Earth-space Propagation Paths Research Articles

A Semi-2D Synthetic Storm Technique for Orbital Diversity on Earth-Space Propagation Paths

In this article, new assumptions are introduced into the well-known synthetic storm technique (SST) proposed by Drufuca and further developed by Matricciani, to address the orbital diversity in satellite links. The new approach receives as input information on collocated rain rate recordings and instantaneous estimates of the storm direction and speed; and assumes that the rain event is transversely constant to the storm movement. The achieved improvements are evaluated by analyzing two example measured rain attenuation events “seen” by two Ka -band beacon receivers looking at two different satellites spaced around in azimuth. A study is made of the cross correlation coefficient between rain attenuation series for these two links. Moreover, a methodology is sketched as to how multiple non-GEO satellite constellation availability (for global Internet access at Ka -band) could be evaluated in the frame of the SST.

Cross‐polarisation discrimination models assessment and improvement on earth‐space propagation paths at Ka and V‐bands

The performance of the satellite communication systems employing polarisation diversity or frequency-reuse schemes to improve the spectral efficiency is degraded due to the depolarisation-induced interference originated by raindrops and ice particles present along the Earth-Space propagation path. Two models account for both rain and ice contributions. One predicts the long-term cumulative distribution function (CDF) of cross-polarisation discrimination (XPD). The other predicts the relationship between XPD and co-polar attenuation (CPA) and it was derived considering exclusively data at the V-band. In this study, the former model is improved by considering the individual ice and rain contributions and their combined effects, while the latter is validated against new measurements at the Ka band. New models are then proposed for the XPD-CPA relationships at the Ka-band taking into account both rain and ice contributions and also their combined effects. Finally, the predictions provided by the first model are usually converted to the corresponding XPD-CPA relationship using the long-term first-order statistics of rain attenuation, (incorrectly) considering that the equiprobability hypothesis applies. A new approach for the conversion of the XPD CDF into the corresponding XPD-CPA relationship is presented.

Statistical Studies of Cross-Polarization Due to Subtropical Rain on SHF Radio Propagation Paths Over Some Stations in South Africa

The employment of frequency re-use in orthogonal polarization continues to gain recognition due to the congestion in the lower frequency bands and the demand for more satellite service applications. However, communication signals operating above 10 GHz and adopting frequency re-use in orthogonal polarization, are often hampered by cross-polarization among others. In this paper, an attempt has been made to estimate cross-polarization discrimination (XPD) due to subtropical rain at super high frequency ranges in order to estimate accurately the signal total availability needed for satellite services in this region. Cross-polarization has been estimated based on the ITU model in the recommendation 618-9 over the Intelsat 17 (IS-17) Satellite (Geostationary at 66°E) with its service footprint links, at the respective elevation angle, to each of the nine locations within the provinces of South Africa. The estimation is based on modification using log-normal distributions of raindrop sizes at 20 °C and assuming circular polarization for Earth-space propagation paths. Some results of the influence of co-polar attenuation, frequency and subtropical rainfall rates are investigated. The overall information will enable the system provider to locate repeater stations for optimum performances within the provinces of South Africa.

Statistical Prediction of Site Diversity Gain on Earth-Space Paths Based on Radar Measurements in the UK

This paper presents an empirical model for the statistical prediction of site diversity gain on earth space propagation paths. A modelling approach is described which incorporates 46 months of Nimrod rain radar data recorded in South England. The dual site diversity (SD) gain is developed as a function of several parameters, including time percentage of average year, site separation, baseline orientation, link frequency and path elevation angle. The model performs with an overall root mean square error of 1.87 dB computed over a wide variety of link configurations with elevation angles ranging from 10° to 50° and transmission frequencies from 16 to 50 GHz. The performance of the new model is checked against satellite beacon measurements as well as the empirical and physical models recommended by ITU-R.

Estimating tropospheric scintillation intensity on earth-space propagation paths

Empirical formulas are presented that improve the estimation of tropospheric scintillation intensity on earth-space propagation paths. The formulas have been checked against measurements on earth-space links spanning elevation angles from 5° to 40° and frequencies from 11 to 50 GHz, and located in regions of average ambient temperature from 5 to 20°C.

