Sunday, 23 September 2012

WiFi Channels On The 5GHz Band In The UK

(Note: I now have a whitepaper on this topic you may find useful: link)

One of the issues of not being in the 'good ole U S of A' is that most of the study and reference literature that is available around WiFi is USA-centric.

This means that when you are trying to get your head around the various spectrum restrictions that apply to the unlicensed 5GHz band that is used by 802.11a/n, there is little off-the-shelf material that applies to regulatory domains  outside of the USA.

Most material that can be found online tends to advise the reader to check the restrictions of their own regulatory domain and any local country restrictions that apply. This is actually a bit trickier than it sounds (in my experience).

I'm based in the UK and recently decide to embark on a quest to find the actual source regulations that apply to the use of the 5Ghz band by (unlicensed) WiFi equipment.

Although they are a little thin on the ground, I managed to find a couple of very good articles which talk about the use of 5Ghz in the UK. You can take a look at them here:

Although the articles are very good, I was keen to find the source materials for the regulations governing 5GHz use (for unlicensed WiFi) in the UK.

After some digging around, I finally found that the use of RF spectrum in the UK is dictated by an independent regulator called Ofcom. They have a number of documents called 'Interface Requirements' which spell out the various regulations that have to be adhered to for various parts of the RF spectrum.

The document covering the use of 5GHz 'RLANs' (that is Ofcom parlance for WLANs) is titled: IR 2006 - Wireless Access Systems (WAS) including RLANs operating in the 5150-5725 MHz band.

In this document, it spells out (in summary) that the UK's (unlicensed) 5GHz band is broken up in to 2 bands:

  • Band A : 5150 - 5350 MHz (channels 36 - 64)
  • Band B: 5470 - 5725 MHz (channels 100 - 140)
Band A channels can only be used indoors. Band B channels may be used indoors or outdoors and may be used at slightly higher power levels if required.

However, the IR 2006 document also refers to an ETSI document for further clarification around the use of the 5GHz band, particularly if you're interested in areas such as TPC and DFS. This document has the rather dry title of :

Broadband Radio Access Networks (BRAN); 5 GHz high performance RLAN; Harmonized EN covering the essential requirements of article 3.2 of the R&TTE Directive

This document also has the rather snappy designation of : ETSI EN 301 893 V1.7.1 (2012-06). (Note there are several versions of this document floating around from previous incarnations, but I'm pretty sure v1.7.1 is the current (at the time of writing) ratified document).

My main interest in reading the ETSI document was to try to understand which channels are subject to DFS, as this is going to be an interesting area in the near future with the anticipated significant rise in uptake of WiFi kit on 5GHz. I have read varying reports on which channels are subject to DFS in the UK  and wanted to find a definitive document which details DFS restrictions in the UK.

If I have read the document correctly (and it is quite a hefty tome to get to grips with), it looks like channels 36 to 48 are not subject to DFS in the UK, but all other channels are required to implement DFS safeguards. This was quite a surprise, as I had previously believed that channels 36 - 64 were not subject to DFS (as they are designated for indoor use), with all remaining (outdoor) channels being subject to DFS.

I spent quite a while looking at both of the documents discussed above and came up with the following tabulated data, after cross referencing them both. (Disclaimer - check the current versions of the documents from both Ofcom & ETSI - things may have changed since I wrote this):


BandChannelCentre
Freq
(Mhz)
UsageMax Power
With TPC
Max Power Without TPCDFS
A365180Indoor23dBm (200mW)23dBm (200mW)No
A405200Indoor23dBm
(200mW)
23dBm (200mW)No
A445220Indoor23dBm
(200mW)
23dBm (200mW)No
A485240Indoor23dBm
(200mW)
23dBm (200mW)No
A525260Indoor23dBm
(200mW)
20dBm (100mW)Yes
A565280Indoor23dBm
(200mW)
20dBm (100mW)Yes
A605300Indoor23dBm
(200mW)
20dBm (100mW)Yes
A645320Indoor23dBm
(200mW)
20dBm (100mW)Yes
B1005500Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1045520Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1085540Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1125560Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1165580Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1205600Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1245620Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1285640Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1325660Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1365680Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes
B1405700Indoor/Outdoor30dBm (1W)27dBm (500mW)Yes


In summary, this appears to give us 19 channels to use on the 5GHz band in the UK for unlicensed WiFi.

Unfortunately, there seems to be a trend among some access point vendors to not support channels 120 - 128. I can't find any Ofcom or ETSI regulations that apply to this, but it may be due to some FCC regulations which have perhaps found their way in to vendor implementations for those of us in the rest of the world (see this article: http://www.cwnp.com/cwnp_wifi_blog/fcc-laying-down-the-unii-law/).

So, for whatever reason, it looks like many vendors have restricted us to 16 x 5GHz channels, which is still a nice large number to play with, but with the advent of increased-width bonded channels in the forthcoming 802.11ac standard, I think we're going to miss those extra channels.

One other area I'm intrigued by is definitions around the terms 'indoor' or 'outdoor' use. With the rise in WiFi deployments in sports arena, temporary venues etc. the lines between indoor and outdoor become a little blurred. For instance, is a temporary marquee with an AP installed outdoors? What about a football stadium? What about a stadium with a roof? If anyone has any official definitions for indoor and outdoor form a WiFi standards or regulatory RF point of view, I'd be interested to hear them.

Hopefully, this article may be of interest to those trying to find out more about 5GHz WiFi in the UK (and perhaps Europe), even if it only points you in the right direction to find your own information - I'm sure there are going to be many more conversations and queries raised around 5GHz its popularity increases as more consumer devices gain 5GHz support.

If you have feedback or additional information about this topic, please feel free to post updates, corrections and comments - I don't claim to be an authoritative resource on this topic, so please feel free to correct me if required.

Nigel.

Update: I've now created a white paper which details 5GHz usage for WiFi in the UK. Find it here