Millimeter wave satellite communication studies. Results of the 1981 propagation modeling effort

Theoretical modeling associated with rain effects on millimeter wave propagation is detailed. Three areas of work are discussed. A simple model for prediction of rain attenuation is developed and evaluated. A method for computing scattering from single rain drops is presented. A complete multiple scattering model is described which permits accurate calculation of the effects on dual polarized signals passing through rain

Semi-empirical modelling of subtropical rain attenuation on earth-satellite microwave links.

Doctoral Degree. University of KwaZulu-Natal, Durban.The exponential rise in demand for high fidelity content on multiple platforms has in recent years made increased use of the higher echelons of radio communication frequency inevitable. At these high frequencies, wavelength becomes small enough to compare with the size of rain drops and in some cases smaller than drop size. This implies that the impairment due to rain, which already usually forms the most severe form of impairment at higher radio frequency bands, will become even more acute and require rigorous parameterization. This thesis investigates both by rigorous measurements and by theoretical approaches, the attenuation effect of rainfall in a subtropical climate (Durban, South Africa) on a microwave earth-satellite link operating at 12.6 GHz. The link was set up and the received signal level monitored via spectrum analyser sweeps conducted every minute. A Joss-Waldvogel impact disdrometer was installed such that its diaphragm is located a few meters away from the link’s receive antenna. From such a location, all precipitation recorded by the disdrometer are assumed to have some effect on the link. The monthly variation in the received signal during clear air was investigated by taking into consideration the average monthly values of temperature, relative humidity and atmospheric pressure. By employing multiple regression, a linear expression was obtained that can be used to predict the change in received signal level in clear air over the link given the values of these three atmospheric parameters. The attenuation due to the rain events was extracted from the data by carrying out an even-by-event matching of rain rate spikes with the corresponding drop observed in the received signal level at and around the time of the precipitation. The average monthly received signal level during clear air was extracted from the spectrum analyser data and used as the base channel power to which the received signal during rain in the particular month is compared. The difference between the two is stored as the attenuation due to rain in that instant of measurement time. The attenuation data thus accumulated were entered into a computer algorithm and a regression fitting procedure carried out to deduce an empirical set of logarithmic and power law models that relate the total path attenuation to rain rate. The models were then validated by a largely favourable comparison with four existing models, one of which is the in-force ITU-recommended model for slant path attenuation estimations. Random number properties of rain attenuation statistics obtained from the measurement model were exploited to develop a Markov chain approach by which seasonal and annual slant path rain attenuation time series can be generated. By investigating the nature of the probability distributions of the seasonal and annual measured path attenuation statistics, which was found to be lognormal, the state probability matrix necessary for implementing a Markov chain prediction model for future patterns of rain attenuation on a similar link was obtained as the lognormal probability density function. The state transition probability vector for each time period was developed by extracting the fade slope statistics of the measured attenuation. The discrete-time Gaussian distributed fade slope PDF forms the basis for the state transition probability matrix. With these, Markov-generated time series of seasonal and annual slant path attenuation for up to five iterations were obtained. The results make useful data that can be used for long-term planning for rain fade mitigation in a subtropical climate easier to generate without the expense of measurements. The theoretical approach called the Synthetic Storm Technique was also applied to investigate the nature of slant path rain attenuation in Durban. Based on the rainfall pattern captured by the disdrometer, SST approximations for the four seasons of the subtropical year and for years of rain data collection were carried out. The results were compared with the values generated from the measurement model. It reveals that the two models exhibit significant agreement because in a majority of the cases, the A0.01 values obtained are very close. Comparison of the performance of SST as a theoretical model with that of the ITU-recommended method also reveals that the ITU performs slightly better as an alternative to measurement than the SST model. It was observed that during certain precipitation events, the satellite link registers significant attenuation levels several minutes before the disdrometer records any precipitation on the ground. This anomaly was investigated in this work and a few conclusions drawn. By proceeding on the assumption that the observed delay was due to the migrating rain cell interacting with the satellite beam several minutes before reaching the receive antenna, it was demonstrated that the time of delay between precipitation and attenuation is related to the rain height during that particular rain event. A simple mathematical analysis is presented that enables the rain height to be estimated from the delay time. The results obtained range between 1.4 km to 6.7 km which is similarity to rain height values obtained by the ITU model which range from 1.36 km to 6.36 km

