VoIP erlang capacity in coordinated cognitive radio networks

Guaranteeing QoS is challenging in cognitive radio networks due to the dynamically changing network resources, especially for stringent delay sensitive traffic. Dynamic spectrum leasing (and coordinated cognitive radio) of primary network resources has been previously proposed in the literature to improve QoS of secondary users. In this paper, the Erlang capacity in coordinated cognitive radio networks with VoIP traffic is investigated. Employing time-scale decomposition technique and conventional continuous and discrete time Markov chain tools, a joint connection-level and packet-level analytical model is developed. For the adequate and fair performance comparison, a call admission strategy with fractional admission threshold and fractional buffering is considered. An algorithm to determine the optimal values (i.e., the ones that maximize Erlang capacity) of the admission threshold and buffer size is proposed. For given QoS requirements at session and packet level (i.e., VoIP session blocking, packet dropping, and packet delay), the Erlang capacity as function of the maximum allowable number of simultaneously rented resources is evaluated. Additionally, the fraction of time that spectrum leasing is needed is calculated.