Among the recent advances in the area of low-density parity-check (LDPC) codes, protograph-based LDPC codes have the advantages of a simple design procedure and highly structured encoders and decoders. These advantages can also be exploited in the design of protograph-based generalized LDPC (G-LDPC) codes. In this dissertation we provide analytical tools which aid the design of protograph-based LDPC and G-LDPC codes. Specifically, we propose a method for computing the codeword-weight enumerators for finite-length protograph-based G-LDPC code ensembles, and then we consider the asymptotic case when the block-length goes to infinity. These results help the designer identify good ensembles of protograph-based G-LDPC codes in the minimum distance sense (i.e., ensembles which have minimum distances grow linearly with code length). Furthermore, good code ensembles can be characterized by good stopping set, trapping set, or pseudocodeword properties, which assist in the design of G-LDPC codes with low floors. We leverage our method for computing codeword-weight enumerators to compute stopping-set, and pseudocodeword enumerators for the finite-length and the asymptotic ensembles of protograph-based G-LDPC codes. Moreover, we introduce a method for computing trapping set enumerators for finite-length (and asymptotic) protograph-based LDPC code ensembles. Trapping set enumerators for G-LDPC codes represents a more complex problem which we do not consider here. Inspired by our method for computing trapping set enumerators for protograph-based LDPC code ensembles, we developed an algorithm for estimating the trapping set enumerators for a specific LDPC code given its parity-check matrix. We used this algorithm to enumerate trapping sets for several LDPC codes from communication standards. Finally, we study coded-modulation schemes with LDPC codes and pulse position modulation (LDPC-PPM) over the free-space optical channel. We present three different decoding schemes and compare their performances. In addition, we developed a new density evolution tool for use in the design of LDPC codes with good performances over this channel.

Despite that we are in the midst of profound changes in communications technologies, there is a remarkable gap in the International Relations literature devoted to exploring the implications of these changes. In part, this can be attributed to the discipline’s conservative tendencies; generally, International Relations theorists have resisted studying major discontinuity in the international system. The few studies that do attempt to account for change typically focus on modes of production or destruction as determinant variables. Though there are rare exceptions, many of them also tend towards a form of mono-causal reductionism. When considered at all, communications technologies are viewed through the prism of, or are reduced to, these other factors. This study seeks to remedy this gap by examining the relationship between large-scale shifts in modes of communication and “world order” transformation -- the structure or architecture of political authority at a world-level. Drawing from the work of various “medium theory” scholars, such as Harold Innis and Marshall McLuhan, the study outlines an open-ended, non-reductive theory at the core of which is the argument that changes in modes of communication facilitate and constrain social forces and ideas latent in society. This hypothesized process can be likened to the interaction between species and a changing natural environment: new communications environments “favour” certain social forces and ideas by means of a functional bias towards some and not others, much the same as environments determine which species prosper by “selecting” for certain physical characteristics. In other words, social forces and ideas survive differentially according to their “fitness” or match with the new communications environment -- a process that is both open ended and contingent. The study is organized into two parts: Part one examines the relationship between printing and the medieval to modem world order transformation in Europe; Part two examines the relationship between new digital-electronic-telecommunications (called “hypermedia”) and the modem to postmodern world order transformation. The study suggests that the hypermedia communications environment is contributing to the dissolution of modern world order by facilitating the transnationalization of production, the globalization of finance, the rise of complex, non-territorial social networks, and the de-massification of “national” identities. The hypermedia environment is also helping to re-focus security concerns from an inter-national to an intra-planetary context. While it is far too early to provide a clear outline of the emerging postmodern world order, the trends that are unearthed in this study point away from single mass identities, linear political boundaries, and exclusive jurisdictions centred on territorial spaces, and towards multiple identities and non-territorial communities, overlapping boundaries, and non-exclusive jurisdictions.

