Masters Degrees (Electronic Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6868

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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.
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.
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.
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.
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.
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.
Human face shaped microstrip patch antennas for ultra-wideband applications.
(2019) Dharmarajan, Anandhi.; Kumar, Pradeep.; Afullo, Thomas Joachim Odhiambo.
Abstract available in pdf.
Metasurface based MIMO microstrip antenna with reduced mutual coupling.
(2022) Dubazane, Sthembile Promise.; Kumar, Pradeep.; Afullo, Thomas Joachim Odhiambo.
In this thesis, a negative permeability (μ) metasurface is used to reduce the mutual coupling of a 2-port Multiple-Input Multiple-Output (MIMO) rectangular inset fed microstrip antenna. That was designed using the transmission model of analysis, simulated and optimized using CST microwave studio. The microstrip antenna that operates at the (5.9-6.1) GHz band is designed for 5G applications, at the extended 6 GHz band (5.925-7.125) GHz. The extended band was chosen because of its new additional spectrum, which results in less noise interference. Three metasurface wall based antenna designs and two metasurface superstrate based antenna designs are conducted. The metasurface wall based antenna designs are formulated by placing a metasurface wall vertically between the two radiating antenna elements. The metasurface superstrate based antenna designs are formulated by suspending a metasurface superstrate above the 2-port microstrip antenna. Both the metasurface wall and superstrate are made up metasurface unit cells, which are formulated by periodic split ring resonators printed on a FR-4 dielectric substrate. The metasurface cells are responsible for introducing a negative permeability medium, which converts the electromagnetic propagating waves into evanescent hence rejecting mutual coupling. In the first metasurface based antenna design, a single metasurface wall is vertically placed between the two microstrip antenna elements. A slight increase of 0.5 dB in mutual coupling is observed. In the second design, a double metasurface wall is vertically placed between the two antenna elements. A mutual coupling reduction of 11 dB is achieved. In the third design a triple metasurface wall is also placed between the two antenna elements, a mutual coupling reduction of 25 dB and up to 17 % bandwidth enhancement is achieved. In the fourth design a single metasurface superstrate is suspended above the 2-port microstrip antenna. A mutual coupling reduction of 32 dB is achieved. Lastly, in the fifth design a metasurface superstrate is also suspended above the 2-port microstrip antenna. A mutual coupling reduction of 22 dB, a 38% bandwidth enhancement and a 2.09 dB gain enhancement is achieved.
Performance analysis of LAN, WAN and WLAN in Eritrea.
(2006) Kakay, Osman Mohammed Osman.; Afullo, Thomas Joachim Odhiambo.
The dissertation addresses the communication issues of interconnecting the different government sectors LANs, and access to the global Internet. Network capacities are being purposely overengineered in today's commercial Internet. Any network provider, be it a commercial Internet Service Provider (ISP) or Information Technology Service department at government sector, company or university site, will design network bandwidth resources in such a way that there will be virtually no data loss, even during the worst possible network utilization scenario. Thus, the service delivered by today's end-to-end wide area Internet would be perfect if it wasn't for the inter-domain connections, such as Internet access link to the ISP, or peering points between ISPs. The thesis studies the performance of the network in Eritrea, displaying the problems of Local Area Networks (LANs) and Wide Area Networks (WAN) and suggesting initial solutions and investigating the performance of (WAN) through the measured traffic analysis between Asmara LAN and Massawa LAN, using queuing theory system (M/M/1 and M/M/2) solution. The dissertation also uses OPNET IT Guru simulation software program ·to study the performance of LAN and WLAN in Eritrea. The items studied include traffic, collision, packet loss, and queue delay. Finally in order to follow the current trends, we study the performance ofVOIP links in Eritrean WANs environment, with a focus on five different link capacities: 28 kbps, 33 kbps, 64 kbps, and 128 kbps for voice and 256/512 kbps for voice and data. Using the R value as a measure of mean opinion score (MOS), we determine that the 33 kbps link would be adequate for Eritrean WANs.
Performance analysis of optical wireless communication systems in a warm-summer Mediterranean climatic region.
(2017) Kolawole, Olabamidele Olanrewaju.; Afullo, Thomas Joachim Odhiambo.; Owolawi, Pius Adewale.
Abstract available in PDF file.
Power line communication (PLC) channel measurements and characterization.
(2014) Mosalaosi, Modisa.; Afullo, Thomas Joachim Odhiambo.
