ABSTRACT
Contents 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
6.1.1 Coexistence of Heterogeneous Communication Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
6.1.2 Common Control Channel Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 6.1.3 Multiple Hidden Terminal Problem . . . . . . . . . . . . . . . . . . . . . . . . . 130 6.1.4 Diversified Local Goals and Actions of CRs . . . . . . . . . . . . . . . . 130 6.1.5 Recursive Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.1.6 Coordination and Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.1.7 Cross-Layer Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.2 Direct-Access-Based Cognitive Radio MAC Protocol . . . . . . . . . . . . . . . 132 6.2.1 Direct Contention-Based MAC Protocols. . . . . . . . . . . . . . . . . . . . 132
6.2.1.1 Common Control Channel Approach . . . . . . . . . . . . . . 133 6.2.1.2 Split-Phase-Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.2.1.3 Frequency-Hopping Sequence Approach . . . . . . . . . 144
6.2.2 Direct Coordination-Based Cognitive Radio MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6.2.3 Centralized MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.3 DSA-Driven Cognitive Radio MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . . 154
6.3.1 Graph DSA-Driven MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 6.3.2 Stochastic DSA-Driven MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . 157 6.3.3 Game-Theoretic DSA-Driven MAC Protocol . . . . . . . . . . . . . . . . 159
6.4 Cross-Layer-Design-Based MAC Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . 169 6.4.1 Routing-Oriented MAC Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 6.4.2 Flow-Oriented MAC Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
6.5 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
6.1 Introduction Cognitive radio (CR) technology offers a much more flexible way to utilize the wireless spectrum than traditional radio technology based on a fixed spectrum access policy. As a result, the medium access control (MAC) layer protocols for CR networks are quite diversified from the perspectives of application scenarios, spectrum sharing mechanisms, control message sets, and the styles of handshakes among CR users. Although the precise definition of cognitive radio is still under debate, it is commonly accepted that MAC protocols for CR networks are meant to possess one or several of the following functionalities:
1. The capability to handle dynamic access over multiple channels. Multichannel access has become a de facto requirement for CR networks. For secondary CRs sharing licensed bands with primary users, the channel availability can be time varying, which requires that medium access be carried out dynamically over multiple channel opportunities. For coexisting CRs in unlicensed bands, multichannel access allows nearby users to share spectrum, which increases the spatial usage efficiency and thus considerably improves the throughput of the entire network. Furthermore, multichannel access makes it feasible to separate the control channel from data channels so as to eliminate collisions between control messages and data packets. When each CR node is equipped with multiple transceivers, the use of multichannel access allows for simultaneous control message exchange and data communication which reduces network latency.
