- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 261 to 270 of 284 (0.026 seconds)| 261 |
Direction Finding and Beamforming Techniques using Antenna Array for Wireless System ApplicationsAl-Sadoon, Mohammed A.G. January 2019 (has links)
This thesis is concentrated on the Angle / Direction of Arrival (A/DOA) estimation and Beamforming techniques that can be used in the current and future engineering applications such as
tracking of targets, wireless mobile communications, radar systems, etc. This thesis firstly investigates different types of AOA and beamforming techniques. A comprehensive comparison between the common AOA algorithms is performed to evaluate the estimation accuracy and
illustrate the computational complexity of each algorithm. The effect of mutual coupling between
the radiators and the impact of the position-error of the antenna elements on the estimation
accuracy is also studied.
Then, several new efficient AOA methods for current wireless localisation systems are proposed. The estimation accuracy and computational complexity are compared with well-known
AOA methods over a wide range of scenarios. New methodologies for Covariance Matrix (CM)
sampling are proposed to enhance and improve operational performance without increasing the
computational burden. A new beamforming algorithm is proposed and implemented on a compact mm-Wave linear and planar antenna arrays to enhance the desired signal and suppress
the interference sources in wireless communication systems.
The issue of asset tracking in dense environments where the performance of the Global Positioning System (GPS) becomes unavailable or unreliable is addressed in the thesis as well. The
proposed solution uses a low-profile array of sensors mounted on a finite conducting ground. A
compact-size omnidirectional spiral sensor array of six electrically small dual-band antenna elements was designed to operate in the 402 and 837 MHz spectrum bands. For the lower band,
a three-element superposition method is applied to support the estimated AOA whereas six
sensors are considered for the higher band. An efficient and low complexity Projection Vector
(PV) AOA method is proposed. An Orthogonal Frequency Division Multiplexing (OFDM) modulation is integrated with the PV technique to enhance the estimation resolution. The system was
found to be suitable for installation on top of vehicles to localise the position of assets. The proposed system was tested to track non-stationary objectives, and then two scenarios were investigated: outdoor to outdoor and outdoor to indoor environments using Wireless In-Site Software. The results confirm that the proposed tracking system works efficiently with a single snapshot. / Higher Commission for Education Development (HCED) in Iraq
Basra Oil Company
Ministry of Oil
|
| 262 |
Radio-Location Techniques for Localization and Monitoring Applications. A study of localisation techniques, using OFDM system under adverse channel conditions and radio frequency identification for object identification and movement trackingShuaieb, Wafa S.A. January 2018 (has links)
A wide range of services and applications become possible when accurate position
information for a radio terminal is available. These include: location-based services;
navigation; safety and security applications. The commercial, industrial and military value
of radio-location is such that considerable research effort has been directed towards
developing related technologies, using satellite, cellular or local area network
infrastructures or stand-alone equipment.
This work studies and investigates two location techniques. The first one presents an
implementation scheme for a wideband transmission and direction finding system using
OFDM multi-carrier communications systems. This approach takes advantage of delay
discrimination to improve angle-of-arrival estimation in a multipath channel with high
levels of additive white Gaussian noise. A new methodology is interpreted over the multi carrier modulation scheme in which the simulation results of the estimated channel
improves the performance of OFDM signal by mitigating the effect of frequency offset
synchronization to give error-free data at the receiver, good angle of arrival accuracy and
improved SNR performance. The full system simulation to explore optimum values such
as channel estimation and AoA including the antenna array model and prove the
operational performance of the OFDM system as implemented in MATLAB.
The second technique proposes a low cost-effective method of tracking and monitoring
objects (examples: patient, device, medicine, document) by employing passive radio
frequency identification (RFID) systems. A multi-tag, (totalling fifty-six tags) with known
ID values are attached to the whole patient’s body to achieve better tracking and
monitoring precision and higher accuracy. Several tests with different positions and
movements are implemented on six patients. The aim is to be able to track the patient if
he/she is walking or sitting; therefore, the tests considered six possible movements for
the patient including walking, standing, sitting, resting, laying on the floor and laying on
the bed, these placements are important to monitor the status of the patient like if he
collapsed and fall on the ground so that the help will be quick. The collected data from
the RFID Reader in terms of Time Stamp, RSS, Tag ID, and a number of channels are
processed using the MATLAB code.
|
| 263 |
Incorporating Environmental Factors into Trip PlanningAl-Ogaili, Farah F. January 2017 (has links)
No description available.
