Home Technician's Notebook Onsite, Out in the Field Wireless-N (802.11n) on the 2.4 MHz Band - Channel and Channel Width
Wireless-N (802.11n) on the 2.4 MHz Band - Channel and Channel Width Print
Written by David Ingalls   
Monday, 30 May 2011 13:12

When setting up your router Wireless-N for use on the 2.4 MHz band there can be a few extra tricks and things to know to try and optimize your Wireless-N performance. This is mainly because the 2.4 MHz band is the band also used for Wireless-G and Wireless-B networking.

When adding Wireless-N to the 2.4 MHz band it is highly likely that you already have Wireless-G and perhaps Wireless-B traffic on it from neighbors or other devices of your own.

To get the most from your Wireless-N and Wireless-G/B traffic on the 2.4 MHz band it can be very helpful to know a bit about two particular settings available on your router or access point: ‘Channel’ and ‘Channel Width’, and how they relate to each other and considerations you may want to think about when choosing what to set these to.

Of course nothing is really better than having an actual picture of your wireless 'neighborhood' so you can really make smart choices to best suit your situation. This article does not cover methods for how to obtain such a survey or picture or how to interrprete the information if you had it. However if you want to save time both from reading this article and to avoid a long blind guessing and testing process to try and determine good settings then you should consider using someone like myself to do exactly this. If I’m working for you to do this I can usually perform such a survey, and in many cases I can do this work remotely for a clients far away. I can map out what wireless networks are in your area, what channel they use, what channel width they use and help recommend choices for your own channel and channel width settings that might be best for your situation.

However this article will just provide general information about what 'channel' you might want to consider and why and the same for the 'channel width' setting for Wireless-N on the 2.4 MHz band without the benefit of specific information of your wireless network ‘neighborhood’. In this case I will, like your router manufacturer, only be able to provide you with some generic advice and recommendations for these settings. However I hope the information below provides a little more information concerning the 'why' that may be behind various recommendations.

It's my hope that for those interested in learning more that this brief overview will show how these two choices relate to each other in the 2.4 GHz band for Wireless-N use and why some choices might be better than others. Specifically:

  • Why out of 11 possible channels that you could choose from we usually are strongly persuaded to choose from only one of 3 very specific channels (channels 1, 6 or 11, or sometimes just ‘auto’.)
  • How ‘Channel Width’ is related to channel selection and specifically how it relates to the three recommended channels.
  • And via a diagram, visually show how ‘Channel Width’ is related to the discussion and why I’m ultimately going to recommend that you choose 20 MHz channel width even though 40 MHz is an option for Wireless-N users.

Please refer to the diagram below for the following discussion. For our purposes we will ignore channels 12, 13 and 14.

Within the 2.4 GHz band for the United States we effectively have the choice of 11 different channels that we can use. Channels 1 through 11.

Even though there are 11 channels to choose from in the 2.4 GHz band, realistically there are typically only 3 good possible choices as the width of the wireless signal is 20 MHz wide (actually the width is 22 MHz wide but most people and devices just refer to it as ‘20’ MHz wide.)

Look at the diagram below of the channels and how a 20 MHz wide channel works. You can see that for instance if you specify your router to use channel 6 as it’s center point the router ends up spanning either side of that channel 6 center point and using all or part of channels 4, 5, 6, 7, and 8 to provide the 20 MHz wide channel that is centered on 6.

2.4 GHz Wi-Fi channels (802.11b, g WLAN)

2.4 GHz Wi-Fi channels (802.11b, g WLAN) [source]

Looking at the 11 channels available to chose from (channels 1-11) you will notice that if we assume 20 MHz channel width and desire to have channels used that don't overlap or interfere with each other then we end up with channels 1, 6 and 11 as the best choices.

Many people will recommend (and devices set to ‘automatically’ choose a channel will typically do this as well) that we choose either channel 1, 6 or 11 for percisely this reason.

Of course if you and one or more of your neighbors all happen to have routers using channel 6 in close range of each other then there certainly is heavier use of those exact same channels for these users which may negatively affect both you and your neighbor’s wireless performance. But many people are completely blind to whether this is the case and if so, how much it may negatively be affecting their wireless performance and just think ‘this is normal – nothing can be done about it’.

A computer support person such as myself using proper knowledge and tools can survey and scan the wireless bands, channels and channel width use in your area and make informed recommendations for possible better channel selection (as well as width and band selection) to hopefully improve your wireless network performance.

