Frequency Hopping Spread Spectrum (FHSS) signaling is used across many devices operating in both regulated and unregulated bands. In either situation, if there is a malicious device operating within these bands, or more simply a user operating out of the required specifications, the identification this user important to insure communication link integrity and interference mitigation. The identification of a user involves the grouping of that users signal transmissions, and the separation of those transmission from transmissions of other users in a shared frequency band. Traditional signal separation methods often require difficult to obtain hardware fingerprinting characteristics or approximate geo-location estimates. This work will consider the characteristics of FHSS signals that can be extracted directly from signal detection. From estimates of these hopping characteristics, novel source separation with classic clustering algorithms can be performed. Background knowledge derived from the time domain representation of received waveforms can improve these clustering methods with the novel application of cannot-link pairwise constraints to signal separation. For equivalent clustering accuracy, constraint-based clustering tolerates higher parameter estimation error, caused by diminishing received signal-to-noise ratio (SNR), for example. Additionally, prior work does not fully cover the implications of detecting and estimating FHSS signals using image segmentation on a Time-Frequency (TF) waterfall. This work will compare several methods of FHSS signal detection, and discuss how each method may effect estimation accuracy and signal separation quality. The use of constraint-based clustering is shown to provide higher clustering accuracy, resulting in more reliable separation and identification of active users in comparison to traditional clustering methods. / Master of Science / The expansion of technology in areas such as smart homes and appliances, personal devices, smart vehicles, and many others, leads to more and more devices using common wireless communication techniques such as WiFi and Bluetooth. While the number of wirelessly connected users expands, the range of frequencies that support wireless communications does not. It is therefore essential that each of these devices unselfishly share the available wireless resources. If a device is using more resources than the required limits, or causing interference with other’s communications, this device will impact many others negatively and therefore preventative action must be taken to prevent further disruption in the wireless environment. Before action can be taken however, the device must first be identified in a mixture of other wireless activity. To identify a specific device, first, a wireless receiver must be in close enough proximity to detect the power that the malicious device is emitting through its wireless communication. This thesis provides a method that can be used to identify a problem user based only off of its wireless transmission behavior. The performance of this identification is shown with respect to the received signal power which represents the necessary range that a listening device must be to identify and separate a problem user from other cooperative users that are communicating wirelessly.

TRANSIMS (Transportation Analysis Simulation System) is part of a multi-track Travel Model Improvement Program sponsored by the U. S. Department of Transportation (DOT), and the Environmental Protection Agency (EPA). The main objective of this thesis is to enhance and implement a principal module in TRANSIMS, called the Route Planner Module. The purpose of the Route Planner Module is to find time-dependent label-constrained shortest paths for transportation activities performed by travelers in the system. There are several variations of shortest path problems and algorithms that vary by application, contexts, complexity, required data, and computer implementation techniques. In general, these variants require some combination of the following inputs: a network consisting of nodes and links, and a travel time function on each link, which could be a time-independent or a time-dependent function, where the time-dependent functions account for time-of-day delays resulting from actual travel conditions such as peak-hour congestion. The problem then seeks a shortest path between one or more origin-destination pairs. A new variant, introduced in the context of TRANSIMS and which is the focus of the present study, also specifies labels for each arc denoting particular modes of travel, along with strings of admissible labels that delineate the permissible travel mode sequences that could be adopted by the user in traveling from the origin to the destination of the trip. The technique adopted by TRANSIMS to identify a suitable travel route for any user is a variant of Dijkstra's procedure for finding shortest paths, which is suitably modified to accommodate time-dependent travel times and label sequence constraints. The underlying problem is referred to as a Time-Dependent Label-Constrained Shortest Path Problem. The main objective of this research is to improve upon this procedure and study its implementation in order to develop a more effective scheme for determining time-dependent label-constrained shortest paths as a practical routing tool in multimodal transportation networks. Specifically, we enhance the following features of this procedure: (a) We recommend a method to work implicitly with a certain composition graph G* that combines the transportation network with the admissible label-sequence graph. This graph G* captures all possible paths for a given single trip starting from the origin node and ending at the destination node, while conforming with the admissible mode string. (b) We use more modern partitioned shortest path algorithmic schemes to implement the time-dependent label-constrained procedure. (c) We introduce the notion of curtailing search based on various indicators of progress and projected travel times to complete the trip. Finally, computer programs in C++ are written to implement the proposed overall algorithm, and are applied to solve some real multimodal transportation network problems. The indicators used to evaluate the performance of the algorithm include (i) time taken for computation on the real network, (ii) quality of solution obtained, (iii) ease of implementation, and (iv) extensibility of the algorithm for solving other variants of the shortest path problem. The results exhibit that the proposed algorithm, even without the approximate curtailing of the search process, exhibits good performance in finding optimal routes for real multimodal transportation networks. Although the various heuristic curtailments result in only approximate solutions, typically, they run much faster than the exact algorithm for the intuitive reason that the shortest path tree developed grows more pointedly in the direction of the destination. Among the different strategies implemented, our results suggest that the scheme based on the geometric structure of the underlying network, using either a constant predictive term, or multiplying this term with a suitable exponential decay function, yields an attractive candidate for heuristically curtailing the search. / Master of Science