|
| 264 |
The Frequency Monitor Network (FNET) Design and Situation Awareness Algorithm DevelopmentZuo, Jian 24 April 2008 (has links)
Wide Area Measurements (WAMs) have been widely used in the energy management system (EMS) of power system for monitoring, operation and control. In recent years, the advent of synchronized Phasor Measurements Unit (PMU) has added another dimension to the field of wide-area measurement. However, the high cost of the PMU, which includes the manufacture and deployment fee, is a hurdle to the wide use of the PMU in power systems. Unlike traditional PMUs, the frequency monitoring network (FNET) developed by the Virginia Tech Power IT lab is an Internet—based, GPS—synchronized, wide-area frequency monitoring network deployed at the distribution level, providing a low-cost and easily deployable WAMs solution. In this dissertation, the research work can be categorized into two parts: FNET Design and Situation Awareness Algorithm Development. / Ph. D.
|
| 265 |
Implementation of Geometrically Based Single-Bounce Models for Simulation of Angle-of-Arrival of Multipath Delay Components in the Wireless Channel Simulation Tools, SMRCIM and SIRCIMNuckols, John Eric 11 August 1999 (has links)
As the demand for wireless communication systems has exploded over the past few years, many researchers have taken on the challenge to model wireless channels more accurately. These models are very useful for enhancing the design of all aspects of wireless communications. Smart antennas and systems used in position location are among the most popular new studies that require signal information such as the amplitude, phase, and angle-of-arrival (AOA) of multipath delay spreads. For proper and efficient implementation of future systems, emerging wireless systems must be able to exploit processing of spatial information. The goal of the work presented in this thesis is to further improve two channel modeling tools, SMRCIM and SIRCIM, by implementing new geometrical models that provide users with angle-of-arrival information as well as amplitude and phase data for wideband wireless communication channels. The new angle-of-arrival models are explained and pseudo code is provided to demonstrate the software implementation of the models. Likewise, the channel models are explained and the usage and results of the simulation tools are described. The SMRCIM and SIRCIM tools are currently being used by researchers throughout the world.
<i>[Vita removed March 5, 2012. Gmc]</i> / Master of Science
|
| 266 |
Channel Probing for an Indoor Wireless Communications ChannelHunter, Brandon 13 March 2003 (has links) (PDF)
The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.
|
| 267 |
Introduktionsverksamhet för nyanlända elever i grundskolans tidiga årSundström Rask, Katarina January 2018 (has links)
Children who migrate to Sweden are usually introduced to the Swedish school through some kind of introduction programme in their new community. This study examines the experiences of newly arrived children participating in school introduction in the early school years, as well as the experiences of the teachers and principals working with the programme. In the community in which this study is situated, newly arrived children participate in a special school unit where the goal is to map their experiences and skills from former education, and where the teaching of Swedish as a second language is seen as an important part of the introduction. Forty-two interviews (40 individual and 2 pairs) were conducted with principals, teachers and newly arrived children (ages appropriate for Years 2, 3, 4 and 5 in elementary school). Employing a social constructivist perspective, together with inspiration from Critical Discourse Analysis, the study aimed at outlining the discourses the participants draw on when speaking about the school introduction and how these discourses affect the participants’ positioning of themselves and other participants in the school practice. Fairclough’s theory of discourse (1992, 2001) provides an understanding of how participants experience being part of the school introduction as well as their own and other participants’ positions in the school practice due to ambient discourses. The results indicate that four discourses dominate the practice and affect the participants’ view of each other and themselves as well as their possibilities to impact the practice and their own situation as being a part of it. The four discourses that were identified are described as 1) the Swedish language as a key to success in school, 2) the adjustment of behaviour as a key to success in school, 3) the substantial immigration as a challenge, and 4) heed.
