Medium Access Control Protocols in Cognitive Radio Networks: Overview and General Classification

The Cognitive Radio and the Cognitive Radio Networks have recently become one of the most intensively studied paradigms in wireless communications. The main distinctive characteristic with respect to the radio environmental conditions in which the Cognitive Radio Network operates is the time/frequency/space-dependent availability of the spectral resources, a phenomenon commonly referred as spectrum hete-rogeneity. This phenomenon imposes redefinition of the protocol stack by introducing new communication protocols for the Cognitive Radio Network including new Medium Access Control protocols. The Cognitive MAC (C-MAC) protocols employ number of mechanisms that address spectrum heterogeneity and provide technical strategies for smart exploitation of spectrum´s current underutilized time/space/frequency regions that enables large spectrum efficiency gains while maximizing the transparency of the Cognitive Radio Networks to the primary system. The classification and systematization of the existing C-MAC proposals is a complex task due to many C-MAC related aspects. This survey introduces and develops generic, modular and easily extensible layout for classification and systematization of C-MAC protocols referred as C-MAC cycle. Each C-MAC protocol can be easily fragmented, mapped and visualized using the C-MAC cycle, regardless of the operational scenario and settings. The survey offers extensive overview on the state-of-the-art advances in C-MAC protocol engineering by reviewing existing and up-to-date technical solutions, identifies their basic characteristics and maps them into the C-MAC cycle. The survey also highlights the role of regulative and standardization activities on C-MAC cycle.