Fade Slope Statistics Research Articles

Analysis of rain fade characteristics from experimental satellite measurements at Ka/Q bands for a temperate location Vigo, Spain

Rain is one of the most dominant factors for satellite communication systems link performance at frequencies above 10 GHz, increasing rapidly at higher frequencies. The prediction of time dynamics of the rain attenuation is required to improve the efficiency of various fade mitigation techniques (FMTs) to reduce signal fading. Fade duration and fade slope statistics are used to describe the dynamic behavior of attenuation experienced by radio communication links. The present study is based on experimental measurements from a Ka band (KaSAT) and Q band (AlphaSAT) beacon receiver at the frequencies 19. 7 GHz and 39. 4 GHz respectively. In this paper, annual and monthly variation of rain attenuation statistics for a temperate location Vigo, Spain is presented. Monthly variation of rain attenuation statistics is much larger than the yearly variation for the present location. This paper also analyzes the fade duration and fade slope statistics for both the bands. The conditional probability density function (PDF) of fade slope shows general symmetry between positive and negative slope values for both Ka and Q bands. All the measured statistics (1st order and 2nd order) are compared with the existing ITU-R and COST-205 models. Predictions of rain attenuation by both the models are close to the measured data. For fade duration statistics, as attenuation threshold increases, performance of both ITU-R and COST-205 models improves for Ka band. For Q band, COST model performs better compared to ITU-R model. Measured probability density function of fade slope fits with the ITU-R model more closely for Q band compared to Ka band.

Rain fade slope model for terrestrial microwave links

AbstractThe dynamic characteristic of rain fade slope is one important factor in determining the availability of a communication system, and it is very useful in the design of fade countermeasures. In the literature, many models were proposed for rain fade slope for earth-to-satellite links. However, there are no models available for rain fade point to point terrestrial microwave links. This paper proposes a new model for the estimation of rain fade slope statistics for terrestrial microwave links in tropical regions. First, the ITU-R model for rain fade slope for earth-to-satellite link was compared with the corresponding statistics obtained from rain attenuation data measured from three terrestrial links in Malaysia. It is found that the expression of its distribution and its standard deviation should be modified. This leads to the derivation of the proposed rain fade slope model based on the statistics of one link. Then, it is tested using the remaining data and its results were very close to the measured statistics for all attenuation levels higher than 1 dB. Moreover, the model was validated using the chi-square goodness-of-fit test.

Performance of synthetic storm technique in estimating fade dynamics in equatorial Malaysia

SummaryIn this paper, the synthetic storm technique (SST) is applied to 1‐minute rainfall rate collected from a rain gauge to predict the fade dynamics of the signal in an earth‐to‐satellite link in an equatorial climate location without the needs of satellite beacon measurements. The obtained results are compared with the statistics calculated from measured rain attenuation and with the ITU recommendation model. As for fade duration, a good agreement with measurements has been found together with a significant improvement in terms of prediction errors with respect to the ITU‐R model. Synthetic storm technique is also able to predict fade slope statistics fairly well and has equivalent performance of ITU‐R model.

Short-Term Rain Attenuation Predictor for Terrestrial Links in Tropical Area

This letter describes a short-term rain attenuation predictor model for terrestrial radio links located in tropical area. The predictor is based on the fade-slope statistics that are modeled by a generalization of Van de Kamp (VDK) distribution for rain attenuation levels between 1 and 30 dB. The predictor can improve adaptive fade countermeasures as it predicts the rain attenuation in the next 10 s based on the current attenuation value. The model is applied to data collected in four links located in tropical region, and its results show that the absolute values of prediction errors are under 2.9 dB for 99.9% of the predictions.

Joint results of long-term earth-space propagation experiments at 20-GHz in Canada and Europe

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Development of a heterogeneous microwave network fade simulation tool applicable to networks that span Europe

[1] Several research groups in Europe are developing joint channel simulators for arbitrarily complex networks of terrestrial and slant path, microwave telecommunications links. Currently, the Hull Rain Fade Network Simulator (HRFNS) developed at University of Hull can simulate rain fade on arbitrary terrestrial networks in the southern United Kingdom, producing joint rain fade time series with a 10 s integration time. This paper reports on work to broaden the function of the existing HRFNS to include slant paths such as Earth-space links and communications to high altitude platforms and unmanned airborne systems. The area of application of the new simulation tool is being extended to the whole of Europe, and other fade mechanisms are being included. Nimrod/OPERA has been chosen as the input meteorological data sets for the new system to simulate rain fade. Zero-degree isotherm heights taken from NCEP/NCAR Reanalysis Data are used in conjunction with the Eden-Bacon sleet (wet snow) model to introduce melting layer effects. Other fading mechanisms, including cloud fade, scintillation and absorption losses by atmospheric gasses, can be added to the simulator. The simulator is tested against ITU-R models for rain fade distribution experienced by terrestrial and Earth-space links in the southern United Kingdom. Statistics of fade dynamics, i.e., fade slope and fade duration, for a simulated Earth-space link are compared to International Telecommunication Union models.

