On Balance Mucking Around In The 5GHz Bands May Not Be A Good Idea
Reluctantly, I have had to spend a surprising amount of time getting to grips with the problems of spectrum sharing in as much as it applies to that part of it used by 802.11ac specification devices.
The problem is that right in the middle of the frequencies earmarked for WiFi, weather radar operates. This doesn't sound like a big deal, at first sight. But weather radars are immensely powerful, mostly range limited by the curve of the earth.and they are not only used for weather forecasting (thunderclouds particularly), but also used at airports to pick up windshear. Windshear might not sound particularly ominous, but in reality its pretty scary for pilots and their passengers. The effect of windshear is to reduce the lift generated by the flow of air over the wings and to reduce the airspeed, eventually to the point where the aircraft will stall. In the past this has caused some very serious air accidents.
There is a network of weather radars across large areas of the world, unless they have been upgraded to s-band units, they are prone to interference by domestic wifi routers and access points..And shipping uses c-band radar, not only ships, but harbours, shore installations and shipping control regimes, such as the Straits of Dover (which is a mass of c-band radar).
In order to make spectrum sharing work, without adversely affecting safety, three (yes 3 not 2) techniques have been specified to make sure that wifi does not cause any problems with the operation of radars. Dynamic Frequency Selection (DFS), Transmit Power Control (TPC) and the less well known and documented Channel Availability Checking (CAC).. These pretty well do what is written on the label. CAC, involves listening on a channel to check it is vacant before using it.
Unfortunately, every part of the world has slightly different rules, even the European Spectrum Management Organisation (ETSI), allows different countries to adjust the rules somewhat as they require. There are considerable variations in broadcast signal strength.
Generally speaking, part of the setup of a wifi router or access point involves specifying the device's location. This enables the onboard firmware to select the appropriate parameters for the device to operate within. There is even talk of providing devices with GPS receivers so the location is set automatically.
If end users can load third party firmware, all these safeguards can be overcome, Locations, frequencies and transmission volumes can be altered at will. Which could well become a major issue as far as safety is concerned.
Governments are not too keen on differentiating between minimal risk and risk, let alone major risk, consequently they tend to err on the safe side; they really are in a no-win situation.
I know some manufacturers are taking this very seriously, but the people who make 3rd party firmware, are thy going to be able to prevent users from creating problems?
Weighing the options, I personally don't mind steps being taken to stop users operating their equipment when it is out of specification., and I know that many have done so in the past. Currently I'm hoping that the introduction of 802.11ad will be brought forward - real soon now.