Aruba Wireless and 5.8GHz Band C in UK

On 13 July 2017 Ofcom announced that from 7th August 2017 the regulations governing the 5.8GHz Band C in the UK would be changed to allow Wi-Fi use. This meant that an additional 125MHz of spectrum would now be available without requiring a license.
The decision is available here.

In summary the change specified in IR2030/1/23 is:

• 5 new 20Mhz Channels: 149, 153, 157, 161 and 165
• 200mW (23dBm) max EIRP
• Requires DFS and TPC
• Can be used indoor and outdoor

On Aruba controllers and Instant APs the channels and powers are controlled by the DRT (Downloadable Regulatory Table) and it was with some expectation that following the Ofcom ruling Aruba would now allow these. And lo and behold channels 149-161 are now allowed.

7c:57:3c:xx:xx:xx# show ap allowed-channels

Allowed Channels for AP Type 303 Country Code GB

------------------------------------------------

PHY Type                   Allowed Channels

--------                   ----------------

802.11g (indoor)           1 2 3 4 5 6 7 8 9 10 11 12 13

802.11a (indoor)           36 40 44 48 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140 149 153 157 161 165

802.11g (outdoor)          1 2 3 4 5 6 7 8 9 10 11 12 13

802.11a (outdoor)          100 104 108 112 116 120 124 128 132 136 140 149 153 157 161 165

802.11g 40MHz (indoor)     1-5 2-6 3-7 4-8 5-9 6-10 7-11 8-12 9-13

802.11a 40MHz (indoor)     36-40 44-48 52-56 60-64 100-104 108-112 116-120 124-128 132-136 149-153 157-161

802.11g 40MHz (outdoor)    1-5 2-6 3-7 4-8 5-9 6-10 7-11 8-12 9-13

802.11a 40MHz (outdoor)    100-104 108-112 116-120 124-128 132-136 149-153 157-161

802.11a 80MHz (indoor)     36-48 52-64 100-112 116-128 149-161

802.11a 80MHz (outdoor)    100-112 116-128 149-161

802.11a 160MHz (indoor)    None

802.11a 160MHz (outdoor)   None

802.11a (DFS)              52 56 60 64 100 104 108 112 116 120 124 128 132 136 140

However, on closer inspection of the last line (802.11a (DFS)) it seems that channels 149-161 are not listed. Also the max allowed EIRP is not 23dBm as expected (I don't know why the command says it has been deprecated as it still shows the information and I couldn't find this elsewhere):

7c:57:3c:xx:xx:xx# show ap allowed-max-EIRP

Warning: This command has been deprecated.

Max EIRP setting for AP-303

---------------------------

Channel ... 144  149   153   157   161   165

------- ... ---  ---   ---   ---   ---   ---

b       ... *    *     *     *     *     *

g/a     ... *    13.4  13.4  13.6  13.5  13.5

HT 20   ... *    13.4  13.4  13.6  13.5  13.5

HT 40   ... *    13.5  13.5  13.6  13.6  *

VHT 80  ... *    13.4  13.4  13.4  13.4  *

Note: Output truncated to for easier display

Following discussions with Aruba support it appears that rather than implement DFS and TPC in Band C they have chosen to cap the EIRP to 14dBm.

The relevent part of the regulation IR2030 is IR2030/8/3 for "Non-specific short-range devices" that permits a maximum EIRP of 25mW (14dBm) and for which interference mitigation techniques are not required.

This is the same as the harmonized ETSI specification of 25mW max EIRP as given here.

It will have to be seen whether the benefit of not requiring DFS and TPC is worth the reduction in available transmit power. In my typical campus deployment we use EIRP upto 18dBm and 15dBm for dense deployments letting ARM take care of channel assignment and power setting. Therefore it is conceivable that for certain circumstances 14dBm could be sufficient.