Rain Attenuation Research Articles

Path loss models for outdoor environment—with a focus on rain attenuation impact on short-range millimeter-wave links

The deployment of a millimeter wave over a short path is one of the keys to enabling technologies for the next generation of wireless communication systems. Path loss (PL) is the most important parameter to indicate the performance of the mm-wave wireless channel. However, the accuracy and efficiency of each model are limited to characterize path loss for an environment that is different in terms of weather conditions and geographical arrangement from that for which they have been designed. This paper analyzed path loss for accurate signal estimation in Malaysia based on outdoor microcellular at 38GHz on a 300 m path length. The impact of rain attenuation on path loss, path loss exponent (PLE), and shadow fading (SF) have been investigated. This paper also presents two-channel models utilized for simulations in terms of the outdoor Large-Scale Path Loss, the statistical spatial channel model NYUSIM (version 2) developed in 2019 by New York University (NYU) and the 3rd Generation Partnership Project (3GPP) TR 38.900 Release 14 channel mode. Even though the CI and 3GPP models are accurate and suitable in the area where the measurement campaign was carried out in the temperate climate and must need modification for different regions, such as tropical climate. The underestimation can be interpreted because of the difference in AF's attenuation factors (pressure, humidity, temperature, rain rate) calculated by the CI model in the NYUSIM simulations and the attenuation factor (AF) obtained from measurement data. The NYUSIM channel model better estimated the measured data of path loss compared with 3GPP. Thus, the CI model is suitable for outdoor environments.

Transfer Functions and Linear Distortions in Ultra-Wideband Channels Faded by Rain in GeoSurf Satellite Constellations

Because of rain attenuation, the equivalent baseband transfer function of large bandwidth radio-links will not be ideal. We report the results concerning radio links to/from satellites orbiting in GeoSurf satellite constellations located at Spino d’Adda, Prague, Madrid, and Tampa, which are all sites in different climatic regions. By calculating rain attenuation and phase delay with the Synthetic Storm Technique, we have found that in a 10-GHz bandwidth centered at 80 GHz (W-Band)—to which we refer to as “ultra-wideband-, both direct and orthogonal channels will introduce significant amplitude and phase distortions, which increase with rain attenuation. Only “narrow-band” channels (100~200 MHz) will not be affected. The ratio between the probability of bit error with rain attenuation and the probability of bit error with no rain attenuation increases with rain attenuation. The estimated loss in the signal-to-noise ratio can reach 3~4 dB. All results depend on the site, Tampa being the worst. To confirm these findings, future work will need a full Monte Carlo digital simulation.

Energy and Spectral Efficiencies of Cell-Free Millimeter-Wave Massive MIMO Systems Under Rain Attenuation Based on Ray Tracing Simulations

Future wireless communication systems depend on the network’s ultra-densification, on the application of massive multiple-input multiple-output (mMIMO) techniques and on the use of higher frequency bands to satisfy the ever-increasing demands for capacity. The operation of cell-free (CF) networks in the millimeter wave (mmWave) spectrum combines those principles, because they are composed of multiple access points (APs) distributed over a geographic region which serve a small number of users. Despite the extensive available bandwidth, the mmWave spectrum imposes high path losses and significant atmospheric molecular absorption to the links. In addition, in this frequency range, rain attenuation can notably degrade communications. Therefore, this article presents a study of the impact of rain attenuation on CF networks operating in the mmWave spectrum, this is in the 26 GHz, 38 GHz and 73 GHz frequency bands, based on site-specific ray tracing simulations. The propagation simulation is characterized under the effects of reflection, diffraction, diffuse scattering, atmospheric molecular absorption, vegetation losses and rain attenuation. The channel model is characterized using a hybrid approach, with the large-scale parameters determined by ray tracing in an environment subject to random Rician small-scale fading. The system performance is measured by the sum spectral efficiency (SSE) and energy efficiency (EE). According to the results, it was observed that AP densification protects the network against the effect of rain attenuation. Furthermore, even in sparse networks, the CF system has low sensitivity with respect to the precipitation rate, resulting in relatively small reductions in the average SSE and EE.

