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Chapter 4 - Operation and Administration
BreezeACCESS VL System Manual
132
available. The SU should be configured with a minimal set of parameters to
ensure that it will be able to automatically detect and use the
frequency/bandwidth used by the AU, including possible changes in this
frequency (Automatic Sub Band Select feature).
To simplify the installation process the SU scans a definable frequencies subset
after power-up. The defined frequencies subsets may include frequencies from
more than one Sub-Band, enabling automatic detection of both frequency and
bandwidth. If the Best AU feature is enabled, the SU will scan the defined subset
and the operating frequency/bandwidth will be determined by the Best AU
mechanism (including the optional use of the Preferred AU feature). Otherwise
the SU will try to associate with the first AU it finds. If no AU is found, the SU will
start another scanning cycle.
4.2.6.2.3.2 Avoiding Frequencies with Radar Activity
In some regions, it is important to ensure that wireless access equipment does
not interfere with certain radar systems in the 5 GHz band. If radar is being
detected, the wireless access network 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 DFS is enabled, the AU monitors the spectrum continuously, searching for
signals with a specific pattern indication radar activity. Upon detecting radar
activity, the AU immediately stops transmitting on this frequency and starts
looking for another radar-free frequency. The subset of viable frequencies is
configurable.
The AU maintains a continuously updated database of all applicable frequencies,
where each frequency is marked as Radar Free, Radar Detected or Adjacent to
Radar. The AU 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 AU 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.