Faculty of Engineering and Built Environment
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Item Performance analysis of filtered Orthogonal Frequency Division Multiplexed LDPC codes for satellite communication in the Ka-Band(2024-05) Gumede, Bonginkosi; Mukubwa, Emmanuel; Pillay, NThe saturation of lower frequency bands and the growing demand for high data rates have presented the need to design future systems at Ka-band frequency, but Ka-band frequency is very fragile because of the millimeter wavelength. Ka-band frequencies range from 26 to 40 GHz, making the signal more susceptible to weather impairments and shadowing than lower frequency bands. Rain attenuation is a major problem in satellite communications systems operating at Ka-band, it causes major signal degradation because the raindrop is about the size of the Ka-band wavelength. To mitigate this problem, you must use powerful Forward Error Correction (FEC) codes such as Low Density Parity Check (LDPC) or Turbo codes. This research presents the performance of LDPC codes for satellite communications in the Ka-band, we enhance the system’s performance by adding adaptive modulation and filtered - Orthogonal Frequency Division Multiplexing (f-OFDM). This research study has been undertaken as follows: First, we studied the operation of LDPC codes, including different encoding and decoding techniques. We decided to use the Quasi Cyclic (QC) parity check matrix, allowing us to employ the QC-LDPC encoding technique, which reduces encoding complexity and improves coding efficiency. We explored various LDPC code decoding techniques and opted for soft decoding techniques, namely Belief Propagation, Layered Belief, Normalised Min-Sum, and Offset-Min Sum, as they are more effective in reducing errors compared to hard decision decoding. The Kaband satellite channel is modeled using the Gaussian distribution, considering that the signal envelope and signal phase change randomly after passing through the Ka-band channel. All parameters were set according to different weather conditions. For the simulations, we utilized the MATLAB software package. The uncoded 16-Quadrature Amplitude Modulation (QAM) OFDM system on moderate rain weather conditions achieved a gain of 4.3 dB against light snow and thunderstorm weather conditions at the BER 10−3. We applied f-OFDM, and the results show that LDPC codes achieve a gain of 2 dB when compared to Turbo codes and a gain of 3 dB compared to Convolutional Codes (CC) at the BER of 10−3 under moderate rain conditions in the Ka-band channel, we can see the effects of f-OFDM and LDPC codes. When adding the adaptive modulation into the system, modulation switches from 16 QAM to 64-QAM at Eb/No of -9 dB and switches from 64-QAM to 256-QAM at Eb/No of -5 dB thus improving spectral efficiency. The system is resilient and feasible in error correction at low Signal to Noise Ratio (SNR).Item Solar energy-battery storage optimization for satellite-to-ground communication(2023-09) Ntlela, Simphiwe A.; Davidson, Innocent Ewaen; Moloi, KThe creation of ubiquitous broadband systems has piqued the interest of both academics and industry to fulfil the exponential growth in demand for multimedia services on mobile devices and to support access anywhere on the earth. The implementation of such systems is anticipated to heavily rely on satellite networks in general and Low Earth Orbit (LEO) satellite constellations. Therefore, increasing their service life has become a significant engineering and scientific challenge. The main finding of this thesis is that by sharing the power of a satellite's batteries with another spacecraft that is still in the sun, one may considerably extend the service life of a satellite. Over 30% of the time that LEO constellation satellites are in the earth's shadow, they are powered by batteries. Although the batteries are replenished by sunlight, the depth of discharge they experience during an eclipse has a major impact on their lifetime and, consequently, the service life of the satellites. A 15% increase in the DoD can almost halve the service life of the batteries. The major section of this thesis includes a variety of strategies we think may help LEO constellations' batteries last longer. The market's demand for satellite communication networks has changed recently. Low-EarthOrbit (LEO) satellite constellations have therefore received increased attention because they are expected to address these needs. In the current LEO satellite constellation-based communication system, the satellite close to the satellite terminal that submits the communication request answers to it regardless of the state of its battery. However, in cases of significant battery deterioration, this communication technique reduces the lifetime of the satellite. This means that in big satellite constellations when operating costs are a concern, this communication mechanism is unsuccessful. To extend the battery's lifespan, we design a communication mechanism in this work that regulates the transmission power and transmission gain of a satellite antenna based on the battery's state of deterioration. Large-scale LEO satellite constellations can be created and used thanks to the decrease in operating expenses that results from extending battery life. Future demands for satellite communication should be met by the system that has been put in place. Through simulation, the usefulness of the suggested approach is confirmed. The