<p>This thesis o ers some prototypes to provide browser-based and mobile video communication services for Deaf people and evaluates these prototypes. The aim of this research is to identify an acceptable video communication technology for Deaf people by designing and evaluating several prototypes. The goal is to nd one that Deaf people would like to use in their day-to-day life. The thesis focuses on two technologies | browser-based systems and mobile applications. Several challenges emerged, for example, speci c Deaf user requirements are di cult to obtain, the technical details must be hidden from end users, and evaluation of prototypes includes both technical and social aspects. This thesis describes work to provide South African Sign Language communication for Deaf users in a disadvantaged Deaf community in Cape Town. We posit an experimental design to evaluate browser-based and mobile technologies in order to learn what constitutes acceptable video communication for Deaf users. Two browser-based prototypes and two mobile prototypes were built to this e ect. Both qualitative data and quantitative data are collected with user tests to evaluate the prototypes. The video quality of Android satis es Deaf people, and the portable asynchronous communication is convenient for Deaf users. The server performance is low on bandwidth, and will therefore cost less than other alternatives, although Deaf people feel the handset is costly.</p>

Performance analysis in cellular networks is the determination of customer orientated grade-of-service parameters, such as call blocking and dropping probabilities, using the methods of stochastic theory. This stochastic theory analysis is built on certain assumptions regarding the arrival and service processes of user-offered calls in a network. In the past, cellular networks were analysed using the classical assumptions, Poisson call arrivals and negative exponential channel holding times, borrowed from earlier fixed network analysis. However, cellular networks are markedly different from fixed networks, in that, they afford the user a unique opportunity: the ability to communicate while on the move. User mobility and various other cellular network characteristics, such as customer-billing, cell· layout and hand·off mechanisms, generally invalidate the use of Poisson arrivals and negative exponential holding times. Recent measurements on live networks substantiate this view. Consequently, over the past few years, there has been a noticeable shift towards using more generalised arrival and service distributions in the performance analysis of cellular networks. However, two shortcomings with the resulting models are that they suffer from state space explosion and / or they represent hand off traffic as a state dependent mean arrival rate (thus ignoring the higher moments of the hand-off arrival process). This thesis's contribution to cellular network analysis is a moment-based approach that avoids full state space description but ensures that the hand-off arrival process is modelled beyond the first moment. The thesis considers a performance analysis model that is based on Poisson new call arrivals, generalised hand-off call arrivals and a variety of channel holding times. The thesis shows that the performance analysis of a cellular network may be loosely decomposed into three parts, a generic cell traffic characterising model, a generic cell traffic blocking model and a quality of service evaluation model. The cell traffic characterising model is employed to determine the mean and variance of hand-off traffic offered by a cell to its neighbour. The cell traffic-blocking model is used to detennine the blocking experienced by the various traffic streams offered to each cell. The quality of service evaluation part is essentially afued-point iteration of the cell traffic characterising and cell traffic blocking parts to determine customer orientated grade-of-service parameters such as blocking and dropping probabilities. The thesis also presents detailed mathematical models for user mobility modelling. Finally, the thesis provides extensive results to validate the proposed analysis and to illustrate the accuracy of the proposed analysis when compared to existing methods. / Thesis (Ph.D.)-University of Natal, Durban, 2000.

Power Line Communications (PLC) is a recent and rapidly evolving technology, aiming at the utilization of the electricity power lines for the transmission of data. PLC technology opens up new opportunities for the mass provision of local, last-mile access at a reasonable cost. PLC can furthermore provide a multitude of new Information Society services - both in the energy and telecom domains - to residential and commercial users that are difficult or costly to implement through other technologies. PLC technology has a number of important strengths: it offers a permanent on-line connection as well as symmetric, two-way communication; it has good performance, very good geographical coverage, and is relatively cheap because most of the infrastructure is already in place. Currently, the main weaknesses of PLC technology are that it is still in the developmental stage. It is likely not to be the only one: rather, it will be part of a range of complementary technologies, because each technology yields a different compromise between bandwidth, reach, noise immunity, and cost. This report starts by looking at access technologies and describing the power line as a communication medium and then frequency response and noise characteristics. A transmission technique (OFDM) that avoids power line noise and uses the common modulation formats is also explained. The results of this work shows that the power line technology can be used as a communication channel for urban areas and fast developing rural areas. This is because of the bandwidth is uses. A proposed future research for slow developing rural areas is found in the conclusion. / Thesis (M.Sc.Eng.)- University of KwaZulu-Natal, 2005.

