Nowadays, the spectrum becomes more crowded and to solve this problem we use the cognitive radio technology, cognitive radio is a promising technology used to improve of spectrum utilization. Among important functions of the cognitive radio is the spectrum sensing. Most of the research works on the spectrum sensing for the cognitive radio networks are considered in a fixed temporal state, they are ignored impact of the mobility of a secondary user. We interested in the concept of the spectrum sensing in realtime. In this paper, we propose an algorithm that examined the impact of the mobility of a secondary user to determine the parameters that affect the spectrum sensing in cognitive radio networks. The performance of the algorithm proposed is evaluated with simulations and results, and of course we will finish by a conclusion and a future perspective.
This paper presents a new concept to implement a tunable filter metamaterial with dual negative refraction composed of ferrite slabs and metallic resonators, including split-ring resonators (SRR), and short wire pairs. The ferrite slabs under an applied magnetics bias provide one magnetic resonance frequency band and the metallic resonators provide another one. The continuous wires within the metamaterials provide the negative permittivity in a wide frequency band covering the two magnetic resonance bands. This type of metamaterialis analyzed in detail, and tunable stop band filters are successfully designed. The effective electromagnetic parameters obtained from the simulation of the S-parameters indicate that metamaterial exhibit negative refraction bands, which can be shifted by changing the magnetic bias.
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