Sharing government spectrum with private users: opportunities and challenges

Measurements of spectrum occupancy typically confirm the expectation that spectrum assigned to government entities often has low average utilization in urban areas despite its potential for peaks during emergencies. By contrast, spectrum assigned to the private sector is usually most heavily used in urban areas. The second generation of government spectrum sharing started in 2004 with cognitive-radio-based sharing of the 5.25-5.35 and 5.47-5.725 GHz radar bands by unlicensed Wi-Fi-like systems. This sharing is called dynamic frequency selection (DFS) in regulatory and standards publications. Although DFS enabled sharing, the technical criteria were very conservative due to the fact that the military radar systems were not designed for sharing and the fact that interference to these radar systems had to be kept to a negligible likelihood.