Wireless Congestion

AllMightyPaul writes "An article on CNN describes the congestion experienced by many users of wireless networks as more and more people begin to use them at home and at work. The unregulated frequencies between 902 and 928, where most Wi-Fi devices operate, sees a lot of traffic, apparently."

Comments

Correction on WiFi freq

[Jerp]

According to the article, WiFi uses the 2.4GHz range ("2.4 to 2.483.5 gigahertz")...

Re:Correction on WiFi freq

[aqua]

I might be mistaken about the significance of it, but while 802.11b at least is capable of a dozen or so channels, most 802.11 networks are using one of only three (1, 6, 11; 2.412, 2.437 and 2.462GHz respectively) of them. So there might be some overuse there.

It'd be interesting to see some mobile spectrum analysis of frequency usage over geographic areas, to see if that plans out -- map spectrum emissions and see if there's an aberrant concentration in spots. Might not be terrifically useful, but cool data.

Aside from broad deployment of spread spectrum for future RF-emitting gadgets (the ones not using it already), it'd be helpful if devices like 802.11b access points could indicate when they're having interference problems, so as to distinguish these problems from those of topography, incorrectly installed antennas, hordes of evil lurking microwave ovens, etc.

Re:Correction on WiFi freq

[mindstrm]

That's because adjacent channels interfere with each other. They are not completely isolated channels as would seem logical.

The three in common use you will notice are the lowest, middlemost, and highest channels. Lots of space in betwen.

Devices DO indicate if they are having problems.. they give you indications of signal strength.

Re:Correction on WiFi freq

[El_Nofx]

ya, so does your microwave, your garage door opener, bluetooth, maybe one of your portable phones, and about 100 other things. You just gotta stay one steap ahead of the game, 802.11a, that works on the 5ghz garbage range. That is still pretty clean. Linksys just made a wireless networking product that works on 5ghz and gets 75mb/s... It is backward compatible with the 802.11a standard.

I don't remember the name but there was a big hacker conference (2600 type stuff) over in the Netherlands that had soo many guys using wifi that they maxed out the spectrum. They also raised a weather balloon with ethernet attached and did a bunch of other wierd stuff.

Re:Correction on WiFi freq

[afidel]

The problem is that the 75Mb/s stuff takes 2 channells and therefore adds to the problem. Not to mention that their receivers are so crappy that it can only do the full rate at 10m or less.

Re:Correction on WiFi freq

[fwr]

That's because companies (even the vendors of the hardware) don't know what they are doing when installing a 802.11b network. The "trick" is to think of it as a 3D Star Trek type chess game. You CAN use adjacent channels, just not in AP's that are physically, or more importantly measured in "RF-distance", close to each other. Most installers are not intelligent enough to think in 3 dimensions, let alone the 4, yes 4, required for a proper facilities analysis. And the 4th would be... the physical makeup of the facility. Two AP's placed on opposite sides of a sheetrock wall are "closer" than two AP's that are placed on opposite sides of a concrete wall, which in turn are "closer" than two AP's placed on opposite sides of radiation shielded wall around a radiology department in a hospital. All WAY too much to think about for the average RF installer, and THAT's why they recommend only using 1, 6, and 11.

Few things.

[mindstrm]

1) so-called Wi-Fi, usually 802.11b, uses the 2.4Ghz ism band, not the 900Mhz one. Most wifi is therefore NOT 900Mhz.

2) Of course it's going to be congested! There is a REASON the 2.4Ghz band is where it is. It's dirty, and unlicensed. It was designated in the first place as an ISM band because it's dirty; it's not as commercially attractive as other bands in the same area. The fcc regulations REQUIRE you to accept interference from other devices.

Re:Few things.

[Muad'Dave]

Common misconception. There's nothing magical going on between water and 2.4GHz - water molecules happen to absorb a good bit of energy at that frequency that gets translated into heat, and it happens to be in an ISM band.

If water was resonant at 2.4GHz, you would boil all of the water out of your food within the first 10 seconds or so of cooking - not the desired result. You want the water to absorb the energy slowly enough to give the heat time to conduct into the rest of the food. See this and this article.

Ehh?

[EchoMirage]

From the article:
Headsets and other gadgets using the Bluetooth standard, newer cordless phones and microwave-powered, energy-saving light bulbs share the 2.4 to 2.483.5 gigahertz frequency range used by Wi-Fi. Household microwave ovens use radio waves in that range to heat leftovers.

802.11b Wi-Fi devices occupy the 2.4 GHz spectrum, not the 900 MHz spectrum as erroneously stated by the article submitter.

