[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.
IET Microwaves Antennas & Propagation 10/2010; · 0.84 Impact Factor
[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.
Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on; 05/2010
[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.
IET Microwaves Antennas & Propagation 04/2009; · 0.84 Impact Factor
[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.
Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
[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.
Computer Systems and Applications, 2007. AICCSA '07. IEEE/ACS International Conference on; 06/2007
[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.
Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on; 09/2006
[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: This paper aims to model the directional spectra in vegetation media using the radiative energy transfer (RET) theory. A generic propagation model (N. C. Rogers, et al., May 2002), developed for the United Kingdom Radiocommunications Agency (formerly RA, now a subsidiary of OFCOM), concentrated on the results of previous work (R. Johnson, and F. Schwering, 1985) which suggested that there are several possible mechanisms of propagation associated with vegetation. Each component is modelled using simple methods, such that the final model can be easily implemented. The scattered component is modelled using the radiative energy transfer theory (RET), as this is a fully deterministic model which may be used by fitting the model input parameters to the specific measurement geometries and then expanded to provide results for more generic cases. This paper concentrates on improving the method of extracting the RET input parameters for the scattered component of the generic propagation model. An improved method to extract these input parameters is presented. The results obtained from measurements performed in a Southern European forest formed by Populus trees are used to assess the performance of the model
Antennas and Propagation Society International Symposium, 2005 IEEE; 02/2005
[show abstract][hide abstract] ABSTRACT: This paper aims to describe the results of a 15 months consortium project to study the effects of microwave and millimetre wave propagation radio signals through vegetation. The aim of the project was to provide a generic model for the determination of propagation loss through vegetation, and was to be achieved by a combination of an extensive campaign of measurements and deterministic modelling. The proposed model is ideally suited to micro- and picocellular radio service planning, and with the aid of a forest database giving dimensions, locations and tree types, the model may be used for macrocellular radio system planning.
[show abstract][hide abstract] ABSTRACT: A method based on the radiative energy transfer theory (RET) to estimate the scattered signals from isolated groups of trees is presented. The proposed method consists of measuring the reradiation function of each tree in the group and subsequently uses these in a discrete algorithm to estimate the overall reradiation at any location within a forest scenario. The estimated scattering is compared with measurements performed inside an anechoic chamber on two tree species at 20 and 62.4 GHz.
Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
[show abstract][hide abstract] ABSTRACT: In cellular communications, requirements for increased system capacity, improved coverage, better quality and reduced transmitter power, along with the need to rationalise cellular system planning, have prompted a considerable interest in the development of valid and efficient radiowave propagation models. This work utilises recent advances that improve the accuracy and efficiency of ray-tracing models, using a three-dimensional representation of the terrain and urban topographies, in conjunction with adaptive and selective ray-tracing. These improvements allow utilisation of the field computation algorithms in the network design and radio coverage planning processes. They include optimum automated selection of base station locations and phased array excitation. A reliable ray-tracing scheme can be utilised directly in the optimum and, potentially, adaptive beamforming of base station antenna systems by interfacing field computations with design aims. The paper addresses a cellular planning process, which involves determination of the antenna array position and beam shape or, equivalently, the array excitation coefficients, for a desired power distribution over the defined cell area.
[show abstract][hide abstract] ABSTRACT: A new model for radiowave propagation through vegetation has been developed by four consortium members under a contract by the UK Radiocommunications Agency (RA). This generic model combines an edge diffraction and ground reflection model with a direct (through vegetation) signal modelled through the application of the theory of radiative energy transfer (RET). RET predicts attenuation vs foliage depth using parameters to describe the absorption and scatter cross-section, albedo, and scatter function of the vegetation. These parameters are determined empirically for each vegetation type, by fitting RET curves to the measurements. The paper, after a brief introduction to the generic model, addresses possible ways of obtaining these input parameters.
