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.     

Rain attenuation successive fade durations and time intervals between fades in a satellite-Earth link

Long-term attenuation data at 11.6 GHz, obtained in a Sirio link, are analysed to provide information on the joint statistics between successive fade durations within a rain event (intrafade) and between different rain events (interfade). The results show that successive fade durations and the interfade or intrafade intervals are approximately statistically independent. Within the same rain event, interfades and fade durations longer than 10 s are statistically identical. These data may be important for planning adaptive systems and for devising prediction models of the dynamic behaviour of rain attenuation.     

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     

Fade Statistics of Wireless Multi-User Systems

In this paper, we propose a new model named effective fade duration envelope to characterize the accumulative conditional fade durations of individual users or groups of users in wireless communication systems. The proposed model has the following novelties: (1) it introduces the statistical upper and lower bounds with the required degree of confidence for accumulative conditional fade durations during any given time interval; (2) it characterizes various conditional fading circumstances in wireless multi-user communication systems.     

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.     

Joint analysis of duration and rate of change of rain attenuation at 11.6 GHz

Positive and negative rates of change of attenuation are studied jointly with the in-between fade duration using Sirio 11.6 GHz beacon four-year data for several attenuation thresholds, collected in northern Italy. The letter shows that the rate conditional distributions are log-normal, and that little correlation exists between negative and positive rates and durations.     

Channel modeling and simulation in satellite mobile communicationsystems

An analog model describing signal amplitude and phase variations on shadowed satellite mobile channels is proposed. A linear combination of log-normal, Rayleigh, and Rice models is used to describe signal variations over an area with constant environment attributes while an M-state Markov chain is applied to represent environment parameter variations. Channel parameters are evaluated from the experimental data and utilized to verify a simulation model. Results, presented in the form of signal waveforms, probability density functions, fade durations, and average bit and block error rates, show close agreement with measurements     

Fade-Duration Statistics of a Rayleigh-Distributed Wave

This paper presents measured fade duration and levelcrossing statistics of a hardware-simulated mobile radio channel. These measurements were taken over a wide range of fade depths. The measurements agree well with existing analytical results and extend them to show the distribution of fade durations for shallow fades. Fine detail in the fade-duration distributions for shallow fades is produced by peaks in the fading spectrum.     

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.     

Outage intensity due to multipath fading in terrestrial links

Measured data of multipath fading from 20 microwave line-of-sight links, operating in the 4 and 6 GHz frequency bands, were analysed to provide statistics of fade durations as a function of the attenuation threshold. From these results, an empirical method for predicting outage intensity due to multipath propagation was derived, which shows good agreement with the measurements.     

Modeling Ka-band scintillation as a fractal process

We propose a model that describes the signal fading process due to scintillation in the presence of rain. We analyzed a data set of uplink (30 GHz) and downlink (20 GHz) attenuation values averaged over 1 s intervals. The data are samples relative to ten significant events, for a total of 180 000 s recorded at the Spino d'Adda (North of Italy) station using the Olympus satellite. Our analysis is based on the fact that the plot of attenuation versus time recalls the behavior of a self-similar process. We then make various considerations, and propose, a fractional Brownian motion model for the scintillation process. We describe the model in detail, with pictures showing the apparent self-similarity of the measured data. We then show that the Hurst parameter of the process is a simple function of the rain fade. We describe a method for producing random data that interpolate the measured samples, while preserving some of their interesting statistical properties. This method can be used for simulating fade countermeasure systems. As a possible application of the model, we show how to optimize fade measurement times for fade countermeasure systems     

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     

Fade slope for four LOS links in Singapore: analyses and prediction

Three-year experimental data on rain attenuation is employed to analyse fade slopes for four terrestrial line of sight (LOS) systems in Singapore. The statistical results of fade slope are presented on both cumulative probability distributions during rain events and relationships with fade level for fade countermeasure. A fade slope occurrence prediction model is also provided for short links based on point rainfall rate     

Modeling and simulation of mobile satellite propagation

Mobile satellite systems are subject to severe fading due to blockage of the line-of-sight (LOS) path by roadside vegetation. A thorough understanding of the fading effects is necessary for the design of a reliable land-mobile satellite system. Analytical and empirical models are presented for predicting fade statistics for vegetative shadowing of mobile satellite terminals. A software simulator for generating simulated fade data is also presented. A physical model relating physical path parameters to propagation model parameters is presented, and results using the model are shown     

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     

Statistical characterization of Rician multipath effects in a mobile-to-mobile communication channel

A statistical model is developed for a narrowband mobile-to-mobile channel taking into consideration Rician scattering near receiving and transmitting antennas both individually and concomitantly. From the proposed channel model we obtain the probability density function of the received signal envelope, the time correlation function and RF spectrum of the received signal, and level crossing rates and average fade durations. We briefly discuss the impact of these parameters on communication networks supporting an intelligent vehicle highway system (IVHS).     

Effects of filtering on statistics of rain-induced fade durations

Time series of rain attenuation on a slant path at 11.6 GHz are analysed with two digital filters to show how they affect the statistics of fade durations. It is found that their influence is strong for the usual process considered in literature and it is shown how to take care of such effects. It also discusses a definition of the process which is much less sensitive to filtering. The first process provides data to plan telecommunications satellites with a common onboard resource, and the latter is useful for the distinction between quality and reliability criteria.     

Radar prediction of absolute rain fade distributions for Earth-satellite paths and general methods for extrapolation of fade statistics to other locations

Two distinct prediction methods are described. The first deals with a technique for establishing absolute fade statistics at a given site using a sampled radar data base. The second is a method for extrapolating absolute fade statistics from one location to another given simultaneously measured fade and rain-rate statistics at the former. Both methods employ similar conditional fade statistic concepts and use long term rain-rate distributious. The radar-predicted levels showed good agreement in probabilities associated with the cumulative fade distribution when compared to directly measured levels of the COMSTAR beacon at 28.56 GHz for the Wallops Island, VA, radar facility, Probability deviations ranging from 2 to 19 percent with an average of 11 percent were obtained upon comparing measured and predicted levels at given attenuations. The extrapolation method was tested employing the Wallops Island measured rain-rate statistics and fade distributious at 28.56 GHz. The method was also tested at 19.04 GHz using measured results for Austin, TX. The extrapolation of fade distributions to other locations at 28 GHz showed very good agreement with measured data at three sites located in the continental temperate region (average probability deviations of 11.5, 9, and 17 percent) and respectable agreement atone site in a wet subtropical region (30 percent deviation). At 19.04GHz,extrapolated levels were generally not as good as at 28 GHz (41, 28, 7, and 27 percent), although they were still quite respectable.