Make sure you have a good frequency/channel plan for the building.
Only channels 1,6,11 have no spectrum overlap. Try to space the Access Points so there is good phisical seperation between the Aps on the same channels.
While 1, 6, and 11 don't overlap in terms of transmit spectrum mask, no commodity WiFi receiver has enough ACR to overcome a strong local signal on an adjacent channel (1 on 6, 6 on 1, 6 on 11, 11 on 6).
IEEE minimum ACR for 11b gear was 35dB. Most good chipsets got 40dB or so.
IEEE minimum ACR for 11g gear is 15dB at the lowest modulation rates. This drops to -1dB at 54Mbps.
The (simple version of) the math goes like this:
+20dBm signal (tx power) + 2dBi antenna gain = 22dBm EIRP (modulo coax/connector losses)
40dB of LOS path loss in 1m 60dB of LOS path loss in 10m
Lets use 10m (30' or so)
signal (be it from an AP or client) arrives at AP (or client) operating on adjacent channel. at 22dBm - 60dB (path loss), or -38dBm. Adjacent Channel rejection is, at most 41dB, for -79dBm into the occupied passband of the receiver.
If this is the case, you're not affected if your receiver sensitivity was -79dBm or worse. Of course, if your card is that bad, you've got other problems.
If you've got any antenna gain on the AP (or client), you need to factor that in as well. (Makes the problem worse.)
Note as well that if you're running a direct-conversion receiver (and I am aware of no commodity 802.11g chipsets that use an I/F stage) then your ACR is very, very likely below 20dB. (This is why the spec got relaxed, all the card mfgs wanted to go to direct conversion because its less expensive, so they got the IEEE to relax the rules.)
Thus, the whole "non-overlapping channel" thing needs to be trashcanned.
BTW, 802.11b doesn't define a minimum alternate channel rejection spec. 802.11g and 802.11a do. Alternate channels in 2.4GHz (DSSS or OFDM) are 1 on 11 (or 11 on 1).
jim
I would not expect a problem using the same SSID, the big benefit is the possibility of roaming.
Frank Keeney Wireless Antennas, Cables and Equipment: http://www.wlanparts.com
IM: Yahoo: wlanparts, AIM: wlanparts, MSN: frank at pasadena.net VOIP: Skype: wlanparts, FWD: 289372
-----Original Message----- On Behalf Of Kuhl, Vince (DotComm)
I was looking for some resources on wlan design. I have a 6 story building
with approx 5 radios per floor. All radio's are in the same SSID. The idea
was to provide redundancy for the users but most pc's only get an acceptable
signal from one radio anyway. It seems as if this one large SSID approach is
causing more of an interference problem than anything else. Would it be
better to break the building up into separate SSID's? Any thoughts or
resources would be appreciated.
Thanks