Since the ascendance of CDMA (Code Division Multiple Access) as the generally accepted multiple access technology of choice for next generation networks, the rate of development of the wireless cellular communication industry has been phenomenal. Next generation wireless cellular networks offer a myriad of voice, video, data and text based information services for the future multimedia and information society. This mixed service scenario implies that the same [mite resource i.e. the air interface must be shared amongst different classes of user, each with a specific quality of service. With multiple services competing for the same resource and with the inherent soft capacity nature of CDMA, call admission control becomes a formidable task. The problem is further compounded by the introduction of priorities between classes. Call admission control is an essential component of these next generation networks and the open nature of the current standards, such as UMTS (Universal Mobile Telecommunication System) allow for vendor implementation of different call admission control policies. The main area of focus in this dissertation is on a proposed downlink, load-based, mixed service call admission policy. In a CDMA environment with symmetrical service and equal bandwidths in each direction, the uplink is commonly considered to be the bottleneck. Based on the asymmetric nature of the expected traffic in next generation networks the downlink is envisaged as the future bottleneck. Some of the more common choices for downlink call admission control include number based as well as power based call admission policies. A load-based call admission policy has been chosen as the maximum load threshold that can be supported varies with the state of the system and thus effectively models the behaviour of a soft capacity CDMA network. This dissertation presents a teletraffic performance analysis model of a load-based call admission control policy for downlink mixed service CDMA cellular networks. The performance analysis yields customer oriented grade-of-service parameters such as call blocking probability which is essential for network planning. In our analysis we incorporate a Birth-Death Markov queuing model. This mathematical model is verified though computer simulation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.

Reviews of possible telecommunication services that can be deployed in the rural areas are highlighted. These services range from narrowband to broadband. The aim of these services is to target rural Kwazulu-Natal areas that are without or with limited telecommunications infrastructure. Policies that govern telecommunications in South Africa are also reviewed with emphasis on Universal Service Obligation. The importance of telecommunications infrastructure in rural areas is also reviewed to the benefit of Kwazulu-Natal. FDMA, TDMA, CDMA, VSAT, MMDS and MVDS are compared for a possible use in rural areas. Cost comparison of GSM and CDMA is conducted with emphasis on fade margin, path loss and penetration rate. CDMA system design and coverage areas are discussed for rural KwaZulu-Natal. Lastly bit error rate graphs and power control algorithms are presented for Kwazulu-Natal scenario. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.

A review of possible distance education services is given. These services range from narrowband to broadband, from real to non-real time and from broadcast to fully interactive services. The service target groups include the rural schools and communities who are scattered in remote areas. The performances of multiple access techniques, FDMA, TDMA and CDMA when in use for the provision of point-to-multipoint multimedia services is compared. A hybrid of the satellite and terrestrial access networks for the implementation of the distance education services is presented. The feasibility of implementing the proposed satellite network as part of the total network using the FDMA technique is presented. The rest of the work done in the thesis concentrates on the terrestrial network. The terrestrial part of the network is based on fixed cellular DS-CDMA techniques. The fixed cellular network's specifications, modeling and a discussion of the capacity, BER performance, bandwidth requirements and coverage are presented. The link budget estimation of the performance is given. Lastly a review of propagation characteristics for a terrestrial rural environment and a review of DS-CDMA concepts are presented in the appendix. / Thesis (M.Sc.Eng.)-University of Durban-Westville, 2001.

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M.Sc.Eng. University of KwaZulu-Natal, Durban 2014.