and insightful. You lack a sense of humor, to be sure, as well as you lack insight. But the truly weird thing is that you've created a series of beliefs for me that I don't hold. Did I say something about progress? Did I say something about natural law? I was just describing what happens. It is you who keeps inserting your value judgements.
Hmmm...let's take an estimate of a half-billion people currently driving cars. I won't tell you what part of my body I pulled that out of, but, for the sake of argument, we'll assume that it's the same one you used for your estimate. Suffice it to say that the U.S. has a quarter-billion residents and most of them drive cars.
I can't recall any missions which had more than a half-dozen people on board, but I'd guess you could fit at least twice that on the shuttle. Let's assume that commercial trips to the moon will be made in vehicles that can fit a hundred people, or something over half what you can fit in a regional airliner.
The back of my envelope now tells me that we'll need fifty million flights to get all those people there.
Nobody I know of is planning commercial space flights (not counting those who're building rockets in their back yards) of civilians in less than five years, and that's to low Earth orbit at best. Let's give them an extra five years to make it to the moon. Never mind that India is adept at putting up communications satelites but is agonizing over whether they can afford to put a probe in orbit around the moon, I'll grant you tourists on the moon by 2010.
So, now we're looking at fifty million moon launches in ten years. Let me consult my envelope again...that's five million a year, or a little under a half-million a month, almost a hundred thousand a week, thirteen thousand and change a day, five hundred and seventy an hour...nine and a half each minute.
Wow.
Tell me, what's there on the moon that, in twenty years, we'll need a spaceport as busy as our busiest airports just to take people there? And where are we going to put all these people once they get there? Who'se going to pay for it all? Or is Microsoft going to relocate to the Sea of Tranquility and require you to sign EULAs in person?
Then again, you did say that you were being optimistic.
b&
All but God can prove this sentence true.
The future of wireless is in TM-UWB (Time Modulated - Ultra Wide Band). Follow this link for details. Basically, TM-UWB involves the transmission of precisely timed pulses which can be decoded by a receiver and compared to a standard pulse stream. The only thing that matters so far as data transfer is concerned is how much the actual pulse differs in time from the standard stream. There is no carrier frequency. With the ability to place pulses a trillionth of a second apart...the bandwidth is huge. There are a lot of details/issues that I don't yet comprehend, but it sounds fascinating.
I'd rather not have a cell phone so when I want to "disconnect" I can. Kirch
Diligence is the price of Freedom
God: 640Khz should be enough for anyone.
The eletromagnetic spectrum is like any other finite natural resource -- it is monopolized by the "developed" nations, ala oil. While the most of the people (in a world-wide sense) look for clean water or safety, "developed" nations will eat up spectrum capacity.
By the time the average villager in Asia has a cell phone, there won't be much spectrum left for them to use...
Some food for Slashdotter thought:
Be careful about saying things like "when everyone goes with cell phones." Even if you limit "everyone" to folks living in "developed" countries, you'll still find a lot of people who just aren't interested in being connected 24/7.
Several billion people need clean water, a reliable food supply, and a safe home -- they couldn't care less about having "PDAs with full screen video capabilities and gigabytes of magnetic RAM".
Just something to think about...
All about me
I think that everybody is missing key point. The question isn't "How many frequency bands CAN we use?", it should be "How many frequency bands SHOULD we use?" At this point, very little is known about the long term effects of non-ionizing radiation on people (remember the cell phone-brain cancer scare?), much less on other forms of life. I already have cell phone conversations, radio stations, satellite TV, and who know what else travelling through my body at any given time. I am leery of adding anything else before we have an idea of how it will affect us. Not to mention the several companies recently petitioned the FCC to open frequency range where elemental hydrogen resonates. I can't think of a better way to kill off radio astronomy that this. Just because we can does not me we should. This is the same thinking that people complain about when discussing the problems of genetic profiling or data-mining.
The Revolution. Now available as a convienent six tape series from PBS.
One thing that occurs to me immediately is that the amount of bandwitdth potential is proportional to the frequency used. Advances in technology can and will increase the bandwidth you can get per Hz, but more Hz will always give you more bandwidth. I guess there would come a point where a "maximum frequency" would be reached, due to reasons of economy (takes too much energy to transmit) or safety (it fries everyone within a 3 mile radius). The question of how much bandwidth we can squeeze in per Hz is much thornier and I have no qualification whatsoever to address it. There probably is a theoretical maximum, although I seem to remember that 28.8k was the theoretical maximum for modems, too. Whatever trick was used to double that over the telephone network might not translate to the ether, though.
Yo dawg, I heard you like the Ackermann function, so OH GOD OH GOD OH GOD
Considering the rate at which such "wireless lans" are gaining range, we absolutly need an international equivalent of the FCC. If not to regulate who uses which spectrums, than to simply regulate range. If not, all sorts of Bad Things(tm) will occur.
That's a good question...also, what kind of penalties are there for "transgressing" on someone elses frequencies?
Also, how would location play into these bandwidth restrictions? Certainly some can be divided up geographically, but as more and more "global" services come into play, won't there need to be some kind of universal frequencies? (Like GUARD on the radio)
you technocrats make me sick. bandwidth of the atmosphere is not the point. bandwidth of living forms is fundamental. with the cellular fones network, the 'atmoshpere bandwidth' started interferring with many forms of electromagnetic activities of numerous cells amongst which's the brain's.
Hopefully an international organization can agree to preserve the space allocated for atronomers researching cosmic radio waves. Does anyone know if astronomers are currently hanging on to more than just the "water hole" range used by SETI?
Here's a good one: http://www.ntia.doc.gov/osmhome/allochrt.pdf
As much as I know, astronomers miss every frequency used by another service. What about the future of the exploration of space? would a message from outerspace go lost in our home made 'noise'?
Such an organization already exists, it's the International Telecommunication Union.
www.itu.intI checked out the posts to see if anybody had mentioned channels. Granted, I did not read through all 200+ in detail, but I did not see anything.
The problem is not the "bandwidth" of the atmosphere, or the "bands". It is the channels. The more channels that are set up, the more data that can be transmitted. Channels are a key concept, for example, in cell phone technology. When all we had was analog cellular, with a few really big towers, we also only had a few users. Once cellular began to explode, into PCS for example, the question arose: how to accomodate all those users? The creation of digital technologies allowed for more than one call on a particular channel, but there was another solution: just put up more antennas!
Say one antenna can handle ten channels for cellular (actually more, because there are both incoming and outgoing for the full-duplex effect, as well as control channels). That means a max of 10 calls on the one antenna. What happens when call 11 gets initiated? "System busy", OR, the phone simply locks onto another antenna a bit further away. The phone is able to sense what antennas are close and which are further away, and they lock onto the best available choice with a free channel. This erection of extra antennas creates additional channels and divides the coverage area into cells (hence, cellular), which can be very small...picocells, for example, can be the size of a room. (Remind me to post something about hierarchical cell structure one day).
So as long as we have antennas, hooked up to land-line switching offices, we can always add new channels. As long as the world can be divided into cells, ever smaller and smaller, we will never run out of broadcast bandwidth. And any radio signal can be split into cells - even cellular TV, for example.