Antennas and Propagation, 2003. (ICAP 2003). Twelfth International Conference on (Conf. Publ. No. 491); 01/2003
[show abstract][hide abstract] ABSTRACT: Modelling radio wave propagation through vegetation is becoming increasingly more important. Many empirical solutions have been suggested in the past. The theory of radiative energy transfer offers an analytical method to the problem. This theory requires however 4 input parameters, which need to be established experimentally. A measurement of the angular scatter pattern, the so called 'phase function', can be utilised to determine 2 of those parameters. In this paper 3 different methods of measuring the phase function for measurements in a real forest environment are presented and compared. One method is presented as the most suitable one.
Personal, Indoor and Mobile Radio Communications, 2002. The 13th IEEE International Symposium on; 10/2002
[show abstract][hide abstract] ABSTRACT: Modelling radio wave propagation through vegetation is becoming increasingly more important. Many empirical solutions have been suggested in the past. This paper outlines the use of the theory of radiative energy transfer (RET) in a generic model for propagation through vegetation at frequencies from 1 to 60 GHz. The RET offers an analytical method to the problem. This theory requires however 4 input parameters, which need to be established experimentally. Some examples of curve fitting for this process are shown. A measurement of the angular scatter pattern, the so called 'phase function', can be utilised to determine 2 of those parameters. The most suitable method is presented of measuring this phase function is presented.
[show abstract][hide abstract] ABSTRACT: User terminals of modern mobile communication systems require
efficient, low profile antennas, capable of broadband and multi-band
operation. In that respect, planar inverted-F antenna (PIFA) designs
have emerged that explore the trade-off between the height above the
ground-plane and the achievable effective bandwidth. Further possible
bandwidth enhancements are studied, as is multi-band operation by
switching and tuning the resonant frequency of the PIFA, while
maintaining a low height above the ground plane
[show abstract][hide abstract] ABSTRACT: Accurate modelling of the propagation modes arising from
vegetation media depends, on the one hand, on the physical parameters
specific to the tree, such as size, shape, orientation and moisture
contents of leaves, branches and trunk. On the other hand, the
parameters of the radio link associated with the operational frequency,
directions of transmit and receive antennas, their heights, beamwidths
and polarisation add extra complexity to the characteristics and
understanding of the scattering modes from single trees. We describe the
development of a novel method, which will enable accurate modelling of
leaves, trunk and branches. The method is aimed at studying the
propagation modes arising from interaction with single trees at 20 GHz,
using the finite difference time domain (FDTD) technique. It is proposed
as a means of accurately computing electromagnetic scattering by
arbitrary-shaped relatively complex metal or dielectric objects excited
by an external plane wave
Antennas and Propagation, 2001. Eleventh International Conference on (IEE Conf. Publ. No. 480); 02/2001
[show abstract][hide abstract] ABSTRACT: In urban and rural areas, radiowave propagation is generally
dominated by diffraction loss and reflections from buildings and trees.
In the case of land mobile systems, trees, singly or in a group, are
usually present in the environment surrounding the receiver. An
important part of the modelling process is aimed at identifying the
individual contributions of the elements giving rise to the scattered
signal. Studies around the 2 GHz band were performed on a mature
deciduous tree in order to characterise the complex propagation modes
emanating from a single tree. Measurement campaigns were conducted in
autumn/winter and spring/summer on the same tree. A measurement system
has been developed for short-range outdoor radio channels incorporating
a vector network analyser (VNA), configured for swept frequency
measurements. The results of an investigation based on the measured
complex impulse response (CIR) at various positions around the tree for
both co-polar and cross-polar received signal components, are presented.
A discrete mathematical model is used to compute RMS delay spread of the
power delay profiles (PDP) for both foliated and de-foliated states of
the tree. Seasonal variations and the effects of leaf movement on the
channel characteristics caused by wind, are also discussed
Antennas and Propagation, 2001. Eleventh International Conference on (IEE Conf. Publ. No. 480); 02/2001