A new formulation for characterization of materials based on measured insertion transfer function

A widely used method for noncontact electromagnetic characterization of materials is based on the measurement of an insertion transfer function. This function, defined as the ratio of two phasor signals measured in the presence and absence of the material under test, is related to the dielectric constant of the material through a complex transcendental equation. Solving this equation requires a numerical two-dimensional root search technique, which is often time consuming due to slow convergence and the existence of spurious solutions. In this paper, a new formulation is presented, which facilitates the evaluation of complex dielectric constant of low-loss materials by means of real equations, thus requiring only one-dimensional root search techniques. Two sample materials are measured, and it is shown that their dielectric constants obtained from the exact complex equation and the new formulation are in excellent agreement. The new formulation reduces the computation time significantly and is highly accurate for the characterization of low-loss materials.     

Multipath Ghosts in Through-the-Wall Radar Imaging: Challenges and Solutions

In through-the-wall radar imaging (TWRI), the presence of front and side walls causes multipath propagation, which creates fake targets called multipath ghosts. They populate the scene and reduce the probability of correct target detection, classification, and localization. In modern TWRI, specular multipath exploitation has received considerable attention for reducing the effects of multipath ghosts. However, this exploitation is challenged by the requirements of the reflecting geometry, which is not always available. Currently, the demand for a high radar image resolution dictates the use of a large aperture and wide bandwidth. This results in a large amount of data. To tackle this problem, compressive sensing (CS) is applied to TWRI. With CS, only a fraction of the data are used to produce a high-quality image, provided that the scene is sparse. However, owing to multipath ghosts, the scene sparsity is highly deteriorated; hence, the performance of the CS algorithms is compromised. This paper presents and discusses the adverse effects of multipath ghosts in TWRI. It describes the physical formation of ghosts, their challenges, and existing suppression techniques.     

Enhanced Upper Bound for Erasure Recovery in SPC Product Codes

Single parity check (SPC) product codes are simple yet powerful codes that are used to correct errors and/or recover erasures. The focus of this paper is to evaluate the performance of such codes under erasure scenarios and to develop a closed‐form tight upper bound for the post‐decoding erasure rate. Closed‐form exact expressions are derived for up to seven erasures. Previously published closed‐form bounds assumed that all unrecoverable patterns should contain four erasures in a square. Additional non‐square patterns are accounted for in the proposed expressions. The derived expressions are verified using exhaustive search. Eight or more erasures are accounted for by using a bound. The developed expressions improve the evaluation of the recoverability of SPC product codes without the need for simulation or search algorithms, whether exhaustive or novel.     

Training Sequence Design for NBI Mitigation in Compressive Sensing UWB Systems

Ultra wideband (UWB) is a promising technology in delivering high data rate for short range wireless communication systems. Because of their large bandwidth, UWB signals may encounter some problems especially with high sampling rate requirements. Moreover, coherence existence with other narrowband systems is a major concern which needs to be addressed through proper mechanisms. The problem becomes so complex if multiple users exist. Since narrowband interference (NBI) signals have sparse representation in the discrete cosine transform (DCT) domain, they can be estimated and suppressed using Compressive Sensing (CS). CS also has the ability to reduce the high sampling rate requirements. For training based NBI mitigation with CS, three groups of pilot symbols are used to estimate the NBI signal subspace, the UWB signal subspace, and to provide information about the channel. In this paper, the distribution of pilot symbols among the three groups is investigated in the presence of strong NBI. The investigation is based on the bit error rate performance and throughput. The influence of each pilot symbols group is studied. The performance is also evaluated in the presence of multiuser interference in addition to the NBI. Simulation results show that the size of the third group of pilot symbols which is used to estimate the channel is the most dominant one.     

Directional modelling of ultra wideband communication channels

Ultra wideband (UWB) propagation is antenna-dependent, and multipath components experiencing specular diffraction or arriving at different angles have different shapes. To utilise the diversity of the multipath components, this study proposes a statistical model which incorporates directional parameters, such as elevation and azimuth angles by extending the IEEE802.15.3a model. Based on this model, a UWB directional simulator is developed. A novel multi-template subtractive deconvolution is applied to an extensive measurement campaign and simulated profiles. The use of multi-templates makes possible the directional estimation of the multipath components with a single receive antenna, and the use of subtractive deconvolution allows for the resolution of overlapping components and higher energy capture. Directional characterisation of UWB channels facilitates performance evaluation studies and achieves more accurate positioning, imaging and Rake receiver design.     

Path-loss and time dispersion parameters for indoor UWB propagation

The propagation of ultra wideband (UWB) signals in indoor environments is an important issue with significant impacts on the future direction and scope of the UWB technology and its applications. The objective of this work is to obtain a better assessment of the potentials of UWB indoor communications by characterizing the UWB indoor communication channels. Channel characterization refers to extracting the channel parameters from measured data. An indoor UWB measurement campaign is undertaken. Time-domain indoor propagation measurements using pulses with less than 100 ps width are carried out. Typical indoor scenarios, including line-of-sight (LOS), non-line-of-sight (NLOS), room-to-room, within-the-room, and hallways, are considered. Results for indoor propagation measurements are presented for local power delay profiles (local PDP) and small-scale averaged power delay profiles (SSA-PDP). Site-specific trends and general observations are discussed. The results for path-loss exponent and time dispersion parameters are presented.