In short: Only use channels 1, 6, 11 (and 14 if you live in Japan) for your 2.4 GHz wireless LAN and simply ignore the other ones. The world will be a better place with no effort at all 🙂
Great! Now you have got a WiFi of your own. As you are a prudent guy you’ll carefully choose a free channel so as not to interfere with your neighbors’ WiFis. Scanning for available networks reveals that channels 1, 6, 9 and 11 are already being used, which leaves channel 3 as the way to go. You are quite confident that everything should be in order now. The truth however is rather disconcerting and may come to you as a shock.
What you have really done is, you have set up a new jammer that will halve the throughput of at least 3 networks – including yours. How can that be true?
Only 3 out of 11 channels do not interfere: 1, 6 and 11
This is due to the channel allocation scheme that is used by 802.11 b/g standards and the behaviour of WiFi equipment: While channels are equally spaced 5 MHz apart, the bandwith consumed by a single transmission path is roughly 20 MHz, effectively occupying 5 channel slots: The center channel it is set to, 2 adjacent channels towards lower frequencies and 2 channels towards higher frequencies as well.
Thus a station set to use channel 1 will occupy channels 1-2-3. The next non-overlapping channel will be 6 occupying channel slots 4-5-6-7-8. The only channel left will be channel 11 occupying channel slots 9-10-11.
Overlapping channels substantially decrease throughput
Assuming urban surroundings and just 3 useable non-overlapping channels, wireless networks are bound to interfere with each other. If interference cannot be avoided, why not try to minimize interference by “filling the gaps”? Two stations using the same channel should most certainly experience much more interference than if they were using different ones, even if they were just one slot apart. Suprisingly enough, this is not true.
Wireless stations are by no means dumb passive devices. Before initiating a transmission they will listen for other ongoing transmissions and abide from starting their own transmission when they find that the channel is currently in use, thus minimizing interference (DCF, CSMA) . Sadly enough, this is an important factor that is often overlooked or set aside, even in academic documents.
Now when you offset two stations by less then 5 channels you’ll impede their capability to properly detect ongoing transmissions – practically blindfolding them and turning them into anti-social criminals.
Furthermore, by virtue of its bandwidth, each transmission that does not adhere to the 1-6-11 rule will use up 2 instead of 1 out of the proper channel bands described. Thus stations set to channels other than 1, 6 or 11 will unknowingly and unneccessarily interfere and disrupt both each other and other adjacent channels, in turn causing frequent re-transmission which will bring throughput down to a crawl.
What about channels 12, 13 and 14
Within Europe and Japan, there are two additional channels available: 12 and 13. But they are of little use, as they both overlap with channel 11. Still worse, devices may refuse to connect to those channels, unless they have been set up properly, e.g. a Nokia E6x will no longer connect to channels 12 and 13 when you remove your SIMM.
Channel 14 is a very special case. It is used in Japan only and despite its number it is spaced 12 MHz apart from channel 13, so it might have been named channel 15.4. Transmissions on channel 14 will interfere only minimally with those on channel 11. Therefore, in Japan there are 4 channels that should be used in order to minimize interference: 1, 6, 11 and 14.
- Channel Deployment Issues for 2.4-GHz 802.11 WLANs (Cisco), as PDF
- 802.11b WiFi Channels (Moonblink)
- DCF (Wikipedia)
- DCF (WiFi Planet)
- CSMA (Wikipadia)
- 802.11 (Wikipedia)
Comming next: Why SuperG and other 108 MBit transmissions often cause more damage than benefit. Why a 3 dB Antenna boosts more than increasing Transmit Power by 12 dB.
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How do I know what channel I’m using with a Belkin N wireless Model F5D8233-4?
By default, the Belkin uses channel 6 (as most routers do). The F5D8233-4 is a draft-N device, that supports faster than 54 MBit transmissions, but at the expense of occupying more channels (about all the available ones). If your PC uses and needs higher data rates within your LAN (you won’t normally need them for internet access, 54 MBit will not slow down downloads of up to 16 MBit), you should stick with these defaults (main channel=6, extension channel=2). Otherwise you might consider disabling 802.11n.
