Channel Availability Check (CAC) and DFS channel
The CAC test applies to devices that are capable of detecting radar signals. In this test, the radio scans a target dynamic frequency selection (DFS) channel for radar signals for 60 seconds (typically – you can increase or decrease the timespan as required).
After the 60-second scan, if no radar signals are detected, the radio can transmit on the target DFS channel. During the 60-second scan, if radar signals are detected on a target DFS channel, the radio must move to another DFS channel and restart the 60-second CAC.
To prove that the CAC mechanism works, the radio will be set to start the CAC and the test house will inject a radar test signal 6 seconds after CAC has started. The passing criteria is determined by monitoring whether the radio moves to another channel.
The test fails when the radio starts transmitting after the 60 seconds have elapsed on the DFS channel that the radar signal was injected on. This test is then repeated with the radar test signal injection occurring 54 seconds after the CAC has started.
WL Commands
Table 1. WL Commands to be Used
|
Commands |
Description |
|
wl down |
Sets the radio to standby mode |
|
wl ap 1 |
Enables the softAP |
|
wl mpc 0 |
Disables the minimum power consumption |
|
wl country US/0 |
Recommended country code – US/0 for FCC, BE/4 for EU, JP/972 for Japan |
|
wl dfs_preism X |
Acts as a timer-counter. It will wait for X-amount of time (in seconds) listening for the radar before initiating a network. The default value is “-1” which corresponds to 60 seconds wait time. |
|
wl spect 1 |
Enables 802.11H for DFS testing |
|
wl chanspec 100/20 |
Controls the operating channel of the radio. Set 100/40 for 40M Hz and 100/80 for 80 MHz |
|
wl up |
Turns ON the radio |
|
wl radar 1 |
Enables the radar detection |
|
wl ssid DFS_AP |
Sets the SSID to identify radio as DFS_AP |
|
wl dfs_status |
Gets the status of DFS. It shows the time elapsed in milliseconds |
|
wl chan_info |
Lists the channels, indicating whether the channel is passive or active |
Output
- t = 0 secs after wl up – channel 100/20
The channel 100/20 is still Passive, which indicates that the radar detection scanning is in progress.
The wl dfs_status shows the time elapsed (in msec) for radar detection. - t = 60 secs after wl up
After the 60-second scan time, channel 100/20 becomes Active, which means that no radar was detected and AP can transmit the beacons on that particular channel.
Note: The WLAN radio should be capable of radar detection, which means that the CAC test using WL command, wl radar 0/1 should pass without any error.
Reference
AN225347 – Wi-Fi CLM Regulatory CLM Manual – section 4.2.6