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Ray-tracing with user-body shadowing in indoor environments
Abstract
In this paper, a ray-tracing technique taking into consideration the effects of user-body shadowing is investigated. With the rapid growth in the applicability of mobile devices, accurate received signal predictions are increasingly important. The user's body especially has a great impact on the received signals, because it is nearly always located close to the mobile device. We consider two deterministic shadowing models based on anechoic chamber measurements and an existing diffraction theory. The both models are established as the power loss on a single propagation path depending on the user's postures and relative positions. A combined method of the user-shadowing models and multipath channel profiles obtained by ray tracing is then introduced and the results are validated by a comparison with in-building measurements.
This study proposes a new method to estimate room shape using radio waves. Unlike existing heuristic methods, the proposed method uses accumulated radio channel data and the neural network to predict room shapes. The radio channel data is generated by three dimensional (3D) ray tracing simulation and actual measurements. The neural network used the channel data for the training process. After training the neural network, we evaluated the performance variation resulting from changes in the channel environment parameters used in the neural network training, the size of the room, hyperparameters of the neural network, and the location of the transceivers. The results showed that better performance was observed when more sets of channel parameters were used as inputs to the neural network. In addition, the results obtained from measurements show that the estimation of the room shape through the neural network works well not only in the simulation but also in the real world.
We investigate the reliability of radio channel simulators in predicting channel responses throughout a well-specified environment. Indoor environments for which the geometric layout and material properties of surfaces are known lend themselves to such site-specific simulation. We assess the performance of this approach by comparing its predictions with measurements in a specific static environment. The good agreement on path loss, Ricean K-factor and RMS delay spread, over the set of paths measured and simulated, suggests that a well-designed radio simulator can be used reliably to predict system behavior. Typically, wireless channel models obtained through this or similar techniques do not capture the temporal variability in the channel response due to people movement in the environment. We treat the time-varying part of the channel response using stochastic processes. Using channel sounding experiments for several typical office scenarios, we show that autoregressive processes can be used to model the time-varying tap gains for several different motion scenarios.
Using wireless sensors worn on the body to monitor health information is a promising new application. To realize transceivers targeted for these applications, it is essential to understand the body area propagation channel. Several numerical, simulated, and measured body area propagation studies have recently been conducted. While many of these studies are useful for evaluating communication systems, they are not compared against or justified by more fundamental physical models derived from basic principles. This type of comparison is necessary to provide better physical insights into expected propagation trends and to justify modeling choices. To address this problem, we have developed a simple and generic body area propagation model derived directly from Maxwell's equations revealing basic propagation trends away, inside, around, and along the body. We have verified the resulting analytical model by comparing it with measurements in an anechoic chamber. This paper develops an analytical model of the body, describes the expected body area pathloss trends predicted by Maxwell's equations, and compares it with measurements of the electric field close to the body.
Research in antennas and propagation for body centric wireless communications continues to grow, in response to increasing demands for body area networks (BANs) for healthcare, defence and personal communications and entertainment. This paper will briefly review recent international work, and then report on advances in three UK BAN research centres, Birmingham, Queen Mary and Queens Belfast. The demand for greater security in BAN links could be met by the use of 60GHz channels, and the likely channel characteristics will be discussed and initial results given. New insights into surface wave excitation on the human body has enabled a novel low profile antenna to be designed that maximises link performance where very thin antennas are necessary. Finally advances in the numerical computation are reported, in which the importance of relating phantoms directly to patients to give subject specific simulations and to allow improved modelling of internal organs.
We demonstrate that in indoor radio propagation modeling, the presence of the human body may be approximated by a conducting circular cylinder at microwave frequencies. Therefore, a perfect tool such as the uniform theory of diffraction may be used to predict the diffracted field over a smooth circular surface. To validate the model, vertically and horizontally polarized continuous wave (CW) measurements were performed at 10.5 GHz between two fixed terminals inside a room along with the presence of an obstacle (person or metallic cylinder) moving along predetermined parallel and perpendicularly crossing paths with respect to the line-of-sight direction. Results indicate that there is a strong correlation between the effects of the human body and those of a conducting circular cylinder. The simulation results successfully agree with the CW experimental measurements.
Body-centric wireless communications refer to human-self and human-to-human networking with the use of wearable and implantable wireless sensors. It is a subject area combining wireless body-area networks (WBANs), Wireless Sensor Networks (WSNs) and Wireless Personal Area Networks (WPANs). Body-centric wireless communications has abundant applications in personal healthcare, smart home, personal entertainment and identification systems, space exploration and military. The human body is an uninviting and often hostile environment for a wireless signal. In general, antennas suffer from reduced efficiency due to electromagnetic absorption in human tissues, radiation pattern fragmentation and variations in impedance at the feed. Typical geometries of wireless wearable and implantable devices, vary from millimetric to centimetric sizes and, hence, compact yet efficient antennas need to be fully characterized and integrated with the RF transceiver. As well as size there are other significant challenges in the design of antennas for body-centric wireless communications. The objective of this talk is to highlight current and emerging research in antennas and propagation for body-centric wireless communications, as well as applications of this technology.
