Enhanced MAC Protocol for Cognitive Radios over IEEE 802.11 Networks

Abstract

The Cognitive Radio (CR) technology is proposed for solving the spectrum underutilization problem and has gained great attention. By allowing unauthorized users to opportunistically access frequencies authorized to specific networks (called primary networks), the CR technology can increase the bandwidth utilization of the radio spectrum in a global perspective. In [1], the authors proposed a MAC protocol for CRs that aims to "borrow" the link bandwidth from IEEE 802.11 networks. This protocol allows CR users to opportunistically exchange data on an idle 802.11 channel. However, the protocol proposed in [1] selects an 802.11 channel for data exchange in a random manner. This random channel selection process is time-consuming for CR users to start a data transmission. In addition, the protocol does not consider the effects of hidden terminals (HTs), which often exist in wireless networks and significantly decrease the goodputs of a network. To address these problems, in this paper we propose enhancements to the protocol proposed in [1]. The proposed protocol is evaluated using extensive simulations. Our simulation results show that our proposed protocol can effectively decrease the time required for finding an idle 802.11 channel to transmit data and therefore increase the network goodputs in networks with and without the existence of HTs.