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- ItemMeasurement and Evaluation of Electromagnetic Radiation Exposure from Antennas in Cellular Networks(KNUST, 2021-07) Akua, AchiaaWireless Technology including that of cellular systems uses radio and microwave energy which is nonionizing in nature, generated at base stations for its transmission via cellular antennas and microwave links to accessible areas for subscribers. The nonionizing radiation (NIR) energy is absorbable by living tissues including human skin and thus, becomes harmful when it exceeds certain thresholds. The health risks associated with exposure from base transceiver stations has gained attention as the demand for cellular services increases. This has led to an increase in communication infrastructures (Base Transceiver Stations), ushering some in human inhabitance to improve quality of service, as these services become a vital part of modern lifestyle. An increase in base transceiver stations, leads to increased cellular radiation pollution which is of public concern. It is therefore necessary to investigate the levels of cellular radiation to ensure that it public health safety limits are not violated. In this thesis, NIR level in power density at forty locations involving residential, commercial and University campuses, considering indoor and outdoor scenarios were measured and estimated with a radio frequency (RF) Explorer 6G Combo Spectrum Analyzer. The results were compared with the minimum safety limits of 4.055 W/m^2 for cellular systems in Ghana, formulated by the International Commission and Non-ionizing Radiation Protection (ICNIRP) and enforced by the National Communication Authority of Ghana (NCA). The maximum total level of radiation consisting of a cumulative of all deployed systems was found to be 862.9 (nW/m^2) for residence near base stations during evening hours and 242.6 (nW/m^2) at day time. The maximum and minimum levels recorded for other locations are 3.96 (nw/m^2) and 0.10 (nw/m^2) at residence away from base stations, 118.5 (nW/m^2) and 0.422 (nW/m^2) for commercial areas and 38.92 (nW/m^2) and 4.97 (nW/m^2) at the campuses. A standard deviation of 49.9 at three different sectors of a single base station was achieved. A highest radiation level of 305.6 (nw/m^2) was recorded at 7 pm of the 24-hour indoor measurement, while the cumulative average of 160.5 (nw/m^2) was recorded at the 24th hour. A percentage of the highest 862.9 (nW/m^2) radiation level recorded is less than 1% of 4.055( w/m^2) minimum safety limits recommended by the International Commission on Nonionizing Protection (ICNIRP). Thus, cellular system radiation emissions of the selected locations do not pose any health threat to the general public in their current capacity.
- ItemFlexible and Wearable Pattern-Reconfigurable Printed Monopole Antenna for On-Body Communication(KNUST, 2021-07) Philip, ArthurThe fundamental feature of reconfigurable antenna (RA) systems is the ability to modify its functional operating characteristics compared to conventional antenna systems. As the size of electronic devices continues to shrink with stringent space constraints, reconfigurable antennas provide a low-cost approach for introducing adjustable properties on a single antenna element. This is to eliminate the need for multiple single-purpose antennas in diversity applications. Recently, reconfigurable antennas have gained popularity in wearable devices and finding applications in health care for the diagnosis and treatment of diseases such as stroke and cancer in tissues. Many applications of wearable antennas in personal communication devices, military gadgets and emergency apparatus are continuously growing. It is required that on-body antennas are unobtrusive and highly efficient with conformable features that can be easily suited to the configuration of the human body. However, due to the conductive nature of the human body, up to about 50% of the radiated energy from conventional printed monopole antennas can be absorbed. This effectively renders the omnidirectional antenna unidirectional when mounted on or close to the human body. To this end, this current work proposes a simple technique to convert the conventional monopolar radiation pattern of a printed monopole antenna into a unidirectional radiation. This is shown among other advantages to significantly reduce specific absorption rate (SAR) and achieve circular polarization. The initial process begins with the design of a compact, low-profile, slotted-stepped planar monopole antenna (PMA) at the 2.45 GHz Industrial, Scientific and Medical (ISM) band. Further analysis presents an optimized reconfigurable extension of the antenna based on two switchable RF PIN diodes. This is incorporated in the antenna to asymmetrically steer the radiation pattern at different directions in specific operating modes. It is also shown that the frequency-radiation characteristics linkage that leads to shifts in the frequency while the radiation pattern is adjusted is fully decoupled in this design. Here, the switching effect of the radiation pattern does not cause any significant detuning in the operating frequency. This is further validated at varying antenna positions and excitation levels. To present a conformable form of the reconfigurable antenna, a flexible substrate material is chosen for the design. Flexibility and wearability tests of the antenna are performed at various degrees of bending and subsequent placement on a human phantom model. The on-body effects on the antenna are characterized in simulation and measured on real human body. Simulated results show stable radiation patterns, reflection coefficient (𝑆11<−20 𝑑𝐵) and a circular polarization at 2.45 GHz. Meanwhile, low simulated peak SAR of 0.46 𝑊/𝑘𝑔 and 0.39 𝑊/𝑘𝑔 averaged over 1𝑔 and 10𝑔 of tissue respectively are recorded when the antenna is mounted directly on the human body. This is achieved without the use of conventional large and bulky cavity-backed structures. Hence, the overall size of the antenna measures only a compact square size of 0.235𝜆, making it a very suitable candidate for on-body applications.
