Improve
Repeater Performance of Linksys WRT54G
Repeater
working slow? Overcome diversity.
One
of the most practical uses for WRT54G wireless router in repeater
mode is to redistribute distant gateway's internet connection.
The distant AP can in some cases be several kilometers away.
You can attach a high gain directional
antenna to one of the WRT54G's antenna ports to connect
to a distant access point. In this setup the second Linksys
stock antenna is used to provide local connectivity [Fig.
1].
Fig. 1 Using WRT54G as a repeater
with asymmetrical antennas
The
problem with the above setup is that you may suffer significant
radio connection issues. Linksys WRT54G is designed to work
with two symmetrical antennas (same kind, relative proximity)
in so-called "diversity" mode. Attaching unequal
antennas which cover different radio cells as in Fig. 1 is
something diversity mode is generally not equipped to deal
with.
What
is this diversity mode? Linksys antennas are never both on
at the same time. Diversity circuitry determines which antenna
has better reception and switches it on in a fraction of a
second while it turns off the other antenna. This complex
behavior is necessary to overcome a radio phenomenon known
as multipath distortion. I recommend a very good white
paper by Cisco which explains multipath distortion and
diversity in a very plain language.
Obviously
diversity is designed with the idea that both antennas will
be used in the same radio cell. Separating the antennas or
using antennas of unequal gain inevitably causes one of the
antennas to be favored by diversity circuitry which leaves
the other antenna in the dark. The reality is not as black
and white. It is not likely that you will experience a complete
shutdown of one of the antennas but favoring one antenna will
cause interrupted communication on the other antenna.
You
can test how much service interruption you are getting. Connect
to the repeater wirelessly and measure
the internet upload and download speed. Repeat the measurement
three times and take a note of the average speed. Then connect
to one of the WRT54G LAN ports with an ethernet cable and
take the same measurement. Compare the averages to see how
much speed you're losing because of diversity.
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