Visual sensor networks (VSNs) merge computer vision, image processing and wireless sensor network disciplines to solve problems in multi-camera applications in large surveillance areas. Although potentially powerful, VSNs also present unique challenges that could hinder their practical deployment because of the unique camera features including the extremely higher data rate, the directional sensing characteristics, and the existence of visual occlusions. In this dissertation, we first present a collaborative approach for target localization in VSNs. Traditionally; the problem is solved by localizing targets at the intersections of the back-projected 2D cones of each target. However, the existence of visual occlusions among targets would generate many false alarms. Instead of resolving the uncertainty about target existence at the intersections, we identify and study the non-occupied areas in 2D cones and generate the so-called certainty map of targets non-existence. We also propose distributed integration of local certainty maps by following a dynamic itinerary where the entire map is progressively clarified. The accuracy of target localization is affected by the existence of faulty nodes in VSNs. Therefore, we present the design of a fault-tolerant localization algorithm that would not only accurately localize targets but also detect the faults in camera orientations, tolerate these errors and further correct them before they cascade. Based on the locations of detected targets in the fault-tolerated final certainty map, we construct a generative image model that estimates the camera orientations, detect inaccuracies and correct them. In order to ensure the required visual coverage to accurately localize targets or tolerate the faulty nodes, we need to calculate the coverage before deploying sensors. Therefore, we derive the closed-form solution for the coverage estimation based on the "certainty-based detection" model that takes directional sensing of cameras and existence of visual occlusions into account. The effectiveness of the proposed collaborative and fault-tolerant target localization algorithms in localization accuracy as well as fault detection and correction performance has been validated through the results obtained from both simulation and real experiments. In addition, conducted simulation shows extreme consistency with results from theoretical closed-form solution for visual coverage estimation, especially when considering the boundary effect.

This dissertation studies the design of an efficient adaptive digital baseband predistorter for modern cellular handsets that combines low power consumption, low implementation complexity, and high performance. The proposed enhancements are optimized for hardware implementation. We first present a thorough study of the optimal spacing of linearly-interpolated lookup table predistorters supported by theoretical calculations and extensive simulations. A constant-SNR compander that increases the predistorter's supported input dynamic range is derived. A corresponding low-complexity approximation that lends itself to efficient hardware design is also implemented in VHDL and synthesized with the Synopsys Design Compiler. This dissertation also proposes an LMS-based predistorter adaptation that is optimized for hardware implementation and compares the effectiveness of the direct and indirect learning architectures. A novel predistorter design with quadrature imbalance correction capability is developed and a corresponding adaptation scheme is proposed. This robust predistorter configuration is designed by combining linearization and I/Q imbalance correction into a single function with the same computational complexity as the widespread complex-gain predistorter.

Emerging "bandwidth hungry" applications such as high definition video distribution and ultra fast multimedia side-loading have extended the need for multi-gigabit wireless solutions beyond the reach of conventional WLAN technology or even more recently emerging UWB and MIMO systems. The availability of 7GHz of unlicensed bandwidth in the 60GHz spectrum, represents a unique opportunity to address such data-throughput requirements. The 60GHz Integrated CMOS digital radio chipset comprises of PHY and MAC layers, RF transceiver, High-Speed Digital Interface and an underlying Serial Communication Fabric. To have a complete communication solution compliant with the latest ECMA-369, ISO/DIS 13156 and IEEE 802.15.3c standards, we build a million gate digital implementation of MAC and PHY. The Serial Peripheral Interface (SPI) serves as the bridge between the higher layers in the communication stack (PAL-MAC) and the lower layers like PHY-RF Front End. The MAC module can setup the communication link on the fly by tuning parameters such as operating channel, channel bonding and bandwidth, data rates, error correction mechanisms, handshaking mechanisms, etc, by using the SPI to communicate with internal components. The SPI interface plays a crucial rule in not only this, but also during the testing and debug phase. Operation of each of the RF modules is monitored through the serial interface using local SPI slaves which are hooked up to the 4-wire serial bus running all through the chip. The SPI host controller emulates an embedded protocol analyzer. For calibration and fine tuning purposes, digital settings can also be loaded onto these modules through the SPI interface. R-2R DACs are used to convert these commands into analog voltages which then provide a tunable bias to the RF and mixed-signal modules. Other key functions of this serial communication and control interface are: Initialization of all of the RF and mixed signal modules, DC calibration of data converter, PLL and other mixed-signal modules, data acquisition, parametric tuning for digital modules such as linear equalizer, Gain Control loops (AGC, VGA), etc. Ultra high speed digital Input-Output buffers are used to provide an external data interface to the radio chipset. These high speed I/Os are also used in the gbps (gigabit-per-second) link for data transfer between the RF transceiver chip and the PHY-MAC baseband chip. The IOs are expected to comply with different signaling standards such as LVDS, SLVS200, SLVS400, etc. A robust system involves a meticulous pad ring design with proper power domains and power cuts. Full-chip integration of the digital PHY, MAC, peripheral logic and IO ring is done in a semi-custom fashion.

