This article surveys the alternative fade mitigation techniques for satellite communication systems operating at Ku, Ka and V frequency bands. The specific phenomena influencing the propagation of radiowaves on Earth-space links are also overviewed. Emphasis is placed on modeling, experimental work carried out in the past, and practical implementations related to each mitigation technique.

Satellite communications at KU, KA, and V bands: Propagation impairments and mitigation techniques

We present a new stochastic-dynamic model useful for the planning and design of gigahertz satellite communications using fade mitigation techniques. It is a generalization of the Maseng-Bakken and targets dual-site dual-frequency rain attenuated satellite links. The outcome is a consistent and comprehensive model capable of yielding theoretical descriptions of: 1) long-term power spectral density of rain attenuation; 2) rain fade slope; 3) rain frequency scaling factor; 4) site diversity; and 5) fade duration statistics using a novel method based on Markov Chains. We also present a simple rain attenuation synthesizer matching the predictions of the theoretical model.

/pdf/spatio-temporal-rain-attenuation-model-for-application-to-3t5pfa43iu.pdf

Spatio-temporal rain attenuation model for application to fade mitigation techniques

The paper discusses the prediction of long-term fade duration statistics in slant paths, obtained from rain attenuation time series simulated with the synthetic storm technique (with input from 1-min rain rate time series). The results of the prediction were tested against the experimental fade duration statistics collected at three sites of the Sirio experiment in Italy at 11.6 GHz. Predicted and measured statistics are very similar for fade durations longer than about 64–128 s, which represent a fundamental lower limit to fade duration prediction using 1-min rain rate time series. The short durations have not been reproduced because they are mainly caused by tropospheric turbulence, not by the space-time structure of rain, well described statistically by the synthetic storm technique. The prediction is not sensitive to rainstorm speed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97RS00501

Prediction of fade durations due to rain in satellite communication systems

The Magical Number Seven, Plus or Minus Two
A moving image and sound collaboration with James Sutherland
“Miller’s Law is the number of objects an average human being can hold in working memory. In this artwork we investigate this to explore Autonoetic Memory and Endel Tulving’s notion of Mental Time Travel, the voluntary or involuntary ability to project one’s self in a past or future situation often triggered by an external stimulus such as a familiar sound, smell or image. The footage is from journeys taken in 2010 and 2013 and will be reminiscent to many but specific to only one. Images and sound work in a generative way, creating moments of synchresis before separating. The quality of the image is painterly, impressionistic and indistinct. A fading memory. The viewer is invited to hold the information and to find the pattern through the multiple layers of image and sound.”

The Magical Number Seven, Plus or Minus Two - PLUNGE

The quality of satellite communication systems can be seriously affected by variable climatic phenomena such as rain and turbulence. For the design of communication systems with a required availability, statistical knowledge of climatic propagation effects is essential. In this thesis three climatic propagation effects are studied: • the fade slope (rate of change) of attenuation due to rain; • scintillation due to tropospheric turbulence; • depolarisation due to rain and ice crystals. For the study, experimental satellite signal measurements are analysed, received from the satellite Olympus at Eindhoven University of Technology and Helsinki University of Technology. The statistical behaviour of the propagation effects is studied in relation with the theoretical background. The results obtained are compared with results from many other measurement sites. This way, relations with link parameters (among which the frequency) and with meteorological parameters are studied. New prediction models for the propagation effects are developed, as well as improvements to existing models. The main conclusions obtained are the following: The rain fade slope is found to have, conditional for a rain attenuation level, a symmetrical distribution. The standard deviation of this distribution is proportional with attenuation, independent of frequency, and dependent on filter bandwidth. It is likely to depend on elevation angle and on the relative contribution of different rain types. The signal level due to tropospheric scintillation is found to have an asymmetrical distribution; the asymmetry increases with scintillation intensity. The frequency dependence of scintillation shows strong variability between different measurement sites; several possible explanations for this observation are given. For global long-term prediction of scintillation, current models use only the wet term of refractivity as a meteorological input, however it is found that the water content of heavy clouds is necessary as an additional meteorological input parameter. An improved prediction model of tropospheric scintillation is presented, based on the conclusions found. The relation between depolarisation and attenuation due to rain is studied using measurements from many different sites; the different dependencies of this relation on link parameters are empirically quantified and the model for this relation is updated. For the case of depolarisation caused by simultaneous rain and ice, a calculation method is developed to separate the contributions of both partial media. The conclusions obtained and the new prediction models developed in this thesis can improve the prediction of propagation effects, which is essential for satellite communication system design in general and for adaptive link control systems in particular.

