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Wireless Networking

4G Broadband May Jam GPS 118

Posted by CmdrTaco
from the jam-and-the-holograms dept.
mferrare noted some rumblings that 4G Broadband may jam GPS. There's a slew of technical bits in an report (PDF). 4G broadband frequencies (1525-1559MHz) are next door to GPS frequencies (1559-1610MHz). Test results won't be out until June.
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4G Broadband May Jam GPS

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  • by Anonymous Coward

    is faulty.

  • This should really help move 4G gear in countries that the US and/or NATO bloc show signs of disapproval toward... And possibly even make subscription free GPS substantially less usable in 4G coverage areas, where those lazy consumers really should have signed up for a $100/month 4G data plan with telco provided location services by now...

    Somebody in engineering just earned themselves a scapegoating in front of the FCC.

    Somebody in marketing just earned themselves a nice fat bonus.
  • Frequencies? (Score:4, Informative)

    by lcreech (1491) on Wednesday February 09, 2011 @10:39AM (#35150046)

    All the GPS satellites transmit on the same frequency, 1.575ghz for L1 and 1.227ghz for L2. The only variance from this is Doppler shifts from the user to satellite perspective.

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      That is not the only variance. One frequency contains no information. To carry a signal it must be modulated, which adds line width.

      • by caluml (551744)
        What about Morse code? You can use a single frequency, and convey information by simply switching it on and off.
        • by Chrisq (894406)

          What about Morse code? You can use a single frequency, and convey information by simply switching it on and off.

          Which will create a sideband [wikipedia.org]. Very small and narrow for the normal rate of Morse code, but present none the less.

        • by timeOday (582209)

          What about Morse code? You can use a single frequency, and convey information by simply switching it on and off.

          OK, how often do you want to switch in on or off? If you go too slow, you won't be able to send many characters each second, but if you go too fast, even the slightest distortion to the signal (e.g. passing through a wall) will blur out the signal.

          Also, what if somebody else wants to send morse code too? How will the receiver know whose dots and dashes they're hearing? I guess maybe you c

        • by drerwk (695572)
          Look up FourierTransform. A signal of finite length; say a dot or dash, can not be represented by a single frequency. The only way to have a carrier at a single frequency is for that signal to exit over all time. Certainly you can get a narrow band of carrier if you have a longing signal, but as hinted elsewhere, in order to convey an increasing amount of information you have to make your dot and dashes ever shorter, which in turn increases your bandwith both of information and of carrier.
      • by fxkr (1343139)
        Amplitude modulation [wikipedia.org]
        • by jpmorgan (517966)

          Sorry, go back to your fourier transforms. AM might not be modulated by design, but it does have signal bandwidth.

          • by Eudial (590661)

            You don't even need Fourier transforms. You can illustrate this happens with kindergarten level trigonometry. Let the carrier be C(t)=sin(kt) and the amplitude modulation be a simple oscillatory modulation given by A(a,b,t)=a cos(ft) + b sin(ft)

            Then as
            sin(x)cos(y) ~ sin(x-y) + sin(x+y)
            sin(x)sin(y) ~ cos(x-y) - cos(x+y)

            you get a modulated signal

            C(t)A(a,b,t) = a sin(kt-ft) + a sin(kt+ft) + b cos(kt-ft) - b cos(kt-ft)

            As this is simple multiplication, you can build arbitrary functions out of a sum of of differe

            • by X0563511 (793323)

              "kindergarten level trigonometry"

              Really now... I thought our education system wasn't doing as best it could, but surely you're exaggerating?

      • by Obfuscant (592200)

        That is not the only variance. One frequency contains no information.

        That is not correct. L1 carries C/A and P codes, L2 carries P.

    • by Anonymous Coward

      Yes, but don't forget L5 (1176.45) and L2c, as well as GLONASS and GALILEO also in that same band.

