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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.
121

Detector design and estimation for a digital communication system

Kontoyannis, Nickos Sotirios 01 November 2008 (has links)
This thesis investigates the behavior of two digital communication systems based on Moving-Average Matched Filters (MAMF). In general, matched filters are instrumental in detecting signals corrupted by noise as they are designed to maximize the probability of detection of the transmitted signals. The MAMF represents a subset of the class of matched filters. The two communication systems under investigation are the classical MAMF system and one of its modifications, the proposed MAMF system. In the traditional system the N-dimensional signal vector, which encodes the bit to be communicated, remains fixed throughout the whole communication process ( transmission and reception). In the proposed system the encoding N-dimensional signal vector is composed of K linearly independent basis vectors spanning a signal vector subspace of dimension M (= N /K). By combining these basis vectors in the receiver, any vector in the signal vector subspace can be formed in order to maximize the Output Signal-to-Noise Ratio (OSNR). The relative measure of comparison for the two systems is the Signal-to-Noise Ratio Improvement (SNRI). The SNRI is the ratio of the OSNR, which is measured at the output of the receiver, to the Input Signal-to-Noise Ratio (ISNR), which is measured at the input of the receiver. Since the ISNR is fixed for a particular transmitted signal vector and noise characteristics, an attempt is made to maximize the SNRI by maximizing the OSNR. / Master of Science
122

Linearity and monotonicity of a 10-bit, 125 MHz, segmented current steering digital to analog converter

Bittle, Charles C. 05 1900 (has links)
The purpose of this research is to determine the linearity and monotonicity of the THS5651IDW digital to analog converter (DAC), a prototype of the future Texas Instruments TLV5651, 10-bit, 125 MHz communication DAC. Testing was conducted at the Texas Instruments facility on Forest Lane, Dallas, Texas. Texas Instruments provided test equipment, software and laboratory space to obtain test data. Analysis of the data found the DAC to be monotonic since the magnitude of the differential nonlinearity (DNL) was less than ± 1 least significant bit (LSB) and the integral nonlinearity (INL) was less than ± 0.5 LSB. The study also showed that the DAC has primarily negative DNL although the DNL is well within the desired specification.
123

Lessons Learned Constructing the NG-Mesh Wireless Test-Bed

Ng, WK Stanley 10 1900 (has links)
<p>This thesis presents the lessons learned from building an IEEE 802.11 wireless mesh network (WMN) test-bed. Each network node consists of a Linux processor with multiple IEEE 802.11b/g transceivers operating in the 2.4 GHz band. Each transceiver consists of a medium access control (MAC) and base-band processor (BBP) in addition to a radio. A device driver was modified to control some of the key transceiver functions. The test-bed's Wi-Fi interfaces can be programmed to implement any mesh communication topology. All Wi-Fi interfaces use omni-directional antennas and the IEEE 802.11b operation mode.</p> <p>The test-bed design is easily extendable to incorporate newer Wi-Fi technologies. Measurements of co-channel interference in each Wi-Fi channel including received signal strength (RSS) and signal-to-interference-and-noise ratio (SINR) are presented. The AutoMin algorithm was developed in order to use the captured physical layer (PHY) metrics to avoid Wi-Fi congestion during test-bed operation. A comparison of a software-based spectrum analyzer to a commercial one is described. Key Wi-Fi functions in the Ralink driver source code are explored in depth. The compliance of the Ralink chip-set to the IEEE 802.11b spectral mask was verified. The maximum driver-induced retuning rate for the popular Ralink radio was found experimentally. This data can be used to optimize the performance of IEEE 802.11 WMNs.</p> / Master of Applied Science (MASc)
124

Power Conservation in Energy Harvesting Sensor Networks

Roberts, Timothy A. 10 1900 (has links)
<p>We examine energy harvesting sensor networks, more specifically, a sensor network using the Geographic Routing with Environmental Energy Supply (GREES) algorithm. We start with a discussion of other sources of energy conservation both in energy harvesting and non-energy harvesting sensor networks. Ideas presented in these works are combined where possible with the GREES algorithm. A sensor network was actually built to test and (if possible) improve the algorithm. There were problems along the way, but they were overcome to produce a functioning energy harvesting sensor network that used solar cells as the energy harvesting unit. Tests were run on the network by giving a consistent light and battery supply, and then changing parameters of the algorithm to see their effect on the lifetime of the network, indicating the network's sensitivity to individual parameters. These results are presented, along with their interpretation, as well as an error analysis detailing the behaviour of the algorithm. We discuss how sensitive the network is to each parameter, indicating which parameters are more important to calibrate or measure correctly.</p> / Master of Applied Science (MASc)
125

