Dissertations / Theses on the topic 'Communication systems'
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Kodikara, Patabandi C. K. "Multimedia communications over 3G wireless communication systems." Thesis, University of Surrey, 2004. http://epubs.surrey.ac.uk/844270/.
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This thesis addresses the transmission of video over third generation radio access networks. The first part of the thesis investigates the capabilities of Universal Terrestrial Radio Access Networks (UTRAN) in terms of the provision of multimedia communications. The error performance and traffic requirements of real-time video transmission over circuit switched and packet switched connections are examined. The effect of network parameter settings upon video performances is evaluated, and optimum radio bearer configurations for the transmission of video are derived. A method of estimating received video quality after transmission over error prone environments is developed. The quality estimation is based on a distortion model, which accurately models the overall distortion seen in decoder frame reconstruction. This includes quantisation distortion, concealment distortion, and error propagation. Based on the developed performance model, optimum MTU (Maximum Transfer Unit) size for efficient wireless video communications over a packet switched access network is derived. The second part of the thesis investigates quality enhancement techniques for multimedia traffic transmitted over wireless channels. Quality enhancement is achieved at three levels of the transmission process: link level, application level and system level. Link level quality enhancement techniques are designed to optimise the allocation of link level parameter values according to the media characteristics. A novel Unequal Error Protection scheme and a novel Unequal Power Allocation scheme are designed to exploit the inherent diversity in the subjective importance of different sections of compressed media. The algorithms are developed and analysed for transmission of video over 3G wireless systems. The effectiveness of these algorithms is demonstrated through the results of simulated transmission over a UMTS channel. Application level quality enhancement techniques are designed to explore the time-varying nature of the wireless channel. A number of link adaptation schemes are proposed for real time video communication and real-time video streaming over 3G wireless systems. These algorithms are designed to enhance the perceptual video quality, and the system utilisation. This is achieved by adapting the allocated radio network parameters and the source parameters, according to a feedback channel condition. Simulation results show a significant performance improvement compared to non-adaptive schemes. Finally, system level adaptation techniques are designed for efficient radio resource allocation in multi-user scenarios. Two adaptive resource allocation schemes are proposed and analysed for real-time video communications in a UMTS system. The proposed algorithms are shown to provide improved performances in terms of average received video quality and user satisfaction. Key words: Wireless Communication, Multimedia communication. Video Transmission.
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Cryan, R. A. "Communication systems." Thesis, University of Huddersfield, 1999. http://eprints.hud.ac.uk/id/eprint/7477/.
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Corley, John T. "Clandestine communication systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401364.
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Thesis (M.S. in Defense Analysis)--Naval Postgraduate School, December 2001.Thesis Advisor(s): McCormick, Gordon. "December 2001." Includes bibliographical references (p. 41-45). Also available in print.
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Wrona, Konrad S. "Cooperative communication systems /." Aachen : Wiss.-Verl. Mainz, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014918520&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Strengier, Dan. "MusicMan communication systems." Click here to view, 2009. http://digitalcommons.calpoly.edu/eesp/10/.
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Thesis (B.S.)--California Polytechnic State University, 2009.Project advisor: Dennis Derickson. Title from PDF title page; viewed on Feb. 4, 2010. Includes bibliographical references. Also available on microfiche.
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Lundy, G. M. "Systems of communicating machines : a model for communication protocols." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/8210.
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Smith, Jill Yvonne. "Communication Quality in Information Systems Development: The Effect of Computer-Mediated Communication on Task-Oriented Problem Solving." Thesis, North Texas State University, 1986. https://digital.library.unt.edu/ark:/67531/metadc331600/.
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The problem motivating this research is that ineffective communication may hamper systems development efforts. Specifically germane to this study are development efforts characterized as task-oriented, and which require information-sharing and problem-solving activities. This research problem motivated an analysis of the communication process and lead to the development of a temporal framework that delineates variables associated with task-oriented, end user/systems analyst communication interactions. Several variables within this framework are depicted in two theoretical models. The first model shows the theoretical relationship between an independent variable, communication mode (represented by asynchronous computer conferencing and face-to-face conferencing), and five dependent variables: (1) the amount of information shared, (2) the significance of the information shared, (3) the comprehensiveness of the information shared, (4) the perception of progress toward the goal, and (5) the perception of freedom to participate. The second model depicts the assumed interaction between communication mode, the five variables cited above (now acting as independent variables), and a dependent variable, communication quality. There are two theoretical components of communication quality: (1) deviation from an optimal set of user requirements, and (2) the degree of convergence (unity based on mutual understanding and mutual agreement) emanating from a communication interaction. Using the theoretical models as a guide, an experiment was designed and performed to test the relationships among the variables. The experimental results led to the rejection of all null hypotheses; the results strongly favored face-to-face conferencing for solving task-oriented, information-sharing problems analagous to the case used in the present study. The findings indicate that asynchronous computer conferencing may have a detrimental effect on the thoroughness of information exchange, on the relevance of the information shared in terms of making the correct decision, and on the completeness of the consideration given to all problem dimensions.
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Liu, Tuo. "Analytical modeling of HSUPA-enabled UMTS networks for capacity planning." Connect to full text, 2008. http://ses.library.usyd.edu.au/handle/2123/4055.
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Thesis (Ph. D.)--University of Sydney, 2009.Title from title screen (viewed February 20, 2009). Includes graphs and tables. Includes list of publications co-authored with others. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Information Technologies, Faculty of Engineering and Information Technologies. Degree awarded 2009; thesis submitted 2008. Includes bibliographical references. Also available in print form.
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O'Such, William R. "Information theoretic analysis of multi-stage communication/imaging systems /." Online version of thesis, 1988. http://hdl.handle.net/1850/10568.
