Measuring the Polarization Parameters of Rain by Inverse Scattering

The theory is presented for one method of determining the effective polarization parameters of the rain medium in the problem of polarization information processing of detecting target. The determination of the effective polarization parameters of the propagation medium is from the data of propagation measurements over a line-of-sight link. The polarization parameters ? the effective average value, σ the effective standard deviation and F the effective shape parameter of the propagation medium are obtained by means of the method of inverse scattering, showing a good agreement with the data from direct measurements.     

First attempts at modelling earth-to-space radio propagation using SIRIO measurements in the 11 and 18 GHz bands

A bi-dimensional statistical model for earth-to-space radio links, characterized by effective rain rates and rain path lengths is proposed. These parameters refer to an equivalent homogeneous slab of rain having depth and rain rate such as to produce similar values of measured attenuations. Input data for the present study were attenuation data at 11.6 GHz (absolute and differential over a 520 MHz band) and 17 GHz, collected by the Sirio satellite: these data were found to be jointly log-normally distributed as were the effective rain rate and path length. A straightforward application of the model is the extrapolation of attenuation statistics to higher frequencies: the effectiveness of the method, when applied to 11.6 GHz data is tested against the data at 17 GHz; both the statistics and the time profiles are excellently reproduced. This suggests the use of a differential radiometer working at a relatively low frequency in order to acquire reliable higher frequency statistics and effective model parameters.     

A method for estimating rain rate and drop size distribution frompolarimetric radar measurements

Polarimetric radar measurements are sensitive to the size, shape and orientation of raindrops and provide information about drop size distribution (DSD), canting angle distribution and rain rate. The authors propose and demonstrate a method for retrieving DSD parameters for calculating rain rate and the characteristic particle size. The DSD is assumed to be a gamma distribution and the governing parameters are retrieved from radar measurements: reflectivity (Z_HH), differential reflectivity (ZDR), and a constrained relation between the shape (CL) and slope (Λ) parameters derived from video disdrometer observations. The estimated rain rate is compared with that obtained from more traditional methods and the calculated characteristic size is compared with the measured values. The calculated K_DP based on the retrieved Gamma DSD is also compared with measurements. The proposed method shows improvement over the existing models and techniques because it can retrieve all three parameters of the gamma distribution. For maintaining the continuity of earlier published results, raindrop shape is assumed to be equilibrium     

Statistical method of deep-level transient spectroscopy in semiconductors

The method of transient spectroscopy is one of the basic methods widely used for determining the parameters of defects, which are the origin of deep levels in the semiconductor-material band gap. With the purpose of increasing the accuracy of determining the concentration and deep-level parameters describing the character of the isothermal capacitance relaxation, a statistical method of processing the results of its measurements based on the statistical solution-search algorithm is proposed.     

Effects of random inhomogeneity on radar measurements and rain rateestimation

The authors study the sampling effect on radar measurements of inhomogeneous media and the resultant rain estimation. A two-level drop size distribution (DSD) model is proposed, in which DSD parameters are assumed to be variable for representing the sampling effects. The dependence of statistical moments on the variation of DSD parameters are calculated and applied to radar-based rain estimation     

On the Space-Time Variations of Rain Attenuation

Rain attenuation shows a considerable temporal and spatial variability. To simulate fade mitigation techniques such as route diversity, a space-time channel model which accounts for the spatial and temporal variation of rain attenuation is needed. In this paper we investigate the space-time correlation of rain attenuation utilizing 42 GHz star-like network measurements. By combining the spatial and temporal correlation properties of rain attenuation, a simulation model for generating multiple correlated rain attenuation time series based on the Maseng–Bakken model is developed. The model is validated by comparing the statistical and angular diversity properties of the model with those of measurements and theoretical diversity gain models. Furthermore, parameters for the Maseng–Bakken dynamic rain attenuation model were extracted from the star-like network measurements. In addition, using a systematic multivariable technique a model for the parameter $beta _{s}$ which controls the dynamics of rain attenuation in the Maseng–Bakken model was developed. Moreover, using available rain attenuation measurements the advantage of route diversity with selection combining is investigated.      

Statistical Prediction Modeling of Rain Induced Attenuation and Depolarization

Millimeter wave rain co-polarization attenuation, CPA, and cross polarization discrimination, XPD, measurements have been made at 35GHz and 94GHz over a line-of-sight link. On the basis of these experimental results, a study of this rain medium has been made with the method of link measurements. In this paper, we presented a statistical prediction modeling of rain-induced attenuation and depolarization from the statistical distribution of the rain intensity, and the size, and canting angle of raindrops. Our computational results are in good agreement with data of measurements.     

