School of Engineering

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A semi-empirical formulation for determination of rain attenuation on terrestrial radio links.
(2010) Odedina, Modupe Olubunmi.; Afullo, Thomas Joachim Odhiambo.
Advances in today’s fast growing communication systems have resulted in congestion in the lower frequency bands and the need for higher capacity broadband services. This has made it inevitable for service providers to migrate to higher frequency bands so as to accommodate the ever increasing demands on radio communication systems. However, the reliability of such systems at these frequency bands tend to be severely degraded due to some natural atmospheric phenomena of which rain is the dominant factor. This is not to say that other factors have become unimportant; however, if attenuation by rain is so severe that a radio link is unavailable for use, then other factors become secondary. Therefore, it is paramount to establish a model capable of predicting the behaviour of these systems in the presence of rain. This study employs a semi-empirical approach for the formulation of rain attenuation models using the knowledge of rain rate, raindrop size distribution, and a signal level measurement recorded at 19.5 GHz on a horizontally polarized terrestrial radio link. The semi-empirical approach was developed by considering the scattering effect of an electromagnetic wave propagating through a medium containing raindrops. The complex forward scattering amplitudes for the raindrops are determined for all raindrop sizes at different frequencies, utilizing the Mie scattering theory on spherical dielectric raindrops. From these scattering amplitudes, the extinction cross-sections for the spherical raindrops are calculated. Applying the power-law regression to the real part of the calculated extinction cross-section, power-law coefficients are determined at different frequencies. The power-law model generated from the extinction crosssection is integrated over different raindrop-size distribution models to formulate theoretical rain attenuation models. The developed rain attenuation models are used with 0.01 R rain rate statistics determined for four locations in different rain climatic zones in South Africa to calculate the specific rain attenuation. From a horizontally polarized 6.73 km terrestrial line-of-sight link in Durban, South Africa,experimental rain attenuation measurements were recorded at 19.5 GHz. These rain attenuation measurements are compared with the results obtained from the developed attenuation models with the same propagation parameters to establish the most appropriate attenuation models that describe the behaviour of radio link performance in the presence of rain. For the purpose of validating the results, it is compared with the ITU-R rain attenuation model. This study also considers the characteristics and variations associated with rain attenuation for terrestrial communication systems. This is achieved by utilizing the ITU-R power-law rain attenuation model on 5-year rain rate data obtained from the four different climatic rain zones in South Africa to estimate the cumulative distributions of rain attenuation. From the raindrop size and 1-minute rain rate measurement recorded in Durban with a distrometer over six months, rain events over the six months are classified into drizzle, widespread, shower and thunderstorm rain types and the mean rain rate statistics determined for each class of rain. Drop-size distribution for all the rain types is estimated. This research has shown a statistical analysis of rain fade data and proposed an empirical rain attenuation model for South Africa localities. This work has also drawn out theoretical rain attenuation prediction models based on the assumption that the shapes of raindrops are spherical. The results predicted from these theoretical attenuation models have shown that it is not the raindrop shapes that determine the attenuation due to rain, but the raindrop size distribution and the rain rate content in the drops. This thesis also provides a good interpretation of cumulative rain attenuation distribution on seasonal and monthly basis. From these distributions, appropriate figures of fade margin are derived for various percentages of link availability in South Africa.
A study of rain attenuation on terrestrial paths at millimetric wavelengths in South Africa.
(2006) Olubunmi, Fashuyi Modupe.; Afullo, Thomas Joachim Odhiambo.
Rain affects the design of any communication system that relies on the propagation of electromagnetic waves. Above a certain threshold of frequency, the attenuation due to rain becomes one of the most important limits to the performance of terrestrial line-of-sight (LOS) microwave links. Rain attenuation which is the dominant fading mechanism at these frequencies is based on nature which can vary from location-to-Iocation and from year-to year. In this dissertation, the ITU-R global prediction techniques for predicting the cumulative distribution of rain attenuation on terrestrial links are studied using a five-year rain rate data for twelve different geographical locations in the Republic of South Africa. The specific attenuation rR (dB/km) for both horizontal and vertical polarization is determined. The path attenuation (dB) exceeded for 0.01% of the time is estimated using the available existing models for the twelve different geographical locations on a I-minute integration time rain rate at 0.01% exceedance of the time averaged over a period of 5 years. A comparison study is done on these available rain attenuation mode'ls; The ITU-R model, Crane Global model, and the Moupfouma models at different frequencies and propagation path lengths based on the actual I-minute integration time rain rate exceeded at 0.01% of the time averaged over a period of 5 years for each geographical locations. Finally, from the actual signal attenuation measurements recorded in Durban over a period of 1 year at 19.5 GHz and a propagation path length of 6.73 km, a logarithmic attenuation model and power attenuation model is proposed for Durban, South Africa. Recommendation for future work is given in the concluding chapter for future improvement on this study. Radio communication designers will find the results obtain in the report useful.
Alternative approach to Power Line Communication (PLC) channel modelling and multipath characterization.
(2016) Awino, Steven Omondi.; Afullo, Thomas Joachim Odhiambo.
Modelling and characterization of the Power Line Communication (PLC) channel is an active research area. The research mainly focuses on ways of fully exploiting the existing and massive power line network for communications. In order to exploit the PLC channel for effective communication solutions, physical properties of the PLC channel need to be studied, especially for high bandwidth signals. In this dissertation, extensive simulations and measurement campaigns for the channel transfer characteristics are carried out at the University of KwaZulu-Natal in selected offices, laboratories and workshops within the Department of Electrical, Electronic and Computer Engineering. Firstly, we employ the Parallel Resonant Circuit (PRC) approach to model the power line channel in chapter 4, which is based on two-wire transmission line theory. The model is developed, simulated and measurements done for validation in the PLC laboratory for different network topologies in the frequency domain. From the results, it is found that the PRC model produces similar results to the Series Resonant Circuit (SRC) model, and hence the model is considered for PLC channel modelling and characterization. Secondly, due to the time variant nature of the power line network, this study also presents the multipath characteristics of the power line communication (PLC) channel in chapter 5. We analyse the effects of the network characteristics on the received signal and derive the multipath characteristics of the PLC channel from measured channel transfer functions by evaluating the channel impulse responses (CIR). The results obtained are compared with results from other parts of the world employing similar approach based on the Root Mean Square (RMS) delay spread and are found to be comparable. Based on the CIR and extracted multipath characteristics, further research in PLC and related topics shall be inspired.
Alternative techniques for the improvement of energy efficiency in cognitive radio networks.
(2016) Orumwense, Efe Francis.; Srivastava, Viranjay Mohan.; Afullo, Thomas Joachim Odhiambo.
Abstract available in PDF file.
An alternative approach to impulsive noise characterisation and statistical modelling for broadband powerline communication networks.
(2024) Chelangat, Florence.; Afullo, Thomas Joachim Odhiambo.
