Ultra-wideband Signal Propagation Research Articles

A Non-Line-of-Sight Mitigation Method for Indoor Ultra-Wideband Localization With Multiple Walls

Ultra-wideband (UWB) ranging techniques can provide accurate distance measurement in line-of-sight (LOS) conditions. However, various walls and obstacles in indoor non-line-of-sight (NLOS) environments, which obstruct the direct propagation of UWB signals, can generate significant ranging errors. Due to the complex through-wall UWB signal propagation, most conventional studies simplify the ranging error model by assuming that the incidence angle is zero or the relative permittivities for different walls are the same to improve the through-wall UWB localization performance. Considering walls are different in realistic settings, this paper presents a through-multiple-wall NLOS mitigation method for UWB indoor positioning. First, spatial geometric equilibrium equations of UWB through-wall propagation and a numerical method are developed for the precise modeling of UWB through-wall ranging errors. Then, calculated error maps are determined numerically without field measurements. Finally, the determined error maps are combined with a gray wolf optimization algorithm for localization. The proposed method is evaluated via field experiments with four rooms, three walls, and six penetration cases. The results demonstrate that the method can strongly mitigate the multi-wall NLOS effects on the performance of UWB positioning systems. This solution can reduce project costs and number of power supplies for UWB indoor positioning applications.

Robust LOS/NLOS Identification for UWB Signals Using Improved Fuzzy Decision Tree Under Volatile Indoor Conditions

Ultra-wideband (UWB) is a very promising indoor wireless positioning technology. However, in the harsh and volatile indoor environment, the propagation of UWB signals is vulnerable to non-line-of-sight (NLOS) conditions, and the contaminated range measurements will degrade the accuracy for UWB localization. Therefore, it is necessary to identify LOS/NLOS. Recent studies mainly focus on the identification of UWB signal propagation conditions by using channel impulse response (CIR) or extracted channel statistical features. However, these studies usually only focus on specific indoor environment or stable indoor conditions. In fact, the indoor environment is harsh and changeable. In order to deal with the dynamic and uncertain information of the indoor environments, this paper proposes a robust method to identify LOS/NLOS using fuzzy decision tree (FDT) based on Bayesian optimization. The proposed method first extracts the classification features from the CIRs, and then fuzzifies the features. Finally, it combines Bayesian optimization to construct the FDT, so as to identify the propagation conditions of UWB signals. The experimental results show that the identification accuracy of the proposed method is higher than 90 % in both static and dynamic experiments, and the overall performance is excellent. Compared with other methods, it has certain advantages and robustness.

Эффект «волновода» при распространении сверхширокополосных сигналов в помещении

“Waveguide” effect that occurs by indoor propagation of ultrawideband signals is shown. The effect exhibits itself in the absence of interference factor of signal dissipation at any distance. Unlike outdoor propagation, the signal attenuation in multipath indoor environment is similar to free space. The effect occurs due to reflections of the incident wave from paired opposite surfaces, e.g., floor – ceiling, parallel walls. As a result, the distance range of indoor ultrawideband communications is essentially higher than outdoors. The effect is simulated in a three-ray reflection model.

Multi-Classification of UWB Signal Propagation Channels Based on One-Dimensional Wavelet Packet Analysis and CNN

Due to the strong penetration ability and high transmission rate of ultra-wideband (UWB) signals, UWB technology plays a very significant role in the field of precise indoor positioning. However, the harsh and volatile indoor environment leads to non-line-of-sight (NLOS) propagation and severe attenuation of UWB signals, which may generate significant ranging and positioning errors. To mitigate NLOS effect and improve positioning accuracy, existing methods use ranging information and channel impulse response (CIR) to identify UWB signal propagation channels. However, these NLOS identification methods often require a priori knowledge and suitable thresholds, and most of them only perform a binary classification between LOS and NLOS in a particular scenario. To address these disadvantages, this paper proposes a novel multi-classification method to classify UWB signal propagation channels based on one-dimensional wavelet packet analysis (ODWPA) and convolutional neural network (CNN). This method first decomposes the CIR of known categories into colored coefficients images using a one-dimensional wavelet packet function, then uses these images to train CNNs with different structures, and finally selects CNN model with the best performance to identify the unknown category of UWB signal propagation channels. The experimental results show that the performance of the proposed method is always the best, regardless of the type of experimental scenario, and the identification accuracy is always higher than 90% and up to 100%.

