Cooperative spectrum sensing in cognitive radio (CR) networks is studied in which each CR performs energy\r\ndetection to obtain a binary decision on the absence/presence of the primary user. The problem of interest is how to\r\nefficiently report and combine the local decisions to/at the fusion center under fading channels. In order to reduce\r\nthe required transmission bandwidth in the reporting phase, the paper examines nonorthogonal transmission of local\r\ndecisions by means of on-off keying. Proposed and analyzed is a novel decoding-based fusion rule that essentially\r\nperforms in three steps: (1) estimating minimum mean-square error of the transmitted information from cognitive\r\nradios, (2) making hard decisions of the transmitted bits based on the estimated information, and (3) combining the\r\nhard decisions in a linear manner. Simulation results support the theoretical analysis and show that the added\r\ncomplexity of the decoding-based fusion rule leads to a considerable performance gain over the simpler\r\nenergy-based fusion rule when the reporting links are reasonably strong.
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