Research into the modelling of powerline communication impulsive noise – which exhibits unpredictable behaviour in its time domain characteristics of amplitude, inter-arrival time, and service time - is still in progress. As a result, in order to propose an appropriate mitigation strategy to address the interference generated by powerline communication impulsive noise, an appropriate characterization of its time domain parameters is crucial. Given the complex structure of the powerline communication network that includes a heavy wiring system, the models proposed for the various noise characteristics are stochastic in nature. In this work, extensive noise measurements were carried out over various indoor networks in the School of Engineering, University of KwaZulu-Natal, Durban, South Africa. The measurements were conducted at the following sites: the Computer Laboratory, the Machines Laboratory, the Electronic Laboratory, the Second-year Laboratory, the Post-graduate office, as well as at an adjacent apartment. This campaign was undertaken to adequately capture the behaviour of powerline communication noise, which varies randomly depending on location, time, and the devices linked to the electrical network. To begin with, the amplitude distribution of the powerline communication impulsive noise was examined. The Gaussian mixture model was used to analyse the amplitude distribution of powerline communication noise, which is essential in estimating the level of noise reaching the receiver. Gaussian mixture models are commonly employed in modelling the powerline communication impulsive noise amplitude distribution. However, the weights of the Gaussian mixture components are derived using statistical distributions, with the most common models employing the Bernoulli and Poisson distributions. These models, however, have been found to be insufficient in describing powerline communication noise. This thesis contributes to the modelling of the amplitude distribution of powerline communication impulsive noise by using unsupervised learning to determine the parameters of the Gaussian mixture. Regression analysis is also proposed to solve the issue of singularity in the likelihood function of this model as well as to determine the optimum number of Gaussian components. Further analysis of the amplitude distribution is performed using a fully Bayesian treatment referred to as the Variational Bayesian model, where the parameters of the Gaussian mixture model are assumed to be random variables, such that prior distributions over the parameters are introduced. Moreover, the optimal number of components is determined from the measurement data through the Variational Bayesian criterion. This ensures that improved accuracy due to the increased number of components in modelling the powerline communication impulsive noise amplitude distribution is eliminated thus reducing the model complexity while adequately describing the data. The variational-expectation algorithm, analogous to the expectation-maximisation algorithm employed in the Gaussian mixture model, is used to determine the model parameters. Measurements have shown that the powerline communication impulsive noise can be modelled as a superposition of several exponential distributions. Consequently, most of the research models proposed for modelling the inter-arrival and service time distribution are based on the Markov chain. There is still no defined method of evaluating the number of states, with existing models employing various curve-fitting techniques to find the optimum model for the measurement data. This work provides an alternative approach based on the queueing theory technique, where the impulsive noise occurrence in the powerline communication channel is modelled as an Erlangian queue. A straightforward method for obtaining the optimum number of exponential phases by employing the mean and the variance of the Erlang-k distribution is presented. The proposed model assumes that the impulsive noise passes through k arrival stages before entering the powerline communication network and another k service stages before leaving the powerline communication network. In all of the measurement data under consideration, impulsive noise events are observed to achieve steady-state in the inter-arrival and service time distributions. In this work, the measurements indicate that the powerline communication noise can occur as a single-impulse noise or a burst-impulse noise. The burst-impulse noise is caused by the overlap of three or more high-amplitude single-impulse noise events that occur successively in an impulse train. The amplitude of the noise, as well as the interarrival and service time distribution, vary depending on the location and time. As a result, the impulsive noise is categorised as low, medium, or highly impulsive, depending on the noise levels. The probability density function of the noise amplitude exhibits heavy tails comparable to the Gaussian mixtures. The performance of the maximum likelihood estimate and the Variational Bayesian model in finding the parameters of the Gaussian mixture are validated through measurements, where the maximum likelihood estimate yields better accuracy. However, cases of singularity are encountered in addition to an increase in performance as the number of impulsive noise components is increased. Therefore, the implementation of the Variational Bayesian approach in modelling the parameters of the Gaussian mixture enables the determination of the appropriate number of Gaussian mixture components and no singularity case is found. Although the Variational Bayesian model provides a good generalization to the measured data, the maximum likelihood technique gives better accuracy since the Variational Bayesian model provides an approximate solution, as it is based on maximising the lower bound. Both models are observed to have a high level of significance as well as a good correlation to the measured data and thus either can be used in modelling the amplitude distribution of the powerline communication noise. In modelling the inter-arrival and service time distributions, the Erlang-k distribution is observed to be more appropriate for modelling the burst-impulse noise events with a high level of significance to the measured data. The exponential distribution, which is a special case of the Erlang-k distribution, is determined to be appropriate in estimating the inter-arrival time of the single-impulse noise events, indicating high variance in the measurement data. The models proposed in this thesis can be used as simulation tools to assist the development of physical layers of powerline communication systems.
ATM performance in rural areas of South Africa.
(2005) Mbatha, Sakhiseni J.; Afullo, Thomas Joachim Odhiambo.
Rural areas in developing countries span vast areas with a variety of climatic zones, vegetation and terrain features, which are hostile to the installation and maintenance of telecommunication infrastructures. Provision of telecommunications services to these areas using traditional wired and existing wiring telephone system with centralized network architecture becomes prohibitively expensive and not viable in many cases, because there is no infrastructure and the area is sparsely populated. Applications of wireless systems seem to provide a cost-effective solution for such a scenario. However, deployment of ATM in rural areas as a backbone technology wide area network (WAN) has not been thoroughly investigated so far. The dissertation investigates the feasibility of deployment of ATM backbone network (WAN) to be implemented in the rural. ATM is a digital transmission service for wide area networks providing speeds from 2 Megabits per second up to 155 Megabits per second. Businesses and institutions that transmit extremely high volumes of virtually error-free information at high speeds over wide area network with high quality and reliable connections currently use this service. For the purpose of saving the utilization of more bandwidth, the network should support or have a high forward bit rate, i.e. it must convey high traffic from base station to the user (i.e. upstream) than from the user to the base station (down stream). This work also investigates the features from the rural areas that degrade the performance of the networks and have a negative impact in the deployment of the telecommunications networks services. Identification of these features will lead to the suggestion of the least cost-effective telecommunication service. For the purpose of evaluating the performance and feasibility of the network, modeling of the ATM network is accomplished using Project Estimation (ProjEstim) Simulation Tool as the comprehensive tool for simulating large communication networks with detailed protocol modeling and performance analysis.
CDMA performance for a rural telecommunication access.
(2005) Rasello, Poloko Freddy.; Afullo, Thomas Joachim Odhiambo.
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.
Channel characterization for broadband powerline communications.
(2014) Mulangu, Chrispin Tshikomba.; Afullo, Thomas Joachim Odhiambo.; Ijumba, Nelson Mutatina.
