A dynamic opportunistic spectrum access MAC protocol for Cognitive Radio networks

Cognitive radio can be regarded as the intelligent wireless devices which can sense the medium and effectively utilize the vacant or underutilized spectrum. The cognitive radio enables the Secondary Users (SU) to opportunistically access the spectrum unused by the Primary Users (PU). There are two basic objectives of Cognitive Radio Medium Access Control (CR MAC): controlling interference and avoiding PUs and avoiding collision between SUs. We propose a MAC protocol for single channel which opportunistically utilizes the spectrum unused by the PUs. It has a licensed channel in the primary network. The time in the network is divided in terms of slot time. Slot time is of equal length and packet transmission in carried out in slots. It is partitioned in two phases which are the contention phase and the data transmission phase. The first phase selects a SU based on 802.11 DCF with RTS/CTS mechanism. The second phase is for data transmission. The SU is allowed to occupy all the time remaining after the contention phase. In case of collision, a dynamic backoff scheme is applied. We compare the results of the OSA MAC for single channel with dynamic MAC scheme. The results show that throughput of proposed scheme is better than the conventional OSA scheme.