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Time diversity (TD) has recently attracted attention as a promising and cost-efficient solution for high-frequency broadcast satellite applications. The present work proposes a general prediction model for the application of TD by approximating the time dynamics of rain attenuation through the use of the joint lognormal distribution. The proposed method is tested against experimental data and its performance is investigated with respect to the basic parameters of a satellite link.

Several diversity reception schemes have been thoroughly investigated in
the past to mitigate rain fading in fixed/broadcast satellite communication
systems operating above 10 GHz. These schemes offer a significant performance
improvement, especially considering the recent trend of commercial satellite
networks to migrate to higher-frequency bands due to spectral and/or orbital
congestion: first, from C to the Ku frequency band and, more
recently, from Ku to the Ka, or even to the EHF frequency
band. The established diversity techniques include [

All the above fade mitigation techniques (FMT) produce significant diversity gains but their use is limited due to specific technical and other factors. For SD, the main limitation comes from cost considerations, since additional earth stations and terrestrial connections enabling the processing of the jointly received signals are required. In OD, limitations are imposed by the switching procedure between the satellites, as well as by the waste of satellite bandwidth. Finally, FD is rather expensive, requiring dual reception at the earth terminals.

Application of the TD technique.

Given that only a few similar models
exist in the open literature (briefly outlined in Section

One of the first TD measurement campaigns was carried
out for the equatorial region of Malaysia using a satellite beacon
receiver at 12 GHz to record data from a MEASAT geostationary satellite. Apart from
presenting the analysis of the 20-month data, an empirical exponential model to
fit the cumulative distribution of TD was developed [

To simplify the notation, the rain attenuation random variables corresponding
to the first and the second transmission of the same signal are here after denoted
by

Returning to the bivariate case and adopting for both
random variables

The parameter ^{-1}] is the

Based on Bayes’ theorem, (

Next, a first attempt to validate the TD statistical
model based on the bivariate lognormal distribution is carried out for a
variety of measured data related to various climatic zones and for links of various
electrical and geometrical characteristics. The measured results for TD are
simply reproduced from the open literature, as briefly outlined in Section

The statistical parameters of the lognormal
distribution

Parameters employed.

Experiment | Frequency | Elevation angle | |||
---|---|---|---|---|---|

Sparsholt, UK | 49.5 GHz | 1.1845 | 0.9359 | ^{-1} | |

Kuala Lumpur, MLA | 12 GHz | 0.03219 | 1.8791 | ^{-1} | |

Spino d’ Adda | 19 GHz | ^{-1} |

In Figure

Performance comparison of the proposed model and measured data from a TD system operating at 50 GHz in Sparsholt, UK.

In Figure

Performance comparison of the proposed model and measured data from a TD system operating at 12 GHz in Kuala Lumpur, MLA.

On the other hand, the overall performance of the proposed TD model
depends critically on the value selected for the dynamic parameter

Proposed model and measured data in terms of time diversity gain for a TD system operating at 19 GHz in Spino d' Adda, IT.

The present paper proposes a general TD prediction method based on the joint correlated bivariate lognormal distribution in the time domain. The correlation function proposed depends critically on the dynamic parameter of rain attenuation. The proposed model exhibits a very satisfactory convergence to experimental data originating from temperate climatic regions.