This paper surveys recent advances in cognitive radio (CR) research. Cognitive radio is a key technology for next-generation communication networks, enabling dynamic spectrum access (DSA) by allowing secondary users to use temporarily unused licensed spectrum without interfering with primary users. CRs can adapt their operating parameters based on the surrounding radio environment, improving spectrum utilization. The paper discusses the fundamentals of CR technology, its architecture, and applications. It reviews existing works in spectrum sensing, including interference temperature, detection techniques, and cooperative sensing. It also investigates important issues in dynamic spectrum allocation and sharing. Spectrum sensing is critical for CRs to detect primary users and identify available spectrum. Several detection techniques are discussed, including energy detection, feature detection, matched filtering, and coherent detection. Energy detection is the most common, but it has limitations in low SNR environments. Feature detection uses cyclostationary features to distinguish primary signals from noise. Matched filtering and coherent detection offer better performance but require prior knowledge of the primary signal. Cooperative sensing improves detection reliability by combining multiple users' information, reducing false alarms and increasing detection probability. Dynamic spectrum allocation and sharing are essential for efficient spectrum utilization. CRs must manage interference with primary users and coordinate with other secondary users. Spectrum management approaches, such as spectrum brokers, help coordinate spectrum usage among secondary networks. Efficient dynamic spectrum allocation and sharing schemes are crucial for maximizing spectrum efficiency. Novel spectrum access control protocols and control channel management should be designed to accommodate dynamic spectrum environments while avoiding collisions with primary users. CRs can be used in various applications, including military communications, public safety, and commercial wireless technologies. They provide adaptive, seamless, and secure communications, enhance public safety by enabling reliable broadband communication, and support diverse services in commercial markets. CRs can also improve interoperability between different communication systems. Spectrum sensing techniques include energy detection, feature detection, matched filtering, and coherent detection. Cooperative sensing improves detection reliability by combining multiple users' information. Efficient information sharing is essential for coordinating spectrum sensing. The paper also discusses challenges in cooperative sensing, such as user selection, decision fusion, and efficient information sharing. It highlights the importance of robust spectrum sensing techniques and efficient dynamic spectrum allocation and sharing in CR networks.This paper surveys recent advances in cognitive radio (CR) research. Cognitive radio is a key technology for next-generation communication networks, enabling dynamic spectrum access (DSA) by allowing secondary users to use temporarily unused licensed spectrum without interfering with primary users. CRs can adapt their operating parameters based on the surrounding radio environment, improving spectrum utilization. The paper discusses the fundamentals of CR technology, its architecture, and applications. It reviews existing works in spectrum sensing, including interference temperature, detection techniques, and cooperative sensing. It also investigates important issues in dynamic spectrum allocation and sharing. Spectrum sensing is critical for CRs to detect primary users and identify available spectrum. Several detection techniques are discussed, including energy detection, feature detection, matched filtering, and coherent detection. Energy detection is the most common, but it has limitations in low SNR environments. Feature detection uses cyclostationary features to distinguish primary signals from noise. Matched filtering and coherent detection offer better performance but require prior knowledge of the primary signal. Cooperative sensing improves detection reliability by combining multiple users' information, reducing false alarms and increasing detection probability. Dynamic spectrum allocation and sharing are essential for efficient spectrum utilization. CRs must manage interference with primary users and coordinate with other secondary users. Spectrum management approaches, such as spectrum brokers, help coordinate spectrum usage among secondary networks. Efficient dynamic spectrum allocation and sharing schemes are crucial for maximizing spectrum efficiency. Novel spectrum access control protocols and control channel management should be designed to accommodate dynamic spectrum environments while avoiding collisions with primary users. CRs can be used in various applications, including military communications, public safety, and commercial wireless technologies. They provide adaptive, seamless, and secure communications, enhance public safety by enabling reliable broadband communication, and support diverse services in commercial markets. CRs can also improve interoperability between different communication systems. Spectrum sensing techniques include energy detection, feature detection, matched filtering, and coherent detection. Cooperative sensing improves detection reliability by combining multiple users' information. Efficient information sharing is essential for coordinating spectrum sensing. The paper also discusses challenges in cooperative sensing, such as user selection, decision fusion, and efficient information sharing. It highlights the importance of robust spectrum sensing techniques and efficient dynamic spectrum allocation and sharing in CR networks.