Cognitive Radio (CR) technology in wireless communication allows unlicensed (secondary) users to access the licensed (primary) frequency bands without interfering with the licensed users in order to realize more effective and reliable communication. Spectrum sensing, as a fundamental functionality of cognitive radio, enables the secondary users to monitor the frequency spectrum and detect vacant channels to use. Among the various sensing schemes for cognitive radio networks (CRN), Spectrum Sensing method stands-out due to its high detection performance of spectrum holes.

Figure 1: Simplified Cognitive Cycle

A simplified cognitive cycle is shown in figure 1 generally includes four main functions as follow:

1. Spectrum Sensing: Spectrum sensing detects and shares the available spectrum without detrimental interference with other users. It is critical for cognitive radio network to find spectrum holes. And the most efficient and effective way to detect spectrum holes is to detect primary users.
2. Spectrum Management: Spectrum management utilizes efficient spectrum among different available spectrums to fulfill the requirements of user.
3. Spectrum Sharing: Spectrum sharing provides the fair spectrum scheduling mechanism. It exhibits some similarities of the classical media access control (MAC) problems in current wireless systems.
4. Spectrum Mobility: It allows the secondary user to shift to other available spectrum channels when primary user required the current channel.

Key benefits:

1. Improved spectrum utilization: It allows a system designer to extract every Hz (Hertz) out of the system and allows efficient spectrum pooling.
2. Improved coverage: Coverage is improved with the help of CRN which allows to communicate information from one node to another node.
3. Improved Quality of Service: It utilizes the available spectrum with high signal to noise ratio (SNR).
4. Avoid Jamming problems: With the help of spectrum sensing and switching algorithms, CRN can avoid the jamming problems.

Challenges:

1. Security: Wireless spectrum is an extremely important resource and an unlicensed communication may interrupt the operation of other radio devices within the network.
2. Implementation difficulties: There are still many technical difficulties in implementation of CRN among hidden or spread spectrum (unlicensed) primary users and licensed primary users.
3. Fading effects: Multipath fading affects the accuracy on spectrum occupancy choice, sensing duration etc.
4. Decision making: Decision on availability of spectrum, approach in channel selection and optimization of radio performance are the main challenges in CRN.

Application of CR:

1. CRN in 5G wireless communication: The integration of CR in 5G networks will meet the capacity demands of spectrum.
2. CRN in cloud computing: The computing using CRN is used in various artificial intelligence (AI) systems, including expert systems, natural language programming, neural networks, robotics and virtual reality (VR).
3. CR in wireless sensor network (WSN): CRWSN sense a signal and collaboratively communicate their measured value continuously over the available spectrum channels.
4. Green CRN: Cognitive Radio (CR) is proposed as an efficient technology to meet the concept of Green communications.

By - Sartajvir Singh, Asst. Prof, ECE, Chitkara University, H.P.

References:-

1. Sood, V., Spectrum utilization of Cognitive Radios, Thesis, Punjab Technical University, Punjab, India, 2011.
2. Van Tam Nguyen, Frederic Villain, and Yann Le Guillou, "Cognitive Radio RF: Overview and Challenges", VLSI Design, 2012, 13 pages, DOI: 10.1155/2012/716476