Specific Rain Attenuation Research Articles

Dependence of rain attenuation on rain rate and drop size distribution for Ka-band satellite communication over India

The Raindrop size distribution (DSD) is the most effective parameter to calculate rain-induced attenuation, which can be severe at Ka-band and higher frequencies. The authors have investigated the impact of rain rate and DSD on rain-induced specific attenuation over a tropical location Kolkata, India. DSD data from disdrometer has been used to calculate the specific rain attenuation with the help of Mie scattering theorem. Low to medium drop diameters (up to 3 mm) are the largest contributors to the various classes of rain rate and attenuation. Double peaks of drop sizes are significant for medium rain rate. The contribution of smaller drop diameters decrease, whereas the contribution of higher drop diameters increase with increasing rain attenuation. At lower rain attenuation, (up to 1.5 dB), complementary cumulative distribution function (CCDF) shows higher value for stratiform rain, with respect to convective rain. The higher attenuation occurrences are mostly observed during 12–18 Indian standard time (IST), i.e., in the afternoon. The results will be helpful for Ka-band (GSAT-14) and higher frequency satellite communication channel modeling over India.

Rain Attenuations Based on Drop Size Distribution (DSD) Model and Empirical Model at Low THz Frequencies

Rain attenuation based on the drop size distribution (DSD) with different rainfall rates (R) at low THz frequencies is investigated in this paper. The rain attenuation is calculated using the DSD measured for one year and the extinction cross-section (ECS) by the Mie scattering theory. Moreover, the obtained specific rain attenuation is verified by the empirical model using the measurement system consisting of a transmitter, a receiver, and weather measurement units. We measured the received power against the uniform transmitted power at 240, 270, and 300 GHz on the rooftop of the National Radio Research Agency (RRA) in Korea during the same period as the DSD measurement period. After curve fitting by regression analysis, we compared both rain attenuations obtained in two methods with the recommendation International Telecommunication Union Radiocommunication Sector (ITU-R) P.838-3. The root mean square errors (RMSEs) of the DSD model are 2.8977, 2.8646, and 2.8331 at 240, 270, and 300 GHz, respectively. The calculated result using the Mie scattering and the measured DSD methods shows the best fit to the data of the ITU-R recommendation for a rainfall rate of up to 5 mm/h. On the other hand, the empirical results using the T/Rx antenna system are slightly higher compared to the data of the ITU-R recommendation. As the rainfall rate increases, the difference between our results and ITU-R recommendation increases. This study will be useful for predicting rain attenuation for terrestrial wireless links operating at low THz frequencies.

Characterization of Rain Attenuation in 80–200 GHz From Experimental Drop Size Distributions

The use of frequencies well into the EHF band (30-300 GHz) is a key element in 5G and beyond technologies. Rain attenuation is the major impairment affecting terrestrial radio links in this band. In the absence of enough experimental measurements, rain attenuation can be estimated by using physical models of radiowave scattering in rain drops combined with information about the rain Drop Size Distributions (DSD). In this work, the characterization of rain attenuation in the 80-200 GHz frequency range is carried out from a large database of twelve years of experimental DSD gathered in Madrid, Spain. Rain attenuation is estimated for each collected minute of rain using two approaches: a first one based on the assumption of raindrops as spherical and the application of the Mie theory, and a second one that uses a non-spherical raindrop model and electromagnetic simulations and is consequently more realistic. The main results show that the currently used ITU-R model generally underestimates rain specific attenuation; the influence of polarization becomes smaller and negligible as frequency approaches 200 GHz; and rain specific attenuation significantly varies due to the spread of the DSD. Moreover, a model for this variability of rain attenuation is also proposed.

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.

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.

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.

