12
Oct
2016

Critical Congestion in the Unlicensed Bands

I was lucky enough to work in Chicago for a short period in my early twenties.  It’s a great city with some fantastic infrastructure.  Water resources are the chief reason for the city’s early success.  The Great Lakes and the Chicago River provided a transport link to the interior, supplied city’s water needs and removed unwanted waste products.  The city boomed and has become and international hub for culture, finance, commerce, industry, technology, telecommunications, and transportation.

However, it hasn’t always been plain sailing.  As happened in many cities around the world, the same shared water resources that drove the city’s growth became the source of huge problems.  Sewage and wastewater drained into the river and hence to the lake, the city’s chief source of drinking water.  Panic ensued in 1885 when a huge storm washed refuse from the river out towards the drinking-water intakes, with fears of an impending cholera epidemic.

The William Dever(L) and Carter Harrison water intake crib (R) connected by a footbridge in Lake Michigan with Downtown Chicago in the background. (Photo: David B. Gleason)

One hundred and thirty years later, I am reminded of this story when I look at how we currently share our spectrum, particularly in the unlicensed Industrial Scientific and Medical (ISM) Band.  Over the last decade and a half, there has been a huge proliferation in wireless devices using this shared resource.  Examples include Wi-Fi networks, Bluetooth devices, wireless video senders, cordless phones and even Google’s Project Loon.

With the abundance of devices, the quality of the ISM bands has steadily deteriorated.  Just ask your friends and neighbours what they think of their home and office Wi-Fi systems. I have noticed with a little amusement how the wireless mouse in our boardroom has steadily advanced towards computer over the years, its range reduced by interference from nearby devices.  And still the number of devices mushrooms.  In most cities, nearly every cable TV box now comes with its own Wi-Fi hub for both public and private use, particularly to help data offload to reduce MVNO costs.  As range reduces, more range extenders are deployed to get one-up on neighbouring devices.  Nearly every smartphone can now be its own Wi-Fi hotspot and you can see just how significant this is by doing a scan in any public area. And now mobile operators are about to pile in with LTE-Unlicensed (LTE-U) or Licensed Assisted Access (LAA).

An interim fix has been to move to the 5GHz band.  The bands are now so congested that many major device manufacturers recommend that the 2.4GHz band not be used anymore. While the propagation characteristics at 5GHz limit range, the band is cleaner and has less interference.  At least for the time being.  Given that there is much more bandwidth at 5GHz, devices such as 802.11ac access points are expanding their channels to fill the available space.  There is now talk of coordinating with weather-RADAR to expand into that band, which won’t be cheap.

Have no doubt, a crunch is coming.  The UK regulator, Ofcom, has predicted that the unlicensed band will become critically congested by 2020.  Before this crunch comes changes are needed.  These changes will require a more intelligent use of spectrum by the devices themselves, a method of coordination so that such devices don’t talk over each other and the release of new spectrum.  In the meantime, those of us who use the existing spectrum need to be more efficient.  Put careful consideration into how our designs impact the radio environment.  Remember more hardware isn’t always better if we can manage interference levels properly.

Incidentally, Chicago’s problem was solved by reversing the flow of the river so that it drained through a canal into the Mississippi River and on into the Gulf of Mexico over 1,000 miles away. In 1999, the system was named a Civil Engineering Monument of the Millennium by the American Society of Civil Engineers (ASCE), showing that when problems arise, engineering can always find a way.  Now they just need to figure out how to stop the Great Lakes from being drained away down the same system.

Can engineering resolve unlicensed band congestion issue today? In short yes, to a degree, however radical changes will be needed to resolve this issue into the future.

– Seán