On opportunistic spectrum access in radar bands: Lessons learned from measurement of weather radar signals

The need for extra spectrum and the fact that a large amount of spectrum below 6 GHz is allocated to radar systems has motivated regulatory bodies and researchers to investigate the feasibility of dynamic spectrum access in radar bands. To design efficient wireless communication schemes that coexist with radar systems, it is essential that the wireless community thoroughly understand the operations of these systems in different bands. This article studies incumbent operations and usage patterns in the 5 GHz band, where weather radar systems dominate, dynamic frequency selection is employed as a sharing mechanism, and recent works have explored the possibility to temporally share the spectrum with such radar systems. We present a measurement-based study of spectrum usage by a weather radar in Finland. Our measurement results show that the weather radar's scan patterns are quasi-periodic, and that use of sensing may not reliably detect radar signals due to its quasi-periodic scanning patterns and different vertical scanning angles. Finally, we present a framework for a database-assisted temporal sharing coexistence mechanism that takes into account the real occupancy behavior of the radar.