[Show abstract][Hide abstract] ABSTRACT: This paper proposes a novel method aimed at modeling microwave scattering and absorption inside a canopy, arising from the interaction with the individual components of the vegetation specimen, starting from primary models for leaves, trunk and branches. The method is based on the Finite-Difference Time-Domain (FDTD) technique to predict the 3-dimensional re-radiation fields of the entire tree, by combining the effects of the single elements forming the tree. Appropriate measurements performed in an anechoic chamber environment at microwave frequencies, i.e. 20 GHz, and in the forward scattering region, provided both model validation and a deeper insight into the problem. The model is shown to be capable of predicting the near-field radiated signal and the radar cross section (RCS). The predictions yielded good agreement with measurements and provides a good basis for a planning model capable of accounting for single trees in the radio path.
Full-text · Article · Oct 2014 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: In this paper, the discrete Radiative Energy Transfer (dRET) model is investigated as a means to model time-variant channel effects in vegetation media at millimetre-wave frequencies. The proposed methodology makes use of time-varying properties of the dRET input parameters to estimate the dynamic (time variant) radio channel effects. The proposed modelling methodology is assessed against measured data in both indoor and outdoor conditions, at 20 and 11 GHz respectively.
[Show abstract][Hide abstract] ABSTRACT: A statistical model based on a coarse representation of urban wireless channel topographies and the prediction of electromagnetic (EM) propagation in fixed wireless links operating at millimetre wavelengths is presented, with potential applications to the characterisation, design and deployment of point-to-point and point-to-multi-point fixed wireless networks. A specific goal of the study is the parameterisation of the main physical attributes of the propagation mechanisms, which at millimetre waves predominantly incorporate scatter from building and ground surfaces, both non-uniformly illuminated by a directive transmitting antenna. The line-of-sight (LOS) received signal is presented in terms of universal probabilistic distribution functions (PDFs) and quantified in terms of their first- and second-order moments. Experimental results validate the physical optics (PO)-based approximation of the building and ground scatter and the resulting stochastic representation of the propagation channel.
No preview · Article · Oct 2010 · IET Microwaves Antennas & Propagation
[Show abstract][Hide abstract] ABSTRACT: This paper presents a method to model the scattered signal from a regular formation of cylinders, both dielectric and metallic, at micro and millimeter wave frequencies. The model, aims to predict the signal emanated inside and around an isolated block of tree trunks, and might be used as part of a larger algorithm intended to model isolated volumes of vegetation. The method presented here, is based on the prior knowledge of the re-radiation function of cylinders and used the dRET (discrete Radiative Energy Transfer) model, to gather the interactions between the trunks present in the formation to predict the directional profile of the received signal power level at various location inside the formation. The re-radiation function from cylinders, is predicted based on a model previously applied to lamp posts, and is assessed by comparison with measurements performed at 18 and 36 GHz. These functions are subsequently used to input the dRET model whose predictions were also assessed with measurements obtained inside an anechoic chamber, using the same spot frequencies.
[Show abstract][Hide abstract] ABSTRACT: Frequency and polarisation reuse for optimum spectral efficiency in local multipoint distribution system (LMDS) networks generate co- and adjacent-channel inter-and intra-cell interference because of the line-of-sight constraints among transmitting and receiving antennas. Such operational constraints limit the system capacity and affect link performance. Measurements at 40 GHz from a number of possible interference scenarios for two different LMDS reuse cellular plans of dual-frequency and dual-polarisation discriminations are presented. An electromagnetic-stochastic propagation model is employed. The model successfully predicts the interference parameters and takes into account the effects of multiple paths and depolarisation caused by reflection and scatter from building surfaces at millimetre-wave frequencies. The probability density function of the signal-to-interference ratio and the statistical channel parameters, such as the average signal strength and the Rician K-factor, are extracted from the measured data and compared with model predictions.
[Show abstract][Hide abstract] ABSTRACT: This book constitutes the best papers of the Third International Conference on E-business and Telecommunication Networks, ICETE 2006, held in Setúbal, Portugal, August 7-10, 2006.
The 29 revised full papers presented were carefully reviewed and selected from 326 submissions. The papers are organized in four parts according to their conferences: ICE-B, SECRYPT, SIGMAP and WINSYS.
[Show abstract][Hide abstract] ABSTRACT: The influence of vegetation has become an important aspect of the design of wireless communication links. In recent years theory of Radiative Energy Transfer (RET) has been adapted as a reliable tool to predict the radiowave propagation through and near vegetation. The developed RET prediction model requires 4 input independent parameters, which so far had to be established from one measurement only, thus limiting their accuracy. An independent measurement which is termed the phase function can readily yield 2 of the 4 input parameters independently, which significantly increases the accuracy of these parameters. However one major factor influencing the phase function measurement is the radiation pattern of the receiving antenna. The measured curve will be the result of the convolution of the antenna radiation pattern and the phase function of the vegetation medium. The measurement curve therefore needs to undergo a deconvolution process before any RET input parameters can be derived from it. This paper presents the deconvolution method developed using optimal compensation deconvolution methods. Deconvolution is demonstrated using both simulation signal shapes and those measured in vegetation set up in the anechoic chamber. This paper discusses different cases of optimal compensation filtering with the relative curves shown.
