Rain fades on low elevation angle Earth-satellite paths:comparative assessment of the Austin, Texas, 11.2 GHz experiment

Only a few years of rain attenuation data for Earth-space paths are available for low elevation angle paths, and these show a consistent tendency by the CCIR fade prediction model to underpredict rain fades. The authors contribute to the database four years of 11.2 GHz measurements, taken on a 5.8° elevation path in Austin, Texas, USA and assess higher than predicted fade results with respect to earlier measurements and the CCIR model. At the fiducial 0.01 percent of time, the rain fall rate was 73 mm/h and the attenuation exceeded the 25 dB measurement fade margin. It is found that the monthly variability of rain fall rates and decibel fades follows a normal distribution. Durations of rainfall and fades are classified into events, episodes, interevent gaps (longer than 4.2 h), and interepisode gaps (shorter than 4.2 h). Rainfall interevent gaps and event durations, as well as fade event, episode, and gap durations are log-normally distributed     

A new method for the prediction of fade duration statistics in satellite links above 10 GHz

A model for the statistical prediction of fade durations, applicable both to scintillation and rain-induced effects, is presented in this paper. It assumes that durations longer than about 1 minute are lognormally distributed whereas shorter durations follow a power-law distribution. The model is assessed using data contained in the CCIR data bank and from measurements performed with the SIRIO and Olympus satellites. The model is tested using the same data, and the results give multiplicative errors in the range from 0.6 to 1.8 (averages) and from 0.3 to 3.0 (r.m.s.) in the estimation of the fade durations exceeded for fixed probability.     

Empirical models for rain fade time on Ku- and Ka-band satellitelinks

Rain attenuation data from the OLYMPUS satellite beacon measurements are used to investigate fade time in the Ku and Ka bands. Using statistical procedures, an empirical model is developed which predicts fade time as a function of attenuation level, frequency of operation, and fade duration interval. Total annual fade times are predicted over a frequency span of 12-30 GHz for attenuation levels in the 3-18 dB range and for fade duration intervals of 30-60 s, 60-120 s, 2-5 min, and 5-20 min. The predicted fade times are in good agreement with the measured values. An alternate model, described by two simple relationships in two different ranges of attenuation level, is also presented by simplifying the original single-equation model. The simplified model accounts for fades associated with stratiform rain and thunderstorms separately     

Multiyear slant-path rain fade statistics at 28.56 GHz for Wallops Island, VA

Multiyear rain fade statistics at 28.56 GHz have been compiled for the region of Wallops Island, VA, covering the time periods April 1, 1977-March 31, 1978, and September 1, 1978-August 31, 1979. The 28.56-GHz attenuations were derived by monitoring the beacon signals from the Comstar geosynchronous satellite,D_{2}, during the first year, and satellite,D_{3}, during the second year. Comparisons are made of yearly, monthly, and time of day fade statistics for the first, second, and combined years. Although considerable year to year variations in exceedance times exist for the monthly and time of day fade statistics, the overall fade distributions for the individual years showed relatively small differences. For example, comparing the second year fades relative to those of the first year at equal percentages of time, less than 20 percent rms deviation was found. The year to year variations of rain rate distributions are also examined and show consistently small differences. The resultant fade distribution at 28.56 GHz for Wallops Island, VA, are compared with that arrived at using a prediction method which is a recent refinement of the International Radio Consultative Committee (CCIR) global model, and an rms decibel deviation of less than 14 percent was noted.     

Effect of Matrix Partitioning on Second Order Statistics of Fading Channels

In this paper, the expressions for level crossing rate and average fade duration of two-branch selection combining are derived using the proposed matrix partitioning based method for a space-diversity system using a two-branch horizontal linear antenna array at the mobile station. It has been observed that when the antennas are perpendicular to the direction of the vehicle motion, the average fade duration is not very much dependent on the antenna spacing and is almost identical to that for independent fading except for very small antenna spacing. On the other hand, when the antennas are parallel to the direction of the vehicle motion, the level crossing rate can be reduced below the value obtained for independent fading, although the average fade duration deteriorates, especially for small antenna spacing. Numerical results are presented and compared with the existing characteristic function based methods including Gaussian fluctuation effects.     

