UBC Theses and Dissertations
Simulation of rain attenuation and scintillation of Ka-band earth-LEO links Liu, Weiwen
Because the motion of a LEO satellite across the sky causes the Earth-space path to pass through any rain cells in the vicinity very quickly, the degree of rain fading on such paths changes more rapidly and leads to steeper fade slopes than in the geostationary case. A simulation model based on synthetic rain field technique is developed to obtain plausible estimates of the fade slope distributions for selected scenarios. Two methods of generating the rain field, Goldhirsh’s method based on the EXCELL model and Feral’s method based on the HYCELL model, are implemented. The simulation results for GEO satellites closely match the measurement data observed during the ACTS program. The results indicate that fade slopes, which could be between two and ten times greater than for GEO satellites at a given probability level, will steepen as: (1) the altitude of the satellite decreases, (2) the carrier frequency increases and (3) the average rain rate increases. The differences between the results yielded by the EXCELL and HYCELL model are very small and the slightly conservative estimates yielded by the EXCELL model are offset to some extent by the greater simplicity of the EXCELL model. Scintillation on Earth-space paths increases greatly at low elevation angles and/or higher frequencies. On Earth-LEO links, because of the rapid change in elevation angle and motion of the satellite, both the length of the slant path to the turbulence layer and the velocity at which the slant path passes across the turbulence layer change rapidly. This affects both the intensity of the scintillation process, which generally reaches its maximum value at low elevation angles and/or periods of rain, and the corner frequency of the scintillation process, which generally reaches its maximum value at high elevation angles. Here a geometric model of propagation through the turbulence layer is developed in conjunction with Tatarskii’s theory of propagation through turbulent media to show that the effect becomes more pronounced as the orbital altitude decreases and as the height of the turbulence layer increases. These results have important implications for the design of power control algorithms and other fade mitigation techniques.
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