Cognitive Radio Sensor Networks

Cognitive Radio Sensor Networks

DOI: 10.4018/978-1-4666-5888-2.ch606
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2. Background

Traditionally, wireless networks follow fixed spectrum assignment policy, regulated by the government. The spectrum is assigned to users, who pay for the assigned spectrum for specific time and frequency. These users are called licensed users (Primary Users or PUs). This policy worked well in the past but now, with the passage of time, most of the spectrum has been assigned to licensed users and very less spectrum is remained. On the other hand, with the advancement in technology, there is a drastic increase in the development of new devices (e.g., smartphones, PDAs, tablets etc.) which operate on unlicensed spectrum. Therefore, the unlicensed spectrum has become overcrowded. Due to these two issues, a problem of spectrum scarcity arises. However, according to the survey, licensed users do not use their assigned spectrum all the time. Hence there is much sparsity in the utilization of licensed (fixed assigned) spectrum bands which resulted in underutilization of licensed spectrum. It is observed that the utilization of licensed spectrum ranges from 15%-85% with high variance in time and location (Akyildiz et al., 2006). Thus, in order to solve the problem of spectrum scarcity, the Federal Communications Commission (FCC, 2003), a regulatory authority in USA has allowed the usage of licensed spectrum by unlicensed devices; subject to the condition that licensed user should not be interfered. Consequently, CRNs are proposed to solve the problem of spectrum scarcity. They exploit Dynamic Spectrum Access (DSA) technique in order to access multiple licensed spectrum bands dynamically. CRNs are composed of CR devices, which opportunistically utilize white spaces in licensed channels. White spaces are the spectrum which is not in use of licensed user for specific time and frequency. Also, CR devices are intelligent devices which can change their parameters based on the interaction with their operating environment (Akyildiz et al., 2009).

On the other hand, a WSN is composed of resource constraint sensor nodes which have limited resources of energy and power. They are deployed densely in the observing environment. WSNs follow fixed spectrum assignment policy; therefore they also suffer from spectrum scarcity problem. Thus, WSNs can exploit CR technology in order to solve the problem of spectrum scarcity. This integration of WSNs and CR technology will improve network performance, spectrum utilization and resource utilization (communication and processing) in WSNs. Sensor nodes in WSNs, equipped with CR technology form Cognitive Radio Sensor Network (CRSN) (Akan et al., 2009).

Key Terms in this Chapter

Sensor Node: A Sensor node is a small and inexpensive device with limited resources of battery and computation power which are deployed in a region to monitor the environment.

Primary Radio User: Primary radio user is a licensed user who has assigned a fixed spectrum band and it can use its spectrum band without any interference or disruption from other users in the network.

Cognitive Radio User: Cognitive radio user is an unlicensed user who either utilizes unlicensed spectrum band or licensed spectrum band of primary radio user when it is idle, i.e., not utilizing by the primary radio user subject to the condition that primary radio user should not be interfered.

Cognitive Radio Sensor Network: Cognitive Radio Sensor Network is composed of resource limited sensor nodes which are equipped with Cognitive Radio (CR) technology by which they can exploit the varying conditions of the spectrum dynamically.

Cognitive Radio Network: Cognitive Radio Network consists of Cognitive Radio (CR) devices which can change their parameters based on the environment in which they operate.

Wireless Sensor Network: Wireless Sensor Network is composed of autonomous sensor nodes, which are deployed in a region to monitor the environmental conditions and collect data from them.

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