Model to Scale Rain Attenuation Time Series With Link Elevation Angle for LEO Satellite Based Systems

AbstractA model to scale time series of rain attenuation along an Earth‐to‐satellite path with variable elevation angle is proposed. Starting from the time series at the lowest elevation the algorithm scales up each sample to the elevation of interest while maintaining the space and time correlation of the rain process and by correctly reproducing the local long‐term rain attenuation statistics. Because of these peculiarities, the model represents a key element for the development of attenuation time series synthesizers for LEO satellite‐based applications, where the time decorrelation of the rain event during the quick spacecraft passage over the ground station (roughly 10 min) is quite limited. Moreover, the comparison with the simple geometric scaling (i.e., the cosecant law) carried out among the attenuation Complementary Cumulative Distribution Functions shows a definite improvement in the prediction accuracy, even more so when the elevation angle falls below 20°.

Rain-Based Attenuation and Dispersion Characteristics of Terahertz Wave in Tropical Climate: Experimentally Verified Reliability Study

In the frontier of next generation communication system, the terahertz spectrum can be treated un-parallel as far as the implementation of wireless link with high data-rate is concerned. Atmospheric condition can affect the electromagnetic/radio signal transmission severely. Since, the presence of seasonal hydrometeors in atmosphere may lead to drastic degradation in the free-space propagation of terahertz signal, therefore thorough and comprehensive investigation is essentially required to optimize the future channel-model for terahertz carrier frequency. The atmospheric attenuation causes power loss and in turn receiver signal amplitude gets attenuated. Rain attenuation has pronounced impact on terahertz signal propagation and attenuation of transmitted wave. In tropical weather scenario, the drop-dimension of seasonal rainfall exceeds the maximum dimension of temperate rain. Through an indigenously developed and experimentally verified Non-Linear Terahertz Rain Attenuation Model simulator, the authors have thoroughly investigated the rain-attenuation characteristics of terahertz signal in tropical climate condition for different hydrometeor properties including rain-rates and drop-size distribution. The effect of tropical thunderstorm has been uniquely incorporated by the authors in the present study along with atmospheric humidity and temperature based fluctuations. The reliability issues that are related with THz communication in tropical rain-fall have also been comprehensively analysed. Besides, a best-fit analysis has also been covered under different drop-size distribution statistics. It has been found that, in Indian Scenario (as a part of tropical climate), the peak attenuation level of THz spectrum under tropical rain-fall can be found in the range of (7THz-9THz). With increase of rain-rate from 2mm/hr to 200mm/hr, the peak attenuation level rises from ~100dB/km to ~1000dB/km. The basic model has been validated through experimental data where close proximity(with ± 10% variation from the mean data) has been observed. The present study on terahertz signal attenuation profile in tropical rainy weather will help the communication engineers to open the new door for the ultra-high speed world of 6G terahertz communication.

Comparative Study of Worst Month Rain Rate and Attenuation Statistics for Satellite Links in Nigeria

AbstractThis study aims to characterize the dynamic trend of the worst case scenario of rain rate and attenuation for satellite links applications in Nigeria. Rain rate data for four locations (Akure, Jos, Ikeja, and Port Harcourt) were obtained from the Tropospheric Data Acquisition Network at the Centre for Atmospheric Research, NASRDA at an integration time of 5 min from January 2013 to December 2014. The statistics of time series of worst month rain induced attenuation were computed using the method of Synthetic Storm Technique. The International Telecommunication Union model was found to overestimate the Q‐factor in Akure, Port Harcourt, and Ikeja by 34%, 115%, and 50%, respectively while a 25% underestimation was observed in Jos. The results obtained in this study will be useful for location based link design in tropical Nigeria to reduce the uncertainty of specification of design for communication links.