use of solar energy for satellite power is an attractive option due to its sustainability and cost-effectiveness. However, satellite communication requires a constant and reliable power supply, which is challenging to achieve with solar energy alone, particularly in periods of low solar activity or during eclipses. This is where battery storage optimization comes into play. In this study, we propose an optimization model for the use of solar energy and battery storage in satellite-to-ground communication systems. The model takes into account various factors such as solar irradiance, battery capacity, and communication power requirements. The optimization objective is to maximize the utilization of solar energy while ensuring uninterrupted communication. We apply the proposed model of Q-theory to a case study of a Low Earth Orbit (LEO) satellite. The simulation results show that the proposed optimization model can significantly improve the performance of the satellite power system. Specifically, it can reduce the reliance on battery power during periods of low solar activity, leading to longer battery life and more reliable communication.Item Combined tropospheric attenuation along satellite path at SHF and EHF bands in subtropical region(2019) Olurotimi, Elijah Olusayo; Sokoya, A. O.; Ojo, J. S.; Owolawi, P. A.The traffic flow of information across the globe is crucial in today’s communication systems, where about 88% population are connected via several smart devices, hence resulting into constraints on the limited available radio resources. Due to the limitations of terrestrial connectivity affecting communication systems, in terms of geographical coverage area and system capacity, which have become serious issues globally. Therefore, there is a need for communication industries to embrace the use of satellite systems. Satellite services have many advantages some of which includes availability, wide coverage area and the ability to accommodate most of the limitations of the terrestrial systems. However, Earth-to-satellite systems, especially those operating at higher frequencies above 7 GHz, usually suffer from degradation due to hydrometeors which are mainly produced in the troposphere. Hydrometeors include rainfall, hail, gases, clouds and snow among others; of which rainfall is the principal factor which contributes highest impairment along the propagation paths, simply termed as rain attenuation. Moreover, the scenario in the tropical and subtropical regions become more pronounced due to the degree of occurrence of precipitation when compared to the temperate region. Other significant factor that usually affects the propagation of signals is attenuation by scattering and absorption due to rain, water vapour, cloudiness and other gases in the atmosphere. Thus, in order to estimate accurate rain attenuation of a location, there is a need for accurate measurements of rain attenuation components such as rain height, rain rate, altitude, slant-path length, among others; of which rain height plays a significant role in the case of satellite links. However, the attenuation due to other tropospheric components cannot be negligible at higher frequencies over any location in order to proffer solution or cater for impairments that may arise as a result of any atmospheric perturbation in a satellite communications system. The significance of rain height in estimating rain attenuation along the satellite path, is ii crucial and this important component has been extensively dealt with in the temperate region, partially in tropical region with no record in subtropical regions. This study, therefore, focuses on the measurement of rain height to assess the degree of attenuation due to precipitation over several locations across South Africa, a subtropical region. In spite of the extensive works that have been carried out on prediction of rain attenuation based on the recommended rain height by the International Telecommunication Union-Regulation over some of the studied locations, the contribution of local rain height data for rain attenuation prediction will enable better results which are the focus of this study. Hence, this thesis presents 5-year rain height measurements based on zero-degree isotherm height (ZDIH) obtained from the Tropical Rainfall Measuring Mission-Precipitation Radar (TRMM-PR) over a subtropical region-South Africa. The component of this work encompasses rain height cumulative distribution, percentage of exceedances, development of the contour maps of rain heights for South Africa, modeling of rain height, tropospheric attenuation prediction due to gas, cloudiness, scintillation, application of rain height for rain attenuation prediction, estimation of total attenuation and prediction of quality of service based on signal to noise ratio. Findings from this work show that the ZDIH distribution is location dependent. Rain heights value ranges from about 4.305 km from the southern region to 5.105 km in the northern region of South Africa. The parameters of the ZDIH distribution models developed with the use of maximum likelihood estimation technique show a wider variation over some selected locations observed. Finally, attenuation due to rain, gas, cloudiness and scintillation were estimated. In addition, the total attenuation and the quality of service based on the propagation signals at SHF and EHF over some selected stations were evaluated and presented in this work.