You might be familiar with the concept of frequency tuning in radio. When you tune your receiver to a certain frequency, you are able to hear the programs from a particular channel. So, when you use an analog rotary tuner to switch channels, you might have noticed that as you rotate the tuner, first a faint sound appears, then you get a strong signal, and then the signal weakens. So, the signals are received (with varying range of amplitudes) over a range of frequencies. When you consider many channels, the used range of frequencies becomes wider.
Similarly, Wireless (Wi-Fi networks) operate mainly in two major frequency bands (ranges) – 2.4Ghz and 5 Ghz. Both are unlicensed ISM band frequencies (Industrial, Scientific and Medical RF band) – Which means, any device / technology can use that band for communications.
2.4 Ghz & 5 Ghz are frequency bands (range of frequencies). The actual communications happen in sub-frequencies called channels, within each spectrum (frequency band). For example, in the 2.4 Ghz spectrum, Channel center frequencies might be like : Channel 1 – 2.412 Ghz; Channel 2 – 2.417 Ghz…… Channel 13 – 2.472 Ghz, etc. A Wireless Radio (on wireless access point) & client radio (wireless client on a laptop) operates in one of these channels to transmit information between them.
Every channel (sub-frequency) overlaps with its adjacent channels. So, Channel 6 for example, might overlap strongly with channels 5, 4 but weakly with channels 3, 2. In the 2.4 Ghz spectrum, Channels 1,6 & 11 are non-overlapping channels. That brings us to the next topic – Interference.
Consider that there are three operational access points situated at a distance of 1 meter from each other (for example). If they operate in channels 1, 2 & 3 (respectively) or channels 1, 1 & 1 (respectively) – there would be a lot of interference that will affect all the clients connecting to these three access points. That’s because, generally access points and clients receive all the communications that are transmitted and reject those that are not in its frequency (channel) of operation. But if different access points operate in same channels (or) adjacent channels, they get confused if messages sent to them were meant for them or not!
But if the three access points are operating in channels 1, 6 & 11 (respectively), even if they are placed very close to each other, there would not be much interference because, the sub-frequencies used by each channel are far apart. In other words, these three channels are non-overlapping channels.
Interference might not allow you to connect to a wireless access point/ network, disconnect you from an existing connection (requiring you to re-connect to the network) or might slow down/ choke the wireless connectivity. Wireless Interference causes noticeable problems with real time applications like voice/ video transmitted over the wireless network. Interference is both a performance issue and a security concern (Rogue Access Points, Wireless DOS attacks, etc).
It can manage that, but the question is... if you leave default settings, how will that affect your coverage. The AP's can hear each other, if within hearing distance, and does calculate. The AP doesn't know what your coverage area should be on your outer edges of your building. So it adjust power to accommodate the RF from what it hears and you might have to change default setting to provide you with coverage you want. This is why a site survey done right is important. AP's in the parameter of the building helps out too.