How Many Frequency Bands Are There? 315
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?
Re:Chart (Score:2)
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 The FCC recycles some bandwidth every now and then, that's out of date, for other uses.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.
One to infinity (Score:2)
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.
Re:Couldn't you just look this up? (Score:2)
International Telecommunications Union, or ITU [itu.int]. It's been around for awhile.
About your other questions... (Score:2)
(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 [itu.int], 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!
Re:Answers (spread specturm) (Score:2)
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
How not to heat your head (Score:2)
Bruce
Re:The air's bandwidth (Score:2)
Atmospheric attenuation is useful, too, because it lets you build microcells.
Thanks
Bruce
GSM (Score:2)
Thanks
Bruce
You don't understand "cellular" (Score:2)
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
Re:Encoding (Score:2)
I'd suggest you read Shannon and a text on modulation before you take this further.
Thanks
Bruce
Re:Encoding (Score:2)
Bruce
Re:Shannon Limit (Score:2)
Thanks
Bruce
Mobile phone bands. (Score:2)
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
Encoding (Score:2)
Thanks
Bruce
Re:Answers (spread specturm) (Score:2)
Thanks
Bruce
Re:The air's bandwidth (Score:2)
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
Re:Cell phones part of solution (Score:2)
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...')
optics. (Score:2)
Infact, someone I know very well is planning on doing this soon - next summer.
Re:Some limits. (Score:2)
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.
Deep in the wastes of Switzerland (Score:2)
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.
Chart (Score:2)
Analog and digital. (Score:2)
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.
Why double-digit GHz is cut off... (Score:2)
] 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.
Re:A couple of shady points here. (Score:2)
] 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.
Re:Answers (Score:2)
Regulation sucks.. (Score:2)
no good answer (Score:2)
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 [itu.int] is an important international regulatory agency.
Re:Chart (Score:2)
Your right, it does look cool. I am going to get a big print version of it and hang it on my office wall so everyone will think I am Super Smart instead of Plain Smart.
Re:Cell phones as repeaters? (Score:2)
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 Will Help (Score:2)
This should stretch out how long we have before we need another breakthrough idea to stuff data through our airwaves a little better!
Re:Chart - Found one! (Score:2)
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
Re:Number of frequencies available... (Score:2)
sound != RF
Re:Waves vs. Photons (Score:2)
You imply distinction where there is none.
Visible light is just EM at the appropriate frequency.
How much bandiwdth is there.. (Score:2)
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.
Re:Wireless, Bands, and Interference (Score:2)
I believe it's from 2.4 to 2.45, but I'm not sure.
BTW.. have you tested the wavelan cards once they were set up? I've done some lab testing, and found that the 11 meg wavelan cards drop down to 5Mbps and then to 2mbps if signal degrades.. and don't go back up until reset.
Also.. what kind of actual throughput do you get? Again.. my lab tests show 11Mbps lucent wavelan cards get about 5.5Mbps of actual throughput while bridging. The 11Mbps refers to the radio channel, and not at all to what you actually get out of them.
Funny.. all other mediums also do this too(specify channel speed rather than throughput), however, in all other mediums, throughput is very close to channel maximum.. but not in radio
HOw much there really is. (Score:2)
Cell phones as repeaters? (Score:2)
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, ???
Once there was... (Score:2)
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.
Re:Frequency charts (Score:2)
Re:Answers (Score:2)
Frequency = cycles / time (Score:2)
It depends on distance (Score:2)
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.
--
Extensive chart from the Office of Spectrum Mgmt. (Score:2)
This lists all allocations from 3KHz to 300GHz.
Forget frequency, what about light? (Score:2)
Re:Couldn't you just look this up? (Score:2)
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.
Carrying capacity is better than you think... (Score:2)
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...
Re:Some limits. (Score:2)
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......
Re:Uhhhh.... (Score:2)
Re:Uhhhh.... (Score:2)
Re:Packing more bits per sample. (Score:2)
Re:Frequency charts (Score:2)
Having a colorful poster of the radio frequencies hanging in your office really makes you look like a geek.
Re:Uhhhh.... (Score:2)
When I was a kid, my dad had a radio-controlled airplane. He flew it a lot for a couple years, then put it up in the attic. 15 years later, I got it out and went to use it. I found that in the intervening years, the frequencies allotted for radio controlled planes had changed. They were a lot finer, so they took up less space in the whole spectrum. I had to get a new transmitter for the plane that was more sensitive and broadcast on a narrower frequency.
