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  • 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.
1

Contextual testing of interactive prototypes at the early stages of the design process

Woolley, Alex January 2008 (has links)
Information appliances combine bespoke hardware with custom interfaces. This presents a challenge when prototyping early in the design process, as it can be difficult to combine both the digital and physical elements of the product to create a viable prototype for user testing. Although a number of prototyping kits have been developed that attempt to address this issue, these have previously only be trialled using “laboratory” based approaches. This thesis demonstrates that although laboratory testing can be beneficial, the use of a contextual testing approach provides better information for the early stages of design. The research comprises an extensive user study comparing data gathered using laboratory and in-context testing approaches, supported by a case study of a usability team working within a multinational mobile phone manufacturer. The case study provides grounding for the research, and was used both to set the user study findings in-context and also to inform the user study method design. The thesis concludes by proposing a workflow for contextual testing in the design process, and identifies areas of future development for prototyping toolkits to better support contextual testing. The contribution of this work to knowledge is a clear demonstration that contextual testing can be conducted early in the information appliance design process; and that this approach delivers better design information, particularly in regard to the physical elements of the design.
2

Performance metrics and routing in vehicular ad hoc networks

Yusof, Zulkefli Muhammed January 2011 (has links)
The aim of this thesis is to propose a method for enhancing the performance of Vehicular Ad hoc Networks (VANETs). The focus is on a routing protocol where performance metrics are used to inform the routing decisions made. The thesis begins by analysing routing protocols in a random mobility scenario with a wide range of node densities. A Cellular Automata algorithm is subsequently applied in order to create a mobility model of a highway, and wide range of density and transmission range are tested. Performance metrics are introduced to assist the prediction of likely route failure. The Good Link Availability (GLA) and Good Route Availability (GRA) metrics are proposed which can be used for a pre-emptive action that has the potential to give better performance. The implementation framework for this method using the AODV routing protocol is also discussed. The main outcomes of this research can be summarised as identifying and formulating methods for pre-emptive actions using a Cellular Automata with NS-2 to simulate VANETs, and the implementation method within the AODV routing protocol.
3

A cluster based incentive mechanism for P2P systems

Zhang, Kan January 2011 (has links)
Peer-to-Peer (P2P) networking is distributed computing paradigm, in which the nodes are self-organized and can directly exploit resources from each other without dedicated servers. Free riders in. the Peer-to-Peer systems are the nodes that only consume services but provide little or nothing in return. They seriously degrade the fault-tolerance, scalability and content availability of the Peer-to-Peer systems. The solution to this problem in Peer-to-Peer systems is to have incentive mechanisms that aim to improve the network utility by influencing the nodes to become more cooperative. This thesisp roposess evend esignr equirementsf or an incentivem echanisma ccording to the characteristics of Peer-to-Peer systems, latest distributed computing development trends and the related implementation techniques. This thesis also provides a classification of the existing incentive mechanisms for Peer-to-Peer systems. For each category, the thesis, outlines their principle, provides typical examples, applications and discusses their limitations. Bartering exchange ring based incentive mechanism was found to have the potential of fulfilling all the proposed design requirements. It organizes the nodes with asymmetric interests in the bartering exchange rings, enforcing the nodes to contribute while consuming. However the existing bartering exchanger ing formation approacheso nly rely on historical search records which may lead to a risk of using out of date information. Moreover, these incentive mechanismsla ck of accountability so that the self-interestedr ational nodes can still obtain complete resources and only contribute before finishing the consumption. A novel cluster based incentive mechanism (CBIM) is proposed in this thesis which enables dynamic ring formation by modifying the Query Protocol of the underlyingP2P systems. The query messages become the media that the nodes can use to publish supply and demand information on. The nodes can then cooperate to form a cluster through the query messages while searching. A cluster can be formed when every node publishes same number of requests and provisions in a query message and all the requests can be satisfied. Graph theoretically, a cluster consists of one or more bartering exchange rings. The CBIM also uses a reputation system to alleviate the effect of malicious behaviours. The nodes try to identify free riders by fully utilizing their local transaction information. The identified free riding nodes are blacklisted and thus isolated. The simulation results indicate that by applying the CBIM, the overall request success rate of the network can be considerably improved since the rational nodes are forced to become more cooperative and the free riding behaviours can be identified to a certain extent
4

Efficient video traffic distribution over WiMAX systems

Tsitserov, Dmitry Vladimirovich January 2012 (has links)
This thesis is dedicated to the development and practical verification of a new video traffic distribution technique for implementation in WiMAX systems. The proposed technique is applicable to M-health and video surveillance application areas and allows for better system resource optimization under the selected case study scenarios. The presented technique incorporates scalable video transmission of MPEG-originated elementary streams, a cross-layer delivery framework and the WiMAX MAC layer enhancement. Video segmentation is achieved through a separate transmission of elementary streams associated with the primitive objects contained in the original MPEG video scene. The introduced MAC entity, such as the Extended Classifier provides selective distribution of arriving packets between WiMAX QoS service connections. The choice of service classes and their quantity, con-elation between segmented video streams, general data streams and selected service connections is the main research focus of this work. The next part of this thesis deals with video broadcasting in WiMAX networks. The problem of variable reception conditions and video instability for broadcasting users is investigated here. A new broadcasting service, termed Enhanced Standard Definition video broadcasting, is proposed for better bandwidth optimization of WiMAX networks. The video distribution technique and the WiMAX delivery framework designated in support of a new broadcasting service are backward compatible with a WiMAX network reference model. NS-2 based computer simulations with the proposed innovations show the efficiency of these contributions that are analyzed by comparing the conventional and the introduced broadcasting algorithms.
5

