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Technology

Sharing the Airwaves: Spread-Spectrum Broadcasting 114

Posted by michael from the frequency-hopping dept.
NaDrew writes "From the SFGate: Hal Plotkin writes about how Spread-Spectrum broadcasting technology could revolutionize the way we listen to the radio, and make it incredibly easy for neo-broadcasters to start their own services. Sadly, he writes, the "often technically inept U.S. Congress has complicated the situation in recent years by shortsightedly instructing the FCC to sell or lease additional bands of spectrum that had been reserved for other uses." Not to mention "the media conglomerates that own most of the nation's TV and radio stations have a vested interest in the status quo and won't easily give up their hammerlock on what, in the end, are public airwaves." A fascinating article that also includes some history of Spread-Spectrum technology (did you know it was patented by Hedy Lamarr?)." A good primer to spread spectrum if you're new to the issue.
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Sharing the Airwaves: Spread-Spectrum Broadcasting More

Sharing the Airwaves: Spread-Spectrum Broadcasting

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  • Blazing Saddles (Score:5, Funny)

    by why-is-it ( 318134 ) on Friday April 12, 2002 @09:01AM (#3329166) Homepage Journal
    (did you know it was patented by Hedy Lamarr?)

    That's Hedly!
    • Read the imdb info!

      Hedy Lamarr

      Birth name: Hedwig Eva Maria Kiesler
      Date of birth: 9 November 1913, Vienna, Austria
      Date of death: 19 January 2000, Altamonte Springs, Florida, USA. (natural causes)
      Mini biography: Hedwig Eva Kiesler from Vienna in Austria was a student of the theatre ...

      Sometimes Credited As:
      Hedwig Kiesler
      Hedy Kiesler

      Here's something else I picked up- her first movie listed there is named "Instant Karma".
      Should make an intresting study to excessive /.ers.

  • The congress tries to give private enterprice what they want. But it is conress fault! Can't they get the story right just once, for their tame little kittens.

  • Spread spectrum isn't a miracle. (Score:4, Informative)

    by TheLink ( 130905 ) on Friday April 12, 2002 @09:09AM (#3329200) Journal
    Sure if you are not tuned in, it looks just like noise.

    But if people are not careful what will happen is the noise floor is raised higher and higher till it drowns out signals.

    Yah that isn't close to happening yet, but the way it's being hyped as if everyone and anyone can broadcast at the same time, it might happen sooner than expected.
    • It's not a noise floor if I can route through them or they route through me; it's called CONNECTIVITY. Don't forget that radiowaves get absorbed in most cases; we don't live in freespace on the earth's surface; so the concept of 'noise floor' is flawed; atleast, at the higher frequencies.

      I'm a big fan of the idea of ad-hoc wireless networks. I think it will give us almost 100% coverage for IP services of all kinds. Wireless is a solution to the last mile issue of how you reach the internet backbones; and firewalls are a solution for how you charge for bandwidth and avoid 'leaching'.

      If a particular service requires priority in certain situations (e.g. military, rescue services etc.), then their packets should be given priority on the network, and handled as such.
      I think we are gradually evolving towards this model, but there's a lot of equipment out there...
      • Personally I think the solution is tightly collimated beams and making sure that you're not leaking radiation everywhere. Broadcast spread spectrum is annoying - it does raise the noise floor. If you're talking about for IP services, and you have highly directional antennas, yah, spread spectrum should be OK. Less interference, more stable signal, should be good. But if you're talking about for cell phone use, no way, and unfortunately, I think that's in general what people want. Put a big tower broadcasting spread spectrum, and that WILL raise the noise floor. Broadcast from inside your house, and no, that won't.

        You can't give wireless things priority, unfortunately. Wireless is wireless, and the only way to make certain things a priority is to use a different frequency. The problem with spread spectrum is that if you're allowed to broadcast it (the cell tower thing I was talking about) then you futz EVERYONE's frequencies, and it really sucks.

        This only applies to ultra spread spectrum, in any case - the stuff that's spread over many GHz of frequency space. Ugh.

        Be careful - the raising of the noise floor idea is real, and it will suck. But you are right that for personal things, it's fine - even an ad-hoc wireless over an entire city would be fine, because probably the connections between each "house" would be weak, but inside the house they'd be fine.

        The worry is for commercial services, and people broadcasting (that is, intention omnidirectional broadcasting) - that will raise the noise floor.

        If we set up an ad-hoc wireless network across a city, that's cool. If everyone decides to broadcast their own spread-spectrum 'SSFM' radio station, that would suck.

        (do I get kudos for using 'suck' a lot? :) )
        • > Personally I think the solution is tightly collimated beams and making sure that you're not leaking radiation everywhere.

          Not a bad idea at all; also making your receiver directional is very a good idea.

          >You can't give wireless things priority, unfortunately.

          Really? Why not- think packet wireless, think prioritised packets.

          > the only way to make certain things a priority is to use a different frequency.

          For packets there are prioritisation in all packet protocols, or its trivial to add. Enforcement is a bit trickier; but to some extent we rely on manufacturers building sensible equipment that doesn't break protocols.

          > The problem with spread spectrum is that if you're allowed to broadcast it (the cell tower thing I was talking about) then you futz EVERYONE's frequencies, and it really sucks.

