Rain Attenuation Research Articles

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.

Frequency scaling of Ku-band signal for rain attenuation prediction and radio link applications over Akure, Nigeria

To get the best performance for a broadband wireless access, this research aims to scale a Ku-band real-time rain attenuation data to higher frequencies and estimate the degree of fading that can be observed under such conditions. Data of simultaneous measurement of satellite radio beacons and rainfall parameters, carried out between January 2017 and December 2018, at Physics Department, Federal University of Technology (07.17°N, 05.18°E, 358 m) Akure, were used for the work. The radio beacon measurement, of horizontally polarized Eutelsat W4/W7 satellite signals at 12.245-GHz frequency, and received through a 90-cm parabolic antenna positioned at 53-deg elevation angle, was conducted at 1 s integration time using Tektronix Y400 NetTek spectrum analyzer. Measurement of rainfall parameters was done at 1-min sampling intervals using Davis Vantage Vue automatic weather station, which is co-located with the receiving antenna of the satellite receiver unit. Comparing measured and estimated attenuation values at 12.245 GHz for 1%, 0.1%, and 0.01% exceedance margins result in about 64%, 40%, and 55% relative error, respectively. Similarly, relative error values between estimated and scaled attenuation values for the same exceedance margins are 72%, 53%, and 27% for 16-GHz frequency, respectively, with similar values for the 20-, 30-, and 40-GHz frequencies as well. A power-law relationship between measured rain attenuation and rain rate was developed and used to generate a location-specific expression for computing rain attenuation. This was equally found to give better performance than the International Telecommunication Union model. The results obtained in this work provide useful information for radio engineers on the rain-induced attenuation needed for the design of radio communication system that can withstand poor weather conditions.

The Effects of Rainfall on Over-the-Horizon Propagation in the Evaporation Duct over the South China Sea

The evaporation duct (ED) is generated by the evaporation of seawater and can be an influential factor of electromagnetic (EM)-wave propagation. Rainfall also affects atmospheric factors and EM-wave propagation. However, the distribution of the ED and path loss (PL) during rainfall has rarely been reported. This paper analyzes the distribution of the atmospheric factors and ED in the South China Sea (SCS). The results show that the evaporation duct height (EDH) in the area of rainfall is generally lower. The effect of the ED on the over-the-horizon (OTH) propagation reaches 0.69 dB km−1 on average, which is 4.3 times stronger than the maximum rain attenuation (0.16 dB km−1) when the rainfall is less than 5 mm h−1. In the SCS, a 53 km long OTH link was established between Donghai Island and Jizhao Bay to observe the PL. The measurement results show that the nearly saturated relative humidity (RH) leads to a high PL. The results also show that the change in the direction of the sea–land breeze causes a 42.4 dB decrease of PL by transferring the moist patches. Rainfall has an attenuation effect on OTH propagation in ED, mainly owing to the high RH.

Range and Capacity Considerations for Terahertz-Systems for 6G Mobile and Wireless Communication

Discussions on research directions towards systems beyond 5G/6G have started. One of the potential elements of future mobile and wireless systems are new radio systems in the (sub)-Terahertz domain above 100 GHz for communication and sensing purposes. This paper is investigating potentially available frequency bands based on the ITU Radio Regulation, basic propagation conditions above 100 GHz including the different additional path loss contributions on top of distance dependent path loss such as atmospheric and rain attenuation, foliage and wall penetration loss. The impact on system performance like range and channel capacity is considered under idealized conditions at Shannon limit and demonstrated by indoor and outdoor, uplink and downlink scenarios. Radiation limits based on internationally accepted regulations are taken into account in scenarios, where humans are directly involved in the communication. In other scenarios less stringent requirements apply. The main purpose of this paper is to get an understanding from a system perspective of the relation between achievable data throughput versus range and system bandwidth for different propagation conditions and carrier frequency ranges and to investigate basic physical limits. This understanding helps in the identification of use cases, applications and economic considerations on system deployment.