Repeated Selfish Routing with Incomplete Information

Yu, He 04 1900 (has links)
<p>Selfish routing is frequently discussed. The general framework of a system of non-cooperative users can be used to model many different optimization problems such as network routing, traffic or transportation problems.</p> <p>It is well known that the Wardrop user equilibria (i.e. the user optima) generally do not optimize the overall system cost in a traffic routing problem.</p> <p>In order to induce the equilibrium flow to be as close to the optimal flow as possible, the term “toll” is introduced. With the addition of tolls, a traffic system does not show the actual cost to the users but the displayed cost of users, which is the summation of the actual cost and the toll. A common behavioral assumption in traffic network modeling is that every user chooses a path which is perceived as the shortest path, then the whole system achieves the equilibrium of the displayed cost. It is proved that there exists an optimal toll which can induce the equilibrium flow under displayed cost to be the optimal flow in reality.</p> <p>However, this conclusion holds only if the selfish routing executes only once. If the game is played repeatedly, the users will detect the difference between the actual and displayed costs. Then, they will not completely trust the information given by the system and calculate the cost. The purpose of this thesis is to find out the optimal strategy given by the system–how to set tolls in order to maintain the flow as close to the optimal flow as possible.</p> / Master of Science (MSc)
126

Analytical evaluation of wireless digital communication performance over fading channels

盧志明, Lo, Chi-ming. January 2001 (has links)
published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy
127

Low power adaptive equaliser architectures for wireless LMMSE receivers

Tennant, Mark P. January 2007 (has links)
Power consumption requires critical consideration during system design for portable wireless communication devices as it has a direct influence on the battery weight and volume required for operation. Wideband Code Division Multiple Access (W-CDMA) techniques are favoured for use in future generation mobile communication systems. This thesis investigates novel low power techniques for use in system blocks within a W-CDMA adaptive linear minimum mean squared error (LMMSE) receiver architecture. Two low power techniques are presented for reducing power dissipation in the LMS adaptive filter, this being the main power consuming block within this receiver. These low power techniques are namely the decorrelating transform, this is a differential coefficient technique, and the variable length update algorithm which is a dynamic tap-length optimisation technique. The decorrelating transform is based on the principle of reducing the wordlength of filter coefficients by using the computed difference between adjacent coefficients in calculation of the filter output. The effect of reducing the wordlength of filter coefficients being presented to multipliers in the filter is a reduction in switching activity within the multiplier thus reducing power consumed. In the case of the LMS adaptive filter, with coefficients being continuously updated, the decorrelating transform is applied to these calculated coefficients with minimal hardware or computational overhead. The correlation between filter coefficients is exploited to achieve a wordlength reduction from 16 bits down to 10 bits in the FIR filter block. The variable length update algorithm is based on the principle of optimising the number of operational filter taps in the LMS adaptive filter according to operating conditions. The number of taps in operation can be increased or decreased dynamically according to the mean squared error at the output of the filter. This algorithm is used to exploit the fact that when the SNR in the channel is low the minimum mean squared error of the short equaliser is almost the same as that of the longer equaliser. Therefore, minimising the length of the equaliser will not result in poorer MSE performance and there is no disadvantage in having fewer taps in operation. If fewer taps are in operation then switching will not only be reduced in the arithmetic blocks but also in the memory blocks required by the LMS algorithm and FIR filter process. This reduces the power consumed by both these computation intensive functional blocks. Power results are obtained for equaliser lengths from 73 to 16 taps and for operation with varying input SNR. This thesis then proposes that the variable length LMS adaptive filter is applied in the adaptive LMMSE receiver to create a low power implementation. Power consumption in the receiver is reduced by the dynamic optimisation of the LMS receiver coefficient calculation. A considerable power saving is seen to be achieved when moving from a fixed length LMS implementation to the variable length design. All design architectures are coded in Verilog hardware description language at register transfer level (RTL). Once functional specification of the design is verified, synthesis is carried out using either Synopsys DesignCompiler or Cadence BuildGates to create a gate level netlist. Power consumption results are determined at the gate level and estimated using the Synopsys DesignPower tool.
128

User driven design of real time passenger information solutions for supporting rural passengers in the context of disruption