Heterogeneous computing (HC) systems are essential parts of modern-day computing architectures such as cloud, cluster, grid, and edge computing. Many algorithms exist within the classical environment for mapping computational tasks to the HC system’s nodes, but this problem is not well explored in the quantum area. In this work, the practicality, accuracy, and computation time of quantum mapping algorithms are compared against eleven classical mapping algorithms. The classical algorithms used for comparison include A-star (A*), Genetic Algorithm (GA), Simulated Annealing (SA), Genetic Simulated Annealing (GSA), Opportunistic Load Balancing (OLB), Minimum Completion Time (MCT), Minimum Execution Time (MET), Tabu, Min-min, Max-min, and Duplex. These algorithms are benchmarked using several different test cases to account for varying system parameters and task characteristics. This study reveals that a quantum mapping algorithm is feasible and can produce results similar to classical algorithms.

The design of reflectarray surface currents that satisfy both radiation and user-defined antenna feasibility constraints is addressed through a novel paradigm which takes advantage of the non-uniqueness of inverse source (IS) problems. To this end, the synthesis is formulated in the IS framework and its non-measurable solutions are employed as a design DoF. Thanks to the adopted framework, a closed-form expression for the design of reflectarray surface currents is derived which does not require any iterative local/global optimization procedure and which inherently satisfies both the radiation and the feasibility design constraints. The features and potentialities of the proposed strategy are assessed through selected numerical experiments dealing with different reflectarray aperture types/sizes and forbidden region definitions.

Temporal reasoning has been an active research area for over twenty years, with most work focussing on either enhancing the efficiency of current temporal reasoning algorithms or enriching the existing algebras. However, there has been little research into handling over-constrained temporal problems except to recognise that a problem is over-constrained and then to terminate. As many real-world temporal reasoning problems are inherently over-constrained, particularly in the scheduling domain, there is a significant need for approaches that can handle over-constrained situations. In this thesis, we propose two backtracking algorithms to gain partial solutions to over-constrained temporal problems. We also propose a new representation, the end-point ordering model, to allow the use of local search algorithms for temporal reasoning. Using this model we propose a constraint weighting local search algorithm as well as tabu and random-restart algorithms to gain partial solutions to over-constrained temporal problems. Specifically, the contributions of this thesis are: The introduction and empirical evaluation of two backtracking algorithms to solve over-constrained temporal problems. We provide two backtracking algorithms to close the gap in current temporal research to solve over-constrained problems; The representation of temporal constraint networks using the end-point ordering model. As current representation models are not suited for local search algorithms, we develop a new model such that local search can be applied efficiently to temporal reasoning; The development of a constraint weighting local search algorithm for under-constrained problems. As constraint weighting has proven to be efficient for solving many CSP problems, we implement a constraint weighting algorithm to solve under-constrained temporal problems; An empirical evaluation of constraint weighting local search against traditional backtracking algorithms. We compare the results of a constraint weighting algorithm with traditional backtracking approaches and find that in many cases constraint weighting has superior performance; The development of a constraint weighting local search, tabu search and random-restart local search algorithm for over-constrained temporal problems. We extend our constraint weighting algorithm to solve under-constrained temporal problems as well as implement two other popular local search algorithms: tabu search and random-restart; An empirical evaluation of all three local search algorithms against the two backtracking algorithms. We compare the results of all three local search algorithms with our twobacktracking algorithms for solving over-constrained temporal reasoning problems and find that local search proves to be considerably superior.

We consider constrained variants of graph homomorphisms such as embeddings, monomorphisms, full homomorphisms, surjective homomorpshims, and locally constrained homomorphisms. We also introduce a new variation on this theme which derives from relations between graphs and is related to multihomomorphisms. This gives a generalization of surjective homomorphisms and naturally leads to notions of R-retractions, R-cores, and R-cocores of graphs. Both \\mbox{R-cores} and R-cocores of graphs are unique up to isomorphism and can be computed in polynomial time. The theory of the graph homomorphism order is well developed, and from it we consider analogous notions defined for orders induced by constrained homomorphisms. We identify corresponding cores, prove or disprove universality, characterize gaps and dualities. We give a new and significantly easier proof of the universality of the homomorphism order by showing that even the class of oriented cycles is universal. We provide a systematic approach to simplify the proofs of several earlier results in this area. We explore in greater detail locally injective homomorphisms on connected graphs, characterize gaps and show universality. We also prove that for every $d\\geq 3$ the homomorphism order on the class of line graphs of graphs with maximum degree $d$ is universal.