Evaluating the performance of free space optical communication (FSOC) system under tropical weather conditions in India

SummaryThe main aim of this study is to examine the performance of the free space optical communication (FSOC) system under the impact of rainfall in various regions of India. The meteorological data of rain intensities, during the years 2014–2017, were outsourced from the India Meteorological Department (IMD) for potential regions in India, comprising the coastal and inland locations for calculating the specific rain attenuation coefficient. Furthermore, we have proposed a 16‐channel FSOC system based on orthogonal frequency division multiplexing (OFDM), employing coherent detection and digital signal processing (DSP) for investigating the system performance for rainy weather conditions in India. For average rain intensities, the attenuation coefficient for the inland region of Hyderabad is 1.91 dB/km, which is the minimum among all locations considered in this work. Consequently, the proposed system design is capable of supporting an FSOC link of 5 km, for delivering a bit error rate (BER) of the order of 10−6 in the case of Hyderabad. On the flip side, the average rainfall intensities are maximum for the coastal region of Mumbai, and the specific attenuation coefficient is maximum with a value of 4.08 dB/km. Due to this, the maximum possible FSOC range for Mumbai gets restricted to 3.5 km only, ensuring BER of the order of 10−6. Likewise, the proposed FSOC system has performed superior for inland regions of India in comparison with coastal areas of India under the worst rainfall scenario as well.

A Review on Rain Signal Attenuation Modeling, Analysis and Validation Techniques: Advances, Challenges and Future Direction

Radio waves are attenuated by atmospheric phenomena such as snow, rain, dust, clouds, and ice, which absorb radio signals. Signal attenuation becomes more severe at extremely high frequencies, usually above 10 GHz. In typical equatorial and tropical locations, rain attenuation is more prevalent. Some established research works have attempted to provide state-of-the-art reviews on modeling and analysis of rain attenuation in the context of extremely high frequencies. However, the existing review works conducted over three decades (1990 to 2022), have not adequately provided comprehensive taxonomies for each method of rain attenuation modeling to expose the trends and possible future research directions. Also, taxonomies of the methods of model validation and regional developmental efforts on rain attenuation modeling have not been explicitly highlighted in the literature. To address these gaps, this paper conducted an extensive literature survey on rain attenuation modeling, methods of analyses, and model validation techniques, leveraging the ITU-R regional categorizations. Specifically, taxonomies in different rain attenuation modeling and analysis areas are extensively discussed. Key findings from the detailed survey have shown that many open research questions, challenges, and applications could open up new research frontiers, leading to novel findings in rain attenuation. Finally, this study is expected to be reference material for the design and analysis of rain attenuation.

Transmission of 1024-QAM OFDM at 28 GHz Radio Frequency Using 5G Millimeter Wave Phased Array Antenna

We experimentally demonstrate the transmission of multiorder quadrature amplitude modulation (QAM) millimeter wave (MMW) orthogonal frequency division (OFDM) signal at 28 GHz radio frequency (RF). To overcome these unfavorable channel properties such as high path loss, propagation loss, rain fading, etc., 5G MMW phased array antenna has been used. Meanwhile, probabilistic shaping (PS) technology is applied to extend transmission distance, and Volterra nonlinearity compensation (VNC) technology is used to alleviate the system nonlinearity. Using 5G MMW phased array antennas and technologies of PS and VNC, 6.72 Gbit/s 1024-QAM OFDM signal at 28 GHz can be transmitted over 55-m wireless distance in our experiment, satisfying the normalized general mutual information (NGMI) threshold of 0.83 with 25% soft-decision forward-error-correction (SD-FEC) overhead. To the best of our knowledge, this is the first time to demonstrate the transmission of multiorder QAM OFDM signal at 28 GHz RF using 5G MMW phased array antenna.

Outage Probability versus Carrier Frequency in GeoSurf Satellite Constellations with Radio-Links Faded by Rain

For sites located in different climatic regions, we estimated the relationship between the annual average probability distributionof exceeding a fixed rain attenuation, and the carrier frequency in the range 16 to 100 GHz, in the zenith paths of GeoSurf satellite constellations. In these constellations rain attenuation is independent of the altitude and number of satellites. Rain attenuation iss calculated with the Synthetic Storm Technique, a reliable prediction method, by using on-site measured rain-rate time series. A suitably defined outage probability factor shows that the outage probability, for fixed power margin, tends to saturate as frequency increases. In wideband radio-links, such as in spread spectrum design, there is very likely a long-term distortion due to the in-band outage probability. The results are oriented to design systems faded by rain attenuation whose value is also the total power margin available due to a mixture of coding and hardware technology, whose combination is not of concern here.

