Imagine a sandwich of several layers of transparent materials. Imagine the
center layer, the core, has a higher index of refraction than the two outer
layers. Light rays traveling at certain angles through the core medium will be
reflected off of the interfaces, according to the law of total internal
reflection. Now imagine a light source emitting at several angles, which would
all be reflected. This is multipath distortion or interference
.
In many
common WLAN installations, the radio waves emitted from a transmitter are
traveling at different angles. They can reflect off of different surfaces and
end up arriving at the receiver at slightly different times. All waves are
traveling at approximately the speed of light. However, only a small amount of
time difference is needed, to result in a distorted microwave signal. Multipath
interference can cause high RF signal strength, but poor signal quality levels.
This is an important issue to consider when installing WLANs.
Utilize
the interactive activity to learn more about multipath distortion. The path of
two reflected rays, from a laptop to an AP, will be shown. Notice that the rays
take different paths. The longer the path, the longer time required to reach
the destination. At the destination, the two rays of light can interfere with
each other, through constructive and destructive interference. If this
interference is destructive enough, the messages will not get through. This is
what can occur with multimode optical fibers.