The main limiting factor in broadband powerline communications is the presence of impedance discontinuities in the wired channel. This phenomenon is present in both outdoor and indoor powerline communication (PLCs) channels. It has been established that the impedance of the electrical loads and line branching are the main causes of impedance discontinuities in PLC channel networks. Accurate knowledge of the expected impedances of the corresponding discontinuity points would be vital in order to characterize the channel for signal transmission. However, the PLC channel network topologies lead to different branching structures. Additionally, the existence of a myriad of electrical loads, whose noise and impedance vary with frequency, are a motivation for a rigorous design methodology in order to achieve a pragmatic channel model. In order to develop such a channel model, an approach similar to the one applied in radio propagation channel modeling is adopted, where specific attenuation determined at a point is used in predicting the attenuation for the entire power cable length. Therefore, the powerline is modeled with the assumption of a randomly spread multitude of scatterers in the vicinity of the channel with only a sufficient number of impedance discontinuity points. The line is considered as a single homogeneous element with its length divided into a grid of small areas with dimensions that range from 0.5 to 3 mm. Thus, each small area transmits an echo and the forward scattered response gets to the receiver. With this approach, point specific attenuation along the line is proposed and used to derive the channel transfer function. Measurement results show that both the analytical specific attenuation model developed in this work and the channel transfer function are feasible novel ideas in PLC channel network characterization. It is seen from the measurements that the signal attenuation is directly proportional to the number of branches, and this is in line with the findings of previous researchers. A comparison between the measured values and the simulation results of the frequency response shows a very good agreement. The agreement demonstrates applicability of the models in a practical enviroment. Thus we conclude that the models developed do not require knowledge either of the link topology or the cable models but requires an extensive measurement campaign.
Characteristics of rain at microwave and millimetric bands for terrestrial and satellite links attenuation in South Africa and surrounding islands.
(2010) Owolawi, Pius Adewale.; Afullo, Thomas Joachim Odhiambo.; Malinga, Sandile B.
The emergence of a vast range of communication devices running on different types of technology has made convergence of technology become the order of the day. This revolution observed in communications technology has resulted in a pressing need for larger bandwidth, higher data rate and better spectrum availability, and it has become important that these factors be addressed. As such, this has resulted in the current resurgence of interest to investigate higher electromagnetic spectrum space that can take care of these needs. For the past decade, microwave (3 GHz-30 GHz) and millimeter waves (30 GHz-300 GHz) have been used as the appropriate frequency ranges for applications with properties such as wide bandwidth, smaller components size, narrow beamwidths, frequency re-use, small antenna, and short deployment time. To optimize the use of these frequency ranges by communication systems, the three tiers of communication system elements - receiver, transmitter and transmission channel or medium must be properly designed and configured. However, if the transmitter and receiver meet the necessary requirements, the medium in which signals are transmitted often becomes an issue at this range of frequencies. The most significant factor that affects the transmission of signals at these bands is attenuation and scattering by rain, snow, water vapour and other gases in the atmosphere. Scattering and absorption by rain at microwave and millimeter bands is thus a main concern for system designers. This study presents results of research into the interaction of rainfall with microwave and millimeter wave propagation as a medium. The study of rainfall characteristics allows estimation of its scattered and attenuated effects in the presence of microwave and millimeter waves. The components of this work encompass rainfall rate integration time, cumulative distribution and modelling of rainfall rate and characteristics of rain drop size and its modelling. The effects of rain on microwave and millimeter wave signals, which result in rain attenuation, are based on rainfall rate variables such as rainfall rate cumulative distribution, raindrop size distribution, total scattering cross sections, rain drop shape, and rain drop terminal velocity. A regional rainfall rate conversion factor from five-minute rainfall data to one-minute integration time is developed using the existing conversion method and a newly developed hybrid method. Based on these conversion factor results from the hybrid method, the rainfall at five-minute integration time was converted to a one-minute equivalent to estimate its cumulative distributions. In addition, new rain zones based on ITU-R and Crane designations are suggested for the entire region of South Africa and the surrounding Islands. The results are compared with past research work done in the other regions. Rain attenuation is acutely influenced by rain drop size distribution (DSD). This study thus also investigates DSD models from previous research work. There are several DSD models commonly used to estimate rain attenuation. They are models which have their root from exponential, gamma, lognormal and Weibull distributions. Since DSD is dynamic and locationdependent, a simple raindrop size distribution model is developed for Durban using maximum likelihood estimation (MLE) method. The MLE method is applied to the three-parameter lognormal distribution in order to model DSD for Durban. Rain drop size depends on rainfall rate, drop diameter and rain drop velocity. Semi-empirical models of terminal velocity from previous studies are investigated in this work and proposed for the estimation of specific rain attenuation.
Characterization and modelling of effects of clear air on multipath fading in terrestrial links.
(2013) Asiyo, Mike Omondi.; Afullo, Thomas Joachim Odhiambo.
The increased application of digital terrestrial microwave radio links in communication networks has renewed attention in techniques of estimating the probability of multipath fading distributions. Nevertheless, the unpredictable variation of the wireless transmission medium remains a challenge. It has been ascertained that the refraction of electromagnetic waves is due to the inhomogeneous spatial distribution of the refractive index, and causes adverse effects such as multipath and diffraction fading. The knowledge of the characteristics of such causes of these fading phenomena is essential for the accurate design of terrestrial line of sight (LOS) links of high performance and availability. Refractivity variation is random in space and time and cannot be described in a deterministic manner and has to be considered as a random variable with probabilistic characteristics. In this dissertation, radiosonde soundings data is used in characterizing the atmospheric conditions and determining the geoclimatic factor K used in predicting the distribution of multipath fading for five locations in South Africa. The limitations of radiosonde measurements are lack of time resolution and poor spatial resolution. The latter has been reduced by spatial interpolation techniques in our study, specifcally, the Inverse Distance Weighting (IDW) method. This is used in determining the point refractivity gradient not exceeded for 1 % of the time from which the geoclimatic factor is estimated. Fade depth and outage probability due to multipath propagation is then predicted from the International Telecommunications Union Recommendations (ITU-R) techniques. The results are compared with values from Central Africa. The results obtained using the ITU-R method are also compared with region-based models of Bannett-Vigants of USA and Morita of Japan. Three spatial interpolation techniques (Kriging, Thin-Plate Spline and Inverse Distance Weighting) are then used in interpolating the geoclimatic factor K in places where radiosonde data is not available. The estimated values have been used to develop contour maps for geoclimatic factor K for South Africa. Statistical assessment of these methods is done by calculating the root mean square error (RMSE) and the mean absolute error (MAE) between a set of control points and the interpolated results. The best performing method is used to map the seasonal geoclimatic factor K for the entire study region. The estimated values of geoclimatic factor will improve accuracy in predicting outage probability due to multipath propagation in LOS links in the region which is a key contribution of this work.