- ItemImproving Cell Edge Performance for LTE Network Using 0.8 Ghz and 2.6 Ghz Frequency Bands(KNUST, 2021-03) Abrokwa, Kofi KwartengTo provide maximum Physical Downlink Shared Channel (PDSCH) capacity for cell-edge Long Term Evolution (LTE) customers, the received signal strength from the Base Station (BS) to the User Equipment (UE) should be high. However, increasing power levels at the BS to ensure signal availability for users at the cell edge presents Inter-Cell Interference (ICI) in the LTE network, which drastically impacts the Quality of Service (QoS) negatively. As a solution to curb this problem, researchers have adopted several techniques such as Geometric Factor Model (GFM), Heterogeneous Network (HN), and Power Variation System (PVS) to assign a carrier frequency to users based on their respective distance from the base station to boost the signal at the cell edge. However, these methods do not include the current channel conditions present in a multipath fading environment which are the main concern that needs to be taken into consideration. It is therefore imperative to investigate the performance of the LTE network by considering the impairment in the wireless channel to see its corresponding effect on the user performance. The inclusion of these challenges in the wireless channel will give an idea of the performance of the LTE network and the means to improve it for the optimum benefit for the users. This work presents the performance of cell-edge users in the LTE network on 0.8 GHz low band and 2.6 GHz high band, signal propagation experiment in MATLAB\Simulink environment based on Markov model. Carrier aggregation provides a technique for LTE users to access the network using multiple frequency bands, which have varying penetration losses and enlarged bandwidth for the user. The low and high band frequencies used in this work help the user at the cell edge to achieve coverage and throughput at the same time in the LTE network. The simulated signal-to-noise ratio of the two frequencies achieves a better performance metric for customers to experience a good internet service. The average bit error rate (BER) for users using 0.8 GHz was 5.50e-5 while the average bit error rate for users using 2.6 GHz was 1.98e-4. Cell edge users using 0.8 GHz frequency carrier experienced an average of 92% throughput while those on 2.6 GHz experienced an average of 70% throughput. These results provide a realistic and reliable approach to mitigate cell edge challenges for LTE users than those achieved by other methods such as GFM, HN, and PVS used by earlier researchers.
- ItemUsing GIS and Multi Criteria Decision Making to Determine Suitable Dam Sites in The Upper West Region of Ghana(KNUST, 2019-10) Reduwan KassimThe availability of water for use is alarmingly becoming an issue of concern globally and if measures are not implemented to curb this, then the world over faces an impending water scarcity crisis. Studies conducted by the United Nations Environment Program (UNEP) indicate that by 2050, over two billion people will live under high water stress situations. This invariably would limit development and affect quality of lives. Water scarcity and water stress situations will also invariably lead to a decrease in Agricultural output. Dams provide an option for harvesting and storing water for various uses. Irrigation could also be a solution to the decline of agricultural output in the country. However, even though dams are designed to collect and store water for use, for them to function at optimum levels, they have to be sited appropriately. In Ghana, the Ghana Irrigation Development Authority (GIDA) is the government agency primarily tasked with the construction and management of dams. However selecting suitable sites for these dams is done manually and quiet subjectively. This traditional site selection process is tedious fails to accentuate certain terrain characteristics that are not readily visible and may only be highlighted in a GIS environment This study employs the use of GIS and Multi Criteria Decision Making (MCDM) in siting dams using five factors namely Slope, Rainfall, Soil type, protected zones and Settlements. The results shows a suitability map for dam sites. From the map, 4.3% of the study area is suitable for dam construction, 33% of the area averagely suitable, 53.9% poorly suitable and 8.8% unsuitable for dam construction. The study goes further to propose four specific dam sites, determined the profiles and estimates volumetric capacities of these sites and it was found that the sites had capacities of 219,000m3, 1,312,500m3, 557,666m3 and 375,000m3 respectively for dam sites 1, 2, 3 and 4. In conclusion, it is asserted that GIS is a powerful tool that can be effectively used to help in determining suitable sites for dam construction and provides an improvement on the current traditional site selection process employed by decision makers.
- ItemStrength Properties of Locally Constructed Rice Bunds in the Adansi North District of Ghana(KNUST, 2019-06) Dzandu Thomas,KwakuThe rice industry in Ghana faces challenges of low productivity, low yield and poor grain quality, resulting in overwhelming import dependence. Rice can be cultivated all year round with bund and irrigation. Also, land originally not suitable for rice cultivation can be used when bund is considered. Successive Governments over the years launch series of flagship programs which are aimed at reducing rice imports, poverty alleviation and employment creation which many have failed. Though bunds are widely used in many countries and other parts of Ghana, the system is relatively new in the Adansi North District of the Ashanti region of Ghana. The purpose of this study is to examine the durability and soil strength properties of rice bund constructed by local farmers. Three farmer’s fields KB, FB and PB were studied to ascertain their strength properties and their durability. Four bunds were constructed on a research plot labeled RB1, RB2, RB3 and RB4. RB1 and RB4 where compacted while RB2 and RB3 where uncompacted. Laboratory test indicates that soils of RB1, RB2 and KB where classified as clay of intermediate plasticity which proved stronger than RB3, RB4, FB and PB which were clay of low plasticity. After 40 days of bund measurements, farmer field bunds reduced in height between 36 to 42 %. Research field measured that uncompacted bunds reduced in height by 34 and 40 % while compacted bunds reduced by 6 % or less. Bund compaction increases operational cost and reduces profit in the first season however, increases profit drastically in the second season. It is therefore concluded that uncompacted bunds erode faster than compacted bunds, compaction increases soil strength and bund strength is determined by soil type and level of compaction.