Overlay Secondary Spectrum Sharing with Independent Re-attempts in   Cognitive Radios
  Opportunistic spectrum access (OSA) is a promising reform paradigm envisioned to address the issue of spectrum scarcity in cognitive radio networks (CRNs). While current models consider various aspects of the OSA scheme, the impact of retrial phenomenon in multi-channel CRNs has not yet been analyzed. In this work, we present a continuous-time Markov chain (CTMC) model in which the blocked/preempted secondary users (SUs) enter a finite retrial group (or orbit) and re-attempt independently for service in an exponentially distributed random manner. Taking into account the inherent retrial tendency of SUs, we numerically assess the performance of the proposed scheme in terms of dropping probability and throughput of SUs. 
Muthukrishnan Senthil Kumar, Aresh Dadlani, Kiseon Kim, Richard O.   Afolabi
cs.PF cs.NI math.PR