|
| 268 |
Antibrouillage de récepteur GNSS embarqué sur hélicoptère / Antijamming of GNSS receiver mounted on helicopterBarbiero, Franck 16 December 2014 (has links)
En environnements hostiles, les signaux GNSS (Global Navigation Satellite System)peuvent être soumis à des risques de brouillages intentionnels. Basées sur un réseau d'antennes adaptatif, les solutions spatio-temporelles (STAP) ont déjà montré de bonnes performances de réjection des interférences. Toutefois, lorsque le module GNSS est placé sous les pales d'un hélicoptère, des effets non-stationnaires, appelés Rotor Blade Modulation (RBM), créés par les multiples réflexions du signal sur les pales du rotor, peuvent dégrader les techniques usuelles d’antibrouillage. Le signal utile GNSS n’est alors plus accessible. Le travail de la thèse consiste donc à élaborer un système de protection des signaux GNSS adapté à la RBM. Pour cela, un modèle innovant de multitrajets, adapté à ce type de phénomène, a été développé. La comparaison de simulations électromagnétiques représentatives et de mesures expérimentales sur hélicoptère EC-120 a permis de valider ce modèle. Celui-ci permet d'estimer, par maximum de vraisemblance, les paramètres de la contribution non-stationnaire du signal reçu. Enfin, l'association d'un algorithme de filtrage des multitrajets par projection oblique et d'un traitement STAP permet d'éliminer la contribution dynamique puis statique de l'interférence. Les simulations montrent que le signal utile GNSS est alors de nouveau exploitable. / In hostile environments, Global Navigation Satellite System (GNSS) can be disturbed by intentional jamming. Using antenna arrays, space-time adaptive algorithm (STAP) isone of the most efficient methods to deal with these threats. However, when a GNSS receiver is placed near rotating bodies, non-stationary effects called Rotor Blade Modulation (RBM) are created by the multipaths on the blades of the helicopter. They can degrade significantly the anti-jamming system and the signal of interest could belost. The work of the thesis is, consequently, to develop a GNSS protection system adapted to the RBM. In this way, an innovative multipath model, adapted to this phenomenon, has been developed. The model is then confirmed by comparison with a symptotic electromagnetic simulations and experiments conducted on an EC-120helicopter. Using a Maximum Likelihood algorithm, the parameters of the non-stationary part of the received signal have been estimated. And finally, the RBM anti-jamming solution, combining oblique projection algorithm and academic STAP, can mitigate dynamic and static contributions of interferences. In the end, the navigation information is available again.
|
| 269 |
Applications of Adaptive Antennas in Third-Generation Mobile Communications SystemsLau, Buon Kiong January 2002 (has links)
Adaptive antenna systems (AAS's) are traditionally of interest only in radar and sonar applications. However, since the onset of the explosive growth in demand for wireless communications during the 1990's, researchers are giving increasing attention to the use of AAS technology to overcome practical challenges in providing the service. The main benefit of the technology lies in its ability to exploit the spatial domain, on top of the temporal and frequency domains, to improve on transceiver performance. This thesis presents a unified study on two classes of preprocessing techniques for uniform circular arrays (UCA's). UCA's are of interest because of their natural ability to provide a full azimuth (i.e. 360') coverage found in typical scenarios for sensor array applications, such as radar, sonar and wireless communications. The two classes of preprocessing techniques studied are the Davies transformation and the interpolated array transformations. These techniques yield a mathematically more convenient form - the Vandermonde form - for the array steering vector via a linear transformation. The Vandermonde form is useful for different applications such as direction-of-arrival (DOA) estimation and optimum or minimum variance distortionless response (MVDR) beamforming in correlated signal environment and beampattem synthesis. A novel interpolated array transformation is proposed to overcome limitations in the existing interpolated array transformations. A disadvantage of the two classes of preprocessing techniques for UCA's with omnidirectional elements is the lack of robustness in the transformed array steering vector to array imperfections under certain conditions. In order to mitigate the robustness problem, optimisation problems are formulated to modify the transformation matrices. / Suitable optimisation techniques are then applied to obtain more robust transformations. The improved transformations are shown to improve robustness but at the cost of larger transformation errors. The benefits of the robustification procedure are most apparent in DOA estimation. In addition to the algorithm level studies, the thesis also investigates the use of AAS technology with respect to two different third generation (3G) mobile communications systems: Enhanced Data rates for Global Evolution (EDGE) and Wideband Code Division Multiple Access (WCDMA). EDGE, or more generally GSM/EDGE Radio Access Network (GERAN), is the evolution of the widely successful GSM system to provide 3G mobile services in the existing radio spectrum. It builds on the TDMA technology of GSM and relies on improved coding and higher order modulation schemes to provide packet-based services at high data rates. WCDMA, on the other hand, is based on CDMA technology and is specially designed and streamlined for 3G mobile services. For WCDMA, a single-user approach to DOA estimation which utilises the user spreading code and the pulse-shaped chip waveform is proposed. It is shown that the proposed approach produces promising performance improvements. The studies with EDGE are concerned with the evaluation of a simple AAS at the system and link levels. / Results from, the system and link level simulations are presented to demonstrate the effectiveness of AAS technology in the new mobile communications system. Finally, it is noted that the WCDMA and EDGE link level simulations employ the newly developed COST259 directional channel model, which is capable of producing accurate channel realisations of macrocell environments for the evaluation of AAS's.