Super Compact UWB Monopole Antenna for Small IoT Devices

This article introduces a novel, ultrawideband (UWB) planar monopole antenna printed on Roger RT/5880 substrate in a compact size for small Internet of Things (IoT) applications. The total electrical dimensions of the proposed compact UWB antenna are 0.19 λo × 0.215 λo × 0.0196 λo with the overall physical sizes of 15 mm × 17 mm × 1.548 mm at the lower resonance frequency of 3.8 GHz. The planar monopole antenna is fed through the linearly tapered microstrip line on a partially structured ground plane to achieve optimum impedance matching for UWB operation. The proposed compact UWB antenna has an operation bandwidth of 9.53 GHz from 3.026 GHz up to 12.556 GHz at −10 dB return loss with a fractional bandwidth (FBW) of about 122%. The numerically computed and experimentally measured results agree well in between. A detailed time-domain analysis is additionally accomplished to verify the radiation efficiency of the proposed antenna design for the ultra-wideband signal propagation. The fabricated prototype of a compact UWB antenna exhibits an omnidirectional radiation pattern with the low peak measured gain required of 2.55 dBi at 10 GHz and promising radiation efficiency of 90%. The proposed compact planar antenna has technical potential to be utilized in UWB and IoT applications.

Construction and analysis of multi-path propagation model for indoor short range Ultra-wideband signal based on time domain ray tracing method

The realization of the Internet of Things can not be separated from the wireless sensor network which was the extension of communication and perception. The shortage of spectrum resources will become one of the bottlenecks that hinder the rapid development of Internet of Things. A large number of sensor communication makes the interference problem of wireless channel more and more serious. Therefore, the research of wireless channel characteristics and model was important for development of Internet of Things. In this paper, the time domain multipath propagation characteristics of direct, reflection, diffraction and transmission were introduced, which provided a more accurate basis for the design of indoor short distance Ultra-wideband (UWB) communication model. Considering the practicability of simulation, the multipath propagation characteristics of UWB signals under indoor short distance environment with wooden furniture were studied. Moreover, Aluminium door partitions, glass partitions, and plastic furnitures were also considered during our simulation. Based on the time domain ray tracing method, the UWB signal propagation characteristics such as received power distribution, root mean square delay spread, multipath arrive delay distribution parameters were also discussed under line-of-sight and non-line-of-sight propagation. The analysis results provided deployment basis of UWB signal under the indoor environment, which benefit to research and develop technology for indoor Internet of Things.

Numerical modelling of ultra wide band signal propagation in human abdominal region

Owing to the growing need for developing implantable wireless transceivers in Body Area Networks (BANs), it becomes necessary to characterise the wireless channel in Ultra Wide Band (UWB) frequency range. In case of BAN with implantable sensors, in-vivo measurement is not practically feasible. Therefore, modelling the electromagnetic wave propagation inside the human body through numerical simulations and characterising the wireless channel would be a good solution. This paper discusses the various steps involved in the development of a generic channel model and proposes an approach using modified ray tracing to predict the channel path loss characteristics of an Implantable Body Area Network in the UWB frequency range. As the human body is a heterogeneous and multilayer environment, the path loss at different depth inside the body is predicted with a four layer human abdomen model and the results are compared with the measured data.

Numerical modelling of ultra wide band signal propagation in human abdominal region

Owing to the growing need for developing implantable wireless transceivers in Body Area Networks (BANs), it becomes necessary to characterise the wireless channel in Ultra Wide Band (UWB) frequency range. In case of BAN with implantable sensors, in-vivo measurement is not practically feasible. Therefore, modelling the electromagnetic wave propagation inside the human body through numerical simulations and characterising the wireless channel would be a good solution. This paper discusses the various steps involved in the development of a generic channel model and proposes an approach using modified ray tracing to predict the channel path loss characteristics of an Implantable Body Area Network in the UWB frequency range. As the human body is a heterogeneous and multilayer environment, the path loss at different depth inside the body is predicted with a four layer human abdomen model and the results are compared with the measured data.

Serial subtractive deconvolution algorithms for time‐domain ultra wide band in‐vehicle channel sounding

Ultra-wide band (UWB) communication is expected to play a key role in next generation broadband intra vehicle wireless applications. The car compartment differs significantly from other well studied indoor or outdoor environments. Hence, channel sounding experiments are crucial for gaining a thorough knowledge of the UWB signal propagation characteristics in such a medium. Time domain channel sounding campaigns often employ some sort of deconvolution during measurement post processing as the measured signal in these experiments is the convolution of the channel response and the probing pulse which violates the Nyquist criterion. In this study, a comparison of two variants of time-domain serial subtractive deconvolution algorithm, popularly known as CLEAN, is presented. Appropriate statistical metrics for assessing the relative merit of a deconvolution technique are identified in the context of intra vehicle UWB transmission, and the better algorithm is selected based on its performance over a standard IEEE channel simulation testbed. The chosen method is then applied to extract power delay profile and delay parameters from an empirical time domain sounding experiment performed inside a passenger car. The effects of passenger occupancy, transmitter receiver separation and absence of direct transmission path are studied.