      And in any case, those frequencies are modulated with a pseudo random sequence at 10 MHz, making the signal 20 MHz wide. An interferer at 1565 will be a problem, so that 4G transmitter better meet its spectral mask requirements with a vengeance. The pretty casual Part 15 style 40dB down sort of requirement probably won't hack it. GPS received signal power is in the -110dBm range, so that 1 watt cellphone (+

      • by icebike (68054)

        But will the chatty Cathy standing to your left STFU long enough for you to get fix on your Google Maps? Eventually there will be a 4G phone every 2 meters.

    • by kybred (795293)

      All the GPS satellites transmit on the same frequency, 1.575ghz for L1 and 1.227ghz for L2. The only variance from this is Doppler shifts from the user to satellite perspective.

      Same frequencies, but each satellite has a unique modulation code [wikipedia.org] that generates its spread spectrum output.

    • Wikipedia LTE Article [wikimedia.org] lists a bunch of different frequency bands used by LTE (and other cellular standards), and this L1 band isn't in there. So while GPS interference problems may affect this particular carrier's frequency band, it's not going to affect the widely announced plans for 4G* LTE or HSPA+, and it doesn't look like it affects the current 4G* WiMax carriers either.

      Of course, I'll be really annoyed if these guys interfere with my el-cheapo car GPS, or my cellphone's GPS, and I'll be really annoye

    • I don't know anything about this company's equipment except what I've read in the article today, but if they do have approval to use a radio band next to GPS and can do so without interfering with it, it's likely that equipment for that data service can use the same radio hardware as they'd use for receiving GPS signals, with just software-defined-radio or similar tuning technology to let handsets do both with less hardware, instead of needing a cellular radio and also a GPS radio.

  • That would be a pretty big screw up by the FCC. So that would pretty much destroy what is left of the already dwindling GPS market. I mean, I saw stand-alone GPS devices becoming niche products, but I never thought the government would help their demise. So who should/will sue whom?
    • Re: (Score:3, Interesting)

      by gblackwo (1087063)
      Just to specify, that was all assuming that the study isn't crap, and that properly designed GPS receivers could infact be affected.
      • by GooberToo (74388) on Wednesday February 09, 2011 @11:16AM (#35150432)

        You're right. The report is likely to be bogus.

        If this is true it means the up and coming cash cow and one of the largest payola maker for representatives is now default for US. Yes, that means UAVs are now unsafe for operation. That also means IFR aviation traffic in inclement weather is many cases is now impossible. It means the entire GPS and navigation markets have been destroyed.

        Simply put, if in fact there is any proof that GPS can be compromised by 4G deployment, the FCC will be forced to move 4G to another frequency. Period.

        Can you imagine headline, "FCC sued for string of airliner crashes - negligent homicide charges filed against head." And that's just the tip of the iceberg.

        No bones about it. *IF* its even remotely true, 4G would be forced to change. Otherwise both safety of the masses and economic damage is just too massive to ignore. Not to mention the possibility of criminally negligent charges.

        • That also means IFR aviation traffic in inclement weather is many cases is now impossible.

          IFR does not, in any airplane, rely solely on GPS. In fact, in many situations the information from GPS is weighted well below the information from other sources which can be much more accurate. This is especially the case in situations where IFR is the most important, namely approach and departure. If you look at the plates for any airport in the world, STARS (standard approaches) and SIDS (standard departures) are laid out based on localizers and VOR stations, not GPS coordinates and there are plenty o

          • by Crewdawg (1421231)

            IFR does not, in any airplane, rely solely on GPS. In fact, in many situations the information from GPS is weighted well below the information from other sources which can be much more accurate. This is especially the case in situations where IFR is the most important, namely approach and departure.

            Well this isn't entirely true and neither is the GP. There are more published Instrument Landing System (ILS) runways using Localizer performance with vertical guidance (LPV) than there are traditional CAT I systems. These rely solely on GPS with WAAS. While WAAS are ground based references they require no equipment or changes to the particular airport.

        • by CompMD (522020)

          The industry report is real and true, I know several of the authors, one of them works down the hall from me.

