ANALYSIS AND SIMULATION OF RAIN ATTENUATION MODELS AT K-V FREQUENCY BANDS FOR SATELLITE SERVICES OVER SOUTHWESTERN NIGERIA

Abstract

Rain attenuation is a major deteriorating factor affecting radio wave signals propagating at microwave and millimetre wave bands for a typical Earth-Space Communication Link (ESCL). Several rain attenuation models have been developed by different researches including the standard ITU-R model for prediction of rain attenuation on any terrestrial radio link. However, the ITU-R model does not perform well in tropical regions. In addition, the model can be supported with appropriate modulation technique to enhance link performance. This research analyses the performance of selected rain attenuation models; ITU-R model, Moupfouma model and Garcἱa-Lὁpez model based on rain types for K-V frequency bands over some selected locations in Southwestern Nigeria. The performance is tested based on different modulation schemes to ascertain the level of improvement due to signal degradation. The result show that the ITU-R and Moupfouma models performed well for drizzle, widespread, and shower rain types from K-Ka frequency band. However, while the ITU-R model underestimated attenuation for thunderstorm rain type from K-V band frequency, Moupfouma model performed fairly well for thunderstorm rain type up to Ka frequency band. Garcίa-Lόpez model on the other hand performed best across all the rain types for K-V frequency band. Also, three modulation techniques namely: On-Off keying (OOK), Pulse Position Modulation (8-PPM) and Differential Phase Shift Keying (DPSK) were used to study the effect of rain attenuation on modulation techniques for radio wave propagating in the selected tropical locations. The effect of selective combining (SC) diversity is also included in this study. It was observed that the bit-error rate (BER) will severely degrade with a high rain rate compared to the low rain rate across different frequencies. The BER for 8-PPM outperforms the other types of modulation schemes that were used in this study. Overall results revealed that modulation technique DPSK with SC diversity gave a marginal improvement with the increase in link distance and operating frequency.