The use of error-correction coding techniques in communication systems has become extremely imperative. Due to the heavy constraints faced by systems engineers more attention has been given to developing codes that converge closer to the Shannon theoretical limit. Turbo codes exhibit a performance a few tenths of a decibel from the theoretical limit and has motivated a lot of good research in the channel coding area in recent years. In the under-mentioned dissertation, motivated by turbo codes, we study the use of three new error-correction coding schemes: Repeat-Punctured Superorthogonal Convolutional Turbo Codes, Dual-Repeat-Punctured Turbo Codes and Dual-Repeat-Punctured Superorthogonal Convolutional Turbo Codes, applied to the additive white Gaussian noise channel and the frequency non-selective or flat Rayleigh fading channel. The performance of turbo codes has been shown to be near the theoretical limit in the AWGN channel. By using orthogonal signaling, which allows for bandwidth expansion, the performance of the turbo coding scheme can be improved even further. Since the resultant is a low-rate code, the code is mainly suitable for spread-spectrum modulation applications. In conventional turbo codes the frame length is set equal to the interleaver size; however, the codeword distance spectrum of turbo codes improves with an increasing interleaver size. It has been reported that the performance of turbo codes can be improved by using repetition and puncturing. Repeat-punctured turbo codes have shown a significant increase in performance at moderate to high signal-to-noise ratios. In this thesis, we study the use of orthogonal signaling and parallel concatenation together with repetition (dual and single) and puncturing, to improve the performance of the superorthogonal convolutional turbo code and the conventional turbo code for reliable and effective communications. During this research, three new coding schemes were adapted from the conventional turbo code; a method to evaluate the union bounds for the AWGN channel and flat Rayleigh fading channel was also established together with a technique for the weight-spectrum evaluation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Transmission of digital information through a wireless channel with resolvable multipaths or a bandwidth limited channel results in intersymbol interference (1SI) among a number of adjacent symbols. The design of an equalizer is thus important to combat the ISI problem for these types of channels and hence provides reliable communication. Channel coding is used to provide reliable data transmission by adding controlled redundancy to the data. Turbo equalization (TE) is the joint design of channel coding and equalization to approach the achievable uniform input information rate of an ISI channel. The main focus of this dissertation is to investigate the different TE techniques used for a static frequency selective additive white Gaussian noise (AWGN) channel. The extrinsic information transfer (EXIT) chart is used to analyse the iterative equalization/decoding process and to determine the minimum signal to noise ratio (SNR) in order to achieve convergence. The use of the Minimum Mean Square Error (MMSE) Linear Equalizer (LE) using a priori information has been shown to achieve the same performance compared with the optimal trellis based Maximum A Posterior (MAP) equalizer for long block lengths. Motivated by improving the performance of the MMSE LE, two equalization schemes are initially proposed: the MMSE Linear Equalizer with Extrinsic information Feedback (LE-EF (1) and (U)). A general structure for the MMSE LE, MMSE Decision Feedback Equalizer (DFE) and two MMSE LE-EF receivers, using a priori information is also presented. The EXIT chart is used to analyse the two proposed equalizers and their characteristics are compared to the existing MAP equalizer, MMSE LE and MMSE DFE. It is shown that the proposed MMSE LE-EF (1) does have an improved performance compared with the existing MMSE LE and approaches the MMSE Linear Equalizer with Perfect Extrinsic information Feedback (LE-PEF) only after a large number of iterations. For this reason the MMSE LE-EF is shown to suffer from the error propagation problem during the early iterations. A novel way to reduce the error propagation problem is proposed to further improve the performance of the MMSE LE-EF (I). The MAP equalizer was shown to offer a much improved performance over the MMSE equalizers, especially during the initial iterations. Motivated by using the good quality of the MAP equalizer during the early iterations and the hybrid MAP/MMSE LE-EF (l) is proposed in order to suppress the error propagation problem inherent in the MMSE LE-EF (I). The EXIT chart analysis reveals that the hybrid MAP/MMSE LE-EF (l) requires fewer iterations in order to achieve convergence relative to the MMSE LE-EF (l). Simulation results demonstrate that the hybrid MAP/MMSE LE-EF (I) has a superior performance compared to the MMSE LE-EF (I) as well as approaches the performance of both the MAP equalizer and MMSE LE-PEF at high SNRs, at the cost of increased complexity relative to the MMSE LEEF (I) receiver. The final part of this dissertation considers the use of precoders in a TE system. It was shown in the literature that a precoder drastically improves the system performance. Motivated by this, the EXIT chart is used to analyse the characteristics of four different precoders for long block lengths. It was shown that using a precoder results in a loss in mutual information during the initial equalization stage. However" we show by analysis and simulations that this phenomenon is not observed in the equalization of all precoded channels. The slope of the transfer function, relating to the MAP equalization of a precoded ISI channel (MEP), during the high input mutual information values is shown to play an important role in determining the convergence of precoded TE systems. Simulation results are presented to show how the precoders' weight affects the convergence of TE systems. The design of the hybrid MAP/MEP equalizer is also proposed. We also show that the EXIT chart can be used to compute the trellis code capacity of a precoded ISI channel. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

