Radiometric rain attenuation measurements at 11.6 GHz in Peru

Rain attenuation is one of the key design parameters when setting up satellite communications systems at frequencies above 10 GHz. Reliable and economical system design requires fairly accurate estimates of this parameter. Although rain attenuation prediction models are available for temperate climates, little has been reported for tropical regions where rain impairments can be very much more severe. This letter presents radiometrically determined rain attenuation results at 11.6 GHz in a tropical climate.<>     

Site-diversity advantage for satellite communication at 11.6 GHz

Two ground stations, used as a site-diversity pair, can substantially reduce the duration of fades on satellite links operating at frequencies about 10 GHz. Changes in sky-noise temperature during severe summer rainstorms have been measured simultaneously by five spaced 11.6 GHz radiometers in SE England, and these observations are used to derive the signal fading that would have occurred on a satellite communication link. The results show that a tenfold reduction in the duration of fades exceeding 3 dB can be obtained by switching between a pair of sites spaced 5 km apart along a line perpendicular to the viewing direction. For fades deeper than 6 dB, the same improvement occurs at a spacing of only 2 km.     

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

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

Instantaneous frequency scaling of rain attenuation at 11.6-17.8 GHz with SIRIO data

The ratio of simultaneous attenuation measurements performed at 11.6 and 17.8 (or 17.0 GHz) with the Italian satellite SIRIO is discussed. The main application of this information is in the field of the "up-path power control" in earth-space telecommunication systems for which the requirement of estimating the uplink attenuation form measurements on the downlink will probably be taken into consideration as a tool to keep constant the total power received on board. The analysis shows that the average ratio between attenuations at 17.8 and 11.6 GHz, conditioned to the downlink attenuation (11.6 GHz) tends to decrease slightly with attenuation; it turns out to be very close to the ratio between equiprobable values of attenuation computed from the concurrent cumulative distributions (long-term frequency scaling ratio); the standard deviation is of the order of 10 percent of the average value and also exhibits some tendency to decrease; both the overall cumulative distributions and the conditional ones are well fitted by log-normal probability models with standard deviation (of the natural logarithm) constant and equal to 0.13-0.14 up to 5.5 dB in the downlink attenuation.     

Attenuation statistics at 11.6 GHz from satellite SIRIO after three years' activity in Italy

Rain attenuation statistics based on SIRIO data at 11.6 GHz collected in three Italian stations are presented. The long-term probability distribution can be excellently fitted by a power law up to a 9 dB attenuation level.     

Worst-month rain attenuation and XPD statistics for satellite paths at 12 GHz

Worst-month attenuation and XPD data are presented from a three year measurement program at Blacksburg, Virginia USA using the SIRIO 11.6 GHz beacon. The ratio of worst month to annual percentage occurrence levels (Q) for the attenuation and XPD data agree closely with each other. They also show excellent agreement to the CCIR model. Comparisons to previously reported experimental results are also given.     

Ka卫星通信系统中雨衰分析

简单介绍了雨衰的机理,并以我国原邮电部给出的雨衰模型为基础,根据我国10个主要城市的降雨数据和地理位置参数,计算出轨道位置在80°E的通信卫星在上行水平极化/下行垂直线极化的情况下,Ka波段(30/20GHz)的雨衰A0.01,并就雨衰对下行卫星链路G/T值恶化带来的影响进行了分析讨论,给出了相应的计算方法,最后总结了几种抗雨衰措施。     

Comparison of antenna noise temperature with rain attenuation of a satellite beacon signal at 12 GHz

Simultaneous measurements of antenna noise temperature Ta and satellite beacon attenuation were made to examine the quantitative relation between them, and to determine the `apparent? effective medium temperature which provides an accurate estimate of slant-path attenuation. The correlation between the attenuation and the increase in Ta due to rain is very good, and the effective medium temperature derived from the `apparent? one is reasonably consistent with a theoretical result.     

Depolarization measurements at 11.6 GHz on Earth-space paths using the SIRIO satellite

Depolarization (XPD) data at 11.6 GHz in circular polarization collected during the SIRIO experiment on the Italian stations of Fucino and Lario are presented and analyzed. The obtained results are presented both in conditional form (i.e., XPD statistics conditioned to the co-polar attenuation (CPA)) and in "equiprobable" form (i.e., by comparing XPD-CPA values exceeded for the same fraction of the total observation time). The conditional XPD appears spread in an interval ofpm5dB around the conditional median value. This latter appears to be very close to the "equiprobable" value. The International Radio Consultative Committee (CCIR) procedure giving the "equiprobable" XPD appears fairly well supported by the Fucino data, while the Lario data give higher depolarization than predicted by CCIR.     

Experimental rain attenuation statistics estimated from radarmeasurements useful to design satellite communication systems for mobileterminals

