Characterization of secondary radioclimatic variables for microwave and millimeter wave link design in Nigeria

A reliable radio propagation data is required in other to propose a well-founded model for radioclimatic study in any area. The two major types of radio propagation data needed are the primary and secondary propagation data. The primary data include temperature, pressure and relative humidity or water vapour pressure, while the secondary radioclimatic data are radio refractivity gradients, geoclimatic factor (K-factor) and the effective earth radius factor (k-factor). In this paper, analyses of the secondary data are carried out instead of the usual primary variables in order to deduce the influences on the Terrestrial line-of-Sight (LOS) based on 5 years data (2009-2013) obtained from five different regions of Nigeria (Akure, Enugu, Minna, Jos and Sokoto). The k-factor values at the surface across the study locations are higher than the prescribed value of 1.33 by the ITU. The same trend could also be observed for the geoclimatic factor K. The overall result will be a very good tool for microwave wireless link design in Nigeria

Assessment of Anomalous Propagation Conditions in Ondo City, South Western Nigeria for Microwave Applications

Recent results of the in-situ measurement of radio climatological parameters of pressure, temperature and relative humidity carried out to investigate the trends in propagation conditions over altitude of 100-m in Ondo city Nigeria are presented. The assessments have been based on the time series of average value of the radio refractivity on the season of the year, characterization of radio refractivity gradient and the impact of secondary radio climatic data on terrestrial line of sight link design in Ondo city. We have used concurrent measurement of pressure, relative humidity and temperature for the period between 2017 and 2018. The results obtained confirmed the assertion that radio refractivity values are higher during the wet season months when compared with the dry season months. Yearly variation shows that the values of refractivity in the year 2018 are much higher than ones obtained in the year 2017. Results of radio refractivity gradient also shows a considerably large negative N value of about 288 N-units/km for the month of October and the value later becomes less negative in the remaining months of the year. Average value of k-factor during the dry and wet seasons for the year under study is about 1.37 and 1.47 respectively. This implies that, for microwave propagation in the Ondo environ, the propagation condition could be largely super-refractive during these seasons. A good relation also exists between Geoclimatic factor and season of the year. The overall will assist in achieving optimum performance of digital terrestrial point to point links in Ondo city. Keywords: Propagation behavior, Time series analysis, Refractivity gradient, k-factor, Geoclimatic factor DOI: 10.7176/JEES/9-4-07 Publication date: April 30th 201

Long term evolution of the surface refractivity for arctic regions

YesIn this paper, local meteorological data for a period of 35 years (from 1979 to 2013) from Kuujuaq station have been used to calculate the surface refractivity, N and to estimate the vertical refractivity gradient, dN1, in the lowest atmospheric layer above the ground. Monthly and yearly variations of the mean of N and dN1 are provided. The values obtained are compared with the corresponding values from the ITU maps. The long-term trend of the surface refractivity is also investigated. The data demonstrate that the indices N and dN1 are subject to an evolution which may have significance in the context of climate change (CC). Monthly means of N show an increasing departure from ITU-R values since 1990. Yearly mean values of the dN1 show a progressive decrease over the period of study. Seasonal means of dN1 show a decrease over time, especially for summer. Such a trend may increase the occurrence of super-refraction. However, currently available ITU-R recommendations for microwave link design assume a stationary climate, so there is a need for a new modelling approach

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

Radio wave propagation modeling under precipitation and clear-air at microwave and millimetric bands over wireless links in the horn of Africa.

Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2017.Abstract available in PDF file

Clear-air radioclimatological modeling for terrestrial line of sight links in Southern Africa.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2010.This thesis has investigated radioclimatological study in a clear-air environment as applicable to terrestrial line of sight link design problems. Radioclimatological phenomena are adequately reviewed both for the precipitation effect and clear-air effect. The research focuses more on the clear-air effect of radioclimatological studies. Two Southern African countries chosen for case study in the report are Botswana and South Africa. To this end, radiosonde data gathered in Maun, Botswana and Durban, South Africa are used for model formulation and verification. The data used in the thesis ranges from three years to ten years in these two stations. Three to ten years of refractivity data gathered in Botswana and South Africa is used for the model formulation. On the other hand, eight months signal level measurement data recorded from the terrestrial line of sight link set up between Howard College and Westville Campuses of the University of KwaZulu-Natal, Durban South Africa is used for model verification. Though various radioclimatic parameters could affect radio signal propagation in the clear-air environment, this report focuses on two of these parameters. These two parameters are the geoclimatic factor and effective earth radius factor (k-factor). The first parameter is useful for multipath fading determination while the second parameter is very important for diffraction fading, modeling and characterization. The two countries chosen have different terrain and topographical structures; thus further underlying the choice for these two parameters. While Maun in Botswana is a gentle flat terrain, Durban in South Africa is characterized by hilly and mountainous terrain structure, which thus affects radioclimatological modeling in the two countries. Two analytical models have been proposed to solve clear-air radioclimatic problems in Southern Africa in the thesis. The first model is the fourth order polynomial analytical expression while the second model is the parabolic equation. The fourth order polynomial model was proposed after an extensive analysis of the eight month signal level measurement data gathered in Durban, South Africa. This model is able to predict the fade exceedance probabilities as a function of fade depth level. The result from the fourth order polynomial model is found to be comparable with other established multipath propagation model reviewed in the thesis. Availability of more measurement data in more location will be necessary in future to further refine this model. The second model proposed to solve clear-air propagation problem in the thesis is the modified parabolic equation. We chose this technique because of its strength and its simplistic adaptation to terrestrial line of sight link design problem. This adaptation is possible because, the parabolic equation can be modified to incorporate clear-air parameters. Hence this modification of the parabolic equation allows the possibility of a hybrid technique that incorporates both the statistical and mathematical procedures perfectly into one single process. As a result of this, most of the very important phenomena in clear-air propagation such as duct occurrence probabilities, diffraction fading and multipath fading is captured by this technique. The standard parabolic equation (SPE) is the unmodified parabolic equation which only accounts for free space propagation, while the modified parabolic equation (MPE) is the modified version of the parabolic equation. The MPE is classified into two in the thesis: the first modified parabolic equation (MPE1) and second modified parabolic equation (MPE2). The MPE1 is designed to incorporate the geoclimatic factor which is intended to study the multipath fading effect in the location of study. On the other hand, MPE2 is the modified parabolic equation designed to incorporate the effective earth radius factor (k-factor) intended to study the diffraction fading in the location of study. The results and analysis of the results after these modifications confirm our expectation. This result shows that signal loss is due primarily to diffraction fading in Durban while in Botswana, signal loss is due primarily to multipath. This confirms our expectation since a flatter terrain attracts signal loss due to multipath while hilly terrain attracts signal loss due to diffraction fading

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

Effective earth radius factor (the k-factor) distribution for southern Africa.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.Proper radio link design requires an accurate prediction of the effective earth radius factor (the kfactor) distribution, for the location where propagation is intended. Though a median value of k equals 4/3 is normally use for communication design purposes, in reality the true k-factor values differ, for different locations, globally. The effective earth radius factor distribution for Southern Africa was evaluated in the dissertation. The two Southern African countries chosen for the study are Botswana and Republic of South Africa. The dissertation reports in detail a study on the topic using three years radiosonde data obtain in Maun, Botswana and ten months radiosonde data collected in Durban, South Africa. An analytical model was proposed, which predicts the probability density function of the k-factor for the Southern Africa using the data from these two countries. Also a comparison of the data from the two countries was done in the analysis and reported in the write-up. The application ofthe work was also investigated and reported by simulating a radio link between Sherwood and Umlazi in Kwazulu-Natal Province of South Africa. The consequence of using inappropriate design value of k on link reliability was also investigated and reported. Recommendation for future work was given in the concluding chapter for future improvement on the study. Radio communication designers will find the results obtain in the report useful

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