Cognitive radio (CR) technology enables multiple wireless networks operating in overlapping regions to opportunistically access fallow spectrum from a common pool of spectrum. This spectrum access paradigm - referred to herein as simply spectrum sharing - holds the promise of significantly greater efficiency in spectrum utilization and alleviating the spectrum shortage problem. CRs have garnered great attention from the research community, and many security and privacy problems relevant to CR networks are being studied actively at this time. However, selfish misbehaviors that can occur in the spectrum contention process have received little attention. In this article we discuss two types of selfish misbehaviors in the context of spectrum contention: selfish spectrum contention and selfish channel negotiation. These misbehaviors deteriorate the fairness and performance of spectrum sharing mechanisms in both infrastructure-based and multi-hop CR networks. We also discuss countermeasures against these threats as well as the technical challenges that must be overcome to implement such countermeasures.
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