Fade duration statistics ofL-band multipath fading due to sea surface reflection

Multipath fading in maritime satellite communications may be caused by a combination of sea surface reflection and tropospheric effects such as ducting and scintillations. Among them, multipath fading due to sea reflection is dominant when receiving satellite signals by use of a wide beamwidth antenna. In this paper, fade duration statistics of multipath fading due to sea surface reflection are analyzed using the data obtained by on-board experiments on theL-band (1.54 GHz). Results indicate that the mean value of fade duration and fade occurrence interval can be determined from the fading power spectrum with fairly good precision, and that the probability density function for a given time percentage, ranging from 50 to 99 percent, approximates well with the exponential distribution. Finally, based on the results obtained, a simple method for estimating the mean values of fade duration and fade occurrence interval is presented.     

Rain-rate duration statistics over a five-year period: a tool forassessing slant path fade durations

A rain gauge network of 10 tipping bucket rain gauges on the Mid-Atlantic coast of the United States has been in continuous operation since June 1, 1986. Rain-rate distributions and estimated slant path fade distributions at 20 and 30 GHz covering the first five-year period have been derived from the gauge network measurements and published data of Goldhirsh, Krichevsky and Gebo (see ibid., vol.40, no.11, p.1408, 1992). In this article, we present rain-rate time duration statistics. The conversion of rain-rate duration statistics derived from in situ measurements to slant path fade duration statistics is complicated because of the vertical and lateral inhomogeneity of the rain. A benchmark set of fade duration statistics at 20 and 30 GHz for a vertical path is derived from the rain-rate duration statistics employing Crane's (1980) global model. These results may be used by investigators for comparison with and/or conversion to slant path fade duration statistics. Such statistics are important for better assessing optimal coding procedures over defined bandwidths     

Space diversity and fade duration statistics at C-band fortwo overwater, line-of-sight propagation paths in the mid-Atlantic coast

The authors characterize space diversity and fade duration statistics at 4.7 GHz for two line-of-sight (LOS) overwater links in the mid-Atlantic coast of the United States. Single-terminal and joint probabilities are generated for both annual and monthly cases for fade and fade duration distributions over the year period from June 1, 1989 to May 31, 1990. The fade and duration distributions during the months November-June were heavily biased by sustained deep fade events. These events were caused by persistent and severe subrefraction, which generally existed simultaneously over both sites. Although the height geometries are dissimilar (13.7 m and 45.5 m), these events mitigated the effectiveness of space diversity. During periods in February and March 1990, for example, fading continuously exceeded 20 dB (relative to the free-space power) at both sites for a duration in excess of 24 h. Space diversity does however appear effective during those months in which fading were predominantly caused by ducting (July-October) and when sustained deep fade events were generally not present     

Fade and non-fade duration statistics for Earth-space satellitelink in Ku-band

The choice of modulation and forward error correction coding for satellite communications depends on fade dynamics and long-term fade occurrence statistics. An investigation is presented of the fade duration and inter-fade duration measured with a dual slope Ku-band radiometer as well as a Ku-band INTELSAT VI beacon receiver in Singapore which has an equatorial climate. A comparison of the results from both the measurements is presented. The normalised fade duration obtained follows a lognormal distribution with median of 1.3 and a standard deviation of 2     

Analysis of 11 GHz slant path fade duration and fade slope

The letter presents results of an analysis of fade slope and fade duration data collected at 11 GHz within the framework of the OTS propagation experiments in Europe. Evidence is given of the fact that on a statistical basis, fade slope and fade duration are related. This could possibly be used in uplink power control systems.     

Global hop length analysis for millimeter-wave radio links

For the CCIR 14-rain climatic zones of the globe, we present a simplified hop length versus fade margin analysis with link reliability as a parameter. The analysis uses Laws-Parsons values for the a and b parameters of A(dB/Km)=a R^b (mm/hr), and considers the two cases of (i) limited rain-cell and (ii) “entire hop in rain”. The result is a family of fade margin vs. hop length curves for various reliability objectives, obtained for each of the 14-rain zones at a frequency of 50 GHz. A simple frequency scaling rule is also devised to enable similar analysis at frequencies in the range 30–70 GHz. It is particularly concluded that an extended hop length of 10–20 Km is possible with reasonable reliability if the reduced cell-size concept is applied. If the entire hop is in rain, a limited hop length of one to five kms can't be exceeded even with modest reliability. It is also demonstrated that high resolution global rain map, together with an accurate cell size definition are mandatory for reliable radio link design at mm-wave lengths.     

