Thèses : « Layer by layer optimization »

1

Angelou, Marianna. « Cross-layer optimization in optical networks ». Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/83925.

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Network planning and operation in core optical networks require processes that lead to a cost-effective network able to effectively accommodate the given traffic demands. Crosslayer techniques that exploit information coming from the transport plane to serve either the network planning or the operation phases have been proposed to achieve optimal resource utilization and network performance. Dynamic impairment-aware networking refers to a solution that utilizes the dynamicity as well as the valuable physical-layer information of a reconfigurable WDM network to provide a smooth transition from the quasi-static networking of today to an intelligent reconfigurable and physical impairment-aware architecture. The concept of physical layer awareness allows intelligent techniques to offer optimal planning, dynamic configuration and management of the network while ensuring strong quality of transmission (QoT). A physical-layer performance estimating tool called Q-tool, has been designed and developed to deliver fast and accurate QoT assessments in dynamic single line-rate WDM networks employing 10 Gb/s OOK systems. The Q-tool was developed so as to feed with QoT evaluations the various cross-layer modules including offline RWA, monitor placement, regenerator placement, online RWA and failure handling. The significance of the physical-layer awareness and the role of Q-tool in the online routing strategy have been experimentally investigated using an impairment-enabled control-plane testbed. A cross-layer module that utilizes physical layer information to optimize the planning phase of single line-rate networks has been also developed; a monitor placement scheme was designed that takes into account partial monitoring information coming from the physical layer to decide the optimum number and locations of the optical monitoring devices. A techno-economic analysis was also conducted to explore the cost implications stemming from the resource optimization of a dynamic single line-rate network. Impairment aware and impairment-unaware algorithms along with the developed QoT tool were used to compare the planning solutions in terms of CapEx and OpEx. The challenges arising in the core networks of the next generation have also been addressed. Flexible optical networking has been introduced by the research community as a way to offer efficient utilization of the available optical resources while offering ultra-high speed rates. As opposed to the rate-specific and fixed-grid solution of a mixed line-rate (MLR) network, flexible networks are bandwidth agnostic and have the ability to adapt on- demand the delivered bit-rate. Yet, the increased level of flexibility imposes complex requirements; during network operation traffic is changing with time, leaving windows of spectrum of variable size unused. Moreover, interference from the neighbouring channels has to be taken into account and sufficient guard-bands ought to be considered. In such context the physical layer requirements for a spectrum-flexible optical superchannel were experimentally investigated by implementing a set of networking scenarios. The importance of the result is that it can act as input for cognitive algorithms that will enable a novel networking paradigm. Finally next generation core networks were evaluated from a cost, spectral and energy perspective so as to give a comprehensive view of the potential of the proposed technologies. The resource optimization achieved by flexible networks has been compared to single and mixed line-rate networks under the prism of cost and energy efficiency. It was shown that the capability of flexible networks to allocate efficiently the available spectrum, counterbalances the additional capital expenditures that are required to migrate to a multi-carrier system. In addition flexible networks achieve low energy per bit as they use just the amount of network resources needed for the given input traffic.

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Gifford, James Hart. « Optimization of the automated spray layer-by-layer technique for thin film deposition ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59883.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 82-83).
The operational parameters of the automated Spray-LbL technique for thin film deposition have been investigated in order to-identify their effects on film thickness and roughness. We use the automated Spray-LbL system developed at MIT by the Hammond lab to build 25 bilayer films of poly (ally amine hydrochloride) (PAH) and poly (acrylic acid) (PAA). Each of the 10 operational parameters of this system are explored individually to isolate each parameter's effect on film thickness and roughness. The parameter effects are analyzed for apparent trends to determine the parameters best suited for adjusting film thickness and roughness. The optimal parameters for thickness adjustment are polyelectrolyte solution concentration, polyelectrolyte spray time, spraying distance, air pressure and polyelectrolyte charge density. These parameters are independent of the type of species used to construct the film, and thus the trends should apply to any species used to construct thin films. The effect of each of the 10 operational parameters is examined in detail. While researching the parameter effects, polyelectrolyte interdiffusion in the films was observed. This interdiffusion is investigated using both the conventional dipped LbL and Spray-LbL deposition techniques. Interdiffusion is shown to be dependent on 3 factors, the charge density of the polyelectrolytes, the molecular weight of the polyelectrolytes, and the contact time between the polyelectrolyte solutions and the surface of the film. Interdiffusion is observed when the PAH is partially charged, the polyelectrolytes chains have a low molecular weight, and the contact time is sufficiently long enough to allow for interdiffusion. The significantly reduced contact time during the automated Spray-LbL process not only speeds up the film deposition time, but also significantly hinders the interdiffusion of PAH resulting in much thinner films than what is possible from dipping. Finally, the uniformity of the films produced using the automated Spray-LbL system is investigated. Films deposited on substrates greater than 1 in diameter area exhibit more than 20% variance in thickness. Adjustments were made to the setup of the system in an effort to expand this area of film thickness uniformity. However, it is determined that the design of this automated Spray-LbL system limits the film uniformity to an area of 1 in diameter.
by James Hart Gifford.
S.M.

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Warren, Christopher L. (Christopher Lane). « Submarine design optimization using boundary layer control ». Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10529.

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Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1997, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.
Includes bibliographical references (leaves 64-67).
by Christopher L. Warren.
M.S.
Nav.E.

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4

Chu, Zheng. « Transmit optimization techniques for physical layer security ». Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3377.

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Over the last several decades, reliable communication has received considerable attention in the area of dynamic network con gurations and distributed processing techniques. Traditional secure communications mainly considered transmission cryptography, which has been developed in the network layer. However, the nature of wireless transmission introduces various challenges of key distribution and management in establishing secure communication links. Physical layer security has been recently recognized as a promising new design paradigm to provide security in wireless networks in addition to existing conventional cryptographic methods, where the physical layer dynamics of fading channels are exploited to establish secure wireless links. On the other hand, with the ever-increasing demand of wireless access users, multi-antenna transmission has been considered as one of e ective approaches to improve the capacity of wireless networks. Multi-antenna transmission applied in physical layer security has extracted more and more attentions by exploiting additional degrees of freedom and diversity gains. In this thesis, di erent multi-antenna transmit optimization techniques are developed for physical layer secure transmission. The secrecy rate optimization problems (i.e., power minimization and secrecy rate maximization) are formulated to guarantee the optimal power allocation. First, transmit optimization for multiple-input single-output (MISO) secrecy channels are developed to design secure transmit beamformer that minimize the transmit power to achieve a target secrecy rate. Besides, the associated robust scheme with the secrecy rate outage probability constraint are presented with statistical channel uncertainty, where the outage probability constraint requires that the achieved secrecy rate exceeds certain thresholds with a speci c probability. Second, multiantenna cooperative jammer (CJ) is presented to provide jamming services that introduces extra interference to assist a multiple-input multipleoutput (MIMO) secure transmission. Transmit optimization for this CJaided MIMO secrecy channel is designed to achieve an optimal power allocation. Moreover, secure transmission is achieved when the CJ introduces charges for its jamming service based on the amount of the interference caused to the eavesdropper, where the Stackelberg game is proposed to handle, and the Stackelberg equilibrium is analytically derived. Finally, transmit optimization for MISO secure simultaneous wireless information and power transfer (SWIPT) is investigated, where secure transmit beamformer is designed with/without the help of arti - cial noise (AN) to maximize the achieved secrecy rate such that satisfy the transmit power budget and the energy harvesting (EH) constraint. The performance of all proposed schemes are validated by MATLAB simulation results.

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Miao, Guowang. « Cross-layer optimization for spectral and energy efficiency ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31807.

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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Li, Geoffrey Ye; Committee Member: Ma, Xiaoli; Committee Member: Stuber, Gordon; Committee Member: Wardi, Yorai; Committee Member: Yu, Xingxing. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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6

Hägg, Ragnar. « Scalable High Efficiency Video Coding : Cross-layer optimization ». Thesis, Uppsala universitet, Avdelningen för visuell information och interaktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-257558.

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In July 2014, the second version of the HEVC/H.265 video coding standard was announced, and it included the Scalable High efficiency Video Coding (SHVC) extension. SHVC is used for coding a video stream with subset streams of the same video with lower quality, and it supports spatial, temporal and SNR scalability among others. This is used to enable easy adaption of a video stream, by dropping or adding packages, to devices with different screen sizes, computing power and bandwidth. In this project SHVC has been implemented in Ericsson's research encoder C65. Some cross-layer optimizations have also been implemented and evaluated. The main goal of these optimizations are to make better decisions when choosing the reference layer's motion parameters and QP, by doing multi-pass coding and using the coded enhancement layer information from the first pass.

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7

Soldati, Pablo. « Cross-layer optimization of wireless multi-hop networks ». Licentiate thesis, Stockholm Stockholm : Elektrotekniska system, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4463.

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Loretti, Simone. « Cross-layer Optimization of CDMA Multihop Radio Networks ». Thesis, KTH, Reglerteknik, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-109471.

