Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 White Paper

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Figure 9. WLAN Coverage Model Based on Data Rates

In any Wi-Fi design, the effects of CCI can be limited by isolating the individual cells from one another through the

use of non-overlapping channels and natural environment attenuation (walls, ceilings, file cabinets and cubes).

We would not place two APs on the same channel directly next to one another intentionally. In a normal design,

the environment and distances we are covering generally permit adequate coverage without a lot of CCI. But in a

high-density network design, the distances are going to be constrained and propagation will be good, as such cell

coupling and resulting CCI will become much more likely.

Design Point #3: Choose a High Minimum Data Rate to Support Increased Efficiency, Lower
Duty Cycle, and Reduce the Effective Size of the Resulting Cell

CCI is not only an issue that will be faced in aggregating channels within the high-density deployment but

something that must be kept in mind regarding existing deployments of surrounding areas. Lecture halls and

classrooms tend to be co-located in the same facility, so overall design must be considered.

The Cisco

Voice over Wireless LAN Design Guide

is an excellent resource that presents CCI and best practices

for Wi-Fi implementation. As an older document, it does not cover the extreme densities found in a high-density

WLAN.

The Cisco WCS and controllers make monitoring co-channel interference and identifying the responsible AP or

APs a fairly straightforward exercise. Cisco Radio Resource Management (RRM) algorithms are centralized and

are a network-wide resource that continuously evaluates every single AP in the RF network to determine its

relationship to every other AP in the system. It does this through the use of over the air (OTA) measurements and

observations. Knowing how well other APs can hear a selected AP is a very useful feature when considering or

planning a high-density WLAN deployment. Using Cisco WCS, it is possible to evaluate how well APs can hear

one another-independent of a channel. This information is shown in a graphic display that shows not only how APs

are effecting each other on a particular map, but also how other APs that are not on the map can impact a WLAN

as well.