On the rain attenuation dynamics: spatial‐temporal analysis of rainfall rate and fade duration statistics

Knowledge about the dynamic characteristics of rain attenuation is of utmost importance for many applications in terrestrial and satellite communication systems operating at frequencies above 10 GHz. Long‐term rain rate statistics and rain rate duration statistics are usually available from meteorological data. In this paper, a spatial–temporal analysis is employed in order to evaluate the rain attenuation power spectrum of a terrestrial/satellite path. The predicted power spectrum is compared with experimental data. Based on the spectral analysis of rainfall rate a method for converting rain rate duration statistics to link fade duration statistics is also proposed. Fade duration statistics are presented for terrestrial and satellite links and compared with available experimental data. The agreement between the predicted results and the experimental data has been found to be quite encouraging. Finally, numerical results are presented for various climatic zones, elevation angles and frequencies. Some very useful conclusions concerning the dynamic properties of rain attenuation for a microwave path are deduced. Copyright © 2003 John Wiley & Sons, Ltd.     

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

In 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.     

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.     

A unified statistical rain-attenuation model for communication link fade predictions and optimal stochastic fade control design using a location-dependent rain-statistics database

The simultaneous demand for increased capacity of communication satellite channels and the demand for such systems to be designed and operate within increasingly stringent economic constraints places severe requirements on the ability to predict, achieve and maintain the reliable operation of these satellite links throughout the United States. The operating frequencies of satellite links are such that the occurrence of rain anywhere along the link will induce attenuation of the signal and is the major source of link reliability degradation. A unified model is presented that describes the relevant static and dynamic statistics of attenuation on an arbitrarily specified satellite link for any location for which there is a long-term data record of rainfall statistics. In addition to providing accurate, location-dependent statistical predictions of the reliability of satellite links, the generality of the model also establishes a basis for the design of optimal stochastic control algorithms used to mitigate the deleterious effects of attenuation and thus maintain link reliability. The rain statistics that are required to characterize the location of interest are derived from extreme value statistics theory. A rain-statistics database has been compiled that allows one to apply the model anywhere in the continental United States with the resolution of 0.5° in latitude and longitude. Comparison of the model predictions is made with available experimental observations and agreement is found to be quite good.     

Short‐scale diversity in a dynamic rain fade environment

This article is concerned with using time‐varying uniformly spaced rainfall data to investigate the concept and values of instantaneous diversity gain. This has been obtained on a minute‐by‐minute basis in order to illustrate the behaviour of a VSAT communication system which switches to the most reliable link every minute. The simulations have been carried out using a whole year of rain data obtained from the recordings of a dense rain gauge network located in Barcelona. After illustrating the concept of instantaneous diversity gain, this paper shows the results obtained for various site separations and 20 GHz. These results have been plotted together with the values given by some long‐term‐based models. The comparison shows that such models are not appropriate for dynamic site diversity. This was found to increase the reliability of a VSAT system, especially under severe rain conditions in which the rainfall rates are spatially arranged in rain cells and the attenuation experienced by the two sites is strongly decorrelated. The correlation coefficient between the attenuation series calculated for several separation distances has also been obtained to illustrate this concept. Finally, the paper gives the attenuation distributions calculated for a VSAT system with and without site diversity and for several site separations. Copyright © 2005 John Wiley & Sons, Ltd.     