Characterization of bright-band in a tropical station for satellite communications

Tropical regions experience signal degradations due to hydrometeors in addition to paucity of database for slant path rain propagation estimations. The melting layer is the region where rain starts to occur; lying just below the 0oC isotherm height. Frozen hydrometeors exhibit peculiar characteristics in the form of increased radar reflectivity as they fall from the sky, morphing from solid to liquid; and manifesting itself as the popular bright-band signature. Knowledge of the formation and recognition of the bright-band is necessary to characterize the melting layer. Adequate information on diurnal, seasonal and annual variation effects on rain height can give valuable information for satellite equipment design and planning. Rain height is highly correlated with signal attenuation and co-channel interference resulting from scattering. This work involves the characterization of bright-band data for UTM Johor Bahru campus, Malaysia. Thirteen months (1 November, 2006 to 30 November, 2007) 3D RAPIC ground radar data at 500 m range bins resolution were sourced from MMS. Additionally, twenty-two months (January 2011 to May 2013) TMPA-RT radar data at 50 x 50 latitude-longitude horizontal resolution were obtained to complement the ground radar data. The reflectivity from these data was analysed to characterize the melting layer. Malaysia experiences two monsoon events yearly: The North-East monsoon and the South-West monsoon. Results from this work suggest that freezing and rain heights are highest in the months of November 2006, March and September 2007; which coincides with the end of the two monsoons. Equally, these parameters are observed to be lowest in February, April, July and October; thus suggesting seasonal and annual variability. The bright-band is thicker in the day, while freezing and rain heights are higher at night than in the day time, suggesting diurnal dependence. However, data for a longer period of time is needed to consolidate these findings. The results show good degree of agreement when compared with similar previous findings from Malaysia. But, ITU-R.P. 618 model largely underestimated the total measured attenuation. Thus, there is a need to include the melting layer effect in satellite communication attenuation prediction in the tropics for improved Quality of Service

Propagation effects handbook for satellite systems design: A summary of propagation impairments on 10 to 100 GHz satellite links with techniques for system design

The major propagation effects experienced on Earth-space communications paths in the 10 to 100 GHz frequency range. Attenuation due to rain is dealt with in detail

Propagation effects handbook for satellite systems design. A summary of propagation impairments on 10 to 100 GHz satellite links with techniques for system design

The NASA Propagation Effects Handbook for Satellite Systems Design provides a systematic compilation of the major propagation effects experienced on space-Earth paths in the 10 to 100 GHz frequency band region. It provides both a detailed description of the propagation phenomenon and a summary of the impact of the effect on the communications system design and performance. Chapter 2 through 5 describe the propagation effects, prediction models, and available experimental data bases. In Chapter 6, design techniques and prediction methods available for evaluating propagation effects on space-Earth communication systems are presented. Chapter 7 addresses the system design process and how the effects of propagation on system design and performance should be considered and how that can be mitigated. Examples of operational and planned Ku, Ka, and EHF satellite communications systems are given

Propagation effects handbook for satellite systems design. A summary of propagation impairments on 10 to 100 GHz satellite links with techniques for system design

This Propagation Handbook provides satellite system engineers with a concise summary of the major propagation effects experienced on Earth-space paths in the 10 to 100 GHz frequency range. The dominant effect, attenuation due to rain, is dealt with in some detail, in terms of both experimental data from measurements made in the U.S. and Canada, and the mathematical and conceptual models devised to explain the data. In order to make the Handbook readily usable to many engineers, it has been arranged in two parts. Chapters 2-5 comprise the descriptive part. They deal in some detail with rain systems, rain and attenuation models, depolarization and experimental data. Chapters 6 and 7 make up the design part of the Handbook and may be used almost independently of the earlier chapters. In Chapter 6, the design techniques recommended for predicting propagation effects in Earth-space communications systems are presented. Chapter 7 addresses the questions of where in the system design process the effects of propagation should be considered, and what precautions should be taken when applying the propagation results

