Spectrum Sharing Mechanisms for CR Networks

dynamic spectrum access (DSA) that promises to alleviate the spectrum shortage problem in wireless networks. By employing spectrum sensing techniques or referring to the geolocation databases, a CR (or a CR-enabled secondary user) is able to intelligently decide which licensed spectrum band is free for use without causing harmful interference to licensed (or primary) users. Besides, the spectrum sharing mechanism allows co-located CRs or CR networks to opportunistically utilize those identified fallow spectrum in a fair and efficient manner. Whereas the use of spectrum sensing and databases helps in the discovery of fallow spectrum from the perspective of licensed operation protections, the spectrum sharing mechanism aims to improve the spectrum usage for unlicensed CR networks. Many security and privacy problems have been identified in both the sensing-based and database-driven CR networks. A single CR that employs the spectrum sensing technique may not be able to verify the authenticity of the received primary user signals or the sensing reports sent from other CRs. Thus, the spectrum sensing mechanism is subject to the primary user emulation attack, falsification of spectrum sensing results, and selfish sensing misbehaviors [1, 2]. Authentication of primary user signals and collaborative spectrum sensing techniques have been proposed to defend against these threats [3–5]. Moreover, privacy issues (e.g. unauthorized release of location information) can arise in both sensing-based and databasedriven CR networks, and privacy preservation techniques have been used to eliminate these privacy concerns [6, 7]. However, security vulnerabilities in the spectrum sharing mechanism, especially those that can be exploited by selfish users, have received little attention. Performing fair spectrum sharing is a challenging task in CR networks. On the one hand, every user is selfish by nature. This implies that a selfish user tends to exploit the vulnerabilities of spectrum sharing mechanisms to gain an unfair advantage in spectrum access, if such misbehaviors cannot be easily detected. On the other hand, coexisting CRs or CR networks may be operated by competing service providers, and it is difficult to establish a centralized spectrum sharing mechanism that can monitor or regulate the behaviors of all the entities. Moreover, a CR may take a stealthy way of misbehaving, e.g. randomly switching between the norm and misbehaviors, which increases the difficulty of detection. Next, we introduce two spectrum sharing mechanisms in infrastructure-based and multi-hop CR networks.