Characterization and modelling of the channel and noise for broadband indoor powerline communication (plc.) networks.
(2016) Mosalaosi, Modisa.; Afullo, Thomas Joachim Odhiambo.
Power Line Communication (PLC) is an interesting approach in establishing last mile broad band access especially in rural areas. PLC provides an already existing medium for broad band internet connectivity as well as monitoring and control functions for both industrial and indoor usage. PLC network is the most ubiquitous network in the world reaching every home. However, it presents a channel that is inherently hostile in nature when used for communication purposes. This hostility is due to the many problematic characteristics of the PLC from a data communications’ perspective. They include multipath propagation due to multiple reflections resulting from impedance mismatches and cable joints, as well as the various types of noise inherent in the channel. Apart from wireless technologies, current high data rate services such as high speed internet are provided through optical fibre links, Ethernet, and VDSL (very-high-bit-rate digital subscriber line) technology. The deployment of a wired network is costly and demands physical effort. The transmission of high frequency signals over power lines, known as power line communications (PLC), plays an important role in contributing towards global goals for broadband services inside the home and office. In this thesis we aim to contribute to this ideal by presenting a powerline channel modeling approach which describes a powerline network as a lattice structure. In a lattice structure, a signal propagates from one end into a network of boundaries (branches) through numerous paths characterized by different reflection/transmission properties. Due to theoretically infi nite number of reflections likely to be experienced by a propagating wave, we determine the optimum number of paths required for meaningful contribution towards the overall signal level at the receiver. The propagation parameters are obtained through measurements and other model parameters are derived from deterministic power system. It is observed that the notch positions in the transfer characteristics are associated with the branch lengths in the network. Short branches will result in fewer notches in a fixed bandwidth as compared to longer branches. Generally, the channel attenuation increase with network size in terms of number of branches. The proposed model compares well with experimental data. This work presents another alternative approach to model the transfer characteristics of power lines for broadband power line communication. The model is developed by considering the power line to be a two-wire transmission line and the theory of transverse electromagnetic (TEM) wave propagation. The characteristic impedance and attenuation constant of the power line v are determined through measurements. These parameters are used in model simplification and determination of other model parameters for typical indoor multi-tapped transmission line system. The transfer function of the PLC channel is determined by considering the branching sections as parallel resonant circuits (PRC) attached to the main line. The model is evaluated through comparison with measured transfer characteristics of known topologies and it is in good agreement with measurements. Apart from the harsh topology of power line networks, the presence of electrical appliances further aggravates the channel conditions by injecting various types of noises into the system. This thesis also discusses the process of estimating powerline communication (PLC) asynchronous impulsive noise volatility by studying the conditional variance of the noise time series residuals. In our approach, we use the Generalized Autoregressive Conditional Heteroskedastic (GARCH) models on the basis that in our observations, the noise time series residuals indicate heteroskedasticity. By per forming an ordinary least squares (OLS) regression of the noise data, the empirical results show that the conditional variance process is highly persistent in the residuals. The variance of the error terms are not uniform, in fact, the error terms are larger at some portions of the data than at other time instances. Thus, PLC impulsive noise often exhibit volatility clustering where the noise time series is comprised of periods of high volatility followed by periods of high volatility and periods of low volatility followed by periods of low volatility. The burstiness of PLC impulsive noise is therefore not spread randomly across the time period, but instead has a degree of autocorrelation. This provides evidence of time-varying conditional second order moment of the noise time series. Based on these properties, the noise time series data is said to suffer from heteroskedasticity. GARCH models addresses the deficiencies of common regression models such as Autoregressive Moving Average (ARMA) which models the conditional expectation of a process given the past, but regards the past conditional variances to be constant. In our approach, we predict the time-varying volatility by using past time-varying variances in the error terms of the noise data series. Subsequent variances are predicted as a weighted average of past squared residuals with declining weights that never completely diminish. The parameter estimates of the model indicates a high de gree of persistence in conditional volatility of impulsive noise which is a strong evidence of explosive volatility. Parameter estimation of linear regression models usually employs least squares (LS) and maximum likelihood (ML) estimators. While maximum likelihood remains one of the best estimators within the classical statistics paradigm to date, it is highly reliant vi on the assumption about the joint probability distribution of the data for optimal results. In our work, we use the Generalized Method of Moments (GMM) to address the deficien cies of LS/ML in order to estimate the underlying data generating process (DGP). We use GMM as a statistical technique that incorporate observed noise data with the information in population moment conditions to determine estimates of unknown parameters of the under lying model. Periodic impulsive noise (short-term) has been measured, deseasonalized and modeled using GMM. The numerical results show that the model captures the noise process accurately. Usually, the impulsive signals originates from connected loads in an electrical power network can often be characterized as cyclostationary processes. A cyclostationary process is described as a non-stationary process whose statistics exhibit periodic time varia tion, and therefore can be described by virtue of its periodic order. The focus of this chapter centres on the utilization of cyclic spectral analysis technique for identification and analysis of the second-order periodicity (SOP) of time sequences like those which are generated by electrical loads connected in the vicinity of a power line communications receiver. Analysis of cyclic spectrum generally incorporates determining the random features besides the pe riodicity of impulsive noise, through the determination of the spectral correlation density (SCD). Its effectiveness on identifying and analysing cyclostationary noise is substantiated in this work by processing data collected at indoor low voltage sites.
Clear-air analytical and empirical K-Factor determination and characterization for terrestrial microwave LOS link applications.
(2013) Nyete, Abraham Mutunga.; Afullo, Thomas Joachim Odhiambo.
The transmission media, that is, the atmosphere, through which terrestrial and satellite signals traverse, is irregular. Thus, one requires proper knowledge on how variations in atmospheric refractive conditions will affect the optimal performance of terrestrial and satellite links. Under clear-air conditions, atmospheric changes will mainly involve variations in atmospheric pressure, relative humidity and temperature, which are the key to defining the way signals are refracted as they travel from the transmitter to the receiver. Accurate knowledge of these variations can be acquired through proper modeling, characterization and mapping of these three atmospheric quantities, in terms of the refractive index, refractivity gradient or the effective earth radius factor (k-factor). In this dissertation, both parametric and non-parametric modeling and characterizing, interpolation and mapping of the k-factor for South Africa is done. Median (k50%) and effective (k99.9%) k-factor values are the ones that determine antenna heights in line of sight (LOS) terrestrial microwave links. Thus, the accurate determination of the two k-factor values is critical for the proper design of LOS links by ensuring that adequate path clearance is achieved, hence steering clear of all obstacles along the radio path. Thus, this study is critical for the proper design of LOS links in South Africa. One parametric method (curve fitting) and one non-parametric method (kernel density estimation) are used to develop three-year annual and seasonal models of the k-factor for seven locations in South Africa. The integral of square error (ISE) is used to optimize the model formulations obtained in both cases. The models are developed using k-factor statistics processed from radiosonde measurements obtained from the South African Weather Service (SAWS) for a three year period (2007-2009). Since the data obtained at the seven locations is scattered, three different interpolation techniques are then explored to extend the three-year annual and seasonal discrete measured k-factor values for the seven locations studied to cover the rest of the country, and the results of the interpolation are then presented in the form of contour maps. The techniques used for the interpolation are kriging, inverse distance weighting (IDW) and radial basis functions (RBFs). The mean absolute error (MAE) and the root mean square error (RMSE) are the metrics used to compare the performance of the different interpolation techniques used. The method that produces the least error is deemed to be the best, and its interpolation results are the ones used for developing the contour maps of the k-factor.