During aircraft development, the impact of vibrations is examined and how this affects the aircraft structure under different conditions. Those vibrations can damage electronic equipment that are installed within the fuselage and can even lead to material fatigue within the structure. To reduce vibrations there are two approaches that are preferred to use, installing vibration insulators attached between the structure and the electrical component or change the design of the structure to a stiffer one. Those methods are easiest to implement in an early stage of the development but in later stages, when vibration problems usually are detected, it is too difficult and expensive to do major changes of the structure and there is lack of space to implement vibration insulators. A third method is then to apply passive damping in form of damper mats to surfaces on structures where critical vibrations occurs.    The effects on the structural behavior when damper mats are applied to a certain structure are studied in this thesis work. The purpose is to get deeper knowledge about how damper mats can be used to reduce vibrations in aircraft structures. The type of damper mat that is studied is known as Constrained Layer Damping, CLD, which is a sandwich of a visco-elastic material layer and a stiffer constraining material layer. Modelling and simulation methods that are based on commercial FE-software have been developed. The analysis method is based on doing a modal analysis with structural damping taken into account. This makes it possible to predict the overall global damping at each structural mode. The models for damper mats have in this project been verified with experimental testing using typical damper mats. The methodology can be used to predict the behavior of damped structures in order to obtain an effective and lightweight passive damping solution. / Under utvecklingen av flygplan undersöks hur vibrationer påverkar flygplansstrukturen under olika förutsättningar. Dessa vibrationer kan skada elektronisk utrustning som är monterad i flygplanskroppen och kan även göra så att materialutmattning uppstår i flygplansstrukturen. För att motverka vibrationer finns det två metoder som är att föredra, antingen att montera vibrationsisolatorer mellan de elektroniska utrustningarna och strukturen eller att ändra designen på strukturer till en styvare. Dessa metoder är enkla att implementera i ett tidigt steg i utvecklingsprocessen men i senare steg, då vibrationsproblem ofta upptäcks, så är det för komplicerat och för dyrt att göra större ändringar på strukturen och så är det ont om plats för att kunna installera vibrations isolatorer. En tredje metod är istället att implementera passiv dämpning i form av dämpningsmattor på ytor av strukturen där kritiska vibrationer uppstår. Effekterna av det strukturella uppförandet när dämpningsmattor är applicerade på en viss struktur har studerats i det här examensarbetet. Syftet är att få en fördjupad kunskap om hur dämpningsmattor kan användas för att reducera vibrationer i flygplan strukturer. Den typ av dämpningsmatta som har studerats är känd som Constrained Layer Damping, CLD, vilken är en sandwich av ett visko-elastiskt lager samt ett styvare lager.  Modellerings och simuleringsmetoder som är baserade på kommersiella FE-mjukvaror har utvecklats. Analysmetoderna är baserade på att utföra modalanalys tillsammans med strukturell dämpning. Detta möjliggör att förutse den övergripande dämpningen vid varje strukturell mod. Modellerna för dämpningsmattorna har i det här projektet verifierats med experimental testning av typiska dämpningsmattor. Metodiken kan användas till att prediktera beteendet av dämpade strukturer för att uppnå en effektiv och lättviktig passiv dämpningslösning.

Various unmanned missions deploy vehicles such as missiles, torpedoes, ground robots, and unmanned aerial vehicles. Guidance strategies for these vehicles aim to intercept a target point and satisfy additional objectives such as specifications on impact angle and interception time. Certain impact angles are crucial for a greater warhead effectiveness, and minimizing the interception time is important for vehicles with limited endurance time and for reducing the probability of detection. This thesis considers the time-optimal impact angle constrained guidance problem for interception of moving targets. In the first part of the thesis, a Dubins paths–based guidance methodology for minimum-time lateral interception of a moving and non-maneuvering target is designed. The existence and the time-optimality of the paths are established for impact angle constrained interception of moving targets. The capture regions are analyzed and a classification of the initial geometries is developed for deducing the time-optimal path type. The corresponding guidance command for optimal interception can be generated from the information of initial engagement geometry and target’s speed. In the next part of the thesis, the concept of equivalent virtual target is introduced to address the problem of impact along a general direction. An algorithm is developed to obtain the optimal interception point for generalized interception scenarios. A proof of convergence is presented for the proposed algorithm. Achieving different impact angles, the interceptor often takes sharp turns. Following such curved trajectories, the interceptor may fail to keep the target inside the seeker field-of-view. In the next part of the thesis, the field-of-view characteristics of the proposed optimal guidance strategies are analyzed. Closed-form expressions are derived for the interceptor’s look-angle to the target. Satisfying field-of-view condition at endpoints of the path segments that constitute the optimal path is proven to guarantee target motion inside the field-of-view throughout the engagement. The stationary target case is also analyzed as a specific scenario. The last part of the thesis presents a method to extend the proposed guidance strategies to maneuvering target scenarios.

