User's Manual

Chapter 4 - Operation and Administration
BreezeACCESSS VL System Manual
4-42
In some regions, it is important to ensure that wireless access
equipment does not interfere with certain radar systems in the 5 GHz
band. In case 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 the DFS Option 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.
Before ceasing transmission on the frequency where radar signals had
been detected, the AU sends a special disassociation message to its
associated SUs. This message includes an indication whether the SUs
should wait for this AU. If the SUs should wait, the message includes
also the waiting time. During this time each SU searches for the AU in
the defined frequencies subset. If the AU was not found within the
waiting time, or if a waiting request was not included in the message,
the SU starts searching for any AU, using the Best AU mechanism if
applicable.