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In this thesis, the problem of finding the jointly Scheduling, Power and Rate allocation for Wireless ad hoc networks is considered. The motivation for this study is limiting multiuser interference in order to increase the total utility, throughput, and spatial reuse of the system. One such algorithm is realized for an S-TDMA (Spatial reuse-Time Division Multiple Access) environment where all communication links share the same frequency band and are power limited. Strong levels of interference inherent to wireless ad hoc network can not be overcome by computationally expensive power control algorithm. Therefore a scheduling algorithm becomes essential to coordinate the transmissions of the users in order to guarantee nonconflicting transmission and an efficient spatial reuse. In this work, firstly an algorithm that tries to simultaneously optimize routing, power/rate control and scheduling for a network composed by fixed nodes and channel gain depend only on distances, is developed. Then, with some modifications, the developed procedure handles node mobility and time-varying flat-fading channel. Numerical results indicate that both ones increase the performances of the system. Furthermore a formulation suitable for the study of energy-constrained networks is introduced. Finally this work investigates the use of multiuser detectors (MUD) in an ad hoc network environment. We demonstrate that multiuser detectors in the terminals give substantial improvements to the total network utility, even when we use very simple schemes for scheduling transmissions.

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Lin, Yuxia. « Cross-layer optimization in wireless local area networks ». Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/7571.

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This thesis studies several research problems in the area of wireless local area networks (WLANs) with an objective of improving network efficiency, quality-of-service and user satisfactions. The I E E E 802.11 Working Group has been under rapid development and expansion in recent years following the successful deployment of the 802.11 network around the globe. The thesis work has been striving to study several key problems in these developments and propose effective schemes to improve network performance. The original 802.11 standard presents a simple and robust design, but has relatively low data rate and lacks QoS support. The recent 802.11e standard and the 8 0 2 . l ln proposals aim to significantly improve the network performance in terms of QoS and throughput. In this thesis, an analytical model of I E E E 802.11e WLANs is first presented. With the help of this throughput model, an admission control scheme for a multi-hop 802.11e W L A N is proposed. To fully utilize the high data rate provided by 802.11n, the performance improvement of the M A C protocol by frame aggregation is studied. Two frame aggregation techniques, namely A - M P D U (MAC Protocol Data Unit Aggregation) and A - M S D U (MAC Service Data Unit Aggregation) are considered. Furthermore, a comprehensive network setup is studied where the QoS requirements of the 802.11e M A C and the MIMO physical layer of 8 0 2 . l ln are both considered. Cross-layer design schemes are proposed for WLANs under two different M A C protocols: the carrier sense multiple access with collision avoidance (CSMA/CA)-based 802.11e M A C , and the slotted Aloha M A C . Lastly, the thesis studies the problem of cooperative transmission in a wireless ad-hoc network with extensions to the 802.11 M A C protocols. A complete system framework is proposed for wireless adhoc networks utilizing two different cooperative relaying techniques at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer, diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Improvements in network performance for the proposed schemes are validated with numerical and simulation tests.

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Dubroca, Sabrina Marjorie. « Cross-Layer optimization in a satellite communication network ». Thesis, KTH, Radio Systems Laboratory (RS Lab), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127401.

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This thesis aims to improve a satellite communication network which carries both data streams and Voice over IP (VoIP) communication sessions with resource reservation. The resource reservations are made using the standard protocols for Traffic Engineering: MPLS-TE and RSVP-TE. The goal of this thesis project is to optimize the number of concurrent VoIP calls that can be made, in order to use the available bandwidth while maintaining a guaranteed Quality of Service (QoS) level, which is not possible in the existing system. This thesis proposes and evaluates a solution to this optimization problem in the specific context of a satellite modem system that was developed by Thales Communications. This optimization improves the system's ability to carry VoIP communications through better use of the available transmission resources. A solution to this problem would also increase the exibility in bandwidth allocation within the modem system, and could provide a framework for future development. The proposed solution allows all of the reservable bandwidth to be used. The amount of reservable bandwidth must be at least a little lower than the channel's available bandwidth in order to avoid congestion. Some areas of future work are proposed.
Detta projekt har försökt förbättra ett datornätverk bestående av satelliter som används till både data och Voice over IP (VoIP) kommunikation. VoIP använder sig av resursreservation som bestäms av standardprotokollen för Traffic Engineering, MPLS-TE och RSVP-TE. Målet är att optimera antalet samtidiga VoIP samtal så att det mesta av den befintliga bandbredden kan utnyttjas samtidigt som Quality of Service (QoS) kan garanteras. Detta är omöjligt i det befintliga systemet. Projektet föreslår en lösning för problemet med modemet som utvecklas av Thales Communications och utvärderar därefter lösningen. Dessa optimeringar förbättrar systemets förmåga att driva VoIP kommunikationer genom att bättre använda de befintliga resurserna. En lösning för det här problemet skulle höja systemets flexibilitet och kunna användas som underlag för kommande utvecklingar. Tack vare lösningen kan hela utsedda bandbredden reserveras. Antalet bandbredd som kan reserveras måsta vara minst lite lågre än total befintling bandbredd för att undvika överbelastning. även några möjliga ideer för vidare undersökning föreslås.
Ce projet a pour but d'améliorer un réseau de communication par satellite utilisé pour transporter des flux de données ainsi que des sessions de communication Voix sur IP (VoIP) avec réservation de ressources. Les réservations sont prises en charge par les protocoles standard de Traffic Engineering que sont MPLS-TE et RSVP-TE. L'objectif de ce projet est d'optimiser le nombre d'appels VoIP pouvant être passés en parallèle afin d'utiliser autant de bande passante que possible tout en offrant un niveau de Qualité de Service (QoS) garanti, chose impossible dans le système actuel. Ce rapport propose et évalue une solution à ce problème d'optimisation dans le contexte spécifique du modem satellite développé par Thales Communications. Ces optimisations amélioreraient la capacité du système à transporter des communications VoIP grâce à une meilleure utilisation des ressources disponibles pour la transmission. Une solution à ce problème rendrait aussi l'allocation de ressources plus flexible au sein du système, et pourrait fournir une base à de futurs développements. La solution proposée permet l'utilisation de toute la bande passante réservable. La quantité réservable doit être un peu inférieure à la bande passante totale disponible afin d'éviter la congestion. Les résultats de ces évaluations sont exposés. Enfin, ce rapport propose de futurs développements possibles.

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Mahajan, Rahul. « Cross-Layer Optimization : System Design and Simulation Methodologies ». Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/35920.

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An important aspect of wireless networks is their dynamic behavior. The conventional protocol stack is inflexible as various protocol layers communicate in a strict manner. In such a case the layers are designed to operate under the worst conditions as opposed to adapting to changing conditions. This leads to inefficient use of spectrum and energy. Adaptation represents the ability of network protocols and applications to observe and respond to channel conditions. Traditional simulation methodologies independently model the physical and higher layers. When multiple layer simulations are required, an abstraction of one layer is inserted into the other to provide the multiple layer simulation. However, recent advances in wireless communication technologies, such as adaptive modulation and adaptive antenna algorithms, demand a cross layer perspective to this problem in order to provide a sufficient level of fidelity. However, a full simulation of both layers often results in excessively burdensome simulation run-times. The benefits and possible parametric characterization issues arising due to the cross-layer integration of lower physical and higher network layers are investigated in this thesis. The primary objective of investigating cross-layer simulation techniques is to increase the fidelity of cross-layer network simulations while minimizing the simulation runtime penalties. As a study of cross-layer system design a medium access control (MAC) scheme is studied for a MANET wherein the nodes are equipped with smart antennas. Traditional MAC protocols assume the use of omnidirectional antennas. Nodes with directional antennas are capable of transmitting in certain directions only and significantly reduce the chances of collision and increase the effective network capacity. MANETs using omni-directional antennas severely limit system performance as the entire space around a node up to its radio range is seen as a single logical channel. In this research a MAC protocol is studied that exploits space division multiple access at the physical layer. This is a strong example where physical and MAC design must be carried out simultaneously for adequate system performance. Power control is a very important in the design of cellular CDMA systems which suffer from the near-far problem. Finally, the interaction between successive interference cancellation (SIC) receivers at the physical layer and power control, which is a layer 2 radio resource management issue, is studied. Traffic for future wireless networks is expected to be a mix of real-time traffic such as voice, multimedia teleconferencing, and games and data traffic such as web browsing, messaging, etc. All these applications will require very diverse quality of service guarantees. A power control algorithm is studied, which drives the average received powers to those required, based on the QoS requirements of the individual users for a cellular CDMA system using SIC receivers.
Master of Science

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Mandal, Pritesh. « Design and Optimization of Boundary Layer Ingesting Propulsor ». University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1573812115023373.

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Yin, Hujun. « Cross layer design and optimization of wireless networks / ». Thesis, Connect to this title online ; UW restricted, 2001. http://hdl.handle.net/1773/5904.

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Sohrmann, Christoph, et Jens Eller. « Optimal Layer Design ». Bachelor's thesis, Universitätsbibliothek Chemnitz, 2004. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200401468.

