Efficient Decision Fusion for Cooperative Spectrum Sensing Based on OR-rule

In this paper, we consider an efficient decision fusion technique for cooperative spectrum sensing based on the logical OR-rule for dynamic spectrum sharing among primary and secondary users (PUs and SUs, respectively). If the OR-rule is employed, the fusion center (FC) only needs to be informed if any of the local decisions is a "1". In this case, it may be a waste of resources to communicate each local decision in an orthogonal channel, as is commonly assumed. To reduce resource consumption, we consider that SUs with local decisions "1" transmit simultaneously in the same channel using continuous wave (CW) signaling, and that the FC declares that the PU is present if it detects the summed CWs. However, since phase synchronization may not be practical, the summed CWs may suffer from destructive interference. Theoretical analysis and simulation results indicate that even with a very large channel gain to noise power ratio (CNR) between the SUs and FC, the system may not achieve error-free signaling. To address this problem, we propose power control (PC) to reduce the effects of destructive interference. This technique makes it possible to guarantee that the CWs will not fully cancel each other. We also propose a phase shifting (PS) technique designed to improve worst-case detection performance by achieving diversity gain. These proposed methods are very simple and, although suboptimal, they provide good detection probabilities. Numerical results indicate that these proposals make it possible to practically attain the upper bound of error-free signaling, even with moderate CNR values.