Cognitive radio networks promise more efficient spectrum utilization by leveraging degrees of freedom and distributing data collection. The actual realization of these promises is challenged by distributed control, and incomplete, uncertain and possibly conflicting knowledge bases. We consider two problems in bootstrapping, evolving, and managing cognitive radio networks. The first is Link Rendezvous, or how separate radio nodes initially find each other in a spectrum band with many degrees of freedom, and little shared knowledge. The second is how radio nodes can negotiate for spectrum access with incomplete information. To address the first problem, we present our Frequency Parallel Blind Link Rendezvous algorithm. This approach, designed for recent generations of digital front-ends, implicitly shares vague information about spectrum occupancy early in the process, speeding the progress towards a solution. Furthermore, it operates in the frequency domain, facilitating a parallel channel rendezvous. Finally, it operates without a control channel and can rendezvous anywhere in the operating band. We present simulations and analysis on the false alarm rate for both a feature detector and a cross-correlation detector. We compare our results to the conventional frequency hopping sequence rendezvous techniques. To address the second problem, we model the network as a multi-agent system and negotiate by exchanging proposals, augmented with arguments. These arguments include information about priority status and the existence of other nodes. We show in a variety of network topologies that this process leads to solutions not otherwise apparent to individual nodes, and achieves superior network throughput, request satisfaction, and total number of connections, compared to our baselines. The agents independently formulate proposals based upon communication desires, evaluate these proposals based upon capacity constraints, create ariii guments in response to proposal rejections, and re-evaluate proposals based upon received arguments. We present our negotiation rules, messages, and protocol and demonstrate how they interoperate in a simulation environment.

Recent disasters, including the 9/11 terrorist attacks, Hurricane Katrina, the London subway bombings, and the California wildfires, have all highlighted the limitations of current mobile communication systems for public safety first responders. First, in a point-to-point configuration, legacy radio systems used by first responders from differing agencies are often made by competing manufacturers and may use incompatible waveforms or channels. In addition, first responder radio systems, which may be licensed and programmed to operate in frequency bands allocated within their home jurisdiction, may be neither licensed nor available in forward-deployed disaster response locations, resulting in an operational scarcity of usable frequencies. To address these problems, first responders need smart radio solutions which can bridge these disparate legacy radio systems together, can incorporate new smart radio solutions, or can replace these existing aging radios. These smart radios need to quickly find each other and adhere to spectrum usage and access policies. Second, in an infrastructure configuration, legacy radio systems may not operate at all if the existing communications backbone has been destroyed by the disaster event. A communication system which can provide a new, temporary infrastructure or can extend an existing infrastructure into a shaded region is needed. Smart radio nodes that make up the public safety infrastructure again must be able to find each other, adhere to spectrum usage policies, and provide access to other smart radios and legacy public safety radios within their coverage area. This work addresses these communications problems in the following ways. First, it applies cognitive radio technology to develop a smart radio system capable of rapidly adapting itself so it can communicate with existing legacy radio systems or other smart radios using a variety of standard and customized waveforms. These smart radios can also assemble themselves into an ad-hoc network capable of providing a temporary communications backbone within the disaster area, or a network extension to a shaded communications area. Second, this work analyzes and characterizes a series of rendezvous protocols which enable the smart radios to rapidly find each other within a particular coverage area. Third, this work develops a spectrum sharing protocol that enables the smart radios to adhere to spectral policies by sharing spectrum with other primary users of the band. Fourth, the performance of the smart radio architecture, as well as the performance of the rendezvous and spectrum sharing protocols, is evaluated on a smart radio network testbed, which has been assembled in a laboratory setting. Results are compared, when applicable, to existing radio systems and protocols. Finally, this work concludes by briefly discussing how the smart radio technologies developed in this dissertation could be combined to form a public safety communications architecture, applicable to the FCC's stated intent for the 700 MHz Band. In the future, this work will be extended to applications outside of the public safety community, specifically, to communications problems faced by warfighters in the military. / Ph. D.