          Yeah, but if everyone else is using spreadspectrum in the same bands you are there's no problem. So certain bands should be allocated for spread spectrum is all you're really saying.

          > Be careful - the raising of the noise floor idea is real, and it will suck.

          The concept of noise floor really applies in free space, or at the lower frequencies. But distance at Ghz frequencies is more like exponential decay- beyond a certain distance you don't get any significant power without line of sight, and there are things you can do about that too.

          > The worry is for commercial services, and people broadcasting (that is, intention omnidirectional broadcasting) - that will raise the noise floor.

          Sure, that's a worry. But it's mainly a worry if you transmit on non-released bands. Besides the rules about omnidirectional broadcasting deliberately limit the power to help ensure minimal range.

          • The reason I said that wireless priority isn't possible is although you could prioritize things inside the actual protocol itself, if you're using an ad-hoc type network, you have to make sure everyone in the network is using the same type of protocol, or if there's enough hops, that you can route enough ways to get to where you want to go. It's doable that way, but I think most emergency services would prefer a dedicated frequency.

            What's causing the exponential decay in GHz frequencies? It should be 1/r^2 with distance unless something's absorbing it, and I don't know anything in the atmosphere that's got a diameter of a few inches to a foot (GHz-ish wavelengths). If you put a tower up on a mountain, and broadcast at GHz frequencies, you should get 1/r^2 with distance.

            The thing I don't like about spread spectrum is that it sucks up a large portion of the spectrum, rather than individual frequencies. That means that for scientists observing in those bands, if you allow stuff like cell towers using really spread spectrum stuff, it's going to not be good for scientists.

            But then, in my opinion, the US is getting way too "radio loud" in areas where we don't need to be, just like light pollution is getting way out of hand. People who put up anything that radiates really should be taking care to ensure that it only goes where it needs to go, and nowhere else.

            The funny thing is that if you do this correctly, it saves money. You know all of those gas stations and parking lots that use these HUGE bulbs that broadcast light everywhere? Why don't they just use a lower power light, and direct the light where they want it to go? That and use a surface that's not very reflective, and boom, instant light pollution reduction. Same idea for radio transmission. If you're trying to get from one point to another, you should definitely be using very directional antennas.

            Don't get me wrong. I'm not against all usage of the EM spectrum like the "EM radiation is going to kill you!" wackos. I'm just of the opinion that people should be a hell of a lot more careful than we're even being now.
            • >It's doable that way, but I think most emergency services would prefer a dedicated frequency.

              Who wouldn't? ;-)

              >What's causing the exponential decay in GHz frequencies? It should be 1/r^2 with distance unless
              >something's absorbing it

              The Ghz frequency bands are near enough the same frequencies as microwave ovens; so any wet stuff around is going to absorb it. People, trees, plumbing. And nearly everything has some water in it. Lots of things are lossy and resistive, so they will attenuate also.

              > If you put a tower up on a mountain, and broadcast at GHz frequencies, you should get 1/r^2
              > with distance.

              Yes, definitely. That will create a noise floor. In scenarios like that, I think its much better to use directional antenna.

              >The thing I don't like about spread spectrum is that it sucks up a large portion of the spectrum,
              >rather than individual frequencies.

              Of course that isn't true in general. IEEE802.11b only sends on multiple channels in an 85 mhz band around 2.4 Ghz, and should not interfere [bluetooth notwithstanding] anymore than any other spectrum user.

              Very wide band and spread sprectrum aren't quite the same thing.

              > But then, in my opinion, the US is getting way too "radio loud" in areas where we don't need to
              > be, just like light pollution is getting way out of hand. People who put up anything that radiates
              > really should be taking care to ensure that it only goes where it needs to go, and nowhere else.

              Yes, at the very least, good power control is required, the hardware should use the minimum power level possible. It helps the user too; battery life is enhanced.
              • For the most part, I was talking about very wide band stuff (I guess "extreme spread spectrum" would be a better term for frequency hopping over a large range?), so that's what I meant by that. I'm mainly against the idea of using signals which have a wide frequency range over a blanket area of the environment (i.e. no 'radio pollution' to compound light pollution). If you're going to use a very directional antenna to link two areas, that's... probably fine. Radio antennas aren't THAT directional (even good Yagi antennas still have what, a 60 degree front lobe or something like that?) and so I think wires over long distances are probably best.

                So if you're saying "spread spectrum is great, should be limited to personal/home use, rather than big huge towers broadcasting" yah, I agree with you totally.

                I think an ad-hoc network will actually spring up quite naturally over time - if I like my neighbor, and trust him, I might actually talk with him and set up a wireless point in my house that can touch a wireless point in his house, and possibly share bandwidth, or if both of us have an ISP, at least be connected. Granted, you have to worry slightly about security and things like that, but it's dealable.

                So here, you'd have a spread spectrum 802.11b network over an entire neighborhood, but the noise floor wouldn't be touched, except for 2.4GHz using stuff, and that's all personal devices. Outside of people's homes, it probably would be negligible, because you'd want the inter-home links to be minimum power links. For that you could do something like a hybrid directional/omnidirectional antenna (ones that have a strong lobe in one direction, but still broadcast in all directions) so you would be okay anywhere in your own home, and you'd be able to link to a neighbor.