The phenomenal growth of digital multimedia applications has forced the communications

This project was undertaken for a commercial electronics company, CONTROL LOGIC (CONLOG) which is involved in the research, design, development and manufacture of data acquisition, control, energy management and automotive equipment. Currently CONLOG uses an inhouse token passing local area network CONET for industrial data communications.The need had arisen to provide a means of data communication amongst widely geographically distributed remote terminal units (RTUs) generating demands at a very low duty cycle. A need for communications between RTUs and a centralised controller was also required. In addition to this, multihop communications between the RTUs was required. Packet switching using a broadcast radio network provides an efficient means of achieving this. An investigation into to the various media access control protocols and contention techniques using packet radio was carried out. The various media access techniques were compared with respect to throughput and normalised delay. This led to the selection of a media access scheme for the packet radio network using RTUs. A protocol specification control is centralised or Interconnect Organisation.The switching protocol (OSI) for the packet radio network, in which distributed, was done. The architechure of specified adheres to the Open Systems model of the International Standards.An experimental packet switching radio network was implemented using the protocol specification defined above. The packet radio network (PACNET) uses existing off the shelf radios and purpose built hardware for the remote terminal units. The thesis describes methods of data communications suitable for widely dispersed industrial data communications, the selection of the packet switching media access methods and control protocols, and the design and implementation of the prototype system. / Thesis (M.Sc.Eng.)-University of Natal, 1992.

No description available.

Communication and networking are vast areas which are developing rapidly. It is very important to know in detail how the system works, how it can be enhanced to meet today's requirement, how to implement the appropriate techniques to obtain desired results etc. To explain all of the above, simulation techniques were adopted. Simulation plays an important role in developming new designs and modifying existing systems to make them more feasible and efficient.Protocols are the back bones of the communication systems and play a major role in data transfer. The review of literature provides an explanation of ISO/OSI models, layered approach and concepts of simulation. The simulation was carried out to explain the concepts of error detection, error correction and flow control in Data Link layer. Ada was used to develop the software, because of its concurrent processing tools called tasks. Also state-of-the-art utilities like Vax/Vms Screen Management System, File Definition Language, and Debugger were us ed in the program development. / Department of Computer Science

Various multiuser schemes have been proposed to efficiently utilize the available bandwidth while ensuring an acceptable service delivery and flexibility. The multicarrier CDMA became an attractive solution to the major challenges confronting the wireless communication system. However, the scheme is plagued with multiple access interference (MAI), which causes conspicuous performance deterioration at the receiver. A low-complexity multiuser scheme called the Interleave Division Multiple Access (IDMA) was proposed recently as a capable solution to the drawback in the multicarrier CDMA scheme. A combined scheme of OFDM-IDMA was later introduced to enhance the performance of the earlier proposed IDMA scheme. The multicarrier IDMA scheme therefore combats inter-symbol interference (ISI) and MAI effectively over multipath with low complexity while ensuring a better cellular performance, high diversity order, and spectral efficiency. Major studies on the OFDM-IDMA scheme emphasis only on the implementation of the scheme in a perfect scenario, where there are no synchronization errors in the system. Like other multicarrier schemes, the OFDM-IDMA scheme however suffers from carrier frequency offset (CFO) errors, which is inherent in the OFDM technique. This research work therefore examines, and analyzes the effect of synchronization errors on the performance of the new OFDM-based hybrid scheme called the OFDM-IDMA. The design of the OFDM-IDMA system developed is such that the cyclic prefix duration of the OFDM component is longer than the maximum channel delay spread of the multipath channel model used. This effectively eliminates ISI as well as timing offsets in the system. Since much work has not been done hitherto to address the deteriorating effect of synchronization errors on the OFDM-IDMA system, this research work therefore focuses on the more challenging issue of carrier frequency synchronization at the uplink. A linear MMSE-based synchronization algorithm is proposed and implemented. The proposed algorithm is a non-data aided method that focuses on the mitigation of the ICI induced by the residual CFOs due to concurrent users in the multicarrier system. However, to obtain a better and improved system performance, the Kernel Least Mean Square (KLMS) algorithm and the normalized KLMS are proposed, implemented, and effectively adapted to combat the degrading influence of carrier frequency offset errors on the OFDM-IDMA scheme. The KLMS synchronization algorithm, which involves the execution of the conventional Least Mean Square (LMS) algorithm in the kernel space, utilizes the modulated input signal in the implementation of the kernel function, thereby enhancing the efficacy of the algorithm and the overall output of the multicarrier system. The algorithms are applied in a Rayleigh fading multipath channel with varying mobile speed to verify their effectiveness and to clearly demonstrate their influence on the performance of the system in a practical scenario. Also, the implemented algorithms are compared to ascertain which of these algorithms offers a better and more efficient system performance. Computer simulations of the bit error performance of the algorithms are presented to verify their respective influence on the overall output of the multicarrier system. Simulation results of the algorithms in both slow fading and fast fading multipath scenarios are documented as well. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