I’m guessing here and I may be completely off-base and wrong but I wonder if in perhaps highly congested wireless areas (say high density apartments, dorms, townhouses, etc.) where there are tens of users using channels 1, 6 and 11 that you may be forced to see if perhaps you get some improvement choosing channels 3 or 4, or channels 8 or 9 knowing that there is congestion but it may provide you a bit more capability rather than running on the very heavily used channels of 1, 6 and 11. That the interference between you and your neighbors due to such a decision in an already highly congested area may not be any worse given the whole area is already very congested. And perhaps you may be a bit better performance at certain times. Again – pure speculation on my part here and I could be very wrong. I welcome feedback on this thought.

Channel Width:

You can see in the diagram above it uses 22 MHz (20 MHz) for channel width. Since we are talking about using Wireless-N on the 2.4 MHz band, you may see that your router provides configuration options for channel width selection of 20 MHz, 40 MHz or “auto”.

A channel width setting of “auto” allows the router the switch back and forth between 20 and 40 MHz channel width as the router deems best. However my experience has shown that 20 MHz is probably best in most situations within the 2.4 GHz band and that it seems that times choosing 20 MHz is better than having the router switch back and forth ‘automatically’ between 40 MHz and 20 MHz. The exception would be if you were extremely far away from any other 2.4 MHz Wireless users. You live in the boondocks with no neighbors. In this case choose 40 MHz.

While it is our human inclination to think usually think that 40 being bigger than 20 must mean ‘'better’, not everything that looks bigger always turns out to be ‘better’. This is especially true within the 2.4 GHz band.

The issue in the 2.4 MHz band is that your Wireless-G neighbors have no other choice but a 20 MHz wide channel and they can only operate in the 2.4 GHz band. In the real world it’s been my experience that an owner of a Wireless-N router with the option of choosing a 40 MHz channel width generally doesn’t get much, if any, extra benefit over your neighbors by choosing a 40 MHz wide channel within the 2.4 MHz band. In fact you may get worse performance trying to use 40 MHz channel width vs. using 20 MHz channel width in the 2.4 MHz band assuming you have neighbors using wireless-G or needing, just like you, to also use Wireless-N on the 2.4 GHz band. And the odds are high that you do have neighbors nearby using wireless-G or wireless-N on the 2.4 GHz band. (Unless you fall in to that rare case mentioned above with no neighbors or other 2.4 MHz band users for a long way off.)

The impact of choosing 40 MHz in the 2.4 MHz band won’t be just to your neighbors wireless network performance. First off you would impact potentially twice as many neighbors if you operate at 40 MHz channel width due to the number of channels it takes to provide 40 MHz of channel width but secondly your own wireless network will then be contending with dealing with potentially twice as much interference as your router deals with interference from more neighbors due to you trying to have it operate over a wider number of channels. So both you and your neighbors suffer.

If you really wanted to try and get absolute highest possible Wireless-N speed then you should really be looking at using the 5.0 GHz band instead of the 2.4 GHz band. Wireless-N was designed to make the best use a 40 MHz channel width with much greater success and less of the interference issues within the 5.0 GHz band than you face within the 2.4 MHz band. Unfortunately there are just too many devices that only provide Wireless-N on the 2.4 GHz band right now. I’m sure we will eventually see more and more devices come out with 5.0 GHz capability at good prices. But right now to move everything to 5.0 GHz Wireless-N could be a costly proposition and since this article focuses on the 2.4 MHz band we won't go any further here talking about the 5.0 GHz band and it's nuancies.

Excuse me for mentioning this a third time, but a better option rather than guessing blindly is to have a computer technician like myself use tools and knowledge to scan your network ‘neighborhood’ so we can ‘see’ what channels might be best for you; whether there’s enough ‘open space’ in either the top 2/3rds or bottom 2/3rds of the 2.4 MHz band for you to benefit from using a 40 MHz wide channel or if you should stick with 20 MHz.

Barring that information my recommendation is to stick with a 20 MHz 'channel width' for Wireless-N on the 2.4 MHz band.

And to summarize the 'channel' selection, choose and test over a period of time whether channel 1, 6 or 11 works best or if 'auto' actually works well for you. I realize this is like shooting in the dark with no lights on but absent any other information these would be my recommendations. And hopefully you can see some logic behind them from my experience and the information presented above about the 2.4 MHz band.

Good Luck and may you find a 'channel' and 'channel width' that suits you well!

 

[source of the “2.4 GHz Wi-Fi channels (802.11b, g WLAN)” picture: Author: Michael Gauthier, Wireless Networking in the Developing World; November 5, 2009; licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Found on Wikipedia.com at http://en.wikipedia.org/wiki/IEEE_802.11 within the "Channels and international compatibility" section; May 24, 2011.]

Last Updated on Monday, 30 May 2011 23:06