A homotopy approach for solving constrained parameter optimization problems is examined. The first order necessary conditions, with the complementarity conditions represented using a technique due to Mangasarian, are solved. The equations are augmented to avoid singularities which occur when the active constraint set changes. The Chow-Yorke algorithm is used to track the homotopy path leading to the solution to the desired problem at the terminal point. Since the Chow-Yorke algorithm requires a fairly accurate computation of the Jacobian matrix, analytical representation of the system of equations is desired. Consequently, equations obtained using the true anomaly regularization of the governing equations were employed for the above purpose. A homotopy map suited for the space-flight rendezvous problem including a minimum radius constraint is developed, which can naturally deform any initial problem into some other valid desired problem. Several coplanar and non-coplanar solutions for circular and elliptic cases have been presented for the restricted time problem with a minimum radius constraint. / Ph. D.

No description available.

Cooperation is increasingly being applied in the control of interconnected multi-agent systems, and it introduces many benefits. In particular, cooperation can improve the efficiency of many types of missions, and adds flexibility and robustness against external disturbances or unknown obstacles. This thesis investigates cooperative maneuvers for aerial vehicles autonomously landing on moving platforms, and how to safely and robustly perform such landings on a real system subject to a variety of disturbances and physical and computational constraints. Two specific examples are considered: the landing of a fixed-wing drone on top of a moving ground carriage; and the landing of a quadcopter on a boat. The maneuvers are executed in a cooperative manner where both vehicles are allowed to take actions to reach their common objective while avoiding safety based spatial constraints. Applications of such systems can be found in, for example, autonomous deliveries, emergency landings, and search and rescue missions. Particular challenges of cooperative landing maneuvers include the heterogeneous and nonlinear dynamics, the coupled control, the sensitivity to disturbances, and the safety criticality of performing a high-velocity landing maneuver. The thesis suggests the design of a cooperative control algorithm for performing autonomous and cooperative landings. The algorithm is based on model predictive control, an optimization-based method where at every sampling instant a finite-horizon optimal control problem is solved. The advantages of applying this control method in this setting arise from its ability to include explicit dynamic equations, constraints, and disturbances directly in the computation of the control inputs. It is shown how the resulting optimization problem of the autonomous landing controller can be decoupled into a horizontal and a vertical sub-problem, a finding which significantly increases the efficiency of the algorithm. The algorithm is derived for two different autonomous landing systems, which are subsequently implemented in realistic simulations and on a drone for real-world flight tests. The results demonstrate both that the controller is practically implementable on real systems with computational limitations, and that the suggested controller can successfully be used to perform the cooperative landing under the influence of external disturbances and under the constraint of various safety requirements. / Samarbete tillämpas i allt högre utsträckning vid reglering av sammankopplade multiagentsystem, vilket medför både ökad robusthet och flexibilitet mot yttre störningar, samt att många typer av uppgifter kan utföras mer effektivt. Denna licentiatavhandling behandlar kooperativa och autonoma landningar av drönare på mobila landingsplatformar, och undersöker hur sådana landningar kan implementeras på ett verkligt system som påverkas av externa störningar och som samtidigt arbetar under fysiska