    • Airplanes (commercial and private) utilize GPS for navigation -- and according to TFA, one such device experienced "Loss of Fix in Open Sky" 5.6 miles from the transmitter.
      • by 0123456 (636235)

        Airplanes (commercial and private) utilize GPS for navigation -- and according to TFA, one such device experienced "Loss of Fix in Open Sky" 5.6 miles from the transmitter.

        Lots of systems use GPS for accurate timing. Servers synced to NTP from a GPS receiver, for example.

        • by ndege (12658)

          Dude, your GPS receiver is 14 seconds off!

          People who use GPS for accurate timing need to be aware that GPS doesn't account for leap-seconds. As such, GPS is ahead of UTC by about 14 seconds. You can read more about the problem here [navy.mil].

          It gets more complicated, however, as some receivers correct for this. You can read more about the correction here. [gpsinformation.net]

          Some have wondered how accurate the time display is on Garmin GPS receivers such as G-12XL, G-II+, and the G-III. Here is an answer provided by Garmin Engineering. This also explains why the GPS can be locked for awhile and still differ from UTC by 11 or 12 seconds. (This answer applies to other brands of GPS receivers as well.)

          Start of Garmin quote>

          Provided the unit has collected current leap second count from the navigation message, (current leap second difference from GPS time is only broadcast once in a 12.5 minute Nav. message), or current leap second has not changed since the last time the unit collected this variable, the time displayed on the front of the unit should be accurate to within 1 second of UTC.

          >end of Garmin Quote

          Joe Mehaffey comments:
          This means that IF your GPS does not have (or does not save) the leap second offset from last time it was operated, your time may be off by perhaps 12 seconds until the complete NAV MESSAGE is received by the GPS. Jack and I have observed that "typically" Garmin GPS receivers display time which is delayed from about 1/2 to 1 second behind UTC. Lowrance GPS receivers are usually between 1 and 2 seconds delayed behind UTC. In both cases, this is a result of the display driver subroutine having low priority as the "GPS internal clock" is within a few nanoseconds of correct.

          Similarly, the NMEA time output on the serial link is typically delayed a second or two depending on various factors.

      • by GooberToo (74388)

        and according to TFA

        The data point is best completely ignored. Outages like that do periodically occur and are well documented. Furthermore, they have occurred long before 4G was deployed. Such a failure could have been anything from wiring problem, faulty antenna, or even a software glitch.

        But, it says it happened 5.6 miles from the transmitter, it almost certainly means the article is completely confused. Which if true, means GPS IS NOT BEING JAMMED. PERIOD. For them to be that close to a transmitter means they are in space

        • But, it says it happened 5.6 miles from the transmitter, it almost certainly means the article is completely confused. Which if true, means GPS IS NOT BEING JAMMED. PERIOD. For them to be that close to a transmitter means they are in space, which simply isn't likely. Likely, they are talking about WAAS [wikipedia.org], which is not GPS in of itself.

          They were talking about distance from the (simulated) Lightsquared 4G transmitter, not the GPS satellites. Airplanes are very often within 5.6 miles of a cell tower, and with "40,000 high-power transmitters close to the GPS frequency, across the United States," you can bet that airplanes will routinely be much closer to the real transmitters (especially near cities/airports).

        • by dslbrian (318993)

          But, it says it happened 5.6 miles from the transmitter, it almost certainly means the article is completely confused. Which if true, means GPS IS NOT BEING JAMMED. PERIOD. For them to be that close to a transmitter means they are in space, which simply isn't likely. Likely, they are talking about WAAS [wikipedia.org], which is not GPS in of itself. Rather, WAAS is ground based signal correction/enhancement which is used to increase GPS accuracy; but GPS still works without it.

          No they are talking about distance to the terrestrial 4G transmit tower. As a vehicle (car or plane) approaches the tower the GPS device loses signal. This effect is real - essentially a powerful enough off-channel signal can saturate the front-end LNA in the GPS receiver and block the on-channel signal. I've had to deal with this before on GSM front-end designs (it's been a while but IIRC blocker specs may be in the GSM spec, I forget). Essentially the front-end SAW filters only provide so much off-cha

    • by LWATCDR (28044)

      dwindling GPS market?
      Stand along GPSs maybe getting smaller and smaller but that is because GPS is in every cell phone and most cars on the planet. Throw in Boats and Aircraft and you have booming market for GPSs just not standalone.

