User manual

Chapter 2 - Managing a Single Device/Cell Air Interface Tx Power Parameters Page
AlvariCRAFT Device Manager 54 User Manual
2.5 Air Interface Tx Power Parameters Page
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/RB according to the actual level at which it is
received by the AU/BU. 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/BU that calculates for each received frame
the average SNR at which it receives transmissions from the specific SU/RB. 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/BU
transmits to the SU/RB a power-up or a power-down message. The target is that
each SU/RB 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/RB tries to associate with the AU/BU (following either a
reset or loss of synchronization), it will initiate transmissions using its Transmit
Power parameters. If after a certain time the SU/RB does not succeed to
synchronize with the AU/BU, it will start increasing the transmit power level.
In an AU/BU 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/RB should be limited to
ensure compliance with applicable regulations or for other reasons.
Different power levels may be used for different modulation levels by taking into
account possible HW limitations or regulatory restrictions.