Most people don't know about them yet, but there is a company already offering broadband access over a LMCS (wireless) system. Maxlink Communications (www.maxlink.com) has 1000 Mhz of licensed frequency up here in Canada. Right now, they're offering up to 10 Mbps access for businesses in most major cities. Not much chance of it appearing in the states though, 'cause no one owns enough licensed bandwidth down there to do it. I've read up about this technology, and it looks pretty damn cool, especially for people outside of DSL-serviced areas. Just thought some of you might be interested.
Has anyone ever heard of TimeDomain(http://www.timedomain.com) They are a Huntsville, AL based company perfecting, ultra-wideband technology. Its 1/100th the power of current cell phones (to send the signal), can go through walls, and has security built in that is always changing. ITS AMAZING. I wrote a paper on it for a college class a few semesters ago. Their site is packed full of information. Basically it removes any need for reserved frequencies. It variably shifts what frequency it broadcasts on (ie the TIME in TIME Domain) - only the transmitter and the reciever know what freq to look at. Using IBM's Geranium chip which enables 40billion cycles per second, it can alter freqs and it sends out bursts of information that is encoded (which changes). Also the patterns as to which freq comes next is altered all the time. Its is virtually undetectable as well!
-- Only a developer would see the 'Go to' part of "Go to Hell" as the problem.
My favorite spectrum allocation chart is here:
http://www.ntia.doc.gov/osmhome/allochrt.html
It's nice a purty. At my last job (software for an RF engineer consulting firm)I did it on a plotter and pasted it on my wall. It's visually appealing.
Okay, so how much spectrum is there? There's a lot. The military has tons of it that you can't use. There are a lot allocated to airlines as well.
Bandwidth isn't the whole story, though. There are other technologies that area based on the number of pulses you can send per second. They don't require riding the old radio wave so much. It gets excellent throughput without using "bandwidth" Also, since they don't go into controlled frequencies, they can use really low power, and for all intents and purpose, it looks like noise. I wish I had a link to this 'cause it's cool technology. The FCC is currently working on deciding whether or not it causes little enough interference to allow it's general use.
As for open bandwidth, there's not that much. The FCC recycles some bandwidth every now and then, that's out of date, for other uses. For example, as HDTV becomes the norm (i.e. when your children are adults), the old analog stations are going to go offline and that spectrum will likely be reassigned for some other use.
Also, as technology allows more efficient use of bandwidth (i.e. CDMA), then we'll effectively have more bandwidth.
Still, we're limited. There are a lot of bands that are just real dangerous for people to be around, at least you don't want to be right next to the transmitter. Besides causing cancer, some bandwidths with high enough power, can make your eyeballs explode (no joke here. I believe it's around 2GHz, and not a PCS or CDMA phone, but the base station antenna on a tower might have enough juice to do it).
Anyway, it's a complex question because it depends on the technology you're using and what frequencies your using.
Also, the higher bands, like microwave, LMDS, and that stuff (around 10GHz+, I believe) can have high throughput, but requires direct line of sight and has very limited distance, whereas shortwave can go REALLY far on less power, but has limited bandwidth.
On the flip-side, there's no restriction on how wide a band can get. Severe leakage into other frequencies, poor (or no) compression, etc, can effectively leave you with space for only the one signal.
Actually, there'd be something neat about a TV signal with the video pulse modulated, the sound phase modulated, the Internet traffic polarity modulated, the subtitles frequency modulated and the penguin caffeine-modulated.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
As for a "global FCC," well that's just a huge stinker of a solution.
International Telecommunications Union, or ITU. It's been around for awhile.
In reguards to radio band, no, there isn't much left, it's a squeze right now, and there isn't really much left for transfering giga-bytes of data. Using convential, non-compressed means, a 10-mbit data channel, you use up, 10megahertz, and it scales 1:1 from there on. With data compression, you can get more, and multiplexing can help, but you can see the start of a problem.
:)
(This is going to be a bit long winded)
The next problem is that differrent frequencies have different characteristics, 500-1700khz am radio, can be used to broadcast over long distances in a direct path, and objects don't tend to make too much of a difference, but nearly every piece of electrical equiptment does.
Next is 1.7-30mhz, shortwave radio, can cover massive distances, if the ionosphere bounces it back, and is why I can listen to radio netherlands in australia without much more than an antennae sticking out of my radio.
Now we get to 30-300Mhz, these frequencies can get some weird effects, the low end, on good days, can make it a few hundred km's, but in most cases, good local communication for up to about 200km, this convers the vhf tv range (0-12 in au).
Next is 300-900, similar to 30-300, but shorter range, and effected by buildings more, many services use this range because there is more bandwidth available to them, at the cost of distance and useability, uhf tv exists around here (21-69 in au).
Next is 900-3000Mhz, where we encounter 3 cell phone bands (analogue/cdma, gsm & gsm 1.8ghz), and some other traffic, such as some sattelite reciever downlinks (from dish too box), point to point links start around here, MDS services (wireless cable), home networking, microwave ovens (~2.5Ghz), and much more. This is about the only feasable area to open mobile computing channels, but there is the problem of transmissions of on these frequencies causing damage to the human body (if it is proven so).
Next is around the 3-30Ghz range, which has some satellite up/downlinks, more point to point links, and not many mobile/portable links, due to the line of sight limitations of this range.
After 30Ghz is a few point to point transmissions, and it gets harder and harder to transmit at higher frequencies, since the smallest objects can cause interference (eg. fog/mist, birds, trees), and lower power transmission can have the same effect as higher power at lower frequencies (2.5ghz) to objects like organic material, or metals. Up around these higher frequencies, is where it is easily possible to make some type of emp gun, they are very dirrectional, and can irradiate things well, and only good shielding can work well, but that needs to be completly shielded, not just sealed (plastic does not stop radio waves).
In the future, to fit all the wireless transmissions that people will want to make, we will need too either come up with some really fancy ideas, or invent a new level of communications, or just wait until we get to home or the office to keep in contact.
And on the subject of an international frequency band regulator, there is the International Telecommunications Union, these are the people that keep most of the world standard, and sane when it comes to radio frequency allocation.
Oh, and long live experimentation in Amateur (Ham) Radio!
VK3TST
-- "People aren't stupid. Usually." -- jd
They appear to be below the noise floor of a non-spread receiver. However, every spread-spectrum transmitter in range raises that noise floor. Also, call it transmitting, the word "broadcasting" is specific to one-to-many transmitting.
and that you didn't need a license or FCC approval to broadcast.
This is part of Part 15 of the FCC rules and regulations. Power limits of up to 1 watt, with antenna size restrictions, are allowed.
Since it's not using one band, but various signal strengths between an upper and lower frequency limit, it didn't fall into the idea/trap of a band or bandwidth.
That's not really the case. You can have some number of spread-spectrum stations take turns on a chip, a frequency that they visit momentarily, but that's controlled by (time you spend on a chip / 1). You can also have some amount of collission between transmitters before the signal degrades too much, but not an infinite amount. So, even with spread-spectrum radio there is an upper limit to the carrying capacity of a band, given a large number of stations in range of each other.
Bruce
Bruce Perens.
Bruce
Bruce Perens.
Atmospheric attenuation is useful, too, because it lets you build microcells.