Realistic Prognostic Modeling of Specific Attenuation due to Rain at Microwave Frequency for Tropical Climate Region

Absorption and scattering of propagated microwave radio signals by atmospheric variables, particularly rainfall, remained a major cause of propagation attenuation losses and service quality degradation over terrestrial communication links. The International Telecommunications Union Radio (ITU-R) reports and other related works in the literature provided information on attenuation due to rain and microwave propagation data. Such propagation attenuation information in the tropical region of Nigeria is destitute, especially at lower radio waves transmission frequencies. Therefore, this study addresses this problem by employing 12-year rainfall datasets to conduct realistic prognostic modeling of rain rate intensity levels. A classification of the rainfall data into three subgroups based on the depth of rainfall in the region is presented. Additionally, an in-depth estimation of specific rain attenuation intensities based on the 12-year rainfall data at 3.5 GHz is demonstrated. On average, the three rainfall classes produced rain rates of about 29.27 mm/hr, 73.71 mm/hr, and 105.39 mm/hr. The respective attenuation values are 0.89 dB, 1.71 dB, and 2.13 dB for the vertical polarisation and 1.09 dB, 1.20 dB, and 2.78 dB for the horizontal polarisation at 0.01% time percentage computation. Generally, results indicate that higher rain attenuation of 12% is observed for the horizontal polarisation compared to the vertical polarisation. These results can provide valuable first-hand information for microwave radio frequency planning in making appropriate decisions on attenuation levels due to different rainfall depths, especially for lower frequency arrays.

Influence of raindrop size distribution variations on the rain specific attenuation coefficients

The raindrop size distribution is one of main term to evaluate microwave attenuation due to rainfall. In this paper, the lognormal distribution is introduced to represent the raindrop-size distribution based on the measurement performed at the Chungnam National University. Since the distribution parameters are strongly scattered around the fitted value, we developed a new statistical model for the lognormal distribution parameters. Based on the new statistical model for raindrop size distribution parameters we have estimated influence of raindrop size distribution variations on the rain specific attenuation coefficients.

Characterization of rain specific attenuation and frequency scaling technique for satellite communication systems in a tropical location

Increased demand for satellite system applications and congestion of the lower frequency bands has mandated the foray into higher frequency spectrum which is more susceptible to rain-induced attenuation. This research explores the characterization of rain specific attenuation and frequency scaling technique for satellite communication system in Akure (7.17°N, 5.18°E, 358 m), Nigeria. Two-year archived rain-attenuation data on Ku-Band satellite link over the earth-space path of Akure was used for the study. Concurrent measurement of rainfall parameters and Eutelsat W4/W7 satellite radio beacons was carried out at the Department of Physics, Federal University of Technology Akure, between January 2017 and December 2018 using Tektronix Y400 NetTek spectrum analyzer. Estimated and measured rain attenuation statistics were compared, and exact determination of the power law coefficients which support the computation of explicit attenuation from measured rain rate was carried out. Recommended frequency scaling technique was also employed to investigate the magnitude of rain-induced attenuation at higher frequency bands. Results show that, at 0.01 percentage exceedance window, combined estimated and measured rain attenuation have respective magnitudes of about 13.09 dB and 21.43 dB. Also, estimated and scaled attenuation at 16 GHz, 20 GHz, 30 GHz and 40 GHz are about 21.97 dB, 31.78 dB, 56.64 dB, 77.23 dB and 28.36 dB, 33.95 dB, 42.17 dB, 46.07 dB respectively.

Evaluation of Concurrent Variation in Rain Specific Attenuation and Tropospheric Amplitude Scintillation Over Akure, Southwest Nigeria

