New approaches and algorithms for the analysis of vertical refractivity profile below 1 KM in a subtropical region

YesIn this paper, 17 years of high resolution surface and radiosonde meteorological data from 1997-2013 for the subtropical Gulf region are analysed. Relationships between the upper air refractivity, Nh, and vertical refractivity gradient, ΔN, in the low troposphere and the commonly available data of surface refractivity, Ns are investigated. A new approach is discussed to estimate Nh and ΔN from the analysis of the dry and wet components of Ns, which gives better results for certain cases. Results are compared with those obtained from existing linear and exponential models in the literature. The investigation focusses on three layer heights at 65 m, 100 m and 1 km above ground level. Correlation between the components of Ns with both Nh and ΔN are studied for each atmospheric layer. Where high correlations were found, empirical models are derived from best-fitting curves

New methodology for predicting vertical atmospheric profile and propagation parameters in sub-tropical Arabian Gulf region

YesA new simplified approach is proposed to evaluate the vertical refractivity profile within the lowest 1 km of atmosphere from the analysis of surface refractivity, Ns, in areas where upper air data are not available. Upper-air measurements from the nearest available radiosonde location with similar surface profile to these sites are utilized. The profiles of Ns and refractivity extrapolated to sea level, No, obtained from surface meteorological data using both fixed stations and radiosonde are investigated and compared. Vertical refractivity gradient, ΔN, is evaluated at three atmospheric layer heights within the first kilometer above the ground in addition to propagation parameters relevant to each atmospheric layer. At six sites, different approaches are compared for the analysis of three important parameters; namely effective earth radius factor, k, anomalous propagation probability parameter, β0, and point refractivity gradient at 65 m not exceeded for 1% of time, dN1. The k-factor parameter is investigated using a new weighted average approach of ΔN at 65 m, 100 m and 1 km layers above the ground. The results are compared with the latest ITU maps and tables for the same area

Characterization and modelling of effects of clear air on multipath fading in terrestrial links.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.The increased application of digital terrestrial microwave radio links in communication networks has renewed attention in techniques of estimating the probability of multipath fading distributions. Nevertheless, the unpredictable variation of the wireless transmission medium remains a challenge. It has been ascertained that the refraction of electromagnetic waves is due to the inhomogeneous spatial distribution of the refractive index, and causes adverse effects such as multipath and diffraction fading. The knowledge of the characteristics of such causes of these fading phenomena is essential for the accurate design of terrestrial line of sight (LOS) links of high performance and availability. Refractivity variation is random in space and time and cannot be described in a deterministic manner and has to be considered as a random variable with probabilistic characteristics. In this dissertation, radiosonde soundings data is used in characterizing the atmospheric conditions and determining the geoclimatic factor K used in predicting the distribution of multipath fading for five locations in South Africa. The limitations of radiosonde measurements are lack of time resolution and poor spatial resolution. The latter has been reduced by spatial interpolation techniques in our study, specifcally, the Inverse Distance Weighting (IDW) method. This is used in determining the point refractivity gradient not exceeded for 1 % of the time from which the geoclimatic factor is estimated. Fade depth and outage probability due to multipath propagation is then predicted from the International Telecommunications Union Recommendations (ITU-R) techniques. The results are compared with values from Central Africa. The results obtained using the ITU-R method are also compared with region-based models of Bannett-Vigants of USA and Morita of Japan. Three spatial interpolation techniques (Kriging, Thin-Plate Spline and Inverse Distance Weighting) are then used in interpolating the geoclimatic factor K in places where radiosonde data is not available. The estimated values have been used to develop contour maps for geoclimatic factor K for South Africa. Statistical assessment of these methods is done by calculating the root mean square error (RMSE) and the mean absolute error (MAE) between a set of control points and the interpolated results. The best performing method is used to map the seasonal geoclimatic factor K for the entire study region. The estimated values of geoclimatic factor will improve accuracy in predicting outage probability due to multipath propagation in LOS links in the region which is a key contribution of this work

An Experimental Investigation and Laboratory Simulation of Atmospheric Fading on a 900 MHz Transhorizon Radio-Link.

Imperial Users onl

Microwave and millimetre radio wave propagation modelling for terrestrial line-of-sight links in Central Africa.

