These airwaves, called "white spaces," allow signals to travel faster, penetrate walls more easily and cover larger geographical areas than the current spectrum used for WiFi.

Tech companies have lobbied to deploy a new, super WiFi system using these airwaves, saying it would boost Internet speeds in homes, businesses, schools and municipalities, help bring broadband to rural areas and improve connectivity for mobile devices.

Device makers such as Dell Inc and Nokia also stand to profit from the Federal Communications Commission's 2008 decision to approve the use of unlicensed wireless devices in the idle white spaces.

Broadcasters feared using the spaces could interfere with their channels and filed suit in 2009 with the U.S. Appeals Court for the D.C. Circuit.

The court held that challenge in abeyance to give the agency time to review petitions for reconsideration. The FCC completed the process last month, adopting modified rules that addressed concerns filed by wireless providers and other critics.

"NAB still has concerns related to possible interference to broadcasting from unlicensed devices, but we felt this petition was no longer necessary," said Dennis Wharton, NAB's executive vice president of communications.

The trade group filed a motion on Thursday to dismiss its petition for review.

"Assuming the court grants the motion, the last potential legal obstacle to the use of this valuable unlicensed spectrum will be removed and the innovations that are just beginning can continue to proceed with new confidence," said Harold Feld, legal director of public interest group Public Knowledge.

The Wireless Innovation Alliance - whose members include Dell, Google Inc and Microsoft Corp - also applauded the NAB's decision to withdraw the challenge.

"The coming wave of white space innovations in rural broadband, WiFi offload, 'smart city' applications and machine-to-machine communications, just to name a few, will create jobs, spur investment and drive U.S. economic growth," the group said in a statement.

The FCC did not immediately provide comment.

(Editing by Andre Grenon)

• A Permanent Economic Emergency