Thanks
Bruce
Bruce Perens.
Thanks
Bruce
Bruce Perens.
PCS is very definitely a cellular system. What you call "cellular" is actually more accurately referred to as NAMPS, for New Automatic Mobile Phone System, and DAMPS, for Digital Automatic Mobile Phone System. The old AMPS was the car-phone of the 60's and 70's (and earlier?), the "Automatic" referred to the fact that calls can be placed without an operator :-)
Bruce
Bruce Perens.
I'd suggest you read Shannon and a text on modulation before you take this further.
Thanks
Bruce
Bruce Perens.
Bruce
Bruce Perens.
My understanding is that one of the GSM bands is allocated in the U.S., is that incorrect?
Regarding the cellular infrastructure, I am thinking of a market for "connections" that cell operators sell as a commodity to cell phone "networks", who would really be billing aggregators rather than networks. It really isn't necessary to build a whole network, you build a cell and make a wireline partnership, and you bill the aggregator per call.
Thanks
Bruce
Bruce Perens.
Thanks
Bruce
Bruce Perens.
Thanks
Bruce
Bruce Perens.
The important thing to keep in mind is that propogation of energy follows an inverse square law. Every time you double your distance from the transmitter your exposure is 1/4 what it was before. Thus, a phone held up to your head is generally a much bigger risk of causing injurious heating than the ambient radio energy in your environment.
Thanks
Bruce
Bruce Perens.
Simply put, I don't want a lot of towers screwing up the Yellowstone natural landscape. You'd either have to do without in our national parks or go back to you low-freq, high-watt counterparts. We have a big hubub here in Washington D.C. when they put those ugly Celular Towers in Rock Creek Park and Congress allowed it because it DOES protect people from muggings and rape, but the idea of placing thousands of towers all over Yellowstone National or the Grand Canyon or Yosemite or Glacier Park or, well, the entire state/territories of Alaska, Yukon, NWT and Nunavut -- it ain't gonna happen my friend. The long and the short of it is, for my sake the fewer towers the better.
Be Seeing You,
Jeffrey.
(One is reminded of the 'Mr. Neutron' episode of Monty Python's Flying Circus -- 'This cell TOWer, is the new cell TOWer for Alviston Road. We hope that this new TOWer will serve Barnsworth, Grenville and Smithe St. in an area of 5 square kilometers. The TOWer will transmit and receive singals for frequencies in the range...')
Time Lord, Dark Horse: The Techno Mage of Gallifrey
Infact, someone I know very well is planning on doing this soon - next summer.
wow. what an amazing honda you must have here. c/(4GHz) = .0749 m. A seven centimeter long car. Simply astounding. c/(20GHz) = .0149 m. 1 cm rain drops. Must be a bitch for those 7 cm hondas.
Also, I highly doubt that actual physical size of obstruction plays any role in the attenuation of signals. Rather, the type of material determines this, I would imagine. A thin wall of lead stops more waves better than a thick wall of jello.
eric.
"They can kill you, but the legalities of eating you are quite a bit dicier" -dfw
Deep in the wastes of Switzerland , surrounded by the eternally white peaks, entrenched in a hidden green valley, there is a place where the protocol mangling and the political division of bandwitdh is carried away by the high priests of an ever lower cult. Through its dark corridors, the life and death of multi-billion dollar companies is decided over cups of tea served by humble servants.
The mitical ITU halls, where no foolish sysadmin or teenager wanna-be hacker was ever admited, where the powers decided how and when the people of Earth will communicate.
Beware ya who speak the high name of ITU in vain. Your life, your sanity and that of your family may well depend on ITU's wisdom and justice.
Anyone know of a good spectrum allocation chart on the web?
No, multi-bit operations aren't the same thing as analog at all. I don't think that they buy you anything, but that doesn't make them analog. Analog signals have fuzzy values between value transitions (that's more like an 8 than a 3, to take an example from my handwriting). Digital signals have precise definitions (e.g., a 1 is .5 V and a 0 is -.5 V). This allows digital signals to be reconsitiuted precisely.
We seem to be using the term "analog" differently.
I am assuming a discrete-time signal for all cases - i.e. a signal that is being sampled at regular intervals.
I am defining a "digital" signal to be a discrete-amplitude signal with two permissible amplitude values.
What I am calling an analog signal is any signal with more than two permissible amplitude values. My justification for calling it "analog" is that it is no longer directly processable by binary logic.
A true analog signal - one with a continuous range of permissible amplitude values - can't be meaningfully talked about for sampled data transmission because there will always be uncertainty in the sample measurement, both due to instrument noise and due to fundamental limits on measuring photon or electron counts.
] If atmospheric and obstruction effects cut
] off everything above, say, 30 GHz
It won't cut off everything above 30 Ghz. As a counter example consider X-rays.
Please click "User Info" above and read my previous posts for a more detailed description.
Short version: Microwaves in double-digit GHz and higher are blocked by rain and by walls. They won't reach your PDA unless you're sitting under the tower or are standing out on a balcony with perfect line of sight with good weather. This is not acceptable.
X-rays and higher energy photons don't interact with matter much at all, which is why they can pass through most materials with impunity. For a better example, look at visible light. It too is blocked by rain and walls.
] The only way to pack in more data is to use
] analog transmission, and the power required to
] get more bits grows exponentially with the
] number of bits per sample (gets impractical very ]quickly).
Huh? You need to use more granualarity, which means more sensitive receivers and more transmission power to achieve the same range, but what's this analogue crap
What do you mean by "granularity?"
If you mean having narrower frequency bands that are more finely spaced, then your assertation does not make sense. A frequency band that is Hz wide gives you at most samples per second of data. Pick up a book on signal processing for more information on why this is a fundamental law.
If you mean packing in more bits of data per sample - that is *done* by having more than two data levels per sample. By definition, this is analog. This is how your 56k modem works (carrier is at 14.4, and you get 4 bits per sample).
See my previous message for why power requirements grow exponentially under these conditions.
GSM is obsolete. The next international wireless phone standard is going to be based on CDMA technology, and will use a different frequency band.
Mea navis aericumbens anguillis abundat
If any regulation is done at all it should be for disallowing the use of any signal over more than x distance.. probably a distance within 100ft in cities and other populated areas and further in low population areas. Nobody should be able to own any of the spectrum. It belongs to all of us. Corporations that buy it up and send their signals over a long range are wasting what belongs to the public. We need a massive peer-peer wireless network using multiple short hopes to pass signals rather than the couple big hopes approach used by the corporate/government owned Internet model. Once we start working on the problem I'm sure there is little limit to the amount of bandwidth. Some of it may be hard to access or use in this way currently but look what we have done with CPU's once we really tried. :)
At what price learning? At what cost wisdom? The price is a man's peace of mind, and the cost is his life.
So, one can make cell sizes so small that only your personal devices matter (which means you get essentially the whole spectrum to yourself), and the relays in the cells can communicate wirelessly via non-interfering directional signals. Or, to put it differently, if you settle on a cell size, you can get as many bits across total as the number of cells you have multiplied by the capacity of the frequency bands you allocate.
Cell sizes can also be limited by other propagation properties. An extreme example of that is IR (as in your IR remote control). From a security point of view and from the point of view of sharing frequencies, that can actually be desirable.
