Ultra-wideband Signal Propagation Research Articles

Characterization of wall dispersive and attenuative effects on UWB radar signals

Abstract This paper addresses the potentials of ultra-wideband (UWB) through-wall imaging radars compared with conventional narrowband systems. The challenges that limit the utilization of high precision UWB systems are examined with the aim of mitigating them. These challenges include multi-path, pulse dispersion, and antenna effects on the pulse shape due to angles of transmission and arrival. The propagation of UWB signals through walls is a crucial factor in determining the success of UWB radar technology. UWB signals, when propagating through walls, not only suffer attenuation but also distortion due to dispersive properties of the walls. This paper examines time- and frequency-domain techniques for measuring the electromagnetic properties of construction materials in the UWB frequency range. The measured parameters provide valuable insights in appreciating the capabilities and limitations of the UWB technology. Special attention is paid to time gating as a mean to extract the direct-path signal from the multi-path components. Both single-pass and multi-pass models are discussed. Multi-pass models account for the multiple reflections within the wall while the single-pass model assumes the possibility of gating out a single transmission. The partition-dependent narrowband propagation model is modified to account for the ultra-wide bandwidth of the signal. The paper illustrates the application of the modified model in indoor environments. The modified model is helpful in estimating the link power budget. It is also useful in studying the performance of UWB systems for indoor communication and positioning applications.

Overview of Research, Development, Standardization, and Regulation Activities in NICT UWB Project

This paper presents an overview of research, development, standardization and regulation activities on ultra wideband (UWB) technologies in National Institute of Information and Communications Technology (NICT). NICT started a project on UWB technologies since 2002, and organized UWB consortium in cooperation with more than 20 companies and 7 universities in Japan. Up to now, we have been conducting numerous UWB R&D including the following main works: i) key technology development such as MMIC chips, antennas and other devices, ii) measurement and channel modeling for UWB signal propagation, iii) standardization in international activities of IEEE 802.15, ITU-R TG1/8 as well as in a national regulatory committee of Ministry of Internal Affair and Communications (MIC). The UWB systems we have studied occupy frequency bands range from microwave band (3--5 GHz) to quasi-millimeter wave band (24--29 GHz). Various prototype UWB systems including multi-functional terminals have been developed. The output of NICT has been succeeded by industrial parties with with national and international standardization and regulation.

UWB signal propagation at the human head

Among different wireless solutions, ultra-wideband (UWB) communication is one promising transmission technology for wireless body area networks (WBANs). To optimize receiver structures and antennas for UWB WBANs with respect to energy efficiency and complexity, the distinct features of the body area network channel have to be considered. Thus, it is necessary to know the propagation mechanisms in the proximity of the human body. In this paper, we limit ourselves to transmission at the head, since the most important human communication organs, such as the mouth, eyes, and ears, are located there. We especially focus on the link between both ears and consider direct transmission, surface waves, reflections, and diffraction as possible propagation mechanisms. We show theoretically and by measurements, which were performed in the frequency range between 1.5-8 GHz, that direct transmission through the head is negligible due to the strong attenuation. We conclude by process of elimination that diffraction is the main propagation mechanism around the human body and verify these conclusions using a finite-difference time-domain simulation. Based on a second measurement campaign, we derive an approximation of the average power delay profile for the ear-to-ear link and calculate values for mean excess delay and delay spread. Finally, we briefly discuss the impact of the distinct ear-to-ear channel characteristic on the design of a WBAN communication system.

Ultra Wideband Signal Propagation in Desktop Environments

Short-range propagation measurements were carried out using ultra wideband (UWB) and continuous wave (CW) signals on a rectangular aluminum conductive plate, simulating typical office desks, with and without a low vertical metal partition panels. The frequency of the UWB signal spanned from 3.1 to 10.6 GHz and that of the CW signal was 6.85 GHz. A vector network analyzer and two omnidirectional UWB antennas were used to obtain the frequency-domain response of the propagation paths. With the partition panel, the CW reception level showed approximately a 20-dB spatial variation, induced by the interference between the direct and the reflected waves, but the UWB reception level had no particular plunges. The additional losses were also measured when the 500-mm propagation path was blocked with a human arm, a coffee cup, and a copy paper pile and when the receiving antenna was covered with a human palm on the plate without the partition panel. The maximum additional propagation losses were found as follows: 10--12 dB by a human arm, 10 dB with a coffee cup, and 2 dB with a paper pile. Further additional loss caused by a palm covering the antenna was found to be 10 to 12 dB, mainly due to palm absorption.

Ultrawideband through-the-wall propagation

The propagation of ultrawideband (UWB) signals in indoor environments is an important issue with significant impacts on the future direction and scope of UWB technology. The propagation of UWB signals is governed, among other things, by the properties of materials in the propagation medium. The information on electromagnetic properties of construction materials in the UWB frequency range would provide valuable insights into the appreciation of the capabilities and limitations of UWB technology. Although electromagnetic properties of certain construction materials over relatively narrow bandwidths in GHz frequency ranges are available, ultrawideband characterisation of most typical construction materials for UWB communication purposes has not been reported. In narrowband wireless communications, only the magnitude of insertion loss has been the quantity of interest. But for UWB signals, in addition to the magnitude, the phase information is an equally important factor that needs to be accounted for. In fact, UWB signals not only suffer attenuation when propagating through walls, but also suffer distortion due to the dispersive properties of the walls. This research examines propagation through typical construction materials and their ultrawideband characterisation. Ten commonly used construction materials are chosen for this investigation. Results for the dielectric constant and loss tangent of the materials over the UWB frequency range are presented. Accuracy of the measured results is discussed and distortions of UWB signals due to the dispersive properties of wall materials are addressed.

Simulation of ultra‐wideband indoor propagation

AbstractA comprehensive simulation of ultra‐wideband signal propagation in indoor environments is presented. The simulation is based on time‐domain electromagnetic modeling of transmitting and receiving antennas and the analysis of wave propagation through indoor channels using the time‐domain uniform theory of diffraction. The antennas are a pair of TEM horns which are modeled as arrays of vee dipoles. The analysis of these antennas is performed directly in the time domain, without the need for transforming the solutions from the frequency domain to the time domain. The frequency dependence of materials utilized in the structure on the indoor channel is accounted for in the channel simulation. The simulation results are compared with the corresponding measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 103–108, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20221

Analysis of ultra‐wide band signal propagation in an indoor environment

AbstractUltra‐wide band signal propagation in an urban environment is measured and studied. The basic concept is to develop, transmit and receive an extremely short duration burst of radio frequency energy‐typically a few tens of pico seconds to a few nanoseconds in duration. The resultant waveforms are extremely broadband, so much so that it is often difficult to determine an actual RF center frequency—thus the term “carrier‐free” [1]. In this paper, the indoor propagation of UWB signals inside an office room is studied. A simulation model of this system is compared with the actual test results. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 13–15, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10656

The effects of the human body on UWB signal propagation in an indoor environment

Ultra-wideband (UWB) communication systems are investigated for their ability to operate in dense multipath environments. While a great deal of time and effort has been spent characterizing both the indoor and outdoor UWB channels, the effects of human body interaction with a close proximity UWB antenna remains unexplored. Measurements of a commercially available UWB antenna performance in an anechoic chamber and in various indoor multipath environments were conducted. Comparisons of these measurement results indicate that while the human body creates a deep null (23.6 dB) in a light multipath environment, this null is drastically reduced (6.8 dB) in a dense multipath environment.