wifi channels

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hamish225

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#116865 12-May-2013 15:38

i know that in NZ you're supposed to use only channels 1, 6 and 11 but i did a scan and noticed a neighbour using channel 3. is that illegal or is it just an unenforced standard?

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#816241 12-May-2013 15:41

you can use any channel between 1 & 14

GregV

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#816257 12-May-2013 16:18

1, 6, and 11 are the non-overlapping channels in the 2.4MHz range. Your neighbour using channel 3 will be subject to - and cause - interference with those using either channel 1 or 6 locally.

kyhwana2

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#816261 12-May-2013 16:32

You can use any channels between 1 and 13, but the signal overlaps other channels. You're probably thinking of hearing about using only those channels due to interferrence/having the signal overlap onto other channels.

sbiddle

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#816267 12-May-2013 16:40

farcus: you can use any channel between 1 & 14

Only 1-13 are legal in NZ.

chevrolux

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#816271 12-May-2013 16:43

Lots of things have issues with ch 12 & 13. So just stick to 1,6 & 11.

hamish225

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#816282 12-May-2013 17:17

sbiddle:
farcus: you can use any channel between 1 & 14

Only 1-13 are legal in NZ.

who uses channel 14?

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farcus

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#816356 12-May-2013 18:59

hamish225:
sbiddle:
farcus: you can use any channel between 1 & 14

Only 1-13 are legal in NZ.

who uses channel 14?

hmmmmmm . . .
I don't use it, but it is available on my router.

farcus

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#816357 12-May-2013 19:02

I see.
If I change the regulatory domain setting in my router to NZ then channel 14 is no longer available.

RunningMan

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#816379 12-May-2013 19:39

hamish225: who uses channel 14?

Japan.

Dratsab

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#816409 12-May-2013 20:44

If you have north American equipment, it's possible you won't see channels 12 and 13 either as they're designated low power only channels so are generally not used.

1080p

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#816418 12-May-2013 21:06

I've seen a few enterprise networks which run multiple wireless networks all on the same channel. This can cause interference, correct?

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sbiddle

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#816421 12-May-2013 21:19

1080p: I've seen a few enterprise networks which run multiple wireless networks all on the same channel. This can cause interference, correct?

It depends if you're meaning multiple networks or merely multiple SSID's, which is pretty common these days.

Multiple SSID's don't cause interference because they're the same AP.

hamish225

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#816439 12-May-2013 21:41

RunningMan:
hamish225: who uses channel 14?

Japan.

whats it used for in NZ though, why is it not allowed? o.o

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richms

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#816445 12-May-2013 22:06

APs on the same channel will often work better than on non overlapping channels since they will see each others transmissions and re-try. It also worked wonders for the handoff between them at work to put them all onto the same channel.

As the actual usage on each is stuff all, just smart phones mostly there are few transmissions to interfere with each other.

Also you are probably seeing them at -80 or worse on your phone outside, so totally useless. Chances are when one AP is usable at -50 inside, the other on the same channel is not there or down in the -80s so will be a non issue

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raytaylor

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#817634 14-May-2013 19:32

In New Zealand, We are allowed to use channels 01-13
A standard wifi signal is 20mhz wide, but the channels are set at 5mhz intervals

Why we have channel 01-13
RSM have allocated the frequency space that channel 14 uses for other purposes.
Radio Spectrum Management at the Ministry of Economic Development are responsible for managing our radio bands and make up these rules.

In the USA they are only allowed channels 01-12. Many electronic devices are hard coded for the US band and will not operate on Channel 13.
In the USA, the FCC manages the radio spectrum and the radio frequency that channel 13 uses is privately owned by a company that has a historic license to use the frequency exclusively. The licence was issued before wifi was developed and the channel table was created. The company has made offers to give up their license but it hasn't happened yet.

So if you have a router that is set to the NZ region and the channel set to Auto, it will often see channel 13 as being available with the least amount of interference and will start to transmit its beacon on that clear channel 13. When you try to connect with a device (most laptops, phones etc) that are set for the USA region, they wont pick up the channel 13 router. This is a common problem for most telecom/thompson routers that are set to NZ:Auto out of the box.

Now channel overlapping

A wifi channel is 20mhz wide.
However the channels are not spaced apart at 20mhz intervals.
In the space between 2402mhz and 2485mhz there is only space for three channels that are 20mhz wide.

At the same time, a channel table (01-13) was developed by the wifi people and uses centre frequencies that are at 5mhz intervals.

So channel 1 is centered on 2412mhz, but channel 2 is centered on 2417mhz.
This is what it looks like

So you can see from the above image that the only channels that dont overlap are 1,6 and 11

So you can have three AP's in close proximity to each other, and they will usually be okay.

This is how we would lay out a floor plan - by turning down the transmit power on the access points, we can reuse channels over another side of a building without causing self interference.
You can see the dick in the building next door has left his router's transmit power on high, and will interfere with nearby routers on channel 11 because most of channel 13 overlaps channel 11.

A big problem with wifi range in urban areas (since ISP's started issuing free wifi routers) is that neighbors will leave their routers set to high transmit power, and cause interference - reducing the range of each router in the street.
By turning down the power, there is less interference and channels can be re-used closer together.

Many routers only look at the amount of SSID's or network names they can pick up on each channel. They dont look at the signal level, overlapping effect or radio noise. So his router has seen channel 13 has the least amount of networks listed and will use that without taking into account that channel 1 is probably the cleanest. Its a good way to get things started but doesnt work well in a dense area.

Wifi channels were only a result of the wifi people creating them and assigning them to frequencies.
Eg. Channel 1 just happens to be 2412mhz
For the common person, its easier to remember channel 1 rather than 2412mhz.

However, you dont need to transmit on a pre-defined channel. Some advanced radios allow you to transmit on any frequency you like with the centre of the transmission being anything between 2412 at the low end, so the bottom of the 20mhz wide channel doesnt use anything below 2402mhz, and the top centre being at 2474mhz so the 20mhz wide channel doesnt go over 2485mhz.

So to sum up
Nothing wrong with transmitting on channel 3 - hes just being a dick and causing interference to both channel 1 and channel 6 leaving you only one channel (8 or higher) that doesnt overlap with him. However if you are in NZ, you could use channel 8 and 13 without any overlapping if other routers nearby didnt use channel 11.

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