Recently, lattices - a mathematical representation of infinite discrete points in the Euclidean space, have become an effective way to describe and analyze communication systems especially system those that can be modeled as linear Gaussian vector channel model. Channel codes based on lattices are preferred due to three facts: lattice codes have simple structure, the code can achieve the limits of the channel, and they can be decoded efficiently using lattice decoders which can be considered as the Closest Lattice Point Search (CLPS). Since the time lattice codes were introduced to Multiple Input Multiple Output (MIMO) channel, Sphere Decoder (SD) has been an efficient way to implement lattice decoders. Sphere decoder offers the optimal performance at the expense of high decoding complexity especially for low signal-to-noise ratios (SNR) and for high- dimensional systems. On the other hand, linear and non-linear receivers, Minimum Mean Square Error (MMSE), and MMSE Decision-Feedback Equalization (DFE), provide the lowest decoding complexity but unfortunately with poor performance. Several studies works have been conducted in the last years to address the problem of designing low complexity decoders for the MIMO channel that can achieve near optimal performance. It was found that sequential decoders using backward tree 
search can bridge the gap between SD and MMSE. The sequential decoder provides an interesting performance-complexity trade-off using a bias term. Yet, the sequential decoder still suffers from high complexity for mid-to-high SNR values. In this work, we propose a new algorithm for Bidirectional Fano sequential Decoder (BFD) in order to reduce the mid-to-high SNR complexity. Our algorithm consists of first constructing a unidirectional Sequential Decoder based on forward search using the QL decomposition. After that, BFD incorporates two searches, forward and backward, to work simultaneously till they merge and find the closest lattice point to the received signal. We show via computer simulations that BFD can reduce the mid-to-high SNR complexity for the sequential decoder without changing the bias value.

This research assesses shifts in tornado occurrence pattens in space and time employing continental United States tornado records with an Enhanced Fujita (EF) rating equal or greater than 1. In similar research, most researchers discard tornado records prior to 1980 due to factors including: magnitude anomalies related to development of the Fujita Scale, unpredictability in tornado reporting (escalating populace, storm spotters, and technologic improvements), and better data records from the Census Bureau. We therefore constructed two datasets using tornados recorded in the National Weather Service Storm Prediction Center’s Severe Weather GIS (SVRGIS) database: 1950-2019 (dataset 1) and 1980-2019 (dataset 2). The goals for this study were to 1) determine whether spatiotemporal patterns of recorded tornado activity have shifted over time, and 2) determine whether inclusion of pre-1980 tornado data changes the findings from 1). This study employed Space-Time Pattern Mining (STPM) to construct four spacetime cubes (STC) in ArcGIS Pro. Emerging Hot Spot Analysis (EHS) was employed to identify the changes in tornado occurrence (number of incidents in a STC cell) and magnitude (sum of tornado EF ratings for all incidents in a STC cell). EHS displayed increased tornado activity in the Southeast and decreased activity for areas in the Great Plains for both occurrence and magnitude in both datasets. This is interpreted as significant intensifying hot spots in the Southeast region and diminishing hot spots in the Great Plains indicating an east-south-east shift for both datasets. Similar findings for both datasets indicate that inclusion of the less reliable pre-1980’s tornado data does not change the results and we recommend that the practice of discarding pre-1980’s tornado data in tornado occurrence research be reconsidered.

L'objectif de cette thèse est de réunir les deux approches suivantes qui existent actuellement pour étudier une foule: ou bien à temps fixé on s'intéresse à la distribution spatiale des individus, ou bien on suit un seul individu à la fois au cours du temps. On se propose de construire des processus spatio-temporels, qui, comme leur nom l'indique, permettraient de rendre compte du caractère aléatoire des usages d'une foule dans un réseau de télécommunication, à la fois du point de vue spatial (modèles de route) et du point de vue temporel (déplacements sur ces routes, usages qui varient au cours de ces déplacements…). Une fois ces processus construits de manière rigoureuse, on étudie leur comportement d'une manière fine. Nous développons trois modèles différents qui chacun mènent à des formules analytiques fermées, ce qui permet de les utiliser d'une manière très confortable à des fins de dimensionnement. / This thesis consists in joining two approaches that currently exist when one wants to study crowds phenomena: either taking a snapshot by freezing time to study the spatial repartition of the individuals, or following one given individual over time.We build space-time processes that let us model random phenomena in a crowd, being on a spatial level (roads models) or a time level (movings on these roads, space-dependent behaviors…). Once we have built them in a rigorous manner, we study their properties, which let us obtain analytical closed formulas that can be widely used for dimensioning purposes.