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In this bachelor thesis we report on our numerical investigations into the optimal design of protective multi-layer coatings subject to an external force of Hertzian form. In view of mechanical reliablity and durability of the substrate and the coating we aim to find the best composition of given materials with the least computational effort. Numerical studies are carried out using the simulation software ELASTICA being the first non-FEM approach for the computation of stress fields within multi-layer coated, elastic materials. We thereby made use of the massive parallel computer CLiC (Chemnitzer Linux Cluster) where we ran our Windows based application in a Wine Environment. The outcome of the optimization is in general very sensitive towards the input parameters(i.e., material properties) which are not always available in the desired accuracy. However, the scheme outlined in this work is shown to produce very good results and could contribute a great deal to find optimal solutions for real applications
Diese Bachelorarbeit befasst sich mit numerischen Untersuchungen zum optimalen Design von schützenden Mehrschichtbeschichtungen, die einer externen, Hertzschen Last ausgesetzt sind. Hinsichtlich der mechanischen Zuverlässigkeit und Haltbarkeit von Substrat und Beschichtung, versuchen wir die beste Zusammensetzung von gegebenen Materialien mit möglichst geringem Rechenaufwand zu finden. Die numerischen Berechungen wurden mit der Simulationssoftware ELASTICA durchgeführt, welches das erste kommerzielle, nicht-FEM-basierte Programm zur Berechnung von Stressfeldern innerhalb mehrfach beschichteter, elastischer Materialien darstellt. Dafür benutzten wir auf dem massiven Parrallelrechner CLiC (Chemnitzer Linux Cluster) unsere Windows basierte Anwendung unter der Emulationssoftware Wine. Das Ergebnis der Optimierung hängt im allgemeinen sehr stark von der Qualität der Eingangsparameter (z.B. Materialeigenschaften) ab, welche nicht immer in der erwünschten Genauigkeit vorliegen. Es wird gezeigt, dass die in dieser Arbeit vorgestellte Vorgehensweise sehr gute Resultate liefert und für reale Anwendungen einen äusserst ressourcenschonenden Lösungsweg darstellt

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Tambwe, Kevin. « P- and e- type Semiconductor layers optimization for efficient perovskite photovoltaics ». University of Western Cape, 2019. http://hdl.handle.net/11394/7414.

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>Magister Scientiae - MSc
Perovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity.

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Al-Ajmi, Mohammed. « Homogenization and topology optimization of constrained layer damping treatments ». College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1537.

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Thesis (Ph.D.) -- University of Maryland, College Park, 2004
Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Lim, Tat Lee. « Cross-layer design and optimization for wireless sensor networks ». Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FLim.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2006.
Thesis Advisor(s): Weilian Su. "March 2006." Includes bibliographical references (p. 61-64). Also available in print.

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CICALO', Sergio. « Cross-layer Optimization for Video Delivery over Wireless Networks ». Doctoral thesis, Università degli studi di Ferrara, 2014. http://hdl.handle.net/11392/2388943.

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As video streaming is becoming the most popular application of Internet mo- bile, the design and the optimization of video communications over wireless networks is attracting increasingly attention from both academia and indus- try. The main challenges are to enhance the quality of service support, and to dynamically adapt the transmitted video streams to the network condition. The cross-layer methods, i.e., the exchange of information among different layers of the system, is one of the key concepts to be exploited to achieve this goals. In this thesis we propose novel cross-layer optimization frameworks for scalable video coding (SVC) delivery and for HTTP adaptive streaming (HAS) application over the downlink and the uplink of Long Term Evolution (LTE) wireless networks. They jointly address optimized content-aware rate adaptation and radio resource allocation (RRA) with the aim of maximiz- ing the sum of the achievable rates while minimizing the quality difference among multiple videos. For multi-user SVC delivery over downlink wireless systems, where IP/TV is the most representative application, we decompose the optimization problem and we propose the novel iterative local approxi- mation algorithm to derive the optimal solution, by also presenting optimal algorithms to solve the resulting two sub-problems. For multiple SVC de- livery over uplink wireless systems, where healt-care services are the most attractive and challenging application, we propose joint video adaptation and aggregation directly performed at the application layer of the transmit- ting equipment, which exploits the guaranteed bit-rate (GBR) provided by the low-complexity sub-optimal RRA solutions proposed. Finally, we pro- pose a quality-fair adaptive streaming solution to deliver fair video quality to HAS clients in a LTE cell by adaptively selecting the prescribed (GBR) of each user according to the video content in addition to the channel condi- tion. Extensive numerical evaluations show the significant enhancements of the proposed strategies with respect to other state-of-the-art frameworks.

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Belleschi, Marco. « Cross-layer optimization protocols in Ad-hoc networks : analysis and practical implementation of transport and network layers ». Thesis, KTH, Reglerteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105891.

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Ad-hoc wireless networks use multi-hop transmissions to communicate, without exploiting any infrastructure. Logical links create unreliable connections between nodes: the capacity of the channel can unpredictably change due to the presence of obstructions, interferences between nodes and stochastic phenomena such as fading. Moreover the medium is multi-access and resources are contended by different users. It is possible to notice that adjusting the power at the physical layer affects the interference perceived, which in turn modifies the resources availability, alters the queue length at the network layer and eventually influences the source rates at the transport layer. To this end, a lot of works have shown that a better understanding of inherent coupling between different layers in the networking stack is worth. Specifically, network performances can be increased if the traditionally separated network layers are jointly optimized. Network utility maximization has emerged as a powerful framework for studying such cross-layer issues and optimizing performances overall the network. In particular, we focus on distributed cross-layer algorithms that achieve a global optimum recurring to local information only. Although the literature is vast in this field, most of works remain as theory. We aim at clarifying the practical feasibility of such theoretical dissertations and what considerations are needed in order to establish a bridge between theory and practice. After analyzing different crosslayer methods, we focus on the work of Papandriopoulos et al.. We first discuss its theoretical benefits in an interference limited system such as CDMA, without accounting physical constraints of the network. In order to validate the performances in a more realistic scenario, we implement the algorithm of Papandriopoulos et al. in the NS-2 network simulator without breaking up the hierarchy of the standard ISO/OSI stack. We focus on modeling physical, data link, network and transport layer, underlining issues and possible solutions from a practical perspective. For instance, we propose a novel approach to calculate the congestion prices of the network. After discussing benefits and drawbacks of the underlying theory, we propose several results under many simulation scenarios and eventually a comparison with the standard protocol for wireless networks IEEE/802.11.

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Pedrola, Escribà Oscar. « Cross-layer modeling and optimization of next-generation internet networks ». Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/113601.

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Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times.

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Ruiz, Ramírez Marc. « Characterization, design and re-optimization on multi-layer optical networks ». Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/97163.