Propagation model for simulating shadowing and multipath fading inland-mobile satellite channel

A land-mobile satellite propagation model which includes multipath fading and shadowing effects using five-state Markov transitions between fade states and nonfade states is proposed. This generates a time-series of the fading, very closely matching statistical characteristics such as fade duration, nonfade duration and fade depth obtained from measured data     

Duration of rain-induced fades of signal from Sirio at 11.6 GHz

Propagation data for significant rain events at 11.6 GHz from satellite Sirio, sampled at 0.1 s and averaged over 1 s, are processed to obtain statistics of fade durations. Two ways of defining the random process of fade duration are stressed and their statistics are given.     

Fade statistics in Nakagami-lognormal channels

New expressions for the average level crossing rate (LCR) and average time fade duration (AFD) of the signal envelope in microcellular mobile radio channels, characterized by Nakagami (1960) fading and lognormal shadowing, so called Nakagami-lognormal (NLN) channels, are derived. New LCR and AFD are computed, and the effects of the Nakagami m factor and shadowing spread σ_s on these fade statistics are discussed. The generality of the NLN model is demonstrated by matching some LCR curves with previously reported measurement for the land mobile satellite channel, commonly described as the Rice-lognormal channels     

Second-order statistics of maximal-ratio and equal-gain combining in Weibull fading

Exact expressions for the level crossing rate and average fade duration of M-branch equal-gain and maximal-ratio combining systems in a Weibull fading environment are presented. The expressions apply to unbalanced, nonidentical, independent diversity channels. In addition, new closed-form solutions for some special cases are obtained.     

Three‐year fade and inter‐fade duration statistics from the Q‐band Alphasat propagation experiment in Madrid

Propagation campaigns are carried out at different frequencies and geographical areas to characterize the slant‐path propagation channel. One of the objectives of the Alphasat Propagation Experiment is to evaluate the performance of satellite links that operate in the Q/V band. Since March 2014, the copolar level of the Alphasat Q‐band beacon signal has been measured at Universidad Politécnica de Madrid, Spain. The fade dynamics—fade and inter‐fade durations—results for three complete years (March 2014 to February 2017) of measurements are presented in this paper. Moreover, the experimental setup and receiver characteristics are described in detail. The collected data (with a mean availability of 97%) can be used to evaluate the atmospheric propagation impairments with a very good degree of accuracy. The probability of occurrence and the fraction of time of fade duration for an average‐year have been compared with the ITU‐R and CRC models with moderate agreement. For this reason, a modeling effort has been made leading to the conclusion that there is room for improvement in the models.     

Average level crossing rate and average fade duration of low-ordermaximal ratio diversity with unbalanced channels

The average level crossing rate and average fade duration of a maximal ratio diversity combiner, operating on independent, unequal power Rayleigh fading branches in isotropic scattering, are derived in closed-form for dual-branch diversity, and as definite integrals for threefold and fourfold diversity     

K-BAND LAND-MOBILE SATELLITE CHANNEL CHARACTERIZATION USING ACTS

K-band pilot tone data collected by the Advanced communications technology satellite (ACTS) mobile terminal (AMT) during 1994 are used to characterize the K-band land-mobile satellite channel. The characterization is twofold: a probability density model is derived which shows that the fade exceedance levels at K-band are much higher than those at lower frequencies, particularly at L-band. Furthermore, the fade statistics are very dependent on the geometry of the surrounding environment. The difference between good and bad environments is much more pronounced at K-band than at L-band. A discrete time model is used to provide insight into the bursty nature of the errors induced by propagation effects on the channel. For a data rate of 9600 bps, the average fade duration for a fade threshold of 6 dB is of the order of a few thousand bits, which corresponds to a fade duration of 2—5 ms. The fade durations are typical of those at L-band which suggests that whereas the K-band fades are more severe than those at L-band, the durations are approximately the same.     

A three-site comparison of fade-duration measurements

Important elements in the design of Ka-band communication systems are the duration of fade and nonfade events at a particular fade depth. The choice of modulation and forward error correcting codes will depend on both the fading time dynamics and annual fade occurrence statistics. This paper examines the fade duration measured at locations in three of the Advanced Communications Technology Satellite (ACTS) propagation experimental regions, namely, Florida (rain zone N of the radiocommunications sector of the International Telecommunications Union [ITU-R] model), New Mexico State University (ITU-R rain zone M), and Alaska (ITU-R rain zone C). Within each region, measures of the underlying uniformity are described and an interregional comparison examines the ability to scale the local results