A router for massively-parallel neural simulation

Wu, Jian January 2010 (has links)
i. The author of this thesis (including any appendices and/or schedules to this thesis) owns any copyright in it (the "Copyright") and s/he has given The University of Manchester the right to use such Copyright for any administrative, promotional, educational and/or teaching purposes. ii. Copies of this thesis, either in full or in extracts, may be made only in accordance with the regulations of the John Rylands University Library of Manchester. Details of these regulations may be obtained from the Librarian. This page must form part of any such copies made. iii. The ownership of any patents, designs, trade marks and any and all other intellectual property rights except for the Copyright (the "Intellectual Property Rights") and any reproductions of copyright works, for example graphs and tables ("Reproductions"), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property Rights and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property Rights and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and exploitation of this thesis, the Copyright and any Intellectual Property Rights and/or Reproductions described in it may take place is available from the Head of School of School of Computer Science (or the Vice-President).
6

Investigation of two problems of airborne radar antennas

Niyomjan, Greepol January 2008 (has links)
One of the airborne radar antenna problems is the integration of microwave circuits with waveguide components. As part of this research, an optimum transition from a waveguide to a microstrip using the short transformer technique is proposed. A layer of dielectric substrate is employed as a matching structure between the waveguide and microstrip line structure, which is optimised using the direct search method. It is shown that the transition has an average return loss value of -19.2 dB throughout the X band (8 - 12.5 GHz) with the best predicted return loss value of - 64 dB. Another issue of airborne radar antennas investigated is the high impedance surface (HIS) structure which could be employed to suppress surface effect usually encountered in conventional low profile antennas so that their efficiency such as radiation pattern and gain can be greatly improved. A 3x3 cells simulation model is proposed to investigate performance of high impedance surface (HIS) structure. This simulation model is used to determine resonant frequencies of the test HIS structure. The obtained actual and additional resonant frequencies are 5 GHz and 3.65 GHz respectively. The additional resonant frequency can be used to determine the start of the band gap frequency. Empirical equations for the additional resonant frequency have been successfully derived based on the behaviour ofthe current distribution along the surface ofthe HIS structure. A suspended microstrip fed slot antenna (MSA) on HIS structure is suggested to overcome bidirectional radiation behaviour exhibited in MSA and at the same time improving the gain, radiation pattern and return loss performance. This proposed antenna offers low side lobe, a maximum gain of 10 dB in the desired direction and a maximum gain ofless than -3 dB in the undesired direction. Radiations in both the E and H planes are symmetrical. The accuracy of the effective medium method is enhanced by applying proper boundary conditions. These rules and limits are derived based on the parametric study. A test structure is designed and created to validate the method. A close agreement b~tween the values of reflection phase angle (-90 to 90 degree) and surface impedance from 4.5 to 8 GHz is obtained by using this proposed improved method and numerical simulation. S21 graph and dispersion diagram are plotted to further confirm validity ofthe proposed method. A new improved enhanced effective medium is proposed to evaluate performance ofthe HIS structure with different patch shapes. This method is a combination of the enhanced effective medium method and the Guass' law. To validate the proposed method, the surface impedance values of the circular and octagonal patch HIS structures obtained from both HFSS simulation tool and the presented theory are compared. Close agreement between the results is observed. An industry standard full wave simulation tool (HFSS) is used to optimise the band gap bandwidth of the mushroom-like HIS structure under limited space condition. The optimisation approach is based on the variation of the patch width. It is shown that a fractional bandwidth of 110% can be achieved using our optimum patch width.
7

The effect of jewellery and the human hand on SAR and antenna performance

Samsuri, Noor Asmawati January 2009 (has links)
This thesis investigates the effect of the human hand and metallic jewellery items worn on the human head and hand on SAR and on the antenna radiation patterns at 900 and 1900 MHz. The field excitation is provided by means of a A./4 monopole antenna on top of a metal box to emulate a simple handset. A planar inverted 'F' antenna (PIFA) is also used for comparison with the monopole. This thesis presents a detailed parametric study utilizing computer simulations via the Transmission Line Matrix (TLM) method and measurements from the DASY 4 SAR measurement system. Two different head and hand geometries are considered. Firstly a homogenous spherical head and block-hand were used in the simpler simulation, while the more realistic head and hand models were employed for the detailed study. The hand models include fingers which allow the metallic jewellery rings to be examined. The human hand has a significant effect on Specific Absorption Rate (SAR) and on the antenna pattern due to energy absorption and possible reflection at the hand dielectric boundary. In addition, the effects of different sizes, orientation, and distance of the metallic loop-like jewellery items relative to the antenna have been investigated. The metallic rings worn on the hand tend to reduce the SAR and could also alter the antenna radiation performance. The wrist worn bangle has very little effect on the results at the frequencies tested due to its position that is relatively far away from the handset antenna. The earrings could significantly influence the SAR and the radiation patterns, but the effects varied depending on the earring's diameter, its position relative to the head, the frequency and the type of antenna in use. The effect of the combination of the hand, the earring and the finger ring only show minor difference on the SAR values and on the antenna radiation patterns. Measurements of the effects of the hand and metallic jewellery items on SAR were performed inside a Standard anthropomorphic model (SAM) head phantom. A novel liquid hand phantom with realistic fingers has been manufactured, which allow the effect of metallic ring to be further investigated. Measurement results support the simulation results.
8