    • by AB3A (192265) on Wednesday February 09, 2011 @11:10AM (#35150366) Homepage Journal

      Feh. It wouldn't be the first time these dimwits at the FCC screwed up. I remember installing 928.8... MHz SCADA (you know, the telemetry that runs your water, electricity, gas...) and it worked great. About nine months later, the FCC allowed 929 MHz paging. In a very short span of time we had enough energy coming down the antenna line to light a neon bulb. They were licensed for 3 kW ERP. Our remotes were licensed for 5 W + some gain from a small Yagi.

      The master receivers went deaf from the continuous blast of high powered paging traffic. A Cavity filter can't do much to get rid of strong signals only 200 kHz away at 900 MHz.

      Yeah, the FCC screwed up. They had no knowledge of the state of the art of receivers. We bought receivers engineered for sensitivity, not strong signals, because at the time, there were no other significant strong signal sources on that band. The state of the art took a while to catch up. We ended up solving the problem by re-licensing our channels for horizontal polarization. The pager stuff remained vertical. We got 20 dB of immunity from them and that was enough.

      And to the jerkwads at the FCC who thought this was acceptable: DO YOU LIKE WATER? DO YOU LIKE ELECTRICITY? DON'T DO THIS TO US!

      spit...

    • Re: (Score:1, Insightful)

      >>>That would be a pretty big screw up by the FCC.

      The FCC has been screwing-up a lot lately. Like the claim "all you need is a digital-to-analog converter box". They forgot to tell the people, per the FCC's own engineering specs, that you also need the antenna raised to 20 feet height. DTV power levels were too low to penetrate into homes unless you live within 15 miles of the transmitter.

      They also screwed-up Digital radio when they specified 1% power levels would provided acceptable range. Lat

  • by the_raptor (652941) on Wednesday February 09, 2011 @10:44AM (#35150104)

    Don't worry about bandwidth overlap (guaranteed to happen with some poorly designed transmitters and antennas) worry about all the other electronic devices which aren't meant to transmit RF but blast it out all over the bands.

    I have recently got into amateur radio and some bands are locally unusable due to something as simple as a transformer power supply blasting out many watts of RFI.

    The slow death of radio bands to RFI is like the "death" of stargazing due to light pollution.

    • by Anonymous Coward

      You need to learn about receiver desense. Then you will see that this could be a problem. This is from someone who has been into amateur radio for over 25 years, not someone who recently got into it.

    • by Anonymous Coward

      These are good points -- however "adjacent channel interference" can be a problem even without bandwidth overlap due to a phenomenon known as "receiver desense". This means that the receiver has been "desensitized" to the signal it's actually meant to receive due to a stronger transmission that overloads the input RF filter such that the detector gets overloaded by the undesired nearby signal. All RF filters are not perfect and have a "rolloff" characteristic where they reject more of the undesired input

    • by thegarbz (1787294)
      A small powersupply is less of a concern than a widely adopted standard with high power transmitter basestations. We have similar issues with the TETRA 2-way radio standard. Sure it's spec says it's 25kHz bandwidth for TETRA V1, and our government license gives us just that, a 25kHz chunk of the 800MHz spectrum in which we can blast 40watt which is enough to pickup the tower on the otherside of the city. However, looking at the actual signal coming out, due to all the fancy modulation and whatnot the actual
  • Depending on the type of bandwidth and modulation within those specific carriers (specifically at or very near 1559 MHz), they could be interfering with each other.

    Using a more highly-compressed modulation type (ie qpsk or 8psk vs. bpsk) with viable harmonic filtering should eliminate any "side lobes" and therefore interference at low power levels. Filtering at the satellite and/or cell tower side should also be present, further eliminating possible treading across bands.

