On optimum sensing time over fading channels for Cognitive Radio system

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Volume Title

Elektroniikan, tietoliikenteen ja automaation tiedekunta | Master's thesis

Date

2010

Department

Major/Subject

Tietoliikennetekniikka

Mcode

S-72

Degree programme

Language

en

Pages

64

Series

Abstract

Cognitive Radio (CR) is widely expected to be the next Big Bang in wireless communications. In a CR network, the secondary users are allowed to utilize the frequency bands of primary users when these bands are not currently being used. For this, the secondary user should be able to detect the presence of the primary user. Therefore, spectrum sensing is of significant importance in CR networks. In this thesis, we consider the antenna selection problem over fading channels to optimize the trade off between probability of detection and power efficiency of CR systems. We formulate a target function consists of detection probability and power efficiency mathematically, and use energy detection sensing scheme to prove that the formulated problem indeed has one optimal sensing time which yields the highest target function value. Two modelling techniques are used to model the Rayleigh fading channels; one without correlations and one with correlations on temporal and frequency domains. For each model, we provide two scenarios for average SNRs of each channel. In the first scenario, the channels have distinguished level of average SNRs. The second scenario provides a condition in which the channels have similar average SNRs. The antenna selection criterion is based on the received signal strength; each simulation is compared with the worst case simulation, where the antennas are selected randomly. Numerical results have shown that the proposed antenna selection criterion enhanced the detection probability as well as it shortened the optimal sensing time. The target function achieved the higher value while maintaining 0.9 detection probability compared to the worst case simulation. The optimal sensing time is varied by other parameters, such as weighting factor of the target function.

Description

Supervisor

Tirkkonen, Olav

Thesis advisor

Wei, Lu

Keywords

cognitive radio, spectrum sensing, energy detecto, energy efficiency

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