Analysis and Synthesis of Raindrop Size Distribution Time Series From Disdrometer Data

Hydrometeorological and radio propagation applications can benefit from the capability to model the time evolution of raindrop size distribution (RSD). A new stochastic vector autoregressive semi-Markov model is proposed to randomly synthesize (generate) the temporal series of the three driving parameters of a normalized gamma RSD. Rainfall intermittence is reproduced through a discrete semi-Markov process, modeled from disdrometer measurements using two-state analytical statistics of rain and dry period duration. The overall model is set up by means of a large set of disdrometer measurements, collected from 2003 to 2005 at Chilbolton, U.K. The driving parameters of the retrieved RSD are estimated using three approaches: the Gamma moment method and the 1D and 3D maximum-likelihood methods. Interestingly, these methodologies lead to quite different results, particularly when one is interested in evaluating RSD higher order moments such as the rain rate. The accuracy of the proposed RSD time-series generation technique is evaluated against available disdrometer measurements, providing excellent statistical scores.     

Rain attenuation study at 11 GHz : Experimental results and investigation on the statistical properties of single attenuative events

This paper deals with the experimental results of attenuation measurements carried out at 11 GHz on two radio links, 10 and 22.5 km in length respectively, for a period of three consecutive years. Besides usual overall statistics, the statistical parameters of the distribution curves of single attenuation events are investigated and simple relationships among them are found. Also, a generalization of the rainfall reduction coefficient method is presented to transform rain rate statistics into attenuation statistics.     

A study of raindrop size distributions in central and northwest China and their effects on some propagation parameters for wavelengths from 0.86 cm to 10 cm

The effect of rain on radio propagation depends on the raindrop dimensions and shapes. For spherical raindrops, results of a statistical analysis of measurements are presented: the parameters of the raindrop size distribution as a function of rainfall rate. Attenuation constants and backscatter coefficients are deduced from these results in fonction of rainfall rate.     

Atmospheric emission measurements of attenuation by microwaveradiometer at 19.4 GHz

Attenuation measurements on an Earth space path are presented using a passive microwave radiometer operating at 19.4 GHz in the emission mode. Attenuation measured under clear weather showed variation between 0.2 to 1.1 dB, whereas for cloud conditions attenuation as high as 1.0 dB have been recorded. Attenuation measurements for rain events have been correlated with rainfall rate using a fast-response 10 seconds opto-electronic rain gauge. The values of attenuation versus rainfall rate varied between A (dB)=0.01+0.18 R(mm/h) at the minimum and A (dB)=0.01+0.25 R(mm/h) at the maximum, showing considerable variability in the values of attenuation from year to year. The attenuation statistics for different seasons have also been computed and they show considerable changes from season to season-the largest attenuation in excess of 10 dB recorded in July-August-September, whereas minimum attenuation in excess of 2 dB recorded in December-March for nearly two years of data. Comparison of measurements made over New Delhi with those reported elsewhere show that for 0.02% of time attenuation values lie between those of Slough, England, and Crawford Hill, NJ. The concept of effective path length has been discussed based on the relationship between effective path length and the rain rate     

Effects of rain fading on the efficiency of the Ka-band LMDS system in the Taiwan area

This work presents the effects of rain on the performance of a Ka-band local multipoint distribution system (LMDS) in Taiwan. The rain distribution statistics, from 2-yr measurements with 1-min temporal resolution and 12-yr measurements with a 1-h temporal resolutions, were analyzed. The rain-attenuation model that takes local rain effects is established statistically. These statistical data are used to analyze the performance of the LMDS in terms of its signal-to-interference (S/I) ratio, bit-error rate (BER), and channel capacity at various service distances. From the analysis, it is found that the light rain events induce better S/I for cellular network service, because other base transceiver station (BTS) interference signals around the main BTS are likely to be blocked by rain. The probability that below the nominal value of the channel capacity, when there is rain fading without cellular interference, meets a margin of BER=10/sup -6/ in a 6-km cell using quaternary phase-shift keying (QPSK) modulation. However, when the cellular interference is presented, the effective BTS service distance greatly shrinks to 2-3 km. In summary, in a cellular network environment, as the cell coverage radius is reduced, the effective BTS service range will be correspondingly compressed, suggesting that the cellular interference is even more serious than the rain attenuation itself.     