You can look up the current setting by logging in to your router (i.e. http://192.168.2.1) and selecting Channel and SSID from its configuration menu.
The Belkin user manual can be downloaded from http://www.belkin.com/support/article/?lid=en&pid=f5d8233-4&aid=8340&scid=0&fid=3558&fn=f5d8233-4_v1_manual.pdf
Hey Reiner, thank you for this great post. I’ve been studying Wireless technology these last few weeks and your explanation as to why to only use 1, 6 and 11 is exactly what I was looking for. Putting it in the context of a Jammer is excellent. Thank you sir!
I’ve worked in tech support for years. While I’ve known that each channel is a few megahertz wide and very similar channels interfere, my experience has been different. I have often resolved my customer’s wireless issues by using channels 3,4, 8 and 9. While I appreciate the theory, I’ve not seen this work in practice.
Very useful article, thanks for all this information!
Very clearly written and enormously useful, thanks, Mr. Saddey!
My experience has been similar to SLeo’s. My neighborhood is crowded with people on channels 1, 6, and 11. When my network was on channel 6, performance was terrible. I switched to 11 and it got a little better but I was still getting poor throughput. Channel 1 was no better. When I switched to channel 9, I suddenly was getting all the performance my router was capable of. The theory of routers coordinating traffic makes sense, but in a suburban environment where the signals from neighbors are strong enough for your laptop to make out the SSID but too weak to get a usable signal to connect, the coordination between devices falls apart all too often.
This website truly has all of the information I wanted about this subject and didn’t know who
Since as you say, “channel 1 will occupy channels 1-2-3…
6 occupying channel slots 4-5-6-7-8…channel 11 occupying channel slots 9-10-11.
It would seem that of channels 1,6 & 11 channel 6 is the least desirable, since it could potentially overlap with more with more channels than channel 6. Correct ?
Of course you’d also have to monitor the wifi environment with something linke InSSider software to see if there are in fact more overlaps on channel 6. If there are not actually more or about the same then you’d choose from 1, 6, or 11 on the basis of other factors like number of co-channel networks and your RSSI versus others on the same channel.
But in general…channel 6 have more potential overlap than do 1 & 11….Correct ?
I think so, but not entirely sure.
Re: “But in general…channel 6 have more potential overlap than do 1 & 11….Correct ?”
You must be mathematician 🙂 And yes, I think, you are right!
Channels 1 and 11 even carry over this statistical advantage when using 211.n devices in wide mode to increase data throughput, i.e. 40 MHz instead of 20 MHz, also called channel-bonding. Thus a Wifi using 1+ will in fact use 40 MHz bandwidth cantered at channel 3. Be warned though, that your mileage may vary for longer distances. See 5 Ways To Fix Slow 802.11n Speed.
It is impossible to use more than one 211.n 40 MHz Wifi without minor overlap, as 2 * 40 MHz = 80 MHz just won’t fit within the total bandwidth of 72 MHz as supplied in the 2.4 GHz band. See Channel Bonding In WiFi: Rules And Regulations.
If you’re free to use state-of-the-art equipment, for faster Wifi speeds at smaller distances, I’d strongly advise using the 5 GHz band (and 211.ac devices as well), as it provides ample bandwidth (when compared to 2.4 GHz) and may not be as crowded as the 2.4 GHz band due to its smaller coverage and its lesser prevalence.
Sorry. I don’t believe entirely in what you are saying. I have one neighbour transmitting on Channel 9, and another transmitting 40 MHz centered on Channel 8. I really believe that I have less interference staying on Channel 13, than by shifting to Channel 11 🙂 (I don’t have Channel 14, or neighbours transmitting above Channel 9.)
Of course, using channel 13 minimizes interference from channel 8, and thus is a better choice than channel 11. But in the US, channels 12 and 13 may only be used according to…