Effect level based parameterization method for diffuse scattering models at millimeter-wave frequencies

This paper proposes a multi-coefficient estimation method for the dielectric parameters of rough materials and an effect level-based parameterization method for diffuse scattering models to characterize and model the diffuse scattering propagation at millimeter-wave frequencies. A series of diffuse scattering propagation measurements and simulations for rough materials have been performed at 40-50 GHz in a typical indoor scenario. Theoretical reflection coefficient, transmission coefficient, and scattering coefficient of rough materials, which are requisite for the proposed estimation method, are derived based on the Fresnel theoretical model and the Gaussian rough surface model. The directive model and double-lobe model are chosen and integrated with ray tracing tool to simulate the diffuse multipath propagation for rough materials based on effect level evaluation results. The optimal model parameters are obtained and various simulation results are compared and in particular, the estimated ranges of scattering coefficients agree well with the measured values. The investigations demonstrate that the proposed parameterization method is reliable and accurate for the diffuse scattering models and can be applied for the determination of model parameters from extensive materials measurement data, especially for millimeter-wave channel analysis and modeling

Empirical multi-band characterization of propagation with modelling aspects for communictions

Diese Arbeit präsentiert eine empirische Untersuchung der Wellenausbreitung für drahtlose Kommunikation im Millimeterwellen- und sub-THz-Band, wobei als Referenz das bereits bekannte und untersuchte sub-6-GHz-Band verwendet wird. Die großen verfügbaren Bandbreiten in diesen hohen Frequenzbändern erlauben die Verwendung hoher instantaner Bandbreiten zur Erfüllung der wesentlichen Anforderungen zukünftiger Mobilfunktechnologien (5G, “5G and beyond” und 6G). Aufgrund zunehmender Pfad- und Eindringverluste bei zunehmender Trägerfrequenz ist die resultierende Abdeckung dabei jedoch stark reduziert. Die entstehenden Pfadverluste können durch die Verwendung hochdirektiver Funkschnittstellen kompensiert werden, wodurch die resultierende Auflösung im Winkelbereich erhöht wird und die Notwendigkeit einer räumlichen Kenntnis der Systeme mit sich bringt: Woher kommt das Signal? Darüber hinaus erhöhen größere Anwendungsbandbreiten die Auflösung im Zeitbereich, reduzieren das small-scale Fading und ermöglichen die Untersuchung innerhalb von Clustern von Mehrwegekomponenten. Daraus ergibt sich für Kommunikationssysteme ein vorhersagbareres Bild im Winkel-, Zeit- und Polarisationsbereich, welches Eigenschaften sind, die in Kanalmodellen für diese Frequenzen widergespiegelt werden müssen. Aus diesem Grund wurde in der vorliegenden Arbeit eine umfassende Charakterisierung der Wellenausbreitung durch simultane Multibandmessungen in den sub-6 GHz-, Millimeterwellen- und sub-THz-Bändern vorgestellt. Zu Beginn wurde die Eignung des simultanen Multiband-Messverfahrens zur Charakterisierung der Ausbreitung von Grenzwert-Leistungsprofilen und large-scale Parametern bewertet. Anschließend wurden wichtige Wellenausbreitungsaspekte für die Ein- und Multibandkanalmodellierung innerhalb mehrerer Säulen der 5G-Technologie identifiziert und Erweiterungen zu verbreiteten räumlichen Kanalmodellen eingeführt und bewertet, welche die oben genannten Systemaspekte abdecken.This thesis presents an empirical characterization of propagation for wireless communications at mm-waves and sub-THz, taking as a reference the already well known and studied sub-6 GHz band. The large blocks of free spectrum available at these high frequency bands makes them particularly suitable to provide the necessary instantaneous bandwidths to meet the requirements of future wireless technologies (5G, 5G and beyond, and 6G). However, isotropic path-loss and penetration-loss are larger with increasing carrier frequency, hence, coverage is severely reduced. Path-loss can be compensated with the utilization of highly directive radio-interfaces, which increases the resolution in the angular domain. Nonetheless, this emphasizes the need of spatial awareness of systems, making more relevant the question “where does the signal come from?” In addition, larger application bandwidths increase the resolution in the time domain, reducing small-scale fading and allowing to observe inside of clusters of multi-path components (MPCs). Consequently, communication systems have a more deterministic picture of the environment in the angular, time, and polarization domain, characteristics that need to be reflected in channel models for these frequencies. Therefore, in the present work we introduce an extensive characterization of propagation by intensive simultaneous multi-band measurements in the sub-6 GHz, mm-waves, and sub-THz bands. Firstly, the suitability of the simultaneous multi-band measurement procedure to characterize propagation from marginal power profiles and large-scale parameters (LSPs) has been evaluated. Then, key propagation aspects for single and multi-band channel modelling in several verticals of 5G have been identified, and extensions to popular spatial channel models (SCMs) covering the aforementioned system aspects have been introduced and evaluated