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Rabie, Khaled Maaiuf. "Power line communication systems." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/power-line-communication-systems(7692173b-5d68-4483-b5ea-d871bfcdafcf).html.
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The remarkably increasing demand for communication systems has recently forced the research community to consider power line (PL) networks for data transmission, which is commonly referred to as power line communications(PLC). In particular, this technology becomes more attractive in harsh wireless environments where radio spectrum is scarce or/and propagation loss is high such as in underground structures and buildings with metal walls. PLC can support many applications such as home-networking, internet and smart grid. More specifically, PLC is considered the backbone of smart grids, not only because no extra wiring installation is required, but also because PLC is a through-grid technology which could reduce the reliance of the utility companies on third party connectivity and, consequently, overcome many security and privacy issues. On the other hand, since PLs were not designed for data transmission, communication signals over such channels can degrade tremendously. Contrary to many other communication channels, noise over PLs cannot be described as additive white Gaussian noise. It is rather categorized broadly into impulsive noise and background noise with the former being the most crucial element influencing PLC systems. With this in mind, this thesis will primarily focus on studying and developing advanced techniques and algorithms to reduce the severity of impulsive noise over PL channels. The contributions of this thesis are described as follows. Initially, a thorough review is provided to introduce and compare the challenges facing PLC, PL channel and noise modelling schemes, as well as some noise mitigation techniques. Next, novel approaches are proposed, with different degrees of effectiveness and complexity, to reduce the effect of impulsive noise in orthogonal frequency-division multiplexing (OFDM)-based PLC systems. Firstly, an adaptive hybrid preprocessing system is introduced to improve the performance of the conventional hybrid approach. In this respect, closed-form expressions for the output signal-to-noise ratio (SNR), probability of missed detection and probability of successful detection are derived. Secondly, and unlike existing works which are entirely based on countering impulsive noise at the receiver side, we show that if the OFDM signal is preprocessed at the transmitter side in such a way to minimize the signal peaks, the noise cancellation process can be made more efficient at the receiver. This is accomplished by applying a peak-to-average power ratio reduction scheme such as selective mapping. A closed-form expression for the probability of blanking error of this system is derived. Thirdly, to eliminate the estimation requirement problem of the short-term noise statistics associated with the aforementioned approaches, we propose the dynamic peak-based threshold estimation (DPTE) method. This method relies on utilizing the OFDM signal peak estimates with which optimal blanking is achieved irrespective of the noise parameters. In addition, to realize DPTE, a look-up table algorithm with uniform quantization is exploited and investigated in various system configurations. Furthermore, this thesis explores the performance of multi-carrier code division multiple access (MC-CDMA) systems over the multipath PL channel contaminated with Middleton class-A noise for various spreading codes, namely, Pseudonoise, Walsh-Hadamard and orthogonal poly-phase sequences. Different nonlinear preprocessors are implemented and the corresponding performance is evaluated in terms of the output SNR and symbol error rate.
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Ma, Ming. "Multiuser mobile communication systems." Thesis, Lancaster University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289069.
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Schworer, William Joseph. "Nationwide mobile communication systems." Thesis, Monterey, California. Naval Postgraduate School, 1990. http://hdl.handle.net/10945/37533.
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Approved for public release; distribution unlimited.This thesis provides a basic understanding of nationwide terrestrial and satellite mobile communications and tracking technologies. Covered are systems currently available and in development. An analysis of user costs is performed for comparison. A more detailed mobile satellite cost/benefit analysis for use by the trucking industry is also presented. Follow-on chapters contain discussions of the basic economic issues faced by satellite system operators and the regulatory history of mobile satellite services. Contained in the appendices are a more detailed discussion of mobile satellite systems and a layman's explanation of communication and navigation technologies. The conclusion presents comments on the possible future direction of these new mobile communication services and makes recommendations for trucking industry use.
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Phongphanphanee, Chai. "Multilayer mobile communication systems." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324001.
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RIBEIRO, MARCELO PEIXOTO. "SYNCHRONIZATION IN COMMUNICATION SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1990. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9258@1.
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O presente texto aborda aspectos do problema de
sincronização em sistemas de telecomunicações, com
enfoque
nas funções de demodulação síncrona, regeneração,
multiplexação/demultiplexação (TDM) e comutação (digital).
São tratados os métodos de obtenção de referência de
portadora e de referência de relógio, os recursos de
malha de amarração de fase (PLL) e de memória elástica.
O objetivo final consiste na descrição dos métodos de
sincronização de rede, nas modalidades plesiócrona (e
plesiócrona com justificação), mestre-escravo e
sincronização mútua.
As subredes de sincronização são analisadas em termos de
topologia, segurança, determinação de freqüência e fases
de operação e de compensação de defasagens na transmissão.
A apresentação é feita em termos de um texto didático
para
a descrição dos problemas e de suas soluções.This text deals with aspects of synchronization in telecommunication systems, with emphasis on the operational functions of synchronous demodulation, signal regeneration, multiplexing/demultiplexing (TDM) and digital switching. The methods of carrier recovery, clock recovery, phase locked loop and elastic store are presented. The final goal consists on the description of network synchronization methods, in the plesiochronous (and plesiochronous with justification), master-slave and mutual synchronization modalities. The synchronization subnetworks are analised in terms of topology, safety, operation frequency and phases, and transmission phase delay compensation. The presentation is made in a didactical way, describing the problems and their possible solutions.
15
Jiang, Junyi. "Optical wireless communication systems." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/387239/.