Rain constitutes a major limitation to the performance and use of terrestrial and satellite communication systems with operational frequencies greater than 10 GHz. The situation gets further complicated by fast fluctuations in the received signal amplitude due to in homogeneities in atmospheric weather conditions; a phenomenon known as amplitude scintillation. The concurrent evaluation of the two phenomena guarantees a better fade margin determination for the planning of radio communication over any location. This work employs 3 years of in-situ measurement of temperature, humidity, rainfall rate and rainfall amount for the estimation of tropospheric amplitude scintillation and rain specific attenuation over Akure (7.17° N, 5.18° E, 358 m) South West Nigeria. Davis vantage pro weather station at 1-min integration time was used for the measurement and the ITU models for rain specific attenuation (ITU-R P.838-3) and amplitude scintillation (ITU–R 618-13) were employed for the estimation. Time series and statistical analyses of the phenomena show that rain attenuation is the more prominent cause of signal degradation at Ku-band frequencies. Nevertheless, the need to make an extra fade margin allowance of about 0.25 dB due to amplitude scintillation fade subsists to forestall any loss of synchronization on the link. Also, a 3-parameter power-law expression developed for estimating amplitude scintillation fade from rain attenuation performed excellently well, as indicated by average root mean square error (RMSE) and coefficient of determination (R2) values of 0.002151 and 0.8747, respectively.

Rain attenuation in millimeter wave, centimeter wave and visible light ranges

The paper presents the results of theoretical simulation of mmWave, cmWave and visible light attenuation in rain based on the Mie scattering theory. Specific rain attenuation has been estimated from the gamma drop size distribution for a spherical drop. Rain attenuation of electromagnetic waves in the visible range, used by video cameras and lidars of «smart» city vehicles, and at the beginning of the millimeter wave range used by radars and positioning systems, have similar values averaging 3-5 dB/km. The attenuation levels of electromagnetic waves in mmWave, cmWave and Visible light ranges must be taken into account when calculating the energy budget of vehicle communications.

Effects of reduction factor on rain attenuation predictions over millimeter-wave links for 5G applications

Millimeter-wave will be the strong contender for the terrestrial link using for 5G networks. So it is imperative to examine these frequency bands to ensure the uninterrupted services when 5G network is connected in tropical regions. A critical challenge of link-budgeting in mm-wave 5G networks is the precise estimation of rain attenuation for short-path links. The difficulties are further intensified in the tropical areas where the rainfall rate is very high. Different models are proposed to predict rain attenuation, however recent measurements show huge discrepancies with predictions for shorter links at mm-wave. The path reduction factor is the main parameter in the prediction model for predicting total attenuation from specific rain attenuation. This study investigates four path reduction factor models for the prediction of rain attenuation. A comparison was made between these models based on rain attenuation data measured at 26 GHz at 300 m and 1.3 km links in Malaysia. All models are found to predict rain attenuation at a 1.3 km link with minimum errors, while tremendous discrepancies are observed for 300 m link. Hence it is highly recommended to further investigate the reduction factor model for shorter links less than 1 km

Spatial variations of rain intensity over a short length propagation for 5G links based on a rain gauge network

Millimeter-wave (mm-wave) frequency range is among operating bands designated for terrestrial 5G networks. A critical challenge of link-budgeting in mm-wave 5G networks is the precise estimation of rain attenuation for short-path links. The difficulties are further amplified in tropical and subtropical regions where the rainfall rate has a higher intensity. Different models have been proposed to predict rain attenuation. The distance factor is an important parameter in predicting total attenuation from specific rain attenuation. This study investigates the distance factor based on rain gauge networks and measured rain attenuation at 26 GHz for a 300 m link in Malaysia. Considerable discrepancies between available models were observed especially when applied for shorter path links. Also, significant variability of rain intensity is observed from the rain gauge network. This study recommends further investigation of the distance factor for a shorter link. Hence, a measurement campaign incorporating rain gauge networks was established to examine spatial variations of rain intensity over a less than 1 km link. The motivation is to develop a suitable distance factor model for 5G mm-wave propagation.

Feasibility Analysis of Optical Wireless Communication for Indian Tropical and Subtropical Climates

Abstract This work investigates the feasibility of terrestrial Optical wireless communication links under tropical and subtropical regions which are characterized by high precipitation. The impact of rain on propagating optical radiation is observed under controlled rainfall conditions using a laboratory testbed. Link degradation in terms of rain specific attenuation (RSA) is calculated experimentally and using known empirical models. A worst case analysis in terms of fade margin is carried out using measured and recorded data from Indian Meteorological Center to estimate the free space link feasibility for Indian tropical/subtropical climates.

