Alvarion BreezeNET B System Manual page 103

4.2.6.2.7 Scanning Mode (RB only)
The Scanning Mode parameter defines whether the RB will use Passive or Active
scanning when searching for a BU.
In passive scanning, the RB "listens" to the wireless media 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 RB decides that it
should start searching for another BU, is approximately seven seconds.
In some situations when there is a high probability that RB might need to roam
among different BUs, 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.
When DFS Option is enabled, Scanning Mode is forced to Passive.
The default selection is Passive.
4.2.6.2.8 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 the RB according to the actual level at which it is received by
the BU. To support proper operation of the system with optimal performance and
minimum interference between neighboring systems, the ATPC algorithm should
be enabled in both BU and RB.
The algorithm is controlled by the BU that calculates for each received frame the
average SNR at which it receives transmissions from the 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 BU
transmits to the RB a power-up or a power-down message. The target is that the
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 RB tries to associate with the BU (following either a reset or
loss of synchronization), it will initiate transmissions using its' Transmit Power
parameters. If after a certain time the RB does not succeed to synchronize with
the BU, it will start increasing the transmit power level.
In a BU the maximum supported transmit power is typically used to provide
maximum coverage. However, there may be a need to decrease the transmitted
Operation and Administration
Menus and Parameters
85