The potential of the power line to transport both power and communication signals simultaneously has been realized and practiced for over a century, dating back to the 1900’s. Since the key aspect of power line communications being its expansivity, its implementations were largely as a retrofit technology. This motivation of power line communication is typical for low-, medium-, and high voltage distribution networks. Beyond the “last mile” part, there’s an uprising appeal for intra-building networks currently targeted for home automation (smart homes/buildings) and in-building networking. The optimum use of the existing power line channels has been a focus area for researchers and designers, with the inherent channel hostility proving a serious drawback for high speed data communications. The low-voltage electrical network has unpredictable noise sources, moreover it has two other main disadvantages as a communication channel. The first short coming has to do with the unknown characteristics of the power cable and topology of the network, the second arises from the time-dependent fluctuation of the impedance level of the power line as the loads are switched into and out of the power line network in an unpredictable manner. These factors determine the behaviour of the power line channel when a high frequency signal is impressed on it. This study has shown that the behaviour of indoor power line channels can be captured using a multipath based model even with limited qualitative and/or quantitative knowledge of the network topology. This model is suitable for typical indoor power line channels where knowledge of the topology is near impossible. Some of the feed parameters are obtained through measurements. With sufficient adjustment of control parameters, this model was successfully validated using sample measured channels from the numerous measurements. Through noise measurements, this study has established that impulsive noise is the rifest in the frequency band of interest. The impulsive energy rises well above background noise, which translates to possible data “black outs”. The statistics of the components of this noise are presented. A model of sufficient simplicity is used to facilitate the qualitative description of the background noise through its power spectral density. Two descriptions are provided in terms of the worst and best case scenarios of the background noise occurrences. The model has a good macroscopic capture of the noise power spectral density, with narrow-band interference visible for the worst case noise. Due to the multipath nature of the power line channel, this study also presents the dispersive characteristics of the power line as a communication channel. The power delay profile is used to determine parameters such as first arrival delay, mean excess delay, root mean square delay spread and maximum delay spread. The statistics of these parameters are presented. Also, the coherence bandwidth of power line channels is studied and its relationship with the rms delay spread is developed. It is in view of this work that further research in power line communication and related topics shall be inspired.
Power line communication channel modelling.
(2014) Zwane, Fulatsa.; Afullo, Thomas Joachim Odhiambo.
Power line communication impedance profiling and matching for broadband applications.
(2018) Chelangat, Florence.; Afullo, Thomas Joachim Odhiambo.; Mosalaosi, Modisa.
Power line communication(PLC) is a wired communication technology that has recently re- ceived a lot of attention due to its attractive prospects towards home and /or neighborhood network applications as well as smart grid technologies. It allows establishing digital com- munications without any additional wiring requirements. Effectively, one’s home and/or neighborhood wiring contributes into a smart grid to deploy various data services. It is well known that the power grid is one of the most pervasive infrastructure built to provide electricity to customers, therefore, utilizing this infrastructure for digital communications will only result in an ubiquitous telecommunications network. It is common practice to use wires to establish a physical connection in many telecommunications channels, but most electronic devices already have a pair of wires connected to the power lines. Therefore, these wires can be used to simultaneously establish digital communications. Thus, power line communications can be used as an alternative solution to more established technologies such as wireless, coaxial and optical communications. As a promising technology, PLC has attracted a lot of research and has become an active area of research which continues to evolve over time. Notwithstanding its advantages, PLC has issues, namely, severe noise at low frequencies and varying characteristic impedance. This is primarily because the power line channel was not originally designed to be used for communications, thus, it remains a harsh channel. Other challenges arise from the fact that there are different wiring practices around the world, unpredictable loading characteristics as well as differential- and common-mode characteristic impedance. As a result, there is a considerable amount of noise signal attenuation during data transmission. Loss of signal can be addressed by increasing the power at the transmitter, noise reduction and/or reducing channel attenuation to improve the signal-to-noise ratio. However, PLC modems are subject to legislation that impose a limit with regards to the signal levels in the lines. Power lines are good radiators at high frequencies which makes them behave like large antennas with the ability to intercept other radiations in the same frequency range. The radiated signal is proportional to the currents in the line, thus, increasing line currents will not solve the problem but would rather lead to violation of electromagnetic compatibility (EMC) regulations. In this work, an alternative solution is provided which seeks to address the issue of signal attenuation caused by the changing input impedance of a typical power line channel. The deleterious effects of noise are not considered since this work focuses on broadband PLC in the 1–30 MHz frequency range. The objective of this work was to design and build an impedance adaptive coupler to mitigate effects of channel attenuation caused by varying impedance. In this way, the propagating signal will “see” a uniform impedance and as a result the data output will be improved. The work was facilitated by measuring several impedance profiles of PLC channels in the band of interest. Typically, the network topology of PLC networks is not known and the building architectural blueprints are not always readily available. To overcome this issue,this work was performed on power line test-beds designed to mimic varied typical PLC network topologies. Moreover, there is an additional benefit in that it is possible to relate the output impedance profile to the network topology. The channel input impedance characteristics were determined in a deterministic manner by considering a power line network as a cascade of parallel resonant circuits and applying transmission line theory to develop the model. The model was validated by measurements with good agreement over the frequency range was considered. Several measurements were then used to determine the minimum, average and maximum input impedance that a signal will experience as it traverses the channel. It was found that, regardless of the network size (in terms of number of branches), the average input impedance is 354 ± 1.1 % Ω in the 1-30 MHz frequency band. Due to the unpredictable nature of the input impedance of the power line network, an impedance adaptive bidirectional coupler for broadband power line communications was designed. The impedance matching is achieved by using typical L-section matching networks in the 1–30 MHz band. The matching section of the coupler has the characteristics of a lowpass filter while the coupling section is a highpass filter, effectively forming a bandpass network. The simulated transfer characteristics of the designed coupler performs very well for impedances starting around 150 Ω and the performance improves a great deal as the impedance increases. The coupler can still be improved to accommodate much lower input impedances (as low as 50 Ω). However, based on the measured results of input impedance, it was observed that the power line channel impedance is statistically higher than 200 Ω most of the time which makes the presented design acceptable.
