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my).⁞ABSTRACT The satellite signal deteriorates as it propagates from the source to the ground antenna on the surface of the earth. While some losses involving the amplitude and energy of the signal are unavoidably recovered due to the long slant path through the atmosphere, the impairment due to precipitation, especially rain, can be mitigated. Site diversity is one of the ways to obtain a less rain-attenuated signal, simply by preparing the other site to receive a link similar to that of the main site. Dual site diversity is common in practice with a site separation distance of at least a rain cell extent. This article presents an overview of the site diversity concept and a description of all parameters involved regarding the factor that contributed to the gain, which has been used as a performance metric to measure the effectiveness of a site diversity scheme. A detailed assessment of the capability of the gain prediction model is presented using site diversity experimental data conducted in two different climatic groups, namely, Greece in a temperate region and India in a tropical climatic region. The models involved in the evaluation were the ITU-R, Hodge, and Panagopoulos models, which were validated using temperate regional data, and the Semire and Yeo models, which were validated using tropical regional data. The observations of model behavior revealed that the Semire and Yeo models of the tropics were consistent with the measured gain obtained from India and Greece, respectively; thus, this demonstrated that the direction of future prediction models should consider both climates in the validation process.⁞INDEX TERMS Signal degradation, model evaluation, tropical region, rain-induced attenuation, atmospheric effect.

⁞ABSTRACT Ensuring site diversity is a fade mitigation technique used to overcome severe rain-induced attenuation encountered in high-frequency signal communications, especially over tropical regions. However, due to the high cost of deploying diverse equipment and terrestrial infrastructures for connections between two sites, gain prediction models are widely used to evaluate the performance of a given scheme. This article presents a study on the behavior of four parameters that contribute to site diversity gain: site separation distance, link frequency, elevation angle, and baseline orientation angle. A correlation between gain and distance is found in the form of an attenuation-dependent logarithmic function instead of the gain being saturated when the increment of the distance exceeds the convective rain cell extent, as was found in the literature. Therefore, a site diversity logarithmic model, SDLog, is proposed. The analysis utilized seven site diversity experiments conducted in the tropics, i.e., in Malaysia, Singapore, and Guam, USA. The performance of the SDLog model was compared with the performances of existing models, namely, the ITU-R, Hodge, Panagopoulos, Semire, and X. Yeo models. The SDLog model reproduces the experimental datasets with an average root mean squared error (RMSE) of 0.12, while those of the ITU-R, Hodge, Panagopoulos, Semire, and X. Yeo models are 0.226, 0.289, 0.19, 0.192, and 0.311, respectively. These models were also evaluated based on diversity experiments conducted in Indonesia, separate from the former evaluation. The RMSE and mean absolute percentage error (MAPE) of all evaluations are presented, and the SDLog model seems to be convincing.

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