ABSTRACT
The scarcity of spectrum resources among unlicensed users is increasing day by day with the increasing number of spectrum band users. The Federal Communications Commission (FCC) responsible for the allocation of the spectrum bands has introduced the industrial, scientic, medical (ISM) bands for utilization by the unlicensed or secondary users (SUs). The scarcity of ISM bands has resulted in the need for spectral resources for the unprivileged users. Further studies have highlighted that in most of the cases, 50% of the spectrum bands allotted for the primary users (PUs) remain underutilized, thereby leading to a wastage of the spectral resources [1,2]. To carry out an efcient spectrum utilization, cognitive radios (CRs) are used which facilitate the effective reconguration to prociently adapt to the surrounding environmental changes along with the cognitive capability. The initial
CONTENTS
9.1 Introduction ........................................................................................................................ 171 9.2 Architectural Overview of the CR .................................................................................. 172 9.3 Physical Layer ..................................................................................................................... 173
9.3.1 Noncooperative Sensing ....................................................................................... 174 9.3.1.1 Energy Detection-Based Method ......................................................... 174 9.3.1.2 Matched-Filter Detection Method ........................................................ 174 9.3.1.3 Cyclostationary-Feature Detection Method ........................................ 175
9.3.2 Cooperative Spectrum-Sensing Method ............................................................ 175 9.3.2.1 Centralized Sensing ................................................................................ 176 9.3.2.2 Distributed Sensing ................................................................................ 176
9.3.3 Interference-Based Sensing .................................................................................. 176 9.4 Data Link Layer .................................................................................................................. 177 9.5 Network Layer .................................................................................................................... 179 9.6 Transport Layer .................................................................................................................. 180 9.7 Application Layer ............................................................................................................... 181 9.8 Conclusion .......................................................................................................................... 181 Acknowledgments ...................................................................................................................... 181 References ..................................................................................................................................... 182
conguration of the radio is done based on the spectrum-sensing techniques employed at the architectural level of the CR. Deployment of the CR requires a detailed knowledge of the layer-wise conguration to bring about the required functionality. The protocol stack of the CR is composed of ve layers namely physical layer, data link layer, network layer, transport layer, and application layer. This type of layer-wise segregation of the functionalities and characteristics aids in the hierarchical addressing of the features of each layer, starting from the modulation schemes, coding techniques, and the sensing techniques that can affect the performance of the system. A complete overview of the layered architecture with the associated applications and limitations is discussed in Sections 9.2 through 9.6.