802.11a, by comparison, uses the mostly-unoccupied 5 GHz spectrum, making it less prone to interference. It also boasts about 5x the theoretical bandwidth of 802.11b.

Furthermore, there are additional 802.11 hybrids that occupy different frequencies and offer different bandwidths.

Re:Ehh?

[conan_albrecht]

Yes, and how long will it be until the 5GHz range is crowded too? It's only a matter of time.

Re:Ehh?

[autocracy]

The article does NOT state that Wi-Fi devices are in the 900 Mhz range - it merely talks about other devices in that range. It's an entirely different paragraph. Poorly worded by the author, yes - but still not wrong...

Poor Equipment

[Bonker]

The company I work for used a wireless link to get a 45mbit/sec data connection between our two offices for more than a year. Different businesses in the same building initiated wireless links after seeing the sucess we had with ours. One, which was aimed at a nearby wireless ISP was illegally overpowered and wiped out our connection regularly, despite the fact that the dishes weren't even facing the same direction. The other, which made a very short hop, was apparently on poorly configured equipment and would also play merry hell with our shot.

IANAWE(I am not a wireless engineer), but I can't help but feeling that if we're to see the 'unlimited spectrum' as it's been mentioned before, then equipment manufacturers are going to have to do a hell of a lot better job of making wireless kit that minimizes signal bleed.

Re:Poor Equipment

[Detritus]

You can have good or cheap. Good microwave equipment is expensive.

This is also the reason that most microwave bands are regulated and licensed. Frequencies need to be coordinated. Equipment needs to meet certain minimum standards. Power levels need to be set at the minimum level that provides a reliable link.

Re:Poor Equipment

[Cef]

With point to point links you really need to evaluate antennas and your area. Many people use antennas with a wider radiation distribution pattern than is necessary, simply because it does the job. A number of cheaper antennas also have terrible front-to-back noise ratio, so noise from behind or the side of the antenna can really affect the signal. Also remember that many antennas allow you to orient the polarisation of the signal by the way they are mounted, and some antennas even have circular polarisation.

With general network setups (eg: an office) many people have a tendancy to put an AP on the edge of the building, particularly in warehouses (simply because there is little else to support it). Semi-directional antennas (with 60-180 degree coverage patterns) are VERY useful for walls and corners, and usually have a higher gain in the direction you want (away from the wall or corner, into your business). The less signal that escapes your premesis, the less chance of interference, and also the harder it is to get an outside connection (ie: war driving).

If your setup doesn't allow for outside interference, and is very succeptable to it, you'll always have problems.

Re:802.11a fix?

[LWolenczak]

The problem for adoption is the price... I'm not going to buy a 600 dollor access point to have 802.11a in my home when i can buy a 150 buck access point for 802.11b.

Re:802.11a fix?

[mindstrm]

Of course it's prone to collisions. The protocol is the same, the frequency is just different.

It's not fundamentally any different.

It is no more or less prone to interference than 802.11b.

It may be that there IS less interference because it's a relatively new band, but it's no less prone to it.

What?!?

[Peridriga]

What the hell about this article about the false theory of spectrum scarcity no less then 2 hours ago?

Re:What?!?

[Detritus]

It's bullshit.

Yes, we can greatly increase the efficiency of spectrum utilization for some applications if we toss out all existing models of spectrum use and their associated equipment, spend huge amounts of money on software defined radios, develop new suites of protocols, and mandate cooperation between all users.

Re:What?!?

[SiliconEntity]

The problem with the idea of unlimited spectrum is that while it is true that there is no interference between EM waves in free space, that is not true once they hit your antenna. Then all the different waves on a particular frequency will interfere like crazy.

The only way to allow multiple use is with exotic directional antenna concepts like phased arrays. Sure, with a perfect directional antenna you can have as many transmitters as you want on one frequency; you just aim perfectly at the one you want to listen to. But of course directional antennas are unworkable for a mobile solution, and they are complicated and expensive to set up for a stationary one.

Really that earlier article was just an attempt to bash the FCC with some theoretical results that don't have much to do with the real world.

Re:Sour grapes

[markov_chain]

I'm not worried. I am posting this comment from a laptop with 802.11b, while a 1.3KW microwave oven 10 feet away is cooking my dinner at full power. At the same time, my laptop is playing MP3s in the most gluttonous manner: using a remote esd connection to a box hooked up to a stereo, without any problems.

Now how am I to take seriously the rest of the points that the article makes, if even the one most obvious and easy to verify is wrong in this one instance?

Re:802.11a fix?