Based on experimental data, we have reported a reliable method to scale the cumulative time T_F,T(A) that rain attenuation A (dB) is exceeded in a fixed satellite system to the time T_M,T(A) that it is exceeded in a satellite system for mobile terminals. Zigzag routes and ring-roads simulated city patterns; straight routes simulated freeways. In all cases, T_M,T(A) can be expressed as T_M,T(A)=ξT_F,T (A) with a probability scaling factor ξ independent of A. The simulations have been made at 19.77 GHz with satellite elevation angle &thetas; of 30.6°, 45°, 60°, 80°, and 90°. For the horizontal structure of rain, we have used a very large number of rain-rate maps of rain storms randomly observed in 1989-1992 by a meteorological radar placed at Spine d'Adda (northern Italy). The vehicle speed was modeled as a log-normal random variable. We found: (a) in zigzag routes, T_M,T(A)F,T(A), i.e., ξ<1, with results depending on vehicle speed modeling and starting conditions; (b) in a ring-road, there is no difference between fixed and mobile systems (ξ=1); and (c) in straight freeways, T_M,T(A)≪T_F,T (A)(ξ≪1); T_M,T(A) can change significantly in different straight lines and in opposite directions (anisotropy and asymmetry) for medium-large attenuation. When compared to zigzag routes or ring-roads, the performance in straight freeways is the most optimistic. For &thetas;>30.6° and for the same pattern, ξ is fairly independent of &thetas;. Since the radar rain maps are a reliable estimate of the horizontal structure of rain, the findings, which can be considered frequency-independent, stand as a very good prediction of the results obtainable by experiments     

中国Ka波段卫星通信线路的雨衰分布特性

利用ITU-R给出的降雨衰减预测模型,根据我国主要城市的分钟降雨率数据,计算出我国Ka波段(30/20GHz),轨道位置为92°E的卫星通信系统在线极化波情况下的降雨衰减等值线分布,此结果可作为Ka波段卫星通信系统设计的理论依据。     

Microwave attenuation due to rain at 110 GHz in south-east England

Fading due to precipitation has been recorded at 110 GHz for a period of one year over a 2.65 km path near Slough, England. The results show that frequencies as high as this could be used for relay links over short distances with acceptable reliability, despite the large attenuation due to heavy rain.     

Depolarisation due to snow at 11.6 GHz

Depolarisation events due to snow covering a period of three years on an 11.6 GHz, 18 km link employing linear and circular polarisation are presented. These are used to demonstrate the variability of wet and dry hydrometeor scattering. By deriving the equivalent differential phase-shift from the measurements it is possible to show the relative importance of differential phase and amplitude effects in depolarisation for the different hydrometeors.     

Prediction of the effects of rain on satellite communication systems

The major propagation effects for satellite communication systems operating above 4 GHz are caused by rain. With the possible exceptions of depolarization and multiple scattering at frequencies above 20 GHz, these effects may be calculated if the distribution of rain intensity is known in both time and space. The major effects-attenuation and interference-require information about path and volume averaged rain intensities. Current prediction models are not capable of adequately estimating the statistical distributions of path and volume averaged values. Radar observations could provide the required data. The best information currently available for modeling these distributions are statistical cell or storm models derived from radar observations.     

Transformation of rain attenuation statistics from fixed to mobilesatellite communication systems

We have proposed and discussed a method to transform rain attenuation probability distributions from fixed to mobile satellite communication systems. For a given outage probability, the power margin needed in the mobile system may be larger or smaller than that in the fixed system, depending on the speed of the vehicle relative to that of the rain storm. Simulations performed using experimental information on vehicle and rain storm speeds show that the probability distribution of the mobile system can be obtained from that of the fixed system, by multiplication of a factor which approximately varies between 0.5 and 2.0, independent of attenuation. The first is a realistic value obtained by averaging over all the possible directions of arrival of vehicles     

Model for estimating rain attenuation at frequencies in range 6-30GHz

The raindrop size distribution (RSD) for various types of rainfall over Guwahti, India is presented. The observed RSD parameters are compared with those given by other models. By employing the observed RSD, the values of a and b in the relation A=aR^b for estimating the rain attenuation at frequencies from 6 to 30 GHz are given. The significance of the type of rainfall in controlling attenuation is discussed     

Theoretical random process for prediction of rain attenuation statistics in site diversity satellite links above 10 GHz

Site diversity systems are foreseen for earth-to-satellite links in localities with high rain-induced attenuation operating at frequencies above 10 GHz. An analytical model for the rain-rate statistical process is developed using radar-derived information on the rain structure collected at Spino d'Adda in the framework of the Sirio experiment. The procedure for estimating rain attenuation in both single and site diversity systems is outlined in a general formulation which makes it applicable to different situations. The model gives results very similar to experimental ones.     

A communication protocol for mobile satellite systems affected byrain attenuation

A protocol that supports real-time data rate selection and change during rain events is presented. The protocol is developed with emphasis on being efficient yet robust to the primary channel impairment in such mobile satellite systems. The system architecture is briefly presented and the analytical framework from which the protocol originates is pointed out. Link, connection, and packet types are introduced, and the protocol procedures and design rationale are discussed. The detailed presentation focuses on link setup with the appropriate data rate(s) and the real-time switching of data rates during a voice conversation to either preserve the link or enhance its quality during rain attenuation events     

Worst month statistics of rain attenuation over an LOS microwavelink at 11 GHz

The worst month statistics of rainfall rate and rain attenuation at 11 GHz are studied for the Assam valley, situated in the world's highest rainfall zone, using an LOS (3.2 km) microwave link of the PS&T Department, Government of India. The relation between the worst month and yearly probabilities of these parameters is presented. The observed relation is verified in the light of the Crane-Debrunner and Brussaard-Watson semi-empirical models. A comparative study on this aspect, with the results published from Japan, is given     

Broadband cryogenic parametric amplifier operating at 11.6 GHz

A machine-cooled cryogenic parametric amplifier that operates at 20 K is described. The 2-stage amplifier has a 0.5 dB bandwidth of 600 MHz at 20 dB gain and an effective input noise temperature in the range 47?51 K over the frequency band of 11.3 to 11.9 GHz