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Optimization of Congnitive Radio Networks Using Computational Intelligence

Thesis Info

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Author

Latif, Shahzad.

Program

PhD

Institute

Isra University

City

Hyderabad

Province

Sindh

Country

Pakistan

Thesis Completing Year

2018

Thesis Completion Status

Completed

Subject

Electronics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/9418/1/Shahzad%20Latif_EE_2018_Isra_PRR.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727804246

Similar


With the advent of high data rate applications and services, the spectrum demand has increased enormously. Moreover, most spectrum bands are underutilized and need be efficiently utilized for new wireless applications. Cognitive communication is promising technology to deal with this spectrum shortage problem. Cognitive radio is an intelligent device capable to utilized licensed bands for unlicensed users incurring the minimum interference to licensed users. The efficient utilization of spectrum resources which includes maximizing throughput and minimizing interference is a key research challenge in cognitive radio networks. This thesis presents efficient spectrum assignment algorithms in order to maximizes throughput, minimize the interference incurred to licensed users and interference among secondary users. Moreover, accumulative cost to buy licensed networks is reduced. The resource allocation is a multi-objective optimization problem.A fuzzy logic based ant colony algorithm is proposedin order to achieve above objectives in cognitive radio heterogeneous network (CRHN). This study presents a fuzzy logic based ant colony algorithm (FLACSA) for interference minimization towards Primary Users (PUs) and overall cost reduction ofsecondary users (SUs) to buy spectrum. Performance of FLACSA and ant colony system algorithm (ACSA) is evaluated againstparticle swarm optimization (PSO) and genetic algorithm (GA) approaches in literature and proposed scheme achieved very attractive results. A repair process based channel assignment algorithm is proposed and spectrum utility is optimized using differential evolutional based particle swarm algorithm and modified genetic algorithm in CRN. The performance of proposed algorithms is investigated against various parameters of network and evaluated against the other studied algorithms in literature. The results of proposed algorithms outclass all other algorithms studied in literature.
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Physical Properties of Yttrium Substituted Ferrites

This dissertation presents a systematic study on five series of spinel ferrites. Three series of spinel ferrites, namely, NiY-ferrites (NiY2xFe2-2xO4, x = 0.0 – 0.12, step: 0.02), MgY-ferrites (MgY2xFe2-2xO4, x = 0.0 – 0.12, step: 0.02) and NiZnY-ferrites (Ni0.6Zn0.4Y2xFe2-2xO4, x = 0.0 - 0.1, step: 0.02) were fabricated in a polycrystalline form by double sintering ceramic method. Two series of CoZnY-ferrites (Co1-xZnxY0.15Fe1.85O4, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) and CoY- ferrites (CoFe2O4 + x Y2O3, x = 0 wt %, 1 wt %, 3 wt %, 5 wt %) were fabricated by co- precipitation method. The samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Vibrating Sample Magnetometery (VSM) and Impedance spectroscopy and Ferromagnetic Resonance. Phase analysis of NiY-, MgY- and NiZnY-ferrites from XRD patterns has shown cubic spinel single phase along with few traces of second phase identified as orthorhombic phase. This phase becomes more conspicuous for higher concentration of yttrium. The lattice constant as a function of yttrium contents changes non-linearly. The behavior of the lattice parameter was explained on the basis of differences in ionic radii of the constituent ions. Analysis of the XRD patterns of the CoZnY-ferrites confirms the formation of cubic spinel phase along with second phase of YFeO3. The lattice seems to expand to accommodate the increased number of Zn2+ ions of relatively larger ionic radii. The phase analysis of the XRD patterns of CoY-ferrites shows that all the samples are dual phase except the sample with x = 0 wt %. The lattice constant was found to decrease with yttrium contents. The lattice seems to compress by the presence of second phase due to difference in thermal expansion coefficients. X-ray density and physical density was found to increase whereas porosity was found to decrease with the increase of yttrium contents. The morphology of the samples shows non-homogeneous distribution of grains in all the samples except CoZnY-ferrites. The near uniform distribution of grain size was observed in CoZnY ferrites. FTIR spectra of NiY-, MgY- and NiZnY-ferrites observed at room temperature in the wave number range 370 – 1100 cm-1 exhibit splitting of the two fundamental absorption bands, thereby confirming the solid state reaction. FMR spectra of NiY- and MgY-ferrites were measured at room temperature at X-band (9.5 GHz). The nominal compositions MgY0.04Fe1.96O4 and NiY0.12Fe1.88O4 have small linewidth, ΔH = 269 Oe and 282 Oe respectively. Hence these ferrites have potential for high frequency applications. A systematic study of variations in resistivity with different concentration of yttrium has been carried out to optimize the resistivity. The room temperature resistivity shows an increasing trend in all series whereas it was decreased in case of Co-Zn-Y ferrites. The addition of Y3+ ions in place of Fe3+ ions reduce the degree of conduction by blocking Verwey’s hopping mechanism resulting in an increase of resistivity. The temperature dependent dc resistivity was found to decrease linearly with rise in temperature. The observed decrease in dc resistivity with temperature is normal behavior for semiconductors which follows the Arrhenius relation. It was observed that the samples having higher values of resistivity also possessed higher activation energy. The saturation magnetization was observed to decrease with yttrium contents which are due to redistribution of cations on the tetrahedral and octahedral sites. The coercivity was observed to increase with yttrium contents. The smaller grains may obstruct the domain wall movement. As a result, the values of initial permeability ( μ i′ ) decreased from 110 to 35, 27 to 6 and 185 to 87 at 1 MHz in NiY-, MgY- and NiZnY- ferrites respectively. The values of magnetic loss tangent decreased from 0.23 to 0.03, 0.04 to 0.007, 1.2 to 0.41 in NiY-, MgY- and NiZnY-ferrites respectively. This may be attributed to the increase in resistivity that reduces the eddy current loss. The frequency dependent behaviors of dielectric constant follow the Maxwell–Wagner’s interfacial polarization in accordance with Koops phenomenological theory. The introduction of yttrium ions decreases the dielectric constant and dielectric loss tangent (tan δ). The results obtained are of great interest for the development of modified spinel ferrites for various industrial applications.