[bridges]

802.11a, which operates in the 5GHz range, is not a significantly different meda access protocol than the one used in 2.5GHz 802.11b. If there are enough people moving into the 5GHz range, then collisions and such are inevitable there. 5GHz is still preferable to 2.5GHz, however. One reason the 2.5GHz range was given to unlicensed spread-spectrum transmitters because it's so noisy to begin with - there are a lot of devices that radiate in the 2.5 range that don't follow *any* network media access protocol like CSMA/CA, like a microwave oven. At least when two access points fight over a single frequency, they might be able to do so in a structured way that's relatively fair to each transmitter. Microwaves, however, don't "play nice." :)

Apparently the 5GHz band is cleaner than the 2.5GHz band, so at least the background noise will be less, and hopefully the transmitters in the range will all use a common media access protocol so that the interference that is there will be more cooperative and not just straight radio interference. One possible solution to this problem might be a configuration protocol is created to allow different access points in the area to automatically negotiate which channels they will use, so there isn't even the collisions that happen when to WiFi devices share the same channel. I've never heard of anything like this before, however.

-Patrick Bridges

Re:802.11a fix?

[mindstrm]

Collisions will happen just the same. You can pack more data in, yes, but the time between a node beginning to transmit and the other nodes seeing that it starts to transmit will be exactly the same. Thank Einstein for that.

The EM spectrum is a limited resource

[hillct]

Like all resources, it will be offered at little or no cost until it becomes sufficiently limited, at which point the cost to utilize the resource will increase, and provision of the service will become proffitable, so we will see the end of community wireless networks, and the re-emergence of for-proffit networks, where access is restricted and the frequencies used will only be available to subscribers.

--CTH

2.4 ghz Co-existence sucks

[PhotoGuy]

I have a 2.4 ghz IEEE 802.11 wireless network in our house. Works great. (All Lucent cards.)

We have a 2.4 ghz phone, with also works great, but when we're on the phone, the throughput on the wireless lan goes down, and similarly, if there's a lot of wireless lan traffic, the phone gets interference. Tried different channels.

Tried out a wireless video relay from Radio Shack which uses 2.4 ghz. The wireless lan (even idle) causes regular noise on the screen, making it unusable. It went back.

Most annoying of all, when our microwave is on, the wireless lan loses most packets, and is almost unusable in the kitchen (and some other places).

The frequency hopping and co-existence in this band doesn't seem to work out as well in practice as it does in theory, unfortunately.

-me

Re:2.4 ghz Co-existence sucks

[wik]

I have noticed that when the microwave is on (and my laptop is in the kitchen with me), things like telnet sessions on 802.11 work fine. However, applications that require transfering longer packets (for instance, MP3 streams) get clobbered. I suspect that this because the longer the packet is, the greater chance it has of being corrupted.

Re:2.4 ghz Co-existence sucks

[ICA]

You mention that the frequency hopping does not work as well as in practice. Lucent however, is a direct sequence solution, not frequency hopping. 802.11 provided for both techniques, but anything Wi-Fi, one of which is Lucent, is using the Direct Sequence technique.

This is unfortunate actually, as a good fh radio would be much better at avoiding the interference.

As a side note, I work for a wireless company involved with all sorts of wireless networking from good old UHF and 902 MHz up to 802.11a. Even we suffer from the interference that our microwaves, lights, etc. generate. Maybe it's time to go back to a regulated spectrum...

Re:2.4 ghz Co-existence sucks

[Nethead]

What the fuck do you expect when you put a 1200W transmitter next to a 0.03W transciever? Just be glad that you don't fry your laptop.

WiFi is at 2.4 GHz

[Tjp($)pjT]

And is an unlicensed user of the spectrum. Fortunately current technology can compensate.

At 900 MHz Government and vehicle location are primary, and amatuers are among the secondary authorized users. Part 15 devices just add to the noise that other services must overcome.

In both bands, amatuer operations are swamped, if low power, by the increase in the noise floor. However, amatuers can operate on those bands with enough power using the same spread spectrum scheme such that the WiFi would be useless for PArt 15 devices. But its unlikely given the nature of the amatuer radio service (recently the FCC relaxed the allowable spread spectrum/frequency hopping restrictions on amatuers).

This is where that portion of the FCC regs. for Part 15 devices is critical, in that they must not create interference for the licensed users of the spectrum and must accept interference from them. Not an exact quote, but you get the drift.

