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Masters Degrees (Electronic Engineering)

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

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Browsing Masters Degrees (Electronic Engineering) by Author "Alonge, Akintunde Ayodeji."

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    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.
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    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.
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    Study of lower sampling intervals on rainfall queue characteristics over Radio Links in South Africa.
    (2017) Mazibuko, Godfrey Nkululeko.; Afullo, Thomas Joachim Odhiambo.; Alonge, Akintunde Ayodeji.
    Rainfall attenuation in tropical and subtropical regions of the world has continued to attract great interest; as there is a urgent emphasis on proper spectrum management and sharing, particularly at microwave and millimeter bands above 10 GHz. To this end, there have been arguments pertaining to the need to improve the ‘sensing’ of rainfall events to enhance the opportunities provided by adaptive rain fade mitigation schemes, while conserving base station power requirements during rainy events. To implement this approach, an extensive understanding of rainfall time series via the available statistical tools is often required to properly harness the characteristics of rainfall behavior. To this end, a study was undertaken to examine the behavior of rainfall and its impact on radio links at 1-minute sampling time by using the Queueing Theory Technique (QTT). Interesting results were obtained in the process of the study, except that the effect of the sampling time on rainfall queues remained unknown. Therefore, this thesis presents the investigation of the sampling time effects on rainfall queues over radio links in Durban, South Africa. Rainfall measurements were collected at 30-second sampling time using the RD-80 Joss–Waldvogel (JW) distrometer in Durban (29o52’S, 30o58’E), the same location where the 1-minute data was previously collected. As before, the rainfall data is classified into four rainfall regimes, namely drizzle, widespread, shower and thunderstorm. The queue parameters required for rainfall traffic analysis such as inter-arrival time and service-time distribution are empirically determined to be Erlang-k distributed, whereas the overlap time is exponentially distributed. It is thus established that the queue discipline for rain spikes over radio waves is a non-Markovian process (Ek/Ek/s/∞/FCFS). Comparison between the 30-second rainfall queues results and previous results of 1-minute sampling time, shows that more rainfall spikes are revealed at 30-second sampling time. Furthermore, it is determined that there is a strong polynomial relationship between the 30-second and 1-minute sampling time data – hence some of the 1-minute data may be converted into 30-second data by using the polynomial function, with the appropriate polynomial coefficients according to rainfall queue parameters in each regime. The converted data is amalgamated with the actual 30-second data for the investigation of the rainfall long-term behavior. It is found that the rainfall long-term behavior resembles the behavior of the short-term data - hence implying that the rainfall process at 30-second sampling time in Durban has the attributes of a self-similar process. From rain attenuation investigation, it is determined that since more rain spikes are evident in the 30-second data, the former has higher rain attenuation exceedance values (R0.01) compared to the 1-minute data.