Wireless Access

We currently have 76 AP's deployed throughout 3 resident halls. The radio configuration for them is auto channel and 802.11n/b/g. We noticed alot of windows N client laptops having a hard time connecting or staying connected. The only thing that seems to help the laptops is turning their N cards to b/g only. Has anyone else ran into this? There are way too many students to go around and change each card that is having a problem.

> 76 AP's deployed throughout 3 resident halls

> auto channel and 802.11n/b/g

That is a lot of overlapping channels in the 2.4Ghz range (n/b/g).

Was a professional site survey done? Is it possible to get someone to do that for you? You need to sort out what the optimal channel selection and transmit power is for your site, and hence for each current AP location. I wouldn't rely too much on auto-channel selection, unless site survey reviews show that it works.

I would suggest 5Ghz in some situations, but for a student resident situation you'll still need to support lots of 2.4Ghz only clients.

My suggestion: Try N in 20Mhz mode only, manually set the AP channels to avoid interference between cells, and reduce the power output to the minimum require for each cell coverage area. Too much power can produce adverse results, by producing more overlapping interference, or by no truly covering clients who cannot transmit at that range.

Do you know about the 3 non-overlapping channel sitation in 2.4Ghz range? Only use channels 1,6,11 and make sure any overlapping same channel areas are minimised.

Regards,

Steve.

Try n/b/g in 20Mhz or N only in 20Mhz?  A site survey was not done. I tried pushing for one 5 years ago because of the building and coverage requirements. As far as manually modifying the channel, what about AP's bleeding through the floor? I would want the next floor up to be on a different channel than the floor below correct?

As far as the N clients not connecting, I have a single access point in our office and when I set my wifi card to n/b/g, my speeds are horribly slow. When I change it to b/g it works great.

> Try n/b/g in 20Mhz or N only in 20Mhz?

N/G/B or N/G if an option. 40Mhz channel width is not good in 2.4Ghz range, it should auto fallback, but I'd suggest disabling it anyway as a rule in congested environments . You may also improve performance by not supporting B, just support G and N - or test each case.

> As far as manually modifying the channel, what about AP's bleeding through the floor?

Yes, it is difficult in a 3-dimensional space to have 3 non-overlapping 2.4Ghz channels. The only way to deal with that is to consider radio lobe patterns, antenna positioning, building construction floor attenuation, radio strength, and frequency selection. It's all about minimising overlapping channels, and if they do have to overlap, then have them do so in a non-client area. In complex multistory buildings, it is very difficult to get right in the 2.4Ghz range, and relying on auto-channel selection won't work.

The only real way to tell what frequency overlapping is a problem is to site visit and survey, my suggestion is at least WiSpy tool and InSSIDer, or better.

> I would want the next floor up to be on a different channel than the floor below correct?

What some people do is alternate APs on each level, so there are never APs on every level at the same position. Example, Level 1 and 3 has similar positions, and Level 2 and 4 have their positions dissimilar to 1 and 3. Sometimes you need to use external antennas to cover an area correctly and not bleed into other areas.

> A site survey was not done. I tried pushing for one 5 years ago because of the building and coverage requirements.

It is still worth having someone professional to review your site. Doing it yourself can cost more, a professional has expert knowledge and tools, and should be able to do your environment in a matter of hours.

> As far as the N clients not connecting, I have a single access point in our office and when I set my wifi card to n/b/g, my speeds are horribly slow. When I change it to b/g it works great.

This may be unrelated to radio frequency spectrum and interference. It could be more of a OS, patch level, driver, firmware and/or chipset issue on either the client or the AP. Try and reproduce the problem with a different N client chipset.