Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 White Paper

Page 16 of 41

The wireless LAN controller maintains two lists of APs, Figure 10, both transmit and receive (TX and RX)

neighbors that indicate how other APs hear a selected AP and how a selected AP hears other APs. This can be

viewed using the Wireless LAN Controller (WLC) Configuration Analyzer tool and used to tune the resulting

network and identify sources of RF as the APs themselves see it. Since this observation is based on OTA metrics

and not based on predictive modeling, these values are independent of the antenna and AP combination.

Figure 10. Dual Lists of APs Maintained by WLAN Controller

2.4 GHz Channel Reuse in High-Density Wireless Design

In 2.4 GHz there are three non-overlapping channels with which to work in achieving isolation. The RF properties

of 2.4 GHz signals give it better range and less attenuation than signals in 5 GHz. In a high-density environment,

there is often only one clean channel reuse within a 10,000 square foot area. Channel reuse in such an area is

opportunistic at best and it is not possible to estimate without careful advanced survey techniques. Results will

vary from no increase in bandwidth to modest gains and will differ from site to site. If faced with such a challenge,

consult with a professional with experience in advanced engineering techniques specific to a high-density RF

deployment. Adding more APs can reduce the number of users per cell and may appear to give more coverage

when the space is empty. But once it fills up, the effect will be that of one large super cell covering the room with

limited bandwidth and sporadic connections for all.

Note:

Before considering a four-channel plan in 2.4 GHz, see

for an excellent discussion on the issues. The conclusion is that it is better for two APs to share a channel

than to have two channels overlapping on the edge. Two APs sharing a channel can demodulate each others’

transmissions and share the bandwidth amicably. When two channels overlap at the edge, it is just noise to both

and will result in collisions, retransmits, and SNR degradation.