Cisco Cisco Aironet 3500p Access Point 정보 가이드

lead to array gain, which increases the directional gain of the device and leads to higher
radiated levels in some directions. The contribution of array gain to the directional gain of the
transmitter must be considered in rule parts where conducted in−band emission limits vary
with directional gain, or in situations where conducted measurements are combined with
directional antenna gain to determine compliance with in−band radiated limits.

Because the Cisco AP 3600 is the first to market Access Point to comply with the new FCC
guidelines, Cisco (and other manufacturers) is now required to reduce RF power in the
UNII−1 band and slightly reduce RF power in the UNII−2 and UNII−2 extended bands when
releasing new products that take advantage of MIMO or Smart Antenna technology. Or, other
methods such as reducing the overall antenna gain permitted by their products.

Again, this is done to reduce potential interference with Aeronautical Radio Navigation
services, Radar and fixed satellite communications services.

The key take−away here is that in order to comply with In−Band PSD requirements under the
new rules, you must consider the number of transmitter paths and how it effects the total RF
power and PSD emissions.

This includes beam−forming whether the beam−forming was intentional or not and given that
under certain conditions, RF power can add up driving up the overall PSD value. In order to
keep that under the FCC limits, in some cases you have to reduce RF power based on the
MCS rate and frequency being used to comply.

The reduced power is more pronounced in the UNII−1 band where PSD limits are lower
especially when multiple transmitter paths exist. For example, in the next screenshot you can
see under the new FCC rules that the more transmitter paths (physical transmitters) the higher
the PSD rises. In some cases, RF power is reduced by 6 dB with four transmitters present.