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In recent years, Optical Wireless (OW) communication techniques have attracted substantial attention as a benefit of their abundant spectral resources in the optical domain, which is a potential solution for satisfying the ever-increasing demand for increased wireless capacity in the conventional Radio Frequency (RF) band. Motivated by the emerging techniques and applications of OW communication, the Institute of Electrical and Electronics Engineers (IEEE) had released the IEEE standard 802.15.7 for short-range optical wireless communications, which categorised the Physical layer (PHY) of the OW communication into three candidate-solutions according to their advantages in different applications and environments: 1) Physical-layer I (PHY I): Free Space Optical (FSO)communication employs high-intensity Light Emitting Diodes (LEDs) or Laser Diodes (LDs) as its transmitter. 2) Physical-layer II (PHY II) uses cost-effective, low-power directional white LEDs for the dual function of illumination and communication. 3) Physical III (PHY-III) relies on the so-called Colour-Shift Keying (CSK) modulation scheme for supporting high-rate communication. Our investigations can be classified into three major categories, namely Optical Orthogonal Frequency Division Multiplexing (OFDM) based Multiple-Input Multiple-Output (MIMO) techniques for FSO communications in the context of PHY I, video streaming in PHY-II and the analysis and design of CSK for PHY-III. To be more explicit, in Chapter 2 we first construct a novel ACO-OFDM based MIMO system and investigate its performance under various FSO turbulence channel conditions. However, MIMO systems require multiple optical chains, hence their power consumption and hardware costs become substantial. Hence, we introduced the concept of Aperture Selection (ApS) to mitigate these problems with the aid of a simple yet efficient ApS algorithm for assisting our ACO-OFDM based MIMO system. Since the channel conditions of indoor Visible Light Communication (VLC) environments are more benign than the FSO-channels of Chapter 2, directional white LEDs are used to create an “attocell” in Chapter 3. More specifically, we investigate video streaming in a multi-Mobile Terminals (MTs) indoor VLC system relying on Unity Frequency Reuse (UFR) as well as on Higher Frequency Reuse Factor based Transmission (HFRFT) and on Vectored Transmission (VT) schemes. We minimise the distortion of video streaming, while satisfying the rate constraints as well as optical constraints of all the MTs. In Chapter 4 we analyse the performance of CSK relying both on joint Maximum Likelihood (ML) Hard-Detection (HD), as well as on the the Maximum A posteriori (MAP) criterion-based Soft-Detection (SD) of CSK. Finally, we conceive both two- stage and three-stage concatenated iterative receivers capable of achieving a substantial iteration gain, leading to a vanishingly low BER.
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Harry, Drew. "Designing complementary communication systems." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78213.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. [163]-172).
We have long assumed that being face to face is the best environment for social interaction. But is "being there" the best we can aspire to? One common approach to improving face-to-face contexts is to add new communication channels - a strategy often described as creating "backchannels." In my work, I use a series of novel complementary communication systems to show how adding communication platforms to collaborative situations can be useful while also arguing for a new conceptual model of a main stage and a side stage (in the Goffman sense) that contrasts with the traditional model of backchannels. I describe a series of projects that embody this approach and explore its limits. My work covers virtual world meetings and presentations, an audience interaction tool for large groups (backchan.nl), a tablet-based system for small group discussions (Tin Can), and a platform for connecting huge distributed audiences (ROAR). In each of these projects I trace my three major research themes: understanding how conversational grounding operates in these environments, how non-verbal actions complement text-based interaction, and how people make decisions about how to manage their attention in environments with multiple simultaneous communication channels.
by Drew Harry.
Ph.D.
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Wu, Xiaoyuan. "Simulation of Communication Systems." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/44993.
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Digital communications and computers are having a tremendous impact on the world today. In order to meet the increasing demand for digital communication services, engineers must design systems in a timely and cost-effective manner. The number of technologies available for providing a given service is growing daily, covering transmission media, devices, and software. The resulting design, analysis, and optimization of performance can be very demanding and difficult. Over the past decades, a large body of computer-aided engineering techniques have been developed to facilitate the design process of complex technological systems. These techniques rely on models of devices and systems, both analytic and simulation, to guide the analysis and design throughout the life cycle of a system. Computer-aided design, analysis, and simulation of communication systems constitute a new and important part of this process.
This thesis studies different aspects of the simulation of communication systems by covering some basic ideas, approaches, and methodologies within the simulation context. Performance measurement of a digital communication is the main focus of this thesis. However, some popular visual indicators of signal quality, which are often generated in a simulation to provide a qualitative sense of the performance of a digital system, are also considered.
Another purpose of this thesis is to serve as a model for developing simulations or template of other systems. In other words, students learning to simulate a system can use the work presented here as a starting point.Master of Science
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Yamashita, Shota. "Coexistence of Wireless Communication and Non-communication Systems." Kyoto University, 2018. http://hdl.handle.net/2433/232420.
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鄭价昌 and Kai-cheong Chang. "Adaptive channel equalisation technique for wideband time-division multiple access digital mobile radio communications systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31212888.
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Manescu, Corneliu. "Video and voice coding for mobile ad-hoc collaboration." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000740.
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Chang, Kai-cheong. "Adaptive channel equalisation technique for wideband time-division multiple access digital mobile radio communications systems /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B17590371.
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Sabelkin, Mykhaylo. "Data transmission oriented on the object, communication media, application, and state of communication systems tactical communication system application." Mémoire, École de technologie supérieure, 2011. http://espace.etsmtl.ca/941/1/SABELKIN_Mykhaylo.pdf.
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L’architecture du système de communication proposé se nomme TOMAS (Transmission de
données orientée sur l’Objet, le Médium de communication, l’Application, et l’état des Systèmes
de communications). En fonction de scénarios particuliers de communication tactique
de transmission d’image par le canal sans fil en ligne de vue directe, le système TOMAS sans
fil obtient une performance supérieure à celle du système combinant le JPEG2000 et la modulation
OFDM sur les paramètres de qualité de l’image restaurée et ce, pour une large gamme
de paramètres du canal. Sans aucun codage ni estimation du canal, le système TOMAS sans fil
fournit une transmission progressive de l’image sans pertes sous l’influence de l’évanouissement
modéré du canal. Le système TOMAS sans fil est basé sur l’algorithme propriétaire breveté
Sabelkin (2011). Il ne contient pas d’opérations de multiplications, et utilise trois fois moins
d’opérations d’additions réelles que celui du système JPEG2000+OFDM. Notre système exploite
la transformation en ondelettes specialisée pour un codage de l’image et une modulation
du canal.