Estimating Rain Attenuation at 72 and 84 GHz From Raindrop Size Distribution Measurements in Albuquerque, NM, USA

The raindrop size distribution (DSD) is essential information for understanding rain attenuation effects at millimeter wavelengths. The DSD was measured in Albuquerque, NM, USA, as a part of the W/V-band Terrestrial Link Experiment. An optical disdrometer from Thies Clima was used to measure both size and velocity of rain droplets. The measured DSD consistently showed a unique property of two log-linear distributions regionally separable by drop size under variable rain rates. The functional fit that best represents our measured data with rain rates under 40 mm/h is presented. Based on the DSD, rain specific attenuation is estimated at 72 and 84 GHz with Mie scattering theory. These estimated rain attenuations can be used and validated for rain attenuation analysis of the millimeter wave propagation experiments under similar climate conditions. This letter will guide millimeter wave communication system designers to estimate the rain attenuation based on their own DSD measurements.

Compensating rain induced impairments in terrestrial FSO links using aperture averaging and receiver diversity

In this paper, we investigate the performance of a free space optical link considering the deteriorations caused by heavy rain. The applicability of receiver diversity and aperture averaging techniques to compensate the rain-induced impairments is analyzed on the basis of outage probability and signal to noise ratio at varying rain intensities. A 10-Mbps on-off keying modulated optical signal is taken as the test signal for which rain specific attenuation is calculated using a laboratory testbed having controlled rainfall conditions up to 250 mm/h. A 15-m single input multi output) optical link with selection combining technique at the receiver is used to observe diversity gain. Significant diversity improvement by a factor of 1.35 is observed by comparing the results with the conventional single input single output link. Experimental observations with and without aperture averaging shows average SNR gain of 1.58 and outage probability reduction of 12.3%.

Effect of wind pressure and modulation schemes on rain interrupted optical wireless links under tropical climates

Tropical and subtropical regions experience heavy rain intensities often accompanied with medium to strong winds. In this work, the effect of perpendicular wind flow and various modulation formats on a rain interrupted optical wireless link is investigated experimentally under controlled laboratory conditions. Attenuation as a function of rain rate is observed at different wind pressure. It is found that rain induced scattering dominates the rain specific attenuation however significant attenuation is expected at much higher wind pressure which normally increases with altitudes. A comparative performance of modulation formats like direct intensity modulation (D-IM), pulse width modulation (PWM) and various subcarrier intensity modulated (SIM) signals under heavy rain conditions is reported. It is found that SIM-FSK and SIM-AM offer better signal to noise performance (approximately two times) followed by subcarrier phase (SIM-PM) and frequency (SIM-FM) respectively. Also, SIM-FSK and PWM are least attenuated in heavy precipitation.