    This sounds like a problem betw
    • by vlm (69642)

      Don't forget phase noise on both transmitter and receiver.

    • by cats-paw (34890)

      The FCC regulates the emissions into GPS bands, like any other allocated frequency band.

      Just because the 4G allowable band extends right up to it, doesn't mean you will be able to use those frequencies.

      Having a transmitter that's "spilling" over due to PA distortion or some other problem would preclude you from using those frequencies if you can't stay under the emission limits.

      So technically they shouldn't be any more of a problem than any other transmitter, WHICH HAS BEEN PROPERLY TESTED.

      The fact is that

    • by kybred (795293)
      This isn't just interference from adjacent signals. A big part of the problem is the huge difference in power levels between a GPS signal (received signal about -130 dBm) and a high power terrestrial transmitter a few miles away. The high power signal will swamp the GPS receiver's front end and play havoc with its AGC.

      From a GPS World [gpsworld.com] article:

      The consumer GPS device began to be jammed at a power level representing a distance of 3.6 miles (5.8 kilometers) from the simulated LightSquared transmitter. The consumer device lost a fix at 0.66 miles (1.1 kilometers) from the transmitter.

      The Federal Aviation Administration (FAA)-certified aviation receiver began to be jammed at a distance of 13.8 miles (22.1 kilometers) and experienced total loss of fix at 5.6 miles (9.0 kilometers) from the transmitter.

      The bottom line is that if this goes through, GPS receivers will get more expensive due to the additional filtering, and existing receivers will operate in a degrade

  • Well, Obama just mentioned in SOTU that he wants to expand 4G out to 98% of the U.S. [broadcastengineering.com] He'll be giving a speech on Thursday [nationaljournal.com] to plug it.
    • >>>expand 4G out to 98% of the U.S.

      That's foolishness. There's simply not enough room in the radio spectrum to have everyone using internet via 4G (plus already-existing radio, television, emergency services). Maybe if the users were throttled to 500k each, then it would work, but not otherwise.

      WIRED internet is the only way we'll ever get people to 3000k minimum speed (per FCC specs) (and as the Japanese have done with their VH-DSL).

      • I tend to agree. If everyone tried to hop on a 4G network and start streaming Netflix in HD, it would go down faster than a Thai hooker.
  • It's time to learn old fashioned orientation again! When driving on car trips as a child, when we got lost, my father would always ask, "Where's the sun?" This to figure out in what direction we were traveling. He grew up on a large, remote ranch, so he learned this skill from my grandpa. Now if some other broadcaster starts sending something that interferes with the Earth's magnetic field . . . the rest of us will be in big trouble.

    • It's time to learn old fashioned orientation again! When driving on car trips as a child, when we got lost, my father would always ask, "Where's the sun?" This to figure out in what direction we were traveling. He grew up on a large, remote ranch, so he learned this skill from my grandpa. Now if some other broadcaster starts sending something that interferes with the Earth's magnetic field . . . the rest of us will be in big trouble.

      I'll just mention that to the Alaska Airlines pilots who are shooting GPS assisted landings into Juneau and Ketchikan (next to mountains) or Sitka (where the airport hangs out over the ocean AND abuts the mountains). I'm sure they still carry their sextants in their flight bags.

      • by jpmorgan (517966)

        Zero-visibility landings use ILS, not GPS, which is broadcast from a calibrated ground transmitted next to the runway. ILS operates at ~110MHz.