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Lukama, L. "Diversity systems for future wideband wireless communication systems." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249495.
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Neo, Soo Sim Daniel. "Free space optics communication for mobile military platforms." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FNeo.pdf.
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Caronni, Germano. "Dynamic security in communication systems /." [S.l.] : [s.n.], 1999. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13156.
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Wilund, Torbjörn. "Robust Distributed Embedded Systems : Communication." Thesis, KTH, Maskinkonstruktion (Inst.), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-100998.
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Detta examensarbete diskuterar i sin teoretiska del vad begreppet robusthet betyder för distribuerade inbyggda system. Utvecklingen går idag generellt emot att byta mekaniska och elektriska lösningar mot mekatroniska styrsystem. Det finns sedan mycket att vinna på att göra dessa inbyggda styrsystem distribuerade, bland annat beroende på oberoende mellan noder för intern övervakning och feldetektering. Delresultatet om robusthet säger att det beror på integritet för att uppnå tillgänglighet och tillförlitlighet, det vill säga att informationen är den samma i alla berörda noder. Tillförlitligheten beror på hur fel i tid och värde hanteras under systemexekvering. Informationen skyddas i samtliga undersökta protokoll genom redundans av diverse algoritmer, exempelvis CRC vilket ger möjlighet till feldetektering. Skillnad finns dock i hur tidssynkronisering hanteras om det ens finns hantering av för detta. Ur detta perspektiv är endast tidsstyrda nätverksprotokoll av nuvarande alternativ mest tekniskt lämpliga. Den praktiska delen försöker utvärdera GAST levererad hårdvara. Arbetet med att få igång någon kommunikation på TTP/C misslyckades, detta beroende på brister i den sammansatta plattformen. Mer specifikt beror detta troligtvis på konstruktionsfel i det fysiska lagret av plattformen. Med valt bakplan blir ej signalerna som förväntat vilket gör att informationen tolkas fel av externa kommunikations kretsar. Därför rekommenderas närmare analys av signalen i databussen och eventuell konstruktion av ett filter till bakplanet om nuvarande hopsättning skall användas. Plattformen har med sin öppenhet en framtid för utveckling och forskning kring distribuerade inbyggda system, dock saknas färdiga drivrutiner för de i plattformen integrerade protokollen. Detta är något som måste åtgärdas ifall plattformen skall få någon form av betydelse innan tekniken är för gammal. Undersökningen av den TTP Plan genererade koden visar att det går att extrahera information från verktyget och på så sätt utnyttja verktyget för konfiguration. För att detta skall fungera bör man tillverka någon form av verktyg för detta.This thesis tries in its theoretical part to discuss what the term of robustness means for distributed embedded systems. Development of today generally tries to exchange mechanical and electrical solutions for embedded control systems. There are a lot of benefits to gain by designing in a distributed way, this due to internal independencies between nodes for monitoring and error detection. The outcome about robustness suggests that it depends on integrity to achieve availability and reliability, or loss of alternations of information in the different nodes in the distributed system. Reliability depends on how faults in terms of time and value are treated during execution. All studied network protocols have protection of information by different redundancy algorithms such as CRC, which gives the opportunity for fault and error detection. However there are differences in how time is handled, if there is any time handling, and possibility for time synchronization in the hardware. From this perspective the best alternatives are time triggered architectures of current technology. The experimental part tries to evaluate the GAST delivered platform. The work to achieve communication on TTP/C controllers failed due to shortage in the assembled platform. More specifically this is probably the case of bugs in the design of the physical layer of the GAST hardware (not the TTP controllers themselves). By use of recommended backplane, the sent signals are not appearing as expected, and information sent is misinterpreted by external communication devices. A suggestion and recommendation for future work is analysis of the signal in the data bus, and possible design of a filter if current assembly shall be used. The platform has a future for development and research in the field of distributed embedded systems due to its openness, however there is a lack of drivers for the platform integrated network protocols. This must be attended if the platform shall have any significance. The evaluation of TTP Plan generated code shows, that there are possibilities to extract configuration information form tool for configuration of platform. To achieve this some kind of extraction script must be developed.
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Douglas, Mark Gordon. "Antennas for personal communication systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0005/NQ34257.pdf.
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Ahl, Annika. "Communication concerning internal information systems." Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-96311.
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För att företag ska kunna vara konkurrenskraftigt på dagens marknad krävs det att det har effektiva arbetsprocesser i sin verksamhet. Ett vanligt sätt att effektivisera processer i en verksamhet är att implementera ett informationssystem. Fördelen med att använda ett informationssystem är att alla anställda på ett företag kan ta del av samma information. En förutsättning för att en verksamhet ska kunna uppnå positiva effekter av användningen av ett informationssystem är att de anställda använder det. Undersökningens syfte är att ta reda på om de anställdas bristande användning av ett informationssystem beror på dålig kommunikation. För att kunna besvara på undersökningens problemformulering genomfördes en enkätundersökning på ett IT- företag. Undersökningen visar att merparten av de tillfrågade mkände till systemets syfte och de kunde även beskriva syftet. Undersökningen visar även att det var en stor andel som ansåg att det inte visste hur användandet av systemet påverkar sitt arbete i verksamheten. En av slutsatserna är att kommunikationen kan förbättras. Den information som de anställda bör tillhandahållas är hur systemet fungerar och hur användningen av detta systemet påverkar deras arbete.