Empirical stairwell propagation models for long term evolution applications

This thesis presents investigation of path loss, PL, and shadowing, Xσ, of signal wave along and about multi floor stairways that have dog-leg stairwell configuration. The objective is to develop frequency-dependent empirical propagation models that could approximate PL and Xσ for two conditions. The first condition is when both transmitter, Tx, and receiver, Rx, are within the stairwell structure. The second condition is when either one of the Tx or Rx is inside adjacent rooms to the stairwells. Attention was also drawn towards the influence of stair flights and floor height to attenuation of signal wave as it propagates within the stairwell. Analysing the impact of the aforementioned structures within the stairwell, signal wave propagating between stairwell and adjacent in-building space as well as developing frequency-dependant empirical propagation model are research areas which have yet to be covered by previous propagation studies pertaining to multi floor stairway. Frequencies of interest, f, ranged from 0.7 GHz up to 2.5 GHz that cover various long term evolution (LTE) and public safety communication bands. Research works involved measurement campaign in four different multi-floor buildings inside Universiti Teknologi Malaysia’s campus. PL’s relations with separation distance between Tx and Rx, d, and f were formulated with auxiliary site-specific terms added to improve two proposed empirical propagation models. It was found that for signal wave propagation where both Tx and Rx were within the stairwell, placing Rx at elevated or lower position than Tx does not influence significantly recorded PL data. However, for propagation between stairwell and adjacent rooms, placing Rx at elevated or lower than Tx may influence significantly recorded PL data. Suitable measurement campaign planning was arranged in the light of this finding. The proposed models were then examined and compared with ITU-R, COST and WINNER II indoor empirical propagation models. From measurement in dedicated testing sites, it was demonstrated that the proposed models have the smallest computed mean, μR, relative to the other standard models. The largest μR was -2.96 dB with a 3.34 dB standard deviation, σR. On the other hand, results from COST, ITU-R and WINNER II models demonstrated lower precision in all inspected settings, with the largest μR being 8.06 dB, 7.71 dB and 15.98 dB respectively and their σR being 3.79 dB, 6.82 dB and 9.40 dB accordingly. The results suggest that the proposed PL models, which considered the impact of building structures within and about the stairwell could provide higher PL prediction’s accuracy for wireless communication planning pertaining to the stairwell environment, particularly for public safety responders

