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.