The expanded access to airwaves offers a solution. The unused bands of spectrum were generated by the conversion of television signals from analog to digital. Because digital transmission uses a smaller slice of spectrum, more “white space” was freed up around each broadcast signal. It is those white spaces that the F.C.C. is now seeking to put to use.

via F.C.C. Is to Open Unlicensed Airwaves to Wireless Innovators – NYTimes.com.