Reconfigurable antennas for wireless network security

Large scale proliferation of wireless technology coupled with the increasingly hostile information security landscape is of serious concern as organizations continue to widely adopt wireless networks to access and distribute critical and con dential information. Private users also face more risks than ever as they exchange more and more sensitive information over home and public networks through their ubiquitous wireless-enabled laptops and hand held devices. The fundamental broadcast nature of wireless data transmission aggravates the situation, since unlike wired networks, it introduces multiple avenues for attack and penetration into a network. Though several traditional mechanisms do exist to protect wireless networks against threats, such schemes are a carryover from the traditional wire based systems. Hence vulnerabilities continue to exist, and have been repeatedly demonstrated to be susceptible to failure under di erent circumstances.The resulting uncertainties have led to a signi cant paradigm shift in the design and implementation of wireless security in recent times, among which wireless channel based security schemes have shown the most promise. Channel based security schemes are rooted on the simple fact that a legitimate user and an adversary cannot be physically co-located and hence the underlying multi-path structure corresponding to the two links cannot be the same. However most wireless systems are constrained in terms of bandwidth, power and number of transceivers, which seriously limit the performance of such channel based security implementations. To overcome these limitations, this thesis proposes a new dimension to the channel based security approach by introducing the capabilities of recon gurable antennas. The main objective of this work is to demonstrate that the ability of recon gurable antennas to generate di erent channel realizations that are uncorrelated between di erent modes will lead to signi cant improvements in intrusion detection rates.To this end, two di erent schemes that make use of channels generated by a recon gurable antenna are proposed and evaluated through measurements. The rstscheme is based on associating a channel based ngerprint to the legitimate user to prevent intrusion. The three main components of this scheme are i ) a ngerprint derived from the di erent modes of the antenna, ii ) a metric to compare two ngerprints and iii ) a hypothesis test based on the proposed metric to classify intruders and legitimate transmitters. The second scheme relies on monitoring the statistics of the channels for the legitimate transmitters' links since any intrusion will result in an observable change in the channel's statistics. The problem is posed as a generalized likelihood ratio test (GLRT) which responds to any change in the channel statistics by a large spike in the likelihood ratio's value. The detector's performance is studied as a function of pattern correlation coe cient for both schemes to provide insights on designing appropriate antenna modes for better performance.Moreover this thesis takes a holistic approach to studying the antenna based security schemes. A novel channel modeling approach which combines the cluster channel model and site speci c ray tracer results is proposed and validated to facilitate the analysis of such schemes through simulations without resorting to comprehensive channel measurements. This approach is motivated by the lack of an intuitive and simple channel model to study systems that use recon gurable antennas for any application.Finally the design of a metamaterial based substrate that can help miniaturize antenna arrays and recon gurable antennas is presented. The magnetic permeabilityenhanced metamaterial's capability to miniaturize an antenna's size while maintaining an acceptable level of isolation between elements in an array is experimentallydemonstrated. The bene ts gained in a wireless communication system that uses a patch antenna arrray built on this substrate is quanti ed in terms of mean e ective gain, correlation between the antennas and channel capacity through channel measurements.Despite their capability to signi cantly improve spectral e ciency, the widespread adoption of recon gurable antennas in wireless devices has been hampered by their complexity, cost and size. The work presented in this thesis is therefore intended to serve as a catalyst to the widespread adoption of recon gurable antenna technology by i ) adding value to such antennas by utilizing them for enhancing system security and ii ) providing a mechanism to miniaturize them to facilitate their integration into modern space constrained wireless devices.Ph.D., Electrical Engineering -- Drexel University, 201

Lattice-Boltzmann simulations of cerebral blood flow

Computational haemodynamics play a central role in the understanding of blood behaviour in the cerebral vasculature, increasing our knowledge in the onset of vascular diseases and their progression, improving diagnosis and ultimately providing better patient prognosis. Computer simulations hold the potential of accurately characterising motion of blood and its interaction with the vessel wall, providing the capability to assess surgical treatments with no danger to the patient. These aspects considerably contribute to better understand of blood circulation processes as well as to augment pre-treatment planning. Existing software environments for treatment planning consist of several stages, each requiring significant user interaction and processing time, significantly limiting their use in clinical scenarios. The aim of this PhD is to provide clinicians and researchers with a tool to aid in the understanding of human cerebral haemodynamics. This tool employs a high performance fluid solver based on the lattice-Boltzmann method (coined HemeLB), high performance distributed computing and grid computing, and various advanced software applications useful to efficiently set up and run patient-specific simulations. A graphical tool is used to segment the vasculature from patient-specific CT or MR data and configure boundary conditions with ease, creating models of the vasculature in real time. Blood flow visualisation is done in real time using in situ rendering techniques implemented within the parallel fluid solver and aided by steering capabilities; these programming strategies allows the clinician to interactively display the simulation results on a local workstation. A separate software application is used to numerically compare simulation results carried out at different spatial resolutions, providing a strategy to approach numerical validation. This developed software and supporting computational infrastructure was used to study various patient-specific intracranial aneurysms with the collaborating interventionalists at the National Hospital for Neurology and Neuroscience (London), using three-dimensional rotational angiography data to define the patient-specific vasculature. Blood flow motion was depicted in detail by the visualisation capabilities, clearly showing vortex fluid ow features and stress distribution at the inner surface of the aneurysms and their surrounding vasculature. These investigations permitted the clinicians to rapidly assess the risk associated with the growth and rupture of each aneurysm. The ultimate goal of this work is to aid clinical practice with an efficient easy-to-use toolkit for real-time decision support

Novel improvements of empirical wireless channel models and proposals of machine-learning-based path loss prediction models for future communication networks.