Rain Attenuation Modelling and Prediction for Optical Wireless Communication Systems in Durban, South Africa.
(2021) Buthelezi, Sabelo Qiniso.; Afullo, Thomas Joachim Odhiambo.; Mosalaosi, Modisa.
The continuous demand for more reliable wireless communication systems with extremely high data rates has accelerated various aspects of research topics to be able to meet future needs. One of the most crucial topics in the field of communication is free-space optics (also known as optical wireless communication). It is well-known that the performance of any optical wireless communication system is strongly influenced by the atmospheric conditions in a given environment. In foggy, rainy, and clear weather conditions, optical signals are known to be attenuated due to scattering. The received signal is diminished in the presence of snow, rain, or even haze. Rain and clear weather conditions will be the focus of this research as there is hardly snow or haze in South Africa, especially Durban since it is a subtropical region. In this research work, rain attenuation modelling and prediction will be done using an empirical method based on the relationship between the observed attenuation distribution and the related observed rain intensity distribution at a 30 second integration period. A disdrometer is used to obtain the rain intensity, and a power meter is used to log the received signal power level every 30 seconds to evaluate the influence of rain on the signal transmitted. The International Telecommunication Union (ITU-R) recommends targeting for 99.99 % system availability; as a result, the rainfall rate (R0.01) in the research region must be estimated for 0.01 percent of the time. The rain intensity and raindrop size distribution (DSD) modelling is then performed from the empirical method, obtaining R0.01 for Durban for all months throughout the experiment period. Using the disdrometer diameter ranges, the spherical droplet assumption is used to estimate the scattering parameters for frequencies between 2 GHz and 1000 GHz. The relationship between the received signal level and the intensity of rain for a particular weather condition at a specific time is then obtained. Transceivers with a fixed length of 7 meters between them, due to shortage of material such as the fiber cables to link the transceivers to the computer for data monitoring and logging, and for accurate alignment, were used to conduct these experiments. This relationship is compared against the French model at a wavelength of 850 nm. The main results obtained from this work reveal that there are extremely high attenuation values compared to the French model, which thus calls for further investigation to provide the optimum model that can accurately predict these effects for reliable optical wireless communications in Durban, South Africa.
Rain attenuation modelling for Southern Africa.
(2008) Mulangu, Chrispin Tshikomba.; Afullo, Thomas Joachim Odhiambo.
In order to address rain attenuation scattering of millimetric waves and microwave sin Botswana, we have employed a comparison technique to determine the Ro.o1 at fourteen diverse locations in Botswana. In addition we have identified two rain climatic zones for Botswana. We note that Matzler employs Mie Scattering technique to determine the specific attenuation due to rain in Central Europe. Both Matzler and Olsen use the exponential distribution of N(D) to calculate y. In this dissertation we use the Mie scattering approach, but assume several distributions, including the log-normal distribution of N(D) as expounded by Ajayi et aI., to determine y for tropical and subtropical regions of Africa. The results show that the extinction coefficients depend more strongly on temperature at lower frequencies than at higher frequencies for lognormal distribution: at selected frequencies, we record high attenuation values at rising SHF bands: at 300 GHz, tropical showers take on values of 12, 12.5, 11.9 and 14 dB/km for Gaborone, Francistown, Kasane and Selebi-Phikwe, respectively. The absorption coefficient is significant but decreases exponentially with rain temperature at lower microwave frequencies. The application of the proposed model (Continental Thunderstorm is shown using practical results from Durban) is corroborated using practical results from Durban. Further, based on attenuation measurements, it is found that the lognormal distribution is suitable for Durban at rain rates greater than or equal to 21 mm/h. At rain rates below this, the loss-Thunderstorm is the better fit. Finally in this dissertation the results show that for rainfall intensity below about 10 mm/h for Marshall-Palmer (MP), Joss-Drizzle (JD), Joss-Thunderstorm (JT) and Law-Parson (LP) distributions, and below about 4 mm/h for Continental-Showers (CS), Tropical Showers (TS), Continental Thunderstorms (CT) and Tropical Thunderstorm (TT) distributions, the specific rain backscattering follows Rayleigh scattering law where the rain drops are small with respect to the wavelength when the frequency is 19.5 GHz. At rain rates above 10 mm/h for exponential distribution, and above 4 mm/h for lognormal distribution, the specific backscattering follows Mie scattering law. When the received echo power from rain becomes significant, it contributes to the rise in the noise floor and the radar receiver can lose its target. In addition, the result shows that Mie backscattering efficiency is highest at a raindrop diameter of 4.7mm.