och beräkningsmässiga begränsningar. Två exempel betraktas särskilt: först landingen av ett autonomt flygplan på en bil, därefter landning av en quadcopter på en båt. Landningarna utförs kooperativt, vilket innebär att båda fordonen har möjlighet att påverka systemet för att fullborda landningen. Denna typ av system har applikationer bland annat inom autonoma leveranser, nödlandningar, samt inom eftersöknings- och räddningsuppdrag. Forskningen motiveras av ett behov av effektiva och säkra autonoma landingsmanövrar, för fordon med heterogen och komplex dynamik som samtidigt måste uppfylla en mängd säkerhetsvillkor. I avhandlingen härleds  kooperativa regleralgoritmer för landningsmanövern. Reglermetoden som appliceras är modell-prediktiv reglerteknik, en optimeringsbaserad metod under vilken ett optimalt reglerproblem med ändlig horisont löses  varje samplingsperiod. Denna metod tillför här fördelar såsom explicit hantering av systemdynamik, och direkt inkludering av störningshantering och bivillkor vid beräkning av insignaler. På så sätt kan vi direkt i optimeringslösaren hantera säkerhetsvillkor och externa störningar. Det visas även hur lösningstiden för optimeringen kan effektiviseras genom att separera den horisontella och den vertikala dynamiken till två subproblem som löses sekvensiellt. Algoritmen implementeras därefter för två olika landingssystem, för att därefter tillämpas och utvärderas i realistiska simuleringsmiljöer med olika typer av störningar, samt med flygtester på en verklig plattform. Resultaten visar dels att reglermetoden ger önskade resultat med avseende både på störningshantering och uppfyllande av bivillkor från säkerhetskrav, och dels att algoritmen är praktiskt implementerbar även på system med begränsad beräkningskraft. / <p>QC 20190315</p>

Researchers who aim to evaluate proposed modifications to the Internet’s architecture face a unique set of challenges. Internet-based measurements provide limited value to such evaluations, as the quantities being measured are easily lost to ambiguity and idiosyncrasy. While simulations offer more control, Internet-like environments are difficult to construct due to the lack of ground truth in critical areas, such as topological structure and traffic patterns. This thesis develops a network topology and traffic models for a simulation-based evaluation of the PURSUIT rendezvous system, the name-based interdomain routing mechanism of an information-centric future Internet architecture. Although the empirical data used to construct the employed models is imperfect, it is nonetheless useful for identifying invariants which can shed light upon significant architectural characteristics. The contribution of this work is twofold. In addition to being directly applicable to the evaluation of PURSUIT’s rendezvous system, the methods used in this thesis may be applied more generally to any studies which aim to simulate Internet-like systems. / Forskare som syftar till att utvärdera föreslagna ändringar av Internet arkitektur står inför en unik uppsättning utmaningar. Internet-baserade mätningar ger begränsat värde för sådana utvärderingar, eftersom de kvantiteter som mäts är lätt förlorade mot tvetydighet och egenhet. Även om simuleringar ger mer kontroll är Internet-liknande miljöer svåra att konstruera på grund av bristen på kända principer i kritiska områden, såsom topologiska struktur och trafikmönster. Denna avhandling utvecklar en nättopologi och trafikmodeller för en simulering baserad utvärdering av PURSUIT mötesplatsen systemet, den namn-baserade interdomän routing mekanismen för en informations-centrerad arkitektur av framtidens Internet. Även om de empiriska data som används för att konstruera modeller är bristfällig, är det ändå användbart för att identifiera invarianter som kan belysa viktiga arkitektoniska egenskaper. Bidraget från detta arbete har två syften. Förutom att vara direkt tillämplig för utvärderingen av PURSUITs rendezvous system, kan de metoder som används i denna avhandling användas mer allmänt för studier som syftar till att simulera Internet-liknande system.

