How to improve RF & performance in a thick concrete bldg?

Unanswered Question
Aug 17th, 2007

We have a solid 2-story concrete building built in the 60s with a nuclear bombshell. The hallways are narrow and low, lined with mostly tiny offices with solid ceiling tiles and at least 6 inch solid concrete walls.

Due to cabling difficulties, on the 2nd floor in a relatively small area incld. a conference room surrounded by hallways and offices on each side of the hallways, we had to mount three 1220B APs on the hallway wall near the ceiling. The antennas are just what comes with the APs -- dipole "rubber duck".

This setup works most of the time, with stationery users frenquently switching associations between the APs. On a couple machines they will disconnect a couple times a day or so and can be repaired most of the time. I also noticed these two machines are situated close to the window and can see a couple unsecured network with strong signals. I wonder if it's the occasional channel conflicts with the neighbor's wlan that causes this intermittent disconnection, or it's the complicated signaling problem inside our building. Since we only leave 3 APS in here at this point, there shouldn't be any channel problem between themselves.

Can someone advise me for antenna choice and replacement in this type of situations.

I am thinking about buying an good omni (for the one in the conference room) and two directionals covering the hallways. I am also considering replacing the B module with G, and get a WLC to manage the RF and channels and diagnostics.

Appreciate your advice.

I have this problem too.
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jake.kappus Sat, 08/18/2007 - 08:52

A comprehensive site survey probably could have helped in this situation.

I would definitely look at replacing the AP's with AP's that can do G, and going with a WLC. OFDM, which is what G uses for modulation, uses multiple frequencies in the spectrum to better handle noisy environments. If you can, do some RF analysis with a tool like NetStumbler or Air Magnet to see what your RF environment looks like. You may have some co-channel interference going on there.

I usually stray away from the rubber ducks if I can and look at a good omni like the 5959 or the 1728. You may get away with doing a patch antenna at the ends of the hallways too. But a good professionally done site survey would tell you exactly what you need.

DANIEL WANG Mon, 08/20/2007 - 05:27

Thanks so much for the input. We did not go for an professional site survey because it's a small area and the situation is not bad enough to justify for such cost.

We decided on on 3 Omnis -- two 1728 and a 3213.

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