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Ghamari, Mohammad. "Reliable communication in embedded systems." Thesis, Lancaster University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663247.
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Embedded computer systems equipped with wireless communication transceivers are nowadays used in a vast number of application scenarios. Energy consumption is important in many of these scenarios as systems are battery operated and long maintenance free operation is required. To achieve this goal, embedded systems employ low-power communication transceivers and protocols. However, currently used protocols cannot operate efficiently when communication channels are highly erroneous. In many application scenarios, we find this characteristic that a large numbers of transmitted packets maybe lost or received corrupted. This work aims to provide solutions to this particular problem. This thesis focuses on one particular class of low-power MAC protocols in embedded systems and investigates its transmission reliability through erroneous channels. Subsequently, this thesis presents a number of techniques which ameliorate the transmission reliability in conjunction with energy efficiency of existing low-power MAC protocols simultaneously in erroneous channels. In this thesis, average diversity combining (ADC) is applied in low-power MAC protocols to ensure that the received corrupted packets can be used to contribute in decoding process. This thesis demonstrates that how ADC is integrated with low-power MAC protocols. It is also shown that the integrated method improves low-power Communication dramatically. The integrated method always reduces the frame error rate; in some investigated scenarios frame error rates are reduced from 20.85% to 1.25%. Furthermore we have shown that the ADC mechanism can be implemented on existing systems without significant impact on system performance. In addition, transmit/receive diversity along with error correction technique is also applied in existing low-power MAC protocols such that high losses of transmitted packets are preventable. This work demonstrates how transmit/receive diversity along with error correction technique is integrated with low-power MAC protocols. It is illustrated that the integrated scheme prevents high losses of transmitted packets. Subsequently, in order to further analyze the transmission reliability cost of the proposed techniques in low-power embedded systems, we have compared different combinations of proposed hardware and software extensions. Surprisingly, our analysis is demonstrated that, although increasing the number of antennas at one particular side of a communication link which is directly proportional to the system cost, always guarantee better transmission reliability, however, there are cases that applying fewer number of antennas along with using appropriate software extensions can provide better transmission reliability compared with cases with more number of antennas.
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Lam, Chi Wa. "Synchronization in OFDM communication systems." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/928/.
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ALMEIDA, MARTA PUDWELL CHAVES DE. "RADIOPROPAGATION IN SATELLITE COMMUNICATION SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9622@1.
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O desenvolvimento de sistemas de comunicações via satélite
requer a introdução de novas tecnologias e novas técnicas,
e o uso de freqüências elevadas superiores a 10 GHZ. Para
aplicações utilizando freqüências acima de 10 GHz, deve
ser considerada predominantemente a atenuação causada pela
chuva.
Este trabalho apresenta resultados intermediários de uma
campanha de medidas realizada no CETUC, na faixa de 12
GHz. Esta campanha foi iniciada em 1987 com a realização
de medidas radiométricas em diferentes regiões climáticas
do Brasil. Em 1995, foram adquiridos sistemas de recepção
de sinais de beacon de satélite. O principal objetivo das
medidas é a aquisição das distribuições estatísticas de
longo termo da atenuação causadas pela chuva, a serem
utilizadas no planejamento e dimensionamento de futuros
sistemas de comunicações via satélite. Além das
distribuições cumulativas de longo termo, são analisadas:
a variabilidade das distribuições ano a ano, as
estatísticas de pior mês, as características dinâmicas da
atenuação por chuva, a dependência da ocorrência de
atenuação com a hora do dia, a distribuição da taxa de
precipitação e a previsão da atenuação a partir da taxa de
precipitação.The development of satellite communication systems requires the introduction of new technologies and techniques as well as the use of high frequencies, above 10GHz. Above such frequencies, rainfall induced attenuation effects, which are strongly frequency dependent, become important as the main source of reliability impairment. Thid work presents the intermediate results from a measurements campaign at 12GHz. This campaign began in CETUC in 1987 with radiometric measurements on several different Brazilian climatic regions. In 1995, systems for receiving satellite beacon signal were acquired. The main objective of the satellite beacon measurements is to obtain the long term distributions of rainfall induced attenuation, which will be used to aid the planning and design of future satellite communication systems. Besides the long term distributions of attenuation, the following results will be sought out: year-to-year variability of the attenuation distributions,worst-month statistics, the dynamic characteristics of rainfall induced attenuation, the daily variation of the occurrence of attenuation events, rainfall rate distributions and the possibility of modelling the attenuation as a function of the rainfall rate.
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Mohanty, Nirode C. "DEMAND ACCESS SATELLITE COMMUNICATION SYSTEMS." International Foundation for Telemetering, 1985. http://hdl.handle.net/10150/615594.
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International Telemetering Conference Proceedings / October 28-31, 1985 / Riviera Hotel, Las Vegas, NevadaA demand access Satellite Communication System for multiple users has been analyzed. A number of channels, m 1, of each satellites are necessary to coordinate the self-served users to allow access to a satellite having s channels. m depends upon traffic intensity and number of top priority users. A waiting time period for a Poisson arrival and exponential holding time M/M/s system for “preemptive resume” discipline has been derived. There is a significant reduction in waiting time in accessing the channel and in transmission time over other access schemes. There is no waiting time for a top priority user, either in accessing the channel or in transmitting its messages, when the appropriate number of order wires is used.
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Parker, Aaron Mark. "Designing communication systems that work." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683941.
