[IEEE 2009 5th International Conference on Testbeds and Research Infrastructures for the Development of Networks & Communities and Workshops - Washington, DC, USA (2009.04.6-2009.04.8)] 2009 5th International Conference on Testbeds and Research Infrastructures for the Development of Networks & Communities and Workshops - Lessons learned from an extensive spectrum occupancy measurement campaign and a stochastic duty cycle model