On the Quasi-Moment-Method as a Rain Attenuation Prediction Modeling Algorithm

A computationally inexpensive, analytically simple, and remarkably efficient rain attenuation prediction algorithm is presented in this paper. The algorithm, here referred to as the Quasi Moment-Method (QMM), has only two main requirements for its implementation. First, rain attenuation measurement data (terrestrial or slant path) for the site of interest must be available; and second, a model, known to have predicted attenuation for any site to a reasonable level of accuracy (base model), and whose analytical format can be expressed as a linear combination of its parameters, is also required. An important novelty introduced by the QMM algorithm is a normalization scheme, through which a modelling difficulty concerning exceedance probabilities outside a 0.01 to 1.00 range, is eliminated. Model validation and performance evaluation using a comprehensive set of data available from the literature clearly demonstrated that the QMM models consistently improved base model performance by more than 90%; and outperformed all published ‘best fit’ models with which they were compared.

COMPARISON OF MEASURED SLANT PATH ATTENUATION AT 10.982 GHZ WITH LARGE-SCALE PREDICTION MODELS IN A TROPICAL CLIMATE

Rain-induced attenuation above 10 GHz can be severe at heavy rain rates resulting in deep fading, which can negatively impact the quality of receive signal level at the Earth station receiver. The dearth of direct measurement data in most of the tropical and equatorial climates has motivated the campaign for collection of rain attenuation data on slant paths in these regions. This is mainly due to a huge receiver margin required for such measurement, and which is very difficult to obtain by using a spectrum analyzer. The measurement results of rain rates and rain-induced attenuation in vertically polarized signals propagating at 10.982 GHz in a tropical Malaysian climate are presented in this study. The measured attenuation is compared with large-scale prediction models. As shown in the statistically-tested results, the Bryant model yields the best overall fit, while the Crane model yields the worst overall fit. The results show that the models have relatively good prediction capabilities in the Malaysian tropical climate; however, their prediction errors still need to be minimized. Therefore, in this study, a correction factor is proposed to enhance their predictions.

Synthetic Rain Models and Optical Flow Algorithms for Improving the Resolution of Rain Attenuation Time Series Simulated From Numerical Weather Prediction

AbstractNew generation of satellite system communication is moving toward frequencies above 20 GHz and non‐geostationary satellites. In order to guaranty the quality of service, specific Fade Mitigation Techniques have to be applied, like Advanced Coding and Modulation (ACM). In order to accurately design ACM, time series of attenuation should be used. As there are no measurements available, the simulation of attenuation times series for non‐geostationary earth‐space links becomes critical. This paper presents a model consisting in a combination of a Numerical Weather Prediction model (Weather Research and Forecasting), a synthetic rain cell model MultiEXCELL and Optical Flow techniques. It gives an efficient method to generate more realistic rain attenuation time series. Long‐term CCDF statistics of simulated attenuation data are validated by comparison with the Alphasat measurement data over 2 years at Louvain‐la‐Neuve ground station.

Effect of Rain Attenuation on Millimeter Wave over Polarization

Millimeter wave has been used in radar applications for a long time, and is increasingly used in new fields, among which high data rate telecommunications is the most prominent. Short wavelength and unique propagation characteristics provide challenges and opportunities for design engineers working in these fields. Millimeter wave has become an indispensable part of 5G mobile communication field due to its excellent spectrum characteristics. In order to help the development of millimeter wave equipment, this paper mainly studies the millimeter wave rain attenuation phenomenon through the combination of theory and simulation. The effects of rainfall rate and polarization mode on millimeter wave propagation attenuation are compared and summarized. In addition, the total attenuation of millimeter wave communication path under different polarization rainfall characteristics is compared. Finally, the total loss of different frequency millimeter wave rainfall links is compared and analyzed. It provides a theoretical basis for the follow-up design and practical application of millimeter wave communication system.

