On the sharing opportunities for ultra-dense networks in the radar bands

Finding additional spectrum for indoor networks with very high capacity (ultra-dense networks, UDN) is a prime concern on the road to 5G wireless systems. Spectrum below or around 10 GHz has attractive propagation properties and previous work has indicated that vertical spectrum sharing between indoor users and outdoor wide-area services is feasible. In this paper, we focus on spectrum sharing between UDNs and radar systems. We propose and evaluate regulatory policies that improve sharing conditions/opportunities in areas with large demand (i.e. hot-spots and urban areas). We consider three regulatory policies: area power regulation, deployment location regulation and the combination of these. We address the scenario where secondary users can reliably exploit time and space domain sharing opportunities in the S- and Ku-Bands by means of geo-location databases and spectrum sensing. We evaluate these opportunities in terms of the required time-averaged separation distance between the radar system and the UDN that both protects the radar system as well as guarantees a minimum secondary transmission probability. Our results show that there are ample adjacent channel sharing opportunities for indoor usage in both the S- and Ku-Bands. In the Ku-Band, even outdoor hot-spot use is feasible with very relaxed restrictions. Co-channel usage in the S-band requires large separation distances that makes it practically unfeasible in cities with nearby radar sites. Overall, deployment location regulation seems to be the most effective means to limit interference to the radar system and improve sharing opportunities.