Rain Attenuation Time Series Synthesizer Based on the Gamma Distribution

This letter describes the application of rain attenuation time series synthesizers to terrestrial links in tropical regions. A model based on the Gamma distribution is developed and results are compared to those obtained with a lognormal synthesizer. The model parameters were retrieved from data collected during two years of experimental measurements at terrestrial links operating at 15 GHz. Long-term statistics of rain attenuation and fade slope obtained from synthesized time series are tested against the corresponding ones derived from experimental data. Useful empirical expressions for the synthesizers dynamics parameters are derived.

Fade Slope Statistics on a Slant Path at 50 GHz

Statistics of fade slope at 50 GHz have been derived from one year of slant path attenuation measurements, using time interval lengths between 2 and 200 s. From these statistics, the dependence of fade slope on the attenuation level and time interval can be quantified. It has been found that the ITU-R model, specified for frequencies up to 30 GHz, fits well the experimental conditional distributions. Nevertheless, some divergences are observed for the lowest attenuations, which may be attributed to cloud effects. Such results are required for the design of communications systems operating in the -band.

Analysis of Rain Fade Slope for Ka and V-Band Satellite Links in Southern England

The fade slope of rain attenuation at Sparsholt, U.K. has been measured for a link with the ITALSAT F1 and F2 satellites at frequencies of 18.7, 39.6, and 49.5 GHz and compared with the corresponding ITU-R model. The model fits the data well visually with a tendency to be less accurate with increasing frequency due to the assumption of constant scaling of equiprobable attenuations being less accurate at higher frequencies. The probability distribution used in the model fails a chi-squared test for all confidence levels when compared with the data. Conditional statistics of fade slope on a diurnal and seasonal basis are also analyzed and reveal that the autumn season has higher fade slopes than any other, which can in part be attributed to the higher ratio of stratiform to convective rain in the autumn season. Fade slope was found to have slightly higher values during midday

Effect of wet antenna attenuation on propagation data statistics

Wet antenna attenuation during rain events is examined through carrying out simulated rain experiments. These were conducted on the receiving antenna of the Vancouver ACTS terminal under conditions similar to those prevalent when the propagation data on the Vancouver ACTS path were collected. The findings from these experiments are used to estimate path attenuation data for that path by adjusting the collected data for wet antenna attenuation via two different models. Primary and secondary statistics of the path attenuation data derived from the models at the two ACTS frequencies, nominally 20 and 27 GHz, are computed and compared with those for the unadjusted, measured data. This was done for the four-year period of December 1993 to November 1997 and includes average and worst month cumulative distribution functions and fade-duration and fade-slope statistics. While the two models yield similar statistics, these differ significantly from those derived from the unadjusted data. The comparison of the two sets of statistics suggests that the use of those of the unadjusted data to represent path attenuation would grossly exaggerate the requirements for system design.

First-order and conditional statistics of rainattenuation fade slope

In accordance with the assumptions of Maseng and Bakken (1981), the distribution of rain fade slope on high frequency GSO links is calculated and its Cauchy approximation is presented. The conditional PDF of the fade slope is finally modelled for application to predictive rain fade mitigation techniques (FMTs).

Descriptive fade slope statistics on INTELSAT Ku-bandcommunication link

Descriptive statistics of fade slope from the INTELSAT VI beacon data at 11.198 GHz and 42.8° elevation are presented. Results indicate a direct positive correlation between the mean values of fade slope and attenuation and show that individual rain events have higher fade slope with deeper fade depths. The absolute fade slopes can be best approximated by a log-normal distribution. Positive and negative fade slopes are symmetrically distributed and the distribution becomes flatter at higher attenuation levels.

Fade slope statistics for three 12-GHz satellite beacon links in Brazil

The fade slope is defined as the rate of increase or decrease of attenuation over time. The possible correlation between the statistics of fade slope values and attenuation levels is investigated. Results show a direct positive correlation between the mean values of fade slope and the attenuation levels. The distributions of fade slope values present a degree of skewness toward the negative values that makes the curves depart from the Gaussian distribution observed by other authors.

Fade slope statistics of 40 GHz beacon signals

Fade slope statistics for negative and positive slopes are presented which are obtained by propagation measurements of the 40 GHz beacon signal of the Italian satellite ITALSAT. Especially, the fade slope and the 3 dB time duration introduced here are evaluated. Measured, fade slopes of up to 3.2 dB/s were recorded. However, in 99.99% of the fading event time the fade slopes are < 1.9 dB/s.

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.

Frequency and attenuation dependent fade slope statistics

Results obtained from slant path propagation experiments carried out with the OLYMPUS satellite are reported. Concurrent attenuation measurements at 12.5, 20 and 30 GHz have been analysed with regard to the rate of change of rain attenuation (fade slope). The results indicate that pronounced fade slopes occur mostly in the high attenuation range.