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I want to first clarify that I am not against disabling the lower data rates, but there can be some side affects.


First, lets talk about data rates and why they exist. This is for the benefit of anyone else reading, not directed at you alone Mark since you are probably aware of this.

Different data rates exist to accommodate an attenuating RF signal. A complex QAM modulation loses its integrity much quicker than a simple DBPSK modulation. So, instead of penalizing the stations with better signal by making them all talk slowly, a Wi-Fi device can adjust its data rate depending on the RF conditions between itself and the intended receiver.

Keep in mind though, a 54Mbps signal travels just as far as a 6Mbps signal, it just isn't understood as far away because the complexity of a 54Mbps TX makes it more vulnerably to failure.

So, lets imagine that you disabled all of your 802.11g (ERP-OFDM) data rates except 54Mbps (extreme example). Is this a good idea if you have the budget for all of those AP's? It probably isn't a good idea because your AP's will be so close together that their RF propagation will certainly overlap the next AP (on the same channel) with too much TX power and cause serious interference.

The disadvantages to disabling the lower data rates is that it reduces the effective range of the AP's which means to have proper coverage the AP's must be placed closer together, thereby increasing the co-channel interference S/N ratio that you were questioning about in the first place. Proper design is a balance between power output and data rate.

Thoughts?