Doctoral Degree. University of KwaZulu-Natal, Durban.Path loss is the primary factor that determines the overall coverage of networks. Therefore, designing reliable wireless communication systems requires accurate path loss prediction models. Future wireless mobile systems will rely mainly on the super-high frequency (SHF) and the millimeter-wave (mmWave) frequency bands due to the massively available bandwidths that will meet projected users’ demands, such as the needs of the fifth-generation (5G) wireless systems and other high-speed multimedia services. However, these bands are more sensitive and exhibit a different propagation behavior compared to the frequency bands below 6 GHz. Hence, improving the existing models and developing new models are vital for characterizing the wireless communication channel in both indoor and outdoor environments for future SHF and mmWave services. This dissertation proposes new path loss and LOS probability models and efficiently improves the well-known close-in (CI) free space reference distance model and the floating-intercept (FI) model. Real measured data was taken for both line-of-sight (LOS) and non-line-of-sight (NLOS) communication scenarios in a typical indoor corridor environment at three selected frequencies within the SHF band, namely 14 GHz, 18 GHz, and 22 GHz. The research finding of this work reveals that the proposed models have better performance in terms of their accuracy in fitting real measured data collected from measurement campaigns. In addition, this research studies the impact of the angle of arrival and the antenna heights on the current and improved CI and FI models. The results show that the proposed improved models provide better stability and sensitivity to the change of these parameters. Furthermore, the mean square error between the models and their improved versions was presented as another proof of the superiority of the proposed improvement. Moreover, this research shows that shadow fading’s standard deviation can have a notable reduction in both the LOS and NLOS scenarios (especially in the NLOS), which means higher precision in predicting the path loss compared to the existing standard models. After that, the dissertation presents investigations on high-ordering the dependency of the standard CI path loss model on the distance between the transmitting and the receiving antennas at the logarithmic scale. Two improved models are provided and discussed: second-order CI and third-order CI models. The main results reveal that the proposed two models outperform the standard CI model and notable reductions in the shadow fading’s standard deviation values as the model’s order increases, which means that more precision is provided. This part of the dissertation also provides a trade-off study between the model’s accuracy and simplicity

Simulated observations of and flow interactions with discs

This thesis presents simulations of the dynamics and radiation processes in accretion discs around young protostars. Firstly the dust continuum and molecular line emission from a graviationally unstable, 0.4M_sol disc around a young 1M_sol mass protostar are calculated. Such massive, unstable discs are thought to be an early stage in the evolution of low mass protostars and the gravitational instabilities in them provide a method of transferring angular momentum outwards and mass inward when there is insufficient ionised material for magnetic instabilities to provide such torques. The potential for observations of such a disc in continuum and line emission with ALMA is explored using radiative transfer and synthetic observations and four molecular traces of spiral structure are identified. Secondly, radiation-hydrodynamic models of accretion discs around 10M_sol protostars of varying radii are presented. The effects of different driving parameters and accretion luminosity are explored. The resulting density distribution is analysed in order to distinguish between ionised and neutral material. The amount of mass lost, the linear and rotational velocity of the winds and the division of the mass between the slow, dense disc wind and the fast rarefied polar wind is analysed for each of the models. The amount of visible mass lost through the disc is found to be strongly related to the luminosity of the disc and most of the disc mass is launched from the inner regions rather than mass loading further out. Finally radiative transfer modeling and synthetic observations are performed for the hydrodynamic models from the previous chapter. These include radio free-free emission, ionised carbon forbidden lines and hydrogen recombination lines. These are compared to observations of discs around MYSOs. The radio free-free emission is used as the input to a telescope simulation in order to provide synthetic interferometer observations with the e-Merlin radio telescope network