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L'augment de volum de tràfic IP provocat per l'increment de serveis multimèdia com HDTV o vídeo conferència planteja nous reptes als operadors de xarxa per tal de proveir transmissió de dades eficient. Tot i que les xarxes mallades amb multiplexació per divisió de longitud d'ona (DWDM) suporten connexions òptiques de gran velocitat, aquestes xarxes manquen de flexibilitat per suportar tràfic d’inferior granularitat, fet que provoca un pobre ús d'ample de banda. Per fer front al transport d'aquest tràfic heterogeni, les xarxes multicapa representen la millor solució. Les xarxes òptiques multicapa permeten optimitzar la capacitat mitjançant l'empaquetament de connexions de baixa velocitat dins de connexions òptiques de gran velocitat. Durant aquesta operació, es crea i modifica constantment una topologia virtual dinàmica gràcies al pla de control responsable d’aquestes operacions. Donada aquesta dinamicitat, un ús sub-òptim de recursos pot existir a la xarxa en un moment donat. En aquest context, una re-optimizació periòdica dels recursos utilitzats pot ser aplicada, millorant així l'ús de recursos. Aquesta tesi està dedicada a la caracterització, planificació, i re-optimització de xarxes òptiques multicapa de nova generació des d’un punt de vista unificat incloent optimització als nivells de capa física, capa òptica, capa virtual i pla de control. Concretament s'han desenvolupat models estadístics i de programació matemàtica i meta-heurístiques. Aquest objectiu principal s'ha assolit mitjançant cinc objectius concrets cobrint diversos temes oberts de recerca. En primer lloc, proposem una metodologia estadística per millorar el càlcul del factor Q en problemes d'assignació de ruta i longitud d'ona considerant interaccions físiques (IA-RWA). Amb aquest objectiu, proposem dos models estadístics per computar l'efecte XPM (el coll d'ampolla en termes de computació i complexitat) per problemes IA-RWA, demostrant la precisió d’ambdós models en el càlcul del factor Q en escenaris reals de tràfic. En segon lloc i fixant-nos a la capa òptica, presentem un nou particionament del conjunt de longituds d'ona que permet maximitzar, respecte el cas habitual, la quantitat de tràfic extra proveït en entorns de protecció compartida. Concretament, definim diversos models estadístics per estimar la quantitat de tràfic donat un grau de servei objectiu, i diferents models de planificació de xarxa amb l'objectiu de maximitzar els ingressos previstos i el valor actual net de la xarxa. Després de resoldre aquests problemes per xarxes reals, concloem que la nostra proposta maximitza ambdós objectius. En tercer lloc, afrontem el disseny de xarxes multicapa robustes davant de fallida simple a la capa IP/MPLS i als enllaços de fibra. Per resoldre aquest problema eficientment, proposem un enfocament basat en sobre-dimensionar l'equipament de la capa IP/MPLS i recuperar la connectivitat i el comparem amb la solució convencional basada en duplicar la capa IP/MPLS. Després de comparar solucions mitjançant models ILP i heurístiques, concloem que la nostra solució permet obtenir un estalvi significatiu en termes de costos de desplegament. Com a quart objectiu, introduïm un mecanisme adaptatiu per reduir l'ús de ports opto-electrònics (O/E) en xarxes multicapa sota escenaris de tràfic dinàmic. Una formulació ILP i diverses heurístiques són desenvolupades per resoldre aquest problema, que permet reduir significativament l’ús de ports O/E en temps molt curts. Finalment, adrecem el problema de disseny resilient del pla de control GMPLS. Després de proposar un nou model analític per quantificar la resiliència en topologies mallades de pla de control, usem aquest model per proposar un problema de disseny de pla de control. Proposem un procediment iteratiu lineal i una heurística i els usem per resoldre instàncies reals, arribant a la conclusió que es pot reduir significativament la quantitat d'enllaços del pla de control sense afectar la qualitat de servei a la xarxa.
The explosion of IP traffic due to the increase of IP-based multimedia services such as HDTV or video conferencing poses new challenges to network operators to provide a cost-effective data transmission. Although Dense Wavelength Division Multiplexing (DWDM) meshed transport networks support high-speed optical connections, these networks lack the flexibility to support sub-wavelength traffic leading to poor bandwidth usage. To cope with the transport of that huge and heterogeneous amount of traffic, multilayer networks represent the most accepted architectural solution. Multilayer optical networks allow optimizing network capacity by means of packing several low-speed traffic streams into higher-speed optical connections (lightpaths). During this operation, a dynamic virtual topology is created and modified the whole time thanks to a control plane responsible for the establishment, maintenance, and release of connections. Because of this dynamicity, a suboptimal allocation of resources may exist at any time. In this context, a periodically resource reallocation could be deployed in the network, thus improving network resource utilization. This thesis is devoted to the characterization, planning, and re-optimization of next-generation multilayer networks from an integral perspective including physical layer, optical layer, virtual layer, and control plane optimization. To this aim, statistical models, mathematical programming models and meta-heuristics are developed. More specifically, this main objective has been attained by developing five goals covering different open issues. First, we provide a statistical methodology to improve the computation of the Q-factor for impairment-aware routing and wavelength assignment problems (IA-RWA). To this aim we propose two statistical models to compute the Cross-Phase Modulation variance (which represents the bottleneck in terms of computation time and complexity) in off-line and on-line IA-RWA problems, proving the accuracy of both models when computing Q-factor values in real traffic scenarios. Second and moving to the optical layer, we present a new wavelength partitioning scheme that allows maximizing the amount of extra traffic provided in shared path protected environments compared with current solutions. Specifically, we define several statistical models to estimate the traffic intensity given a target grade of service, and different network planning problems for maximizing the expected revenues and net present value. After solving these problems for real networks, we conclude that our proposed scheme maximizes both revenues and NPV. Third, we tackle the design of survivable multilayer networks against single failures at the IP/MPLS layer and WSON links. To efficiently solve this problem, we propose a new approach based on over-dimensioning IP/MPLS devices and lightpath connectivity and recovery and we compare it against the conventional solution based on duplicating backbone IP/MPLS nodes. After evaluating both approaches by means of ILP models and heuristic algorithms, we conclude that our proposed approach leads to significant CAPEX savings. Fourth, we introduce an adaptive mechanism to reduce the usage of opto-electronic (O/E) ports of IP/MPLS-over-WSON multilayer networks in dynamic scenarios. A ILP formulation and several heuristics are developed to solve this problem, which allows significantly reducing the usage of O/E ports in very short running times. Finally, we address the design of resilient control plane topologies in GMPLS-enabled transport networks. After proposing a novel analytical model to quantify the resilience in mesh control plane topologies, we use this model to propose a problem to design the control plane topology. An iterative model and a heuristic are proposed and used to solve real instances, concluding that a significant reduction in the number of control plane links can be performed without affecting the quality of service of the network.

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Chen, Jack Szu-Shen. « Distortion-free tolerance-based layer setup optimization for layered manufacturing ». Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/27268.

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Layer manufacturing has emerged as a highly versatile process to produce complex parts compared to conventional manufacturing processes, which are either too costly to implement or just downright not possible. However, this relatively new manufacturing process is characterized by a few outstanding issues that have kept the process from being widely applied. The most detrimental is the lack of a reliable method on a computational geometry level to predict the resulting part error. Layer setup with regard to the contour profile and thickness of each layer is often rendered to operator-deemed best. As a result, the manufactured part accuracy is not guaranteed and the build time is not easily optimized. Even with the availability of a scheme to predict the resulting finished part, optimal layer setup cannot be determined. Current practice generates the layer contours by simply intersecting a set of parallel planes through the computer model of the design part. The volumetric geometry of each layer is then constructed by extruding the layer contour by the layer thickness in the part building direction. This practice often leads to distorted part geometry due to the unidirectional bias of the extruded layers. Because of this, excessive layers are often employed to alleviate the effect of the part distortion. Such form of the distortion, referred to as systematic distortion, needs to be removed during layer setup. This thesis proposes methods to first remove the systematic distortion and then to determine the optimal layer setup based on a tolerance measure. A scheme to emulate the final polished part geometry is also presented. Case studies are performed in order to validate that the proposed method. The proposed scheme is shown to have significantly reduced the number of layers for constructing an LM part while satisfying a user specified error bound. Therefore, accuracy is better guaranteed due to the existence of error measure and control. Efficiency is greatly increased.

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Shojaeifard, Arman. « Cross-layer design and optimization of heterogeneous cellular mobile networks ». Thesis, King's College London (University of London), 2013. https://kclpure.kcl.ac.uk/portal/en/theses/crosslayer-design-and-optimization-of-heterogeneous-cellular-mobile-networks(dfe31556-d8f0-4fdc-a9e3-8f01fed258ed).html.

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The rapid growth of wireless communication and access, in conjunction with increasing demand and sophistication of wireless applications, supplicate intelligent and reliable systems to support the exchange of large classes of traffic with rising quality of service (QoS) requirements. In addition, co-operation among cellular systems that incorporate different radio access technologies is notably important as the current third generation (3G) universal mobile telecommunication systems (UMTS) are expected to co-exist with the emerging fourth generation (4G) long term evolution (LTE) technologies for years to come. To these ends, radio resource management (RRM) techniques across different network layers, conjointly with spectrum sharing strategies, are vital in achieving desirable performance in heterogeneous networks. In this thesis, novel cross-layer design strategies, for jointly optimizing the physical (PHY)-layer and data link layer (DLL) parameters, are proposed in the contexts of code division multiple access (CDMA) and shared-spectrum heterogeneous orthogonal frequency division multiplexing (OFDM)/CDMA networks. These strategies facilitate dynamic radio resource allocation by exploiting the random variations of channel and network activity. Transmit power and QoS constraints are imposed on systems to maintain communication costs, effectiveness and quality. This thesis makes four main contributions. Firstly, in the proposed cross-layer techniques, based on automatic repeat request (ARQ) delay limits and prescribed maximum packet loss rates in the DLL, the optimum outer-loop power control (OLPC) SNR-targets and the corresponding adaptive spreading factors are derived in the PHY-layer, as functions of the number of active users in the cell. The optimality is, in this sense, maximization of cell effective throughput. Secondly, the performance of the proposed interference-based resource allocation schemes are evaluated over Nakagami-m frequency -flat and -selective fading channels. In particular, frequency-selective channels with maximum ratio combining (MRC) RAKE receiver are considered. Thirdly, I consider the uplink in multi-user cellular communication systems with single- and multi- service traffic scenarios, which are respectively modelled with one- and multi- dimensional discrete Markov chains. Finally, a dynamic cross-layer resource allocation algorithm in the context of shared-spectrum heterogeneous OFDM/CDMA networks is proposed. Opportunistic spectrum access (OSA) is employed to utilize the idle parts of the primary spectrum, effectively minimizing the interference levels, to maximize the total deliverable secondary throughput. Throughput performance of the optimized schemes and the achieved improvements, relative to the non-optimized and state-of-the-art schemes, are demonstrated with theoretical and simulation results for various settings of system parameters.

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Chen, Yen-Lin. « Cross-layer design and optimization for wireless networked control systems ». Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61089/1/Yen-Lin_Chen_Thesis.pdf.

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Wireless networked control systems (WNCSs) have been widely used in the areas of manufacturing and industrial processing over the last few years. They provide real-time control with a unique characteristic: periodic traffic. These systems have a time-critical requirement. Due to current wireless mechanisms, the WNCS performance suffers from long time-varying delays, packet dropout, and inefficient channel utilization. Current wirelessly networked applications like WNCSs are designed upon the layered architecture basis. The features of this layered architecture constrain the performance of these demanding applications. Numerous efforts have attempted to use cross-layer design (CLD) approaches to improve the performance of various networked applications. However, the existing research rarely considers large-scale networks and congestion network conditions in WNCSs. In addition, there is a lack of discussions on how to apply CLD approaches in WNCSs. This thesis proposes a cross-layer design methodology to address the issues of periodic traffic timeliness, as well as to promote the efficiency of channel utilization in WNCSs. The design of the proposed CLD is highlighted by the measurement of the underlying network condition, the classification of the network state, and the adjustment of sampling period between sensors and controllers. This period adjustment is able to maintain the minimally allowable sampling period, and also maximize the control performance. Extensive simulations are conducted using the network simulator NS-2 to evaluate the performance of the proposed CLD. The comparative studies involve two aspects of communications, with and without using the proposed CLD, respectively. The results show that the proposed CLD is capable of fulfilling the timeliness requirement under congested network conditions, and is also able to improve the channel utilization efficiency and the proportion of effective data in WNCSs.