During the last decade, the number of devices capable of connecting to the Internet has grown enormously. The Internet of Things describes a scenario where Internet connected devices are ubiquitous and even the smallest device has a connection to the Internet. Many of these devices will be running on constrained platforms with limited power and computing resources. Implementing protocols that are both secure and resource efficient is challenging. Current protocols have generally been designed for mains powered devices; hence, they are not optimized for running on constrained devices. The Constrained Application Protocol (CoAP) is a protocol for network communication specifically designed for constrained devices. This thesis project examines CoAP and presents an extension that adds authentication in a way that is suitable for constrained devices, with respect to minimizing resource use. The proposed solution has been compared and contrasted with other alternatives for authentication, particularly those alternatives used with CoAP. It has also been implemented in code and experimentally evaluated with regards to performance versus vanilla CoAP. The main goal of this project is to implement a lightweight authentication extension for CoAP to be deployed and evaluated on constrained devices. This extension, called Short Message Authentication ChecK (SMACK), can be used on devices that require a method for secure authentication of messages while using only limited power. The main goal of the extension is to protect against battery exhaustion and denial of sleep attacks. Other benefits are that the extension adds no additional overhead when compared with the packet structure described in the latest CoAP specification. Minimizing overhead is important since some constrained networks may only support low bandwidth communication. / Under det senaste århundradet har antalet enheter som kan ansluta sig till Internet ökat enormt. ”The Internet of Things” beskriver ett scenario där Internet-anslutna enheter är närvarande överallt och även den minsta enhet har en uppkoppling till Internet. Många av dessa enheter kommer att vara begränsade plattformar med restriktioner på både kraft- och beräkningsresurser. Att implementera protokoll som både är säkra och resurseffektiva är en utmaning. Tillgängliga protokoll har i regel varit designade för enheter med anslutning till det fasta kraftnätet; på grund av detta är de inte optimerade för att köras på begränsade plattformar. Constrained Application Protocol (CoAP) är ett protokoll för nätverkskommunikation speciellt framtaget för begränsade plattformar. Denna uppsats undersöker CoAP protokollet och presenterar ett tillägg som erbjuder autentisering på ett sätt som passar begränsade plattformar, med avseende på att minimera resursanvändning. Den föreslagna lösningen har blivit beskriven och jämförd med andra alternativ för autentisering, speciellt de alternativ som används med CoAP. Lösningen har också implementerats i kod och blivit experimentellt utvärderad när det gäller prestanda jämfört med standardversionen av CoAP. Det huvudsakliga målet för detta projekt är att implementera en lättviktslösning för autentisering till CoAP som ska installeras och utvärderas på begränsade plattformar. Detta tillägg, Short Message Authentication checK (SMACK), kan användas på enheter som behöver en metod för säker autentisering av meddelanden samtidigt som kraftåtgången hålls låg. Huvudmålet för detta tillägg är att skydda mot batteridräneringsattacker och attacker som hindrar en enhet från att gå i viloläge. Andra fördelar är att tillägget inte kräver någon extra dataanvändning jämfört med paketstrukturen som beskrivs i den senaste CoAP-specifikationen. Att minimera overhead i kommunikationsprotokoll är viktigt eftersom vissa begränsade nätverk endast stödjer kommunikation över låg bandbredd.

This thesis focuses on vision-based detection and observation of small, slow-moving targets using a gimballed fixed-wing unmanned aircraft system (UAS). Generally, visual tracking algorithms are tuned to detect motion of relatively large objects in the scene with noticeably significant motion; therefore, applications such as high-altitude visual searches for human motion often ignore target motion as noise. Furthermore, after a target is identified, arbitrary maneuvers for transitioning to overhead orbits for better observation may result in temporary or permanent loss of target visibility. We present guidelines for tuning parameters of the Visual Multiple Target Tracking (Visual MTT) algorithm to enhance its detection capabilities for very small, slow-moving targets in high-resolution images. We show that the tuning approach is able to detect walking motion of a human described by 10-15 pixels from high altitudes. An algorithm is then presented for defining rotational bounds on the controllable degrees of freedom of an aircraft and gimballed camera system for maintaining visibility of a known ground target. Critical rotations associated with the fastest loss or acquisition of target visibility are also defined. The accuracy of these bounds are demonstrated in simulation and simple applications of the algorithm are described for UAS. We also present a path planning and control framework for defining and following both dynamically and visually feasibly transition trajectories from an arbitrary point to an orbit over a known target for further observation. We demonstrate the effectiveness of this framework in maintaining constant target visibility while transitioning to the intended orbit as well as in transitioning to a lower altitude orbit for more detailed visual analysis of the intended target.