Sensors 2015, 15, 19783-19818; doi:10.3390/s150819783 OPEN ACCESS sensors ISSN 1424-8220 www.mdpi.com/journal/sensors Article An Energy-Efficient Spectrum-Aware Reinforcement Learning-Based Clustering Algorithm for Cognitive Radio Sensor Networks Ibrahim Mustapha 1,2,†, Borhanuddin Mohd Ali 1,*, Mohd Fadlee A. Rasid 1,†, Aduwati Sali 1,† and Hafizal Mohamad 3,† 1 Department of Computer and Communications Systems Engineering and Wireless and Photonics Research Centre, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia; E-Mails:
[email protected] (I.M.);
[email protected] (M.F.A.R.);
[email protected] (A.S.) 2 Department of Electrical and Electronics Engineering, Faculty of Engineering, University of Maiduguri, P. M. B. 1069, Maiduguri, Nigeria 3 Wireless Networks and Protocol Research Lab, MIMOS Berhad, Technology Park Malaysia, 57000 Kuala Lumpur, Malaysia; E-Mail:
[email protected] † These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail:
[email protected]; Tel.: +60-3-8946-6443; Fax: +60-3-8656-7127. Academic Editor: Davide Brunelli Received: 25 May 2015 / Accepted: 31 July 2015 / Published: 13 August 2015 Abstract: It is well-known that clustering partitions network into logical groups of nodes in order to achieve energy efficiency and to enhance dynamic channel access in cognitive radio through cooperative sensing. While the topic of energy efficiency has been well investigated in conventional wireless sensor networks, the latter has not been extensively explored. In this paper, we propose a reinforcement learning-based spectrum-aware clustering algorithm that allows a member node to learn the energy and cooperative sensing costs for neighboring clusters to achieve an optimal solution.