Synthetic rain models and optical flow algorithms for improving the resolution of rain attenuation time series simulated from Numerical Weather Prediction

Synthetic rain models and optical flow algorithms for improving the resolution of rain attenuation time series simulated from Numerical Weather Prediction

Effective Path Length for Estimating Rain Attenuation Over an Earth‐Space Path Using Features of Stratiform and Convective Precipitation at a Tropical Location

AbstractThe effective path length (LE) for the rain attenuation estimation over the Earth‐space path depends on rain cell size, rain rate, and rain height which in turn are determined by the types of rain. The present study examines the variation of LE based on the experimental measurements of Ku‐band attenuation and rain rate at a tropical location Kolkata (22°34′N, 88°22′E) in comparison with the ITU‐R. The study also utilizes measurements from a 24‐GHz micro rain Doppler radar to differentiate the precipitation types as stratiform and convective rain on the basis of the presence and absence of a melting layer. Power‐law models of LE in terms of rain rate are proposed for convective and stratiform types of rain. The investigation reveals the physical phenomena behind the variability of LE at low and high rain rates which are associated with stratiform and convective rain respectively. The proposed models provide a significantly better agreement with the experimental data compared to the ITU‐R model and also account for distinguishing features of two types of rain, thus giving a physical basis of the proposed model which is not reflected in the ITU‐R formulations.

Ka-Band Satellite Propagation Experiment at the Guiana Space Centre

From January 2017 to December 2021, Office National d’Etudes et de Recherches Aérospatiales (ONERA) and Centre National d’Etudes Spatiales (CNES) operated a beacon receiver able to record the 20.1995 GHz beacon signal of the Amazonas-3 satellite at the Guiana Space Centre in Kourou, French Guiana. A rain gauge was also deployed on site to collect rainfall rate measurements concurrently to beacon data. All years of the experiment, except 2019, had excellent data availability, hence giving four full years of data (2017, 2018, 2020, and 2021). First, the climatic characteristics of French Guiana are shown. Second, the propagation experiment and the data processing methodology are described. Third, the results of the statistical analysis are highlighted and commented. Comparisons are performed with the prediction methods of Recommendation ITU-R P.837-7 (rainfall rate), Recommendation ITU-R P.618-13 (rain attenuation), Recommendation ITU-R P.678-3 (variability of propagation phenomena), and Recommendation ITU-R P.1623-1 (fade dynamics).

Prediction and analysis of seasonal rain attenuation in the South-western region of Nigeria for future microwave applications

The demand for good quality satellite signals in earth-space communication multimedia services has continuously increased due to the expansion of service providers for various telecommunication companies and internet network providers such as MTN, ETISALAT, GLOBACOM, and AIRTEL. Therefore, a radio engineer needs continuous information on the statistics of rain-induced attenuation to overcome the degradation of satellite signals due to heavy rain downpours. In the present study, an algorithm for the future prediction of rain attenuation based on the Feed Forward Neural Networks (FFNN) prediction model is presented. The seasonal assessment of rain rate and rain attenuation is also investigated for five stations (Okitipupa, Ikole-Ekiti, Ile-Ife, Ogbomosho, and Sagamu) covering the Southwestern region of Nigeria using the Global Precipitation Mission (GPM) satellite observations data. The study revealed that the intensive season exhibited the highest rainfall regime compared to the pre-monsoon, cessation, and dry seasons, which implies maximum rain attenuation during the intensive period of the year. The results of this study would be helpful for radio engineers to plan future link budgets for the provision of adequate signals for link availability.

A Cooperative Routing Scheme Using Inter-Satellite Links to Assist Data Downloading for LEO Satellite Networks.

Low earth orbit (LEO) satellite networks can provide Internet service to users in areas where cellular networks are difficult to deploy. One critical function of satellites is to transfer data from satellite networks to ground core network through earth stations (ESs). The Ka-band multiple-input multiple-output (MIMO) can be used to establish feeder links with larger bandwidth between satellites and ESs. However, propagation at the Ka band is subjected to rain attenuation and various atmospheric fading mechanisms, which severely reduce the maximum link capacity. As a result, the insufficient capacity of feed link becomes the throughput bottleneck of satellite networks. In order to increase network throughput, it is important to fully use feeder link resources. In this paper, we propose a cooperation scheme to route packets to ESs through a well-resourced feeder link, such that the bandwidth of the feeder links can be fully utilized and the throughput of data downloading at the ESs is maximized. Firstly, we model the satellite network system and the feeder link based on MIMO technology. Then, a Maximum-Flow-Minimum-Cost (MCMF) routing algorithm consisting of two Linear Programs (LPs) is presented to compute maximum-flow routings for data download. Eventually, a variety of simulations are conducted to assess the proposed scheme, which shows that the cooperative routing scheme outperforms the existing SiRRS method in terms of throughput and delay.

