Earth-space Communication Links Research Articles

Elevation angle effect on slant path attenuation along earth-space paths: A Northern Nigeria perspective

In the network planning and design of terrestrial and earth-space communication links, the slant path attenuation caused by rain and its associated strong winds is of interest. Rain causes severe link degradation to radio links by absorbing parts or the whole signal during propagation. This study predicts slant path attenuation by rain in three (3) Northern Nigerian zones using the International Telecommunications Unions (ITU-R) model for 10 to 40 GHz. The effect of specific attenuation, rain attenuation, and elevation angle on the received signal strength is analyzed. The ITU-R model suggests rain attenuation values ranging from 4.26 dB to 31.67 dB for Jaji, Wudil, and Potiskum. The results further indicate a decrease in rain attenuation with an increase in elevation angle up to 50.1° elevation for the three (3) monitored stations, which starts to decrease steadily after this threshold. Results from this study can aid the network engineer in anticipating network changes and planning fade mitigation techniques where necessary.

Prediction of Tropospheric Amplitude Scintillation for Accurate Design of Earth-Space Communication Link over Akure, Nigeria

Prediction of Tropospheric Amplitude Scintillation for Accurate Design of Earth-Space Communication Link over Akure, Nigeria

English

Rain-based attenuation (RBA) is a major deteriorating factor affecting radio wave signals operating at microwave and millimetre wave bands for a typical Earth-Space Communication Link (ESCL). Although the international telecommunication union (ITU) recommended a standard model for predicting RBA along the terrestrial and ESCL, the technique underperforms in tropical environments. However, the model can be supported by appropriate modulation to enhance link performance. The present study assesses the performance of selected RBA models, namely the ITU, Moupfouma, and Garcá¼±a-Lὁpez models based on rain types for K-V frequency bands over some selected locations in Southwestern Nigeria. Link performance was further tested based on different modulation scaling to minimize signal degradation. The result shows that Garcίa-Lá½¹pez and ITU models performed well at low rain rate R ≤2 mm/h but underestimated at higher rain rates (except thunderstorms rain type) at the high-frequency band. However, the Moupfouma model performed well for all the rain types irrespective of the selected frequency band, while the ITU model underestimated attenuation for R < 5 mm/h (shower) and R > 30 mm/h (thunderstorm) rain type from the K-V band frequency, Garcia Lopez underestimates the RBA value for R < 5 mm/h and R > 5 mm/h up to the Ka frequency band. Considering the modulation scaling on link performance shows that the bit-error-rate (BER) will severely degrade with a high rain rate compared to the low rain rate across different frequencies. The BER for 8-PPM outperforms the other types of modulation schemes that were used in this study. Overall results revealed that modulation technique DPSK with selective combining diversity gave a marginal improvement with the increase in link distance and operating frequency. Key words: ESCL, rain attenuation models, modulation techniques, K-V frequency bands.

An Analysis on the Propagation Prediction Model of Earth-space Communication Link using Local Data

An Analysis on the Propagation Prediction Model of Earth-space Communication Link using Local Data

Analysis of Time Diversity Gain for Satellite Communication Link based on Ku-Band Rain Attenuation Data Measured in Malaysia

<p><span>This paper reports a study on mitigation of propagation impairments on Earth–space communication links. The study uses time diversity as a technique for mitigating rain propagation impairment in order to rectify rain fade. Rain attenuation time series along earth-to-satellite link were measured for two years period at 12.255 GHz in Malaysia. The time diversity technique was applied on measured rain fade to investigate the level of possible improvement in system. Time diversity gain from measured one-minute rain attenuation for two years period was estimated and significant improvement was observed with different delays of time. These findings will be utilized as a useful tool for link designers to apply time diversity as a rain fade mitigation technique in Earth-satellite communications systems.</span></p>

Performance Analysis and Simulation of Rain Attenuation Models at 12–40 GHz Band for an Earth Space Path over Indian Cities

As the shortage of the radio spectrum infers challenges in the Earth–Space Communication Link (ESCL) particularly in satellite communication, it is important to gauge the measure of attenuation to guarantee proficient usage of the spectrum. By the shortage in the frequency spectrum, the coming period will request more information to be exchanged at unquestionably more speed. Furthermore, this will interest for the higher frequencies. Keeping in mind the end goal to exploit present day space communications innovation, acknowledgment of a household correspondence satellite framework with impressive communication limit at Ku–band is attainable. Climate is exceptionally unverifiable and labile hydrometeor activities make issue in a satellite communication. The real issue connected with the communication links at these high frequency radio waves is the rain attenuation estimation. In this paper, a performance analysis and simulation of rain attenuation models is shown for frequency range of 12–40 GHz over ESCL at real urban communities of India by considering information of NSS–6 satellite.

Rain attenuation prediction during rain events in different climatic regions

A rain attenuation prediction method has been applied to different climatic regions to test the validity of the model. The significant difference in rain rate and attenuation statistics for the tropical and temperate region needs to be considered in developing channel model to predict time series of rain attenuation for earth space communication links. Model parameters obtained for a tropical location has been successfully applied to predict time series of rain attenuation at other tropical locations. Separate model parameters are derived from the experimental data obtained at a temperate location and these are used to predict rain attenuation during rain events for other temperate locations showing the effectiveness of the technique.