Cooperative control of autonomous multi-agent systems is a research areawhich is getting significant attention in recent years. Multi-agent systemsallow for a broad spectrum of applications and cooperation can increasetheir flexibility, efficiency and robustness to changes in external constraintsand disturbances. Focusing on autonomous vehicles, examples of possibleapplications of cooperative multi-agent systems include search and rescuemissions, autonomous delivery and performing of emergency landings.The purpose of the thesis is to develop and implement a cooperativerendezvous algorithm based on model predictive control and apply it to theproblem of autonomous landing in an indoor setting. The agents involved in themaneuver are a quadcopter and a ground carrier. The two agents cooperativelynegotiate on the optimal location for the touchdown taking also into accountrelevant spatial constraints and, if necessary, update that location, also referredto as rendezvous point, in real-time throughout the maneuver.The algorithm is first tested and validated in a simulated environment andfinally on the physical system during real-time operations.Additional scenarios are tested in the simulated environment in order tofurther inspect the potential capabilities of the developed algorithm. Thoseadditional simulations analyse how the algorithm behaves when a constantlateral wind influences the quadcopter; when the controllers operate at areduced frequency; and when the quadcopter is affected by an external Gaussiandisturbance.The developed algorithm proved to be suitable for the purpose, allowingthe agents to perform the desired maneuver in a relatively short time and witha high degree of precision. / Kooperativ reglering av autonoma fleragentsystem är ett forskningsområdesom har fått stor uppmärksamhet de senaste åren. Fleragentsystem möjliggörett brett spektrum av applikationer samtidigt som kooperation kan öka derasflexibilitet, effektivitet och robusthet mot förändringar i yttre begränsningar ochstörningar. Med fokus på autonoma fordon, exempel på möjliga tillämpningarav kooperativa fleragentsystem inkluderar sök- och räddningsuppdrag, autonomleverans och utförande av nödlandningar.Syftet med rapporten är att utveckla och implementera en kooperativrendezvous -algoritm baserad på modellprediktiv reglerteknik samt att tillämpaden för att utföra en inomhus autonom landning. I vår uppställning beståragenterna i manövern av en quadcopter och en markbärare. De två agenternaförhandlar samarbetsvilligt om den optimala platsen för landning samtidigtsom de beaktar relevanta rumsliga begränsningar och uppdaterar vid behovden platsen i realtid under hela manövern.Algoritmen testas och valideras först i en simulerad miljö och slutligen pådet fysiska systemet under en realtidsmiljö.Ytterligare scenarier testas i den simulerade miljön för att bortre inspekterapotentialen hos den utvecklade algoritmen. Dessa extra simuleringar illustrerarhur algoritmen beter sig när en konstant sidovind påverkar quadcoptern; närstyrenheterna arbetar med reducerad frekvens; och när quadcoptern påverkasav en yttre Gaussisk störning.Den utvecklade algoritmen visade sig vara lämplig för ändamålet, vilketgjorde att agenterna kunde utföra önskad manöver på relativt kort tid och medhög precision.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / The Near Earth Asteroid Rendezvous (NEAR) satellite will travel to the asteroid 433 Eros, arriving there early in 1999, and orbit the asteroid for 1 year taking measurements that will map the surface features and determine its elemental composition. NEAR is the first satellite to use the rate-1/6 convolutional encoding on its telemetry downlink. Due to the scarcity and complexity of full decoders, APL designed and built a less capable but inexpensive version of the decoder for use in the integration, test, and prelaunch checkout of the rate-1/6 encoder. This paper describes the rationale for the design, how it works, and the features that are included.