It seems that theoretically, better recievers and transmitters could be developed constantly, splitting the frequencies more and more finely. How much room is there between 98.5 and 98.6 on the FM dial? It's infinite. There is 98.55, 98.555, 98.5555, etc. It depends on the sensitivity of the equipment.
Re:The Answer: Earth's Carrying Capacity (Score:2)
Which is not to be confused with the Bog of Eternal Stench.
Re:Endless? (Score:2)
We can transmit at very low freqs, like ELF, which takes awhile (submarines use ELF) but can go through lots of water.
As the frequency increases, so does the power requirement to transmit it.
Also, once you move into infrared and visible light, the atmosphere really sucks. Lasers are good for short-to-medium range (like between buildings) but the air scatters the light. So you need fiber optics for long ranges.
Now, you could theoretically transmit a LOT of data on, say, an X-ray or gamma ray signal. Of course, in order to have a good signal over long distances, you'd need to keep the transmitter cooled in liquid helium to prevent melting and you'd probably give everybody in town a brain tumor from the radiation. And a gamma ray generator is a little hard to get.
Then you get into the various ways to transmit data-- amplitude modulation, frequency modulation, pulse-width modulation... I'll defer those to the experts to define the [dis]advantages of each.
Here are some more frequency lists: (Score:2)
http://netlec.com/html/frequencybands.html
Re:What's the source of the "Mr. Owl" gag? (Score:2)
Lots of space available.. (Score:2)
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
Re:A couple of shady points here. (Score:2)
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
Low Power FM - Using More Frequencies (Score:2)
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.
Re:Shannon's law: beaten severely (Score:2)
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.
Try the ARRL (Score:2)
Propagation (Score:2)
Incidentally, by international agreement, radio regulation ends at 3 terahertz, which is sometimes considered to be very long infrared light.
Re:Propagation (Score:2)
Re:Answers (Score:2)
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).
Not jsut bandwidth ... (Score:2)
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 ?
Error 3921: This is an ill-formed question. (Score:2)
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.
protocols (Score:2)
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....
The air's bandwidth (Score:2)
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?
Effectively infinite (Score:2)
Promise of short-range optical wireless (Score:2)
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 [lightpointecom.com] for a sense of what's available now and where industry sees this going.
Solar powered airplane repeaters (Score:2)
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?
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Bits/symbol implementation examples (Score:2)
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
plant infestation (Score:2)
You'll get used to it, they did. It's all natural.
Wireless Bandwidth (Score:2)
Earth has bandwidth-o-plenty (Score:2)
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!
Changing Questions and Answers. (Score:3)
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.Re:wrong (Score:3)
Bruce
Yes, SS is old tech, but new to the consumer (Score:3)
Bruce
Re:High Frequencies (Score:3)
To state it simplisticaly, you can get something less than 1/2 symbol per second per Hertz, and if you use phase for encoding, you can have more than two symbols, so this is more than 1/2 bit per second but in practice less than 15 bits per second.
The key is reuse, not carrying capacity.
Bruce
Ultra-wide-band and limits. (Score:3)
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).
Packing more bits per sample. (Score:3)
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.
DC to daylight. And beyond (Score:3)
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
Re:Answers (Score:3)
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.
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Multiplexing (Score:3)
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...
There is a "global" FCC. (Score:3)
It's homepage is here [itu.int].
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).
Bluetooth Allocation Problems (Score:3)
Re:The potential has no true upper limit (Score:3)
Our understanding of physics may change...and we may find clever ways to get around limitations... but this does not change or invalidate physics.
Normally "limits" that are broken are NOT defined by physics but by other things...the need to interoperate with existing systems is a big one. Current day manafactuing technology is another.
These are not physics. If you push something beyond the limit that current physical laws dictate it must have...then you have undeniable proof that those laws are wrong and must be further researched and modified to meet the new data. THAT is the very essence of science.
Couldn't you just look this up? (Score:3)
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....
Ever heard of the ITU? (Score:3)
Re:Chart - Found one! (Score:4)
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.
Re:The Answer: Earth's Carrying Capacity (Score:4)
Is that an African Atmosphere or a European atmosphere?
How many frequency bands are there? (Score:4)
Mr. Owl: One... two... three... **CRUNCH**
Three.
How many parallel lines per inch can you draw? (Score:4)
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
Cell phones part of solution (Score:5)
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)
Answers (Score:5)
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)
Some limits. (Score:5)
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.
A couple of shady points here. (Score:5)
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).
A more detailed chart from 137MHz - 10GHz (Score:5)
Frequency charts (Score:5)
http://www.naval.com/radio-bands.htm [naval.com]
Re:Chart (Score:5)