Channel Setup
Overview

There are two critical steps for a good WLAN deployment:

  1. Determine placement of access points or bridges – This includes determining where they should be placed and deciding how many are required for the desired coverage. Very few gaps in the coverage should be left. These gaps are essentially dead air and the client will lack connectivity in these locations. As discussed before, bandwidth requirements have an impact on the coverage areas.
  2. Map out the channel assignments – There should be as little overlap as possible between channels that use the same frequency.

IEEE 802.11b
In the example shown in Figure , the goal was to cover the whole office area with wireless coverage. A full 11 Mbps is provided everywhere, due to the density of users.

Figure shows a design that uses only the three non-overlapping 802.11b channels that are available in the U.S. As can be seen in Figure , Channels 1, 6, and 11 do not overlap frequencies. This concept can be correlated to the placement of FM radio stations throughout the country. There will never be two radio stations, in the same geographic area, on the exact same channel or frequency.

IEEE 802.11a
Using the same diagram as on the 802.11b example, Figure shows how, by using 802.11a products, the throughput of any individual user can be increased. This is due to the increased data rate of each cell. A full 54 Mbps is to be available in any cell.

With 802.11a products the user has eight non-overlapping channels. This means there can be more cells, on a per area basis. It also means that it will be easier to deploy multiple APs. Since there are eight channels to work with, it is not as important, to be concerned about the co-channel interference. This is shown in Figure .

The process to achieve optimum placement and channel mapping will be discussed in later modules. These later modules will also cover site survey and design in more detail.