Jun Xiang Yeo

Performance of Site Diversity Investigated Through RADAR Derived Results

Site diversity is an effective rain attenuation mitigation technique, especially in the tropical region with high rainfall rate. The impact of different factors such as site separation distance, frequency, elevation angle, polarization angle, baseline orientation and wind direction is assessed. Results are compared to those reported in existing literature and also compared to the commonly used ITU-R site diversity prediction models. The effect of the wind direction on site diversity is also presented. It can be observed that diversity gain is highly dependent on the site separation distance, elevation angle and wind direction but independent of the frequency, baseline angle and polarization angle of the signal. This study is useful for the implementation of site diversity as a rain attenuation mitigation technique.

Comparison of S-Band Radar Attenuation Prediction With Beacon Measurements

A comparative analysis of the rain attenuation evaluated from beacon measurements and from a single polarization S-band Radar is performed. The beacon measurements are obtained for two slant satellite paths with different elevation angles in the Ku- and Ka-band. The single polarization S-band Radar reflectivity data is used to predict the attenuation along the satellite propagation paths. This is done by first converting the reflectivity into rain rate using the Z-R relations suitable for the tropical region and, afterwards, by evaluating the slant path attenuation through the integration of the specific rain attenuation derived from the point rainfall rate. An empirical calibration factor for the Radar reflectivity is provided. A comparison of the rain fade suffered from the two satellite paths is presented both on event basis and in terms of cumulative distribution functions. The empirical calibration factor and a single Z-R relation suitable for the tropical region are used for rain attenuation evaluation from single polarization Radar data.

Modified ITU-R slant path rain attenuation model for the tropical region

This paper proposes a model for predicting the rain attenuation along the earth-space slant propagation path. The experiment results collected for rainfall rate and for rain attenuation is described. The rainfall rate from a rain gauge and the rain attenuation for three satellite signal in both the Ku and Ka band are analyzed and used. Based on the rainfall rate data and the Ku and Ka-band beacon data collected in Singapore, a modification to the existing ITU-R rain attenuation prediction model is proposed. The proposed rain attenuation model uses the complete rainfall rate cumulative distribution, frequency and elevation angle as the input data. The proposed model shows significant improvement in term of rain attenuation prediction error over the ITU-R model.

Rain Attenuation Prediction Model for Satellite Communications in Tropical Regions

This paper proposes a model for predicting rain attenuation in the tropical region. Slant path rain attenuation measurements were carried out in Singapore by analyzing the beacon signals from two satellites, namely WINDS and GE23, operating at frequencies of 18.9 and 12.75 GHz, respectively. Rainfall rates at the location of the beacon receivers were recorded. The cumulative distributions of the rainfall rate and the corresponding rain attenuation are presented and analyzed. It is found that the cumulative distribution of the measured rainfall rate is close to that predicted by the ITU-R model. Measurement data from a total of nine countries are compared with four existing rain attenuation prediction models, namely the Yamada, DAH, Karasawa, and Ramachandran models. Results show that although three of these models have relatively good prediction capability for the tropical region, they could be improved. Therefore, in this paper, a slant path rain attenuation model suitable for the tropical region is proposed. This is done by using the complementary cumulative distributions of rain attenuation for satellite links measured in Singapore and five other tropical countries. The proposed model is found to outperform exisitng models.

Ka-band satellite beacon attenuation and rain rate measurements in Singapore - comparison with ITU-R models

The preliminary results of these analyses suggest that the rainfall rate with 1 min integration time has a good agreement with the rainfall rate predicted from ITU-R model, regardless of yearly or worst month statistics. However ITU-R P.618-9 tends to underestimate the rain attenuation for the earth-space link in tropical areas like Singapore. A modified model of rain attenuation prediction is proposed. Beacon data are still collected and the effect of raindrop on antenna should be studied further.

Site diversity gain at the equator : radar-derived results modeling in Singapore

Summary Site diversity is an effective rain attenuation mitigation technique, especially in the tropical region where high rainfall rates are common. According to our previous study, site diversity gain is found to be dependent on the site separation distance and path elevation angle while it is independent of signal frequency, baseline angle and polarization angle. Therefore, using 28 months of radar data, a simple site diversity gain prediction model is proposed. The proposed model is compared with the existing ITU-R models. The seasonal wind direction, another factor that might affect the site diversity gain prediction model, is shown to have negligible effect on site diversity gain. Triple-site diversity is also investigated, and although it is found to provide gain improvement over dual-site diversity, this gain improvement is too little to justify for the cost of setting up an additional site. This study is useful for the implementation of site diversity as a rain attenuation mitigation technique in the tropical region. Copyright

Cloud attenuation on Ka-band satellite link in the tropical region: Preliminary results and analysis

In this paper, preliminary results and analysis of cloud attenuation on a Ka-band satellite propagation link in tropical island of Singapore are reported. The received signal by a ground-based beacon receiver at 18.9 GHz was processed with a sliding window technique to minimize the system and scintillation effects. The results show that the Ka-band cloud attenuation is highly correlated with the observed solar radiation.

Statistical Study of Cloud Attenuation on Ka-Band Satellite Signal in Tropical Region

A two-year statistical study of cloud induced attenuation on Ka-band satellite communication link in the tropical region is presented. Different from other publications, experimental results from an 18.9-GHz beacon receiver is analyzed for cloud attenuation. Several new cloud detection methods are proposed in order to achieve accurate cloud attenuation estimation. These results are compared to the ITU-R model for the same frequency and elevation angle. The complementary cumulative distribution function of two-year cloud attenuation shows that at time exceedance of 0.01%, cloud attenuation in the Ka-band can reach up to 4 dB. It is found that the ITU-R model underestimate the cloud attenuation in the tropical region.

Use of weather radar rain cell motion forecasting for site diversity system

Site diversity is an effective rain attenuation mitigation technique, especially in the tropical region where high rainfall rates are common. In order to improve the performance of the site diversity system, the selection of the diversity sites becomes critical. With the implementation of the Radar data, we are able to use the 1 degree forecasted PPI image to determine the location of the diversity sites which have no or less effect of rain attenuation that caused by the rain cells. With the selected sites, we are able to improve the overall site diversity system.