Spectrum Sensing (SS) constitutes the most critical task i n Cognitive Radio(CR) systems for Primary User (PU) detection. Cooperative Spectrum Sensing(CSS) is introduced to enhance the detection reliability of the PU in fadingenvironments. In this paper, we propose a soft decision based CSS algorithmusing energy detection by taking into account the noise uncertainty effect. Inthe proposed algorithm, two threshold levels are utilized based on predictingthe current PU activity, which can be successfully expected using a simplesuccessive averaging process with time. The two threshold levels are evaluatedbased on estimating the noise uncertainty factor. In addition, they are toggledin a dynamic manner to compensate the noise uncertainty effect and to increasethe probability of detection and decrease the probability of false alarm.Theoretical analysis is performed on the proposed algorithm to evaluate itsenhanced false alarm and detection probabilities over the conventional softdecision CSS using different combining schemes. In addition, simulation resultsshow the high efficiency of the proposed scheme compared to the conventionalsoft decision CSS, with high computational complexity enhancements.
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