Near‐optimum short‐term fade prediction on satellite links at Ka and V‐bands

Several short‐term predictors of rain attenuation are implemented and tested using data recorded from a satellite link in Southern England, and a comparison is made in terms of the root‐mean‐square error and the cumulative distribution of under‐predictions. A hybrid of an autoregressive moving average and adaptive linear element predictor is created that makes use of Gauss–Newton and gradient direction coefficient updates and exhibits the best prediction error performance of all prediction methods in the majority of cases. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparison of measured rain attenuation in the 10.982‐GHz band with predictions and sensitivity analysis

The campaign to collect rain attenuation data on terrestrial links had commenced in Malaysian tropical climates for almost two decades. The terrestrial data so far collected have been greatly utilized to derive useful statistics for various microwave applications, such as frequency scaling, rain rate conversion factor, 1‐min rain rate contour maps, wet antenna losses, and fade slope duration analysis. However, there is still severe scarcity of rain attenuation data on earth–space links in Malaysia. The results of the 2‐year measurement (January 2009–December 2010) of rain rates and rain‐induced attenuation in vertically polarized signals propagating at 10.982 GHz have been presented in this paper. The rain attenuation over the link path was measured at Islamic International University Malaysia and compared with ITU‐R P.618‐10 and Crane global models in this paper. The test results show that the two prediction models seem inadequate for predicting rain attenuation in the Ku‐band in Malaysia. Sensitivity analysis performed on measured data also reveals that the sensitivity variables depend on rain rate. Copyright © 2014 John Wiley & Sons, Ltd.     

Probability distributions of rain attenuation obtainable with linear combining techniques in space‐to‐Earth links using time diversity

The purpose of this paper is to show how the complementary probability distribution of rain attenuation is drastically changed in the lower rain attenuation range by applying linear combining techniques, namely, equal‐gain combining and the maximal‐ratio combining, discussed in the historical paper by Brennan in 1959. These combing techniques can also be applied to the Automatic Repeat Request techniques. Defined the instantaneous processing gain and the equivalent attenuation in the 3 cases, we show examples of time series of the various parameters, based on the experimental rain attenuation time series recorded with the ITALSAT 18.7 GHz beacon, in a 37.8° slant path in Spino d'Adda (Italy). Then, we report long‐term complementary probability distribution functions of the instantaneous gain and equivalent attenuation, by simulating rain attenuation time series at 19.7 and 39.4 GHz, path elevation angle 35.5°, with the Synthetic Storm Technique, using on‐site measured rain rate time series of 10 years, by simulating the ALPHASAT link at Spino d'Adda. Similar results are also found at different frequencies and elevation angles in Tampa (Advanced Communications Technology Satellite, ACTS result test), the Isle of Guam, and Prague. The main conclusions are as follows: (1) As expected, the instantaneous time diversity gain can be large when the delay time is large and rain attenuation is large; (2) scintillation affects time diversity links as the direct links; (3) equal‐gain and maximal‐ratio combining can add up to 3 dB to the selection diversity gain when the time diversity gain is very small; and (4) equal‐gain and maximal‐ratio combining reduce the fraction of time of rain attenuation in an average year to a value less than the probability of exceeding 3 dB in the link without diversity.     

Diurnal variations in rain attenuation on Ku band earth–space paths

This paper presents analytical results of the diurnal variations in Ku band rain attenuation along earth–space paths at four locations in Southeast Asia and proposes a new model that can predict rain fade in a short period of every 2 h daily. Data from four radiometers and four rain gauges over a 3 year period were analysed to obtain the characteristics of diurnal variations in rain attenuation and rainfall as well as cumulative attenuation distributions in every 2 h interval. The results of this analysis are applied to develop an intensive prediction model using the knowledge of rainfall and attenuation statistics. This model is tested with the measured data and is found to be useful for the design of a more efficient Ku band satellite system especially between 99 per cent and 99·9 per cent link availability in an area of heavy rainfall. © 1998 John Wiley & Sons, Ltd.     

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.     

