Cross-Layer Design of Opportunistic Spectrum Access in the Presence of Sensing Error

We address the design of cognitive MAC protocols for opportunistic spectrum access in the presence of sensing error. Decentralized protocols are presented for ad hoc networks where there is no central coordinator or dedicated communication/control channel. Secondary users search for and access spectrum opportunities independently without exchanging local information on spectrum availability. We assume on-demand partial spectrum monitoring subject to sensing errors. Specifically, a secondary user may not be able to simultaneously sense the whole spectrum of interest due to hardware limitation and may only monitor the spectrum when it has data to transmit in order to conserve energy. We propose two approaches to formulating opportunistic spectrum access in the presence of sensing error by considering either a constraint on the probability of colliding with primary users or a penalty imposed on each collision. Under these formulations, we address the joint design of both the spectrum sensor at the physical layer and the cognitive protocol at the MAC layer to maximize spectrum efficiency while limiting the interference to primary users.