Spectrum Utilization Study in Support of Dynamic Spectrum Access for Public Safety

Radios for public safety communication have some of the most stringent requirements for access, reliability and robustness. While wireless technology has seen tremendous strides in the past decade, large parts of the public safety infrastructure have unfortunately lagged behind. Today the majority of the Land Mobile Radios (LMR) used by police and fire departments, among others, utilize bandwidth inefficient analog FM radio systems, despite the limited available radio spectrum allocated for these applications. Additionally, numerous interoperability issues continue to exist between the various agencies, jurisdictions and disciplines; for example, radios from the state law enforcement authorities may not be able to communicate with Federal ones. This paper presents data from spectral measurements carried out over several public safety bands in the city of Chicago. Occupancy estimates over a period of several months are given and analyzed, and seasonal/event-driven variation and trends are discussed. The results demonstrate an imbalance in occupancy between public safety channels, which show high peak occupancy during normal day to day operations, and adjacent commercial LMR channels, which have much lower usage. This indicates potential opportunities for the application of dynamic spectrum access techniques to increase the capacity of public safety channels during emergencies. Furthermore, the spectrum utilization data may be useful for planning for the expansion or optimization of present-day systems.