Author(s): M. B Sidiku, S. M Sani, M. B Mu\'azu, A. Mohammad
Published in: International Journal of Engineering Research & Technology
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
Volume/Issue: Volume. 6 - Issue. 09 , September - 2017
In this paper, a modified link budget model for Low Earth Orbiting (LEO)-based land mobile satellite communications system operating at Ku, K and Ka frequency bands is presented. The model takes into account the effect of additional loss due to Doppler frequency shift. Effect of losses due to Doppler frequency shift on satellite link budget was investigated at different satellite orbits (LEO, MEO and GEO). The results obtained show that at maximum satellite converge angle and central frequencies for Ku, K and Ka bands, the Doppler frequencies for LEO (780 km) are: 325.50 kHz, 423.20 kHz and 726.90 kHz; for MEO (20000 km) we have 88.33 kHz, 114.80 kHz and 197.30 kHz; while GEO (35786 km) stood at 55.26 kHz, 71.84 kHz and 123.40 kHz. Comparative analyses between the conventional and the modified link budget at Ku, K and Ka bands was carried out thereof. The results showed that the Carrier to Noise density ratio (𝐂𝐍𝟎⁄) at Ku frequency band dropped by 58% (from 31dB without Doppler shift to 13dB with Doppler shift). Similarly, at K band, the 𝐂𝐍𝟎⁄ dropped by 62% (from 54dB without Doppler shift to 20dB with Doppler shift). At Ka band, 55% drop of 𝐂𝐍𝟎⁄ (from 85dB without Doppler shift to 38dB with Doppler shift) was also observed. With these, it could be concluded that Doppler shift is most pronounced at LEO orbit and therefore, should not be ignored during satellite link budget analysis; because it will give the designer an insightful view as to the amount of margins required for most efficient communication link design.
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