MSM7xx Controllers Configuration Guide v6.4.0

Physical characteristics of the location
To maximize coverage of a wireless cell, wireless APs are best installed in an open area with as
few obstructions as possible. Try to choose a location that is central to the area being served.
Radio waves cannot penetrate metal; they are reflected instead. A wireless AP can transmit through
wood or plaster walls and closed windows; however, the steel reinforcing found in concrete walls
and floors may block transmissions or reduce signal quality by creating reflections. This can make
it difficult or impossible for a single AP to serve users on different floors in a concrete building.
Such installations require a separate wireless AP on each floor.
Configuring overlapping wireless cells
Overlapping wireless cells occur when two or more APs are operating within transmission range
of each other. This may be under your control, (for example, when you use several cells to cover
a large location), or out of your control (for example, when your neighbors set up their own wireless
networks). When APs are operating in the 2.4 GHz band, overlapping wireless cells can cause
performance degradation due to insufficient channel separation.
Performance degradation and channel separation
When two wireless cells operating on the same frequency overlap, throughput can be reduced in
both cells. Reduced throughput occurs because a wireless user that is attempting to transmit data
defers (delays) transmission if another station is transmitting. In a network with many users and
much traffic, these delayed transmissions can severely affect performance, because wireless users
may defer several times before the channel becomes available. If a wireless user is forced to delay
transmission too many times, data can be lost.
Delays and lost transmissions can severely reduce throughput on a network. To view this information
about your network, select Controller > Controlled APs > [group] > [AP] >> Status > Wireless. For
recommendations on using this information to diagnose wireless problems, see the online help for
this page.
The following example shows two overlapping wireless cells operating on the same channel
(frequency). Since both APs are within range of each other, the number of deferred transmissions
can be large.
The solution to this problem is to configure the two AP to operate on different channels. Unfortunately,
in the 2.4 GHz band, adjacent channels overlap. So even though APs are operating on different
channels, interference can still our. This is not an issue in the 5 GHz band, as all channels are
non-overlapping.
Wireless coverage 81