Clear-air radioclimatological modeling for terrestrial line of sight links in Southern Africa.
(2010) Kemi, Odedina Peter.; Afullo, Thomas Joachim Odhiambo.
This thesis has investigated radioclimatological study in a clear-air environment as applicable to terrestrial line of sight link design problems. Radioclimatological phenomena are adequately reviewed both for the precipitation effect and clear-air effect. The research focuses more on the clear-air effect of radioclimatological studies. Two Southern African countries chosen for case study in the report are Botswana and South Africa. To this end, radiosonde data gathered in Maun, Botswana and Durban, South Africa are used for model formulation and verification. The data used in the thesis ranges from three years to ten years in these two stations. Three to ten years of refractivity data gathered in Botswana and South Africa is used for the model formulation. On the other hand, eight months signal level measurement data recorded from the terrestrial line of sight link set up between Howard College and Westville Campuses of the University of KwaZulu-Natal, Durban South Africa is used for model verification. Though various radioclimatic parameters could affect radio signal propagation in the clear-air environment, this report focuses on two of these parameters. These two parameters are the geoclimatic factor and effective earth radius factor (k-factor). The first parameter is useful for multipath fading determination while the second parameter is very important for diffraction fading, modeling and characterization. The two countries chosen have different terrain and topographical structures; thus further underlying the choice for these two parameters. While Maun in Botswana is a gentle flat terrain, Durban in South Africa is characterized by hilly and mountainous terrain structure, which thus affects radioclimatological modeling in the two countries. Two analytical models have been proposed to solve clear-air radioclimatic problems in Southern Africa in the thesis. The first model is the fourth order polynomial analytical expression while the second model is the parabolic equation. The fourth order polynomial model was proposed after an extensive analysis of the eight month signal level measurement data gathered in Durban, South Africa. This model is able to predict the fade exceedance probabilities as a function of fade depth level. The result from the fourth order polynomial model is found to be comparable with other established multipath propagation model reviewed in the thesis. Availability of more measurement data in more location will be necessary in future to further refine this model. The second model proposed to solve clear-air propagation problem in the thesis is the modified parabolic equation. We chose this technique because of its strength and its simplistic adaptation to terrestrial line of sight link design problem. This adaptation is possible because, the parabolic equation can be modified to incorporate clear-air parameters. Hence this modification of the parabolic equation allows the possibility of a hybrid technique that incorporates both the statistical and mathematical procedures perfectly into one single process. As a result of this, most of the very important phenomena in clear-air propagation such as duct occurrence probabilities, diffraction fading and multipath fading is captured by this technique. The standard parabolic equation (SPE) is the unmodified parabolic equation which only accounts for free space propagation, while the modified parabolic equation (MPE) is the modified version of the parabolic equation. The MPE is classified into two in the thesis: the first modified parabolic equation (MPE1) and second modified parabolic equation (MPE2). The MPE1 is designed to incorporate the geoclimatic factor which is intended to study the multipath fading effect in the location of study. On the other hand, MPE2 is the modified parabolic equation designed to incorporate the effective earth radius factor (k-factor) intended to study the diffraction fading in the location of study. The results and analysis of the results after these modifications confirm our expectation. This result shows that signal loss is due primarily to diffraction fading in Durban while in Botswana, signal loss is due primarily to multipath. This confirms our expectation since a flatter terrain attracts signal loss due to multipath while hilly terrain attracts signal loss due to diffraction fading.
Correlation of rain dropsize distribution with rain rate derived from disdrometers and rain gauge networks in Southern Africa.
(2011) Alonge, Akintunde Ayodeji.; Afullo, Thomas Joachim Odhiambo.
Natural phenomena such as rainfall are responsible for communication service disruption, leading to severe outages and bandwidth inefficiency in both terrestrial and satellite systems, especially above 10 GHz. Rainfall attenuation is a source of concern to radio engineers in link budgeting and is primarily related to the rainfall mechanism of absorption and scattering of millimetric signal energy. Therefore, the study of rainfall microstructure can serve as a veritable means of optimizing network parameters for the design and deployment of millimetric and microwave links. Rainfall rate and rainfall drop-size are two microstructural parameters essential for the appropriate estimation of local rainfall attenuation. There are several existing analytical and empirical models for the prediction of rainfall attenuation and their performances largely depend on regional and climatic characteristics of interest. In this study, the thrust is to establish the most appropriate models in South African areas for rainfall rate and rainfall drop-size. Statistical analysis is derived from disdrometer measurements sampled at one-minute interval over a period of two years in Durban, a subtropical site in South Africa. The measurements are further categorized according to temporal rainfall regimes: drizzle, widespread, shower and thunderstorm. The analysis is modified to develop statistical and empirical models for rainfall rate using gamma, lognormal, Moupfouma and other ITU-R compliant models for the control site. Additionally, rain drop-size distribution (DSD) parameters are developed from the modified gamma, lognormal, negative exponential and Weibull models. The spherical droplet assumption is used to estimate the scattering parameters for frequencies between 2 GHz and 1000 GHz using the disdrometer diameter ranges. The resulting proposed DSD models are used, alongside the scattering parameters, for the prediction and estimation of rainfall attenuation. Finally, the study employs correlation and regression techniques to extend the results to other locations in South Africa. The cumulative density function analysis of rainfall parameters is applied for the selected locations to obtain their equivalent models for rainfall rate and rainfall DSD required for the estimation of rainfall attenuation.
Design and analysis of metamaterial based microstrip patch antennas for wireless applications.
(2023) Ajewole, Bukola Doyinsola.; Kumar, Pradeep.; Afullo, Thomas Joachim Odhiambo.
