Tips for Assigning Wi-Fi Channels

Introduction

Wi-Fi is much more sensitive than Ethernet. Unlike wired networks, Wi-Fi networks are susceptible to interference from neighboring wireless networks and even noise from other RF and electronic devices—some of which you may have no control over if coming from a neighbor. Wi-Fi is also only half-duplex as well—only one device can transmit at a time on a given channel—so interference-free channels and high speeds are important.

Understanding 2.4GHz channels

There are up to 11 channels (in North America) that Wi-Fi devices can use in the 2.4 GHz frequency band, but as you’ll see, that number is very misleading. Keep in mind there is overlap between the channels. For instance, if you set a wireless router or access point (AP) to channel 6, it actually uses channels 4 – 8

When setting the channels on your APs, try to stick with 1, 6, or 11. They are the only channels that don’t overlap.

If you have multiple APs, make sure they don’t interfere with each other. You want the signal of each AP to overlap so there are no gaps in coverage, but make sure that the overlapping signals are from APs on different non-overlapping channels. For instance, you could overlap the signals of three APs that are using channels 1, 6, and 11. If you have more than three APs, you can certainly reuse these three channels, but make sure APs on the same channels are far enough apart that their coverage does’nt overlap.

What makes 2.4GHz even worse is that currently it is the most used frequency band by far for Wi-Fi. In apartment buildings, storefronts, and shared office buildings it’s almost impossible to get a clear channel. But as I share next, there’s an alternative frequency band that’s far less congested.

Understanding 5GHz channels

The 5GHz frequency band offers many more usable channels for Wi-Fi devices. The exact amount of channels depends upon your particular wireless router or access point (AP) and also what region of the World the device is set to. Some APs will only display 8 or 9 channels: typically channels 36, 40, 44, 48, 149, 153, 157, 161, and sometimes 165. Keep in mind, these channels don’t overlap unless you use larger channel widths, which we’ll discuss later. Some APs support even more channels (up to 15 more) with some limitations.

As you see, 5GHz has a huge advantage over 2.4GHz when it comes to the number of channels, interference, and congestion. In a dense area with many neighboring networks, you might see a big improvement of performance when on the higher frequency band.

However, 5GHz typically has less range due to the higher frequencies not being able to travel through walls and other objects as easily as the lower frequencies. Thus if you’re utilizing 5GHz, ensure it’s coverage is adequate as the location of APs may have been chosen in the past based upon 2.4GHz ranges. You may want a professional RF site survey completed to help check coverage and design the wireless network.

Double-check auto channel assignments

Most wireless routers or access points (APs) have the channel set to 6 by default or chosen automatically. When chosen automatically, they’re supposed to select the best channel—with no or little interference—but often I don’t see that happen correctly. For most cases, I suggest turning off the automatic channel feature and manually assign channels after checking channel usage, which we’ll discuss later.

Be careful with channel widths

When discussing the channels thus far for 2.4GHz and 5GHz, I assume the use of the default 20MHz wide channels. However, newer technologies have came out to increase throughput by optionally making the channel widths larger; 40MHz with 802.11n in both bands and 80MHz or 160MHz with 802.11ac in the 5GHz.

Using 40MHz wide channels in the 2.4GHz band means there will only be one usable channel in the area where the router or AP is located. For instance, if you set the center frequency for 40MHz at channel 6, it would use channels 2 through 10. Thus 40MHz wide channels in the 2.4GHz band should only be used where you don’t need more than one AP and where there aren’t any other neighboring networks nearby.

The larger channel widths, however, can be a more practical way to increase throughput in the 5GHz band for those users or client devices that support it. For 40MHz widths, you could have up to 11 channels if all frequencies are supported by the router or AP and your region; 5 channels for 80MHz widths and 2 channels for 160MHz widths.

Most routers and APs come with channel widths set to auto. I suggest enabling the default 20MHz channels, unless you have properly planned your network and are sure the larger channels won’t interfere with any neighboring networks.

How to check channel usage

Before setting channels or channel widths, you should first check the channels used by any neighboring wireless networks to avoid inference with them. If the building requires more than a few APs I’d certainly suggest a professional RF site survey and design to help find AP locations as well.

For smaller networks, you may be able to perform a simple site survey and channel check with free software. For instance, InSSIDer or Vistumbler on a Windows laptop or WiFi Analyzer on an Android phone or tablet. You can walk around the building to see channel usage and make note of neighboring networks and any rogue APs within your building. They can also serve as a simple tool to verify signal levels and coverage of your network.

Utilize the 5GHz band

Since the 5GHz band has much less interference and congestion, try to utilize it. If you don’t already, use dual-band APs that provide both 2.4GHz and 5GHz connectivity. For computer and mobile devices that don’t already have 5GHz support, try to upgrade them.

When choosing dual-band APs, consider those that offer 5GHz band steering functionality. This type of feature uses a technique to guide devices that are dual-band capable onto 5GHz, rather than leave it up to the user or device. Without this functionality, users would either have to choose the 5GHz network when connecting—which they maybe not understand—or the device would somehow make a decision on which band to connect to if the SSIDs for both bands are the same.

Limit users from installing additional wireless routers

It’s never a good idea to allow non-IT staff to install wireless routers or APs due to security risks, since they could leave it unsecured and open your entire network up to the public. It could also interfere with the existing wireless network, which could certainly be the case if there are already three or more APs in the building in the 2.4GHz band. Adding additional routers or APs in this case would require some analysis of the channels.

Summary

Remember, with the 2.4GHz band you only have three usable channels and even then you have to worry about interference from yours and your neighbor’s networks. Consider band steering features so dual-band Wi-Fi devices are more apt to utilize the much less congested 5GHz channels.

Always analyze channel usage, channel widths, and consider full professional RF site surveys.