[Show abstract][Hide abstract] ABSTRACT: A Physical statistical model based on GIS terrain incorporation, along with the computationally efficient simulations of the electromagnetic channel and interferences in fixed wireless links at mm-wavelengths, operating within sub-urban channels are presented. The abil-ity for such predictions is highly demanded since it aids in the characterization, design and deployment of the pertinent networks. Massive measurement campaigns were conducted over several paths, for the purposes of modeling assessing. Since both the desired and interference links in a cellular structure attain a dominant signal, knowledge of the Rician and the carrier-to-interference ratio (CIR) distributions becomes an essential principle measure in determining performances of millmetric channels; hence they were used for model evaluation purposes.
[Show abstract][Hide abstract] ABSTRACT: This paper compares the performance of the radiative energy transfer (RET) model and an enhanced discrete version of the RET, the so called dRET, when predicting the scattered signals emanating from inhomogeneous vegetation volumes. The analysis of each model performance was carried out by comparing the model predictions with the actual scattered signal measured in a selected inhomogeneous tree formation at 11.2 and 62.4 GHz. It is shown that both models perform satisfactorily provided that the vegetation surrounding the receiver remains relatively homogenous. Nevertheless, when the vegetation geometry is more irregular, and therefore consists of differing types of vegetation, only the dRET model was observed to provide reasonable signal level estimates over the entire angular range.
[Show abstract][Hide abstract] ABSTRACT: The work presented here aims at providing deeper knowledge on the behavior of non-line-of-sight (NLOS) links that particularly benefit from a specular reflection for fixed wired access systems (FWA) operating in the 40 GHz bands. For comparison purposes, the performance of the proposed NLOS link has been assessed in contrast with that of an unobstructed line-of sight (LOS) link. Both of the measured links were carried out in urban environments in order to explore the statistical propagation effects in such areas. Both links attain a dominant signal and hence are modeled using a Rician envelope distribution. Comparisons considered in terms of signal variations, cumulative curves and Rician K-factor have indicated the potential usefulness of the received reflected signals.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a radiowave propagation model for inhomogeneous forests based on the radiative energy transfer theory (RET). This model, which is a discretised version of the RET, is able to simulate the behaviour of radiowaves inside a forest which contains various kinds of vegetation and free space gaps. To do this, the forest is divided into non-overlapping square cells, each one with different propagation characteristics. The propagation properties of each cell rely on specific propagation parameters, which are extracted from the vegetation using an appropriate practical method which is also described in this paper. The model performance is assessed through comparison with directional spectrum measurements carried out in an isolated inhomogeneous forest at 11.2 and 40 GHz.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a method to improve extraction the radiative energy transfer (RET) theory input parameters for application in vegetation attenuation modelling. The input parameters for this model, which are extracted from specific measurement data, are normally influenced by the radiation pattern of the receiver antenna. A new method to improve the accuracy of the scattering function parameters obtained from measurements is presented. This method is based on the inverse convolution, allowing mitigation of the receiver antenna radiation pattern effects on the extracted parameters. The method was tested with measurements at 20 and 40 GHz using several different receiver antennas.
[Show abstract][Hide abstract] ABSTRACT: For fixed wireless access systems in urban areas, reflection or scattering from building surfaces can cause propagation impairments and influence system planning, deployment and quality of service. This paper presents a statistical model for fixed radio links operating at microwave/millimeter frequencies and predicts the radiowave propagation characteristics. The model considers the underlying propagation modes, where buildings give rise to multipath due to reflection or scattering. In addition, the model accounts for the antenna properties, including relative height, orientation and radiation patterns. Measurement campaigns were conducted using both 20 and 40 GHz radio links set up in the university campus. The measured and prediction results conducted at 20 and 40 GHz were compared. Agreement between the statistical properties of narrowband measurements and those from simulations using the model are demonstrated
[Show abstract][Hide abstract] ABSTRACT: For fixed wireless access systems in urban areas, reflection or scattering from building surfaces can cause propagation impairments and influence system planning, deployment and quality of service. A statistical model is presented for such fixed radio links operating at microwave and mm-wave frequencies to predict the radiowave propagation characteristics. The model considers the fundamental underlying propagation, where buildings give rise to multipath due to reflection or scattering. In addition, the model accounts for the antenna properties, including relative height, orientation and radiation patterns. Overall good agreement between the statistical properties of narrowband measurements and simulations is demonstrated.
No preview · Article · Sep 2005 · IEE Proceedings - Microwaves Antennas and Propagation