As for an international FCC, the frequency bands used by personal devices do not travel far, so they don't need to be regulated internationally to prevent interference. But the ITU is an important international regulatory agency.
I was thinking a while back, why not use cell phones as repeaters themselves? That is, your cell phone acts to relay cell phone calls from other distant callers.
Can't do it. Here's why:
One of the things that makes cell phones small is that they transmit very low power signals. They can do this because there is a whole little hut of electronics equipment at the cell site that pulls the very specific frequency of the transmission out of the noise. (For you chemists out there, it is kind like NMR. Each cell phone is a nucleus that has changed states, and the cell site is like the instrument that detects this 1 in a million signal).
On the flip-side, the cell site can transmit with much more power to make it easy for the cheesy cell phone antenna to pick it up.
So what I am saying here is that cell phones can't hear each other very far away from each other cause they don't have the signal processing meat to do so. To do what you propose would require like wall to wall coverage by people with cell phones that are on and have this capability.
Pulse Transmission, which uses synchronized transmitter/receiver pairs that act essentially like a serial bus will help. It transmits pulses rather than a modulated-carrier signal, so it interferes very little (if one is to believe the articles about it) with existing carrier-based transmitters, or other pulse-based transmitters. Power requirements are lower, too.
This should stretch out how long we have before we need another breakthrough idea to stuff data through our airwaves a little better!
I have to protest reading this! Information theory is not as simple as this (bandwith of 3000 Hz -> 3 kbps throughput).
Half a century ago a clear mind named SHANNON found a formula on data rate:
R = B * log2 [ 1 + P/N ]
where B is the bandwidth and P/N the signal to noise ratio (SNR) of the channel.
This formular gives an UPPER BOUND on what may be transmitted through a given band. It get's worse when noise is present (what always is the case) and one may compensate by increasing power.
I found the formula and more interesting information at this URL: http://www.adc.com/Corp/BWG/MSD/qammmds.html
It's a good topic.
I think we need to remember something, though:
The way we use the spectrum is compltely subjective. "Channels" only exist due to the use of current modulation schemes, and regulation.
Radio bands, or channels, do not really exist. There is no real 'division' between bands, other than those we impose on ourselves.
I have read several papers, and other sources that would lead me to believe that the future of wireless is not in specific channel allocation for different tasks, but a completely new use of spectrum.
Something like this:
Various frequency regions in RF exhibit various different properties. Low frequencies can circle the globe unaided, and travel through just about anything.. higher frequencies can carry much more data, but require line-of-sight, but also require much less power to go the distance.
I think something that acts comceptually as a wideband transciever (something that can go from DC to light, ideally) with a good power range, and a modulation scheme that may not exist yet, coupled with a smart digital element to handle routing and such..
say a million of these radio units are placed all over the US. They can all see numerous other units. They can all talk to each other on an amazing number of bands. We will have the electronics figure it out for us.
There's more than enough bandwidth, if we do it this way, for everyone to do everything, without having to allocate spectrum.
Well.. the *real* answer to this question is... there is *LOTS and LOTS*. Remember, the airwaves *belong* to the people, and are only licensed to others to keep things orderly. Companies that have a license for band XXX don't *own* that band, and their license is only temporary, and must be renewed. If a switch to massive broadband digital were to be enforced, many existing services could switch to digital, and TONS of bandwidth could be recovered.
I was thinking a while back, why not use cell phones as repeaters themselves? That is, your cell phone acts to relay cell phone calls from other distant callers. This could drastically reduce the cost of deployment. The biggest argument next to how to figure who does the relaying, is the reduction of battery life. But if you have enough users then your phone would not have to relay most of the time.
Users are very flaky and can instantly turn off their phone, so you would have to select a few repeaters to ensure a consistant signal. On long stretches of highway or in urban areas this wouldn't work but in a big city it would be perfect. You could concievably start your own cell phone company with one or two actual repeaters per city.
Privacy issues exsist, but I'm assuming the data would be encrypted. I'm sure this idea has occured to all cell phone engineers - yet it hasn't appeared. Anyone want to explain why this doesn't work? Too small of a coverage map, too much latency, ???
-- Virtual Windows Project
CB radio, that had 40 channels. But they got crowded, so someone developed side-band. The same spectrum was used, but it was split into smaller sections. So the question then becomes, "How small can we make the spectrum slices?" We only have one spectrum, and its size was set by a very strong being a long time ago. Now you can increase bandwidth by increasing the bits Hz on each channel, or increase the number of channels.
Because of innacurrasy(sp?) in manufacturing and other sloppiness, we can't asign an entity a frequency +-1 Hz. You have to spread things out to give everyone some room, or they'll be stepping all over each other. But technology improves, and as it does, equipment can hone in on the proper frequency much more precisely. This removes some of the need to spread stations out so far. It used to be that a radio station needed every bit of their spectrum to transmit music without stepping on the next station. Now stations can actually use part of their spectrum to transmit data.
With this in mind, the bandwidth is (for all intent and purposes) at this point endless.
Aah, change is good. -- Rafiki
Yeah, but it ain't easy. -- Simba
Why is this funny?
GSM only works in high density areas. This is why it is a total and complete flop in many parts of the world even though it is "the standard". It is a poor system to cover long distance roads in places like Kasnas or 95% of Australia or most of Africia. At least with the old alanlog system you could boost the power and talk to a cell site 20 miles away. Some of the experimental CDMA sites in Australia are covering 100 miles (160km)
The question answers itself. Sure, there may be a *physical* maximum carrying capacity on earth. But since frequency is cycles / time...we just have to find more clever ways of pumping data back and forth faster. If we ever fill the carrying capacity of T1-Earth...we'll have to start sending data over *faster*. So theoretically, Time is the limiting factor.
It's 10 PM. Do you know if you're un-American?
From a practical point of view, it also depends on distance. Take, for instance, cellular phones. By using lower power transmissions, you can use a certain frequency band to send data as someone else is 100 miles away. As you decrease the size of a cell (macrocell->microcell->picocell), each individual user gets to use a higher percentage of the cell's bandwidth because there are fewer individuals. Also, there are antennas that can direct their transmissions in one direction, further multiplying the amount of usable bandwidth there is.
--
http://sss-mag.com/pdf/freqchrt.pdf
This lists all allocations from 3KHz to 300GHz.
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
Long distance, invisible, laser-light transmission is being worked on right now. In fact, I work down the hall from a guy who is developing it. *If* we run out of bandwidth in the atmosphere as far as wireless is concerned, the move to invisible light is not far away, and a very fast (100 Gb/s currently) medium. Granted, it is a *very* young technology.
It's only when we've lost everything, that we are free to do anything...
What kind of patriot are you? The CRTC protects
Canadian culture by allowing us to listen the music that we really want to. I know that Mrs. Copps knows best, and i even respect canadian content laws while listening to cd and mp3s. Just remember, culture is whatever the government wants to shove down our throat.
Well at least we still have Molsons to keep us patriotic.
One thing... With wireless, the only spectrum area you need is from the nearest land link (cell, whatever) to your phone/PDA/whatchamacallit. So theoretically, you could RE-USE spectrum simultaneously in different parts of the world (like TV channels), as long as you know where the end node is.