Slant path rain attenuation predictions for Ku and Ka band frequencies from rain cell size distribution over a tropical region in southern India

SummaryRain cell size distribution that provides an insight into the modelling of effective slant path length and also imperative for site diversity studies are carried out for a tropical inland location, Tirupati (13.6°N, 76.3°E), India. Rain cell size distribution obtained from 5 years (2013–2015 and 2017–2018) of Parsivel disdrometer measurements is observed to follow the power law. Reduction factor that accounts for the inhomogeneity of the rain along the propagation path for the region of study is modified in terms of the rain cell size distribution of the area. Slant path rain attenuation, a major propagation impediment at Ku and Ka‐band links, is then studied using the results from the regional rain characteristics by modifying the CCIR 564‐4 report. The attenuation results are compared with Garcia‐Lopez, Excell, Bryant, and Ramachandran models while considering the ITU‐R P. 618‐13 as the standard model.

Evaluation of Two-Part rain attenuation model at Ku-band for tropical and equatorial regions

The current ITU rain attenuation model that is used in the design of satellite-earth communication link was derived using data collected predominantly from temperate regions and has limitations when applied to tropical and equatorial regions that are characterized by heavy rainfall. Elevation and frequency scaling was applied to the rain attenuation data obtained from tropical and equatorial regions to validate the linear relationship for rain rates above 90 mm/h in the TPRA model. Analysis of the data from these regions also confirms the linear relationship between the rain attenuation and rain rates above 90 mm/h. The TPRA model can be considered as an alternative model for a reliable satellite-earth link for use in the tropical and equatorial regions.

Ku-band specific attenuation coefficients for high-throughput satellites in equatorial region

Ku-band have a larger attenuation during heavy rain in the equatorial region. Despite that, Ku-band has been identified as a frequency band in high-throughput satellite systems (HTS) for broadband satellite communication. The available rain fade prediction models are still not able to accurately predict rain attenuation in the equatorial region. The models depend on the specific attenuation parameters produced based on the international telecommunication union radiocommunication sector (ITU-R) instead of the measured value. Direct measurement of specific attenuation is more accurate but difficult to obtain because the correlation of rainfall rate and satellite signal loss due to rain must be obtained simultaneously. This paper aims to derive new specific attenuation frequency-dependent coefficients for Ku-band using the semi-empirical method. The Malaysia East Asia Satellite 3 (MEASAT-3) satellite data was collected using a 13 m antenna located at Cyberjaya, Selangor while the rainfall data was collected by the nearby hydrological station. The specific attenuation was obtained from correlations of the direct measurement of rain attenuation and rainfall rate. The new frequency-dependent coefficients for Ku-band specific attenuation values are k = 4.6690 and α = 0.1941. The newly acquired specific attenuation coefficients have improved the rain attenuation model prediction for the equatorial region.

A new multiple gateway transmit diversity technique for future satellite networks

The next generation of High Throughput Satellite (HTS) will exploit Q/V band for the feeder link and Ka band for the user link. The exploitation of multiple gateways (GWs) is a transmit diversity measure to compensate severe rain attenuation of Q/V band feeder links. This paper introduces a new smart gateway diversity combination scheme that combinates N-active (K = 2) and N + 1 diversity method in detail from the working principle, gateway switching strategy, evaluation of system availability and implementation complexity. In addition, a feeder link outage event prediction algorithm featuring combination scheme is given detailly based on modified time-adaptive linear regression. Compared with the existing N + P scheme, the proposed scheme can provide higher system availability and more stable user's experience under the condition of properly increasing the complexity of payload design. Compared with N-active scheme that has been reported, it is much easier to implement in engineering and more cost-effective. As a result, the combination scheme is a realistic solution based on a trade-off between performance improvement and implementation complexity.

Evaluation of 1-Minute Integration Time Rain Rate Statistics in Ecuador for Radio Propagation Applications

In this letter, rain rate measurements performed in Ecuador are used to evaluate the performance of prediction models for estimating complementary cumulative distributions (CCDs) of rainfall rate at 1-minute integration time, which are required, for example, for rain attenuation estimation in wireless communication systems operating at frequencies above 10 GHz. Additionally, the aforementioned measurements are utilized in order to analyze the interannual variability of the rain rate, useful for the assessment of the reliability of the CCDs in terms of communication system availability. It was observed that overall the Recommendation ITU-R P.837-7 Annex 1 exhibited the best performance in estimating equivalent 1-minute integration time rain rate statistics. Furthermore, it was found that the lowest level of inter-annual variability of the rainfall rate was observed in the western zone adjacent to the Andes Cordillera of Ecuador.