Due to the tremendous growth of wireless communication applications, there is an enormous demand for more compact antennas with high speed, wider coverage, high gain, and multi-band properties. The microstrip patch antennas (MPAs) and multiple-input multiple-output (MIMO) antennas with high gain and multi-band properties are suitable to fulfil these requirements. MPAs have been found to possess unique qualities such as light weight, low profile, easy fabrication, and integration. However, the low gain, narrow bandwidth, and mutual coupling in the MIMO antennas limit the performance of MIMO systems. Several techniques have been studied and implemented over the years, but they are not without limitations. The utilization of artificial materials such as metamaterials has proven to be efficient in overcoming the limitations of MPAs. Due to the advancement in modern technology, it is necessary to study and use recently developed metamaterial structures. Metamaterials (MeTMs) are artificially engineered materials with electromagnetic properties that are not found in nature. MeTMs are used due to their electric and magnetic properties. The goal of this thesis is to design and investigate a novel metamaterial structure which can be integrated into the microstrip patch antennas for improving their performance. The design, simulation, and measurement of the metamaterial is carried out on the Computer Simulation Technology (CST) studio suite, Advance Design Systems (ADS) software, MATLAB, and the Rohde and Schwarz network analyzer etc. In this thesis, a novel I-shaped metamaterial (ISMeTM) structure is proposed, designed, and investigated. The proposed novel ISMeTM unit cell structure in this work has a characteristic shape that distinguishes it from earlier multi-band MeTMs in the literature. The structure's unit cell is designed to have an overall compact size of 10 mm × 10 mm. The structure generates transmission coefficients at 6.31 GHz, 7.79 GHz, 9.98 GHz, 10.82 GHz, 11.86 GHz, 13.36 GHz, and 15. 5 GHz. These frequency bands are ideal for multi-band satellite communication systems, C, X, and Ku-bands, and radar applications etc. The performance of the MPA is improved in this work, by integrating a novel square split ring resonator (SSRR) metamaterial. The performance of the proposed antenna is investigated and analyzed. The SSRR is designed to have a dimension of 25 x 21.4 x 1.6 mm2 which is the same dimension as the radiating patch of the MPA. The SSRR is etched over the antenna, and it operates at single operating frequency of 5.8 GHz with improved gain from 4.04 to 5.3 dBi. Further, the MPA with improved parameters for multiband wireless systems is designed, analyzed, fabricated, and measured. The proposed design utilizes the ISMeTM array as superstrate with the area of 70 x 70 mm2. The superstrate is etched over a rectangular MPA exhibiting multi-band properties. This antenna resonates at 6.31, 9.65, 11.45 GHz with increased bandwidth at 240 MHz, 850 MHz, and 1010 MHz. The overall gain of the antenna increases by 74.18%. The antenna is fabricated and measured. The simulated results and the measured results are found to be in good agreement. The mutual coupling and low gain problems in MIMO patch antennas is also addressed in this thesis. A 3 x 5-unit cell array of the ISMeTM is used as a superstrate over a two port MIMO patch antenna. The two port MIMO antenna with the superstrate provides triple-band operation and operates over three resonance frequencies at 6.31, 9.09, and 11.41 GHz. A mutual coupling reduction of 26 dB, 33 dB, and 22 dB for the first band, second band and third band, respectively is attained. In this thesis, a novel I-shaped metamaterial structure is introduced, which produces multiband operation. The presented metamaterial is suitable for various multiband wireless communication applications. The integration of a square split ring resonator metamaterial enhances the performance of the antenna. Using the I-shaped metamaterial a high gain multiband microstrip antenna is designed. The I-shaped metamaterial array is utilized to improve the performance of the MIMO antenna. Various antenna parameters confirm that the presented MIMO antenna is suitable for multiband wireless communications.
Design and investigation on substrate integrated waveguide fed dielectric resonator antennas for d-band applications.
(2023) Chemweno, Emmanuel Kiprop.; Kumar, Pradeep.; Afullo, Thomas Joachim Odhiambo.
This thesis is devoted to the design of substrate integrated waveguide (SIW) fed dielectric resonator antennas (DRAs) for D-band applications. These antennas are necessary to establish high-speed communication links in wireless communication networks so as to support the emerging broadband applications such as the internet of things (IoTs), smart cities, virtual reality among others. Some of these applications demand for networks that can support high data rates and low latencies that exceed the capabilities of 5G networks. Consequently, communication systems are projected to operate in the millimeter wave (mm-wave) and terahertz (THz) frequencies. The D-band frequency spectrum is attractive for utilization in 6G communication systems owing to its vast bandwidths and is capable of very high data rates up to terabits per second (Tbps). However, this band suffers the limitations of short propagation distances due to the increased path losses at high frequencies. These effects can be mitigated by efficient antenna designs characterized by broad bandwidths and high-gains with low-loss interconnect networks. In addition, antenna structures with low profiles are attractive for ease of integration with other front-end devices. In this work, the substrate integrated waveguide fed dielectric resonator antenna is the preferred topology for the antenna design. Three different wideband antenna designs are presented and analyzed. The wideband operation of the presented designs is achieved through the higher-order mode (HOM) excitation of the dielectric resonator (DR) element to achieve multiple resonances in this frequency band. Adjacent resonances are merged together using various impedance matching techniques to enhance the antenna bandwidth. These designs investigate on different impedance matching techniques such as the use of defected ground structures (DGS), inductive metal vias (posts), cross-slots among others for antenna bandwidth enhancement and gain improvement. This work extends further the design of single element antenna to multiple-input multiple-output (MIMO) antenna design. A technique for mutual coupling reduction in closely packed antenna elements, which is based on metamaterial polarization rotation is presented and investigated. The investigation on the performance of the antennas is carried out using the commercial CST Microwave Studio full-wave electromagnetic simulator. The simulation results are analyzed in terms of the bandwidth, gain, radiation efficiency and radiation characteristics. The first design presents a SIW-DRA operating between 122.58 GHz and 139.51 GHz. The antenna exhibits multiple resonances at 123.64 GHz, 125.76 GHz, 127.4 GHz, 129.9 GHz, 134.9 GHz and 137.7 GHz. The design investigates the use of DGS and iristype discontinuity techniques for impedance matching improvement of a multi-resonant antenna. Simulation results show that the applied techniques are effective in merging together the adjacent bands of a multiband antenna for bandwidth enhancement. The antenna achieves a -10 dB impedance bandwidth of 13.4%, a peak gain of 12.3 dBi maximum directivity of 13.14 dBi and a high radiation efficiency of 84%. In addition, the antenna possesses stable broadband radiation patterns across the frequency band of operation. The second design presents a novel approach for the transformation of a dual-band SIW-DRA to a broadband antenna design. The design proposes systematic and sequential application of impedance matching techniques to improve the impedance matching in the stop band of the dual-band antenna without deterioration of its performance in the passbands. In the development of this approach, two preliminary designs are presented and investigated. The first preliminary design investigates the use of inductive metal vias in the SIW feeding structure for bandwidth enhancement. The effects of incorporating inductive via and DGS on the SIW feed structure of a dual-band antenna operating between 140.82 GHz - 145.24 GHz and 147.27 GHz - 151.02 GHz with a relatively narrow stop band of 2.03 GHz are investigated. The simulated results show that the inductive via and DGS effectively merge together the passbands of a dual-band antenna to achieve a wideband response of 138.27 GHz - 150.95 GHz. The second preliminary design presents a dual-band antenna operating between 126.95 GHz - 136.5 GHz and 139.67 GHz - 149.48 GHz in the lower and upper-frequency bands. The antenna is optimized for dual-band operation through the modification of the feeding slot to an I-shape to