Parents and children increasingly spend time living apart due to marital separation and work travel. I investigated parent--child separation in both of these contexts to find that current technologies frequently do not meet the needs of families. The telephone is easy-to-use and ubiquitous but does not provide an engaging way of communicating with children. Videochat is more emotionally expressive and has a greater potential for engagement but is difficult to set up and cannot be used by a child without the help of an adult. Both telephone and videochat fail to meet the needs of remote parenting because they focus on conversation rather than care and play activities, which are the mechanism by which parents and children build closeness. I also saw that in both types of separation the motivation to connect at times conflicted with desire to reduce disruption of the remote household. To address some of these issues, I designed a system called the ShareTable, which provides easy-to-initiate videochat with a shared tabletop activity space. After an initial lab-based evaluation confirmed the promise of this approach, I deployed the ShareTable to four households (two sets of divorced families). I collected data about the families' remote interactions before and during the deployment. Remote communication more than doubled for each of these families while using the ShareTable and I saw a marked increase in the number of communication sessions initiated by the child. The ShareTable provided benefits over previous communication systems and supported activities that are impossible with other currently available technologies. One of the biggest successes of the system was in providing an overlapped video space that families appropriated to communicate metaphorical touch and a sense of closeness. However, the ShareTable also introduced a new source of conflict for parents and challenged the families as they tried to develop practices of using the system that would be acceptable to all involved. The families' approach to these challenges as well as explicit feedback about the system informs future directions for synchronous communication systems for separated families.

Σε αυτή την εργασία μελετάμε τους αλγορίθμους που χρησιμοποιούνται στην αποκωδικοποίηση των LDPC, με έμφαση στους κώδικες του προτύπου 802.11n. Αντιμετωπίζουμε τις δυσκολίες που αντιμετωπίζουν στην υλοποίηση στο υλικό, κυρίως στην εκτέλεση αριθμητικών πράξεων, και προτείνουμε πρακτικές λύσεις. Χρησιμοποιώντας τα αποτελέσματα εκτενών εξομοιώσεων, καταλήγουμε στις βέλτιστες παραμέτρους που θα έχουν οι προτεινόμενες υλοποιήσεις. / In this thesis, we study the LDPC decoding algorithms, with emphasis on the 802.11n standard codes. We tackle the hardware implementation difficulties, especially those related to arithmetic computations, and propose practical solutions. Leveraging the results of extensive simulations, we find the optimal parameters of the proposed implementations.

Abstract not available. / Thesis (M.A.)-University of KwaZulu-Natal, Durban, 2008.

This study discusses the potential for promoting cyber democracy through interactivity, on the Internet. Both interactivity and cyber democracy will lead to a broadening of the Zimbabwean public sphere by including online newspapers in the media circle. It views interactivity, cyber democracy and the public sphere as central to free expression. Zimbabwean online newspapers are not fully exploiting the Internet’s potentials to promote the threefold ideal for public deliberations identified in this study. The content analysis of 22 Zimbabwean online newspapers revealed that many newspapers are providing interactive tools that are of limited relevance to interactive communication. The different models for assessing interactivity, cyber democracy and the public sphere in the online newspapers that were employed in this study point to very low levels of interactivity, hence the rest of the components were affected. The three aspects of public deliberation identified in this study were found to be interdependent on each other. The qualitative research procedure confirms and provided reasons for low interactivity on Zimbabwe’s online newspapers from the editors’ perspectives. The online editors are cautious in their approach to a free-form type of public deliberations. Interactivity, potentials for cyber democracy and possibilities of a broadened public sphere were found to be very low on Zimbabwe’s online newspapers. However, the Internet itself is endowed with great possibilities for political deliberations that remain untapped. The onus is upon the newspapers to accord citizens opportunities for participation by making available tools for higher levels of interactive communication. / Thesis (M.A.) - University of KwaZulu-natal, Pietermaritzburg, 2009.

Concurrent cooperative transmission (CCT) occurs when a collection of power-constrained single-antenna radios transmit simultaneously to form a distributed multi-input and multi-output (DMIMO) link. DMIMO can be a means for highly reliable and low-latency cooperative routing, when the MIMO channel is exploited for transmit and receive diversity; in this context, the range extension benefit is emphasized. Alternatively, DMIMO can be a means for high-throughput ad hoc networking, when the MIMO channel is used with spatial multiplexing. In both cases, concatenated DMIMO links are treated. The key contribution of this dissertation is a method of pre-synchronization of distributed single-antenna transmitters to form a virtual antenna array, in the absence of a global clock, such as a global positioning system (GPS) receiver or a network time protocol (NTP) to provide reference signals for the synchronization. Instead, the reference for synchronization comes from a packet, transmitted by the previous virtual array and simultaneously received by all the cooperative transmitters for the next hop. The method is realized for two types of modulation: narrowband non-coherent binary frequency-shift keying (NCBFSK) and wideband orthogonal frequency division multiplexing (OFDM). The pre-synchronization algorithms for transmission are designed to minimize the root-mean-square (RMS) transmit time, sampling and carrier frequency error between cooperative transmitters, with low implementation complexity. Since CCT is not supported by any existing standard or off-the-shelf radios, CT must be demonstrated by using software-defined radios (SDRs). Therefore, another contribution is a fully self-contained and real-time SDR testbed for CCT-based networking. The NCBFSK and OFDM systems have been designed and implemented in C++ and Python programming languages in the SDR testbed, providing practical performance of the CCT-based systems.

Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 2003. / "January 2003" Includes bibliographical references (leaves 120-129).

Thesis (M.Sc. (Computer Science)) - Rhodes University, 2008.