Inter‐annual variability,risk and confidence intervals associated with propagation statistics. Part I: theory of estimation

This set of two companion papers aims at providing a statistical framework to quantify the inter‐annual variability observed on the statistics of rain attenuation or rainfall rate derived from Earth‐space propagation measurements. This part I is more specifically devoted to the theoretical study of the variance of estimation of empirical complementary cumulative distribution functions (ECCDFs) derived from Earth‐space rain attenuation or rainfall rate time series. To focus the analysis on the statistical variability but without loss of generality, synthetic rain attenuation time series are considered. A large variability on the ECCDFs, which depends on the duration of the synthetic data, is first put into evidence. The variance of estimation is then derived from the properties of the statistical estimator. The formulation is validated numerically, by comparison with the ECCDF variances derived from the synthetic data. The variance of the fluctuations around the CCDF is then shown to be dependent on the average of the correlation function of the time series, on the probability level and on the measurement duration. This variance of estimation is needed as a prerequisite in conjunction with the knowledge of the climatic variability to characterize the yearly fluctuations of propagation statistics computed from experimental time series. The extensions from simulations to experiments as well as the application to system planning are detailed in part II. Copyright © 2013 John Wiley & Sons, Ltd.     

Total CNIDR degradation during rain fade conditions of a dual polarized satellite link suffering from double adjacent satellite interference

Atmospheric impairments have a significant influence on the performance of modern satellite communication networks, working at Ku, Ka and potentially Q/V frequency bands. Both differential rain attenuation from an adjacent satellite system, operating at the same frequency range, and cross‐polarization phenomena on dual polarized satellite systems due to rain and ice crystals, induce a further aggravation on the already limited signal‐to‐noise‐plus‐total‐interference ratio (CNIDR), due to the frequency and orbital congestion of today's global communication satellite constellation. In the present paper, a new statistical methodology, towards the modelling of CNIDR under rain fade conditions, is proposed to include interference effects by two adjacent satellites, incorporating the impact of correlated fading channels (spatial rainfall inhomogeneity) of multiple slant paths. The method is based on a convective raincell model and the lognormal assumption for both the point rain‐rate statistics and the slant‐path rain attenuation. The obtained numerical results indicate the significant impact of the second interfering satellite on the aggravation of total interference effects. Some simple mathematical formulas for the prediction of the CNIDR, based on the derived theoretical results, and demonstrating the influence of various link parameters on the total link availability statistics, are also presented. Copyright © 2009 John Wiley & Sons, Ltd.     

SDN‐based fault‐tolerant on‐demand and in‐advance bandwidth reservation in data center interconnects

Geographically distributed data centers are interconnected through provisioned dedicated WAN links, realized by circuit/wavelength–switching that support large‐scale data transfer between data centers. These dedicated WAN links are typically shared by multiple services through on‐demand and in‐advance resource reservations, resulting in varying bandwidth availability in future time periods. Such an inter‐data center network provides a dynamic and virtualized environment when augmented with cloud infrastructure supporting end‐host migration. In such an environment, dynamically provisioned network resources are recognized as extremely useful capabilities for many types of network services. However, the existing approaches to in‐advance reservation services provide limited reservation capabilities, eg, limited connections over links returned by the traceroute over traditional IP‐based networks. Moreover, most existing approaches do not address fault tolerance in the event of node or link failures and do not handle end‐host migrations; thus, they do not provide a reliability guarantee for in‐advance reservation frameworks. In this paper, we propose using multiple paths to increase bandwidth usage in the WAN links between data centers when a single path does not provide the requested bandwidth. Emulation‐based evaluations of the proposed path computation show a higher reservation acceptance rate compared to state‐of‐art reservation frameworks, and such computed paths can be configured with a limited number of static forwarding rules on switches. Our prototype provides the RESTful Web service interface for link‐fail and end‐host migration event management and reroutes paths for all the affected reservations.     