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Developments in computer-mediated communications are changing the way people communicate. Yet for every system that succeeds, many others fail. The failure of seemingly superior systems, such as the Picturephone, and success of simpler ones, such as Twitter, have challenged common-sense notions of what makes for a successful communications system. This thesis proposes that computer-mediated communication systems should not be compared relative to the quality of the communicative cues they transmit. Instead, they should be viewed relative to their ability to offer channels of communication that may be creatively repurposed to compensate for restrictions. Together with a new tool for enquiry, termed the integrative framework, it is proposed that needs and trade-offs occur across four interrelated levels. These four levels are the task, the group, the self, and the system. Studies 1 and 2 applied the integrative framework to a new form of high-quality videoconferencing called telepresence. Anecdotal evidence suggested that users were enthusiastic towards these systems, unlike with standard videoconferencing products. In Study 1, user interviews supported this and also provided evidence that users were adapting the system for activities it was not designed. An investigation into the effects of system latency on collaboration by telepresence followed in Study 2. Again, results were atypical of videoconferencing, suggesting that telepresence offers mechanisms through which the effects of latency can be mitigated. Studies 3, 4 and 5 investigated the use of paralanguage (operationalised as the unusual informal elements of written language) in text-based communications as an example where users adapt to the restrictions of a medium. In Study 3, it was discovered that users of a virtual world utilised paralanguage extensively, even in a formal context. Through grounded theory it was discovered that paralanguage had a self-presentation role. In Study 5, the association of para language with the levels of the integrative framework was investigated. Associations were discovered, highlighting the users' role in improving restrictive media. The thesis extends the theoretical understanding of computer mediated communication by demonstrating that users engage in compensatory behaviour to adapt to system restrictions. It also introduces the integrative framework as a tool for the design and evaluation of effective communication systems.
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Djamal-Eddine, Berraki. "Beamforming for mmWave communication systems." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.691176.
Full textAbstract:
Historically, wireless systems were designed to meet the demand of relatively low speed connections for calls, web browsing and emails. However, recent developments in consumer electronics has led to the proliferation of new applications such as High Definition Television, mobile TV, Online Multimedia and high resolution internet which put pressure on wireless systems to meet the generated data traffic. Standards such as IEEE 802.1 lac and LTE-AlB have adopted more advanced configurations such as MTMO architectures, beamforming, spatial sharing and channel aggregation to ease this high demand. However, even with such complex configurations, the highly congested 0-6GHz band is incapable to offer multi-user multi-gigabit wireless performance. This spectmm shortage has motivated the investigation of possible usage of unlicensed/light-licensed mmWave bands within the range of 30-100GHz where large chunks of spectmm are available.
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Alhartomi, Mohammed. "Collaborative optical wireless communication systems." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/13153/.
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Martwick, Andrew Wayne. "Clock Jitter in Communication Systems." PDXScholar, 2018. https://pdxscholar.library.pdx.edu/open_access_etds/4375.
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For reliable digital communication between devices, the sources that contribute to data sampling errors must be properly modeled and understood. Clock jitter is one such error source occurring during data transfer between integrated circuits. Clock jitter is a noise source in a communication link similar to electrical noise, but is a time domain noise variable affecting many different parts of the sampling process. Presented in this dissertation, the clock jitter effect on sampling is modeled for communication systems with the degree of accuracy needed for modern high speed data communication. The models developed and presented here have been used to develop the clocking specifications and silicon budgets for industry standards such as PCI Express, USB3.0, GDDR5 Memory, and HBM Memory interfaces.
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Toni, Laura <1982>. "Adaptive wireless multimedia communication systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2117/1/Laura_Toni_tesi.pdf.
Full textAbstract:
In recent years, due to the rapid convergence of multimedia services, Internet and wireless communications, there has been a growing trend of heterogeneity (in terms of channel bandwidths, mobility levels of terminals, end-user quality-of-service (QoS) requirements) for emerging integrated wired/wireless networks. Moreover, in nowadays systems, a multitude of users coexists within the same network, each of them with his own QoS requirement and bandwidth availability. In this framework, embedded source coding allowing partial decoding at various resolution is an appealing technique for multimedia transmissions. This dissertation includes my PhD research, mainly devoted to the study of embedded multimedia bitstreams in heterogenous networks, developed at the University of Bologna, advised by Prof. O. Andrisano and Prof. A. Conti, and at the University of California, San Diego (UCSD), where I spent
eighteen months as a visiting scholar, advised by Prof. L. B. Milstein and Prof. P. C. Cosman. In order to improve the multimedia transmission quality over wireless channels, joint source and channel coding optimization is investigated in a 2D time-frequency resource block for an
OFDM system. We show that knowing the order of diversity in time and/or frequency domain can assist image (video) coding in selecting optimal channel code rates (source and channel code rates). Then, adaptive modulation techniques, aimed at maximizing the spectral efficiency, are investigated as another possible solution for improving multimedia transmissions. For both slow and fast adaptive modulations, the effects of imperfect channel estimation errors are evaluated, showing that the fast technique, optimal in ideal systems, might be outperformed by the slow adaptive modulation, when a real test case is considered. Finally, the effects of co-channel interference and approximated bit error probability (BEP) are evaluated in adaptive modulation techniques, providing new decision regions concepts, and showing how the widely used BEP
approximations lead to a substantial loss in the overall performance.
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Toni, Laura <1982>. "Adaptive wireless multimedia communication systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2117/.