                Here's a thought. We already do know that raising the noise floor by careless use of devices happens. It's called light pollution. Hadn't thought of it that way before...
              • By the way, just to add, that "microwave frequencies are absorbed by water" bit is just junk - GHz-ish frequencies are roughly foot-long in wavelength (1 GHz = 1 ns = 1 foot, roughly. 2 GHz = 1/2 ns = 1/2 foot), and water molecules are surely not that long at all. Microwaves work because they're flooding a compartment with radiation, not because they're using frequencies that water alone absorbs. Put a piece of metal in a microwave and turn it on - you'll get a heckuva light show because metal is very conductive and absorbs the energy very quickly.

                Anyway, I'll buy an exponential decay if you've got a bunch of absorbers in line (houses, etc.) but it's definitely 1/r^2 in unimpeded space.

                Just wanted to make sure that the 'water myth' doesn't get propagated much more. :)
                • I had this same theory for a while, inspite of what I learnt in my physics degree course. Microwave frequencies ARE absorbed by water due to resonances in the molecules. Even ants and other tiny critters get fried in a microwave if you can keep them from dodging the hotspots; and they are much smaller than the wavelength. I've tried it with small drops of water too- they evaporate away really quickly and get hot. It's not a resistive thing at all (although that can happen as well.)

                  Basically what happens is the molecules get spun around by the microwaves and this causes the molecules to a) bump into each other and trigger heat b) generate out of phase signals that tend to cancel the microwaves out.

                  The metal in a microwave bit is a red herring. I've done it plenty of times with no light show at all. You only get sparking if the voltages generated cause arcing; otherwise they don't usually get hot because they reflect the waves away. The microwave itself is made of metal anyway.

                  p.s. I have a degree in physics, and we studied this during my degree. Also, I've seen the graphs of absorption curves by water for microwaves in that whole frequency band. Still, 1/r^2 in freespace is correct.
    • EXACTLY

      First off, let me just say that as a designer of wireless data devices I would love it if the FCC would open up more license-free spectrum like the Industrial Scientific and Medical bands(ISM) that cordless phones and 802.11(b) devices use.

      Second, spread spectrum only increases the number of users that can fit into a specific slice of spectrum with minimal interference. It DOES NOT open up the "airwaves" to unlimited use, so the FCC is still neccessary. Just look at cell phones. Digital cell phones use spread spectrum technology. This greatly increases the number of users that their chunk of spectrum can accommodate but it still has a limit. Also, cell phones have a limited range (a few miles or so maybe), so the cell phone companies count on the fact that someone on a phone in Chicago is not going to interfere with someone in St. Louis. 802.11(b) devices have an even more limited range (100 meters inside an office if you're lucky, unless you do some aftermarket antenna modifications). This allows lots of people in a relatively small area to use the same spectrum. However, if everyone started broadcasting to a large area from their back yard, the spectrum available would get crowded really fast.

      In short, the article makes some good points that the available spectrum could be used more efficiently. However, there is a limit and regulation of spectrum use is neccessary for reliable services to co-exist.

    • I don't think anybody is claiming that this increases the total available bandwidth. What they are claiming is that it makes more efficient use of the available bandwidth by making formerly unusable bandwidth usable.

  • can the SETI search find a spread spectrum source (Score:4, Interesting)

    by asmithmd1 ( 239950 ) on Friday April 12, 2002 @09:11AM (#3329207) Homepage Journal
    Using spread spectrum technology greatly increases bandwidth available. We are figuring this out 75 years after the invention of radio, so wouldn't any one else out there be doing the same thing? Are we wasting time looking for a strong signal from space when a spread spectrum signal would look just like increased static coming from a planet.
    • That's what Pulsars [etheric.com] are, basically a big galactic GPS / messaging system.

    • You're assuming aliens would be using radio at all and haven't discovered a far better means of
      communication. After all, across space almost any form of EM radiation travels as well as radio
      waves , they could just as easily be using light.
      • Um. Radio is light is electromagnetic radiation. But radio has a benefit, because it is not absorbed by air. Why? Because it's long-wavelength. Basically any gaseous atmosphere is going to be transparent to radio waves, so they are probably using that - probably a liquid environment will also be transparent to it.

        You're also wrong that any form of EM radiation travels well in space - dust really sucks, and it preferentially absorbs higher wavelengths (because the dust can absorb them). Radio travels well in space, light does not.

        Besides, SETI is looking at an 'intelligent' portion of the spectrum (I believe... they may have switched) - the 21 cm line of hydrogen. We can't look at any large portion of the spectrum - that's really friggin' difficult. So we assume that if they're trying to contact us, they're using an intelligent wavelength.

        SETI isn't looking for stray communications, in any case. They're looking for a signal intended for us to notice. If SETI fails, that doesn't mean that there isn't anything out there - it simply means they aren't trying to contact us in the way we think they are, OR they aren't trying to contact us at all.
        • Light is EM radiation too? Gee , thats for letting
          me know, I'd never have guessed.
          And interstellar dust will absorb wavelengths that
          are similar to the grain size which is why some
          clouds absord infrared more than visible light
          and x-rays go straight through. It depends where
          you are. Yes radio travels better in gases but
          if these aliens communicate between planets they
          could be using anything as I said since interstellar
          absorbtion is not relevant on the solar system
          (or indeed even local star group) scales.
          • "Light" usually implies "electromagnetic radiation". If you meant visible light, you should've said visible light. I was just saying that your terminology was a little ambiguous.

