Why is 2.4Ghz Wifi NOT hard-limited to channels 1, 6 and 11? Wifi interference from overlapping adjacent channels is worse than same channel interference. Channels 1, 6, and 11 are the only ones that don’t overlap with each other. Shouldn’t all modems be only allowed to use 1, 6 or 11?

Question

Edit: Wireless Access Points, not Modems

I read some time ago that overlapping interference is a lot worse so all modems should use either 1, 6, or 11. But I see a lot of modems in my neighbourhood using all the channels from 1-11, causing an overlapping nightmare. Why do modem manufacturers allow overlapping to happen in the first place?

Edit: To clarify my question, some countries allow use of all channels and some don’t. This means some countries’ optimal channels are 1, 5, 9, 13, while other countries’ optimal channels are 1, 6, 11. Whichever the case, in those specific countries, all modems manufactured should be hard limited to use those optimal channels only. But modems can use any channel and cause overlapping interference. I just don’t understand why modems manufacturers allow overlapping to happen in the first place. The manufacturers, of all people, should know that overlapping is worse than same channel interference…

To add a scenario, in a street of houses closely placed, it would be ideal for modems to use 1, 6, 11. So the first house on the street use channel 1, second house over use channel 6, next house over use channel 11, next house use channel 1, and so on. But somewhere in between house channel 1 and 6, someone uses channel 3. This introduces overlapping interference for all the 3 houses that use channels 1, 3, 6. In this case, the modem manufacturer should hard limit the modems to only use 1, 6, 11 to prevent this overlapping to happen in the first place. But they are manufactured to be able to use any channel and cause the overlap to happen. Why? This is what I am most confused about.

In: Technology

Answer 1

The real answer is that the ISM band where wifi operates existed long before wifi existed. The band was split into narrow channels suitable for the various equipment used in it at the time. Wifi needed wider channels.

Wifi channel 6 is centered on ISM channel 6, but occupies ISM channels 4 through 8. The three wifi channels fully occupy the US ISM band.

Different countries have different ISM bands. The channels line up across countries, but the top and bottom channels are not the same. The wifi scheme in these other countries centers on different channels, with the intention of fully using the available band.

The final piece of the puzzle is that manufacturers want to produce one device to serve multiple markets. Which means they have to be able to operate on that market’s scheme.