Spectrum measurement, sensing, analysis and simulation in the context of cognitive radio

The radio frequency (RF) spectrum is a scarce natural resource, currently regulated locally by national agencies. Spectrum has been assigned to different services and it is very difficult for emerging wireless technologies to gain access due to rigid spectmm policy and heavy opportunity cost. Current spectrum management by licensing causes artificial spectrum scarcity. Spectrum monitoring shows that many frequencies and times are unused. Dynamic spectrum access (DSA) is a potential solution to low spectrum efficiency. In DSA, an unlicensed user opportunistically uses vacant licensed spectrum with the help of cognitive radio. Cognitive radio is a key enabling technology for DSA. In a cognitive radio system, an unlicensed Secondary User (SU) identifies vacant licensed spectrum allocated to a Primary User (PU) and uses it without harmful interference to the PU. Cognitive radio increases spectrum usage efficiency while protecting legacy-licensed systems. The purpose of this thesis is to bring together a group of CR concepts and explore how we can make the transition from conventional radio to cognitive radio. Specific goals of the thesis are firstly the measurement of the radio spectrum to understand the current spectrum usage in the Humber region, UK in the context of cognitive radio. Secondly, to characterise the performance of cyclostationary feature detectors through theoretical analysis, hardware implementation, and real-time performance measurements. Thirdly, to mitigate the effect of degradation due to multipath fading and shadowing, the use of -wideband cooperative sensing techniques using adaptive sensing technique and multi-bit soft decision is proposed, which it is believed will introduce more spectral opportunities over wider frequency ranges and achieve higher opportunistic aggregate throughput.Understanding spectrum usage is the first step toward the future deployment of cognitive radio systems. Several spectrum usage measurement campaigns have been performed, mainly in the USA and Europe. These studies show locality and time dependence. In the first part of this thesis a spectrum usage measurement campaign in the Humber region, is reported. Spectrum usage patterns are identified and noise is characterised. A significant amount of spectrum was shown to be underutilized and available for the secondary use. The second part addresses the question: how can you tell if a spectrum channel is being used? Two spectrum sensing techniques are evaluated: Energy Detection and Cyclostationary Feature Detection. The performance of these techniques is compared using the measurements performed in the second part of the thesis. Cyclostationary feature detection is shown to be more robust to noise. The final part of the thesis considers the identification of vacant channels by combining spectrum measurements from multiple locations, known as cooperative sensing. Wideband cooperative sensing is proposed using multi resolution spectrum sensing (MRSS) with a multi-bit decision technique. Next, a two-stage adaptive system with cooperative wideband sensing is proposed based on the combination of energy detection and cyclostationary feature detection. Simulations using the system above indicate that the two-stage adaptive sensing cooperative wideband outperforms single site detection in terms of detection success and mean detection time in the context of wideband cooperative sensing

Effect of flow patterns on two-phase flow rate in vertical pipes

During two-phase gas-liquid flow in pipelines, the fluids may take up different flow patterns. The exact nature of the flow pattern varies according to conduit size and geometry, fluids’ properties, and each phase’s velocity. When the conduit size and fluid properties are constant, then any changes in individual flow rates will result in changes to the flow regime. Predicting the flow patterns within a pipe is essential as it is a critical parameter that determines the pressure gradient and liquid holdup in the conduit. This paper presents the results in predicting the multiphase flow patterns and their effects on flow measurements in vertical pipes. The study was conducted on vertical upward multiphase flow using well and reservoir properties. OLGA dynamic simulator was used to predict flow pattern in a vertical pipeline for 35 oil wells using electrical submersible pumps (ESP) with external pipe diameters of 3.5 inch. The predicted oil flow rates of 35 ESP oil wells were compared with measured flow rates and a good agreement was observed. Indeed, the results indicated that the variation of the flow pattern had insignificant impact and it was insensitive to the accuracy of the flow rate values of the ESP oil wells where the average overall flow rates accuracy was lower than +/-10%. Additionally, simulation results demonstrated a promising model performance and showed the magnitude of possible variation between the oil rates measured with different methods

Fractional Ostrowski type inequalities for functions whose derivatives are s-preinvex

In this paper, we establish a new integral identity, and then we derive some new fractional Ostrowski type inequalities for functions whose derivatives are s-preinvexpeerReviewe

SIMULATION OF THE PRE- AND POST-TRANSIT TIME OF FLIGHT METHODS IN AMORPHOUS SILICON-LIKE. N+-I-P+ -CELLS SIMULATION DES METHODES DE PRE- ET POST-TRANSIT DE LA TECHNIQUE TEMPS DE VOL POUR LES CELLULES N+-I-P+ EN MATERIAU DE TYPE a-Si:H.

