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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."
According to the article, WiFi uses the 2.4GHz range ("2.4 to 2.483.5 gigahertz")...
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.
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.
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.
The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
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
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.)
- Tjp
I am in wallow with my inner money grubbing capitalistic pig. ... Oink!
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.