        In general we've been using radio navigation in aircraft long before GPS became widely available. Lookup VOR and NDB. GPS is useful for aircraft navigation, since it lets you take more direct routes than strictly following the VOR/NDB defined airways. If GPS became useless, it would make air travel more expensive (and less fuel efficient), but planes aren't going to

        • by elijahmm (697865)
          Check the FAA's next gen initiative and look at the new WAAS GPS approaches. Many airports now have precision approaches (can't see anything until 200 feet above the ground) based on GPS alone. A certified WAAS GPS installation is considered legal for primary instrument navigation in IMC (instrument meteorological conditions). Translated? You loose the GPS signal at a critical point in flight and it DOES mean crashing into mountains, the ground, etc.
        • by Daa (9883)
          there are no more NDB stations left in the USA and the FAA is working on turning off the VOR stations as soon as they finally get the WAAS GPS based nexgen navigation system working. The whole idea of the Nexgen Navigation system is to stop flying on airways defined by VORs and move to flying directly from point to point navigating by GPS only.. i predict a huge fight between the FAA and the FCC
  • by Anonymous Coward

    Note that this is not all 4G as that term is more a marketing term than a technical term. This is a specific band granted to a specific company (Lightsquared) so if it really is an issue, it will be easier to revoke as it doesn't effect currently established 4G networks (Verizon LTE, Sprint WiMAX, TMobile or AT&T HSPA+).

  • by Anonymous Coward

    This isn't a problem so much with 4G as it is with low-end GPS receivers. Most of the mass-market GPS receivers have poor filtering of the bands around the GPS frequencies (this makes the hardware cheaper). They had done this under the assumption that those bands near the GPS frequencies would never be utilized.

    Now enter 4G in the surrounding frequencies. There isn't a problem with 4G spilling over into the other frequencies, but with the GPS receivers being sensitive in frequencies that they shouldn't be

  • This just in... (Score:4, Insightful)

    by Erich (151) on Wednesday February 09, 2011 @11:40AM (#35150702) Homepage Journal
    FM Radio could interfere with television broadcast channels 5 and 6, or aircraft navigation, since they're right next to each other!

    AM Radio could interfere with aircraft beacons, since they're right next to each other!

    Please. We've been allocating spectrum for things for a long time. Interference can be monitored and controlled. Do you really think that mobile telephone companies would put up with broadcasters puking all over their spectrum? Or vice versa? Or either putting up with amateur radio interference?

    Or, perhaps worst of all, do you think the Hams would put up with someone interfering with their spectrum? They can triangulate secret government projects [wikipedia.org] accidentally using their shortwave spectrum.

    Yes, interference happens from all sorts of places. You'll likely find that devices in your adjacent spectrum are less likely to interfere than other sources of interference.

    • by caluml (551744)

      Interference can be monitored and controlled.

      I suspect that the tiny signals received from from the satellites, and the lack of any sort of decent antenna in most GPS devices mean that it wouldn't take much to cause problems.

    • Re: (Score:3, Informative)

      by cadeon (977561)

      >>AM Radio could interfere with aircraft beacons, since they're right next to each other!

      These intentionally overlap. Back in the day, AM radio stations were just as useful at navigation as proper NDBs. You can tune in and listen to most of the AM band using your aircraft's (very old) ADF.

  • Not all 4G (Score:5, Informative)

    by Zouden (232738) on Wednesday February 09, 2011 @11:40AM (#35150704)

    Contrary to what the headline and summary implies, "4G" doesn't always use 1500Mhz. In fact, I'd never heard of a 1500Mhz cellular network until now. Apparently a startup called "Lightsquared" has bought that patch of spectrum and wants to roll out an LTE network. No other 4G network is in that frequency range. For example, Verizon's LTE network is at 700Mhz and Sprint's Wimax network is 2500Mhz.

    So, really, this is no concern to anyone but Lightsquared. Either there's no interference and they can go ahead with their rollout, or there is interference and the FCC has to step in. In either case, the other 4G networks are unaffected.

    • The concern isn't how Lightsquared will affect other 4G services, the concern is how it will affect GPS service.

    • by SrJsignal (753163)

      You fail to understand the issue. Lightsquared's transmitters could screw up GPS service for EVERYONE. The FCC waived their own rules to allow this, rollout. If you RTFA (I know I know, this is slashdot) you would see the large distances a single transmitter can jam GPS devices at.

      • by Zouden (232738)

        Do you really think that Lightsquared will be allowed to continue if their transmitters are found to interfere with GPS? The FCC will revoke their license in a heartbeat. That might result in a lawsuit from Lightsquared but the rest of us will forget about it and get back to using our GPS-enabled 4G phones.