This paper presents a path-shadowing model for indoor populated environments that has been developed based on computer simulations. The propagation paths between the transmitting and receiving points in an empty rectangular space are determined using the ray-tracing method, in which moving quasi-human bodies that are modeled as cylinders with a finite height are generated in the space, and intersections of the paths with the bodies are counted. From the results, the shadowing probabilities, durations, and intervals are evaluated for each propagation path, and this shadowing process is characterized as a Markov process. This paper proposes a method that individually generates the shadowing effects on each propagation path. The measurement results of the path-shadowing characteristics using a 5.2-GHz high-resolution channel sounder are presented, and the validity of this model is confirmed. Similar measurement results using a photoelectric sensor are also presented to reinforce the channel-sounding measurement results.
This letter investigates the channel variations in wireless body area networks (WBANs). For the purpose of the investigation, a ray solution for multiple closed surfaces is proposed that utilizes a modified slope uniform theory of diffraction (UTD) technique and can be applied to model scattering, radiation, coupling effects, or a combination of the three in a single formulation. The solution considers all possible ray paths and is valid at the transition boundaries of the scenario. The human bodies are represented as closed cylindrical surfaces with constitutive parameters based on the “Muscle” model. The proposed algorithm predicts channel variations in a ray format that requires less CPU and is characterized by lower complexity compared to full-wave techniques. Body-to-access point (BAP) and body-to-body networks are investigated .
Using seven strategically placed, time-synchronized body worn receivers covering the head, upper front and back torso, and the limbs, we have investigated the effect of user state: stationary or mobile and local environment: anechoic chamber, open office area and hallway upon first and second order statistics for on-body fading channels. Three candidate models were considered: Nakagami, Rice and lognormal. Using maximum likelihood estimation and the Akaike information criterion it was established that the Nakagami-m distribution best described small-scale fading for the majority of on-body channels over all the measurement scenarios. When the user was stationary, Nakagami-m parameters were found to be much greater than 1, irrespective of local surroundings. For mobile channels, Nakagami-m parameters significantly decreased, with channels in the open office area and hallway experiencing the worst fading conditions.
Several models exist for the statistical characterization of
microwave propagation within buildings. Statistical models do not
provide site-specific information. A hybrid model is proposed, in which
ray tracing is used to predict, at any given location, the local mean of
the received power and the delay profile. Variations about the mean
values can then be captured via a statistical description matched to the
local environment. An efficient 3-D ray tracing algorithm is described
which accounts for all (transmitted as well as reflected) rays reaching
the receiver location after an arbitrary number of reflections. The
effects of the angle of incidence, the material dielectric constant and
the antenna patterns are included. The predicted values for the local
means of the received power are then compared against measurements to
establish the accuracy of this approach
Designing a low-power system for wireless communication within a
building might seem simple. Not so-walls can affect signal strength in
ways that are hard to calculate. The paper considers how AT&T's WISE
software uses CAD, computational geometry, and optimization to quickly
plan where to place base-station transceivers
Efficient radio ray tracing programs developed particularly for reflector-rich environments are described. These image-based, dual-grid, scalar, coherent, ray tracing programs generate maps, (two-dimensional slices) of three-dimensional standing wave patterns for continuous wave illumination. The calculated maps are used to estimate system coverage quality in a macroscopic sense and to investigate design alternatives regarding antenna beamwidths, boresight orientations, spatially averaged signal strengths, and so forth. The programs run fast enough on engineering workstation to support indoor radio system design, but not fast enough for interactive use. Examples are given to illustrate the use of the programs.< >
Problems with the use of ray-tracing techniques in indoor
propagation environments are identified, and a new set of widely
applicable diffraction coefficients is developed. The limitations on the
accuracy of the ray-tracing method in indoor propagation environments
are first assessed. The effects of scatterers with dimensions
approaching the wavelength of operation and of scatterers with finite
conductivity are considered. The accuracy of ray tracing is quantified
by comparison to a full-wave simulation technique, which combines the
finite-difference time-domain method with a spatial transformation
technique, the Kirchhoff surface integral formulation. Simulation
results demonstrate that when the magnitude and phase of the received
signal components are properly accounted for, the ray-tracing solution
may be accurate down to a fraction of a wavelength. A new set of
diffraction coefficients is presented for calculations involving
obstacles with finite conductivity. The new coefficients eliminate an
artificial dip in the diffracted field strength, which is often
encountered when currently available techniques are used. Validation is
provided by comparison with full-wave simulations and measurements.
Improved accuracy in both the illuminated and shadowed regions is
demonstrated
Deterministic propagation prediction methods proposed for indoor
radio are useful for estimating the average propagation loss in real
environments, which usually have complicated geometries. On the other
hand, these methods generally fail to accommodate human body shadowing,
which is a significant propagation effect in indoor picocells. Several
empirical models to describe body shadowing have been reported. However,
to our knowledge, no appropriate model that can be used in combination
with deterministic propagation prediction methods has been provided in
the literature. In this paper, a new practical model is introduced,
which provides a way to estimate body-shadowing effects
deterministically with the existing ray-determination methods. The
detailed procedure to combine our body-shadowing model with the
ray-determination methods is described. Several examples are shown
applying the procedure to a simple office layout