Book excerpt: As wireless services rapidly expand, the inefficient use of limited spectrum resources poses a critical challenge. The conventional approach to spectrum allocation, based on fixed assignments, could be more effective in meeting the escalating demand for wireless devices and systems. Cognitive radio technology offers a transformative solution by reimagining the spectrum as a multidimensional space, enabling opportunistic access to underutilized bands. However, the field of cognitive radio is still in its early stages, needing more in-depth analyses and descriptions of crucial processes. Spectrum and Power Allocation in Cognitive Radio Systems addresses this pressing need by offering a comprehensive guide for academic scholars, researchers, and industry professionals. This book delves into cognitive radio technology's foundations, organization, and challenges, providing insights into dynamic spectrum access, networking protocols, hardware architecture, and emerging applications. It presents advanced topics such as spectrum sensing algorithms, cooperative spectrum sensing, and multi-user access, offering practical solutions to enhance spectrum efficiency.