BACKGROUND
Spectrum usage of TV broadcast industries
the average TV market in the United States uses approximately 7 high-power channels of the 67 that it is allocated. This leaves an abundance of free channels that could be used for wireless access.
With both the House and the Senate having recently passed bills requiring television broadcasts to switch from analog to digital sometime in early 2009, the 700-MHz band (channels 52 to 69) will be cleared of programming and moved to lower frequencies (channels 2 to 51). The 700-MHz band will be set aside for public-safety emergency transponders and for bidding by wireless networks.
in this proposal only channels 2 to 51 are considered.
Three possible ways suggested in one article to protect interference with incumbent users
Listen-Before-Talk (LBT)
Geolocation/Database: GPS receivers installed in CPEs
Local beacon: locally transmitted signal used to identify incumbent users