Frequency domain techniques for void spectrum detection in cognitive radio network for emulation attack prevention

Cognitive Radio is relatively new standard for mobile communication, especially designed to meet the challenges of high spectrum demand for packet data. As spectrum is limited and expensive, unutilized spectrum is an economic constraint for the service provider. Cognitive radio provides a solution for this by providing means of reallocating the unused spectrum to secondary user (SU) when part of spectrum is unused by primary users (PU). Several past works have addressed this issue using various algorithm which ranges from statistical analysis to predictive analysis. In this paper we propose a novel solution for spectrum sensing using frequency domain analysis of the transmitted data. However one of the lesser addressed issues in this direction has been the consideration of PU emulation attack. If a SU has sufficient means of estimating void spectrum, then it can emulate a PU spectrum which then results is low accuracy in void spectrum detection. In this work we primarily focus on frequency domain analysis for void spectrum detection such that free spectrum can be padded up to prevent emulation attacks. We consider a cognitive radio network and adopt BPSK transmission. We assume that the access points are time synchronized and have preliminary knowledge of beginning of a transmission cycle. FFT of signal data in a time slot reveals the energy in the bands. By adaptive thresholding the energy of distinct bands we determine the free spectrum. Further we also demonstrate the means of reallocating this band by injecting secondary user data in the spectrum. We analyze the solution under AWGN channel. Comparison with QR based spectrum sensing technique reveals that the proposed work provides better sensing under high noise by triggering fewer false alarms and through more accurate prediction of the unused spectrum.