A sub-band based CAC scheme using adaptive codec switching for improved capacity and GoS of cognitive VoIP users

Cognitive Radio Network (CRN) is one of the emerging technologies to improve the spectrum utilization where Secondary Users (SUs) opportunistically uses the spectrum without creating significant interference to Primary Users (PUs). However, in CRN channel characteristics varies widely due to the random arrival of PUs which leads to call dropping/call blocking. Excessive call dropping reduces the quality of VoIP communication for SU's. Quality of Service (QoS) can be improved by exclusive channel reservation for SUs which involves policy formation and cost implication. To avoid the complexity, we have used sub-banding concept for Call Admission Control (CAC) scheme and utilized the scheme for VoIP applications using Adaptive Codec Switching Policy. Test bed analysis is performed to evaluate the behavior of some well known high/low bit rate codecs in CRN. Overall system performance is evaluated by using two dimensional Markov Model. Analysis shows that there is significant improvement in system capacity as probability of dropping and probability of blocking reduces. Finally Grade of Service (GoS) is considered as overall system performance metric which shows nearly 39% improvement under high SU traffic condition.