Alvarion BreezeNET B System Manual page 96

Chapter 4 - Operations
subset and the operating frequency will be determined by the Best BU
mechanism (including the optional use of the Preferred BU feature). Otherwise
the RB will try to associate with the first BU it finds. If no BU is found, the RB
will start another scanning cycle.
Each unit is delivered with one or more pre-configured Sub-Bands, according to
the country code. These sets of parameters include also the frequencies that can
be used and the bandwidth. If more than one Sub-Band is available, the sub-
band to be used can be selected in both the BU and the RB. If only one Sub-Band
is supported, then the sub-band selection option is not available.
4.2.6.2.3.2 Avoiding Frequencies with Radar Activity
In some regions, it is important to ensure that wireless equipment does not
interfere with certain radar systems in the 5 GHz band. In case radar is being
detected, the wireless equipment should move automatically to a frequency that
does not interfere with the radar system.
The country dependent set of parameters includes also an indication whether
DFS (Dynamic Frequency Selection) should be used. The DFS algorithm is
designed to detect and avoid operation in channels with radar activity. If the
current sub-band does not support DFS, then the DFS parameters configuration
submenu is not available.
When the DFS Option is enabled, the BU monitors the spectrum continuously,
searching for signals with a specific pattern indication radar activity. Upon
detecting radar activity, the BU immediately stops transmitting on this frequency
and starts looking for another radar-free frequency. The subset of viable
frequencies is configurable.
The BU maintains a continuously updated database of all applicable frequencies,
where each frequency is marked as Radar Free, Radar Detected or Adjacent to
Radar. The BU attempts to check a new frequency only if it is marked as Radar
Free. If a radar activity was detected on a certain frequency, it will be marked in
the database as a Radar Detected frequency. The BU will not attempt to check for
radar activity in frequencies marked as Radar Detected. A certain time after
detecting radar activity on a frequency, it will be removed from the list of Radar
Detected frequencies and will be marked as Radar Free. If radar activity was
detected on a certain frequency, adjacent channels should not be used as well,
according to the bandwidth. For instance, if the bandwidth is 20 MHz, then if
radar activity was detected in 5800 MHz, frequencies 5790 MHz and 5810 MHz
should not be used as well. These frequencies are marked in the database as
Adjacent to Radar, and will be treated the same as Radar Detected frequencies.
Before ceasing transmission on the frequency where radar signals had been
detected, the BU sends a special disassociation message to its associated RB.
This message includes an indication whether the RB should wait for this BU. If
the RB should wait, the message includes also the waiting time. During this time
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BreezeNET B System Manual