Full textAbstract:
In recent years, due to the rapid convergence of multimedia services, Internet and wireless communications, there has been a growing trend of heterogeneity (in terms of channel bandwidths, mobility levels of terminals, end-user quality-of-service (QoS) requirements) for emerging integrated wired/wireless networks. Moreover, in nowadays systems, a multitude of users coexists within the same network, each of them with his own QoS requirement and bandwidth availability. In this framework, embedded source coding allowing partial decoding at various resolution is an appealing technique for multimedia transmissions. This dissertation includes my PhD research, mainly devoted to the study of embedded multimedia bitstreams in heterogenous networks, developed at the University of Bologna, advised by Prof. O. Andrisano and Prof. A. Conti, and at the University of California, San Diego (UCSD), where I spent
eighteen months as a visiting scholar, advised by Prof. L. B. Milstein and Prof. P. C. Cosman. In order to improve the multimedia transmission quality over wireless channels, joint source and channel coding optimization is investigated in a 2D time-frequency resource block for an
OFDM system. We show that knowing the order of diversity in time and/or frequency domain can assist image (video) coding in selecting optimal channel code rates (source and channel code rates). Then, adaptive modulation techniques, aimed at maximizing the spectral efficiency, are investigated as another possible solution for improving multimedia transmissions. For both slow and fast adaptive modulations, the effects of imperfect channel estimation errors are evaluated, showing that the fast technique, optimal in ideal systems, might be outperformed by the slow adaptive modulation, when a real test case is considered. Finally, the effects of co-channel interference and approximated bit error probability (BEP) are evaluated in adaptive modulation techniques, providing new decision regions concepts, and showing how the widely used BEP
approximations lead to a substantial loss in the overall performance.
39
Wang, Shendi. "Efficient transmission design for machine type communications in future wireless communication systems." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23647.
Full textAbstract:
With a wide range of potential applications, the machine type communication (MTC) is gaining a tremendous interest among mobile network operators, system designers, MTC specialist companies, and research institutes. The idea of having electronic devices and systems automatically connected to each other without human intervention is one of the most significant objectives for future wireless communications. Low data rate transmission and the requirement for low energy consumption are two typical characteristics for MTC applications. In terms of supporting low cots MTC devices, industrial standards will be more efficient if designers can re-use many features of existing radio access technologies. This will yield a cost effective solution to support MTC in future communication systems. This thesis investigates efficient MTC waveform and receiver designs for superior signal transmission quality with low operational costs. In terms of the downlink receiver design, this thesis proposes a novel virtual carrier (VC) receiver system for MTC receivers, which aims to reduce the maximum bandwidth to improve the data processing efficiency and cost-efficiency by using analogue filters to extract only sub-carriers of interest. For the VC receiver systems, we thus reduce the sampling rate in order to reduce the number of subsequent processing operations, which significantly reduces the analogue-to-digital converter (ADC) cost and power consumption while providing high signal to interference noise ratio (SINR) and low bit to error rate (BER) to support low data rate MTC devices. Our theoretical equations account for the interference effect of aliasing on the sub-carrier location, and this helps the system designer to evaluate what kind of filters and receiver sampling rate can be used to balance the energy cost and detection performance. In terms of the uplink waveform design, considering the enhanced number of MTC devices in the future communication systems, i.e. the fifth generation (5G) communications, the same tight synchronisation as used in today appears not to be cost-effective or even possible. Synchronisation signals, which aim to provide a perfect time or frequency synchronisation in the current fourth generation (4G) communication systems (known as the long-term evolution, LTE), is much more costly for low data rate MTC transmissions. The system bandwidth will be significantly reduced if a base station tries to synchronise all received signals among hundreds or thousands MTC devices in one transmission time period. In terms of relaxing the synchronisation requirements, this thesis compares and analyses the side-lobe reduction performance for several candidate multi-carrier waveforms to avoid these problems. We also propose the infinite impulse response universal filtered multi-carrier (UFMC) system and the overlap and add UFMC system, which significantly reduce the processing complexity compared with the state of the art UFMC techniques. This thesis derives closed-form expressions for the interference caused by time offsets between adjacent unsynchronised MTC users. Our analytical equations can be used in both simple and complex time-offset transmission scenarios, and enable the system designer to evaluate the SINR, the theoretical Shannon capacity and the BER performance.
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Holton, Carolyn F. "The impact of computer mediated communication systems monitoring on organizational communications content." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002440.
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Arredondo, Alberto. "Downlink beamforming for mobile communications." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035934.
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Todd, Stephen Ross Carleton University Dissertation Engineering Electrical. "Empirical evaluation of diversity techniques for indoor digital radio at 1.75 GHz." Ottawa, 1992.
Find full text
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Bambha, Neal Kumar. "Communication-driven codesign for multiprocessor systems." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1429.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Electrical 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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Spampinato, Daniele. "Modeling Communication on Multi-GPU Systems." Thesis, Norwegian University of Science and Technology, Department of Computer and Information Science, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9068.
Full textAbstract:
Coupling commodity CPUs and modern GPUs give you heterogeneous systems that are cheap, high-performance with incredible FLOPS counts. Recent evolution of GPGPU models and technologies make these systems even more appealing as compute devices for a range of HPC applications including image processing, seismic processing and other physical modeling, as well as linear programming applications. In fact, graphics vendor such as NVIDIA and AMD are now targeting HPC with some of their products. Due to the power and frequency walls, the trend is now to use multiple GPUs on a given system, much like you will find multiple cores on CPU-based systems. However, increasing the hierarchy of resource wides the spectrum of factors that may impact on the performance of the system. The lack of good models for GPU-based, heterogeneous systems also makes it harder to understand which factors impact performance the most. The goal of this thesis is to analyze such factors by investigating and benchmarking NVIDIA's multi-GPU solution, their recent NVIDIA Tesla S1070 Computing System. This system combines four T10 GPUs making available up to 4 TFLOPS of computational power. Based on a comparative study of fundamental parallel computing models and on the specific heterogeneous features exposed by the system, we define a test space for performance analysis. As a case study, we develop a red-black, SOR PDE solver for Laplace equations with Dirichlet boundaries, well known for requiring constant communication in order to exchange neighboring data. To aid both design and analysis, we propose a model for multi-GPU systems targeting communication between the several GPUs. The main variables exposed by the benchmark application are: domain size and shape, kind of data partitioning, number of GPUs, width of the borders to exchange, kernels to use, and kind of synchronization between the GPU contexts. Among other results, the framework is able to point out the most critical bounds of the S1070 system when dealing with applications like the one in our case study. We show that the multi-GPU system greatly benefits from using all its four GPUs on very large data volumes. Our results show the four GPUs almost four times faster than a single GPU, and twice as fast as two. Our analysis outcomes also allow us to refine our static communication model, enriching it with regression-based predictions.
