• Andrew Campbell

Wi-Fi Myth: Most People Use Channel 1, 6, or 11 so choose another channel.

Updated: Aug 16, 2018

This is the first of a series, which intends to debunk widely publicized statements about Wi-Fi networks.

Myth Theory


Most wireless routers default to channels 6 or 11. If you see networks using a network discovery tool (software/app that shows Wi-Fi networks nearby) around you that operate on channels 1, 6, and 11 then selecting a channel such as channel 4 you will avoid interference with your neighbors.


Source: LifeHacker and others.

Reality


While the premise is true that most wireless routers default to channel 6, you should stick to channels that don't overlap frequency space (e.g. 1, 6, or 11).


Wi-Fi channels are 20, 40, 80, or 160 MHz wide. 802.11abg are 22 MHz wide with a 3 MHz gap between non-overlapping channels, 802.11n operates on 20 MHz channels and adds 40 MHz channels that are two 20 MHz channels bonded together, and 802.11ac adds 80 and 160 MHz channels.


802.11bgn radios utilize the 2.400-2.500 GHz spectrum, which is a 100 MHz subset of the Industrial, Scientific, and Medical (ISM) radio band. Depending on the regional regulatory domain some channels may not be available for use. Within the United States, the Federal Communications Commission (FCC) only allocates channels 1-11 for use.


If you look at the image below, the maximum number of non-overlapping channels in the frequency band is three (channels 1, 6, 11). The center frequency of the channels must be 25 MHz apart to avoid interference.


Meaning if someone is on channel 4, they would be interfering with channels 1,2,3,4,5,6,7,8 and the maximum number of non-overlapping channels would be two (channels 4 and 9/10/11).


But you may be asking what if there are four wireless routers on channel 6 and none on channel 4, wouldn't I be better off on channel 4?


Simply, no. Well I should say in a vast majority of cases.


If the wireless routers are operating on the same channel, medium contention overhead will occur. The 802.11 standard uses what is called Clear Channel Assessment (CCA), which causes the router to “listen” before they can “talk” to ensure only one radio communicates on a channel at any given time.


If a router on channel 6 is transmitting, all nearby routers and clients on channel 6 will have to defer transmissions. The result is that throughput is adversely affected. Nearby routers and clients will have to wait their turn to transmit. This unnecessary medium contention is referred to as CCI, but in fact is more of a cooperation mechanism in which radios take turns talking. In general CCI is not a major problem until there are numerous devices operating on the same channel.


Meanwhile, an even greater issue is that of Adjacent Channel Interference (ACI). Some people will use every available channel and not consider overlap (i.e. channels 1,2,3,4, etc.). Instead of the devices cooperating as with CCI, with ACI the devices will add noise to the network causing excessive retransmissions, CRC (Cyclic Redundancy Check) errors will increase, and data rates will drop significantly.


An easy way to remember this is to imagine being at a loud dinner table with everyone speaking at the same time. It is difficult to hear any particular conversation and due to the noise it is nearly impossible to communicate. This would be an example of ACI, where devices all talk at the same time. Now let’s take the same example of the dinner table, but with everyone waiting their turn to speak. Each person will say what they want then another individual will speak when it is their turn. This is the equivalent of the CCI, where devices will cooperate with each other by waiting their turn to speak.


Knowing how CCI and ACI work, it is clear that ACI is worse than CCI. At least with CCI some devices will be able to communicate given their turn, while with ACI in a congested environment no one will be able to communicate.

What Does This Mean?


Stick to channels 1, 6, 11 with 20 MHz bandwidth. Wireless routers on the same channel will cooperate with your neighbors, if you choose a channel that is within 5 channels of your neighbor then you will be interfering with them (talking over each other).


Better yet, use the 5 GHz band if your wireless router is capable. Adjacent 5 GHz channels do not overlap with each other (unless routers are very close to each other), i.e. channel 36 will not overlap with channel 40. There are also more non-overlapping channels in the 5 GHz band compared to the 2.4 GHz band (~25 vs. 3).

© 2018 by Syranova

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