Ofcom Shun WiFi Interference Fears to Prep 2.3GHz Auction for Mobile

The communications regulator has assessed the impact for both licensed and licence-exempt uses of the 2.3GHz and 3.4GHz radio spectrum bands and found that the risk of interference with other services, such as WiFi (adjacent 2.4GHz band), did exist but wasn’t big enough to be worth worrying about.

The spectrum, which includes 40MHz in the 2.3GHz band (between 2350MHz and 2390MHz) and 150MHz above 3.4GHz (between 3410MHz and 3600MHz), was formerly used by the Ministry of Defence (MoD) but will now be repurposed for use by high and or low powered LTE (4G) based Mobile Broadband services instead.

Ofcom believes that this spectrum could be released through an auction in 2015-16 and so they’ve been busy conducting various preliminary consultations on the process. One of those is the need to assess whether releasing 2.3GHz and 3.4GHz for mobile connectivity might create problems for other services.

In particular the regulator spent a lot of time examining whether 2.3GHz would cause problems for 2.4GHz wifi networks, such as the one you have at home or in the office.

Ofcoms Statement on 2.3GHz Interference with Wi-Fi

Our technical analysis confirms a risk of interference, in specific circumstances, to both Wi-Fi routers/access points and to client devices. We identify the main source of interference as LTE base stations. Interference is most likely in urban environments where there may by a dense deployment of both LTE base stations and Wi-Fi networks. In the very worst cases, customers would not be able to use services – but it is much more likely they will experience a drop in performance, unless mitigations are applied.

Overall, the extent and severity of interference on a nationwide basis is not high: our analysis suggests only around 0.1% of households with Wi-Fi are at risk of interference (based on central assumptions). If realised, this could potentially affect around 17,400 households – assuming there was a full GB wide roll-out of LTE in the 2.3 GHz band.

For public Wi-Fi, our testing suggests that interference may affect around 6.8% of the 4,000 postcode locations where outdoor networks are established . Certain parts of the 78,000 indoor public Wi-Fi locations (around 1.4%) and the 680,000 self-contained enterprise networks in large and medium sized organisations (around 1.2%) may be affected.

But if people do happen to suffer from this interference then Ofcom recommends a solution of “simply moving [the] equipment” away to somewhere else, such as “moving routers away from a window or changing the position in which a mobile device is held“. In other cases it notes that some Wi-Fi kit may be able to access the alternative 5GHz Wi-Fi band, which is true but this would hurt the concurrent dual-band transmission speeds.

Ofcom also examined the impact of both bands upon satellite communications, Maritime radar and Aeronautical radar to find only a very low or limited impact and “in almost all cases, appropriate mitigations can be applied through expected market developments“.

But the regulator did recognise that its analysis had only focussed “necessarily” upon a small number of representative devices, which it said left some room for uncertainty. As a result we have today’s new coexistence consultation, which will run until Thursday 15th May 2014.