| Cognitive radio (CR) technique is a new paradigm of designing wireless communications systems which aims to enhance the utilization of the spectrum. The core idea of CR is to allow the unlicensed user to access the spectrum by spectrum sensing without interference for the licensed user. From the core idea of CR, we can get that the spectrum sensing and interference estimation are the key techniques.This thesis mainly investigates the spectrum sensing and interference estimation techniques. According to the researches in this thesis, it can be divided into three parts:The first part of this thesis study some problems, including local spectrum sensing, cooperative spectrum sensing and wideband sensing. Many algorithms about these problems and their advantages and disadvantages are researched. For the local spectrum sensing, this thesis proposes a sensing algorithm using the cyclo-stationary feature of the OFDM signal. The simulation result shows that this algorithm has good performance.For sensing the primary signal reliably, a new detection algorithm based on the stochastic resonance (SR) is proposed in the second part of this thesis. The basic theory about the SR system and how to set the optimal SR noise are researched. Based on the SR theory in signal detection, we propose the new sensing method for the local SR sensing and the cooperative SR sensing. The performance of the proposed algorithm is analysed by theory formulas and simulation figures.In the last part of this thesis the problem of interference estimation is researched. A statistical model of interference based on the spectrum-sensing result is developed considering the parameters such as the CR users'density, number, location, and the underlying propagation environment. This thesis gives the comprehensive analysis of the distribution of the interference and gets the final distribution formulas. It is proved these formulas are correct and can be applied in the actual system using the simulations. |
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