Characterization of Low-Antenna Ultrawideband Propagation in a Forest Environment

Impulse ultrawideband (UWB) communication promises a number of benefits for use in wireless sensor networks, particularly in forest environments, where it has the potential to provide robust operation, along with the ability to combine communications with precision position location. In this paper, we present measurement results and empirical models for UWB signal propagation in a forest environment. Path-loss measurements were performed using a 620-ps duration UWB pulse with a frequency range of 830-4200 MHz. More than 22 000 measurements were recorded in 165 locations in four diverse forest environments in Virginia and Maryland, USA. Transmitters and receivers were separated by distances that range from 4 m to 50 m. Large-scale path loss was most closely modeled by log-distance propagation, with path-loss exponents ranging from 2.5 to 3.8. Small-scale fading analysis indicated that UWB signals experience Rician fading, with K-factors in the range of 10-16 dB. K-factors were found to depend on forest type, with the medium-density forest providing the greatest number of multipath components and highest overall K-factor. Multipath component analysis demonstrated that a forest is a fairly rich multipath environment; however, in most cases, approximately 90% of the available energy was contained within the strongest 3-15 multipath components. Postprocessing analysis divided the UWB pulse into three frequency subbands and demonstrated that model parameters also had frequency dependence. These measurements and models should aid in the development of future UWB outdoor sensor networks.

Noise immunity of the wireless communications scheme based on ultrawideband chaotic radio pulses in multipath channels

The problem of determining the noise immunity of wireless data transmission based on ultrawide-band (UWB) chaotic radio pulses in the multipath channel with white noise is substantiated. The results have been calculated via numerical simulation using the multipath channel models describing UWB signal propagation in rooms of different classes at distances as long as several tens of meters. The direct chaotic communications method is shown to have the noise immunity high enough to employ this scheme in practical wireless applications where information is transmitted under severe conditions of multipath propagation. In this case, the ultimate data transfer rates are found to 25 Mb/s.

Computational study of ultra-wideband wave propagation into the human chest

Ultra-wideband (UWB) has potential applications in a variety of medical areas such as implant wireless sensors, microwave hyperthermia, imaging and radar. The wave propagation inside the human body must be known for an efficient system design of these different e-health applications. Nevertheless, little is known about the propagation of UWB signals inside the human body despite the enormous research efforts devoted to characterising radio propagation around the body. Therefore in this study, the UWB wave propagation through the human chest is characterised by electromagnetic simulations. For this sake, a voxel model of the human body that incorporates the frequency-dependent material properties of the human tissues is used. The wave propagation for line-of-sight (LOS) scenarios in the frequency bands of 100-1000 MHz and 1-5 GHz are evaluated. Both vertical and horizontal wave polarisations are considered. The power radiographs of the received signals inside the human chest are presented, which display the frequency and polarisation-dependent variations. The spectral analysis of the received signals reveals that the frequency range of 100-250 MHz, offers the minimum propagation loss. This frequency range of 250-1000 MHz is depicted as a region with less variant loss against frequency. Furthermore, the power delay profile (PDP) and the root mean square delay spread of the in-body channels is presented for different depths inside the body. These insightful results further the understanding of the propagation behaviour of UWB signals inside the human body, which will ease the development of in-body e-health applications.

A Human Body Model for Efficient Numerical Characterization of UWB Signal Propagation in Wireless Body Area Networks

Wireless body area network (WBAN) is a new enabling system with promising applications in areas such as remote health monitoring and interpersonal communication. Reliable and optimum design of a WBAN system relies on a good understanding and in-depth studies of the wave propagation around a human body. However, the human body is a very complex structure and is computationally demanding to model. This paper aims to investigate the effects of the numerical model's structure complexity and feature details on the simulation results. Depending on the application, a simplified numerical model that meets desired simulation accuracy can be employed for efficient simulations. Measurements of ultra wideband (UWB) signal propagation along a human arm are performed and compared to the simulation results obtained with numerical arm models of different complexity levels. The influence of the arm shape and size, as well as tissue composition and complexity is investigated.