            Interstellar absorption is VERY important on local star group scales! Anything smaller than about 1 micron is basically unusable on space scales: it's a power concern. For anything less than 1 micron, you have to transmit MORE power to get the same signal to the receiver. In that case, you'd be an idiot to use that frequency and not the clearer, low power one.

            There's a reason we use radio to communicate with satellites and space probes - because it's intelligent, and far easier than visible light (aka lasers). While they MIGHT use lasers, they'd probably only do it for point-to-point connections (planets) and not for spacecraft.

            Radio will never go away, not until we find a new medium to broadcast through. And in other civilizations, it won't go away either. It's fundamentally a good region of the frequency spectrum to use.
        • Pardon my FCC frequency allocation ignorance, but how much does Earth radiate at 21cm? (roughly 1.4GHz) There appears to be this presumption in SETI that they're trying to contact us. But other than a couple of bursts, are we trying to contact them? Or have we set the band aside as a quite space for radio astronomy, so on a random sampling nobody would find us?
          • You're exactly correct. This is a fundamental question that I have. SETI would not find the Earth.

            We've tried to contact other planets, but we've contacted them for only a ridiculously short period of time (like, 5 years or something like that).

            My personal opinion is that we're not going to find life and civilizations out there until we GO out there and look. And then I think we're going to find out that "where there's water, there's life."
        • That makes me curious... if WE aren't sending out directed transmissions to other stars on the 21cm line, why do we think that alien civilizations would be?
          • Because if you're trying to contact other civilizations, the 21 cm line makes sense. It's a scientifically interesting wavelength (Neutral hydrogen has a forbidden line at 21 cm) and the Universe is basically transparent to it.

            The reverse argument, that we don't transmit at 21 cm, why should they, which implies if we aren't trying to contact them, why are they trying to contact us, is a valid criticism. I think SETI has basically acknowledged that unless an alien civilization is trying to contact us (or any other civilization), we won't contact them. It's fairly evident that within a few years, "leaking" radiation from Earth will be indistinguishable from noise, so we can expect other civilizations did the same.

            This is why if SETI fails, it does not imply there aren't any other civilizations out there. It just implies that none of them are far more gung-ho about contacting other civilizations than we are.
    • SS transmissions still use discrete frequencies at any one point in time as they hop around the spectrum. Since SETI monitors wide portions of the spectrum simultaneously, you would actually be able to observe the hopping in real time as the different frequency bands become active with non-random signals. No matter what method of SS transmission you use, as soon as you send non-random data, this will be detectable at any frequency point of the used spectrum. Unless of course your objective is to not be observed and you hide your data in white noise (using steganographic techniques).
    • I sincerely doubt that an ET would transmit anything we could understand unless they are specifically trying to communicate with young civilizations.

      Firstly, compression, by its nature, removes redundancy and order from a signal. Since we would expect an advanced civilization to use near perfect compression to communicate, their signal would look like noise.

      Secondly, how long have we had technology that could communicate between the stars? 100 years, tops. We're already discovering that the way we've been doing it is not the best way. 100 years is a blink of an eye in the age of the universe. Very, very few civilizations would be this early in their development right now. So very nearly all civilizations are probably using something that we've never even had the vaguest notion of to communicate. We're still cave men looking for fire signals while everyone else is using compressed spread spectrum radio for communication.
    • I've had this argument with the SETI@Home people, and they admit they can't find anything that lacks a strong constant-frequency carrier. Other SETI projects have already eliminated all the possible signals that have strong carriers above the noise, and so SETI@Home is looking for carriers well below the noise threshold. This relies on seeing a constant frequency over a period of time.

      This reminds me of the old joke of a drunk looking for his keys under a streetlight. Asked if he lost his keys there, he says "no, but the light's better here."

    • Handwaving does not increase bandwidth (Score:4, Insightful)

      by MarkusQ ( 450076 ) on Friday April 12, 2002 @12:08PM (#3330236) Journal

      Using spread spectrum technology greatly increases bandwidth available

      This just isn't true, any more than weaving around increases the width of a roadway. Sure, it might let you dodge some obstructions, but in the process you become an obstruction to other trafic. The total amount of information that can be carried doesn't increase. Just like in the weaving-around-on-the-road analogy, you have to ask, what would happen if everyone did this? The answer, of course, is that to a good first aproximation all those other SS broadcasters would look like noise to you; so the ambient noise level goes up and the S/N ratio falls, meaning less information gets through.

      How much less? well, in an ideal world, if you do everything right you only lose exactly as much as you thought you'd gained. TNSTAAFL.

      Each photon you reveive can only tell you so much. You can't beat the uncertanty principle with hand waving.

      -- MarkusQ

  • Hedy's Patent (Score:3, Funny)

    by kindbud ( 90044 ) on Friday April 12, 2002 @09:20AM (#3329253) Homepage
    No! You don't say! What an obscure piece [google.com] of historical trivia. Wherever did you discover that?