Doctoral Degree. University of KwaZulu-Natal, Durban.The rapid expansion of the global telecommunication has led to an exponential growth in the demand of wireless services. This has led to the migration to higher frequency bands in the microwave and millimeter wave spectrum. Research has shown that rainfall is the most dominant factor affecting the provision of network services in these bands. Rainfall attenuation is among the major factors often considered in the design of wireless networks operating at higher bands within microwave and millimeter wave spectrum. At tropical and equatorial locations, not only is the occurrence frequency of rainfall events of serious concern to terrestrial and satellite communication systems, but also the high intensity of rain rates and drop size distribution result in extreme fading of line of sight (LOS) system during such events. In this work, daily rainfall measurements from the Rwanda Meteorology Agency (Meteo Rwanda) are obtained for 60 locations within equatorial Rwanda (between latitudes of 1o2'S and 2o45'S and longitudes of 280 45'E and 30052'E), in Central Africa, to develop rain rate and rain attenuation maps for wireless radio links. From these long term annual rainfall measurements spanning a minimum of 10 years at these locations, rainfall rate statistics and drop size distribution result in extreme fading of line of sight (LOS) system during such events. In this work, daily rainfall measurements from the Rwanda Meteorology Agency (Meteo Rwanda) are obtained for 60 locations within equatorial Rwanda (between latitudes of 1o2'S and 2o45'S and longitudes of 280 45'E and 30052'E), in Central Africa, to develop rain rate and rain attenuation maps for wireless radio links. From these long term annual rainfall measurements spanning a minimum of 10 years at these locations, rainfall rate statistics estimated from appropriate models are applied to determine fade margin for radio link availabilities between 99% and 99.999%. Furthermore, specific attenuation estimates due to rainfall are proposed from International Telecommunication Union (ITU) recommendations at selected frequencies of the microwave and millimeter bands, for the design of wireless networks. Results obtained from this approach incorporating both rainfall rate zones and specific attenuation over Rwanda are presented as spatial contour maps representations for different ranges of link availability. Further, disdrometer data collected in Butare, Rwanda (20 35' 53.88” S and 290 44' 31.5” E) for a period of 32 months between 2012 and 2015 have been use to develop a suitable model on drop size distribution in the region. Rainfall data was classified into four different regimes, namely, drizzle, widespread, shower and thunderstorm. Different raindrop size distribution (DSD) models such as Lognormal, Gamma, Marshall-Palmer and Weibull distributions are selected and the method of moment technique is applied for estimating input DSD fit-parameters for those DSD models. From the results, it is observed that different models have varying performances as the rainfall regime varies from drizzle to widespread, shower and later as thunderstorm, except the Marshall- Palmer model which shows the inadequacy for the region. It is found that neither the Lognormal nor other models match perfectly wel I with the measured DSD, particularly at high rainfall rates. Therefore, a new rainfall DSD model or Central Africa is developed and found to be an improvement over the existing models. The Mie Scattering technique (spherical method) is employed to derive the scattering parameters. Therefore, the derived scattering parameters with DSD models are used for the estimation of rainfall attenuation in the region of Central Africa. Finally, the synthetic storm techniques (SST) is applied for comparison with other rainfall attenuation models

Modelling Terrestrial Clear-Air Microwave Radio Fading

The technology of communication systems between population centres has undergone much change over the last century an a half, but radio links continue to be an important part of communication networks. A challenging part of their design is allowing for variations in received signal level, known as radio fading and enhancement, due to the atmosphere between transmitter and receiver. At high frequencies rain fading is the limiting factor, but below about 10 GHz, temperature and humidity gradients, in the absence of precipitation, may produce clear-air fading that becomes the limiting factor. As the refractive index of the air at radio frequencies depends on temperature and humidity, vertical gradients of these parameters cause bending of ray-paths. Multiple signals may arrive at the receiver over different paths, resulting in multipath fading. Sometimes almost no signal at all is able to find its way from transmitter to receiver, resulting in an impairment known as median depression; this may last for an hour or more, with median signal level up to 50 dB below normal. Recent long-term observations show this fading to be particularly severe in some parts of Australia, but not well predicted by pre-existing models. This thesis develops a new international model for clear-air fading. Weather forecasting has made significant progress in recent years due to numerical weather prediction (NWP) models, so radio propagation researchers have aimed to use these models to predict the state of the atmosphere, and Fourier split-step parabolic equation modelling (PEM) to predict radio propagation. Considering this, we begin this thesis by investigating Fourier split-step PEM, developing new techniques for dealing with finite conductivity lower boundaries, estimating the absorbing upper boundary height, and for dealing with irregular terrain, in both two and three dimensions. A brief description of the internationally adopted empirical model for diffraction over terrain (Rec. ITU-R P526-15, 2019), completes this chapter. We then examine radio refractivity gradient cumulative distributions derived from NWP data, comparing them with measurements from radiosondes, and data from sensors mounted on towers. We find the NWP prediction of anomalous gradients in the surface atmospheric layer to be poor, and develop a new parameter, surface refractivity anomaly, derived from surface weather station time-series data. We find this parameter useful in predicting vertical radio refractivity gradients in the atmospheric surface layer. Due to NWP surface gradient accuracy problems, we adopt the empirical regression model approach to fading severity prediction. This is not new, but we now have the benefit of more fading data from more regions of the world, and we have our new prediction parameters, generated from several years of data from thousands of worldwide weather stations. We make novel refinements to the modelling of clear-air fading, by first replacing ordinary least squares (OLS) regression with generalised least squares (GLS) regression, to take spatial correlation into account. We then employ the geostatistical technique of universal kriging, to further improve prediction accuracy. Our new fading model, as described in this thesis, is now the internationally approved terrestrial line-of-sight model for fading due to multipath and related mechanisms (Rec. ITU-R P.530-18, 2021).Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

Modelling of radio wave propagation using Finite Element Analysis.

Fourth generation (4G) wireless communication systems are intended to support high data rates which requires careful and accurate modelling of the radio environment. In this thesis, for the first time finite clement based accurate and computationally efficient models of wave propagation in different outdoor and indoor environments has been developed. Three different environments were considered: the troposphere, vegetation and tunnels and wave propagation in these environments were modelled using finite element analysis. Use of finite elements in wave propagation modelling is a novel idea although many propagation models and approaches were used in past. Coverage diagrams, path loss contours and power levels were calculated using developed models in the troposphere, vegetation and tunnels. Results obtained were compared with commercially available software Advanced Refractive Effects Prediction Software (AREPS) to validate the accuracy of the developed approach and it is shown that results were accurate with an accuracy of 3dB. The developed models were very flexible in handling complex geometries and similar analysis can be easily extended to other environments. A fully vectored finite element base propagation model was developed for straight and curved tunnels. An optimum range of values of different electrical parameters for tunnels of different shapes has been derived. The thesis delivered a novel approach to modelling radio channels that provided a fast and accurate solution of radio wave propagation in realistic environments. The results of this thesis will have a great impact in modelling and characterisation of future wireless communication systems