Papangelis, Konstantinos January 2015 (has links)
Rural communities face a range of challenges associated with accessibility and connectivity. Though real-time passenger information systems (RTPIS) have been long heralded as offering the potential to mitigate some of these challenges their deployment in rural areas has been very limited. The lack of real-time passenger information has been identified as a contributing factor to a multitude of issues, such as high car usage, low public transport use and travel uncertainty. There is considerable potential for appropriate technologies to contribute to the alleviation of these issues, as evidence exists that they can influence travel behaviour, and cultivate positive attitudes towards the service and the operator. This thesis investigated the interplay between rural passenger experience and real-time information provision. Overall, this work aims to provide an initial stepping point on to understanding the interplay between passenger behaviour, disruptions, passenger experience, and real-time information. In order to explore the aforementioned, first, a series of interviews and focus groups with rural public transport passengers, rural transport operators, government agencies and members of academia have been carried out to study the rural passengers' responses to planned and unplanned travel disruption. Based on these i) a conceptual model that aims to describe the passenger recovery phases to disruption and the associated passenger information requirements, ii) and a framework that highlights characteristics of transport behaviour, and aligns them with drivers of transport behaviour adaptation have been created. Next, through a series of co-designed sessions in various rural areas throughout the UK a mobile technology probe, which provides public transport real time information to the passengers has been developed. Then using the technology probe a two-week before-and-after intervention study with 15 participants has been carried out. The results indicate that real-time information provided through the technology probe adjusted the travel behaviour of the participants. Namely, it improved the utilisation of waiting time of the participants, improved the efficiency of their travelling, and enabled them to find alternatives when needed. Further, to get a better picture of the effect of real-time information on rural travellers, during the intervention study 6 of the participants in their everyday travels for 7 days have been actively observed by the author. The outcomes from this supplemented the data from the study and illustrated how the rural public transport travellers used the system in their day-to-day travels. Finally, all our findings have been combined to co-create a system design with rural public transport passengers that aims to improve their experience during disruption. The final design mainly concentrated on providing information regarding pre-trip, on-trip and on boarding point, journey planning, supporting the rural passenger experience through social media, and disruption. In order to evaluate the applicability and suitability of the design, and explore how it relates to the needs of the rural passengers, two focus groups have been conducted. The results of the evaluation activity illustrate that the mobile RTPI system design was perceived as highly useful and relevant to the needs of the rural passenger.
129

Performance analysis of M-QAM with Viterbi soft-decision decoding

Manso, Rogerio C. 03 1900
Approved for public release; distribution is unlimited / This thesis derives design tools for determining and improving performances of communication links that use M - QAM coherent demodulators associated with Viterbi soft-decision decoding (SDD) in Additive White Gaussian Noise (AWGN) and Nakagami-m channels. Performance analyses for 16-QAM, 64-QAM, QPSK and BPSK associated with up to three convolutional codes, including the one used by the IEEE 802.11a standard and the dual-k code, are presented as practical applications. The main tools relate to the analytical derivation of upper bounds of the probability of bit error (Pb) for any M -ary coherent demodulator followed by SDD, a methodology for improving an upper bound of Pb tightening it to realistic data, and the obtaining of the specific ( ) d b spectrum for any convolutional code intended to operate with a certain M-symbol modulation. All derivations involve statistical considerations over the AWGN and Nakagami-m channels, as well as in-depth analyses of modulator constellations. The tools and models developed can provide great optimization to bandwidth-limited system designs that require high data rates, especially the wireless ones. Consequently, they have great application to many fields of digital communications, such as cellular telephony, wireless networking, satellite links, ship-to-shore and ship -to-ship communications. / http://hdl.handle.net/10945/1090 / Lieutenant Commander, Brazilian Navy
130

Combating channels with long impulse response using combined turbo equalization and turbo decoding.

January 2000 (has links)
by Chan Yiu Tong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 56-[59]). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Communications and Coding Technology --- p.2 / Chapter 1.2 --- The Emerge of Turbo Codes --- p.3 / Chapter 1.3 --- The Extension of Turbo Principle --- p.3 / Chapter 1.4 --- Receiver Structures for Practical Situations --- p.4 / Chapter 1.5 --- Thesis Overview --- p.5 / Chapter 2 --- ISI Channel Model and Channel Equalization --- p.6 / Chapter 2.1 --- A Discrete Time ISI Channel Model --- p.6 / Chapter 2.1.1 --- Optimum Maximum Likelihood Receiver --- p.8 / Chapter 2.1.2 --- The Whitened Matched Filter --- p.11 / Chapter 2.2 --- Equalization Techniques for Combating ISI --- p.13 / Chapter 2.2.1 --- Linear MMSE Equalizer --- p.13 / Chapter 2.2.2 --- MLSE Equalizer in Viterbi Algorithm --- p.15 / Chapter 3 --- An Overview of Turbo Codes --- p.18 / Chapter 3.1 --- The Turbo Encoder --- p.19 / Chapter 3.2 --- The Turbo Interleaver --- p.21 / Chapter 3.3 --- The Iterative Decoder --- p.22 / Chapter 3.3.1 --- The MAP Algorithm --- p.23 / Chapter 3.3.2 --- The Max-Log MAP Algorithm --- p.25 / Chapter 3.3.3 --- The Log-MAP Algorithm --- p.28 / Chapter 4 --- Receivers for Channels with Long Impulse Responses --- p.29 / Chapter 4.1 --- Shortcomings for the Existing Models --- p.30 / Chapter 4.2 --- Proposed System Architecture --- p.30 / Chapter 4.2.1 --- Optimized Model for Channel Shortening Filter --- p.31 / Chapter 4.2.2 --- Method One - Separate Trellises for EQ and DEC --- p.35 / Chapter 4.2.3 --- Method Two - Combined Trellises for EQ and DEC --- p.37 / Chapter 5 --- Performance Analysis --- p.40 / Chapter 5.1 --- Simulation Model and Settings --- p.40 / Chapter 5.2 --- Performance Expectations --- p.43 / Chapter 5.3 --- Simulation Results and Discussions --- p.49 / Chapter 6 --- Concluding Remarks --- p.55 / Bibliography --- p.56

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