Rain cell size attenuation modelling for terrestrial and satellite radio links.
(2011) Akuon, Peter Odero.; Afullo, Thomas Joachim Odhiambo.
There is need to improve prediction results in rain attenuation in order to achieve reliable wireless communication systems. Existing models require improvements or we need fresh approaches. This dissertation presents a model of rain attenuation prediction for terrestrial and satellite radio links based on a novel approach. This approach postulates that the difference in rain attenuation for various locations is attributed to the dissimilar rain drop sizes and rain cell diameter sizes and that cell sizes derived from local measurements would depict the true nature of rain cells better than the cells derived from long term rain data gathered from different climates. Therefore all other link parameters used in the attenuation equation are presented by the use of mathematical analysis; but the rain cell size is derived from local rain rate measurements. The physical link aspects considered in the mathematical attenuation model are: the Fresnel ellipsoid of the link path, the effect of elevation angle, the rain cell diameter size and the shape of growth of rain rates in the cell. The effect of the elevation angle of the link on the scale of attenuation is accounted for through the proposed coefficient of elevation equation. The coefficient of elevation is considered to modify the size of the rain cell diameter in proportion to the elevation angle of the link and the rain rate growth is taken to be of the truncated-Gaussian form. On the other hand, the rain cell diameter is derived from rain rate measurements as a power law model and substituted in the attenuation expression. The rain cell size model evaluated in this dissertation is based on point rain rate measurement data from the disdrometer located at the University of KwaZulu-Natal, South Africa. The “Synthetic Storm” technique is applied to develop the rain cell diameter distributions and the rain cell diameter model. In addition, the impact of the rain cell diameter size model in site diversity and cellular network-area planning for the region is discussed. To validate the model for terrestrial links, attenuation data collected from Durban, South Africa is used while that for satellite links, attenuation data from 15 links which are located in tropical climatic zones are used. In each case, the new model is tested against some well-known global rain attenuation prediction models including the standard ITU-R models. The performance of the proposed models for the sampled radio links based on error estimations shows that improvements have been achieved and may be regarded as a universal tropical model especially for satellite links.
Rain rate and rain drop size distribution models for line-of-sight millimetric systems in South Africa.
(2006) Owolawi, Pius Adewale.; Afullo, Thomas Joachim Odhiambo.
Radio frequencies at millimeter wavelengths suffer greatly from rain attenuation. It is therefore essential to study rainfall characteristics for efficient and reliable design of radio networks at frequencies above 10GHz. These characteristics of rain are geographically based, which need to be studied for estimation of rain induced attenuation. The ITU-R, through recommendations P.837 and P.838, have presented global approaches to rain-rate variation and rain-induced attenuation in line-of-sight radio links. Therefore, in this dissertation characteristics of rainfall rate and its applications for South Africa are evaluated. The cumulative distributions of rain intensity for 12 locations in seven regions in South Africa are presented in this dissertation based on five-year rainfall data. The rain rate with an integration time of 60 minutes is converted into an integration time of 1 minute in accordance with ITU-R recommendations. The resulting cumulative rain intensities and relations between them are compared with the global figures presented in ITU-R Recommendation P.837, as well as with the work in other African countries, notably by Moupfuma and Martin. Based on this work, additional rain-climatic zones are proposed alongside the five identified by ITU-R for South Africa. Finally, the study compares the semi-empirical raindrop-size distribution models such as Laws and Parsons, Marshall and Palmer, Joss, Thams and Waldvogel, and Gamma distribution with the estimated South Africa models.

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Browsing Masters Degrees (Electronic Engineering) by Author "Afullo, Thomas Joachim Odhiambo."