Working in IT, I'm often asked if I can help with computer issues and more recently issues with wireless. Fortunately wireless is something I have some understanding of, and have used it in a domestic environment for over eight years.
Without getting into too much detail, there are two frequencies that wireless devices will run on the very common 2.4GHz or the less common 5GHz.
2.4GHz is commonly used within the domestic environment, so not only does wireless use this frequency, you also have the DECT telephones, wireless video senders, alarm system PIR sensors, wireless mice/keyboards, baby monitors, etc. As you would expect, this can cause conflict and make your wireless network run slowly.
How many times have you struggled with a poor wireless connection, but when you connect to the wired network it's fast? You may have tried looking on your wireless router and see that there are channels 1 to 11 or 1 to 13, but changing them may make little difference.
Here is a diagram, I've borrowed from Xirrus:
As this diagram explains, there are three non-conflicting channels on the 2.4GHz frequency. These are channels 1, 6 and 11. As you can see, if you use channel 2, it will overlap with channel 1 and channel 6, causing issues for all. Imagine a number of radio stations broadcasting on similar or close by frequencies, and the interference that this would cause.
As you can see from the diagram, you'd just use the 5GHz channel which will has 24 non-overlapping channels, rather than 2.4GHz with 3 non-overlapping channels.
So 5GHz is the answer?
This brings other challenges, not all hardware supports 5GHz, so if you have an iPad 2 or newer, an iPhone 4S or newer, many of the newer Android phones, some new laptops, or a MacBook, you probably don't have a client device which will support it. That said, you wireless access point or wireless router will also need a 5GHz radio (which seems to be either rarer) and these are normally a premium over the 2.4GHz equivalent.
What frequency do your client devices support?
If like me you have a number of legacy devices, such as a Nintendo Wii, a PS3 or an older laptop/tablet/phone, then you will have 2.4GHz client devices on your network. You probably also only have a 2.4GHz access point/wireless router, so unless you are investing a new hardware you need to optimise what you have.
I know my channel, what about my neighbours?
One of the biggest issues is knowing what wireless channel your neighbours are running. There are a number of tools available and one of the best free ones I've seen is insider, and you can download the computer software here or download the app for your Android phone from Google Play.
Here is a capture I got when I was on a train to York from my Nexus 4:
You can see a majority of the networks are on channels 1, 6 and 11, but there are also a couple that span and will cause conflict.
Which channel to choose?
I would normally pick one that has the weakest signals on it, but also balance the number of the networks on that channel as well. Remember to walk around your environment to check the signal strength in all the locations you would normally use the wireless network.
What about the other devices that can cause congestion?
I always use baby monitors as the example as when my daughter was born, she or rather her baby monitor broke my wireless network.
I bought a Wi-Spy to see what was going on in the air, so unlike the software above, which only shows wireless networks, the Wi-Spy shows the interference in the air from other devices running on the 2.4GHz frequency.
Test it to make sure it works, but more importantly secure your wireless network... but we'll discuss that another time!