Rain Attenuation Study over an 18 GHz Terrestrial Microwave Link in South Korea

Absorption of microwave radio frequency signal by atmospheric rain and losses is prevalent at frequencies above 5 GHz. The functioning frequencies of 18 GHz are taken for the point-to-point microwave link system. This paper presents studies on rain attenuation at 18 GHz, which specifies minimum performance parameters for terrestrial fixed service digital radio communication equipment. It presents a 3.2 km experimental link at 18 GHz between Khumdang (Korea Telecom, KT station) and Icheon (National Radio Research Agency, RRA station). The received signal data for rain attenuation and the rain rate were collected at 10-second intervals over three year’s periods from 2013 to 2015. During the observation period, rain rates of about 50 mm/hr and attenuation values of 33.38 dB and 21.88 dB occurred for 0.01% of the time for horizontal and vertical polarization. This paper highlights the discussion and comparison of ITU-R P.530-16, Moupfouma, Silva Mello, and Abdulrahman models and proposed an attenuation prediction approach where it presents the relationship between theoretical specific rain attenuation as specified by ITU-R P.838-3, γ%p, and effective specific rain attenuation, γeff. Additionally, it studies 1-minute rain rates derived from higher time integration of 5-minute, 10-minute, 20-minute, 30-minute, and 60-minute instances which are obtained from experimental 1-minute rainfall amounts that are maintained by the Korea Meteorological Administration (KMA). The effectiveness of the proposed approach is further analyzed for 38 and 75 GHz links which shows better prediction capability. Particularly, in an 18 GHz link under horizontal polarization, ITU-R P. 530-16 shows the relative error margin of 71%, 60%, and 38% where as 64%, 49%, and 42% were obtained under vertical polarization for 0.1%, 0.01%, and 0.001% of the time, respectively. The limitation of research lies on the experimental system that is set up in only one location; however, the preliminary results indicate the application of a suitable 1-minute rain attenuation model for a specific site. The method provides useful information for microwave engineers and researchers in making decisions over the choice of the most suitable rain attenuation prediction for terrestrial links operating in the South Korea region, particularly for lower frequency ranges.

Rain attenuation of millimetre wave above 10 GHz for terrestrial links in tropical regions

AbstractMillimeter waves (mm‐waves) within frequency bands of 10 to 86 GHz will be used for both microwave and access link fifth‐generation (5G) systems. Thus, it is very important to investigate these bands to ensure reliability when 5G is applied in tropical regions like Malaysia in the coming few years. One of the major obstacles facing the propagation of mm‐waves in tropical regions is the rain attenuation. Rainfall results in the absorption, scattering, and diffraction of radio waves. This contributes to increased transmission losses and a reduction in the received signal levels. The effect is more severe in tropical regions that are characterized by intense heavy rainfall and large raindrop sizes. This paper provides a general overview on rain attenuation of mm‐wave bands. It highlights the nature of rain in tropical regions and its effects on the propagation of mm‐waves. It also reports the latest measurement studies focused on rain attenuation in mm‐wave frequency bands and the prediction methods used to estimate rain attenuation in mm‐waves. It contributes to the understanding of channel behavior and the characterization of mm‐wave bands during rainfall in tropical regions, especially in Malaysia. This study further strives to determine research gaps in this field as well as the future work and various propagation measurement systems that can be used to conduct real measurements and to develop prediction models for rain attenuation in mm‐waves for 5G systems. Furthermore, this paper analyzes the rain rate and rain attenuation on the basis of real measurement data conducted in Universiti Teknologi Malaysia at Skudai Campus, Malaysia. The analyzed results indicated that the rain attenuation at 38 GHz is critical and it can result in 18.4 dB/km as specific rain attenuation at 0.01% percentage of the time.

Real Measurement Study for Rain Rate and Rain Attenuation Conducted Over 26 GHz Microwave 5G Link System in Malaysia

In this paper, real measurements were conducted to investigate the impact of rain on the propagation of millimeter waves at 26 GHz. The measurements were accomplished using a microwave fifth generation radio link system with 1.3 km path length implemented at Universiti Teknologi Malaysia Johor Bahru, Malaysia. The implemented system consisted of Ericsson CN500 mini E-link, radio unit, rain gauge, and data logger. The measurements were attained and logged daily for a continuous year, with 1-min time intervals. Next, the MATLAB software was used to process and analyze the annual rain rate and rain attenuation, including for the worst month. From the analyzed results, it was found that at 0.01% percentage of time, the rain rate was 120 mm/hr; while the specific rain attenuation was 26.2 dB/km and the total rain attenuation over 1.3 km was 34 dB. In addition, the statistics acquired from the measurements for the worst month were lower than what was predicted by the international telecommunication union (ITU) model; around 51% and 34% for the rain rate and rain attenuation, respectively. The average percentage of error calculated between the measurements and predicted results for the rain rate and rain attenuation were 143% and 159%, respectively. Thus, it can be concluded that the statistics for the worst month in Malaysia is lower than what was predicted by the ITU model.