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This thesis is an examination and evaluation of the development of Russell's theory of perception and its relation to the external world from 1905 to 1919. During this period Russell attempted a reductionist analysis of empirical knowledge, the foundations of which are sense-data with which we have direct acquaintance in perception. In the course of its development, Russell's theory of perception underwent considerable changes and modifications. I show that these changes and modifications do not seriously alter his main epistemological position which I identify as realism. The explicit treatment of Russell's realist theory of perception during the stipulated period had two clearly distinguishable subsidiary stages. The first stage, replacing his pre-"On Denoting" absolute realism, was between 1905 and 1912. Immediately after the publication of The Problems of Philosophy in 1912 there was a transitional period of scepticism which ultimately gave rise to the theory of logical construction. This period was between 1912 and 1919. These two stages represent what I take to be the periods of significant change and modification within Russell's realism. However, only during the first stage can Russell properly be called a committed representative realist. The first chapter introduces the issues to be addressed in this thesis. Chapters two and three cover the foundational aspects of Russell's theory of perception. In chapter two Russell's theory of acquaintance is thoroughly examined. The items discussed are the nature, objects and principle of acquaintance. I show that it is with regard to the objects of acquaintance that Russell's theory of acquaintance underwent considerable changes and revisions. I also present a detailed discussion of the principle of acquaintance and its role in Russell's epistemology, and suggest that it performs two important functions, one epistemological and the other semantical. Both of them are seen to run hand in hand. Chapter three is devoted to the doctrine of sense-data which, according to Russell, is the foundation of empirical knowledge during the stipulated period. Some obvious difficulties in interpreting sense-data are seen to disappear on closer inspection. I defend Russell from a certain arrount of misunderstanding regarding the sensibilia theory. I also trace and present the justification for a major modification of his notion of the judgment of perception from Principia Mathematica volume I to The Problems of Philosophy and from The Problems of Philosophy to subsequent works. It is suggested that such a modification is required for the internal consistency of Russell's theory of perception. Chapters four and five are devoted to the relation of perception to our knowledge of the external world. In chapter four the Problems of Philosophy view of the existence and nature of physical objects is investigated. I explain why Russell was right to hold that the naive realist's view is contradictory. I also show that after rejecting naive realism Russell explicitly coornitted himself to representative realism by holding a causal theory of perception. It is also shown that the episterrological dimension of the theory of descriptions allows him to overcome restrictions arising from the principle of acquaintance. The last part of this chapter explains the transition between Russell's preconstructionist and constructionist approaches to the relation of perception to physical objects. I show conclusively that Russell became a constructionist as early as 1912. In chapter five the construction of physical objects is discussed. The emphasis is placed on Russell's episte11Dlo:;ical motivation for such construction. I defend much of what Russell says about sensibilia and argue that the inclusion of unsensed sensibilia in construction violates neither the spirit of logical construction nor Occam's razor. I also defend Russell from the charge of phenomenalism. I argue that his constructionism does not comnit him to phenomenalism and that he always remained a realist. Chapter six examines the construction of space and time. I concede that Russell's attempt to construct a six-dimensional space is a failure but suggest that he does not need a six-dimensional space to give an account to the problem of perception. Regarding the construction of time, I show that Russell is for the most part correct in his construction of instants out of experienced events. In chapter seven I evaluate Russell's theory of perception. I show that Russell is neither completely consistent nor successful in his construction of physical objects. At the same time, I show that there is a consistency of purpose and direction which motivated Russell to introduce logical constructions. The purpose was to secure empirical knowledge from possible sceptical attack and to strike a compromise between his realism and his empiricism. The direction is towards the goal of establishing a bridge between perception and physics. I suggest that the constructionist view is a better approach towards, and a viable solution to, the problem of perception. / Thesis / Doctor of Philosophy (PhD)

A common practice for government defense agencies and commercial aeronautical companies is to use dual antennas on test flight air vehicles in order to overcome occlusion issues during high-speed telemetric maneuvers. The dual antennas, though never being masked at the same time, unfortunately lead to a drastic increase in nulls in the signal pattern. The result of this interference pattern can be compared to the effect of fading in a multiple-input multiple-output (MIMO) multi-path scattering environment. Confidence in this comparison leads to the use of unitary space-time MIMO codes to overcome the signal self-interference. The possibility and performance of several of these codes will be examined. Such criteria as training for channel estimation, use of shaped offset quadrature phase shift keying (SOQPSK), hardware facility, and data throughput will be compared for each code. A realistic telemetry channel will be derived to increase accuracy of simulated results and conclusions.

