Re: [WIRELESS-LAN] AP radio interference

[John J. Brassil]

It works OK - our engineering school recently completed a new wing that has a large central atrium similar to the one you describe. This is an extremely dense environment for RF - 84 APs for this single wing! They wanted as much throughput as possible, so our contractor designed a picocell network with as many as 3 APs in a single room, one on 1, one on 6 and one on 11, dialed to 1mW and in some cases futher attenuated with inline 10 and 25 dB resistors (I know resistors aren't measured in dB but that's the net effect of the attenuation.)

Unfortuanely, depspite their best efforts, there is still a lot of leakage outside the intended coverage areas - not a lot of signal strength, but single- and low double-digit signal strength from non-primary APs in lots of areas, the worst of which is the atrium which has at least 5 devices visible to Netstumbler or AirMagnet in most places on all three channels!

We haven't benchmarked the throughput rates but I would imagine they are not full rate (we fix our APs at 11mbps) but my laptop at least has been able to hold a connection in there every time I have tried. Others' MMV.

The good news is that it all still works. For the situation you are describing, I wouldn't screw around with 4 channels, that's just a hack since the frequencies are what they are and playing games with 1 5 9 & 11 or some other such silliness doesn't change that. Keep your same channel APs as far apart as possible and do the best you can.

Or buy some 5MHz radios and do it properly. :)

John

John J. Brassil | Network Engineer, Vanderbilt Data/Video Engineering
voice 615.322.2496 | ICQ 9660375

--On Thursday, November 13, 2003 3:33 PM -0500 James Savage <[EMAIL PROTECTED]> wrote:

> Hi,
> We're sharing a building with another institution and must also share
> the airspace. We've agreed to go to the four non-overlapping channel
> model instead of three. Each institution will use two channels. This is
> my first shot at full building coverage and foresee channel interference
> issues as I'm restricted to two instead of three channels. Presumably,
> this can be addressed with directional antennas and adjustment of signal
> strength but I thought I might ask more experienced folks who might have
> already experimented with channel interference. If two APs operating on
> the same channel can 'hear' each other, is it simply a throughput hit or
> do things just not work at all? Presumably, there's a relationship to
> how close the APs are to each other (signal strength-wise)...'closer'
> means more interference? Also, the amount of traffic is a factor as
> well? This particular building has a central open area surrounded by
> offices/classrooms with glass windows overlooking the open space. The
> signal seems to easily penetrate the glass and cover the open space as
> well.....ie....I have multiple APs operating on the same channel bleeding
> into the open space. Is this a show-stopper for the open space or is it
> possibly a slow but liveable scenario?
>
> ....advice or comments are greatly appreciated.
>
> ......thanks in advance.........Jamie
>
> James Savage York University
> Senior Com. Tech. 108 Steacie Bldg.
> [EMAIL PROTECTED] 4700 Keele Street
> phone: 416-736-2100 ext.22605 Toronto, Ontario
> fax: 416-736-5701 M3J 1P3, CANADA
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