Climatic radiowave propagation models for the design of satellite communication systems

This paper reports the statistical relationship between 1-s averaged rain attenuation (A, in decibels) and standard deviation (σ, in decibels) of simultaneous tropospheric scintillation in 1-s intervals, derived from high-resolution (50 samples/s) experimental 12.5-GHz attenuation time series recorded at Spino d'Adda (45.4°N) in a 30.6° slant path to satellite Olympus during an observation time of approximately 1 year. The statistical relationship can be fitted by the power law σ=0.068A5/12 derivable from a thin turbulent layer model. A similar relationship was also previously obtained in the same slant path at 19.77 GHz. As a consequence, we have concluded that at least up to 20 GHz, the modeling is independent of frequency.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97RS01458

Scintillation and simultaneous rain attenuation at 12.5 GHz to satellite Olympus

We show that the Synthetic Storm Technique can be applied to slant paths of very low elevation angle, but with caution and some limitations. To this end, we have processed the rain attenuation measurements collected in the years 1999 and 2000, in a 5° slant path radio link at 44.5 GHz between the top of Pic du Midi (altitude 2865 m) and Lannemezan (altitude 600 m), a 28-km path length, in the French Pyrenees (experiment known as CELESTE), to obtain the exceedance probability distributions of rain attenuation and fade duration. Then we have compared the experimental distributions to those predicted by the Synthetic Storm Technique with strictly concurrent measurements of rain rate time series. We have found that if the rainy path length assumed in the Synthetic Storm Technique modeling is limited to 13~15 km, instead of 28 km, then, for a large attenuation range: (a) the probability distribution of rain attenuation is well reproduced; (b) the experimental probability distribution of fade duration is well reproduced for fade durations longer than about 10 minutes.

Performance of the Synthetic Storm Technique in a low elevation 5° slant path at 44.5 GHz in the French Pyrénées

Diversity systems are foreseen for earth to satellite links operating at frequencies above 10 GHz in localities with high rain-induced attenuation. The paper discusses orbital diversity, which uses two satellites and an earth receiving site, through an analytical model for the rainfall random process. The model uses rain gauge measurements and radar-derived information on the slant structure; it gives results that are similar to experimental data and physically meaningful. A comparison is also carried out with corresponding site diversity, and the procedure for computing both attenuation statistics is given. It is shown that orbital diversity may replace site diversity as far as rain attenuation is concerned and may give the same performance up to a certain limit of geometry which depends little on attenuation. It is also shown that site diversity gain can be converted to orbital diversity gain and that the geometrical parameters (site separation and angle aperture) which yield this conversion are related by linear relationships, which are independent of frequency.

An orbital diversity model for earth to space links under rain and comparisons with site diversity

We have studied how the rain attenuation A (dB) predicted with the Synthetic Storm Technique in a slant path of precipitation path length L is built up by parts ?A (dB) due to partial precipitation path lengths ?L . We have found that ?A/ A can be estimated from ?L / L independently of the value of A and L, and that this relationship leads to a differential equation whose integral yields the average relationship A [CokAR?A+(1 ? Co)kB(3.134R)?B]L0.90 with Co and L constants that depend only on latitude in a known way, and k and ? are the usual constants that transform rain rate into specific (dB/km) rain attenuation for the two layers A and B of precipitation modelled in the SST. With this expression, which links monotonically rain attenuation of a slant path (an integral) to the rain rate measured at a point by a rain gauge, we show that it is possible to reliably estimate the same cumulative probability distribution of rain attenuation predicted by the SST, without knowing the rain rate time series. The method could be extended to real time predictions.

A fundamental differential equation that links rain attenuation to the rain rate measured at one point, and its applications in slant paths

Summary
The purpose of this paper is to show how the complementary probability distribution of rain attenuation is drastically changed in the lower rain attenuation range by applying linear combining techniques, namely, equal-gain combining and the maximal-ratio combining, discussed in the historical paper by Brennan in 1959. These combing techniques can also be applied to the Automatic Repeat Request techniques. Defined the instantaneous processing gain and the equivalent attenuation in the 3 cases, we show examples of time series of the various parameters, based on the experimental rain attenuation time series recorded with the ITALSAT 18.7 GHz beacon, in a 37.8° slant path in Spino d'Adda (Italy). Then, we report long-term complementary probability distribution functions of the instantaneous gain and equivalent attenuation, by simulating rain attenuation time series at 19.7 and 39.4 GHz, path elevation angle 35.5°, with the Synthetic Storm Technique, using on-site measured rain rate time series of 10 years, by simulating the ALPHASAT link at Spino d'Adda. Similar results are also found at different frequencies and elevation angles in Tampa (Advanced Communications Technology Satellite, ACTS result test), the Isle of Guam, and Prague. The main conclusions are as follows: (1) As expected, the instantaneous time diversity gain can be large when the delay time is large and rain attenuation is large; (2) scintillation affects time diversity links as the direct links; (3) equal-gain and maximal-ratio combining can add up to 3 dB to the selection diversity gain when the time diversity gain is very small; and (4) equal-gain and maximal-ratio combining reduce the fraction of time of rain attenuation in an average year to a value less than the probability of exceeding 3 dB in the link without diversity.

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Emilio Matricciani

Papers

Scintillation and simultaneous rain attenuation at 12.5 GHz to satellite Olympus

Performance of the Synthetic Storm Technique in a low elevation 5° slant path at 44.5 GHz in the French Pyrénées

An orbital diversity model for earth to space links under rain and comparisons with site diversity

A fundamental differential equation that links rain attenuation to the rain rate measured at one point, and its applications in slant paths

Probability distributions of rain attenuation obtainable with linear combining techniques in space-to-Earth links using time diversity