Tropospheric scintillation and attenuation on satellite-to-Earth links at Ka and Q band: modeling, validation and experimental applications

Link budget is a crucial step during the design of every communication system. For this reason it is fundamental to identify and estimate the effects of the atmosphere on the electromagnetic signal along the path from the source to the sink. Troposphere represent the bigger source of attenuation and scintillation for signals in the microwave and upper frequency spectrum. During last years we have participated in the European Space Agency “AlphaSat Aldo Paraboni” experimental campaigns to acquire up to date propagation data at two frequencies of interest for future communication systems. We realized two high performance low-noise receiver located in Rome, one at Ka and one at Q band (19.701 and 39.402 GHz) to detect the two signal beacons sent from the AlphaSat geostationary satellite to a wide area over Europe. Collected data from Rome receiving station have been analysed to measure excess attenuation and scintillation along the path. Such statistics collected in a database together with data from other experimenter will be in the near future a useful instrument, giving professionals updated data for their custom application design. Classical link budget techniques rely on climatological atmospheric statistics based on different time-scales, usually data collected for several years. In the background of the European Space Agency “STEAM” project, we proposed the use of high resolution 3D weather forecast models (up to 166m pixel resolution) for the calculation of excess attenuation and tropospheric scintillation for satellite to earth link. As a result, the estimation of these electromagnetic parameters to use in link budgets could be given no more as a statistical analysis of past events as in the case of Internation Telecommunication Union recommendation but as time-series forecast specific for the selected receiving station and along the slant path of the transmitted signal. Case studies for the use of this technique have been deeply analysed and results compared with data from the AlphaSat measurement campaign for the Rome and Spino d’Adda receiving station, confirming the validity even in different geographical regions. In everyday situations, propagation models based on statistics are often replaced by the use of easier to apply parametric models. Those have the advantage of the simplicity and the need of less input parameter to be applied. In particular, for what concerning the tropospheric scintillation, the Hufnagel-Valley refractive index structure constant (C2n ) parametric model is actually the most used, due to the simplicity and the relative accuracy. We here propose a new Cn2 polynomial parametric model (CPP) based just on the altitude z and a function C2 n0(to,RH0) that allow to calculate the ground refractive index structure constant just using the ground temperature (T0) and the relative humidity (RH0). In this work CPP and Hufnagel-Valley models are applied to different location around the globe to prove their accuracy. The obtained model could be also used in the future to realize a simulator able to generate random C2n vertical profiles specific for the receiver site

Měření vlivu kapek pro optický bezvlaknový spoj a matematické modelování vícefázového proudění

Free space optics will emerge alongside major communications technologies as an important player in the field of wireless communications. This technology, like other technologies, has to face the challenges caused by unstable and unfavorable atmospheric conditions that determine the resulting quality of the transmitted signal. The paper is intended to determine the extent of a deterioration of the transmitted signal during rainfall. The precipitation is simulated in laboratory conditions, and the resulting knowledge of the droplet formation is transferred to a mathematical model that helps simulate multiphase flow under given conditions.Optické bezvláknové spoje se v budoucnosti vyskytnou po boku majoritních komunikačních technologií jako důležitý hráč na poli bezdrátových komunikací. Tato technologie, stejně jako jiné technologie, musí čelit výzvám pramenícím z nestálých a nepříznivých atmosférických podmínek, které rozhodují o výsledné kvalitě přenášeného signálu. Tato práce má za úkol zjistit míru zhoršení přenášeného signálu během dešťových srážek. Srážkový úhrn je simulován v laboratorních podmínkách a výsledné poznatky o tvorbě dešťových kapek jsou přeneseny do matematického modelu, který napomáhá simulování vícefázového proudění v daných podmínkách.440 - Katedra telekomunikační technikyvýborn