A simple model for orbital diversity gain on earth-space propagation paths

Simple formulas, appropriate for use by the system designer, have been generated to estimate orbital diversity gain on Earth-space propagation paths, as a function of satellite aperture angle, link frequency and elevation angles. The proposed relationships are based on a regression fitting analysis implemented on an analytical propagation model for calculating the outage probability of an orbital diversity protection scheme. The root mean square error of the simple model is less than 0.5 dB in all tested situations and over the entire range of angular separation, frequency and elevation angle. The resulting simple model is tested with experimental data taken from Japan. The agreement was found to be quite encouraging. Tabulated values for the 12 parameters are presented for some heavy rain climatic regions. The dependence on climatic zone is obvious.

Statistics of differential rain attenuation on adjacent earth-space propagation paths

Forty hours of observations of the three-dimensional radar reflectivity structure of rain in the Montreal area were used to simulate the centimetre-wavelength attenuations occurring simultaneously over a multitude of earth-space propagation paths. The same data base had been used in a previous study which confirmed that the radar estimates of attenuation statistics are in good agreement with attenuation distributions measured independently by passive radiometers. Differences between the attenuations occurring simultaneously over pairs of paths to a common point at the ground were tabulated as a function of angular path separation, viewing direction, radio frequency, and system margin. These data are required for evaluating the possibility of interference at an earth station caused by a signal from an adjacent satellite. In this study, values of angular separation from 2 to 9 degrees, radio frequencies from 11 to 30 GHz, elevation angles from 5 to 30 degrees, and system margins from 2 to 10 dB were considered. It was found that the cumulative distributions of differential attenuation could be characterized effectively by the attenuation difference occurring during 1 % of the time that the carrier signal suffered some attenuation, but not an attenuation exceeding the system margin. It was also found that this characteristic differential attenuation could be expressed to good approximation as a simple analytical function of the system parameters.

Effective canting angle of distorted raindrops along Earth-space propagation path

The effective canting angle of distorted raindrops along an earth-space propagation path has been obtained from a one-year phase amplitude measurement of two orthogonal components of satellite signals. It is shown that the distribution of canting angles is centred around the horizontal orientation, with the standard deviation of about 11°.

Phase fluctuations of cross-polarized signals at 4 GHz in fine weather on earth-space paths

On an earthspace propagation path with the low elevation angle of 10 deg, the phase between co- and crosspolar signals occasionally showed rapid and irregular fluctuations during fine weather. These fluctuations were generally significant during the daytime, and were strongly in phase with the occurrence of the copolar amplitude scintillations. This could be attributed to the combined effects of the crosspolar phase pattern of the receiving antenna and small fluctuations of the angle of arrival of the radiowaves.

Phase and amplitude dispersion for Earth-satellite propagation in the 20- to 30-GHz frequency range

Amplitude and phase dispersion have been measured for over a year on a 19- and 28-GHz earth-space propagation path. In the experiment amplitude and phase differences were compared for a 28-GHz carrier with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm264</tex> -MHz sidebands and a 19-GHz carrier, all transmitted from a COMSTAR satellite. No dispersion (frequency selective fading) was found of the type caused by multipath propagation with a large spread in time delay or by resonances in the propagation medium. The only frequency dependences evident were due to the bulk properties of water in rain. The conclusion from this investigation is that amplitude and phase dispersion should not pose a problem for wideband (on the order of 1 GHz) satellite communication systems operating at frequencies greater than 10 GHz with elevation angles from the earth terminals of greater than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15\deg</tex> .

Rain Attenuation Statistics from a 19 and 28 GHz COMSTAR Beacon Propagation Experiment: One Year Cumulative Distributions and Relationships Between the Two Frequencies

Cumulative attenuation distributions for one year and relationships between attenuations at 19 GHz and 28 GHz are presented for an earth-space propagation path terminating at Crawford Hill, New Jersey. An example from the distributions indicates that 20 dB attenuation was exceeded for 0.012% of the year at 19.04 GHz and for 0.06% at 28.56 GHz. For both frequencies the polarization was linear and oriented 21° from vertical at the receiver. When the attenuation at 19 GHz was less than 20 dB, the attenuation in dB at 28 GHz averaged 2.1 times that at 19 GHz. This ratio was lower at higher attenuations.

An empirical relationship for path diversity gain

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.