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Wireless Growth & Wireless Interference
windowpain writes "An article in Monday's Washington Post says "The explosive growth of the mobile phone industry has crowded and tangled the nation's airwaves to such an extent that wireless company signals are increasingly interfering with emergency radio frequencies used by police and firefighters, public safety agencies said." Wifi is not a problem, evidently. Understandable, given its short range."
if the FCC (or whoever) made reasonable specs and if everyone's following the specs how can this mess happen.
=> fire people at FCC or sue mobile companies.
"Wifi is not a problem, evidently. Understandable, given its short range." Yah, that and the fact that the public safety networks operate in the 700 and 800 Mhz bands, whereas 802.11a and b currently operate primarily at 2.4 Ghz.
I'm not surprised it's the Washington Post who is reporting on this. I live in Washington, DC as a consultant, and travel a lot to other cities. I have had cell phones with three carriers, and with all of them I've had much worse trouble here than in cities elsewhere, without exception. On one hand, we have some serious density of equipment here, but on the other hand there are zones where one knows one will lose their cell phone signal; the worst two zones are adjacent to the CIA's facility and the Pentagon, for example. This sort of thing can't be helping the matter.
For your security, this post has been encrypted with ROT-13, twice.
This problem has been around for some time in the hearing impaired community.
- If spectrum is reshuffled, could this be an opportunity for the wifi-friendly (but still evil) Powell to allocate more unlicensed spectrum?
- Alternately, does the emergence of the interference bogeyman in such a prominent publication imply a tough PR road for more free spectrum?
- Could this be an opportunity for the cell carriers operating in the 800MHz band to switch to different technologies, or roll out newer services?
- Could these sorts of problems be used to get some federal money thrown toward development of software radio? would multi-format devices help avoid this problem?
As the submitter mentions, these emergency bands don't appear to be abutting or affecting the 2.4GHz range, but I imagine these issues will be relevant as wifi expands and interference problems begin cropping up.*Laughs at /. editor as he types this over a 6.1mile 802.11b link*
Really... the main reason for the interference between cell and emergency is that they are all moving into the same spectrum space. 800mhz is a busy place these days.
True wireless (802.11a,b,g) are all in FAR different spectrums so other than cordless phones and some radar equipment interference is a moot point.
Telcos have alot of dark fibre in the States. Most people assume that's optical fibre...but it's actually moral fibre.
I do some home and small business tech support in New York, and I've seen some interesting things happen with Wi-Fi.
The most interesting being the fact that I found 20 open and join-able networks on the corner of 20th and Broadway last week. I'd say some people need a lesson in security...
Also, I've seen people name their network things like "get the fuck off my shit" when neighbors try to join their network.
I'll also be interested to see if Wi-Fi networks effect piracy at all- what if the RIAA manages to crack down on piracy to a point that it cripples internet file trading (it wont happen, but come with me on this for a sec) and the only safe way to trade files is by sharing them on a local AirPort network. Then people can run around with their Wi-Fi PDAs with 1GB or greater flash cards, and download stuff from open networks they find on the street.
> Meantime, Fisher said many colleagues on the Anne Arundel County police force have found their own solution: They carry cell phones in case their radios go dead.
...)
so that being an option, why not have the cell companies take over administration of all the systems in these ranges, subcontracted thru local government offices? have the companies then manage (and be liable for) the need for non-overlapping frequencies separating critical traffic from the general public. especially the ones that shouldn't be driving and yapping on a cell phone as they hurtle through traffic (you know who you are!!!)
and yes, i know this puts a consumer-driven entity in charge of systems that are depended upon by lcoal/stage/regional entities, but hasn't private enterprise often proven its ability to manage complex systems a tad better than the government? could be a re-birth of telecom spending and contracts (which could mean jobs, more bottom-line investing, more attention on the nation's eroding infrastructure
when it rains, it gets real soggy. when it pours, i'm under the tap just _waiting_ for the joy
the cutoff you describe is actually dependant upon the ability of the receive to discern between the signals. Has absoulutely nothing to do with anything on the broadcasting end. More expensive receivers may be able to tell the difference between 800.0000001 and 800.0000002, but you regular cell might static up from both of these trying to receive on 800.
Speak for yourself.
Wifi is not a problem, evidently. Understandable, given its short range.
:-)
Ummm, no. Here's a frequency chart of the radio spectrum. People seem to think everyone uses all frequencies and it's one big radio spectrum blob. Radio spectrum resembles IP space, except in this case you can't create more of it. Print out the chart on a big plotter, hang it on the wall and impress your techie friends, and consult it when a wireless article is posted on Slashdot.
K3NG
Tired of being "punished" by the Slashdot $rtbl since 2002. I'm now over at http://soylentnews.org/ .
It's a combination of frequency, bandwidth, and a few other factors. For example, when something is at 800mhz, that's the center frequency. It will have a bandwidth associated that may be a few khz or a few mhz, depending on the application.