A system is developed which facilitates communication between a Personal Computer and a Mainframe, and can do both directions, and lets the user execute Unix shell commands while the file transfer is in process. This communication system consists of two programs, one named "Thesis.EXE" that runs on a DOS based machine, and one named named "COMMGREEK" that runs on a Unix based machine. / Department of Computer Science

Parallel processing can provide the huge computational resources that are required to solve todays grand challenges, at a fraction of the cost of developing sequential machines of equal power. However, even with such attractive benefits the parallel software industry is still very small compared to its sequential counterpart. This has been attributed to the lack of an accepted parallel model of computation, therefore leading to software which is architecture dependent with unpredictable performance. The Bulk Synchronous Parallel (BSP) model provides a solution to these problems and can be compared to the Von Neumann model of sequential computation. In this thesis we investigate the issues involved in providing a modular programming environment based on the BSP model. Using our results we present Opal, a BSP programming language that has been designed for parallel programming-in-the-large. While other BSP languages and libraries have been developed, none of them provide support for libraries of parallel algorithms. A library mechanism must be introduced into BSP without destroying the existing cost model. We examine such issues and show that the active library mechanism of Opal leads to algorithms which still have predictable performance. If algorithms are to retain acceptable levels of performance across a range of machines then they must be able to adapt to the architecture that they are executing on. Such adaptive algorithms require support from the programming language, an issue that has been addressed in Opal. To demonstrate the Opal language and its modular features we present a number of example algorithms. Using an Opal compiler that has been developed we show that we can accurately predict the performance of these algorithms. The thesis concludes that by using Opal it is possible to program the BSP model in a modular fashion that follows good software engineering principles. This enables large scale parallel software to be developed that is architecture independent, has predictable performance and is adaptive to the target architecture.

Dissertation (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Though not so prominent as the wide band, high speed, mainstream development of data communication networks, cost and particular bandwidth limitations, still ensure extensive and continuing use of low-speed, half-duplex data link equipment. Most of these applications are radio based and aimed towards telemetry systems serving a wide range of utilities. Experience has shown that systems engineering for this type of installation, is seldom undertaken to a satisfactory analytical level. Investigation of published analyses of CSMA protocols in general, has indicated scope of extension of theoretical work to include system parameters for the type of protocol investigated in this dissertation. This dissertation describes the mathematical modeling of such a strategy by utilising a significantly modified, finite source, transition state-matrix approach derived from queueing theory. The contribution of the dissertation is to include system overhead parameters, such as backoff strategy, channel noise, equipment rise times, propagation- and retry delays, into the abovementioned model. The latter provides a relatively straightforward and readily applicable method for system analysis and performance prediction. A further contribution is the presentation of a software emulation with which different strategies could be simulated, allowing for adjustment of all design parameters. The simulation is intended for parallel and confimatory use with the theoretical model. A dual set of tools, theoretical and emulation based, is thus contributed to assist with the system design, performance prediction and protocol selection process. / AFRIKAANSE OPSOMMING: Alhoewel nie so prominent soos die wyeband, hoëspoed, hoofstroom ontwikkeling van datakommunikasie netwerke nie, verseker koste en spesifieke bandwydte beperkings nog die uitgebreide en voortdurende gebruik van laespoed half-dupleks data verbindingstoerusting. Meeste van die toepassings is radio gebaseer en gerig op telemetriestelsels wat deur 'n wye verskeidenheid diensverskaffers benut word. Stelselontwerp vir hierdie tipe installasies word selde op analitiese vlak benader. Ondersoek van gepubliseerde analises van kontensieprotokolle in die algemeen, het ruimte aangetoon vir die uitbreiding van bestaande teoretiese werk om stelselveranderlikes soos van toepassing op die tipe protokol in hierdie proefskrif ondersoek, in te sluit. Hierdie proefskrif beskryf die wiskundige modelering van sodanige strategie, deur gebruik te maak van 'n beduidend veranderde eindige bron, oorgangs-toestandmatriks benadering, afgelei van touteorie. Die bydrae van hierdie proefskrif is die insluiting van oorhoofse stelselveranderlikes, soos herhaal strategie, kanaalruis, toerusting stygtye, herhaal- en voortplantingsvertragings, in bogenoemde model. Laasgenoemde verskaf 'n relatief eenvoudige en maklik toepasbare metode vir stelselanalise en werkverrigtingvoorspelling. 'n Verder bydrae is die daarstelling van 'n sagteware simulasie waarmee verskillende strategieë nageboots kan word. Verstelling van alle ontwerpparameters word ondersteun. Die simulasie is bedoel vir parallelle en bevestigende gebruik tesame met die teoretiese model. 'n Dubbele, teoreties- en simulasie gebaseerde benadering, word dus aangebied vir gebruik by stelselontwerp, gedragsvoorspelling en optimale protokolseleksie.