LNT est un langage formel de spécification récent, basé sur les algèbres de processus, où plusieurs processus concurrents et asynchrones peuvent interagir par rendez-vous multiple, c'est-à-dire à deux ou plus, avec échange de données. La boite à outils CADP (Construction and Analysis of Distributed Processes) offre plusieurs techniques relatives à l'exploration d'espace d'états, comme le model checking, pour vérifier formellement une spécification LNT. Cette thèse présente une méthode de génération d'implémentation distribuée à partir d'un modèle formel LNT décrivant une composition parallèle de processus. En s'appuyant sur CADP, nous avons mis au point le nouvel outil DLC (Distributed LNT Compiler), capable de générer, à partir d'une spécification LNT, une implémentation distribuée en C qui peut ensuite être déployée sur plusieurs machines distinctes reliées par un réseau. Pour implémenter de manière correcte et efficace les rendez-vous multiples avec échange de données entre processus distants, nous avons élaboré un protocole de synchronisation qui regroupe différentes approches proposées par le passé. Nous avons mis au point une méthode de vérification de ce type de protocole qui, en utilisant LNT et CADP, permet de détecter des boucles infinies ou des interblocages dus au protocole, et de vérifier que le protocole réalise des rendez-vous cohérents par rapport à une spécification donnée. Cette méthode nous a permis d'identifier de possibles interblocages dans un protocole de la littérature, et de vérifier le bon comportement de notre propre protocole. Nous avons aussi développé un mécanisme qui permet, en embarquant au sein d'une implémentation des procédures C librement définies par l'utilisateur, de mettre en place des interactions entre une implémentation générée et d'autres systèmes de son environnement. Enfin, nous avons appliqué DLC au nouvel algorithme de consensus Raft, qui nous sert de cas d'étude, notamment pour mesurer les performances d'une implémentation générée par DLC. / LNT is a recent formal specification language, based on process algebras, where several concurrent asynchronous processes can interact by multiway rendezvous (i.e., involving two or more processes), with data exchange. The CADP (Construction and Analysis of Distributed Processes) toolbox offers several techniques related to state space exploration, like model checking, to formally verify an LNT specification. This thesis introduces a distributed implementation generation method, starting from an LNT formal model of a parallel composition of processes. Taking advantage of CADP, we developed the new DLC (Distributed LNT Compiler) tool, which is able to generate, from an LNT specification, a distributed implementation in C that can be deployed on several distinct machines linked by a network. In order to handle multiway rendezvous with data exchange between distant processes in a correct and efficient manner, we designed a synchronization protocol that gathers different approaches suggested in the past. We set up a verification method for this kind of protocol, which, using LNT and CADP, can detect livelocks or deadlocks due to the protocol, and also check that the protocol leads to valid interactions with respect to a given specification. This method allowed us to identify possible deadlocks in a protocol from the literature, and to verify the good behavior of our own protocol. We also designed a mechanism that enables the final user, by embedding user-defined C procedures into the implementation, to set up interactions between the generated implementation and other systems in the environment. Finally, we used the new consensus algorithm Raft as a case study, in particular to measure the performances of an implementation generated by DLC.

Cognitive radio (CR) is seen as one of the enabling technologies for realizing a new regulatory spectrum management paradigm, viz. opportunistic spectrum sharing (OSS). In the OSS paradigm, unlicensed users (a.k.a. secondary users) opportunistically operate in fallow licensed spectrum on a non-interference basis to licensed users (a.k.a. incumbent or primary users). Incumbent users have absolute priority in licensed bands, and secondary users must vacate the channel where incumbent user signals are detected. A CR network is composed of secondary users equipped with CRs and it can coexist with incumbent users in licensed bands under the OSS paradigm. The coexistence between incumbent users and secondary users is referred to as incumbent coexistence, and the coexistence between CR networks of the same type is referred to as self-coexistence. In this dissertation, we address three coexistence-related problems at the medium access control (MAC) layer in CR networks: (1) the rendezvous (control channel) establishment problem, (2) the channel assignment problem in an ad hoc CR network, and (3) the spectrum sharing problem between infrastructure-based CR networks, i.e., the 802.22 wireless regional area networks (WRANs). Existing MAC layer protocols in conventional wireless networks fail to adequately address the key issues concerning incumbent and self coexistence that emerge in CR networks. To solve the rendezvous establishment problem, we present a systematic approach, based on quorum systems, for designing channel hopping protocols that ensure a pair of CRs to "rendezvous" within an upper-bounded time over a common channel that is free of incumbent user signals. In a single radio interface, ad hoc CR network, we propose a distributed channel assignment scheme that assigns channels at the granularity of "segments" for minimizing the channel switching overhead. By taking into account the coexistence requirements, we propose an inter-network spectrum sharing protocol that enables the sharing of vacant TV white space among coexisting WRANs. Our analytical and simulation results show that these proposed schemes can effectively address the aforementioned MAC layer coexistence problems in CR networks. / Ph. D.