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Xiong, Haozhi. « Delay-Aware Cross-Layer Design in Multi-hop Networks ». The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290107298.

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Ngo, Minh Hanh. « Cross-layer adaptive transmission scheduling in wireless networks ». Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/432.

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A new promising approach for wireless network optimization is from a cross-layer perspective. This thesis focuses on exploiting channel state information (CSI) from the physical layer for optimal transmission scheduling at the medium access control (MAC) layer. The first part of the thesis considers exploiting CSI via a distributed channel-aware MAC protocol. The MAC protocol is analysed using a centralized design approach and a non-cooperative game theoretic approach. Structural results are obtained and provably convergent stochastic approximation algorithms that can estimate the optimal transmission policies are proposed. Especially, in the game theoretic MAC formulation, it is proved that the best response transmission policies are threshold in the channel state and there exists a Nash equilibrium at which every user deploys a threshold transmission policy. This threshold result leads to a particularly efficient stochastic-approximation-based adaptive learning algorithm and a simple distributed implementation of the MAC protocol. Simulations show that the channel-aware MAC protocols result in system throughputs that increase with the number of users. The thesis also considers opportunistic transmission scheduling from the perspective of a single user using Markov Decision Process (MDP) approaches. Both channel state in-formation and channel memory are exploited for opportunistic transmission. First, a finite horizon MDP transmission scheduling problem is considered. The finite horizon formulation is suitable for short-term delay constraints. It is proved for the finite horizon opportunistic transmission scheduling problem that the optimal transmission policy is threshold in the buffer occupancy state and the transmission time. This two-dimensional threshold structure substantially reduces the computational complexity required to compute and implement the optimal policy. Second, the opportunistic transmission scheduling problem is formulated as an infinite horizon average cost MDP with a constraint on the average waiting cost. An advantage of the infinite horizon formulation is that the optimal policy is stationary. Using the Lagrange dynamic programming theory and the super modularity method, it is proved that the stationary optimal transmission scheduling policy is a randomized mixture of two policies that are threshold in the buffer occupancy state. A stochastic approximation algorithm and a Q-learning based algorithm that can adaptively estimate the optimal transmission scheduling policies are then proposed.

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Merlin, Simone. « Cross-layer design in wireless networks ». Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3426273.

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In this thesis, cross-layer optimization techniques for wireless networks are investigated. An introduction to the concept of cross-layer design is provided, reviewing the related literature, from both an architectural and an analytical point of view. Three original contributions, which jointly address the optimization at different levels of the protocol stack are then presented. The first contribution refers to a theoretical approach to channel allocation in multichannel ad hoc networks, where each node is provided with multiple radio interfaces. An algorithm for the joint solution of congestion control, channel allocation and transmission scheduling is proposed. The second contribution refers to a cross-layer optimization framework in the context of standard IEEE 802.11WLAN. A mathematical model for the link performance is developed, and a sufficient description for the medium status is defined which allows to account for propagation and interference conditions. The optimization framework is used to develop algorithms for rate adaptation and VoIP quality enhancement which are adaptive to a broad range of working conditions. Resource allocation in wireless cellular networks is also addressed and the problem of trading fairness for physical layer efficiency is investigated by means of a simple algorithm spanning PHY, MAC and LL layers. In the end, additional published contributions related to the cross-layer paradigm are introduced, regarding microeconomic aspects in resource allocation and efficiency considerations about scatternet topologies in Bluetooth networks.

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Buburuzan, Teodor [Verfasser]. « Optimization of an Interface Abstraction Layer for Heterogeneous Networks / Teodor Buburuzan ». Aachen : Shaker, 2011. http://d-nb.info/1071528947/34.

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Dely, Peter. « Cross-Layer Optimization of Voice over IP in Wireless Mesh Networks ». Licentiate thesis, Karlstads universitet, Avdelningen för datavetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-6280.

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Wireless Mesh Networks (WMNs) have emerged as a promising network technology, which combines the benefits of cellular networks and Wireless Local Area Networks (WLANs). In a WMN mesh routers wirelessly relay traffic on behalf of other mesh routers or clients and thereby provide coverage areas comparable to cellular networks, while having the low complexity and low costs of WLANs. As Voice over IP (VoIP) is a very important Internet service, it is critical for the success of WMNs to support high quality VoIP. However, currentWMNs are not adapted well for VoIP. The capacity and scalability of single-radio WMNs is low, especially for small packet transmissions of VoIP calls, because the MAC and PHY layer overhead for small packets is high. The scalability of multiradio/multi-channel WMNs is usually higher, since fewer nodes contend for a channel. However channel scheduling might be required, which can lead to excessive delay and jitter and result in poor VoIP quality. In this thesis we investigate how to deliver high quality VoIP in single radio and multi-radio networks by using cross-layer optimization. For single radio WMNs, we consider the use of IP packet aggregation and IEEE 802.11e transmission opportunities. We conclude that IP packet aggregation greatly improves the capacity and thereby the scalability of WMNs. We show that the key for providing good quality is to artificially delay packets prior to aggregation. We propose a distributed cross-layer optimization system, which, based on Fuzzy Logic Inference, derives an aggregation delay that enhances the capacity and quality. For multi-radio/multi-channel WMNs, we demonstrate the importance of qualityof- service-aware channel scheduling. We develop a quality-of-serviceaware channel scheduler that compared to a basic round-robin scheme significantly reduces jitter and in that way increases VoIP quality. Our analysis shows that there is a trade-off between the jitter of high priority VoIP traffic and the throughput of background TCP traffic. The proposed optimizations significantly increase the capacity of singleradio and multi-radio WMNs. This allows network operators to serve more users with an existing mesh infrastructure or provide better service delivery to existing users.

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Sehlstedt, Martin. « Physical layer optimization for transportation of scalable media over AWGN channels / ». Luleå, 2005. http://epubl.luth.se/1402-1544/2005/27.

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Noordin, Kamarul Ariffin. « Cross-layer optimization of WiMAX system with quality of service guarantee ». Thesis, Lancaster University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551638.

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The increasing demand for last mile high speed internet access has contributed to the popularity of the broadband wireless access (BW A) systems for fulfilling such requirement since they can realized it with lower cost compared to the wired solutions. WiMAX which is based on the IEEE802.16 standard and is one of the latest offerings in the BW A systems promises to provide high speed access with Quality of Service (QoS) support. Different service classes are defined together with their associated QoS parameters in order to support different types of user applications. However, no scheduling architecture is defined to guarantee these defined QoS requirements. In this thesis, a scheduling algorithm which observes the QoS requirements of all service classes in both uplink and downlink directions has been proposed. Using the service class type to determine the priority for transmission and the calculation of required slots, the QoS of users from higher service- classes could be guaranteed without starving users from the lowest service class. To gain from multiuser diversity, channel-aware scheduling algorithm based on cross-layer optimization in band Adaptive Modulation and Coding (AMC) has also been developed. The algorithm not only aims to fulfil the QoS requirements and increase the system throughput but also aims to be practical and conform to the standard. Instead of finding the optimal solution which is too complex for practical implementation a suboptimal solution using heuristic method has been proposed. The cross-layer approach has been extended to provide cross-system optimization in which WiMAX and WiFi networks are selected for the case study. The optimization between the Medium Access Controls (MACs) of the two networks has been facilitated by QoS mapping of the application types between the two networks. Combined with the cross-layer optimization, the system throughput could be increased while guaranteeing the end-to-end QoS.

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Winslow, Michael A. « OPTIMIZATION OF ELECTROMAGNETIC WAVE PROPAGATION THROUGH A HETEROGENEOUS LIQUID CRYSTAL LAYER ». Monterey, California. Naval Postgraduate School, 2013. http://hdl.handle.net/10945/32919.

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Advances in technology have given way to concepts in warfare that were once constrained to the world of science fiction. In an effort to stay ahead of any potential adversarys weapons development, we must look down the path of countermeasures to high-energy electromagnetic weapons. In the attempt to engineer a material that can reduce transmitted beam intensity by the greatest factor, we look to liquid crystals. They have great potential to provide a starting point to engineer a material in order to show increased protection of DoD assets from high-energy beam weapons. We first develop one-dimensional finite-difference time-domain codes to solve Maxwells equations in order to model the electromagnetic wave propagation in a liquid crystal layer. After validating numerical results with analytical results for matched anchoring, we investigate the heterogeneous liquid crystal structures with mismatched anchoring conditions and determine the best anchoring conditions to minimize transmitted beam intensity. The main result of the simulation is that for a known incident wave the maximum reduction of the transmitted intensity is achieved with matched anchoring conditions. However, for mixed anchoring conditions, there is evidence that the mixed structure can reduce the intensity for a wider range of waves.

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Chen, Si. « Cross-Layer Optimization and Dynamic Spectrum Access for Distributed Wireless Networks ». Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/1067.