Now obvioulsly, with TV, it's a one-way communication process, but for two way, if you're worried about overlap, all you'd really need to do is make sure that the receiver could re-tune to the new frequency of the new cell you're moving into, and that there was no overlap between connected cells (kind of like the fill-in-the-map-using-only-four-colors problem), OR, have a DCHP-ish system, perhaps, where each new end-node in a cell's range is assigned a new frequency, like a DHCP lease...
I think by "Higher Frequencies", he meant multiple gigahertz, not 144 Mhz. In this case, he is correct. The waves around 4 gigahertz may be the size of a Honda, so a rainstorm would only cause a minor disruption of a waveform. But at 20 gigahertz, the waves are about the size of a raindrop, so a raindrops passing through the waves will cause a major disruption.
I would consider 144 Mhz to be a very conventional frequency, considering that the most common band (FM) is in the 100 Mhz range. High frequency would be somewhere in the 10-30 gigahertz range. Just my opinion, though.
Exactly how high is high? I need to do some experiments on that. Hmmm......
--- "So THAT's what an invisible barrier looks like!" - Time Bandits
This is true, but not particularly relevant to the original question. The answer to that is that the "bandwidth" of the atmosphere is for all practical purposes infinite. Even if you have only a narrow band to use, communications can be either directional or local (or both). For local transmission, simply use low powered transmitters that are not detectable beyond a limited range. For directional, use something like a laser, maser or phased-array transmitter. Either of these approaches allows a vast increase in the total throughput over a simple "broadcast everywhere" approach. Of course, they have their own headaches, like crossing cell boundaries and tracking directions, but in theory the amount of information that you could send is much greater than the amount that you would in practice want to send.
Having a colorful poster of the radio frequencies hanging in your office really makes you look like a geek.
http://www.dxzone.com/catalog/Reference/Radio_Spec trum/index.shtml
http://netlec.com/html/frequencybands.html
FM, AM, visible spectrum, and audible sound are mere blips in the size of the spectrum. You're talking about Ghz of space available, while these take up mere Khz.
That aside, there are boatloads of bands already taken up:
Marine
Military
Commercial satellite
Military satellite
HAM
Public use (CB)
Shortwave
Cell phones
Freqs. set aside for radio astronomers
..to name a few.
I wouldn't worry about running out of bandwidth for PDA/wireless devices. The nice thing is it's mostly packet data, meaning you can have many devices use the same frequency if you throw in some collision avoidance, same that's used for Ethernet.
Wish I had one of those charts. An FCC testing house usually has one of them up to show customers.
-Mark
-- Ever notice that fast-burning fuse looks exactly the same as slow-burning fuse? I didn't... (Edgar Montrose)
Ow. Hey. You're right for the most part on my calculations. That's why I'm a software guy and not a hardware one.
Collision avoidance works by _reducing_ the data rate on each device when too many devices are trying to use a data pipe at once. It does NOT give you more total bandwidth - it just makes sure that any bandwidth available is allocated fairly and not wasted in an electronic shouting match.
But it allows a large number of devices to share a certain amount of bandwidth, which is really the point.
For a bandwidth of "foo" GHz, you will have _roughly_ "foo" gigabits of _shared_ bandwidth between all users in range of one tower. The only way to pack in more data is to use analog transmission, and the power required to get more bits grows exponentially with the number of bits per sample (gets impractical very quickly).
Digital compression will allow for more bandwidth without a change to the signal.
-Mark
-- Ever notice that fast-burning fuse looks exactly the same as slow-burning fuse? I didn't... (Edgar Montrose)
Naturally this bugs the broadcasters, who claim that this would cause all kinds of technical problems for current radio signals. This isn't true. The engineer who studied this for the Media Access Project found that less than 1.6% of listeners would suffer interference in current radio signals. (http://www.mediaaccess.org/programs/lpfm/raptest. html)
Still, Congress is considering overruling the FCC's decision to create and license LPFM stations. (http://www.mediaaccess.org/programs/lpfm/webcong. html)
Too bad for the 700+ groups who applied for LPFM licenses during the first application period. (Which only allowed applications from 10 states!) (http://www.fcc.gov/Bureaus/Mass_Media/News_Releas es/2000/nrmm0029.html) At the end of August, the application process will be opened to communities in 10 more states.
These opinions are my own. My employer is not aware of them, does not endorse them, and is not responsible for them.
Shannon's work defines the theoretical maximum carrying capacity for a communications channel . The guys at Bell Labs found a clever way to add more channels to a wireless transmission using fancy signal processing techniques. None of their individual channels beats Shannon's limitations. If they'd beaten Shannon, they'd be crowing about it.
One viagra in the morning before work; I just know I'm gonna be screwed
You might want to start with the ARRL and the ARRL Operating Manual it will give you a good guide to this and anything radio oriented. I do rember in one of my college classrooms a big poster saying who 'ownes' what band.
Incidentally, by international agreement, radio regulation ends at 3 terahertz, which is sometimes considered to be very long infrared light.
The problem with transmitting bits of data is that they have sharp corners, where the frequency or amplitude of a signal has some difficulty in making those corners, which means it takes some time to move the frequency or amplitude or phase of a signal to signify a one or a zero. We need some quantity of the signal we can change and detect to signify data, like dividing a change in frequency of a carrier signal into descrete phase angle changes relative to a reference signal into many parts (like 256 different phase angles which would encode 8bits of information). The carrier is good so you can lock onto the signal and know what you are detecting is the signal and not noise (signal to noise ratio is high). As long as we can find more and clever ways to encode data, and more precise ways of descriminating it we can squeeze more out of any frequency.
One major problem is repeating the signal without addition of errors. Analog signals always add error at each step so the signal degrades the more times it is repeated on route. Digital signals on the other hand can be descriminated and reconstitued anew at each stage so you can send digital signals through more stages without loss of quality. The phone system's analog repeaters guarentee a bandwidth of only 3k or so as this is all that is needed for acceptable voice transmission. Digital networks do much better, with error correcting codes and such can almost guarentee good data (or tell you its not).
So I think a purely digital distributed light network with an IR station in each room (possibly an addition to each light bulb, and street light) would solve a lot of problems. Who knows maybe all this RF in the air is really responsible for all the global warming (that losted energy does end up in heat).
Cell structures also multiply bandwidth. If you have a protocol that uses a slice of the spectrum to deliever X bytes/sec, then having N cells can increase the available bandwidth up to N*X - so long as all the active users happen to be in different cells.
And, as someone else sort of mentioned, partitioning can help. Fiber for big pipes to nodes, wideband in cells and micro cells from there to local distribution, short range micro and pico cells for within a neighborhood or building.
The real problem is how long to we have before the machine intelligences hear all this racket we're making, and come to wipe us out ?
The question then really becomes: 1) how good can we make existing equipment wrt to signal to noise ratios, 2) how directional can we send our signals so we don't step on the next guy, and 3) what are the natural phenomina in the channel to begin with.
A better [perhaps] approach might be to consolidate large sections of the spectrum under a single "data carrier" protocol, with a much more end to end approach (like the Internet). As we've all seen, freeing the users (whether they be hardware builders or cellphone callers) with open connectivty--where you just put your data 'on the air' and let it arrive at your target--generates lots of good things. It should also be more efficient overall.