    I suppose next you're going to bust out with the news that Milton Berle was hung like a horse [hollywoodpulse.com].

  • Various Reactions... (Score:3, Funny)

    by MacDork ( 560499 ) on Friday April 12, 2002 @09:24AM (#3329270) Journal
    RIAA: What, a new way to distribute music? Kill it quick, before we figure out that it could make us a boatload of money!!

    US Military: That's our bandwidth! We need all the spectrum we can get to bomb an Afghan hut!

    Steve Case: Did the military say bandwidth?? We should buy that up and meter it.
    • Bill Gates: Can you imagine the size of the PaperClip we could push down to XP .NET users with this?
    • US Military: That's our bandwidth! We need all the spectrum we can get to bomb an Afghan hut!

      Given that:

      Their choice is to view it and bomb it from far away by remote control or view it and bomb it close-up-and-personal.

      It's still full of terrorists armed with hi-tek antiaircraft missiles when they need to bomb it.

      Doing it by remote control needs a lot more bandwidth.
      I'd say they have a good case that they DO need all the bandwidth they can get.

      Or at least all the bandwidth they currently have MIL-spec remote-sensing and remote-bombing equipment set up to use, so they don't have to go have more designed and built while the terrorists are moving to a new hut and blowing up more skyscrapers.

  • gack, I need coffe this morning

    but I thought that part of the spectrum under consideration had also been set aside for wireless.

    I know there was a small flap on something like this [radiofreenation.net] back last October, while everyone had their attention elsewhere.

    Greed moves on

  • The possibility of unfettered access to spread-spectrum technology for broadcasting must scares the bejeezus out of the RIAA. So far, their whole arguement against the web-based radio stations has been easy for them to try to enforce it because the pay-per-listen criteria is trackable.

    However, if this technology becomes feasible to the average web-caster to broadcast their favorites tunes over the airwaves, then the measurement criteria for tracking who's listening goes out the window, and the RIAA has no power to enforce their rules.

    Expect the RIAA to be on the side of the radio station conglomerates on this one.
  • If spread-spectrum is allowed to flourish, everyone will have their own home-station, just like the web allowed them to have their own homepage...

    Get ready for broadcasts of little Jimmy's first burp, and little Sara's first oboe recital.

    For a preview of things to come, review the recent history of mp3.com--high quantity, low quality (followed by corporate buyout?).
    • Not true. The more peopel share spread spectrum areas, the worse the overall bit-error rate becomes. It's not a hard limit like in AM radio where you can ONLY divide the spectrum into a few chunks. But it cannot expand forever. Every spread spectrum transmission reduces the fidelity of every other spread specturm transmission in that range. The other transmitters just look liek noise sources.
    • Does anybody know what the maximum number of possible stations will be in the AM/FM range, given the current spread spectrum technology and the desire to maintain clear signals?

      I would think that range/wattage of the stations would be a determining factor. Perhaps if we were to limit individuals broadcasting range to a 2 or 3 mile radius, we could increase the number of stations without affecting signal quality too much (except in heavily populated areas where a smaller range limit could apply).

      Anyone with the math skillz to tackle this problem, please reply!
  • The european Digital TV and Radion systems already
    use spread spectrum technology (though not
    frequency hopping AFAIK) and have been since
    they came online years ago. Time for the US to
    play catch up (again).

  • This is a load of crap (Score:1)

    by Anonymous Coward
    I have been at the forefront of communications R&D
    for 30 years. I can absolutely tell you this is
    a load of crap.

    Because of the near/far problem, spread spectrum
    can't be suitable for broadcasting.

  • regs (Score:3, Insightful)

    by Kallahar ( 227430 ) <kallahar@quickwired.com> on Friday April 12, 2002 @10:24AM (#3329611) Homepage
    The FCC isn't interested in increasing the number of radio stations out there. The RIAA doesn't want more broadcasters competing with them. What the government and big business want is as few channels and companies as possible so that they can have tighter and tighter control. For example, if you set up a pirate radio station (ie. you don't pay the FCC's fees), then the FCC will come and shut you down ASAP. This isn't because they're "protecting the airwaves", it's because you aren't paying them. It's been affordable to set up your own FM station for a long time, but the FCC's licenses are extremely high in order to keep normal people off the air.

    I'm not sure about the actual numbers, but I think it's in the hundreds of thousands of dollars a year to keep an FM music station on the air.

    Travis

    • Re:regs (Score:3, Informative)

      by oldave ( 160729 )
      Annual regulatory fee for an FM stations (depends on the class of station and the population of your city of license):

      6. FM Classes A, B1 and C3

      1,000,000 population $3,750

      7. FM Classes B, C, C1 and C2

      1,000,000 population $4,550

      The fee that must accompany an application for a construction permit:

      $3385

      Now, we've just scratched the surface.

      First, we have to find a frequency. Let's ask a consulting engineer to find us one: $450.

      OK, but we have to have the table of allotments amended to make this frequency available in the city we want it to be in... again, get on the horn to the consulting engineer, and send him $1900 to do the petition for rulemaking.

      Now, we have our frequency, it's alloted to our town. Time to file an application for a construction permit... $4000 to the consulting engineer, $3385 to the FCC.