Dependence of raindrop size and shape parameters on rain attenuation prediction over a tropical location

Rain attenuation is a phenomenon that weakens signal propagation, particularly in high frequency bands and in areas with significant rainfall rates, one of which is the tropical area. Falling raindrops undergo changes in shapes as they grow in sizes. The goal of this research is to use a theoretical method to examine the impact of drop shapes and sizes on rain attenuation prediction. The extinction cross section of spherical and non-spherical raindrops was calculated using the Mie theory and T-matrix respectively. The specific rain attenuation for spherical and non-spherical raindrops was computed at various frequencies in the microwave band and compared with the ITU-R838 model. It was observed that the non-spherical drops model has higher values for rain attenuation, and thus is best suitable for predicting rain attenuation.

Multibeam FSO-based 5G communication system using M-ary DPSK encoder

Abstract Optical wireless technologies like Free Space Optics (FSO) have proven to be a perfect choice for 5G communication systems. FSO can offer low latency, high capacity, extensive connectivity, and high reliability at a low cost. However, the major limitation of FSO is its susceptibility to atmospheric turbulences, especially rain at high frequencies. In this paper, a rain efficient 10 Gbps 5G communication system using multibeam FSO and multilevel Differential Phase Shift Keying (M-ary DPSK) encoder is proposed. To evaluate the system performance at different rain intensities, the state-of-the-art Charbonneau channel model for rain attenuation has been used. The performance efficiency of the proposed system is evaluated in terms of quality factor (Q-factor), bit error rate (BER), optical signal-to-noise ratio (OSNR), and received power. The results convey that the proposed system can perform well up to 4.25 km, 3.24 km, and 2.55 km under below average, average, and above average rain conditions, respectively, with attenuation of 6.28 dB/km, 9.65 dB/km, and 19.27 dB/km, respectively. Moreover, the comparative analyses show that the proposed system performs better than the recent conventional systems in terms of bandwidth and power efficiency.

Weighted Mean Annual Rain Height Applied to Rain Attenuation Prediction on Earth-Space Links

Rain height is crucial for rain attenuation prediction along slant paths, such as Earth-space links. The global digital map of the mean annual rain height is given in Recommendation ITU-R P.839-4. The disadvantage of this model is that heavy rainfall in most regions of the middle and high latitudes of the world is typically concentrated over a few months, such as summer in North China, and the mean rain height during these months and the mean annual rain height are often significantly different. In this study, a new weighted mean annual rain height is proposed by using the ratio of the mean monthly rainfall to the mean annual rainfall as the weight. The analysis shows that the weighted mean annual rain heights have been closer to the statistical rain heights during heavy rainfall in general. On the other hand, the work of this paper helps to improve the accuracy of the rain attenuation prediction model on Earth-space links in China. However, the weighted mean annual rain heights have different characteristics for different rainfall climate zones. This study will contribute to the research of rain attenuation modelling on Earth-space links.

Prediction of Time Diversity Gain – Comparison Between ITU-R P.618-13 Using a Concept of Rain Rate with Delay and Synthetic Storm Technique

Future satellite companies will use higher Ka and V bands. Rain fade is the most important issue in establishing reliable communication between Earth and satellites outside the 10 GHz band. The problem is exacerbated in the tropics by significant rainfall throughout the year. One way to deal with rainfall attenuation is to use a time-diversity strategy. Real-time rainfall attenuation data is needed to analyze time variability. However, data from higher frequency bands such as Ka and V bands cannot be used. As a result, the Synthetic Storm Technique (SST) was proposed to convert the measured real time rainfall data into rainfall attenuation data and predict the time diversity gain. The measured rainfall data was converted to rainfall attenuation data using the traditional SST method. Time diversity gains were predicted using Converted rainfall attenuation and the Matriciani model, and the measurements were significantly overestimated. A new concept of realtime rainfall with and without time delay is proposed and used to predict time diversity gain using ITU-R P. 618-13 and the measured rainfall distribution with delay. Therefore, the proposed method recommends using the measured long-term precipitation data to predict the gain from time diversity at the desired frequency.