Specifications

Chapter 4 - Operation and Administration Menus and Parameters
BreezeACCESS 4900 119 System Manual
In passive scanning, the SU "listens" to the wireless medium for approximately
two seconds at each frequency, searching for beacons. The disassociation period,
which is the time from the moment the link was lost until the SU decides that it
should start searching for another AU, is approximately seven seconds when the
Roaming Option is disabled.
In some situations when there is a high probability that SUs might need to roam
among different AUs, the use of active scanning enables to significantly reduce the
link establishment time. This is achieved by using shorter dwell periods,
transmitting a Probe Request at each frequency. This reduces the time spent at
each frequency as well as the disassociation period.
The default selection is Passive.
4.2.6.2.7 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.