Synthetic aperture sonar

Gida, Avtar S. January 1988 (has links)
Synthetic aperture techniques have been applied very successfully for many years in astronomy and radar to obtain high resolution images, an outstanding example in recent years being the use in remote sensing satellite systems. In underwater acoustics, because of the inherent problems caused by random fluctuations in the signal path, the slow velocity of the acoustic wave and the unknown movements of the transducer as it traverses the aperture, the application of the synthetic aperture technique has mainly been limited to the very useful but rather inferior non-coherent technique known as side-scan sonar. However the rapid advances that are being made in micro-chip technology and fast digital signal processing, and the development in image processing algorithms has created renewed interest in the possible application of the synthetic aperture technique to underwater acoustics. This thesis describes such a study.
9

Adaptive detection of digital suppressed-carrier A.M. signals

Harvey, John D. January 1978 (has links)
The thesis describes various detection processes which are suitable for use in a synchronous serial data-transmission system operating at a transmission rate of up to 20,000 bits per second over a slowly time-varying channel, The methods of operation of different detection processes are first described, with reference to binary and quaternary baseband signals, which includes the case when V,S,B,signals are transmitted over ·telephone circuits or H,F,radio links. The results of computer simulation tests are presented, comparing the tolerances of the detection processes to additive white Gaussian noise with the tolerances of conventional linear and non-linear equalisers. Several different time invariant channels are used in the tests. It is shown that two relatively simple detection processes can achieve a considerable improvement in tolerance to noise over both linear and non-linear equalisers of optimum design, Several of the most promising detection processes and a few new detection processes are then modified to use 4-point, 16-point and 32-point Q,A,M,signals. The methods of operation of the different detection processes are then described for the signal format being considered. The results of computer simulation tests are presented comparing their tolerances to additive white Gaussian noise with those · of the linear and non-linear equalisers of optimum design. It is shown that these detection processes operate most efficiently, in terms of tolerance to noise and in the number of sequential operations, if the transmitted signal contains the smallest number of possible signal levels. Finally, several simple methods of estimating the sampled impulse response of the channel are presented. One of these channel estimation techniques gives a very low error in the estimated response, while giving a good rate of adaptation to a time-varying channel.
10

On instantaneously adaptive delta modulation and encoding of video signals

Sakane, Fernando T. January 1977 (has links)
Conventional pulse-code and differential pulse-code modulators for encoding video signals are difficult to realise economically. To alleviate this problem, a technique which divides the modulators into two stages is proposed. The first stage is a two-bit instantaneously adaptive delta modulator operating at a high clock rate and using low-precision components. Two-bit signals conveying polarity and magnitude information are produced by this delta modulator and used as the input to the second stage, a code converter. The code converter transforms, digitally, delta modulated signals into Pulse Code Modulation (PCM) or Differential Pulse Code Modulation (DPCM) signals. The resolution of the final PCM or DPCM encoder depends on the performance of the delta modulator used as the input stage. For that reason, the performance of the two-bit Instantaneously Adaptive Delta Modulation (2BIADM) encoder is evaluated. This evaluation is made in two steps. First, a semi-empirical anaysis of the High Information Delta Modulation (HIDM) is made, because the 2BIADM system is derived from the HIDM. Then the performance of the 2BIADM is derived considering the HIDM as a reference. For the HIDM and 2BIADM modulators operating at the same sampling frequency, the 2BIADM presents an improvement in peak signal-to-noise ratio (SNR) Of 6 to 8 dB. Expressions are established to enable SNR to be calculated for the HIDM as a function of the encoding parameters. The expressions also apply to Constant Factor Delta Modulation, and represent the only known method of estimating numerically the SNR for instantaneously adaptive delta modulators. The 2BIADM was tested, built and operated at a low sampling rate. This gave an insight into the operation of the proposed system, and complemented the computer simuLation analyses. The principles for the code conversion from the 2BIADM to PCM or DPCM are fully discussed. The 2BIADM does not impose restrictions on the values that the coefficients of the digital low-pass filter required in the code converter can assume. For low bandwidth expansion rates, it was verified that a 2BIADM-to-PCM conversion filter with 5 stages performs better than a HIDM-to-PCM conversion with a filter having 256 stages (both encoders operating at the same word-rate). A generalization of the 2-bit encoder to a N-bit adaptive DPCM system is outlined.

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