In this paper, we study, by numerical simulation, the Transient Photocurrent (TPC) resulting from the application of the 'TimeOf Flight' (TOF) technique to a-Si:H n+-i-p+ cell by using a typical Density Of States (DOS) of amorphous silicon. The preandpost-transit methods, currently used to probe the energy distribution of localised states, are then applied to reconstruct theproposed DOS from the simulated TPC. We demonstrate that the two methods of reconstruction are complementary andprovide an efficient tool of determining the transit time

MECANISMES DE FORMATION DES DEFAUTS DANS LE a-Si:H A L'EQUILIBRE ET SOUS L'ILLUMINATION. DEFECT FORMATION MECHANISMS IN a-Si:H AT EQUILIBRIUM STATE AND UNDER LIGHT-SOAKING

RESUMEA l'équilibre thermodynamique, la création des défauts dans la structure du silicium amorphe hydrogéné (a-Si:H) est le résultatde la conversion des liaisons faibles en liaisons pendantes provoquée par la diffusion de l'hydrogène. L'application de la loi del'effet de masse à cette réaction suivant le modèle defect pool permet la détermination de la densité d'états des défauts dans legap d'énergie. Lorsque le matériau est exposé à la lumière, la densité totale des défauts augmente. Nous proposons un nouveaumodèle pour simuler la cinétique de création des défauts induits par la lumière selon lequel l'évolution de la densité totale desdéfauts se trouve en accord avec les mesures expérimentales généralement observées.ABSTRACTAt thermodynamic equilibrium state, the defect creation process in hydrogenated amorphous silicon (a-Si:H) is the result ofdangling bonds weak bonds conversion induced by hydrogen diffusion. The application of the law of mass action to thisreaction according to defect pool model allows the determination of the defect state density in the gap. When the material isexposed to light, the total defect density increases. We propose a new model to simulate the light induced defect creationkinetic where the total defect density evolution is found to agree with observed experimental measurements

Experimental investigation of gas–oil–water phase flow in vertical pipes: influence of gas injection on the total pressure gradient

Experimental work has been conducted to study the infuence of gas injection on the phase inversion between oil and water fowing in a vertical pipe. A vertical transparent pipe test section line of 40 mm ID and 50 cm length was used. The test fuids used were synthetic oil and fltered tap water. Measurements were taken for mixture velocity, superfcial water velocity, superfcial gas velocity, and input superfcial oil velocity ranging from 0.4 to 3 m/s, 0.18 to 2 m/s, 0 to 0.9 m/s, and 0 to 1.1 m/s. Most of the experiments were conducted more than two times, and the reproducibility of the experiments was quite good. Special attention was given to the efect of oil and water concentration where phase inversion took place with and without gas injection. The results showed that the phase inversion point was close to water fraction of ~30%, for both water friction direction changes (from water to oil or from oil to water) and that the efective viscosity increases once the mixture velocity increases. On the other hand, the results with gas injection showed that gas injection had no efect on the oil or water concentration where phase inversion occurred. Furthermore, the study investigated the efect of gas–oil–water superfcial velocity on the total pressure gradient in the vertical pipe. It was found that the total pressure gradient was fast and increased at high superfcial gas velocity but was slow at low superfcial gas velocity. When the superfcial oil velocity increased, the total pressure gradient approached the pressure gradient of an oil–water two-phase fow. The obtained results were compared with few correlations found in the literature, and the comparison showed that the uncertainty of the fow pattern transition peak in this study is very lo

Analytical Study and Modeling of Free Vibrations of Functionally Graded Plates Using a Higher Shear Deformation Theory

In this paper, we have used an analytical method to analyze the vibratory behavior of plates in materials with gradient of properties, simply supported, proposing a refined non polynomial theory. The number of unknown functions involved in this theory is only four, as compared to five in the case of other higher shear deformation theories. The transverse shearing effects are studied according to the thickness of the plate. The motion equations for the FGM plates are obtained by the Hamilton principle application, the solutions are obtained using the Navier method, and then the fundamental frequencies are found, solving an eigenvalue equation system, the results of this analysis are presented and compared to those available in the literature

Regression analysis of masked competing risks data under cumulative incidence function framework

In the studies that involve competing risks, somehow, masking issues might arise. That is, the cause of failure for some subjects is only known as a subset of possible causes. In this study, a Bayesian analysis is developed to assess the effect of risks factor on the Cumulative Incidence Function (CIF) by adopting the proportional subdistribution hazard model. Simulation is conducted to evaluate the performance of the proposed model and it shows that the model is feasible for the possible applications

Some new Hermite–Hadamard type inequalities for functions whose nth derivatives are convex

We first create an integral identity for n-times differentiable functions. Relying on this identity, we establish some new Hermite–Hadamard type inequalities for functions whose nth derivatives are convex

Helioseismology with PICARD

PICARD is a CNES micro-satellite launched in June 2010 (Thuillier at al. 2006). Its main goal is to measure the solar shape, total and spectral irradiance during the ascending phase of the activity cycle. The SODISM telescope onboard PICARD also allows us to conduct a program for helioseismology in intensity at 535.7 nm (Corbard et al. 2008). One-minute cadence low-resolution full images are available for a so-called medium-$l$ program, and high-resolution images of the limb recorded every 2 minutes are used to study mode amplification near the limb in the perspective of g-mode search. First analyses and results from these two programs are presented here.Comment: 6 pages, 6 figures, Eclipse on the Coral Sea: Cycle 24 Ascending, GONG 2012 / LWS/SDO-5 / SOHO 27, November 12 - 16, 2012, Palm Cove, Queensland. Accepted for publication in Journal of Physics Conference Series on March 1st 201