Spectrum Sensing and Multiple Access Schemes for Cognitive Radio Networks

Increasing demands on the radio spectrum have driven wireless engineers to rethink approaches by which devices should access this natural, and arguably scarce, re- source. Cognitive Radio (CR) has arisen as a new wireless communication paradigm aimed at solving the spectrum underutilization problem. In this thesis, we explore a novel variety of techniques aimed at spectrum sensing which serves as a fundamental mechanism to find unused portions of the electromagnetic spectrum. We present several spectrum sensing methods based on multiple antennas and evaluate their receiving operating characteristics. We study a cyclostationary feature detection technique by means of multiple cyclic frequencies. We make use of a spec- trum sensing method called sequential analysis that allows us to significantly decrease the time needed for detecting the presence of a licensed user. We extend this scheme allowing each CR user to perform the sequential analysis algorithm and send their local decision to a fusion centre. This enables for an average faster and more accurate detection. We present an original technique for accounting for spatial and temporal cor- relation influence in spectrum sensing. This reflects on the impact of the scattering environment on detection methods using multiple antennas. The approach is based on the scattering geometry and resulting correlation properties of the received signal at each CR device. Finally, the problem of spectrum sharing for CR networks is addressed in or- der to take advantage of the detected unused frequency bands. We proposed a new multiple access scheme based on the Game Theory. We examine the scenario where a random number of CR users (considered as players) compete to access the radio spec- trum. We calculate the optimal probability of transmission which maximizes the CR throughput along with the minimum harm caused to the licensed users’ performance

Cooperative spectrum sensing with censoring of cognitive radios with majority logic fusion in Hoyt fading

In this paper, the performance of cooperative spectrum sensing (CSS) is assessed in the presence of Hoyt fading. A cognitive radio (CR) user, which senses the primary users (PUs) using an energy detector (ED) in sensing channel (S-channel), is censored on the basis of the quality of the reporting channel (R-channel). A threshold-based censoring scheme is used: CR users, whose estimated R-channel fading coefficients towards the fusion center (FC) exceed a predefined threshold (denoted as censoring threshold), are allowed to transmit. Majority logic fusion is considered at the FC to estimate the performance in terms of average missed detection and total error probabilities for various values of the censoring threshold, the number of CRs, the false alarm probability, the average S-channel and R-channel signal-to-noise ratios (SNRs), under both perfect and imperfect channel coefficient estimations. The impact of the Hoyt fading parameter on the average missed detection probability is highlighted. Furthermore, an analytical expression for the probability of selection of CRs, in terms of the censoring threshold, is derived and validated with simulations

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen

Bowdoin Orient v.132, no.1-24 (2002-2003)

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