|
| 270 |
Performance Analysis Of A Variation Of The Distributed Queueing Access ProtocolGautam, S Vijay 06 1900 (has links)
"A distributed queueing Medium Access Control (MAC) protocol is used in Distributed Queue Dual Bus (DQDB) networks. A modified version of the MAC protocol was proposed by R.R. Pillai and U. Mukherji in an attempt to overcome some of the shortcomings of the DQDB MAC protocol. They analyzed the performance of the system for Bernoulli arrivals and for large propagation delays between the nodes. We extend the performance analysis of the modified MAC protocol for a DQDB type of Network. The parameter of interest to us is the bus access delay. This has two components, viz., the request bus access delay and the data bu6 access delay. We use the model at the request point at node and present methods to evaluate the delay experienced in such a model. The model is an n-priority ./D/l queue with D vacations (non-preemptive priority) where n is the number of nodes sending requests on the request bus for transmission on the data bus. The methods presented help to evaluate the request bus access delay when the arrivals at each node are Markovian Arrival Processes (MAPs). The algorithms for evaluating the mean request bus access delay are based on matrix geometric techniques. Thus, one can use the algorithms developed in the literature to solve for the finite buffers case too. This model, for the request bus access delay, holds irrespective of the propagation delay between the nodes.
We also evaluate the inter-departure time of class 1 customers and virtual customers in a 2-priority M/G/l system with G vacations (non-preemptive priority). In the case of Poisson arrivals at all the nodes, we would have a 2-priority M/D/l system with D vacations (non-preemptive priority). We thus evaluate the inter-arrival time of the free slots on the data bus as seen by Node 2. Note that this is independent of the number of active nodes in the network
We then develop methods to evaluate the mean data bus access delay experienced by the customers at Node 2 in a three-node network with 2 nodes communicating with the third when the propagation delay between the nodes is large. We consider the case of finite Local Queue buffers at the two nodes. Using this assumption we arrive at process of arrivals to the Combined Queue and the process of free slots on the data bus to be Markov Modulated Bernoulli processes. The model at the combined queue at Node 2 then has a Quasi Birth-Death evolution. Thus, this system is solved by using the Ramaswami-Latouche algorithm. The stationary probabilities are then used to evaluate the mean data bus access delay experienced at Node 2. The finite buffer case of this system can be solved by G.Wi Stewart's algorithm. The method in modelling the system and the results are presented in detail for Poisson arrivals. The extension of this to more complex processes is also explained. We encounter in the analysis an explosion of the state-space of the system. We try to counter this by considering approximations to the process of free slots on the data bus. The approximations considered are on the basis of what are known as Idealized Aggregates. The performance of the approximation is also detailed. It works very well under low and moderate load but underestimates the mean delay under heavy load.
Thereafter, we discuss the performance of the system with reference to the mean of the access delay and the standard deviation of the access delay under varying traffic at the two nodes. For this part we use simulation results to discuss the performance. The comparison between the performance measures at both the nodes is also done.
Then we develop methods/techniques to understand the performance of the system when we have finite propagation delays between the nodes. We concentrate on the 3-node problem and calculate performance bounds based on linear programs. This is illustrated in detail for Bernoulli arrivals for the case of 1 slot propagation delay between the nodes as well as for the case of 2 slots propagation delay. The performance of the bounds obtained is also detailed. The presence of an idling system at the combined queue of Node 2 makes the bounds somewhat loose. Finally, we discuss the performance of the system with reference to the mean access delay and the standard deviation of the access delay under varying load on the system. Again, we rely on simulation studies.
Finally, we study the performance of the system as a multiplexer. For this, we restrict the traffic to Markov Modulated Processes (or those which would satisfy the Gartner-Ellis Theorem requirements). The traffic is characterized by what are known as Envelope Processes - Lower and Upper. The class of processes which satisfy the conditions of the
Gartner-Ellis theorem come under the category where both the Envelope Processes exist and the Minimum Envelope Rate and the Maximum Lower Envelope Rate are the same. We use the system evolution equations at the combined queue at any node to develop relations between the various input and output processes. First, this is done for a. system of this kind, in isolation. Then, we consider this system as a part of the modified protocol and present relations, among the various input and output processes, which are specific to the modified protocol. The possible use of all of the above to do Admission Control at the entry point to the Asynchronous Transfer Mode (ATM) network is also presented.
|
Page generated in 0.0335 seconds