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"We proposed a novel spectrum allocation approach for distributed cognitive radio networks. Cognitive radio systems are capable of sensing the prevailing environmental conditions and automatically adapting its operating parameters in order to enhance system and network performance. Using this technology, our proposed approach optimizes each individual wireless device and its single-hop communication links using the partial operating parameter and environmental information from adjacent devices within the wireless network. Assuming stationary wireless nodes, all wireless communication links employ non-contiguous orthogonal frequency division multiplexing (NC-OFDM) in order to enable dynamic spectrum access (DSA). The proposed approach will attempt to simultaneously minimize the bit error rate, minimize out-of-band (OOB) interference, and maximize overall throughput using a multi-objective fitness function. Without loss in generality, genetic algorithms are employed to perform the actual optimization. Two generic optimization approaches, subcarrier-wise approach and block-wise approach, were proposed to access spectrum. We also proposed and analyzed several approaches implemented via genetic algorithms (GA), such as quantizing variables, using adaptive variable ranges, and Multi-Objective Genetic Algorithms, for increasing the speed and improving the results of combined spectrum utilization/cross-layer optimization approaches proposed, together with several assisting processes and modifications devised to make the optimization to improve efficiency and execution time."

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Gwanvoma, Stephen B. « Systems Approach to Cross-Layer Optimization of a Complex Wireless Environment ». International Foundation for Telemetering, 2011. http://hdl.handle.net/10150/595765.

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ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada
This paper presents a method for the optimization of mixed networks that incorporates a mixed layer optimization of performance features. The expanded integrated Network Enhanced Telemetry (iNET) system envisioned telemetering for large and complex networks which will require core telemetry networks with ad hoc extensions for coverage. Organizing such a network has been successfully accomplished in simulations using a K-mean clustering algorithm. This paper shows how the features of these network elements will be captured and disseminated in a real system. This management of network elements across multiple layers is characterized as cross-layer optimization. This paper will also show how such cross layer features can be combined for a globally optimum solution. It shows by example how the iNET system comprising multiple ground stations, gateways, frequency, nodes, and three performance measures can be optimized to achieve overall optimal system performance.

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Saki, Hadi. « Cross-layer design and optimization of OFDMA-based cognitive radio networks ». Thesis, King's College London (University of London), 2014. http://kclpure.kcl.ac.uk/portal/en/theses/crosslayer-design-and-optimization-of-ofdmabased-cognitive-radio-networks(448efa7d-9d55-423c-adb3-8a5ae8cd51f8).html.

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Increasing demand and sophistication of wireless applications require intelligent systems which, along with performing efficient and reliable adaptive operations, should be simple to implement. Cognitive radio (CR) is one such system which has the capability of adapting to its surroundings. In this thesis, the role of different layers of network in carrying out the functionalities of CR systems is investigated and cross-layer design strategies involving the physical (PHY), the media access control (MAC), and the application are proposed. This thesis makes several contributions. Firstly, we propose novel optimal radio resource allocation (RRA) algorithms under different scenarios with deterministic and probabilistic interference violation limits based on perfect and imperfect availability of cross-link channel state information (CSI). In particular, in contrast to the ‘average case’ and ‘worst case’ estimation error scenarios in the literature, we propose a probabilistic approach to mitigate the total imposed interference on the primary service under imperfect cross-link CSI. An expression for the cumulative density function (cdf) of the received signal-tointerference-plus-noise ratio (SINR) is developed to evaluate the average spectral efficiency. Through simulation results, we investigate the achievable performance and the impact of parameters uncertainty on the overall system performance. Secondly, we implement stochastic RRA algorithms in both hybrid- (i.e., mixed underlay and overlay) and opportunistic (i.e., overlay) access orthogonal frequencydivision multiple access (OFDMA)-based CR systems. The proposed solutions allocate power and subcarrier to cognitive users over wireless fading channels in order to maximize the total transmission rate based on the probabilities of channel availability obtained through spectrum sensing. In order to protect the primary service operation from harmful intervention, stochastic transmit and interference power constrains are imposed on the cognitive users. The performance of the proposed stochastic algorithms and their advantages over the conventional hard-decision-based approaches are assessed and demonstrated through simulation results. Finally a specific cross-layer design for multi scalable video application transmission in an interference-limited spectrum sharing system is proposed. The proposed design jointly considers the parameters from the PHY and the application layers in order to maximize the overall peak signal-to-noise ratio (PSNR). Results indicate that significant improvement in secondary receivers (SRxs) average video quality is achieved through our proposed algorithm over other state-of-the-art non-qualityaware (NQA) designs in the literature. The enhanced performance was obtained whilst guaranteeing SRx minimum quality and primary receiver (PRx) prescribed quality of service (QoS) constraints.

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Kassab, Mohamed. « Layer-2 hancover optimization for intra-technologies and inter-technologies mobility ». Télécom Bretagne, 2008. http://www.theses.fr/2008TELB0098.

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De nos jours, la démocratisation des réseaux sans fil a permis l'émergence de nombreuses applications qui profitent de la mobilité. Cependant, la gestion de cette mobilité et en particulier de la procédure de handover (HO) introduit des délais et des interruptions dans les communications, ce qui viole les contraintes temps-réel imposées par certains types d'applications. Les HOs posent des problèmes d'autant plus importants que des mécanismes supplémentaires sont mis en place pour sécuriser l'accès au réseau ou pour gérer la qualité de service. Effet, ils requièrent le plus souvent l'établissement d'un contexte dans les points d'accès. Dans ce travail, nous nous intéresserons à la réduction de ces délais en optimisant la phase d'exécution du HO au niveau de la couche liaison (L2-HO) grâce à des mécanismes d'établissement anticipé des contextes. Dans la première partie de notre travail, nous avons proposé un cadre général pour l'optimisation de la phase d'exécution du L2-HO. Il se base sur une analyse des informations et paramètres inclus dans les contextes associés a une station mobile pour évaluer dans quelles conditions ils peuvent être transférés. Ce cadre propose un ensemble de mécanismes de re-établissement adaptés à une architecture d'un réseau d'opérateurs. Dans une deuxième partie, nous nous sommes intéressés à l'application du cadre général pour l'optimisation du L2-HO à des cas particuliers. Dans une première application, nous avons considéré un réseau sans fil classique basé sur une technologie d'accès uniforme : les réseaux WiFi. Nous avons proposé un ensemble de mécanismes d'authentification rapides qui satisfont les contraintes de sécurité et de rapidité des applications pseudo-temps réel. Dans une deuxième application, nous nous sommes intéressés à l'optimalisation du L2-HO dans des réseaux sans fils hétérogènes basés sur les technologies WiFi et WiMAX. Nous avons proposé un ensemble de mécanismes qui optimisent les handovers verticaux et horizontaux tout en assurant une continuité de la gestion de la qualité de service et la sécurisation de l'accès. Enfin, nous avons évalué les solutions proposées en nous basant sur des tests sur plate-forme réelle, des expériences de simulation ainsi que des études analytiques

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Rahman, Tasnim. « Optimization of Cross-Layer Network Data based on Multimedia Application Requirements ». Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1348.

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This thesis proposes a convex network utility maximization (NUM) problem that can be solved to optimize a cross-layer network based on user and system defined requirements for quality and link capacity of multimedia applications. The problem can also be converged to a distributed solution using dual decomposition. Current techniques do not address the changing system's requirements for the network in addition to the user's requirements for an application when optimizing a cross-layer network, but rather focus on optimizing a dynamic network to conform to a real-time application or for a specific performance. Optimizing the cross-layer network for the changing system and user requirements allows a more accurate optimization of the overall cross-layer network of any given multi-node, ad-hoc wireless application for data transmission quality and link capacity to meet overall mission demands.

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38

Hernandez, Herrero Sandra. « Cross-layer optimization for visual-inertial localization on resource-constrained devices ». Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-296834.

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Mobile devices are increasingly expected to support high-performance cyber- physical applications in resource-constrained devices, such as drones and rovers. However, the gap between hardware limitations of these devices and application requirements is still prohibitive – conflicting goals such as robust, accurate, and efficient execution must be managed carefully to achieve acceptable operation. This thesis is focus on the exploration of the tradeoff between performance and efficiency in such cyber-physical systems, specifically with respect to localization, a core task for any mobile autonomous device. We perform a design space exploration (DSE) given a number of configurable parameters for both localization algorithm and platform layers. Given the configuration space, we formulate a cross-layer multi-objective optimization problem to explore the tradeoff between localization accuracy and power consumption. For our experiments we execute maplab – a visual-inertial localization and mapping framework – monolithically on the Nvidia Jetson AGX and NX platforms. We then propose a predictive model for robust execution that can be used to determine desirable configurations at runtime in the face of environmental changes.
Mobila enheter med begränsade resurser, som drönare och rovers, förväntas stödja mer och mer krävande cyberfysiska applikationer. Glappet mellan enheternas begränsningar i hårdvara och applikationskrav är dock fortfarande stort - motstridiga mål som robust, noggrann och effektiv körning måste uppfyllas för att uppnå acceptabel drift. Detta examensarbete undersöker avvägningen mellan prestanda och effektivitet i cyberfysiska system, särskilt med avseende på lokalisering som är en av de viktigaste uppgifterna för alla mobila autonoma enheter. Vi gör en design space exploration (DSE) genom att variera ett antal parametrar för både lokaliseringsalgoritm och plattformslager. Baserat på konfigurationsrummet formulerar vi ett tvärlageroptimeringsproblem med flera mål för att utforska avvägningen mellan noggrannhet i lokaliseringen och energiåtgång. I våra experiment kör vi maplab – ett visuellt tröghetsramverk för lokalisering och kartläggning – på Nvidia Jetson AGXoch NX-plattformarna. Vi presenterar sedan en robust prediktiv modell som kan användas för att välja konfigurationer vid körning i en föränderlig miljö.