In a nutshell, if you use unlicensed devices in spectrum where other services are authorized for higher power, you get what you'd expect. Now 5GHz is a great place to be! BTW when I key up on 2.4 GHz with 10 watts, my 802.11b network shuts down pretty hard. With only 50 feet or so of seperation the front end of the WiFi receivers gets overloaded even though I am not all that close in frequency, it is just the radio circuitry in the WiFi devices is just barely adequate so they can meet their price point and comply with the FCC regs. Better frequency agile receivers could be put in the devices and most likely will be as more devices crowd in. Also automatic power control will get better and the potentially they'll create a third scheme for the spread spectrum use that is more adaptive and as such would accomadate more users.

Last, everyone knows that they can change the channel their network is on, right. I have found several swamped WiFi networks all clashing on channel 1 when there was plenty of usable spectrum up the band. (Powerbooks are great portable diagnostic tools even though the UI is cheesy for the Airport software and the third party tools are scarce due to lack of internal Airport info.)

That is why there is a choice of channels...

[HiyaPower]

The standard 802.11b usually is preconfigured to be on channel 6. Do yourself a favor, change it when you install your network to something else... The average folks will just plug in the WAP and let it run on that channel. You can have a brain and not compete there.

One minor correction...

[Andy Dodd]

I don't believe the 2.4 GHz ham band overlaps with the ISM band in the USA - It's directly adjacent, I think.

The Australian (Maybe another country) 2.4 GHz ISM band is a different story - There's an article for hams on hacking old Proxim Symphony cards that said that if you send in a photocopy of your ham license, Proxim would send you a card normally only legal in Australia.

Uh, ok...

[Anonymous Coward]

"I know that there have been reports of people using cell-phone amplifiers getting cancer "

There have been reports of people being kidnapped by space aliens.

But barring any evidence, neither seems to be true.

Re:Uh, ok...

[aminorex]

It would be irrational to believe that no molecular
disruption will occur in living tissue as a result of
proximate emission of radiation. While the evidence
of causation is anecdotal, it is also quite persuasive
in some cases, as when the form of a tumor mimics the
form of an applied device. The bulk of research on the
subject is currently funded by interested parties, so that
inconclusive results are unpersuasive.

Eventually, the common-sense conclusion that some level
of cancer incidence is directly tracable to body-hugging
microwave transmitters will probably be borne out by
specific statistical analysis of the accumulating mass
of case studies. In the meanwhile, I use a headset, on
the belief that it's much easier to get a hip replaced
than a big chunk of cerebrum. I am sufficiently reckless,
however, to sit with a wifi card in my lap most of the day.
May God Almighty bless my gonads.

Hopefully this will mean more free-space optics :)

[timothy]

(somewhat informative: http://www.freespaceoptics.org -- one of many sites on the topic, but one which had a nice pic near the top ;) )

The site I can't find quickly (anyone?) is one that I know has been mentioned on Slashdot a few times, home-built optical transmitters (In the Czech republic, IIRC) using modified ethernet cards and powerful LEDs to beam multi-kilometer distances ...

5 years ago I would not have guessed how widespread and cheap 802.11 stuff would be today; right now, you (point of reference, Americans in the lower 48) can get an 802.11 base station for under $100. Glut isn't quite the right word, but lets say there's *a lot* of somewhat decent, moderately versatile wireless gear available for what is in 1st countries not a huge chunk of disposable income, at least for folks middle-class-and-up. The cost of 7 cds gets a working base station ...

Wouldn't it be nice to see a similar flood of products for optical gear? Yes, there will be lawsuits (eye damage! you hurt my eye!), and ugly warning labels, and ISP crackdowns for retransmission and who knows what else, but ... I think it will happen. Wait til last year's optical gear is on clearance at Walmart ;)

timothy

RF interference?

[Wierd Willy]

My pop solved this problem last year, with copper mesh underneath the new siding he had put on his house. He also limited the nework to only a smaller area, running printers and such. And the copper mesh wasnt all that expensive. He now is interference free. The trouble is, he also has to go outside to use his cellphone, and the cordless phone wont work outside the house. Trade-offs are a bitch.

Re:802.11a fix?

[afidel]

If you don't think OFDM is significantly different from DSSS then you need to sit down and talk to a wireless engineer. Second, microwave that leaks enough power to do anything to your wirless network should be replaced as it is radiating too much power to be healthy for YOU. Finally, until the cost of the MAC comes down I don't expect to see too many portable phones on the 5Ghz ISM band.

Re:802.11a fix?

[fwr]

I'd agree. He makes it sound so convincing, but he really doesn't know what he's talking about. Probably doesn't even know what DSSS and OFDM stand for.

Perhaps if he read

IEEE 802.11, 1999 Edition

IEEE 802.11a-1999

IEEE 802.11b-1999

IEEE 802.11d-2001

he would be more informed...