47 U.S. Code § 1454 - Guard bands and unlicensed use
Such guard bands shall be no larger than is technically reasonable to prevent harmful interference between licensed services outside the guard bands.
The Commission may permit the use of such guard bands for unlicensed use.
Unlicensed use shall rely on a database or subsequent methodology as determined by the Commission.
The Commission may not permit any use of a guard band that the Commission determines would cause harmful interference to licensed services.