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."

Comments

How can this happen?

[rokzy]

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.

Re:How can this happen?

[Phreakiture]

NEXTEL is the prime culprit. The problem stems from what NEXTEL is.

a NEXTEL phone appears to be a cell phone, but legally it is a handheld, trunked two-way radio with full-duplex capability and access to a phone patch. While this accurately describes a cell phone, the evolution differs.

"Cell phones" that follow the CDMA, GSM, TDMA or even AMPS (analog) standards are all using standards that were originally developed for use as telephones. They are licensed as telephones, and use portions of the spectrum that are reserved for telephones.

Cell phones that follow the iDEN standard (this would be NEXTEL) use a protocol that evolved from a half-duplex digital trunked two-way radio system.

What NEXTEL used to be in the business of (under a different name, which I can't recall at the moment) was providing nationwide fleets with trunked digital two-way radio service. Someone in NEXTEL had this brilliant idea that if you could add full-duplex capability and a massive banked phone patch that you could compete with the cellular companies, and this is what they did.

The problem with this is that NEXTEL, being an operator of a Commercial Land Mobile Radio Service (CLMRS), gets to license portions of the spectrum intended for Land Mobile Radio Service users.

...and there is the rub. Police, fire departments, ambulances, tow trucks, taxis, and just about every business except sometimes aviation and maritime businesses, are users of the Land Mobile Radio Service. Like NEXTEL, they license portions of the spectrum that are there for the Land Mobile Radio Service (there is no distinction in spectrum allocation between a commercial and a private LMRS license).

The biggest pain here is involved in that NEXTEL does not operate on the same frequencies everywhere. They go from location to location, licensing 5-20 frequencies in the 800MHz LMRS band (and I think sometimes in the 900MHz LMRS band) in any given location, but the frequency that they allocate in one city may be the same frequency that a police department in another adjacent city is using.

Yes, the FCC probably should have prevented this. However, their allocation scheme was good enough for systems that had a low duty cycle, and it worked for decades. Introduction of a high duty cycle system such as NEXTEL broke the system.

Incidentally, I strongly advocate that police, fire and other services should not move to 800MHz trunked systems if they don't have a serious need to. The fire department in my home town of Selkirk still uses the same frequency (46.06MHz) with no repeater, no trunking, nothing except for a remote base (which communicates to the three firehouses on 460.6375 and 455.6375MHz) and provides complete coverage for the fire district with minimal vulnerabilities, including immunity from interference from NEXTEL.

BTW, WiFi is not a problem because the frequencies are nowhere near 800MHz.

Understandable

[rednaxela]

"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.

Locally even worse...

[Shoten]

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.

Police chatter in the classroom

[awtbfb]

This problem has been around for some time in the hearing impaired community.

some obvious questions that

[sbma44]

I don't know the answers to:

• 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.

wifi = different spectrum, limited deployment

[aldousd666]

Most of the WiFi I know of uses 2.4 Ghz band (I know there are others out there though) And there doesn't seem to be a whole hell of a lot of it out there yet. Maybe it will one day be a bigger problem as it's deployment picks up. I'm looking forward to the seeded frequency hopping options rolling out in the long term, which won't cause very many people problems (at least for more than a fraction of a second) The frequency hopping method also adds the 'security by obscurity' slant to the signal as well -- if you don't have the seed and the algorithm by which the frequency is determined, you may have trouble sniffing out the data on the signal. All really neat stuff. I don't see the wireless stuff, at least the internet variety, as being all that useful, (pardon me all of you blackberry junkies) I think wifi has the solution to it all, conceivably (someday) even cellular could just use some of that bandwidth. It's just a matter of changing the infrastructure -- something that seems to take forever with folks like Verizon involved.

Exactly how crowded?

[Faust7]

As organized, the spectrum, which is a limited resource, simply can't accommodate everyone...

There are several wireless companies operating in the 800 megahertz band...

How finely split can the spectrum be before there's danger of overlap? Is it possible for, say, one phone to send signals at 800.0001 MHz while another does so at 800.0002 MHz? Where is the precision cutoff for neighboring frequencies before things start to interfere?

Re:Exactly how crowded?

[aldousd666]

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.

Re:Exactly how crowded?

[Pedrito]

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.

Re:Exactly how crowded?

[mgs1000]

FYI

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.

Short Range?

[Gaewyn L Knight]

*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.

Correction

[Faust7]

802.11a and b currently operate primarily at 2.4 Ghz.

Actually, only 802.11b operates at 2.4 GHz. 802.11a operates at 5 GHz.

The emerging 802.11g standard is intended to deliver the same data rate as 802.11a but on the 2.4-GHz band.

Open Spectrum

[schnarff]

Seems like we need to point the FCC towards Open Spectrum (mentioned in a previous Slashdot article). After all, why go to all the trouble of reshuffling the tiny spectrum we've got now when the proper devices and management can give us more bandwidth than we know what to do with yet?

NYC Wi-Fi

[TrippTDF]

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.

here's a thought ...

[dlasley]

> 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 ...)

Re:here's a thought ...

[sbma44]

but hasn't private enterprise often proven its ability to manage complex systems a tad better than the government?

Like, say, with energy deregulation in California? Or privatized public schools? Or the free market for health insurance, which has left millions uninsured?