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Zhou, Yi. « Physical Layer Security and Latency Optimization for Internet of Things Communications ». Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23553.

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The Internet of Things (IoT) aims to connect all things to the internet to facilitate intelligent identifying, locating, tracking, monitoring, and managing of objects and information. The IoT paradigm will be supported by advanced wireless communications technologies and fifth-generation (5G) cellular networks. As such, new network architectures and protocols should be developed to ensure successful deployments of IoT communications systems in many domains including smart homes, transportation, logistics, smart grids and healthcare. In order to extend existing wireless network coverage and support the robustness and connectivity of IoT, unmanned aerial vehicle (UAV) has been proposed as an ideal IoT platform due to its flexibility and mobility. Moreover, mobile edge computing (MEC) which provides considerable computing resource at the edge of the network to support IoT applications and services in real time is another key enabling technology for IoT. However, realizing the vision of IoT is challenging due to many difficulties that need to be addressed. Particularly, physical layer security (PLS) and low-latency design are the two main challenges. On the one hand, due to the openness of wireless transmission medium, the communications between the legitimate transmitter-receiver pair can be readily attacked by eavesdroppers or spoofers where the confidentiality and integrity of the information cannot be guaranteed. On the other hand, with the tremendous amount and variety of data to be collected and processed in IoT networks, achieving low-latency communications is challenging and has become one of the major bottlenecks of IoT. In this thesis, we develop new efficient algorithms to improve the PLS and latency in IoT communications based on UAV and MEC technologies to address the aforementioned challenges of IoT. We first develop a secure UAV-enabled communication framework by exploiting a UAV-based friendly jammer which emits artificial noise to prevent eavesdropping attacks on legitimate ground nodes when the eavesdropper location is unknown. We propose an efficient algorithm to maximize the security performance by jointly optimizing the 3D deployment and jamming power of the UAV jammer. Numerical results show that our proposed iterative algorithm performs close to an exhaustive search with significantly reduced complexity. Next, we propose a more general IoT communications model where both the latency and PLS performance are jointly considered in an MEC network. We formulate a latency minimization problem by jointly optimizing the user's transmit power, computing capacity allocation, and user association subject to PLS performance and computing resource constraints. Numerical results show that our proposed solution outperforms baseline strategies over a wide range of computing capacities and highlight a fundamental tradeoff between latency and security in an MEC network. Subsequently, we extend the latency-security tradeoff analysis to a UAV-enabled MEC network, where multiple ground users offload large computing tasks to a nearby legitimate UAV in the presence of multiple eavesdropping UAVs with imperfect locations. For this system, we design a low-complexity iterative algorithm to maximize the minimum secrecy capacity subject to latency, minimum offloading and total power constraints. Numerical results show that our proposed algorithm significantly outperforms baseline strategies over a wide range of UAV self-interference (SI) efficiencies, locations and packet sizes of ground users. Furthermore, we show that there exists a fundamental tradeoff between the security and latency of UAV-enabled MEC systems. Finally, to protect wireless communications from potential spoofing attacks, we investigate received signal strength (RSS)-based physical layer authentication (PLA) in UAV-enabled communication systems based on game theory. We first model an authentication hypothesis test based on the RSS distance and derive the false alarm rate and miss detection rate. We then formulate a zero-sum PLA game to model the interactions between the spoofer and the UAV receiver. The Nash equilibrium (NE) and its existence condition for the proposed PLA game are also derived. Monte Carlo simulation results accurately verify our analytical expressions for the false alarm rate and miss detection rate.

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Yadav, Anita [Verfasser]. « Cross Layer Optimization for Protocols in Mobile Adhoc Networks / Anita Yadav ». München : GRIN Verlag, 2020. http://d-nb.info/1206641002/34.

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Oskooi, Ardavan F. « An investigation of the perfectly matched layer for inhomogeneous media ». Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43738.

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Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2008.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 41-45).
Although perfectly matched layers (PMLs) have been widely used to truncate numerical simulations of electromagnetism and other wave equations, we point out important cases in which a PML fails to be reflectionless even in the limit of infinite resolution. In particular, the underlying coordinate-stretching idea behind PML breaks down in photonic crystals and in other structures where the material is not an analytic function in the direction perpendicular to the boundary, leading to substantial reflections. The alternative is an adiabatic absorber, in which reflections are made negligible by gradually increasing the material absorption at the boundaries, similar to a common strategy to combat discretization reflections in PMLs. We demonstrate the fundamental connection between such reflections and the smoothness of the absorption profile via coupled-mode theory, and show how to obtain higher-order and even exponential vanishing of the reflection with absorber thickness.
by Ardavan F. Oskooi.
S.M.

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Zarakovitis, Charilaos C. « Convex optimization-based resource scheduling for multi-user wireless systems ». Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/11068.

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Shi, Yi. « Algorithms and Optimization for Wireless Networks ». Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29480.

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Recently, many new types of wireless networks have emerged for both civil and military applications, such as wireless sensor networks, ad hoc networks, among others. To improve the performance of these wireless networks, many advanced communication techniques have been developed at the physical layer. For both theoretical and practical purposes, it is important for a network researcher to understand the performance limits of these new wireless networks. Such performance limits are important not only for theoretical understanding, but also in that they can be used as benchmarks for the design of distributed algorithms and protocols. However, due to some unique characteristics associated with these networks, existing analytical technologies may not be applied directly. As a result, new theoretical results, along with new mathematical techniques, need to be developed. In this dissertation, we focus on the design of new algorithms and optimization techniques to study theoretical performance limits associated with these new wireless networks. In this dissertation, we mainly focus on sensor networks and ad hoc networks. Wireless sensor networks consist of battery-powered nodes that are endowed with a multitude of sensing modalities. A wireless sensor network can provide in-situ, unattended, high-precision, and real-time observation over a vast area. Wireless ad hoc networks are characterized by the absence of infrastructure support. Nodes in an ad hoc network are able to organize themselves into a multi-hop network. An ad hoc network can operate in a stand-alone fashion or could possibly be connected to a larger network such as the Internet (also known as mesh networks). For these new wireless networks, a number of advanced physical layer techniques, e.g., ultra wideband (UWB), multiple-input and multiple-output (MIMO), and cognitive radio (CR), have been employed. These new physical layer technologies have the potential to improve network performance. However, they also introduce some unique design challenges. For example, CR is capable of reconfiguring RF (on the fly) and switching to newly-selected frequency bands. It is much more advanced than the current multi-channel multi-radio (MC-MR) technology. MC-MR remains hardware-based radio technology: each radio can only operate on a single channel at a time and the number of concurrent channels that can be used at a wireless node is limited by the number of radio interfaces. While a CR can use multiple bands at the same time. In addition, an MC-MR based wireless network typically assumes there is a set of "common channels" available for all nodes in the network. While for CR networks, each node may have a different set of frequency bands based on its particular location. These important differences between MC-MR and CR warrant that the algorithmic design for a CR network is substantially more complex than that under MC-MR. Due to the unique characteristics of these new wireless networks, it is necessary to consider models and constraints at multiple layers (e.g., physical, link, and network) when we explore network performance limits. The formulations of these cross-layer problems are usually in very complex forms and are mathematically challenging. We aim to develop some novel algorithmic design and optimization techniques that provide optimal or near-optimal solutions. The main contributions of this dissertation are summarized as follows. 1. Node lifetime and rate allocation We study the sensor node lifetime problem by considering not only maximizing the time until the first node fails, but also maximizing the lifetimes for all the nodes in the network. For fairness, we maximize node lifetimes under the lexicographic max-min (LMM) criteria. Our contributions are two-fold. First, we develop a polynomial-time algorithm based on a parametric analysis (PA) technique, which has a much lower computational complexity than an existing state-of-the-art approach. We also present a polynomial-time algorithm to calculate the flow routing schedule such that the LMM-optimal node lifetime vector can be achieved. Second, we show that the same approach can be employed to address a different but related problem, called LMM rate allocation problem. More important, we discover an elegant duality relationship between the LMM node lifetime problem and the LMM rate allocation problem. We show that it is sufficient to solve only one of the two problems and that important insights can be obtained by inferring the duality results. 2. Base station placement Base station location has a significant impact on sensor network lifetime. We aim to determine the best location for the base station so as to maximize the network lifetime. For a multi-hop sensor network, this problem is particularly challenging as data routing strategies also affect the network lifetime performance. We present an approximation algorithm that can guarantee $(1- \varepsilon)$-optimal network lifetime performance with any desired error bound $\varepsilon >0$. The key step is to divide the continuous search space into a finite number of subareas and represent each subarea with a "fictitious cost point" (FCP). We prove that the largest network lifetime achieved by one of these FCPs is $(1- \varepsilon)$-optimal. This approximation algorithm offers a significant reduction in complexity when compared to a state-of-the-art algorithm, and represents the best known result to this problem. 3. Mobile base station The benefits of using a mobile base station to prolong sensor network lifetime have been well recognized. However, due to the complexity of the problem (time-dependent network topology and traffic routing), theoretical performance limits and provably optimal algorithms remain difficult to develop. Our main result hinges upon a novel transformation of the joint base station movement and flow routing problem from the time domain to the space domain. Based on this transformation, we first show that if the base station is allowed to be present only on a set of pre-defined points, then we can find the optimal sojourn time for the base station on each of these points so that the overall network lifetime is maximized. Based on this finding, we show that when the location of the base station is un-constrained (i.e., can move to any point in the two-dimensional plane), we can develop an approximation algorithm for the joint mobile base station and flow routing problem such that the network lifetime is guaranteed to be at least $(1- \varepsilon)$ of the maximum network lifetime, where $\varepsilon$ can be made arbitrarily small. This is the first theoretical result with performance guarantee on this problem. 4. Spectrum sharing in CR networks Cognitive radio is a revolution in radio technology that promises unprecedented flexibility in radio communications and is viewed as an enabling technology for dynamic spectrum access. We consider a cross-layer design of scheduling and routing with the objective of minimizing the required network-wide radio spectrum usage to support a set of user sessions. Here, scheduling considers how to use a pool of unequal size frequency bands for concurrent transmissions and routing considers how to transmit data for each user session. We develop a near-optimal algorithm based on a sequential fixing (SF) technique, where the determination of scheduling variables is performed iteratively through a sequence of linear programs (LPs). Upon completing the fixing of these scheduling variables, the value of the other variables in the optimization problem can be obtained by solving an LP. 5. Power control in CR networks We further consider the case of variable transmission power in CR networks. Now, our objective is minimizing the total required bandwidth footprint product (BFP) to support a set of user sessions. As a basis, we first develop an interference model for scheduling when power control is performed at each node. This model extends existing so-called protocol models for wireless networks where transmission power is deterministic. As a result, this model can be used for a broad range of problems where power control is part of the optimization space. An efficient solution procedure based on the branch-and-bound framework and convex hull relaxations is proposed to provide $(1- \varepsilon)$-optimal solutions. This is the first theoretical result on this important problem.
Ph. D.

