Showing posts with the label DFS

The 5GHz “Problem” For Wi-Fi Networks: DFS

Wi-Fi networking provides us with 2 bands for the operation of wireless LAN networks: the 2.4Ghz band and the 5GHz band. The 2.4GHz band has a reputation of being something of a “sewer” of a band, due to its limited number of usable channels, the number of Wi-Fi devices already using the band, and the high levels of non-Wi-Fi interference that it experiences. Many wireless LAN professionals will generally advise that you put your “important stuff” on the 5GHz band whenever possible. 5GHz has far more channels available, a corresponding lower number of devices per channel, and generally suffers much lower non-Wi-Fi interference. However, beneath the headline of “2.4Ghz = bad, 5Ghz = good”, there lurks a shadowy figure that can be troublesome if you’re not aware of its potential impact: DFS. Background Wi-Fi networks operate in areas of RF spectrum that require no licence to operate. This is in contrast to many other areas of the radio spectrum that generally require some form of (p

Updated White Paper on Licence-Exempt Spectrum in the 5GHz band for Wireless LANs in the UK

For the past few years, I've maintained a white paper on the use of the 5GHz spectrum for Wi-Fi networks here in the UK. As Wi-Fi text books tend to focus on the spectrum available in the USA, I put this document together to clarify how 5GHz spectrum may be used in the UK. Following the release of a Voluntary National Specification document by Ofcom in August 2017 ( VNS 2030/8/3 ), additional channels became available for use in the UK on 5GHz. As we now have additional spectrum, it's time for an update to my white paper to detail the new spectrum that is available. Prior to updating the white paper, I published a summary sheet that shows the new spectrum allocation. This can be obtained obtain from my previous blog article:  UK 5GHz WLAN Spectrum Allocation (August 2017)  (this is definitely one to print off and laminate). I have now completed my updates to the white paper, which I am pleased to share with you now. Note that in addition to adding the new spectrum det

5GHz in the UK White Paper (Version 2)

[Note: The information in this white paper has been superseded. Check out my updated white paper: ] I decided it was time to update my white paper detailing the use of the 5GHz band here in the UK for wireless LANs. I've tidied a few things up and added some information around 802.11ac channel planning within the constraints of UK 5GHz spectrum. You can download the whitepaper from here: PDF download Google docs Scribd

802.11ac & 5GHz: The Emperors New Clothes? - Part 1

The WiFi industry has been buzzing with excitement around the recently ratified 802.11ac standard. The promise of higher speeds, lower battery usage for mobile devices and the enforced move to the higher-capacity 5GHz band is enough to put a smile on the face of even the most curmudgeonly members of the WiFi fraternity. I've been giving some serious thought recently to what the best approaches might be in terms of designing and deploying 802.11ac networks. There are obviously challenges as we move through the transition from legacy standards to the shiny new 802.11ac standard:  new cabling requirements for higher uplink speeds to 802.11ac APs Increased power requirements for our 802.11ac APs accommodating the mix of new and legacy clients figuring out exactly how we plan our channels for the brave new world of 802.11ac The 802.11ac standard mandates that access points and clients using the new standard will only be supported on the 5GHz band, which is great news

5GHz - 3 Missing Channels in Europe

Last year, I put up a  posting  which highlighted the fact that here in the UK (and I suspect all of Europe) we often have 3 channels missing from our allocation of unlicensed channels in the 5GHz band.  Looking at many manufacturer data sheets, channels 120, 124 and 128 are often shown as not being supported. This is despite the fact that they are allocated for use by local regulatory bodies (OFCOM here in the UK). I recently posted a question about this on a partner forum of a major WiFi vendor that I deal with and finally got a definitive answer on this. In this post, I'll share my findings. The reason that these particular channels (120 - 128) receive special treatment is that they occupy frequencies that are used by weather radar systems. WiFi systems have to be very careful not to interfere with those systems during their normal operation. Therefore, WiFi equipment has some additional checks and tests imposed on it to make sure that it does not inadvertently cause any int

The Missing Channels on 5GHz in the UK : 120, 124, 128

In my recent article : ' WiFi Channels On The 5GHz Band In The UK ', I noted that although the 5GHz channels 120, 124 and 128 are unlicensed channels available for use by WiFi equipment in the UK, it appears that a few major WiFi equipment manufacturers do not allow their use (in the UK or EU). I spoke with a major vendor representative today who advised me that the 3 channels are available for use, but that an update to the ETSI standard  301 893 v1.5.1  introduced some detection techniques for various military equipment used in the EU. However, many access points that were already manufactured (or using chip-sets that had already been manufactured) did not support the granularity of detection that is required for this equipment. So, it was decided to simply disable support for the affected channels. Apparently, later APs which use an updated chip-set will not be subject to the same limitations (once a few firmware updates are sorted out). I had a poke about in the stand