Then you get a combination of different technologies. Someone else mentioned TDMA, CDMA, GSM, and some others. Some of these operate in the same bandwidth without significant interference because the way they operate is so different. CDMA for example, doesn't suffer from the same kind of interference that TDMA, GSM and a few others do.
There's a technology called Ultra Wide Band that may take off over the next decade. While it covers a very large bandwidth (as the name would imply) that would normally interfere with other technologies, because of the way it operates, there's little, if any interference. The nice thing about it is, you can operate a number of different devices, each paid of sender and receivers has a "code" that allows them to communicate. Nothing else will interfere and many devices with different codes can operate in proximity.
Most technologies operate on the basic principal of sending a signal via the actual radio wave. They do this by modulating some part of the wave, usually frequency or amplitude (hence FM and AM radio).
UWB doesn't do that. Instead, it sends pulses very quickly (in picosecond lengths) and the pattern created by the pulses (think binary, on and off), are what are used to create teh signal.
Another advantage of UWB is that it works at a lower power (given the same range). Also, unlike the higher frequency applicatons (particularly when you get up to 5+ ghz), it doesn't have the same issues penetrating walls and such. Nice technology. Hope it makes headway.
The basic argument, like the article makes for first responders, is that the military band for communications is being encroached upon by civilian use. Having fewer frequencies directly impacts the military's ability to conduct training operations and exercises.
The Navy (Department of Defense) has a page which educates visitors and range spectrum users on how to defend against civilian encroachment of DoD frequency spectrum.
The Electromagnetic Spectrum Training Chart shows military uses of certain frequencies and the competing civilian use.
Still Mud? Try www.phoenixmud.org!
There are two sets of frequencies for cell phones in the U.S. The orginial band at 800 Mhz(actually uses 825-895Mhz, IIRC) and the "PCS" frequencies at 1900MHz(1850-1990Mhz, once again, IIRC)
You'll find CDMA and TDMA networks in both bands. GSM uses mostly just the PCS bands, and Analog uses the 800Mhz exclusively.
To preface my comments, I am a holder of a First Class Radiotelephone FCC license, and an active Amateur Radio Operator. I have been involved in communications of all types, from TV and FM transmitters to engineering two-way radio installations. Now with that said --
What a load of crap! It's not the problem of the wireless providers, it's a problem of coverage due to poor system engineering.
Most, if not all, 800 mhz emergency service systems operate on what is call a "Trunking System". What this is, essentially, a system of linked towers that communicate with the vehicle or officer on the street, then relay from tower to tower ultimately connecting to either the dispatcher or another officer. These systems are designed to be interoperable with each service, such as police, fire, ambulance, etc, so a single dispatch facility can communicate with everyone, and all services can communicate with each other.
To work effectively, you must have sufficient towers properly placed to assure that there is no dead zones. Given the expense involved in site purchase, permits, tower erection, equipment installation, and backup generators, the bare minimum is pretty much the rule. Plus, you cannot physically survey the entire area of coverage, you use topo charts to try to make sure your engineering is sound.
To blame the wireless providers is silly and stupid. Modern 800 mhz equipment is very selective, most newer systems operate via spread spectrum digital, and the chances of interference are minimum.
Additionally, emergency services have priority so if there is a provable case of direct intererence, the wireless provider must take steps to either stop the interfering signal, or cease operations entirely.
A radio signal, unless it's a pure sine wave, uses a certain amount of bandwidth. Double the amount of data pushed through, and you double the bandwidth used, all other things being equal.
For example, my R/C plane uses 72.450 mhz, and the bandwidth used is 20 khz, so 72.441 mhz -> 72.459 mhz are what's in use. Well, that's what's allocated anyways -- the radio should use a little less. The transmitter should not transmit signifigant amounts of power outside of that range, and the receiver should ignore any signals outside of that range.
(For comparison, morse code can use less than one khz of bandwidth. FM voice transmissions (such as used by police radios) take up 3-6 khz. SSB and FM use less, but the sound quality is less too. More bandwidth = more quality, though certain modulation types work better with little bandwidth. I don't know how much bandwith a commercial FM radio station (88-108 mhz) uses, but it's probably more like 100 khz (after all, it's music.)
If you start reducing the bandwidth used, you lose data. If it's an AM signal, you'll start losing the higher frequencies. I'd have to think about what it would do to other modulation types ...
The real problem here is that the FCC has done some really wonky allocations of bandwidth. For example, the 72.450 mhz frequency I mentioned earlier -- the 72 mhz band is for R/C planes, but it's also shared with pagers. So 72.450 mhz is channel 33 for planes, but 72.460 mhz is probably used by a pager company. If they put their tower near our R/C field, and I fly my plane over near that end, and a page goes out ... their signal can overpower my wimpy little 1 watt transmitter, and guess what happens to the plane? (Actually, 1 watt isn't that wimpy -- R/C plane transmitters have a range of about 1.5 miles. But the pager tower may use something like 750 watts ...)
In any event, that exact same problem has happened in the 800 mhz band -- 801.4 mhz may be allocated to a police band, but 801.5 mhz may be used by a cell phone tower ...