      We've spent $9735 - almost $10,000 - and we still aren't sure we'll even get a permit.

      Some time passes, and assuming there are no amendments to our application (which will cost us more), we get our construction permit in the mail.

      We now have 18 months to build our station and apply for a license - the construction permit just grants authority to build the station, test it and operate it until the license is applied for and granted.

      The costs really start to add up now... tower, tower installation (you're not actually going to go out to the tower site and haul tower sections up by hand are you?)... antenna... transmission line... transmitter... unless our studio will be at the transmitter site, we have to buy a microwave unit to send the signal from our studio to the transmitter... then we have to have a studio, with control console, CD players, etc... oops, don't forget the audio processor and stereo generator...

      Building the station actually costs a lot more than operating it... or it can, unless you are very frugal and buy a lot of used equipment!

      The ongoing costs that any business has include rent, power, insurance, payroll, business license.

      Then you get to pay ASCAP, BMI and SESAC their fees - and they all have an annual minimum, even if you're losing money.

      Fortunately, you don't have to pay the RIAA... the only bright spot...

      Of course, every year we get to pay the regulatory fee listed above.

      Yes, operating a music FM can be costly - but with today's computers and software, and if you don't actually make money the ASCAP/BMI/SESAC fees aren't that much, you can keep costs to less than a lot of other businesses.
    • I live in southern california. We recently bought a home stereo with 40 channel presets (AM and FM shared). When we told it to "preset all stations", it barely got through the FM channels, stored about 5 AM channels, and then ran out of presets !! So in some areas, the AM and FM frequency bands are very very crowded.

      It's criminal, however, to charge $10k for a license in South San Francisco and $10k for a license in South Dakota. The cost should be something like this : If you want to put out K watts (e.g. roughly K miles of transmission), then you should pay $.01 for every citizen that lives within K miles of your transmitter, every year.

      That would be fair. But the Poli(criminal)ticians would never hear of it !!
  • spread spectrum is noisy, tears up vital communications necessary for storm chasing, wipes out or interferes with repeater operations, and is a general nuisance to the Amatuer radio community. We provide many disaster relief services, not to mention the tornado and heavy storm tracking to help the weathermen confirm or deny potential problems shown on doppler and other radar systems. The ARRL and several other ham friendly organizations have been fighting the spread spectrum lobbyers as well as the little leo (low earth orbit) sattelites that infringe on our allocated spectrum. and..... lets not even get started on lowjack.......... Seriously, this is a budding problem that needs to be fixed!!!
    • Divvying up the spectrum is a concept that is as old as ham radio, and almost as outdated. The whole concept of spectrum allocation is being turned on its ear by new technology which now allows for coherence in the time domain instead of the traditional frequency domain approach. And yes, there has been quite a bit of work on spread spectrum done on amateur frequencies, and yes, this does raise the noise floor for traditional narrowband users.

      The amateur service is intended to be more than merely a backup yacking system to cellphones. It's supposed to encourage experimentation with new systems. Sadly, the current FCC rules don't allow for much useful spread spectrum experimentation by hams, but the truth of the matter is that existing commercial systems could be ported to the amateur frequencies, and do the jobs you mention (emergency communications) far, far better than the 1950s FM technology you're clinging to.

      Look at what happened to Packet Radio in the Amateur Service; we built it, they came, but then the FCC issued and enforced inane and archaic content restrictions on the use of packet, and the experimentation died out. The FCC is doing it to us again, all in the name of control.

  • I think the #1 thing the Electrical Engineers out there are missing is the impact of data compression algorithms. I'll grant them for now that its less efficient (how about some numbers as to how inefficient it is), but with proper compression/decompression algorithms, the same signals today should be ten times smaller, or, the same frequency can broadcast 10 stations more than it used to. That opens up a lot of space if the "property rights" aspects of transmission were shattered. If a concept like spread is used which fundamentally is less efficient but destroys the monopolies is implemented, I think data compression can bypass any inefficiencies.

    • Screaming to be heard. (Score:4, Insightful)

      by cryptochrome ( 303529 ) on Friday April 12, 2002 @11:12AM (#3329921) Journal
      Therin lies the real problem with spread spectrum vs. conventional broadcasting channels. The limitations of conventional communications techniques is part of what stimulated the development of these more efficient algorithms. And since different groups are confined to their own frequencies, there was little stepping on toes.

      But with spread spectrum, there is no pressure to be efficient, because there are no direct limitations on how much you can broadcast. The only problem is background "noise" from other broadcasters, and the easiest way to overcome that is with a more powerful broadcast. The obvious result is an escalation of more people talking louder.

      It's like being in a nightclub, where everybody has to scream and repeat themselves to make themselves heard, but communication is near impossible anyway. The only one that can really be heard are the super-amplified guys on stage.

      What we need is a more efficient and publicly-accessible use of the airwaves. Deregulating them will give the folks with the big antennas more control, not less.
    • Actually, electrical engineers are quite aware of compression. They just do it in hardware.
      Signals sent using RF cannot be completely compressed. You need some extra sync information and redundancy in the data to actually demodulate the signal and to confirm that a valid packet was received. The power in RF signals is like 1/1000000 of a normal digital signal. There is always noise masking your signal. When you try to amplify the signal to make it easier to process, you are adding more noise in the process.

