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Slave DFS implementation

A slave device (Client/STA device) whose maximum Tx power is greater than or equal to 200 mW has to follow DFS. In the current implementation the driver does not automatically detect it, if the maximum Tx power for the client is greater than or equal to 200 mW. The following command enables or disables client/STA mode DFS.

cfg80211tool wifiX staDFSEn 0/1

Configuration

There are a few parameters that can be affected during the process of loading the DFS module

  • domainoverride This parameter can take one of the following values: 0 = Uninitialized (default) 1 = FCC Domain (FCC3, US) 2 = ETSI Domain (Europe) 3 = Japan Domain
  • usenol Setting this parameter to 0 causes the DFS module to not change (vacate) a channel even if RADAR is detected. This is used only for DFS certification and test purposes. On 11ax chipsets, it is also necessary to enter the wifitool ath0 setUnitTestCmd 43 3 0 1 0x8002 command after setting usenol as 0 to enable packets to data packets to be processed by the AP.
  • countrycode This parameter can be used to set the country code. If this parameter is set, this value is used to automatically select the corresponding DFS domain. Use country code 0x1ff for demo channels

Dynamic frequency selection (DFS)

Dynamic Frequency Selection (DFS) is a mechanism that allows unlicensed devices to use the 5 GHz frequency bands already allocated to RADAR systems without causing interference to those RADARs. The concept of DFS is to have the unlicensed device detect the presence of a RADAR system on the channel they are using and, if the level of the RADAR is above a certain threshold, vacate that channel and select an alternate channel. The objectives of DFS are:

  1. Coexist in 5 GHz channels with RADAR
  2. Perform uniform loading or spreading across the spectrum. There are many channels in the 5 GHz bandwidth in which wireless device can operate. DFS also requires random channel selection so that channels are uniformly utilized across the spectrum. Compliant operation in the 5 GHz band requires that access point equipment detect the presence of in-band RADAR signals. Generally these signals take the form of periodic narrow band pulses of length 1 – 100 µs, or chirp pulses of 50 – 100 µs. In the event of a RADAR detection, the access point is required to vacate the RADAR co-existed channel (within 10 s), and hop to a different channel. This section of the document describes the DFS software implementation For more detailed descriptions of the specific regulatory requirements, please refer to the relevant documents from IEEE (802.11h), ETSI, ITU and other regulatory bodies.