Artificial Neural Networks for Earth-Space Link Applications: A Prediction Approach and Intercomparison of Rain-influenced Attenuation Models

The impact of rain-influenced attenuation (RIA) has a more pronounced effect as frequency increases, especially in the tropical zones with heavier rainfall than the temperate zones. The International Telecommunication Union (ITU) has recommended a universal model which may not fit well in this tropical region due to the temperate data used to develop the model. It is therefore necessary to adopt locally measured data to develop a suitable model for each region, as also recommended by ITU recommendation 618-13. The experimental site for this study is at the Department of Physics, Federal University of Technology, Akure, Nigeria (7.299° N, 5.147° E) in the tropical rainforest region of Nigeria. In the present work, the backpropagation neural network (BPNN) of the artificial neural network (ANN) is trained based on time-series rain rates data collected between 2015 and 2019 to predict time-series RIA. Based on four inputs (rain rate, rain heights, elevation angle, and polarization angle), the generated data was subjected to training, validation, and testing. The ANN was further trained using the Levenberg-Marquardt algorithm to fit the inputs and the targets to create a dynamic model for RIA forecasting. Further validation was tested using actual data of rain attenuation from a Ku-band beacon at the site. Subsequently, the RIA model created by the ANN was compared to those generated using the synthetic storm technique, ITU, and the actual rain attenuation obtained from a beacon measurement. The highest rain rate observed was about 225.8 mm/hr with a corresponding rain attenuation of about 61 dB as estimated by the SST model and about 68 dB by the ITU model, while the predicted attenuation by the ANN is 55 dB. This implies that an extra power of 6 dB and 13 dB is added by the SST model and ITU model, respectively, for the downlink signal, to compensate for the rain attenuation link. The results also reveal that during 0.01 percent of an average year that signal may be attenuated, a relatively tiny margin of error between anticipated rain attenuation using ANN and the SST model is exceeded. In general, the new ANN-generated RIA model had the lowest root mean square error, average relative error, and standard deviation at the selected time percentages, according to the model validation. Hence, the new ANN model can predict more effective RIA in the region when compared with the global ITU-R model.

Aspects of melting layer and fall streaks in stratiform cloud system over the Western Ghats, India from Ka-band polarimetric radar observations

During the Indian summer monsoon, high temporal and spatial resolution observations from Ka-band dual-polarization radar deployed in the Western Ghats (WG), India are utilized to investigate the vertical structure of the stratiform precipitating system. First, the radar reflectivity (Z) measurements are corrected for rain attenuation, based on the relationship between specific attenuation (A) and Z. The disdrometer dataset is used to calculate the expected value of A at Ka-band for a given Z using microwave scattering simulation. The radar data are also corrected for wet radome transmission loss, gaseous, and melting layer (ML) attenuation. Within the ML, a change in Z and other radar polarimetric variables suggest hydrometeors phase change. In addition to Z, polarimetric measurements such as differential reflectivity (ZDR), linear depolarization ratio (LDR), and copolar correlation coefficient between horizontal and vertical channel (ρHV) are used to determine the ML height. Ka-band polarimetric radar signatures near the ML are characterized by a low ρHV (∼0.93), high Z (∼25–30 dBZ), ZDR (∼3 dB), and LDR (∼ −15 dB) values. In the stratiform precipitation region, well-defined fall streaks are observed above ML, which descends through 0 °C isotherm into the rain region. When the fall streaks are present above the ML, Z increases below the ML, indicating a seeder-feeder mechanism. Because there is little observational evidence concerning the vertical distribution of stratiform clouds over the Indian subcontinent, the current study may help to understand stratiform clouds and the ice processes that occur within them.