achieve a bandwidth 9.55 GHz and 9.81 GHz, representing fractional bandwidths of 7.2% and 6.78% in the lower and upper-frequency bands respectively. The impedance matching in the relatively wide stop band can be improved to merge together the passbands of the dual-band antenna to achieve a wideband response. This transformation is achieved through the use of inductive via, matching stub and DRA offset techniques in the dual-band antenna design. These techniques are systematically applied to the dual-band design and the parameters optimized to achieve a high-gain and wide bandwidth SIW-DRA. The antenna operates between 123.97 GHz and 152.13 GHz, with a -10 dB impedance bandwidth of 20.39% at the center frequency of 138.05 GHz, exhibiting a high gain of 11.67 dBi, directivity of 13.36 dBi and maximum total radiation efficiency of 79%. The radiation characteristics of the higher-order resonances excited at 124.38 GHz, 125.22 GHz, 130.28 GHz, 140.72 GHz, 141.59 GHz, 143.47 GHz, 149.7 GHz and 151.17 GHz show broadside radiation patterns. The research also focuses on the design of a wideband and low-isolation 2 × 2 SIWDRA based MIMO antenna. Initially, a single-element SIW-DRA is designed based on higher-order mode excitation with the antenna exhibiting multiple resonances. Different impedance matching techniques involving the embedding of inductive metal vias in the SIW feed, cross-slot feed and stepped-impedance sections are employed to minimize reflections and to achieve a good impedance matching between 136.68 GHz – 166.28 GHz. A -10 dB bandwidth performance of 19.5%, a gain of 11.06 dBi and a high radiation efficiency of 84% is achieved. Two antenna elements are linearly arranged with zero interelement distance in a 2 × 2 MIMO configuration to achieve high integration of antenna elements in a given space. A metamaterial-based decoupling network is investigated for isolation enhancement in the 2 × 2 MIMO configuration. The decoupling network is designed as a metamaterial polarization rotator (MTMPR) wall to rotate the polarization state of the electromagnetic wave transmitting through it. The MTMPR wall is integrated with the MIMO antenna for mutual coupling reduction. The Simulation results show that the MTMPR wall does not degrade the bandwidth performance of the MIMO antenna, and the presented design achieves an isolation performance greater than 21.16 dB across the entire bandwidth of operation. Besides the isolation, the antenna is analyzed by evaluating its diversity metrics. MIMO diversity metrics such as the envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), channel capacity loss (CCL) and the total active reflection coefficient (TARC) are evaluated. The MIMO design achieves an ECC of 0.008, DG > 9.9 between the two ports, MEG < 3 dB, TARC close to -10 dB for different phase angles of the input excitation and a CCL below 0.4 bits/s/Hz. The performances of the presented SIW-DRA designs are compared with published results and confirmed to meet the established minimum criteria for the appraisal of the presented designs. The results show that the presented designs are suitable for application in future 6G wireless systems.
Determination of millimetric signal attenuation due to rain using rain rate and raindrop size distribution models for Southern Africa.
(2014) Malinga, Senzo Jerome.; Afullo, Thomas Joachim Odhiambo.
The advantages offered by Super High Frequency (SHF) and Extremely High Frequency (EHF) bands such as large bandwidth, small antenna size, and easy installation or deployment have motivated the interest of researchers to study those factors that prevent optimum utilization of these bands. Under precipitation conditions, factors such as clouds, hail, fog, snow, ice crystals and rain degrade link performance. Rain fade, however, remains the dominant factor in the signal loss or signal fading over satellite and terrestrial links especially in the tropical and sub-tropical regions within which South Africa falls. At millimetre-wave frequencies the signal wavelength approaches the size of the raindrops, adversely impacting on radio links through signal scattering and absorption. In this work factors that may hinder the effective use of the super high frequency and extremely high frequency bands in the Southern African region are investigated. Rainfall constitutes the most serious impairment to short wavelength signal propagation in the region under study. In order to quantify the degree of impairment that may arise as a result of signal propagation through rain, the raindrops scattering amplitude functions were calculated by assuming the falling raindrops to be oblate spheroidal in shape. A comparison is made between the performance of the models that assume raindrops to be oblate spheroidal and those that assume them to be spherical. Raindrops sizes are measured using the Joss-Waldvogel RD-80 Distrometer. The study then proposes various expressions for models of raindrops size distributions for four types of rainfall in the Southern Africa region. Rainfall rates in the provinces in South Africa are measured and the result of the cumulative distribution of the rainfall rates is presented. Using the information obtained from the above, an extensive calculation of specific attenuation and phase shift in the region of Southern Africa is carried out. The results obtained are compared with the ITU-R and those obtained from earlier campaigns in the West African sub region. Finally, this work also attempts to determine and characterize the scattering process and micro-physical properties of raindrops for sub-tropical regions like South Africa. Data collected through a raindrop size measurement campaign in Durban is used to compare and validate the developed models.
Determination of rainfall parameters for specific attenuation due to rain for different integration times for terrestrial line-of-sight links in South Africa.
(2016) Nabangala, Mary.; Afullo, Thomas Joachim Odhiambo.; Alonge, Akintunde Ayodeji.
Currently, there have been large demand for end-user services that use large bandwidths, while requiring best throughputs; these requirements are often not realistic because of meagre allocation of radio resources. Consequently, for many networks, the traditional option of migrating to higher frequency bands in the microwave and millimeter wave spectrum (3-300 GHz) is often the immediate solution. However, this option suffers a huge drawback most especially at geographical locations which experience signal deterioration from larger levels of hydrometeors (presence of water in the atmosphere). More importantly, the influence of ubiquitous hydrometeors such as precipitation, is reputed to be a major constraint to communication links between base stations at microwave and millimeter bands. This often cripples many radio networks, as a result of incessant and spontaneous outages experienced during rainfall events. Therefore, there is need for radio system engineers to acquire sufficient information on effects of rain in a particular locality for planning and design of reliable communication links. In this work, the choice of approaching this problem tallies with the International Telecommunication Union (ITU) concept of rainfall rate point estimation but with emphasis on measurements at lower integration time of 30-seconds. This dissertation considers local rainfall rate measurements from 10 locations across South Africa at 5-minute integration time as obtained from South African Weather Services. Using rainfall measurements at one-minute and 30-second data from the coastal city of Durban (29°52’S, 30°58’E), various rainfall rate conversion models are obtained for these selected locations by applying rainfall statistics at higher integration time. Power-law functions obtained over South Africa reveals that rainfall statistics at 30-second integration time provides more information compared with one-minute and 5-minute integration times. In addition, a comparison of these results with ITU-R estimations have shown a close agreement with rainfall rates at 99.99% availability at the investigated locations. Furthermore, a comparison of rainfall Drop Size Distribution (DSD) at 30-second and one-minute integration time over Durban is undertaken to establish temporal variability in disdrometer measurements. These variations are compared using statistical DSD models of lognormal and modified gamma distributions with two parameter estimation techniques: Method of Moments (MM) and Method of Maximum Likelihood (ML). Datasets employed are subset rainfall measurements with seasonal cycles comprising of summer, autumn, winter and spring, and on lumped yearly basis. Finally, investigations of the effects of rainfall integration time on rainfall attenuation are compared over Durban using one-minute and 30-second data. For this purpose, Mie scattering theory is employed to calculate the power-law coefficients and the frequency dependency of rainfall measurements at 30-seconds integration time.
