Spatial Capacity of Narrowband vs. Ultra-wideband Cognitive Radio Systems

Cognitive radio (CR) networks have emerged as attractive candidates to enhance radio spectral utilization efficiency on both licensed bands and license-free bands. This paper investigates the achievable sum capacity of spectrum-sharing CR networks, taking into account of channel multipath profiles, transmit power constraints, as well as the outage probability requirements from primary users holding spectrum licenses. Two transmission formats, narrowband versus ultra-wideband, are compared for adoption in CR networks. Capacity analysis indicates that ultra-wideband CRs are in general more suitable for networks operating over licensed bands, when strict outage requirements are imposed for protecting primary users. On license-free bands, on the other hand, narrowband CRs employing orthogonal channelization offer higher network capacity, while its ultra-wideband counterparts become competitive only when the multipath effect is moderate. In the presence of primary users, the interference temperature constraint limits the narrowband network more than its ultra-wideband counterpart.