The FCC's long-awaited incentive auction of 600 MHz spectrum effectively kicks off tonight as the Commission begins to reconfigure TV broadcasters' airwaves for use by mobile service providers. But while the auction has been six years in the making, much work is yet to be done.

TV broadcasters have until tonight to apply to participate in a "reverse auction" that will see the FCC compile those airwaves before putting them up for bid later this year in the forward auction. The Commission will spend the next few weeks reconfiguring the airwaves and setting a "clearing target," revealing how much spectrum it thinks it can free up based on the amount of spectrum broadcasters are willing to part with.

The "forward auction" is likely to begin in earnest in June, with the government striking the best deals it can to secure broadcasters' spectrum. Verizon, AT&T and T-Mobile are all expected to participate actively in the forward auction -- as are many other companies -- to score the low-bandwidth spectrum, which is prized for its ability to both cover long distances and penetrate building walls.

The airwaves are seen as crucial to support ever-increasing demand for mobile data by consumers as well as the emergence of the IoT, which promises to provide connectivity to a vast array of devices and services. Wireless service providers and others will bid for the spectrum in a forward auction expected to begin sometime this summer.

"This auction is pivotal to making more spectrum available for commercial wireless use so that Americans can continue to enjoy a mobile-first lifestyle," CTIA CEO Meredith Attwell Baker said in a prepared statement.

Many questions have yet to be addressed, however, and it will be at least a few years before carriers can put their new 600 MHz spectrum to use. The FCC must still determine how much spectrum it can make available during the forward auction -- it's hoping for as much as 126 MHz -- and it may have hold a second reverse auction if the forward auction doesn't generate enough cash. And predictions for how much money the auction will raise are all over the place, ranging from $25 billion to $80 billion.

Finally, the FCC faces a huge challenge in "repacking" the spectrum once the auction ends to make it available for mobile use and to move TV broadcasters to other channels. The FCC has proposed a 39-month timeframe for that process, although the National Association of Broadcasters has consistently protested that schedule, saying it doesn't provide ample time.

Special Report: 600 MHz incentive auction primer: Who will bid, when it will happen, how it will work, and how much money it will raise

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