Dynamic spectrum access opportunities for public safety in land mobile radio bands

We present the results of a preliminary assessment of the potential for applying Dynamic Spectrum Access (DSA) methods to improve radio frequency spectrum utilization in the land mobile radio (LMR) bands in the U.S. This band includes both public safety and commercial user frequency assignments. First, using RF spectrum measurements made in Chicago, occupancy statistics in the widely used 450-470 MHz band are presented for several days during 2009 and 2011. The results show an increase in the average occupancy, and also in the total number of active channels detected. In view of the 2013 narrowbanding mandate from the FCC, a surprising find was that between 2009 to 2011, only about 10% of the wideband (25 kHz) LMR channels studied have shifted to 12.5 kHz transmissions. While the detected number of active LMR channels has increased by 15% in just 15 months, overall occupancy remains rather low, suggesting good opportunity for Dynamic Spectrum Access (DSA) systems, even with the impending transition to narrower channels. Finally, and somewhat opportunistically, we illustrate the effect of a major weather event (the Chicago Blizzard of 2011) on the utilization of the spectrum in the LMR band. The event reveals that while overall LMR utilization decreased during this weather event, public safety utilization increased, indicating that DSA could provide additional capacity for public safety during similar events.