Effective earth radius factor (the k-factor) distribution for southern Africa.
(2005) Kemi, Odedina Peter.; Afullo, Thomas Joachim Odhiambo.
Proper radio link design requires an accurate prediction of the effective earth radius factor (the kfactor) distribution, for the location where propagation is intended. Though a median value of k equals 4/3 is normally use for communication design purposes, in reality the true k-factor values differ, for different locations, globally. The effective earth radius factor distribution for Southern Africa was evaluated in the dissertation. The two Southern African countries chosen for the study are Botswana and Republic of South Africa. The dissertation reports in detail a study on the topic using three years radiosonde data obtain in Maun, Botswana and ten months radiosonde data collected in Durban, South Africa. An analytical model was proposed, which predicts the probability density function of the k-factor for the Southern Africa using the data from these two countries. Also a comparison of the data from the two countries was done in the analysis and reported in the write-up. The application ofthe work was also investigated and reported by simulating a radio link between Sherwood and Umlazi in Kwazulu-Natal Province of South Africa. The consequence of using inappropriate design value of k on link reliability was also investigated and reported. Recommendation for future work was given in the concluding chapter for future improvement on the study. Radio communication designers will find the results obtain in the report useful.
A flexible statistical framework for the characterization and modelling of noise in powerline communication channels.
(2015) Nyete, Abraham Mutunga.; Afullo, Thomas Joachim Odhiambo.; Davidson, Innocent Ewean.
One communication medium that has received a lot of interest in recent years is the power line channel, especially for the delivery of broadband content. This channel has been traditionally used to carry electrical power only. But with the recent advancements in digital signal processing, it is now possible to realize communications through the power grid, both in narrowband and broadband. The use of the power line network for telecommunication purposes constitutes what is referred to as powerline carrier communications or simply powerline communications (PLC). The biggest incentive for PLC technology use is the fact that the power line network is already in place, which greatly reduces the communication network set up cost, since no new cabling layout is required. PLC technology is widely applied in home networking, broadband internet provision and smart grid solutions. However, the PLC channel presents a very hostile communication environment. And as such, no consideration has been made in the design of traditional power line network to accommodate communication services. Of all the PLC channel impairments which include frequency-dependent attenuation, frequency selectivity, multipath and noise, noise is the biggest threat to communication signals. This noise manifests itself in form of coloured background noise, narrowband interference and impulsive noise. A thorough understanding of this noise distribution is therefore crucial for the design of a reliable and high performing PLC system. A proper understanding of the noise characteristics in the PLC channel can only be realized through noise measurements in live power networks, and then analyzing and modeling the noise appropriately. Moreover, the noise scenario in power line networks is very complex and therefore cannot be modeled through mere analytical methods. Additionally, most of the models that have been proposed for the PLC noise previously are mere adaptations of the measured noise to some existing impulsive noise models. These earlier modeling approaches are also rigid and model the noise via a fixed set of parameters. In the introductory work in this thesis, a study of orthogonal frequency division multiplexing (OFDM) as the modulation of choice for PLC systems is presented. A thorough survey of the salient features of this modulation scheme that make it the perfect candidate for PLC modulation needs is presented. In the end, a performance analysis study on the impact of impulsive noise on an OFDM based binary phase shift keying (BPSK) system is done. This study differs from earlier ones in that its focus is on how the elementary parameters that define the impulsive noise affect the system, a departure from the usual norm of considering the overall noise distribution. This study focuses on the impact of interarrival times (IAT), pulse amplitudes as well as pulse widths, among other parameters. In the first part of the main work in this thesis, results of an intensive noise measurement campaign for indoor low voltage power line noise carried out in various power line networks, in the Department of Electrical, Electronic and Computer Engineering buildings at the University of KwaZulu-Natal, Howard campus are presented. The noise measurements are carried out in both time and frequency domains. Next, the noise measurements are then analyzed and modeled using two very flexible data modeling tools; nonparametric kernel density estimators and parametric alpha stable (α-stable) distributions. The kernel method’s ability to overcome all the shortcomings of the primitive histogram method makes it very attractive. In this method, the noise data structure is derived straight from the data itself, with no prior assumptions or restrictions on the data structure, thus effectively overcoming the rigidity associated with previous noise models for power line channels. As such, it results in density estimates that “hug” the measured density as much as possible. The models obtained using the kernel methods are therefore better than any parametric equivalent; something that can always be proven through goodness of fit tests. These models therefore form an excellent reference for parametric modeling of the power line noise. This work forms the author’s first main contribution to PLC research. As a demonstration of the kernel models suitability to act as a reference, parametric models of the noise distribution using the alpha stable (α-stable) distribution are also developed. This distribution is chosen due to its flexibility and ability to capture impulsiveness (long-tailed behaviour), such as the one found in power line noise. Stable distributions are characterized by long/fat tails than those of the Gaussian distribution, and that is the main reason why they are preferable here since the noise characteritics obtained in the kernel technique show visible long/heavy tailed behavior. A parameter estimation technique that is based on quantiles and another on the empirical characteristic function are employed in the extraction of the four parameters that define the characteristic function of the α-stable distribution. The application of the α-stable distribution in other signal processing problems has often been over-simplied by considering the symmetric alpha stable distribution, but in this thesis, the general α-stable distribution is used to model the power line noise. This is necessary so as to ensure that no features of the noise distribution are missed. All the models obtained are validated through error analysis and Chi-square fitness tests. This work forms the author’s second main contribution to PLC research. The author’s last contribution in this thesis is the development of an algorithm for the synthesis of the power line as a Levy stable stochastic process. The algorithm developed is then used to generate the PLC noise process for a random number of alpha stable noise samples using the alpha stable noise parameters obtained in the parametric modeling using stable distributions. This algorithm is generalized for all admissible values of alpha stable noise parameters and therefore results for a Levy stable Gaussian process are also presented for the same number of random noise samples for comparison purposes.

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