Commercial Off The Shelf (COTS) hardware has the advantages of low cost, modularity, and is easily upgraded. For Multiple-Input Multiple-Output (MIMO) space-time algorithms to be practical they must have the processing capability to execute in real-time. This makes COTS ideal for real-time MIMO research where the processing power increases exponentially with a linear increase in antennas. The BYU Electrical Engineering wireless lab has designed and built an eight processor transmitter and a twenty processor receiver to research and develop MIMO wireless communication. The Alamouti, 2 x 2 and 4 x 4 differential space-time MIMO algorithms have been partially implemented on the receiver using a variety of common parallel processing topologies to include: bus, line/ring, star, grid, hypercube, binary tree, and pyramid. Processor and inter-processor communication benchmarks were measured and used to quickly explore the performance of the previously mentioned topologies without expending time and effort on a full implementation of these MIMO algorithms using each topology. This methodology has the benefit of the creation of software libraries that can be used for testing or for complete MIMO algorithm implementation in the future. This thesis shows that a simple bus-based topology gives the best results when combined with the 4 x 4 differential space-time algorithm. This thesis also shows that if the number of receiving channels and processors increase at the same rate as the 2 x 2 to the 4 x 4 differential cases, then the ratio of decoding processing time to inter-processor communication time is reduced. If this trend continues, inter-processor communication will require more processing time than the actual space-time decoding algorithm. Due to the exponential increase in required processing, doubling the processing requirements obtained from the 4 x 4 case is not an adequate solution to implement real-time 8 x 8 differential decoding. As such, the BYU wireless lab's test system does not have enough processors to implement real-time 8 x 8 differential decoding. The BYU wireless lab should concentrate on a complete 4 x 4 implementation with increased bandwidth to make full use of the available processing power. The 8 x 8 case should also be explored but without the expectation of real-time communication. However, with the test system, additional DSP processors can easily be added to allow for increased processing requirements.

This research estimated the spatial-temporal patterns of tornadoes in the continental United States from 1950-2019 using the National Weather Service Storm Prediction Center’s Severe Weather GIS (SVRGIS) database. This study employed Space-Time Cube Analysis and Linear Kernel Density (Kernel Density Linear Process, (KDLP)) rather than the standard Kernel Density Estimation (KDE) approach; to evaluate whether tornado hotspot locations and intensities shift over time. The first phase of the study utilized KDLP to map changes in tornado hotspots and qualitatively assess decadal shifts in hotspot locations and intensities by occurrence and magnitude between decades using ArcGIS Pro and CrimeStat. Next an Emerging Hot Spot Analysis (EHSA) was employed to identify the changes in tornado occurrence and magnitude. ESHA results identified, by both occurrence and magnitude, significant intensifying hot spots in the Southeast region and diminishing hot spots in the Great Plains indicating an east-south-east shift.

Denna studie syftar till att undersöka sambandet mellan kriminalitet, viktimisering och exponering för kriminogena situationer. Självrapporterad data samlades in vid tre tillfällen från 525 Malmöungdomar, varav 320 uppfyllde studiens inkluderingskriterier. Resultaten visar att mycket tid spenderad oövervakad, mycket tid ägnad åt ostrukturerade aktiviteter, mycket tid i sällskap med vänner samt alkoholkonsumtion samvarierar med brottslighet och viktimisering i varierande utsträckning. Sambanden varierar dock i förhållande till de båda utfallsvariablerna och deltagarnas ålder. Livsstils-rutinaktivitetsteorin kan förklara resultaten men behöver i framtiden ta större hänsyn till ålder. Studiens två slutsatser är att (1) brottslighet och viktimisering bör betraktas som två olika men klart relaterade företeelser i förhållande till exponering för kriminogena situationer och att (2) ålder måste tas i beaktande i forskning om exponering för kriminogena situationer eftersom sambanden mellan exponering och de båda utfallsvariablerna varierar från tidiga till sena tonår. / This study aims to examine offending and victimization in relation to situational criminogenic exposure. Self-reported data was collected at three occasions from a sample of 525 adolescents in Malmö, of which 320 fulfilled the study’s inclusion criteria. The results show that spending a lot of time unsupervised, pursuing unstructured activities, spending a lot of time with peers, and alcohol use, are associated with offending and victimization to various extent. However, the associations vary according to outcome and in relation to the participants’ age. Lifestyle-Routine Activities Theory may explain the findings, but needs to consider age as an important factor in the future. The two conclusions from this study are that (1) offending and victimization should be treated as two different, yet related concepts in relation to situational criminogenic exposure, and that (2) it is important to add an age dimension to the study of situational criminogenic exposure because the associations between the exposure variables and the outcome variables vary from early to late adolescence.

The two-antenna problem in aeronautical mobile telemetry is created by the reception of two copies of the same RF waveform with different phases and time delays. Alamouti and Alamouti-like space time block codes can solve the two-antenna problem, but the decoder/detector needs to account for the different time delays between the signals received from the two transmit antennas. In this thesis, a comparison is made between the performance of Alamouti space-time block codes and time-reversed space-time block codes with 16-APSK to solve the two-antenna problem. The maximum likelihood decoder/detector for Alamouti-encoded 16-APSK is a sequence detector operating on a trellis with a large number of states. A practical state-reduction technique is presented. The results produce a trellis with 256 states and a small loss in bit error rate performance as long as the delay difference is not too big. The decoder/detector for the time-reversed space time block requires only waveform manipulations and channel matched filtering in the case where the two channels are simple delays. For the more general case of multipath propagation between the two transmit antennas and the receiver, the decoder/detector requires an equalizer; simulation results using a channel pair measured at a test range show that the decoder/detector is capable of achieving near AWGN performance with a modest equalizer.