User's Manual

Chapter 4 - Operation and Administration
BreezeACCESSS VL System Manual
4-50
Power Control Parameters
The Automatic Transmit Power Control (ATPC) algorithm simplifies the
installation process and ensures optimal performance while minimizing
interference to other units. This is achieved by automatically adjusting
the power level transmitted by each SU according to the actual level at
which it is received by the AU. To support proper operation of the
system with optimal performance and minimum interference between
neighboring sectors, the ATPC algorithm should be enabled in all units.
The algorithm is controlled by the AU that calculates for each received
frame the average SNR at which it receives transmissions from the
specific SU. The average calculation takes into account the previous
calculated average, thus reducing the effect of short temporary changes
in link conditions. The weight of history (the previous value) in the
formula used for calculating the average SNR is determined by a
configurable parameter. In addition, the higher the time that has passed
since the last calculation, the lower the impact of history on the
calculated average. If the average SNR is not in the configured target
range, the AU transmits to the SU a power-up or a power-down
message. The target is that each SU will be received at an optimal level,
or as high (or low) as possible if the optimal range cannot be reached
because of specific link conditions.
Each time that the SU tries to associate with the AU (following either a
reset or loss of synchronization), it will initiate transmissions using its'
Transmit Power parameters. If after a certain time the SU does not
succeed to synchronize with the AU, it will start increasing the transmit
power level.
In an AU the maximum supported transmit power is typically used to
provide maximum coverage. However, there may be a need to decrease
the transmitted power level in order to support relatively small cells and
to minimize the interference with the operation of neighboring cells, or
for compliance with local regulatory requirements.
In some cases the maximum transmit power of the SU should be limited
to ensure compliance with applicable regulations or due to other
reasons.
Different power levels may be used for different modulation levels to
optimize performance taking into account the different modulation
schemes as well as possible regulatory restrictions.