The DARPA Spectrum Challenge

darpaDARPA (the Defense Advanced Research Projects Agency) has launched a grant challenge to find a way to more efficiently use spectrum in the US. The prize is called the Spectrum Collaboration Challenge (SC2) and DARPA is offering a $2 million reward to whoever comes up with the best way to adapt in real-time to congested spectrum conditions while maximizing the use of our spectrum. The winner of the challenge won’t be a solution that dominates the use of spectrum, but will instead be looking at solutions that collaboratively share spectrum in the best manner between multiple users.

DARPA assumes that it’s going to require artificial intelligence to be able to make real-time decisions about spectrum sharing. They realize there is no easy answer and so the competition will start in 2017 and last until 2020. What is probably the coolest thing about the challenge is that DARPA is creating a large wireless test-bed they are calling the Colosseum that is going to let participants try out their ideas. This will provide researchers with remote capabilities to conduct experiments in simulated real-life environments such as a busy urban street or a battlefield (which is primary the main reason they are interested in this).

It’s a great idea because our spectrum in this country is certainly a mess. There are certain bands of spectrum that are used very heavily and other spectrum that lies fallow and unused. Further, the FCC has chopped most spectrum up into discrete channels and provided buffers between channels that go largely unused.

What really makes spectrum a challenge is that different bands are ‘owned’ by different parties and the whole point of buying spectrum from the FCC is for the buyer to use it in almost any way that makes sense to them. But the consequence of spectrum ownership is that huge swaths of spectrum are unused or at least unusable by everybody except the spectrum owner. But one would think in a battlefield situation that just about any spectrum can be used without worrying about the rules.

And while any solution that is found will probably benefit the military more than anybody else, there is still a huge amount of good that could be done with better spectrum collaboration. Certainly spectrum owners could make some or all of the spectrum they control open to collaborative sharing, for some sort of compensation.

A lot of people might look at this idea and think that this could mean great things for cellphones and other mobile communications. But cellphones have a whole different issue that makes them a very poor candidate for sharing in too many different swaths of spectrum. A primary issue goal for cellphones is power conservation and it costs a lot of power to operate antennas in too many frequencies.

Most cellphone makers today limit a phone to only using a few different frequencies at once. This is one of the reasons for the huge variance people get in 3G and 4G data rates – many of the phones on the market only look at a few different frequencies, to the detriment of how much bandwidth can be downloaded at any one time. This is something that cellphone makers don’t talk about and you have to look deep into a cellphone’s specifications to understand the frequency capabilities of a given handset.

There are software defined radios today that are a lot larger than handsets and which can be easily tuned to different frequencies. But this is something that is incredibly challenging today to do on the fly and to do accurately. And of course, to do what DARPA has in mind means coordination and collaboration so that a given sender and receiver are using the same frequencies at the same time. It’s the kind of challenge that can make a wireless engineer’s head hurt and it probably will take an AI to be able to handle the complexities involved in truly sharing multiple spectrum bands in real time.