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The radar detection mechanisms implementation was connected with the air scanning methods and transition between frequency channels. These methods were included in the requirements for wireless systems and were called dynamic frequency selection (DFS).
Dynamic
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frequency selection and radar detection
It is necessary to separate the mechanisms of dynamic frequency selection and radar detection:
- The dynamic frequency selection implementation require the available frequency channels scanning and the selection of the least noisy channel. Thus, the wireless data transmission systems distribution over the frequency spectrum is performed.
- A radar detection mechanism is necessary to a ban the use using of frequency channels that radars operate on. Thus, the DFS technology retains the possibility of using such channels by broadband systems, in case they are immediately released when radar operation is detected.
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The limitations in InfiNet devices can be performed by the license which includes the set of frequencies used in for the configuration and the presence of the radar detection option. A license may be issued in accordance with the regulations for a particular territory.
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- Turn on the device.
- Sequential channel scanning in accordance with the frequency grid. The scanning result is a filled DFS table, in which each channel corresponds to the level of the detected interference signal.
- The maximum signal level for each frequency channel is recorded in the DFS table. To eliminate false positives, when assessing the signal level, its spectral density is also taken into account.
- By default, the scan duration on each frequency channel is 3 seconds, this parameter is configurable.
- The total scan duration depends on the number of channels in the frequency grid.
- Analyze the DFS table and select the frequency channel with the lowest signal level.
- Set the selected channel center frequency as the operating center frequency of the wireless device.
- Establishing a link with subscriber devices.
- Data transmission.
- Establishing a link with subscriber devices.
- After 24 hours, rescan and reselect the frequency (steps 2-4). User can manually set the re-scanning time.
An example of the dynamic frequency selection algorithm is shown in the video 1.
The base station (BS) sector and the subscriber (CPE) are installed and configured to establish a wireless link between the two buildings, and the dynamic frequency selection support is activated on the BS. After turning on, the BS starts a sequential available frequency channels scanning, fill adding the signal levels in the DFS table the signal levels. The table has the following form:
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The DFS mechanism disadvantage is the inability to quickly assess the radio parameters and timely change the operating frequency in accordance to the situation on the air. First solution is to make scanning the air more frequent, however, it should be understood that the time spent on updating information about the radio parameters is not used to transmit data, i.e. communication system performance decreases.
InfiNet devices use proprietary technology called Instant DFS, which allows to obtain current information about the radio state, without breaking the connection.
Instant DFS
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operation principles
Instant DFS operation principle is similar to the described DFS algorithm, but it has the following differences:
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