One of the first catches I see to such use is that realtime use (e.g. cellphones) would require more reliablity--and I mean reliablity on a quality sense, not a basic funcationality sense-- than the Internet generally provides. Perhaps you could split the protocol up into 'reliablity zones', where some of it uses more bandwidth to provide better service. Companies could pay a premium for putting data onto this network. More time-tolerent services might use a more latency prone slice, and pay less.
Hmm, and any inefficiences in having sectioned spectrum might be alleviated if this magical protocol had some kind of dynamic frequency allocation scheme. Need more real-time bandwidth? Expand the RealTime block of frequencies. Need less? Open up some room for more latency tolerent devices (e.g. text messaging). Actually, this problem reminds me of my OS classes I took in college....
-- PondScum, SamThe
This is a fascinating article. I had never considered the issue of the "bandwidth" of the atmosphere - i.e. whether it could only handle a certain number of wireless transmissions.
I'm also a little skeptical that increasing these transmissions exponentially is a Good Thing. I mean, we have to live in this stuff. I'm fully aware that right now waves are bombarding--and passing through--my body, transmitting Joe Blow's phone call to his grandmother, the new Britney Spears "song", and pictures of Natalie Portman. But I wonder if there's a critical mass issue somewhere. I've read that in areas inundated with too much sonar, dolphins become confused and may change their hunting, mating, and migratory patterns.
We know our brains put out electrical waves. Are they restricted to transmission--or do they also receive information on some subconscious level?
"Beware he who would deny you access to information, for in his heart he deems himself your master."
The carrying capacity of available frequencies is effectively infinite if properly handled. The purpose of commmunications is to get information from one place to another, and if one uses excess power to do so, it's wasted and is a potential source of interference for those wanting to use the same frequency, who could otherwise use it to carry their own information. A good example of a system that limits power and reuses frequencies is the the cellular phone network. The cells reuse the same set of frequencies over and over, so their carrying capacity is multiplied manyfold. There are now radios in use that employ spread-spectrum and adaptive power-limitation to use just the bare minimum necessary to carry the information. I was told by one user that he had set up a 10-mile comm link that used only 1/1000 of a watt. If we were to use such techniques on all of our radio communication, we would have a vast amount of capacity available to us. I'm optimistic that we're heading that way already.
The long-term prospect for wireless networking, then, looks to short-range optical transmission. This suffers significantly from its limitation to direct line-of-sight transmission, but benefits from the fact that receivers can be enormously more efficient and that the potentially available information bandwidth of visible light is of order 10000 times that of the rf/microwave spectrum. Ubiquitous inexpensive low-power optical transceivers would have the advantages of great bandwidth and short range---allowing the city to be subdivided into an enormous number of cells. Rural users would still need to bring in the signal with radiofrequency or land-line or else face difficulties communicating during inclement weather (light doesn't go through clouds and rain too effectively) but in a dense urban environment, short-range optical seems to hold a lot of promise for the long run.
Much of this is in the pipe-dream stage at the moment, but you might want to check out Light Pointe for a sense of what's available now and where industry sees this going.
I remember an article a while back (I can't remember where I saw it) about a company who wanted to put together a cellular-type model using very-high-flying, solar-powered robot airplines that would fly around in set patterns, providing communication. I think it was meant for worldwide phones, but I see no reason that a model like this wouldn't work for Internet access.
This would also eliminate a lot of the problems of access in outlying areas, like national parks, where we wouldn't want to have comm towers.
Anyone have any more information about who was thinking about this?
--
Sometimes it's best to just let stupid people be stupid.
You can always use bigger and fancier digital modulation schemes to pack in more bits per symbol (BPSK -> QPSK -> 16QAM -> 36QAM -> etc.). But you need more and more power to do this, AND/OR you need a cleaner and cleaner transmission media
One simple rule for its versus it's
You'll get used to it, they did. It's all natural.
The question shouldn't be how much bandwidth there is, it should be how much _usable_ bandwidth there is. The answer to either, however, is "a lot." Quite a bit of the bandwidth is wasted right now. But as we become able to transmit at lower and lower power levels, the amount of frequency reuse will go nowhere but up, providing us with quite a lot of bandwidth. The only real problem is that there are upper and lower bounds to the usable frequency spectrum. Go too high, and you're talking about IR. Too low, and you're in the ultra low frequency band, where it takes a good deal of time just to get three letters across. With technologies like CDMA, one can get quite a lot out of a small chunk of spectrum, and by just changing the code used, avoid interference with other transmitters and recievers. Can't wait for it to take off for more than cellphones...
Care about freedom?
Become a card carrying member of the GOA.
Assuming that frequencies are assigned semi-intelligently lack of wireless bandwidth will not be a problem...
:)
Granted, these few things would help:
1. Radio and TV broadcasts will eventually be migrated from air to internet
2. Other remote communications tools will also be converted to a standard (Wireless IP?) protocol.
3. An efficient Wireless IP protocol is implemented for Internet use.
Doing that frees a substantial amount of bandwidth. But if lack of bandwidth were going to be a problem, I think we'd be hearing more about problems already existing in areas of high population density.
I fully expect, however, that more bandwidth would be available in less populated areas (although it would have to be somewhat populated for the service to exist there in the first place).
As for a total wireless conversion, I don't see that ever happening. Fiber is too fast of a medium to throw away. Every building will receive fiber eventually. Perhaps the high speed wireless would be propogated that way through very low power connections from building to building.
Your house will be a mini cell-tower... fun!
Example: Newtonian kinetic energy is mv^2/2. Special relativity shows that, yes, mv^2/2 is correct if v is small. As v gets larger, a different expression (not going to look it up now) is more accurate. So the implicit assumption in the statement "kinetic energy is mv^2/2" is "if v is small."
Similarly, technological advancements often occur not because someone changed their answer to the question of "how fast can you go", but rather someone changed the question because they didn't like the answer.
That's where the real genius is. Answering questions is one thing, but realizing that your are asking the wrong question to begin with is another.Bruce
Bruce Perens.
Bruce
Bruce Perens.
A while back there was a /. story about Ultra Wideband radio technology. According to Time Domain's webpage, the FCC has recently (May 10, 2000) "adopted a proposal to consider permitting the operation of Ultra-wideband (UWB) technology." If the US government ever decides to stop strangling this technology, there wouldn't be nearly as much of a need to move into the higher gigahertz frequencies.
The problem is that, while UWB transmitters might be easier to build than conventional transmistters, they still _use_ the higher spectrum frequencies (data is just spread out over the time and frequency domains instead of just the time domain).
If atmospheric and obstruction effects cut off everything above, say, 30 GHz, and your wideband transmitter makes use of parts of the spectrum above the cutoff point, the received data will be garbled (what will actually happen is that the pulses will smear out and start interfering with each other).
UWB is an interesting technology, but the data rate limits imposed by bandwidth limits are independent of the encoding of the data (see my posts re. analog transmission for the caveat to this).
Put another way, 1 MHz of radio bandwith does not equal 1 million bits per second, at least not as far as my limited knowlege implies.
