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In this paper, we present a modified Otsu 's algorithm for solving the automatic threshold estimation problem in energy detection based Cognitive Radio (CR) application. The modified algorithm was tested extensively and compared with other known algorithms using both simulated and real datasets. In particular, our findings reveal that the modified algorithm provides an averagely lower false alarm rate than the other techniques compared with in this paper. Furthermore, the results obtained show that the algorithm is independent of the bandwidth's size, while having a total complexity of O(V), where V is the total sample size. Thus, from the results of this paper, full and effective automatic blind spectrum sensing using an Energy Detector is possible in CR. This can be achieved at a Signal-to-Noise Ratio of 5 dB to meet the IEEE 802.22 draft standard of P >90% and P <10%.

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This paper studies the effect of correlation and fading parameter on the performance of an N-order conventional selection diversity system. A Nakagami fading channel with identical but nonindependent fading on the diversity branches is assumed. The joint distribution of the output of the combiner is expressed in terms of the Laguerre polynomials. This analysis can be applied to both coherent and noncoherent demodulation schemes and an arbitrary number of diversity branches. Numerical results are presented showing the effect of correlation and the degree of fading on the system performance for the dual diversity case.

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