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YODER, DENNIS ALLEN. « ALGEBRAIC REYNOLDS STRESS MODELING OF PLANAR MIXING LAYER FLOWS ». University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1115637717.

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Dufresne, Sophie. « Optimization of an airfoil's performance through moving boundary control ». Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09292009-020211/.

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Liu, Weigang. « Enhancing physical layer security in wireless networks with cooperative approaches ». Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/19565.

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Motivated by recent developments in wireless communication, this thesis aims to characterize the secrecy performance in several types of typical wireless networks. Advanced techniques are designed and evaluated to enhance physical layer security in these networks with realistic assumptions, such as signal propagation loss, random node distribution and non-instantaneous channel state information (CSI). The first part of the thesis investigates secret communication through relay-assisted cognitive interference channel. The primary and secondary base stations (PBS and SBS) communicate with the primary and secondary receivers (PR and SR) respectively in the presence of multiple eavesdroppers. The SBS is allowed to transmit simultaneously with the PBS over the same spectrum instead of waiting for an idle channel. To improve security, cognitive relays transmit cooperative jamming (CJ) signals to create additional interferences in the direction of the eavesdroppers. Two CJ schemes are proposed to improve the secrecy rate of cognitive interference channels depending on the structure of cooperative relays. In the scheme where the multiple-antenna relay transmits weighted jamming signals, the combined approach of CJ and beamforming is investigated. In the scheme with multiple relays transmitting weighted jamming signals, the combined approach of CJ and relay selection is analyzed. Numerical results show that both these two schemes are effective in improving physical layer security of cognitive interference channel. In the second part, the focus is shifted to physical layer security in a random wireless network where both legitimate and eavesdropping nodes are randomly distributed. Three scenarios are analyzed to investigate the impact of various factors on security. In scenario one, the basic scheme is studied without a protected zone and interference. The probability distribution function (PDF) of channel gain with both fading and path loss has been derived and further applied to derive secrecy connectivity and ergodic secrecy capacity. In the second scenario, we studied using a protected zone surrounding the source node to enhance security where interference is absent. Both the cases that eavesdroppers are aware and unaware of the protected zone boundary are investigated. Based on the above scenarios, further deployment of the protected zones at legitimate receivers is designed to convert detrimental interference into a beneficial factor. Numerical results are investigated to check the reliability of the PDF for reciprocal of channel gain and to analyze the impact of protected zones on secrecy performance. In the third part, physical layer security in the downlink transmission of cellular network is studied. To model the repulsive property of the cellular network planning, we assume that the base stations (BSs) follow the Mat´ern hard-core point process (HCPP), while the eavesdroppers are deployed as an independent Poisson point process (PPP). The distribution function of the distances from a typical point to the nodes of the HCPP is derived. The noise-limited and interference-limited cellular networks are investigated by applying the fractional frequency reuse (FFR) in the system. For the noise-limited network, we derive the secrecy outage probability with two different strategies, i.e. the best BS serve and the nearest BS serve, by analyzing the statistics of channel gains. For the interference-limited network with the nearest BS serve, two transmission schemes are analyzed, i.e., transmission with and without the FFR. Numerical results reveal that both the schemes of transmitting with the best BS and the application of the FFR are beneficial for physical layer security in the downlink cellular networks, while the improvement due to the application of the FFR is limited by the capacity of the legitimate channel.

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Kim, Sung Hyun. « Multi-layer approach to motion planning in obstacle rich environment ». [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2621.

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Kartsakli, Elli. « Cross-layer design and optimization of medium access control protocols for wlans ». Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/81116.

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This thesis provides a contribution to the field of Medium Access Control (MAC) layer protocol design for wireless networks by proposing and evaluating mechanisms that enhance different aspects of the network performance. These enhancements are achieved through the exchange of information between different layers of the traditional protocol stack, a concept known as Cross-Layer (CL) design. The main thesis contributions are divided into two parts. The first part of the thesis introduces a novel MAC layer protocol named Distributed Queuing Collision Avoidance (DQCA). DQCA behaves as a reservation scheme that ensures collision-free data transmissions at the majority of the time and switches automatically to an Aloha-like random access mechanism when the traffic load is low. DQCA can be enriched by more advanced scheduling algorithms based on a CL dialogue between the MAC and other protocol layers, to provide higher throughput and Quality of Service (QoS) guarantees. The second part of the thesis explores a different challenge in MAC layer design, related to the ability of multiple antenna systems to offer point-to-multipoint communications. Some modifications to the recently approved IEEE 802.11n standard are proposed in order to handle simultaneous multiuser downlink transmissions. A number of multiuser MAC schemes that handle channel access and scheduling issues and provide mechanisms for feedback acquisition have been presented and evaluated. The obtained performance enhancements have been demonstrated with the help of both theoretical analysis and simulation obtained results.

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Kong, Lei. « Performance analysis and optimization for MAC-layer IEEE 802.16e power saving mechanism / ». View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20KONG.

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Erpek, Tugba. « Multi-layer Optimization Aspects of Deep Learning and MIMO-based Communication Systems ». Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/102705.

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This dissertation addresses multi-layer optimization aspects of multiple input multiple output (MIMO) and deep learning-based communication systems. The initial focus is on the rate optimization for multi-user MIMO (MU-MIMO) configurations; specifically, multiple access channel (MAC) and interference channel (IC). First, the ergodic sum rates of MIMO MAC and IC configurations are determined by jointly integrating the error and overhead effects due to channel estimation (training) and feedback into the rate optimization. Then, we investigated methods that will increase the achievable rate for parallel Gaussian IC (PGIC) which is a special case of MIMO IC where there is no interference between multiple antenna elements. We derive a generalized iterative waterfilling algorithm for power allocation that maximizes the ergodic achievable rate. We verified the sum rate improvement with our proposed scheme through extensive simulation tests. Next, we introduce a novel physical layer scheme for single user MIMO spatial multiplexing systems based on unsupervised deep learning using an autoencoder. Both transmitter and receiver are designed as feedforward neural networks (FNN) and constellation diagrams are optimized to minimize the symbol error rate (SER) based on the channel characteristics. We first evaluate the SER in the presence of a constant Rayleigh-fading channel as a performance upper bound. Then, we quantize the Gaussian distribution and train the autoencoder with multiple quantized channel matrices. The channel is provided as an input to both the transmitter and the receiver. The performance exceeds that of conventional communication systems both when the autoencoder is trained and tested with single and multiple channels and the performance gain is sustained after accounting for the channel estimation error. Moreover, we evaluate the performance with increasing number of quantization points and when there is a difference between training and test channels. We show that the performance loss is minimal when training is performed with sufficiently large number of quantization points and number of channels. Finally, we develop a distributed and decentralized MU-MIMO link selection and activation protocol that enables MU-MIMO operation in wireless networks. We verified the performance gains with the proposed protocol in terms of average network throughput.
Doctor of Philosophy

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