      I hate when comp sci guys talk about RF. RF is hard enough for electrical engineers. You are not simply pushing bits into a register when you transmit signals - you have to deal with InterSymbol Interference, fading, and lots of other fun effects.

      What do you want to do - go back to the good ol days of AM and FM? There are only a few blocks of spectrum left after the parcels that have been sold off or reserved for military. The only reason that 2.4GHz is available for Bluetooth and 802.11 is because it was considered "undersirable property" because H2O has a resonance there - so 1000W microwave ovens are working that frequency over.

      Finally, it sucks that amateur bands and ham radio keeps getting spectrum stolen.

  • Several years ago a considerable amount of spectrum was sold by North American and European governements for huge prices in the tens of billions of dollars. However, little money exchanged hands. The bidding "down payment" was small, so many sham companies speculated. These huge amounts are just coming off the books. Some of the companies went into backrupcy with these huge debts. The governments also have to write off huge revenues that never materialized.
  • As usual, everybody tends to oversimplify spread spectrum and it "magically" works. Nope. Not at all. I wish it were so simple, just like CDMA was supposed to be. Well, because the signal is supposed to look like noise, at least in a CDMA cell phone, you have to effectively manage all the power levels of the users on the system so they don't step on each other. Thats why you have specs like ACPR (Adjacent Channel Power Ratio). Well, power control is a bitch. And you wonder why CDMA cell phones are much larger than their GSM counterparts.

    In theory, the real sell on CDMA is spectrum reuse (and security), but thats theory. Its still better than GSM, but like a friend of mine told me once: people only develop complexity to hide mediocrity. And the academics might love the spread spectrum stuff, but its academics... not the people working in the field who have to deal with all the nasty issues academics don't deal with.

    I'm not a know-all of spread spectrum issues, and it definitely has some great uses. But I don't think it would be very useful for 1 way communications like radio(unless it needs to be secure - like say...a cruise missile). It really peeves me off when somebody writes about something they no idea about.

    • "And you wonder why CDMA cell phones are much larger than their GSM counterparts".

      Yes, I would wonder that, if there were any truth to it. My Motorola CDMA Vader is just as small as the GSM Vader. And I have an 802.11b card (Symbol's CF Wi-Fi) that's smaller than any GSM phone. Don't overgeneralize.

      When it comes down to it, Spread Spectrum is nothing more than a spectrum allocation algorithm that depends on the orthogonality of the chipping sequences. This orthogonality is further degraded by Rayleigh fading (aka multipathing), which is why ACPR or diversity reception is essential to CDMA. The primary benefit, however, is that that as an allocation scheme, spread spectrum is time based, and can take advantage of the bursty nature of most communications, be they human-to-human or machine-machine. And that's why time domain approaches are more efficient.

  • Is there anyone who is doing a Spread Spectrum audio or video project?

    It would be kind cool if an open Spread Spectrum video standard came out.

    Use a 802.11 switch with a 1 watt amp to cover your neighborhood with reruns of Wargames or Commander Taco Eats Michigan.
  • Why wouldn't UWB be used for everything that must be transmitted if it's so great?
  • the "[multiple derisive characterizations deleted] U.S. Congress has ... shortsightedly instructing the FCC to sell ... spectrum that had been reserved for other uses."

    "... what, in the end, are public airwaves."

    Like the land is all public land, and we're all tennants in government housing projects?

    One of the problems with the radio spectrum is that there's a limited amount of it. With the "public airwaves" and "licencing this public trust" model the government's central planners have kept large blocks of spectrum unutilized or underutilized by older technoligies that make less efficient use of it.

    One of the most effective methods known to handle the allocation of a scarce resource is a market, where people can OWN pieces of it, subdividiing and trading them as convenient and profitable - which, in the absense of government interference, often ends up with the pieces being used for the most-valuable-to-people purposes.

    Like land, there's only so much spectrum. Like land, some uses can "leak out" and pollute neighboring pieces.

    The government has decided to try an experiment and switch from the central-planning model to the property/market model for part of the spectrum, to see if that works better.

    Of course this gores the oxen of the people who are currently using the spectrum they're selling, so they complain (and often rightly so).

    And of course it also gores the oxen of people who have a political leaning toward central-planning, prompting them to spew rhetoric. This set of people apparently includes Hal Plotkin of SFGate.

    It's a pity, because the rhetoric obscures anything of interest he might have had to say.
    • Ok, so there is a limited amount of Spectrum. Can you explain why, then, the amount of "public" spectrum is FAR FAR LESS than the amount of "public" parks in the United States ??

      In the 2.4 Ghz band we have 83 Mhz of spectrum.
      In the 900 Mhz band we have 26 Mhz of spectrum.
      In the 418 Mhz band we have ?? Mhz of spectrum.
      In the 5.7 Ghz band we have 125 Mhz of spectrum.

      In total, from 0 .. 20 Ghz, we have about 250 Mhz of public space. In other words, only about 1% of this spectrum is publically owned !! The rest has been usurped by your federal government, in the same way that they damned the grand canyon, flooded the HetchHetchee Valley of California, and any number of other federal abominations done for "The good of everyone !!!" (yeah, because the benefactors made huge campaign contributions, that's who is "everyone")... like RCA and Sarnoff ... sheesh.

