Scaling and increasing the performance of the wireless communication systems in the 5 GHz frequency range required an increase in the allowed frequency channels number by additionally using the channels that were initially assigned only for military and meteorological radars. To reduce the impact of the wireless broadband systems on radars, the data exchange protocol included requirements for detecting radar signals and immediately clearing the operating frequency.

The implementation of the radar detection mechanisms was related to the air scanning methods and to the transition between the frequency channels. These methods were included in the requirements for the operation of the wireless systems and were called dynamic frequency selection (DFS).

Dynamic frequency selection and radar detection

It is necessary to point out the differences between the dynamic frequency selection technology and the radar detection mechanism:

Regulatory requirements

Regulatory requirements for wireless communication systems vary by country. The most common requirements for the implementation of dynamic frequency selection and radar detection, were created by the Federal Communications Commission (FCC) and by the European Telecommunications Standards Institute (ETSI). It is described by following standards:

Detection Requirements

CAC (Channel Availability Check)

Off-Channel CAC (Off-channel Channel Availability Check)

In-service monitoring

The process by which the operating channel is monitored for the presence of radar signals; the detection thresholds are the same as in case of CAC.

In-service monitoring is performed in between each data transmission and its duration is of µs order.

Detection probability


Detection probability

Channels whose nominal bandwidth falls partly or completely within the 5600 – 5650 МHz band

Other channels

CAC / Off-Channel CAC

99,99 %

60 %

In-Service Monitoring


60 %

Response requirements

Channel shutdown

Non-occupancy period

Time values



Channel Availability Check Time

60 s*

Minimum Off-Channel CAC Time

6 minutes**

Maximum Off-Channel CAC Time

4 hours**

Channel Move Time

10 s

Channel Closing Transmission Time

1 s

Non-Occupancy Period

30 minutes

* - For channels whose nominal bandwidth falls completely or partly within the band 5 600 – 5 650 МHz, the value shall be 10 minutes.

** - For channels whose nominal bandwidth falls completely or partly within the band 5 600 – 5 650 МHz, the Off-Channel CAC Time shall be within the range 1 h to 24 h.

Infinet approach

The standards specify the performance requirements for the wireless systems in order to avoid interferences with the radars, but do not specify how to practically implement DFS. 

For the Infinet devices, the regulatory limitations are performed by license which includes the set of frequencies and by the presence of the radar detection configuration option. A license may be issued in accordance with the regulations for a particular territory. For the InfiLINK Evolution / InfiMAN Evolution and Quanta 5 families devices restrictions are determined by the selected regulatory domain, which can be changed in the link settings section (if the appropriate license is installed).

DFS operation principles

The dynamic frequency selection algorithm consists of the following steps:

  1. Turn on the device.
  2. Sequential channel scanning in accordance with the frequency grid. The scanning results are filled in the DFS table, where each channel is associated with the level of the detected signal.
    1. 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.
    2. By default, the scan duration on each frequency channel is 3 seconds and this parameter is configurable.
    3. The total scan duration depends on the number of channels in the frequency grid.
  3. Analyze the DFS table and select the frequency channel with the lowest signal level.
  4. Set the selected channel center frequency as the operating frequency of the wireless device.
    1. Establishing a link with the subscriber devices.
    2. Data transmission.
    3. If the SNR value of the operational channel decreases below a certain threshold, another frequency channel with the lowest level of interference sets as operational.
  5. After 24 hours, rescan and reselect the frequency (steps 2-4). The re-scanning time can be manually set.

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 two buildings and the dynamic frequency selection feature is activated on the BS. After power-up, the BS begins a sequential available frequency channels scanning, adding the signal levels in the DFS table. The table has the following form:

Frequency channelSignal level, dBm

The BS device analyzes the table and selects the frequency channel with the minimum signal level value, i.e. channel F3. The selected channel center frequency is set as operational.

The center frequency changing causes an interruption in the wireless connection. The CPE device starts to look over the allowed frequency channels list, while searching for a BS device. After the BS is detected, the wireless devices perform the association, establish a link, and the data exchange resumes.

Video 1 - Dynamic frequency selection algorithm

The radar detection principle

The radar detection algorithm operation can be described by the following steps:

  1. Turning on the device.
  2. Sequential frequency channel scanning. The device scans the air in accordance with the configured frequency grid.
    1. Signals over the air are checked whether they belong to the known radars.
    2. The channel availability check time is 60 seconds, for a channel within 5600 - 5650 MHz frequency grid - 10 minutes.
    3. In case a radar is detected on the channel being checked, system switches to the next channel with minimal interference.
  3. Frequency channels with radar detected are marked as inaccessible for use.
    1. The channel is excluded from the table for 30 minutes.
  4. The next scan repeats the procedure for radar detection (steps 2-3).
    1. The radar detection procedure is performed simultaneously with the DFS mechanism operation.

An example of the radar detection algorithm is shown in the video 2.

The BS and the CPE are installed and configured to establish a wireless link between two buildings and the BS supports the dynamic frequency selection mechanism with radar detection. A meteorological radar is installed on the building next to the BS and using frequency channel F3.

Same as in the previous example (see video 1), the BS starts a sequential available frequency channels scanning and fills in the table. During the F3 frequency channel scanning the BS detects the radar operation. Although the signal level in channel F3 is lower than in other channels, it is excluded from the decision-making process. Thus, the updated table looks as follows and the BS sets F1 as the operating frequency:

Frequency channelSignal level, dBm

Video 2 - Radar detection algorithm

Instant DFS

The DFS mechanism disadvantage is the inability to quickly assess the radio parameters and timely change the operating frequency in accordance to the situation. In addition, when a radar is detected, a new channel availability check is performed within 60 seconds. During this time, transmission is interrupted and is not restored until it is switched to a new channel with the lowest interference level and is free from radar.

A first solution is to perform the scan more frequently, however, it should be understood that the time spent on updating the information about the radio parameters is not used to transmit data, i.e. the communication system performance decreases.

Infinet devices use a proprietary technology called Instant DFS, which allows to obtain current information about the radio state, without interrupting the connection.

Instant DFS operation principles

The Instant DFS operation principle is similar to the described DFS algorithm, but it has the following differences:

An example of the proprietary Instant DFS mechanism is shown in the video 3:

Video 3 - Proprietary Instant DFS algorithm

Instant DFS application patterns

Devices with Instant DFS support can be used in point-to-point and point-to-multipoint topologies. Please note that the scan results are valid only for the received signal, therefore:

Instant DFS implementation in the InfiNet devices

Instant DFS proprietary technology support is implemented for the InfiLINK 2x2 and InfiMAN 2x2 families operating in the 5 GHz frequency band through the additional radio module installation. Lowercase letter "s" in the device part number indicates the presence of the second radio module, for example, R5000-Mmxbs/5.300.2x500.2x16.

All InfiLINK Evolution / InfiMAN Evolution, InfiLINK XG and Quanta 5 families devices operating in the 5 GHz frequency band support the Instant DFS technology.

Additional information

  1. DFS configuration process for InfiLINK 2x2 and InfiMAN 2x2 family devices (web / CLI)
  2. DFS configuration process for InfiLINK Evolution and InfiMAN Evolution family devices (web / CLI)
  3. Online course "InfiLINK 2x2 / InfiMAN 2x2: Initial Link Configuration and Installation"
  4. DFS configuration process for the InfiLINK XG family devices (web / CLI)
  5. DFS configuration process for the Quanta 5 family devices (web)
  6. Online course "InfiLINK XG Family Product"
  7. Units Numbering Convention