Minimum test chip sample size selection for characterizing process parameters

A method for determining a test chip sample size to estimate effectively the electrical parameter distributions on an integrated circuit wafer is presented. This method gives relations among sample size and the figure of merit for four statistical techniques (trimmed mean, biweighted mean, median, and arithmetic mean) by which estimates are calculated. To demonstrate its use, the method has been applied to the evaluation of a CMOS fabrication process. Measurements on wafers completely patterned with identical test chips were used to determine actual parameter distributions for an entire wafer (true parameter values). Estimates of true parameters were determined using a site selection plan which is representative of sampling plans employed in industry. The above four statistical techniques were used to compute estimates for electrical parameters and their respective figures of merit. These estimates were compared with the true parameter values determined from testing all test chips on the wafer. This method may be used in conjunction with other criteria for determining test chip sample size and enables one to make judgments on the effectiveness of sampling strategies for various processes and process technologies. The results, reported in this paper for CMOS processes, are interpreted using graphs of the figure of merit versus the sample size.     

Minimum test chip sample size selection for characterizing process parameters

A method for determining a test-chip sample size to estimate effectively the electrical parameter distributions on an integrated circuit wafer is presented. This method gives relations among sample size and the figure of merit for four statistical techniques (trimmed mean, biweighted mean, median, and arithmetic mean) by which estimates are calculated. To demonstrate its use, the method has been applied to the evaluation of a CMOS fabrication process. Measurements on wafers completely patterned with identical test chips were used to determine actual parameter distributions for an entire wafer (true parameter values). Estimates of true parameters were determined using a site-selection plan which is representative of sampling plans used in industry. The four statistical techniques were used to compute estimates for electrical parameters and their respective figures of merit. These estimates were compared with the true parameter values determined from testing all test chips on the wafer.     

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

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

Rain attenuation statistics useful for the design of mobilesatellite communication systems

We have investigated how rain attenuation statistics, necessary to design fixed satellite systems working at frequencies greater than 10 GHz, are transformed to those applicable to the design of mobile satellite systems working in the same frequency bands and weather conditions in the special case of vehicles driven in zig-zag patterns to simulate city streets. The vehicles' speed has been modeled as a lognormal random variable, a mathematical model derived from measurements performed in freeways or in city traffic. We have used a large number of rain-rate time series collected in Italy (Gera Lario and Fucino) and in Canada (Montreal) to simulate rain-rate spatial fields and radio links at 19.77 GHz along a 30.6° slant path. The simulations have shown that a receiving or transmitting terminal moving in zig-zag patterns may experience, in the long term and for a given attenuation, a smaller outage probability, compared to the fixed terminal. For a given rain attenuation, the ratio between the outage probability of the mobile system and that of the fixed system (probability extrapolation factor ξ) is estimated to be around 0.2-0.3 in the optimistic case in which the probability of encountering rain is the same for all observers (fixed or in motion)-a less optimistic estimate shows that the probability of encountering rain might be twice as large and that, as a consequence, the values of ξ mentioned must be doubled. Conservative values of ξ can be calculated by using average values of rain storm speed and vehicles and average distances covered in the rain by fixed and mobile terminals. The results are less sensitive to changes in the geometrical or other parameters of the simulations     

A simple bandwidth management strategy based on measurements ofinstantaneous virtual path utilization in ATM networks

A new connection admission control method based on actual virtual path traffic measurements is proposed to achieve high bandwidth efficiency for various types of traffic. The proposed method is based on the measurement of instantaneous virtual path utilization, which is defined as the total cell rate of the active virtual channels normalized by the virtual path capacity. A low-pass filter is used to determine the instantaneous virtual path utilization from crude measurements. A smoothing coefficient formula is derived as a function of the peak rate of the virtual channel. The residual bandwidth is derived from the maximum instantaneous utilization observed during a monitoring period. Simulation shows that the proposed method achieves statistical multiplexing gains of up to 80% of the limit possible with optimum control for similar traffic sources. It can be implemented with very simple hardware. The admission decision is simple: the requested bandwidth is compared with the residual bandwidth. This method is therefore well suited for practical asynchronous transfer mode switching systems     

Instantaneous diversity gain in 10-30 GHz satellite systems

As usually defined, diversity gain is a statistical measure which conveys little or no information about the instantaneous behavior of site-diversity reception in a satellite communications system. A new quantity called instantaneous diversity gain is introduced and some measurements of it from an 11.6 GHz low-angle two-site downlink are presented. It is shown how instantaneous diversity gain is related to system reliability and some results are presented which indicate that designs based on statistical diversity gain will achieve their intended reliability levels.     

Frequency dependence of effective path length in prediction of rain attenuation statistics

Theoretical and numerical results are presented which demonstrate that the effective path length commonly used in the prediction of rain attenuation statistics for earth-space paths is frequency dependent. Also presented is a method of translating effective path length measurements in frequency.