During my work in TAC I have seen a lot of configs with improper usage of EIRP for APs with external antennas.
Basically for the APS with bult-in antennas, the system knows about the antenna gain and calculates properly the EIRP, not exceeding the regulations of the region.
When we use external antennas for indoor or outdoor environment, the system doesn’t know which antenna is installed. If that parameter is omitted, than the AP transmits with the power excluding the true value of the antenna gain. As a final result the EIRP sometimes exceeds the regulations.
WLC#show wireless regulatory device-type ap7522 pl --------------------------------------------------------------------------------------------------- # Channel Set Power(mW) Power (dBm) Placement DFS CAC(mins) TPC ---------------------------------------------------------------------------------------------------- 1 1-13 100 20 Indoor/Outdoor NA NA NA 2 36-48 200 23 Indoor Not Required 0 Not Required 3 52-64 200 23 Indoor Required 1 Required 4 52-64 100 20 Indoor Required 1 Not Required 5 100-116 1000 30 Indoor/Outdoor Required 1 Required 6 100-116 500 27 Indoor/Outdoor Required 1 Not Required 7 120-128 1000 30 Indoor/Outdoor Required 10 Required 8 120-128 500 27 Indoor/Outdoor Required 10 Not Required 9 132-140 1000 30 Indoor/Outdoor Required 1 Required 10 132-140 500 27 Indoor/Outdoor Required 1 Not Required ----------------------------------------------------------------------------------------------------
Example:
The AP on channel 132 with power 30 transmitting with no knowledge of antenna gain. Antenna in use is 14dBi panel antenna. The EIRP will be around 44dBm (30+14-loss on cable) which far exceeds the ETSI regulations.
In 802.11n/ac’ APs there will be also MIMO gain based on the number of chains, therefore the initial power will be lower.
We will now focus how the issue might be resolved for each vendor.
Cisco (firmware version 8.0.152.0):
Wireless -> 802.11a/n/ac or 802.11b/g/n -> AP -> configure
At the bottom there is a configuration for the antenna gain. Strange thing is Cisco uses 0.5 dBi as an unit, therefore to use 3.5dBi value, 7 x 0.5 dBi shall be used.
As antenna gain is different for each band, 2 different entries should be configured, one for 802.11b/g/n radio and second one for 802.11a/n/ac radio.
Aruba (firmware version 8.2.1.0):
In Aruba’s world, an AP needs to be first provisioned with the basic networking settings and AP group.
An AP with an external antenna will not be provisioned unless the antenna gain values are entered.
As an example, taken from the user guide for version 8.3.x:
Extreme Wireless (firmware version 10.41.06.0013):
The configuration is in the AP settings:
An Extreme AP with external antennas’ SKU won’t start its radios and won’t broadcast any SSID if there are no antennas selected in the settings above.
What is interesting, Extreme provides a list of all available Extreme antennas for that specific SKU.
Extreme Wireless WING (firmware version 5.9.1.0):
The AP(s) might be configured as device override (single AP) or profile (the same AP SKU). The configuration needs to be done separately per each radio.
Summary:
Aruba and Extreme Wireless made systems, in which there is no possibility to have an AP with external antennas broadcasting SSIDs without configured antenna gain.
This aspect of the configuration of the wireless system shouldn’t be skipped as it might cause problems related to exceeding regulations and unintentionally broadcasting SSIDs in a greater distance than expected.
