Spatial Capacity of Cognitive Radio Networks: Narrowband Versus Ultra-Wideband Systems

For cognitive wireless networks, this paper analyzes the achievable sum capacity of spectrum-sharing cognitive radio (CR) networks, taking into account of a number of factors including channel multipath profile, transmit power constraints, as well as the outage probability at a primary legacy user. Two transmission formats, narrowband versus ultra-wideband, are compared for adoption in CRs. 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 deteriorates a narrowband cognitive network more than its ultra-wideband counterpart.