Atmospheric Effects on Free Space Earth-to-Satellite Optical Link in Tropical Climate

Free Space Optic (FSO) vulnerability towards atmospheric phenomena is becoming a main issue towards its implementation. A lot of studies have been conducted to estimate the climatological effects on FSO links but most of them are based on terrestrial link with short path lengths and centred in temperate regions.Hence, this paper aims to analyse the performance of FSO links from earth-to-LEO satellite in tropical regions where rain and haze are the main concerns. This analysis is based on available methods and data to predict earth-to-satellite FSO links with the scaled up data from the measurement on terrestrial FSO link installed at International Islamic University Malaysia (IIUM) Kuala Lumpur campus. Data collected from terrestrial link are FSO received signal levels, corresponding rain intensity and visibility variations. The measured data are scaled up to the effective distance of slant path lengths and then compared with the predicted values. These findings will be very useful for FSO earth-space communication link designers and can be as a benchmark of FSO system design.

Melting layer characteristics at different climatic conditions in the Indian region: Ground based measurements and satellite observations

Melting layer height, which is normally assumed to be the limits of rain region, is an important parameter to consider the performance of earth space communication link above 10 GHz. In this paper, the variation of melting layer observed by a vertically looking Micro Rain Radar (MRR) for 3 years has been presented for two different climatic locations in Indian tropical region — Shillong (25°34′ N, 91°53′ E, 1050 m) and Trivandrum (8°29′ N, 76°57′ E, 4 m). The analyses show that the variation is quite significant for different months in Shillong but not for Trivandrum. The height of melting layer shows a strong correlation with ground temperature of these locations. The results agree well with the long term Tropical Rainfall Measuring Mission (TRMM) measurements of melting layer indicating suitability of using TRMM data for such study. A comparison of MRR with the nearest Radiosonde measurement indicates that MRR can have potential application in the study of zero degree isotherm height in rainy conditions. Results also clearly indicate that the assumption of constant rain height is not a valid one for all tropical locations.

Rain induced attenuation studies for V-band satellite communication in tropical region

Satellite communications operating at 10 GHz and above in the tropics suffer severe signal degradation due to rain. Attenuation due to rain at 38 GHz had been measured for a period of 20 months in Malaysia. Analyses carried out include seasonal variations, diurnal effects and the annual cumulative distributions. Obtained results were compared with several established prediction models including the ITU-R. The rain fade characteristics were also investigated in determining the levels of signal loss and fading. In addition, the studies highlight several potential fade mitigation techniques that can be embarked. These fundamental aprehensions are very critical for future earth space communication link design and can be exploited as preliminary groundwork plan for the researchers as well as engineers.

V-Band Fade Dynamics Characteristics Analysis in Tropical Region

Problem statement: Satellite operations at V-band in tropical and equatorial regions are constrained as a result of attenuation from rain. Approach: Statistics for 20 consecutive months of V-band terrestrial link signal attenuation measurements in Malaysia were presented in this analysis. Such information was considered very pertinent for Earth-space communication link design and can be used for initial groundwork plan for the engineers as well as researchers. Results: The measured statistics were then fittingly scaled up to fit Earth-satellite link. The statistics were then broken down to examine diurnal variations. Characteristics of rain events such as fade duration and inter-fade interval were presented. Conclusion/Recommendations: It is essential to identify such characteristics for the design and implementation of future fade countermeasure techniques on satellite links.

Characterization and modelling of time diversity statistics for satellite communications from 12 to 50 GHz

AbstractTo compensate propagation impairments on Earth–space communication links, a specific fade mitigation technique to make up for rain propagation impairments is studied in this paper: the time diversity. This process consists in sending the information when the propagation channel allows to get it through. Here the time diversity technique is applied to different experimental attenuation time series collected in Europe: Spino d'Adda (Italy), Louvain‐la‐Neuve and Lessive (Belgium). These propagation measurements have been collected from 12 to 50 GHz and the performance of time diversity technique is assessed from the generation of time diversity statistics conditioned to the time delay. A prediction method of these statistics is also described. The proposed model relies on the time correlation of the attenuation time series. The model is validated and its accuracy analysed in terms of prediction error calculated using the different databases. Copyright © 2009 John Wiley & Sons, Ltd.

