This paper addresses the problem of the opportunistic spectrum access in Cognitive Radio. Indeed, most spectrum sensing algorithms suffer from a high computational cost to achieve the detection process. They need a prior knowledge of signal characteristics and present a bad performance in low Signal to Noise Ratio (SNR) environment. The choice of the optimal detection threshold is another issue for these spectrum sensing algorithms. To overcome the limits of spectrum detectors, we propose in this paper, a blind detection method based on the cyclostationary features of communication signals. Our detector evaluates the level of hidden periodicity contained in the observed signal to make decision on the state of a bandwidth. In order to reduce the computational cost, we take advantage of the FFT Accumulation Method to estimate the cyclic spectrum of the observed signal. Then, we generate the Cyclic Domain Profile of the cyclic spectrum which allows us to evaluate the level of the hidden periodicity in the signal. This level of periodicity is quantified through the crest factor of Cyclic Domain Profile, which represents the decision statistic of the proposed detector. We have established the analytic expression of the optimal threshold of the detection and the probability of detection to evaluate the performance of the proposed detector. Simulation results show that the proposed detector is able to detect the presence of a communication signal on a bandwidth in a very low SNR scenario.

Larger wireless access networks are required to meet the growing demand for mobile traffic and multimedia services. The use of RoF (Radio over Fiber) technology in combination with millimeter waves is a potential response to the requirements of broadband applications and high capacity networks. In this paper, we proposed a RoF architecture able to provide very high-speed wireless access points up to Gbps considering an indoor and outdoor environment conform to IEEE 802.11ad and IEEE 802.15.3c standard. Optical transmission and radio coverage have been studied by considering the uplink and downlink. System performance has been evaluated in the relation to the Error Vector Magnitude (EVM) for various modulation formats (BPSK, QPSK and 16QAM). Results showed that millimeter wave signals are successfully delivered over a 50 km fiber link and a wireless channel up to 32 m. Data throughput up to 5.28 Gbps has been reached. The proposed architecture can extend the range of applications for wireless communications in association with the unlicensed 60 GHz band with the advantages of better capacity, a wider coverage area and a reduction in the investment cost.

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