Conor Brennan

Application of the fast far-field approximation to the computation of UHF pathloss over irregular terrain

The availability of fast numerical methods has rendered the integral-equation approach suitable for practical application to radio planning and site optimization for UHF mobile radio systems. In this paper, we describe a conceptually simple scheme for the efficient computation of UHF radial propagation loss over irregular terrain, which is based on the fast far-field approximation. The method is substantially faster than conventional integral-equation (IE) solution techniques. The technique is improved by incorporating the Greens function perturbation method and we outline a way in which the formulation can be made more exact. Computational issues such as terrain profile truncation and the effect of small-scale roughness are addressed. The method has been applied to gently undulating terrain and compared to published experimental results in the 900-MHz band. It has also been successfully applied to more hilly terrain and to surfaces with buildings added.

Tabulated interaction method for UHF terrain propagation problems

An integral equation (IE) solution to UHF terrain path-loss computation is described that dramatically reduces computation times (compared to both standard IE techniques and the fast far-field method) for typical propagation problems while maintaining the full-wave accuracy associated with IE solutions. Results are provided, which are in excellent agreement with published measured data.

An efficient nonlinear circuit simulation technique

This paper proposes a novel method for the analysis and simulation of integrated circuits (ICs) with the potential to greatly shorten the IC design cycle. The circuits are assumed to be subjected to input signals that have widely separated rates of variation, e.g., in communication systems, an RF carrier modulated by a low-frequency information signal. The proposed technique involves two stages. Initially, a particular order result for the circuit response is obtained using a multiresolution collocation scheme involving cubic spline wavelet decomposition. A more accurate solution is then obtained by adding another layer to the wavelet series approximation. However, the novel technique presented here enables the reuse of results acquired in the first stage to obtain the second-stage result. Therefore, vast gains in efficiency are obtained. Furthermore, a nonlinear model-order reduction technique can readily be used in both stages making the calculations even more efficient. Results will highlight the efficacy of the proposed approach

SEAMLOC: Seamless Indoor Localization Based on Reduced Number of Calibration Points

Indoor localization based on ubiquitous WLAN has exhibited the capability of being a cheap and relatively precise technology and has been verified by many successful examples. Its performance is subject to change due to multipath propagation and changes in the environment (people, building layouts, antenna characteristics, etc.) which cannot be eliminated easily. An indoor localization and tracking algorithm is described which is based on the creation of a database of WLAN signal strengths at pre-chosen calibration points (CPs). The need for fewer CPs than in standard methods is due to use of a novel interpolation algorithm, based on the specification of robust, range and angle-dependent likelihood functions that describe the probability of a user being in the vicinity of each CP. The actual location of the user is estimated by solving a system of two non-linear equations with two unknowns derived for a pair of CPs. Different pairs of CPs can be chosen to make several estimates which then can be combined to increase the accuracy of the estimate. A variety of results are presented using challenging data collected in a typical office environment which demonstrate the accuracy that can be achieved with a reduced number of CPs.)) The method is compared to several competing localization methods and is shown to give superior results.

A Hybridized Forward Backward Method Applied to Electromagnetic Wave Scattering Problems

This communication presents an improved forward backward technique for the solution of electromagnetic wave scattering problems. The forward backward method displays rapid convergence when the eigenvalues of the associated iteration matrix are small. Conversely when the eigenvalues are large it displays poorer convergence. The hybridized method presented in this communication helps to circumvent the poor convergence of the forward backward method in the latter case by introducing an optimally sized correction in the approximate direction of the eigenvector associated with the iteration matrixs dominant eigenvalue. Numerical results are presented in order to demonstrate the convergence of the improved forward backward method.

Performance Analysis of Plant Monitoring Nanosensor Networks at THz Frequencies

Future wireless nanosensor networks are envisioned to operate in the THz band, due to the tiny size of the network components. Among the diverse range of applications that such networks promise, high-resolution plant monitoring systems are the categories which can benefit from the size and high sensitivity of nanosensor devices and also the high bandwidth provided by them. However, communications at the THz frequency band, especially within a hybrid channel like plant foliage, undergo peculiar types of attenuation and distortion. These phenomena, which can challenge the feasibility of the aforementioned applications, need to be addressed/modeled precisely. Therefore, in this paper, we propose the first THz path-loss model within a plant environment. In addition, we provide a simplified model of plant structure as well as a model for the probability of successful transmissions between nanosensors and microscale receivers mounted on the plant stem. The introduced models consider the limited capability of THz radiation to propagate through plant leaves, and also the high free-space path-loss as the main sources of signal loss in the network communications. Furthermore, these models can be customized based on the structural characteristics of a plant, e.g., leaves size and distribution, to account for a variety of plant species. Finally, the performance of communications based on the provided models is evaluated for different network scenarios.

On comparison of integral equation approaches for indoor wave propagation

Two integral equation formulations for the analysis of two-dimensional indoor EM wave propagation are discussed in this paper. The volume and the surface electric fleld integral equations are discretised by the Method of Moments, resulting in dense linear systems whose iterative solutions are accelerated by using acceleration techniques. Numerical results are presented to compare the performance of the two approaches when applied to the same indoor propagation problem.

Efficient Wideband Electromagnetic Scattering Computation for Frequency Dependent Lossy Dielectrics Using WCAWE

This paper presents a model order reduction algorithm for the volume electric field integral equation (EFIE) formulation, that achieves fast and accurate frequency sweep calculations of electromagnetic wave scattering. An inhomogeneous, two-dimensional, lossy dielectric object whose material is characterized by a complex permittivity which varies with frequency is considered. The variation in the dielectric properties of the ceramic BaxLa4Ti 2+xO 12+3x in the <1 GHz frequency range is investigated for various values of x in a frequency sweep analysis. We apply the well-conditioned asymptotic waveform evaluation (WCAWE) method to circumvent the computational complexity associated with the numerical solution of such formulations. A multipoint automatic WCAWE method is also demonstrated which can produce an accurate solution over a much broader bandwidth. Several numerical examples are given on order to illustrate the accuracy and robustness of the proposed methods.

An MFIE-based tabulated interaction method for UHF terrain propagation problems

Approximations are introduced into a magnetic field integral equation (MFIE) formulation of a two-dimensional (2-D) terrain scattering problem, which allow most of the integrals inherent in the MFIE to be performed analytically. The implementation of the method is discussed and an example is given comparing its performance against a reference solution and measured data. The new formulation applies to both TM/sup z/ and TE/sup z/ polarizations and is an improvement over the electric field integral equation (EFIE) formulation of the tabulated interaction method (TIM) in that far-field patterns can be calculated analytically leading to increased flexibility of the method.

Improved Forward Backward Method With Spectral Acceleration for Scattering From Randomly Rough Lossy Surfaces

An efficient and accurate iterative method is proposed for computing electromagnetic (EM) scattering from 1-D dielectric rough surfaces. The communication improves the convergence of forward backward method, applying it to the problem of 2D wave scattering from random lossy rough surfaces using a coupled surface integral equation formulation. A matrix splitting technique is introduced to reduce the number of matrix-vector multiplications required by the correction step and Spectral Acceleration (SA) is applied to reduce the computational complexity of each matrix-vector product from O(N2) to O(N). The proposed method is called the improved forward backward method with spectral acceleration (IFBM-SA). The numerical analysis demonstrates that IFBM-SA has a higher convergence rate than FBM-SA and a recent technique which is used as a reference method. Moreover, IFBM-SA is more robust than the reference method and has smaller storage requirements meaning that it can readily scale to larger problems. In addition an eigenvalue based analysis is provided illustrating how the improvement step works.