Bureacracy will inevitably develop when such systems reach a certain size, and bureacracies will inevitably suffer inefficiencies. But I don't think adding profit motive to the equation necessarily makes the systems run any better -- it just shifts the mandate of the organization to revenue generation by system maintenance, rather than purely system maintenance -- and consequently opens the door to Worldcom/Enron-type problems.

I would rather not have market forces detemining whether I get 911 service on my cell, thanks

Is the FCC doing its job?

[Brahmastra]

I thought one of the reasons the FCC exists is to allocate frequency blocks precisely to avoid problems like this? Aren't wireless devices supposed to be certified by the FCC?

Re:Is the FCC doing its job?

[nchip]

IANARFE (Radio Freqency Enginerd)

I think this is caused because the FCC specs say that a device X must use frequency y, and less than backgound noise on other frequencies.

Now, every RF transmitter is a analog device and as such it's impossible to transmit perfectly in the mandated frequency, so some leak to the neighbouring frequencies is inevitable. Still OK, a single device X will not produce noticable interference, as it produces less than background noise.

Now, instead of one device, you get thousands of RF transmitters, and the interference starts adding up, finally surpassing the background noise.

I believe this is also the reason why people are worried of UWB tech as well.

Instead of measuring interference produced by a single device, FCC will probably have to move measuring the interference created by an operational, full network.

Ofcourse this begs to ask why FCC allocated 800Mhz for mobile phones while knowing public safety departments use it AND the whole fucking entire other world uses 900Mhz. Thus making american phones incompatible with the entire other world for a long time...

WiFi Is Not Near Public Safety Bands

[Goody]

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

Backup measures

[GillBates0]

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.

I would've thought emergency services always had some backup mechanisms in place to get back to the station in case of emergency.

Heck, I even thought the dash-cam that police cars are all supposed to have also relayed video back to a surveillance team back at HQ. Apparently it is not so. With risky, unpredictable work like emergency services at hand, I for one, am surprised they thought of fallback procedures only now.

I know transmitting live video from the surveillance cams is difficult, and multiple backup contact mechanisms would be expensive (cellphones, satellite phones et al), but then, I thought these guys would be the ones who deserve it most of all.

Artificial scarcity?

[heironymouscoward]

Is it possible that the FCC benefits from the artificial scarcity that its own policies impose on frequencies? There exist technologies to make much more efficient use of frequencies and to eliminate all interference, but mysteriously we still get all our services squashed into a small and crowded space where the right to broadcast commands high fees and prestige for the authorizing body (=FCC).

Frequency Encroachment

[hobbespatch]

I had the opportunity to attend a few hearings on Capitol Hill this year regarding the impact of spectrum/frequency encroachment on military communications and training.

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.

You'll need both

[siskbc]

Has absoulutely nothing to do with anything on the broadcasting end.

I really don't know about that. Just as receivers have tolerances, transmitters do too. So if I have a crappy transmitter and I tell it to broadcast at a certain frequency, there will be a certain tolerance there, unless I'm using a laser. They're certainly not. Even with a good transmitter, there's a certain +/- to the frequency distribution, although presumably less.

So ultimately, his question was quite a fair one - for someone to tell the difference between two signals 800.0000001 and 800.0000002, the two transmitters will have to be good enough to send out precise, narrow signals, and his receiver will have to be good enough to tell the difference.

Re:You'll need both

[dougmc]

So if I have a crappy transmitter and I tell it to broadcast at a certain frequency, there will be a certain tolerance there

Yes, you're right. But it's not a function of a `crappy transmitter' ... it's called `bandwidth' -- and while you may have heard the term before, *this* is where it originated.

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 ...

Wireless Interference

[brain1]

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.

Shannons Law Re:Exactly how crowded?

[WolfWithoutAClause]

The answer to how close you can put the channels is known as Shannons Theorem. This basically says that the radio channels can't be put closer together than a certain amount, since each channel needs a certain bandwidth.

The amount of bandwidth basically depends on you much noise there is around- you can pack much more data into a narrow channel if the channel has hardly any noise, whereas if the channel is very noise you'll need a wide channel to send the same data.

Also in practice you need a gap between neighbouring channels- the receivers need to filter out the other channels and they don't do this perfectly (although the better the receivers are, the closer you can pack them in.)

However Shannons law only deals with broadcast communications where everyone can 'hear' everyone else equally, if you use directional antennas then it doesn't necessarily apply- two communications could use the very same channels.

Good timing!

[Anml4ixoye]

How funny that this should come up. I was just in a meeting last week talking about this very thing.

I am the Assistant Chief of a volunteer department north of Tampa, Florida. We operate off of the 800mhz radio system, and for all of the money we spent on it, you would think it would work better. Instead, we have spots where we can hear but not transmit, or just plain not get reception at all.

While we were talking about this one of the Hillsborough County chiefs brought up the fact that when he is at headquarters (where our central towers and dispatch are) he can't use his little car-alarm-door-unlock-gadget-thingy unless he is almost touching his vehicle. When he is at home, he can activate it from 200-300 yards away.

We have always blamed it on the hardware and crappy company, but now I think I might have to look a little more into what other kinds of interference would cause transmission and reception problems in the areas where we are having difficuly.