Imagine - What if you had to send 40 megabytes of data every single second (about the same amount of data as 10 YouTube videos streaming at the same time) over a distance of 100 miles wirelessly. To complicate matters, one of the transmitters can’t be bigger than a pack of chewing gum. And it’s going to be traveling onboard an object 30,000 feet overhead at double the speed of sound. Ohh, also your miniaturized, high-powered transmitters must convey all that data on some of the trickier frequencies of the electromagnetic spectrum.
A group of researchers at the University of Kansas plan to do just that! They have been awarded a $2.5 million contract from the National Spectrum Consortium to develop a new generation of communication technologies for airborne vehicles on U.S. test ranges. Their engineering work will help remake test-flight communications in the wake of a Federal Communications Commission auction of frequencies once used by the government.
The electromagnetic spectrum is a limited natural resource that, like other types of resources is valuable, scarce and highly in demand. A number of wireless network operators had told the FCC that the spectrum was not being used efficiently. The wanted to use it better and were willing to pay for it. The FCC agreed to auction this spectrum and expected to bring in $10 to $15 billion from this, however they ended up they ended up earning more than $40 billion!
Of the $40 Billion, $500 million was as set aside to relocate some government users to less-desirable real estate on the spectrum, funding projects that include the project spearheaded by Perrins and KU colleague Andy Gill, along with collaborators at Brigham Young University and students at both institutions. Their task is to utilize higher frequencies that don’t penetrate buildings as well as lower segments of the electromagnetic spectrum.
The KU research will optimize communications at about 5 GHz, roughly three or four times farther up the frequency dial than previous communications at U.S. test ranges. Initially, the work will take place in labs at KU and later will move to the Air Force Test Center at Edwards Air Force Base in California, perhaps most famous as the setting where Chuck Yeager broke the sound barrier in 1947. There, equipment developed in Lawrence will be tested aboard a Beechcraft C-12 Huron, a twin-engine turboprop aircraft.
The project has to deal with efficiency. Researchers are trying to pack more information into the same amount of space as before. It’s a little like putting a multistory building on a parcel of land instead of a single-level structure, using a more efficient type of modulation than they’ve used previously. The power consumption is going to be different, as it’s going to take a more powerful signal to propagate through the airwaves.
Because transmissions at 5 GHz can be problematic, a key element of the research is to combine higher efficiency modulation with technology known as forward error control codes. Error control coding is a way to protect the bits in the signal, so when errors occur they can be detected and corrected automatically. It’s an added redundancy. For instance, when we’re speaking using the English language, not every sound is a word, and not all words form a valid sentence. Because of that structure, if a word gets erased from a sentence, we still can guess what’s missing. That’s what you do with error control coding. You add patterns that when they get disrupted you can correct them on the other side - and that allows you to communicate with a weaker signal.
The communications between test vehicles and ground-based receivers will carry much of the same kind of information that would be recorded to an aircraft’s flight recorder, revealing aircraft performance and flight characteristics following a crash or malfunction. This will transmit the kind of data that a black box harvests, but in routine flight that data typically isn’t sent to the ground because there are too many planes, there’s not enough spectrum for that to take place. But at a test range, because the test articles are in development, scientists will need to get data to the ground immediately.
