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I've read everywhere that wireless access points interfere with each other and should be put on distant channels. This even applies to access points on the same wired network with the same SSID from what I've read.

Doesn't that imply that wireless clients, especially higher-powered ones, will also interfere with each other on nearby channels - or the same channel? Even when they are connecting to the same access point?

If this client-to-client interference exists, are there any rules of thumb for when it becomes a problem?

Peter Mortensen
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The Phil Lee
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2 Answers2

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You may be somewhat misinterpreting what you've read. Most (recent) wifi radios are good at rejecting adjacent channel interference, so your concern shouldn't be with radios on different channels. An AP on channel 1 will not cause much interference with another on ch 6, for example. The same goes for clients.

Edit:

When two workstations are associated with the same AP, the AP coordinates their transmissions using CSMA/CA. So they don't interfere so much as they compete for available time slots. The more clients you have, the more competition there is for airtime and throughput decreases.

Co-channel interference can occur when there are two nearby APs on the same channel. In this case, the APs are not in sync, so clients associated with AP1 are not in sync with clients associated to AP2. The clients will interfere with each other and the other AP, causing deferred transmissions, retransmissions, etc, all taking a big bite out of your throughput.

Using nonstandard frequencies (like channel 7) is just wrong and will cause everyone problems.

Also, +1 to everything @RickyBeam said.

Ron Trunk
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Two clients connected to the same AP... aren't supposed to interfere -- it's the AP's job to coordinate things (RTS/CTS handshake.) The collision avoidance system checks for an active transmitter (which might not be associated with the same AP) before transmitting. But as with all things in the Real World(TM), there are cases where it can still happen because the radios are spaced far enough apart to not be able to hear each other.

Co-channel interference from the inherent overlap of 2.4G channels does cause problems. The stronger the signal the worse it will be. 802.11N in the 2.4G band will almost never be able to use a wide channel, as it's required to drop to a narrow channel if it detects anything in the side channels -- bluetooth, cordless phone, baby monitor, any thing.

Ricky
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