While this is true, there are strong practical limits to how many bits per sample you can have.
The problem is that to encode n bits in one sample, you need to have 2^n distinguishable analog levels in your sample. You also can't space these levels arbitrarily closely - noise from your electronics and fundamental limits to the certainty with which you can count the number of radio photons in your sample both limit your spacing. As spacing grows exponentially with the number of bits, you soon reach a limit for any given power level.
In principle, you can just increase the power to compensate, but the power required goes up exponentially once you hit your level spacing limit.
In practice, you typically have only a handful of bits per sample to keep the power requirements sane.
In theory, the electromagnetic spectrum spans from zero Hz to infinity Hz, but it's not practical to use it all.
Low frequencies need large antennas. Nobody wants to hang a 160 meter dipole off their web-pad, do they? No. And high frequencies become extremely line-of-site and easily attenuated or blocked. You don't want to have to precisely aim a laser out the window at your ISP either. You probably don't want more than a few cm of antenna so a minimum freq. of what, 2 GHz? And anything over maybe 25 GHz will be absorbed by a heavy shower of rain, so maybe that will be a practical top limit.
Antennas (and your radio-connected web-pad will need one) are designed to operate at a resonant frequency. They will function when operated off-frequency, but with reduced efficiency. You probably won't get practical operation at about more than +/-10% from your resonant frequency, so if you have a resonant frequency of 20 GHz your web-pad won't want to transmit any lower than 18 GHz or higher than 22 GHz, so you have a useable radio bandwidth of 4 GHz, and that is very line-of-site and with lots of path-loss. Drop your carrier to 10 GHz will improve on the path-loss and directionality, but halve the radio bandwidth.
When you modulate a carrier it occupies more bandwidth as the data rate increases. Someone (Nyquist?) says that your bandwidth usage is twice your data rate. At a 20 GHz carrier you only have 4 GHz useable radio bandwidth (the antenna won't handle anything wider) so your data-rate can only be 2Gbit/sec. That 2Gbit/sec has to be shared by everyone within range of your transmitters. Using CSMA/CD (Carrier Sense Multiple Access/Collision Detection) you can share this bandwidth, but there is a theoretical maximum data rate which is less than the unshared maximum. The figure 18% is ringing a bell - someone please correct me! Anyway, 18% of 2 Gbit/sec is 360 Mbit/sec, assuming that nobody else is using sharing the bandwidth. Multiple users will cause interference with each other, pushing the actual, practical data rates way down.
Reducing the size of "cells" and increasing their number will help. The cells can be linked via fibre. The range to the heart of the cell will be smaller, so path-loss/attenuation will not be as important a factor, allowing the use of higher carrier frequencies, giving higher data rates.
Who knows? Some of what I just said might even be correct!
73, de Gus
Eight Papa Six Sly Mongoose
I was with you until the last paragraph. I'll assume that in your last paragraph you are refering to the frequencies allocated for PCS use (ie digital cell phones). There are not 5 redundant bands, but one band in the 1900 Mhz range that has been defined for use with PCS. This band has then been split up into several different blocks that can be auctioned off individually to different operators. The reason you want to have several blocks available in the same band is to promote competition and to allow the "Mom and Pop" shops a chance to enter the market. This is no different than how things are done for, say, GSM in the rest of the world.
I'm not sure that I understand your comment about costs of cellular infrastrcuture though. Vendors are the ones that build the equipment (usually called manufacturers), you are probably referring to operators here. Assuming you mean operators, why would they want to share the cost of the cellular infrastructure? They each have to build their own network in order to accomodate their own customers? Why would I let a competitor use my base station? Most of the signalling and such that takes place on the ground is done using leased-lines, so the cost for that portion of the network is already shared anyway. As I already mentioned, they are already all using the same band, so that isn't a problem. And when usage increases, they do just as you suggest: add more cells. Adding more cells is possible for all operators using the blocks that they have licensed using frequency reuse patterns.
Disclaimer: I work for Ericsson, however these views are my own and have not been endorsed by my employer.
---
I know the question already touched on this somewhat, but multiplexing is basically the way to go with this... CDMA can already squeeze more than 12 times the bandwidth out of a frequency and it's bound to only get better.
I'd say the only problem with this is that it makes the hardware more intricate and more expensive. CDMA (Code Division Multiple Access) requires precise power regulation because nothing can be louder than another sender... This means that your power has to be ramped as your distance from a cell changes and handshaking with new cells is more complex as well.
I also think that there are a lot of bands which are currently allocated that should be scrapped for newer tech or at least re-appropriated... Nextel, the wireless company, for example operates on what used to be a 2-way business radio band. Because of this they're in almost every major market but didn't have to bother with licensing. At the same time, their frequencies aren't necessarily guaranteed either. I could definitely see a lot of the PDA stuff getting into this band if a standard's ever developed.
Check out alt.cellular for a lot of good info on this stuff...
-- atomly
It's called the International Telecommunications Union, or ITU for short.
It's homepage is here.
It's purpose is to develop and foster global standards for bandwidth usage, among other things. Most modern countries have communications ministries or bureaus that abide by them (the FCC for example).
ozone pilot
Finding and common band is a real problem. The Bluethooth folks assumed that they had it all worked out and spend billions on infrastructure, ASICS, etc. Bluetooth just got a nasty shock. The French military refuses to open up their portion of the 2.45 MHz band required for Bluetooth. They could very well make it illeagal to have a bluetooth device in France. Imagine getting your laptop nicked at the airport because it has Bluetooth! The truth is, their is no universal chunk of bandwidth in the world and the death of Bluetooth is going to prove it.
As for a "global FCC," well that's just a huge stinker of a solution. After all, look at the marvelous job they do here in the US, holding back low-power FM for years so that the mega-media could dominate/satuarate/placate the masses....
sig not found
There already is an organization, the Iternational Telecommunications Union (ITU) that administers international RF frequency allocation on a nation by nation basis, among other things. It mostly deals with surface to space and long-range bands, and adjudicates international bandwidth disputes. It is then up to national governments to administer their spectrum as they see fit.
Of course, I'm not sure this answers the question posed -- it just shows how frequencies are used, but doesn't show how much "bandwidth" is available.
I'm not sure of the easiset way to answer that question, anyway -- think about telephone lines, for example. Used to be, everyone figured that they had an "audio bandwidth" of about 3000 Hz (or am I way off here?) So you might figure that means about 3kbps total maximum throughput. However, we're getting 56k (or so) over those same lines, through clever use of multiple channels, multiple bits per baud, etc, etc.
Put another way, 1 MHz of radio bandwith does not equal 1 million bits per second, at least not as far as my limited knowlege implies.
So, maybe, the question is really this: If we scrapped all existing modulation systems (FM, AM, whatever), turned all communications into digital bits, and selected the best (most efficient, best range, etc.) scheme for modulating and encoding those bits, what's the maximum bandwidth available? Interesting question, but basically academic, 'cause I don't see everyone throwing out all their TVs, radios, and cell phones for a maximum-efficiency digital system.
And, besides, isn't sub-space communicaiton right around the corner? :-) david.
Let's ask Mr. Owl!
Mr. Owl: One... two... three... **CRUNCH**
Three.