Estimation of Effective Rain Height at 29 GHz at Amritsar (Tropical Region)

The effect of precipitation present in the path of Earth-space communication links, in terms of fading of the signal, is well known. The calculation of fade margin required for 99.99% of the time availability of such links requires the knowledge of various location-specific meteorological parameters, amongst which rain height is prominent. This paper presents results from measurements conducted at Amritsar during a single rain event that took place on September 19, 2005, using a zenith-pointing Dicke-type radiometer at 29 GHz in the form of sky noise temperature. The output of the radiometer along with rain rate, derived from colocated tipping-bucket rain gauge, has been used to obtain a formula relating zenith path attenuation and rain rate. Further, the values of zenith path attenuation and rain rate along with specific attenuation coefficients a and b to obtain effective rain height. It was found that rain height cannot be taken as constant as it is dependent on rain rate. The average rain height during the event was estimated to be 3.54 km with root mean square error of 3.0 km

A novel method for the statistical prediction of rain attenuation in site diversity systems: theory and comparative testing against experimental data

Site diversity is a promising technique to overcome severe attenuation on earth–space communication links. This technique is based on the experimental evidence that intense rain cells are limited in extent, so that the replacement of one station with two or more stations separated by a few kilometres may substantially reduce the outage probability of the communication system. In this paper the physical EXCELL rain cell model, developed at our laboratory for the prediction of single-site rain attenuation statistics, has been extended to the case of diversity configuration systems. For comparison purposes, two among the best-performing models found in the literature, proposed by Hodge and Matricciani, have been considered. The values predicted by the three models have been compared against data of 41 experiments with a maximum separation distance between ground stations of 15 km, collected both from the ITU-R databank and from the open literature. This site separation range is the most interesting one, because attenuations in diversity paths tend to be uncorrelated above 20–30 km and hence the benefit obtained by a diversity scheme becomes marginal. The measured and predicted ‘relative diversity gains’ at various time percentages have been compared: the RMS values of relative gain error show that EXCELL is the best-performing model. © 1998 John Wiley & Sons, Ltd.

A novel method for the statistical prediction of rain attenuation in site diversity systems: theory and comparative testing against experimental data

Site diversity is a promising technique to overcome severe attenuation on earth–space communication links. This technique is based on the experimental evidence that intense rain cells are limited in extent, so that the replacement of one station with two or more stations separated by a few kilometres may substantially reduce the outage probability of the communication system. In this paper the physical EXCELL rain cell model, developed at our laboratory for the prediction of single-site rain attenuation statistics, has been extended to the case of diversity configuration systems. For comparison purposes, two among the best-performing models found in the literature, proposed by Hodge and Matricciani, have been considered. The values predicted by the three models have been compared against data of 41 experiments with a maximum separation distance between ground stations of 15 km, collected both from the ITU-R databank and from the open literature. This site separation range is the most interesting one, because attenuations in diversity paths tend to be uncorrelated above 20–30 km and hence the benefit obtained by a diversity scheme becomes marginal. The measured and predicted ‘relative diversity gains’ at various time percentages have been compared: the RMS values of relative gain error show that EXCELL is the best-performing model. © 1998 John Wiley & Sons, Ltd.

Fade slope on 10 to 30 GHz Earth-space communication links — measurements and modelling

One year of atmospheric propagation data were collected and analysed at Blacksburg, Virginia, USA, using the Olympus satellite 12.5, 20 and 30 GHz beacons. The results are in the form of statistics which communication system designers can use to quantify precipitation effects on Ka-band links. The paper presents the results for rain fade dynamics including fade slope statistics as well as a simple model for estimating fade slope statistics for any frequency in the range 10 to 30 GHz.

Diversity measurements of attenuation at 37 GHz with sun-tracking radiometers in a 3-site network

The results of a site-diversity experiment at 37 GHz with sun-tracking radiometers at three sites 10.3, 12.7 and 18 km apart, near Slough, UK, are described in relation to Earth-space communication links. Data for observation periods of 16, 8 and 9 months from the three pairs of sites are presented in the form of cumulative distributions and of diversity advantage as a function of attenuation, together with histograms of the number and duration of individual fades exceeding 10 dB. The largest diversity advantage was found for the 18 km spacing and the least advantage was with the 12.7 km spacing for which the sites were aligned approximately perpendicularly to the direction of movement of prevailing storms. A method is given for predicting diversity characteristics at one frequency from measurements made at another, based on two sets of measurements made at Slough; one made concurrently at 19 and 37 GHz, the other made concurrently at 37 and 71 GHz.

Radiometer measurements of atmospheric attenuation at 19 and 37 GHz along Sun-Earth paths

The measurements of attenuation described in the paper refer to data recorded over a 3-year period at a frequency of 19 GHz, and over a 1-year period at 37 GHz. The relevance of these data to Earth-space communication links is discussed. Statistics showing the percentage of observation time for which the attenuation exceeds various values are given for each year for various ranges of elevation angle. At 19 GHz, the values of attenuation obtained from the extreme annual distributions differ by a factor of about two at a given percentage of time. Also, the percentage of time for which the attenuation at 19 GHz exceeded 10 dB for the ‘worst’ month is an order of magnitude larger than the corresponding value for the 3-year period. Statistics derived from data obtained during periods of common observation at 19 and 37 GHz are compared for various ranges of elevation angle. Histograms showing the number of fades as a function of the duration of the fade are presented for both frequencies for fades greater than 5 and 10 dB, and a comparison of the instantaneous values of attenuation at 19 and 37 GHz at fade maxima has been made.