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Aigner, Ronald. "Communication in Microkernel-Based Operating Systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-68373.
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Communication in microkernel-based systems is much more frequent than system calls known from monolithic kernels. This can be attributed to the placement of system services into their own protection domains. Communication has to be fast to avoid unnecessary overhead. Also, communication channels in microkernel-based systems are used for more than just remote procedure calls. In distributed systems, which also have a componentized design, it is state of the art to use tools to generate stubs for the communication between components. The communication interfaces of components are described in an interface definition language (IDL). In contrast to distributed systems, components of a microkernel-based system run on the same architecture and message delivery is guaranteed.
In this Thesis, I explore the different kinds of communication, which can be used in microkernel-based systems, as well as their possible representation in IDL. Specifically, I introduce the syntax to describe kernel objects in IDL. I discuss the complexity of IDL compilers and its relation to the complexity of the IDL. Furthermore, I evaluate the performance of the communication stubs generated by different IDL compilers and discuss techniques to minimize performance overhead in generated stubs. I validated these techniques by implementing the Drops IDL Compiler - Dice. Finally, this Thesis presents a mechanism to measure the frequency and performance of invocations of generated communication code. I used this technique to conduct measurements in highly complex systems and introducing the least possible overhead.
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Zhang, Zheshen. "New techniques for quantum communication systems." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42843.
Full textAbstract:
Although mathematical cryptography has been widely used, its security has only been proven under certain assumptions such as the computational power of opponents. As an alternative, quantum communication, in particular quantum key distribution (QKD) can get around unproven assumptions and achieve unconditional security. However, the key generation rate of practical QKD systems is limited by device imperfections, excess noise from the quantum channel, limited rate of true random-number generation, quantum entanglement preparation, and/or post-processing efficiency. This dissertation contributes to improving the performance of quantum communication systems. First, it proposes a new continuous-variable QKD (CVQKD) protocol that loosens the efficiency requirement on post-processing, a bottleneck for long-distance CVQKD systems. It also demonstrates an experimental implementation of the proposed protocol. To achieve high rates, the CVQKD experiment uses a continuous-wave local oscillator (CWLO). The excess noise caused by guided acoustic-wave Brillioun scattering (GAWBS) is avoided by a frequency-shift scheme, resulting in a 32 dB noise reduction. The statistical distribution of the GAWBS noise is characterized by quantum tomography. Measurements show Gaussian statistics upto 55 dB of dynamical range, which validates the security calculations in the proposed CVQKD protocol. True random numbers are required in quantum and classical cryptography. A second contribution of this thesis is that it experimentally demonstrates an ultrafast quantum random-number generator (QRNG) based on amplified spontaneous emission (ASE). Random numbers are produced by a multi-mode photon counting measurement on ASE light. The performance of the QRNG is analyzed with quantum information theory and verified with NIST standard random-number test. The QRNG experiment demonstrates a random-number generation rate at 20 Gbits/s. Theoretical studies show fundamental limits for such QRNGs. Quantum entanglement produced in nonlinear optical processes can help to increase quantum communication distance. A third contribution is the research on nonlinear optics of graphene, a novel 2D material with unconventional physical properties. Based on a quantum-dynamical model, optical responses of graphene are derived, showing for the first time a link between the complex linear optical conductivity and the quantum decoherence. Nonlinear optical responses, in particular four-wave mixing, is studied for the first time. The theory predicts saturation effects in graphene and relates the saturation threshold to the ultrafast quantum decoherence and carrier relaxation in graphene. For the experimental part, four-wave mixing in graphene is demonstrated. Twin-photon production in graphene is under investigation.
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Navaratnam, Srivallipuranandan. "Reliable group communication in distributed systems." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26505.
Full textAbstract:
This work describes the design and implementation details of a reliable group communication mechanism. The mechanism guarantees that messages will be received by all the operational members of the group or by none of them (atomicity). In addition, the sequence of messages will be the same at each of the recipients (order). The message ordering property can be used to simplify distributed database systems and distributed processing algorithms. The proposed mechanism continues to operate despite process, host and communication link failures (survivability). Survivability is essential in fault-tolerant applications.Science, Faculty of
Computer Science, Department of
Graduate
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Nilsson, Christoffer, and Sebastian Karlsson. "Adaptive Checkpointing for Emergency Communication Systems." Thesis, Linköpings universitet, Institutionen för datavetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-130876.
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The purpose of an emergency communication system is to be ready andavailable at all times during an emergency situation. This means that emergencysystems have specic usage characteristics, they experience long idleperiods followed by usage spikes. To achieve high availability it is importantto have a fault-tolerant solution. In this report, warm passive replication isin focus. When using warm passive replication, checkpointing is the procedureof transfering the current state from a primary server to its replicas. Inorder to utilize resources in a more eective manner compared to when usinga xed interval checkpointing method an adaptive checkpointing method isproposed. A simulation-based comparison is carried out using MATLABand Simulink to test both the proposed adaptive method and the xed intervalmethod. Two metrics, response time and time to recover, and fourparameters are used in the simulation. The results show that an adaptivemethod can increase eciency, but in order to make a good adaptive methodit is necessary to have specic information regarding system congurationand usage characteristics.
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Meijerink, Arjan. "Coherence multiplexing for optical communication systems." Enschede : University of Twente [Host], 2005. http://doc.utwente.nl/50841.
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Ding, Zhihong. "ARQ Techniques for MIMO Communication Systems." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1385.pdf.
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