Opportunistic spectrum access: from stochastic channels to non-stochastic channels

Opportunistic spectrum access (OSA), which is considered as the core technology of hierarchical access model of dynamic spectrum access (DSA), has been extensively researched recently. Most of the existing OSA protocols, albeit theoretically sound with almost optimal performance, have to require the preknowledge of static known distributions under stochastic channels. These assumptions, however, make them impractical for more general application scenarios where channel statistics may not be readily available a priori and channel availabilities cannot be modeled as a stochastic process due to malicious jamming. More seriously, the existing OSA protocols are subject to malicious jamming attacks. That is, a cognitive jammer can always disrupt the legitimate network communication by leveraging the publicly-available channel statistic information to effectively jam the channels and thus lead to serious spectrum underutilization. In this article, we first present an in-depth overview of the existing spectrum sensing and access protocols under stochastic channels, achieving almost optimal performance in jamming- free scenarios. We then analyze the vulnerabilities of these protocols to malicious jamming attacks. Finally, we discuss spectrum sensing and access protocols under non-stochastic channels and show their robustness and resilience against various malicious jamming attacks.