      If we sold LAND the way we sold SPECTRUM, then the sale would be something like this :

      How much am i bid for all the rivers in america?
      How much am i bid for all the valleys in america?

      The fact is, cellular technology makes modern spectrum auctions STUPID AND IDIOTIC. Modern spectrum should be sold ONLY WHEN ATTACHED TO A PIECE OF LAND BENEATH IT. To do otherwise is to GROSSLY waste public resources.

  • Putting it plainly. (Score:3, Insightful)

    by mindstrm ( 20013 ) on Friday April 12, 2002 @12:12PM (#3330264)
    Spread Spectrum is no magic bullet.

    Instead of taking a section of spectrum, and, say, dividing it into a hundred equal slices frequency-wise and assigning a slice to each of a hundred users, you take that same spectrum and allow thos ehundred people and divide the spectrum up time-wise, ,or.. that other way (how does one describe DSSS?).
    The point is.. it's not a magic bullet. There is still limited spectrum, and hence, limited bandwidth.

    Whether it's common spread spectrum (DSSS, FHSS) or the new UWB thing everyone talks about every six months... it's still limited.

    The benefit of spread spectrum over other methods is simply that radios can all be equal, and the 'sharing' can be accomplished algorithmically, rather than by physical frequency boundaries... which should make things more flexbile.

    • Spread spectrum is no magic bullet, but there is something that you can do with it that you can't with the non-spread spectrum system. You can run it over the top of narrow band transmissions. So you could have a spectrum divided into 100 parts for 100 people, then run another 100 spread spectrum over that. It increases the noise floor of the narrow band transceivers, but generally not enough to be an issue. Now you have 200 people using the spectrum that only 100 people could before (there are other benefits, such as fitting more people on the same spectrum than dedicated narrow band frequencies could support).

      Spread spectrum is also resistant to multipath problems. So if you are in an area with mountains or metal buildings you shouldn't have multipath signal problems.
  • (did you know it was patented by Hedy Lamarr?)

    I thought it was common knowledge

  • I think there is too much power and money concentrated over the holding a broadcast spectrum. We have to run ahead of competition and install as many of IPv6 routers as possible, hopefully converting internet, to have multicast.
    Multicast will allow *anyone* to have a radiostation, and few even a video station, at flat cost.
    Running smashing your head against the wall is not the best way to use yourhead, perhaps, run around the wall, remove supporting beams and it will fall by itself. I think cause of bandwidth to be shared by companies is a lost cause...

  • Why Spread Spectrum won't happen (Score:3, Insightful)

    by AB3A ( 192265 ) on Friday April 12, 2002 @03:31PM (#3331509) Homepage Journal
    1) Near/Far problem. If you're listening to a broadcast farther away and you're traveling closer to a transmitter on the same band, but a difference sequency, the noise level will rise until you won't be able to hear the distant station. Process gain is nice, but it can't obliterate that problem.

    2) Inter-Modulation Distortion. This is a general class of problems resulting from non-linearity in amplifiers. It manfests itself on a spread spectrum link as noise --just like the near/far problem. Your options for getting around this problem in a spread spectrum receiver are few: Basically all you can do is build a higher power front end amplifier (consume more power). With narrowband systems you can take advantage of resonant circuits as well.

    3) Sequency management. Someone has to coordinate these things somehow. Many are embracing spread spectrum as a way to get rid of the FCC. That's unfortunate. Yes, they're doing their job quite poorly and yes, it's been this way for a long time. That doesn't mean anarchy is better, or that the FCC's mission is irrelevant.

    4) Data transmission != spread spectrum. Efficient use of spectrum is laudable. That doesn't mean that you must spread to be efficient, however. There are plenty of very well known modulation techniques which can be used for data transmission. The discussion of data broadcast or point to point data transmission has no bearing on whether one ought to use spread spectrum or not.

    5) Making a transition from narrowband communications to spread spectrum communications systems is too expensive, difficult, and impractical to consider. You simply can't change every aircraft radio and air traffic control facility overnight. You can't just shut off all broadcast stations and tell everybody to buy new radios. You'd have a major riot on your hands.

    6) Current Broadcast programming sucks. Did adding all those channels to Cable TV improve regular TV programming? Does anyone think XM radio will do good things for FM radio? Get real.

    Most of the discussion on spread spectrum right now is more about the disadvatages of narrowband when scaled up and the advantages of spread spectrum on a small scale. However spread spectrum doesn't scale up any better than narrowband communications has. The technologies and limits are still the same. This is not a magic solution. This is merely one method out of several for signal multiplexing.

    I can imagine a day when spread spectrum systems will be more common. However it does very little to solve issues such as re-engineering the FCC to be less flaccid and useless, sending high speed data over the airwaves, or how to improve broadcast programming. It's just a technology, it's not a way of doing business.

  • According to a conversation I had with Robert Pepper, entities in Europe owning spectrum can't lease them like in the U.S. With 3G spectrum being so expensive in Europe, UWB could bypass the regulation issues that may take forever to to fix thus jumpstarting the 3G wireless efforts. No wonder why Intel is pushing 3G efforts, to sell more microprocessors.

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