-Denor
Low-grade primer on EM radiation frequency and wavelength: Speed == Wavelength * Frequency. Travelling electromagnetic waves all have the same speed (3x10^8 meters/second), but different frequencies. Different colors of visible light (that you can see with your eye) have frequencies on the order of 10^-15 seconds, hence wavelengths on the order of 500x10^-9 meters == 500 nm. UV light is around 300 nm, blue is around 450 nm, green is about 530 nm, red is 700 nm or so, infrared starts around 800 nm, etc. So visible light frequencies are around a petahertz (a million gigahertz). As another poster mentioned, this means that really high-frequency EM waves, like visible light, don't transmit through walls and trees (nor even curtains) very well, but you already knew that was true. :) ) This problem is overcome by sending the light down fibers that can make it bend around walls.
So here's my main point: We should worry about how many different wavelengths (or frequencies, or colors) we can discriminate among within a certain frequency band. The reason people like the guy down the hall from netcurl use visible light (and near-visible light like ultraviolet and infrared) to send and receive signals is that one can get amazingly monochromatic light out of a laser. For example, I used to use a (yttrium vanadate) laser that emitted light at 532.40 nm plus or minus 0.03 nm (I forget the exact figures). That means, in principle, that we could send signals at 532.4 nm, 532.6 nm, 532. 8 nm, etc. simultaneously down the same fiber.
However, discriminating among these different colors is kind of hard because of color filters not having sharp cutoffs and because of frequency-spreading that can occur in fibers. The cutting edge of research in fibers, then, is largely in a) making fibers that prevent or correct for spreading, and b) finding clever ways of distinguishing between two nearly identical colors.
I've probably forgotten something, but hope this helps.
--jd
One of these days/I'm going to cut you into little pieces.
Not directly, but we need only look to cell phone to see part of the solution: more towers with lower power. Lets say there is a limit of 1 gigabit/second. (Obviously low). That is more then enough for me and a few neightbors. All I need is some way to get it to land lines which don't suffer the bandwidth problem.
In other words, I want high speed wireless, but I'd be content with a many cell phone like towers scattered around. In fact I prefer this model to others.
Even if someone invents technology that would allow my equipment to talk to anything else in the world via short wave I wouldn't want it. To power a signal around the world needs more watts then to send it to a local tower. There is no gain for me in the US use direct wireless to get to someone in Autrillia. I would much prefer much lower powered transmitters that can only go a short distance. Now if I was in the middle of the ocean there would be.
Remember our usage: lap/palmtops in the backyard covers most people. Sailors will need more, but there are not many of them (and they will probably want a bigger transmitter on the ship acting as a repeator to small ones onboard). Atsronaughts will need more, but they should be considered like sailors. (I'm being optimistic here and assuming that in 20 years more people have will have walked on the moon then currently drive a car)
Of course my point is that we don't need to worry because low power/distance transmittors have limits well byond our needs, and high power transmittors can be directional and in any case are not needed very much. Just think, we can get rid of the entire FM and AM dials in the future because eveyrone will have a digital device getting streams from the local tower. (Accually In propose that we keep the old AM towers for diaster - crystal sets are easy to make from junk and can be valuable in some cases)
The radio spectrum is a natural resource, nobody owns it.
Bands are a synthetic thing, what you actually want to know is how much bandwidth you can use. Essentially, we don't run out if we manage it well. The best way to manage it we know of so far is by using cellular techniques, which allow you to re-use the same spectrum every few miles, to connect wireless devices to the wired Internet. When spectrum gets tight, you build more cells, closer together, and reuse spectrum within smaller areas.
Where is the ceiling? Currently, it is defined by how high a frequency you can build an effective radio for. We can get into the milimeter waves, extremely high frequencies which theoreticaly contain much more bandwidth than we are using today. Current equipment for these frequencies is very primitive and tends to be wasteful of bandwidth, that will improve. Eventually we hit a ceiling defined by how well very-high-frequency radio propogates through objects - if it won't go through walls or windows, etc., its use may be limited to in-building use. There are also new technologies like spread-spectrum and ultrawideband that may allow us some additional frequency reuse.
The way the FCC is currently managing spectrum could be improved. They tried auctioning license rights off, and are still doing it, and this has resulted in 5 redundant bands for cellular phones, with about the same thing going on in each of those bands. If they'd worked out a way to better share the costs of the cellular infrastructure between vendors, we could have been doing the same thing in one band, building more cells as usage increased instead of adding more frequencies. .
Thanks
Bruce (K6BP)
Bruce Perens.
Penetration distance of radio waves through a non-conducting substance (like concrete) is proportional to the wavelength of the signal (very roughly). This means that ordinary radio has no problem going trough walls and floors, but that things like cell phone signals in the GHz range are more easily blocked if there are a couple of buildings between you and the tower. This problem will get much, much worse as frequency increases. Expect your 20 GHz wireless PDA to stop working indoors (unless you have a repeater).
Radio of conventional wavelengths will pass through rain, smog, and clouds with little difficulty. Higher frequencies, however, have problems. Again, this is just a question of there being a lot of matter between the transmitter and the receiver. This means that as wireless transmission moves higher up the microwave scale, you'll either have to space the towers more closely or have signal cut out whenever it rains.
IMO, the practial limit is going to be in the 10-30 GHz range, with degradation setting in long before that. This is more than enough for rural areas. In cities, the best approach IMO is to provide wireless service on a per-building basis, with a short-range wireless hub inside the building connected to a fiber grid networking the city. The frequency is practical, and the hubs will serve few enough users that everyone will still be able to download all the video clips and pr0n they want.
FM, AM, visible spectrum, and audible sound are mere blips in the size of the spectrum. You're talking about Ghz of space available, while these take up mere Khz.
Um, no.
The FM and AM spectra take up on the order of a few MHz, not kHz. Each station needs several kHz to sound decent, and there are many stations.
TV needs about 10 MHz per station to transmit video data, and there are many stations on your UHF dial.
Visible light runs from around 700 nm to 400 nm - a bandwidth of about 3.2e14 Hz (320 THz).
The question being asked is, "what is the total usable bandwidth within Earth's atmosphere for carrying digital data". Ignoring other things that use bandwidth, this ranges from 0 Hz up to the frequency range where rain and fog and walls block your broadcast data - somewhere in the double-digit GHz range.
This bandwidth has to be shared with all users within a tower's transmission radius. In a city, this will be a lot of users.
The nice thing is it's mostly packet data, meaning you can have many devices use the same frequency if you throw in some collision avoidance, same that's used for Ethernet.
Collision avoidance works by _reducing_ the data rate on each device when too many devices are trying to use a data pipe at once. It does NOT give you more total bandwidth - it just makes sure that any bandwidth available is allocated fairly and not wasted in an electronic shouting match.
For a bandwidth of "foo" GHz, you will have _roughly_ "foo" gigabits of _shared_ bandwidth between all users in range of one tower. The only way to pack in more data is to use analog transmission, and the power required to get more bits grows exponentially with the number of bits per sample (gets impractical very quickly).
This is a more detailed chart which lists the users/uses of the spectrum between 137MHz and 10GHz in the US. Here's one from the UK. And here is a more general chart posted as reply in this thread.
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http://www.naval.com/radio-bands.htm