ABSTRACT
Contents 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 7.2 MAC Protocols for Cognitive Radio Networks: Challenges
and Existing Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7.3 Cognitive MAC Protocols for Optimal Channel Sensing
and Optimal Channel Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 7.3.1 Cognitive MAC Protocol for Joint Spectrum Sensing
and Spectrum Access Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 187 7.3.2 MAC Protocol for Hardware-Constrained
Cognitive Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 7.3.3 Cognitive MAC Protocol for Efficient Discovery
of Spectrum Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 7.3.4 Cognitive MAC with Learning-Based Optimal
Channel Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
7.3.5 Ad Hoc Secondary System MAC (AS-MAC) for Spectrum Sharing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
7.4 MAC Protocols with Synchronization Between Cognitive Radios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 7.4.1 Slotted Beaconing Period and Rendezvous Channel . . . . . . . 194 7.4.2 Dynamic Open Spectrum Sharing (DOSS) Protocol . . . . . . . . 195
7.5 Cognitive MAC Based on Channel Allocation and Scheduling . . . . 196 7.5.1 Multichannel Cognitive Radio MAC with Rate
and Power Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 7.5.2 Statistical Channel Allocation MAC (SCA-MAC)
for Cognitive Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7.5.3 MAC-Layer Scheduling in Cognitive Radio Networks . . . . . . 199 7.5.4 Rental Protocol for Dynamic Channel Allocation . . . . . . . . . . . 200 7.5.5 Centralized Cognitive MAC Protocol for Coordinated
Spectrum Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 7.6 Adaptive Cognitive MAC Protocols and Performance
Analysis Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.6.1 Adaptive MAC Protocol for Cognitive Radio . . . . . . . . . . . . . . . . 201 7.6.2 Queueing Performance Model for Cognitive
MAC Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.7 Open Research Issues in Cognitive MAC Protocol Design . . . . . . . . 203 7.8 Cognitive MAC Protocols for the IEEE 802.22
Standard-Based WRANs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 7.8.1 802.22 MAC Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 7.8.2 Spectrum Management and Sensing in 802.22 MAC . . . . . . . 206 7.8.3 Challenges in Designing IEEE 802.22 MAC . . . . . . . . . . . . . . . . . 207 7.8.4 Enhancements to the IEEE 802.22 Air Interface . . . . . . . . . . . . 207 7.8.5 Dynamic Frequency Hopping MAC for IEEE 802.22 . . . . . . . 209
7.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
7.1 Introduction In a traditional wireless communication system, frequency spectrum is statically allocated to licensed users (i.e., primary users) only. However, since licensed users may not always occupy the allocated radio spectrum, this static spectrum allocation results in spectrum underutilization. This was confirmed in a report from the FCC (Federal Communications Commission)1
where it was shown that even in a crowded area, more than half of the radio spectrum is not occupied at any given time. This, along with the increasing spectrum demand from emerging wireless applications, is driving the development of new spectrum allocation policies to allow unlicensed users (i.e., secondary users) to access radio spectrum when it is not occupied by primary users. These new spectrum allocation policies, which
will be implemented through the cognitive radio technology, are expected to improve spectrum utilization while satisfying the spectrum demand for new wireless applications.