    • by Svartalf (2997)

      Heh... That's what I thought was going on.

  • As a pilot I would be concerned about GPS degradation (we get reports of it). This could lead to a number of issues with aircraft navigation, especially for pilots flying VFR with handheld units that do not have RAIM. (The FAA says those are for situational awareness only, but that is frequently abused.)
    • by elijahmm (697865)
      It's far worse than you think. GPS degradation, jamming, loss of fix, etc. will completely destroy the FAA's next gen plan since it's based on GPS as primary navigation. LORAN is dead, the NDB network is unmonitored and unmaintained, and new ILS installations few and far between. WAAS GPS is the primary avenue being used for expanding low precision approaches throughout the nation's air transport network (which is considered part of the emergency response system). Due to the FAA's decisions to retire th
      • Well, yes... this is just poor planning o the FAA's part.I don't trust GPS to always be available. Of course your ADF can still be used to listen to AM radio (or find your way to a good radio tower...)
        • by elijahmm (697865)
          yup, that's the main thing I use it for. Listening to traffic reports and laughing at the people stuck in traffic as I fly by.
      • I'm a pilot, and an engineer who designed some of the equipment in the panel of my aircraft. This idiocy at the FCC scares the crap out of me when you consider the NextGen ATC system the FAA is rolling out. This will lead to loss of situational awareness for pilots and air traffic controllers resulting inevitably in death, just so someone can say OMG i HAVE TEH FOUR GEES.

        • by elijahmm (697865)
          I could not agree more. The FCC has been running into the FAA far too frequently (such as the ELT issue last year). Maybe it's time to start developing transmitter agnostic navigation systems that use ANY transmitter (ground or space) to triangulate position based on a database and an initial known position. Isn't this basically the way LORAN worked but with a specialized set of towers? Like you I'm a pilot and while I did not design the equipment in my panel I did install it all myself (with the help o
          • by CompMD (522020)

            Being transmitter agnostic is a problem because various ranging technologies have different implementations. Sure, you could conceivably use information from three VORs to accomplish this, but the accuracy would probably only be good to 1/10 nm. AM radio stations are handy navaids if you know where they are and you have an ADF. I could fly most of the way from Kansas City to Chicago by tuning the ADF to 720kHz. However, this doesn't tell you where you are, and no new aircraft come equipped with an ADF t

  • This could be somewhat worrisome to us urban geocachers. It's gonna be harder to use the multi-billion dollar military satellite network to find that little tupperware container.
  • Can you imagine how chaotic the eletromagnetic spectrum will be when the Bieber's 6G Fever [youtube.com] hits off ??
  • by CaseyB (1105) on Wednesday February 09, 2011 @12:43PM (#35151550)

    I would stress too much about this. Anything that has even a remote chance of interfering with the US military's use of GPS is never going to be deployed. Period.

    • The military uses "m" codes which are supposedly more resistant to jamming. With the exception of the nation guard, they shouldn't really care about how bad gps is in the US. In fact, wouldn't it be better for fighting Terrorism if there was no more GPS!

  • Am I the only person who read that and hoped it would be more of the other way around? Got some disruptive douchebag slapping away on her cellphone near you? Turn on your GPS and toss it in your pocket.
  • by marciot (598356) on Wednesday February 09, 2011 @03:29PM (#35153648)

    The GPS manufacturers and 4G companies are colluding to get us all to buy new GPS devices and GPS-enabled phones with better band-pass filters!

  • GPS World [gpsworld.com] has a good write-up on this.

    On January 26, the FCC waived its own rules and granted permission for the potential interferer to broadcast in the L Band 1 (1525 MHz—1559 MHz) from powerful land-based transmitters. This band lies adjacent to the GPS band (1559—1610 MHz) where GPS and other satellite-based radio navigation systems operate.

Every nonzero finite dimensional inner product space has an orthonormal basis. It makes sense, when you don't think about it.

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