There are two critical steps for a good WLAN deployment:
-
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.
-
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.