12 GHz diurnal fade variations in the tropics

In satellite transmission at frequencies above 10 GHz, signal fading, and hence outage, is mainly attributed to rain. Annual and worst month cumulative statistics may not provide sufficient information to design services adequately in the tropics. Statistics of seasonal and diurnal fade variations will give the detailed insights required for direct-to-home/very small aperture terminals (DTH/VSAT) system designs in tropical climates subjected to heavy rain. Diurnal fading statistics for a wet, tropical location in Lae, Papua New Guinea, are presented     

Experimental assessment of slant‐path rain attenuation variability in the Ka‐band

This study is based on the results of a slant‐path Ka‐band propagation experiment carried out in Madrid, Spain, regarding rain attenuation, which is the main propagation impairment in this frequency band. The experimental and statistical results correspond to seven complete years of measurements, a period large enough to accomplish a comprehensive analysis in order to characterize the variability of rain rate and attenuation. It is shown that year‐to‐year variability is significant in temperate climates as Madrid's. The aforementioned significance is also apparent with regards to seasonal, monthly, worst‐month and hourly variability concerning rain attenuation, which are also discussed and related when possible to the variability of the rain phenomena, either represented by the total amounts of rainfall in the different periods or by rain rate statistics. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling of short‐term frequency scaling for rain attenuation using ITALSAT data

In this article we describe a statistical model for the assessment of the short‐term frequency scaling ratio between rain attenuations at cm and mm wavelengths, taking into consideration the fluctuations arising from the type of rain (mainly the raindrop size distribution). The model has been derived from measured data, using the large attenuation database collected in Spino d'Adda, Italy, during the ITALSAT 8‐years experiment at 18.7, 39.6 and 49.5 GHz, but can be applied to any pair of frequencies. By applying the model it is possible to generate, by means of a generator of random Gaussian numbers, samples of the up‐link attenuation, for a given down link attenuation, to be employed in the simulation of up‐link power control (ULPC) slant path channels. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel down link rain fade mitigation technique for Ka‐band multibeam systems

Rain fades at Ka‐Band degrades the link quality and performance significantly. Several rain fade mitigation techniques for Ka‐band satellite systems are being investigated to improve the channel capacity. Methods such as power control and adaptive waveform techniques have been proposed for use in the uplink as they are capable of straightforward implementation. A novel down link power control technique for multi‐beam Ka‐band system has been proposed in this paper. It is based on the use of multi‐port amplifier, which is commonly used for dynamic power sharing of the beams depending upon the traffic. Payload architecture for multi‐beam coverage using multi‐port amplifiers has been designed for the proposed technique. The simulation results to compensate for the rain fade attenuation of one beam by sharing the unused power from other beams have been presented Copyright © 2006 John Wiley & Sons, Ltd.     

Railway satellite channel at Ku band and above: Composite dynamic modeling for the design of fade mitigation techniques

Past studies on the railway satellite channel (RSC) at Ku band and above consider exclusively the attenuation coming from the metal power arches (PAs) along the railway route, producing significant though deterministic periodical fast fading. Nevertheless, limited attention has been given to model tropospheric effects on the RSC. The present paper takes a more comprehensive view of the RSC by introducing a novel stochastic dynamic model of rain fading in mobile satellite systems on top of the diffraction because of PAs. The proposed approach builds upon well‐established research on rain attenuation time series synthesizers employing stochastic differential equations. It is shown that this propagation tool may provide significant aid, in general, in mobile satellite system simulations and in the design of fade mitigation techniques (FMTs), particularly aiming at the railway scenario. The tool enables the generation of fade events, fade duration statistics, rain attenuation power spectrum and predicting the necessary FMT control loop margin. This is particularly useful for the RSC because most of the proposed FMTs focusing on PAs are not appropriate for compensating atmospheric fading. Copyright © 2011 John Wiley & Sons, Ltd.     

Modified rain attenuation model for tropical regions for Ku‐Band signals

Attenuation measurement on Ku‐ band satellite signal in a tropical site, Fiji is presented. Rain‐attenuation prediction by ITU‐R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain‐rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain‐rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU‐R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles <60° and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU‐R model, one for rain‐rates lower than the breakpoint rain‐rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku‐band attenuation in seven tropical sites. Copyright © 2006 John Wiley & Sons, Ltd.