An Efficient Simulation Technology for Characterizing the Ultra-Wide Band Signal Propagation in a Wireless Body Area Network

This paper presents an efficient simulation technology to characterize the Ultra-Wide Band signal propagation between the antennas in close proximity to a human body, where the human body works as a Wireless Body Area Network. The first technique is the hybrid Method of Moments and asymptotic Physical Optics in which the formulation is extended for modeling the dielectric body. The second technique combines the modification of the Multilevel Fast Multipole Algorithm with the Impedance Boundary Condition. These two techniques drastically reduce the computational complexity to model and simulate an electrically very large and complex structure including antennas and human body. Numerical examples showing the effects of the human body on the Ultra-Wide Band signal transmission between two antennas are presented to demonstrate the efficiency of our proposed method.

Ultra-Wideband Signal Propagation Experiments in Liquid Media

Ultra-wideband (UWB) signals exhibit different characteristics upon propagation through matter compared with narrow-band signals. The latter keeps a sinusoidal shape during different forms of signal propagation. The behavior of narrow-band signals does not apply to UWB signals in many cases. Presently, the possibilities for development of UWB signaling technology remain largely unexplored. Few applications have been developed due to strict regulations by the Federal Communications Commission (FCC). In this paper, we describe a series of experiments that have been carried out to determine the behavior of UWB signals and their properties. A transverse electromagnetic (TEM) horn antenna has been made for radiating UWB signals. A procedure for propagating UWB signals through a liquid medium of given salt concentration has been demonstrated, providing a basis for studying UWB signal propagation in biological matter. A new pulsewidth definition was adopted, which is suitable for propagated UWB signals.

Propagation analysis of ultrashort pulses in resonant dielectric media

The space-frequency theory of the propagation of an ultrawideband radiation in dielectric media is presented. Characterization of the material via its susceptibility leads to a transfer function, which describes the response of the medium in the frequency domain. This description enables the consideration of broadband signals, taking into account inhomogeneous absorptive and dispersive effects of the medium. Analytical expressions are derived when a pulse-modulated signal is propagating in a general dielectric material. Conditions for apparent “superluminal” and pulse compression effects are identified. The theory is applied for a special case of transmission inside a resonant medium, revealing analytical approximations for the parameters of a Gaussian propagating pulse in terms of initial pulse width, carrier frequency, and medium parameters. Constraints of the derived analytical expressions are discussed, pointing out conditions of approximation validity. We demonstrate the approach by studying the propagation of ultrawideband signals, while transmitted in the vicinity of the 60 GHz absorption peak of the atmospheric medium at millimeter wavelengths.

Time Domain Characteristics of Band-Notched Ultrawideband Antenna

A study of time domain characteristics of band-notched ultrawideband (UWB) antennas is presented. Two parameters - the correlation factor and the pulse width stretch ratio (SR) are resorted to estimate the time domain characteristics. The high correlation and the values of SR show that the previously proposed antennas are suitable for short-range UWB impulse radio. Ringing distortion of receiving antenna signals caused by the band-notched characteristics is discussed. Measured magnitudes of transfer function and group delay are exhibited. The primary study in this communication is to demonstrate the good performances of the previously proposed band-notched UWB antennas in short-range UWB signal transmission, propagation and reception in time domain.

Noninvasive probing of the human body with electromagnetic pulses: Modeling of the signal path

The biomedical applications of ultrawideband (UWB) radar promise a very important means to remotely monitor physiological signatures such as myocardial deformation and respiration. Accurate numerical and analytical techniques to predict the propagation of UWB signals in biological tissue are of great interests to researchers as an aid in developing signal processing algorithms. We propose applying an analytic transmit/receive signal path model considering the antennas, the human body, and the signal processing part of the UWB unit. Furthermore, the frequency dependency of the different biological tissues’ dielectric properties and the individual continuous motion of intrathoracic tissue layers are incorporated.

Planar 4‐element UWB antenna array and time domain characterization

AbstractIn this article, a novel planar ultra‐wideband (UWB) antenna array based on four identical UWB antenna elements for UWB applications is presented. The proposed antenna array yields an impedance bandwidth of 3.1–10.6 GHz with VSWR <2. Over the entire bandwidths, it has constant high gain, which is about 6.5–10.5 dBi, and a 60° 3‐dB beamwidth is obtained within the operational band. A planar 2‐element UWB antenna array and a band‐notched 4‐element UWB antenna array are also provided for references. Time domain descriptors of the proposed antenna array have been used to estimate short‐range UWB signal transmission, propagation, and reception. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3118–3123, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23874

Estimation of the information transmission rate in local area ultrawideband communication systems in the multipath propagation environment

The problem of indoor multipath propagation of ultrawideband signals is considered for direct chaotic communications systems. The values of the guard interval between the information symbols, which provides the quality of reception at a level of Perr ∼ 10−3 to 10−5, are estimated theoretically. The estimation procedure is based on the models of the multipath channels of wireless area networks that have been proposed by the IEEE workgroup.