Preliminary Investigation of the Potentialities of a Mesoscale Meteorological Model to Reproduce Experimental Statistics of Rain Attenuation on Earth-Space Links

Current spatial resolutions achieved by mesoscale weather forecast models allow them to be used to generate the state of the lowest layers of the atmosphere over areas as small as a few square kilometers which corresponds to the typical size of the tropospheric area crossed by Earth-space links. Furthermore, they allow the evolution of the troposphere to be predicted with a time stamp of five minutes instead of every hour with large-scale weather forecast models which makes them attractive for radio propagation predictions for satellite communication applications. This paper aims at studying the capability of the Weather Research and Forecast (WRF) model coupled with an electromagnetic physical model to reproduce rain attenuation statistics for Earth-space paths at Ka-band. To this purpose, one year of propagation measurements collected at 20 GHz in different places at midlatitudes in Toulouse and Salon de Provence (France), Spino d’Adda (Italy), Aveiro (Portugal), and Madrid (Spain), at high latitudes in Svalbard (Norway) and at low latitudes in Kourou are used to make comparisons between simulations and measurements. Comparisons between the simulated and the experimental annual statistics considered in this paper provide encouraging results, with a similar accuracy as Recommendation ITU-R P.618–13 for midlatitude European locations and with better accuracy for a high latitude area in Svalbard and for an equatorial location in French Guiana.

Channel fading attenuation based on rainfall rate for future 5G wireless communication system over 38-GHz

In this paper, the effect of heavy rainfall on the propagation of a 38-GHz in a tropical region was studied and analyzed. Real measurement was collected, with a path length of 300 meters, for a (5G) radio linkage in Malaysia, installed at the Universiti Teknologi Malaysia (UTM) Johor Bahru campus. The employed system entails an Ericsson MINI-Link 38 E-0.6 mm, with a horizontal polarization (HP) antenna at the top integrated with a rain gauge and a data logger. Daily registered samples with a single minute span, for a full study period of 1 month, were collected and evaluated. The obtained rain rate was found as 56 mm/hr with a specific rain attenuation of 18.4 dB/km for 0.01% of the time. In addition to that, a calculated average rain attenuation of 5.5 dB for the transmission path of 300 meters length, was calculated. Based on these findings, a recommendation to update the International Telecommunication Union (ITU) specification of the rain attenuation for Malaysia is proposed. Based on the results, we suggest shifting the zone classification of Malaysia from zone P to zone N-P. Therefore, accurate design for future 5G systems would rely on more precise estimated attenuation levels leading to enhanced performance.

Radio Refractive Index of Wet Atmosphere Estimated From Site Test Interferometer Data

AbstractThe atmosphere plays a significant role in degrading Ka‐band (32 GHz) radio and optical communications for single antenna communications as well as degrading interferometric measurements such as used for radio astronomy and multi‐antenna arrays. Higher frequencies such as deep space Ka‐band (32 GHz) and near‐Earth K‐band (26 GHz) are more susceptible to this atmospheric degradation than at the lower frequency bands of S‐band (2.3 GHz) and X‐band (8.4 GHz). The various sources of atmospheric degradation include rain attenuation, cloud attenuation, gaseous attenuation, atmospheric noise temperature increase, and scintillation. For this study, we have focused on the strength of the turbulence caused principally by the wet atmosphere represented by the refractive index structure parameter Cn2, which is a measure of the variance of the refractive index over small incremental distances along the signal path, and thus is a strong function of water vapor variations at microwave frequencies. Here we provide a comprehensive study of this parameter derived from years of Site Test Interferometer measurements acquired from a variety of climates. We found that the strongest diurnal variation and correlation of Cn2 measurements with its model occurred for Goldstone, California representing a high‐desert climate, while weaker correlations were found for Kennedy Space Center representing a sub‐tropical climate, and Canberra, Australia and Madrid, Spain representing temperate climates. We quantified periods where the strongest correlation was observed such as Goldstone summers (as high as 0.7 for ∼3‐day periods) where the days are typically hot and humid while nights tend to be colder and drier.