PMP 450 Configuration and User Guide
Task 6: Configuring radio parameters
pmp-0050 (May 2012)
2-81
Attribute
Meaning
Cyclic Prefix
OFDM technology uses a cyclic prefix, where a portion of the end of a symbol
(slot) is repeated at the beginning of the symbol to allow multi-pathing to
settle before receiving the desired data. A 1/4 cyclic prefix means that for
every 4 bits of throughput data transmitted, an additional bit is used. A 1/8
cyclic prefix means that for every 8 bits of throughput data transmitted, an
additional bit is used, and a 1/16 cyclic prefix means that for every 16 bits of
throughput data transmitted, an additional bit is used.
PMP 450 radios use a default cyclic prefix of 1/4 that is configurable by the
operator to 1/8 or 1/16. The cyclic prefix is set on the Configuration > Radio
page of the AP. Changing the default from 1/4 to 1/8 can increase throughput
by ~12% (assuming a 75% duty cycle ) in installations with low multipath
conditions. Moving from a 1/8 cyclic prefix to a 1/16 cyclic prefix can increase
throughput by another ~12%. It is recommended to test 1/8 or 1/16 cyclic
prefix configurations to determine actual performance based on RF
conditions. Deploying networks using 1/8 or 1/16 cyclic prefixes is feasible in
all but the worst multi-path environments (urban areas with buildings causing
many reflections).
During installation use Link Tests to confirm link quality per standard
installation and alignment procedures. If a Link Test shows low throughput
or low efficiency, consider changing the Cyclic Prefix to 1/4 on
both
the AP and
SM along with other standard installation troubleshooting procedures such as
re-aiming, off-axis aiming, changing location, raising or lowing the height of
the radio, adjusting the Transmission Power up or down, or identifying and
mitigating sources of interference.
The cyclic prefix must be set the same on both the AP and the SM. If
they don‘t match, the SM will not register to the AP.
Color Code
Specify a value from 0 to 254. For registration to occur, the color code of the
SM and the AP
must
match. Color code is not a security feature. Instead, color
code is a management feature, typically for assigning each sector a different
color code.
Color code allows you to force an SM to register to only a specific AP, even
where the SM can communicate with multiple APs. The default setting for the
color code value is 0. This value matches only the color code of 0 (
not
all 255
color codes).
Summary of Contents for PMP 450
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