IJIREEICE IJIREEICE ISSN (Online) 2321 – 2004 ISSN (Print) 2321 – 5526 International Journal of Innovative Research in Electrical, Electronics, Instrumentation and Control Engineering ISO 3297:2007 Certified Vol. 5, Issue 6, June 2017 Copyright to IJIREEICE DOI 10.17148/IJIREEICE.2017.5616 89 Enhancement in Gain for Centralized Cooperative Spectrum Sensing in Cognitive Radio Network using Improved Local Sensing Charu Bhatnagar 1 , Anjali Potnis 2 , Prashant Dwivedy 3 Student, Digital Communication DEEE, NITTTR, Bhopal, India 1,3 Asstt.Professor, Digital Communication DEEE, NITTTR, Bhopal, India 2 Abstract: The parallel fusion model universalizes centralized and decentralized cooperative spectrum sensing as a three step process comprising of: local sensing, information reporting and information fusion. It is quite obvious that any amelioration in the performance quality of the constitutional steps would strengthen the overall performance of the cooperative spectrum sensing network. The performance metrics for a cooperative spectrum sensing network are the gain provided and overhead occurring (both in comparison with non cooperative scenario). An efficient cooperative sensing scheme promises a good tradeoff between both the metrics. In this work, the authors present a scheme providing improved cooperative gain for a centralized cooperative spectrum sensing network which employs hard combination at the fusion centre. Keywords: Cognitive Radio (CR); Primary User (PU), Secondary User (SU); Cooperative Spectrum Sensing; Centralized Cooperative Spectrum Sensing; Hard combination. I. INTRODUCTION The concept of cooperative spectrum sensing for cognitive radio networks emerged to combat difficulties such as multipath fading, shadowing and receiver uncertainty issues which could not be resisted by the non- cooperative spectrum sensing scheme [1]. Several recent works have shown that cooperative spectrum sensing can greatly increase the detection probability for fading channels. Cooperation can be among the CRs belonging to the network or external sensors can also be used to cooperate with the network nodes. Cooperative spectrum sensing among the CRs, in literature, is classified as centralized and decentralized cooperative spectrum sensing. Cooperation for spectrum sensing can be described in the following steps:  Stage 1 :Local Sensing  Stage 2: Reporting of locally sensed information  Stage 3: Information Fusion Local spectrum sensing, as the name suggests, refers to the sensing carried out by the individual nodes by examining their respective environments. Local sensing can be carried out through any of the basic transmitter detection techniques viz. matched filter detection, cyclostationary detection, entropy-based detection or energy detection. Energy detection is the most popular and widely used method because unlike the other three techniques, it does not require any a priori knowledge of the PU signal being detected and possess lower computational complexity. The stage followed by local sensing is the reporting where individual nodes ‘report’ the information gathered by them as a result of the local sensing carried out. The reported information can be in the form of single or multi bit decisions (as in hard and quantized combination) or in the form of raw locally sensed information (as in soft combination). In case of centralized cooperative sensing, there is a node-fusion centre reporting whereas in the decentralized scenario, node-node reporting takes place. Information fusion refers to the amalgamation of the information collected from the nodes into a unified/global decision on the state of the PU. Information fusion takes place at the fusion centre for the centralized cooperation whereas for the decentralized scenario, it takes place within a node. Information fusion techniques are broadly classified as ‘decision’ or ‘data’ fusion and are named as hard, soft and quantized combining schemes. The centralized cooperative spectrum sensing revolves around a central unit called the 'fusion centre (FC)' which controls all the phases of cooperation. The fusion centre selects frequency band for sensing and all CR nodes are instructed to perform individual sensing for the desired band. The CR users report their sensing results to the fusion centre through the