Francesco Mani

Directional Spreads of Dense Multipath Components in Indoor Environments: Experimental Validation of a Ray-Tracing Approach

This paper investigates the prediction capabilities of a Ray-Tracing tool with advanced features, i.e., diffuse scattering and penetration, in terms of the angular spreads and spectra of the directional propagation channel. In particular, it highlights the angular behavior of dense multipaths, which may represent a non-negligible part of the received power, by comparing Ray-Tracing simulations with experimental data (office and laboratory environments). Results show that a Ray-Tracing approach including diffuse scattering is able to reproduce the dense multipath angular spreads, with errors around 4 to 20 degrees, and that scattering from ceiling is significant to predict the elevation spread. The assumption that diffuse scattering is clustered and strongly related to the most significant specular components is also successfully validated.

Polarimetric Properties of Diffuse Scattering From Building Walls: Experimental Parameterization of a Ray-Tracing Model

Dense multipath components may represent an important part of wireless transmission channels, yet little is known about their physical properties. For this reason, we parameterize an ad hoc diffuse scattering model, which can be easily included in ray-tracing tools. The work, focusing on the polarimetric properties of diffuse contributions scattered off building walls, relies on experimental data. By means of a joint post-processing of the data in conjunction with ray-tracing simulations, characteristic parameters of diffuse scattering are extracted. The analysis reveals that diffuse scattering represents an crucial part of the received power. Regarding depolarization caused by diffuse scattering, our work highlights that depolarization appears to be small for homogeneous brick walls, but is far from negligible for more complex wall structures.

Accuracy of depolarization and delay spread predictions using advanced ray-based modeling in indoor scenarios

This article investigates the prediction accuracy of an advanced deterministic propagation model in terms of channel depolarization and frequency selectivity for indoor wireless propagation. In addition to specular reflection and diffraction, the developed ray tracing tool considers penetration through dielectric blocks and/or diffuse scattering mechanisms. The sensitivity and prediction accuracy analysis is based on two measurement campaigns carried out in a warehouse and an office building. It is shown that the implementation of diffuse scattering into RT significantly increases the accuracy of the cross-polar discrimination prediction, whereas the delay-spread prediction is only marginally improved.

On the use of ray tracing for performance prediction of UWB indoor localization systems

The most important factors impairing the performance of radio-based indoor localization systems are propagation effects like strong reflections or diffuse scattering. To the full extent, these effects can be captured only by time-consuming measurement campaigns. Ray tracing (RT) offers the possibility to predict the radio channel for a certain environment, avoiding the need for measurements. However, it is crucial to include all relevant propagation mechanisms in the RT as well as to validate the obtained results. In this paper, we analyze if sub-band divided RT can yield realistic ultra-wideband channel impulse responses. We use the RT results for performance analysis of multipath-assisted localization, which depends directly upon the above mentioned propagation effects. In particular, it has been shown that the ratio of the signal energies of deterministically reflected paths to interfering diffuse components quantifies the amount of position-related information of deterministic multipath components. Comparison of this ratio to measurement data is thus useful to validate the sub-band divided RT. The results highlight the need for proper modeling of the diffuse multipath, as estimates of this energy ratio using RT are often overly optimistic. However, the obtained localization performance predictions using measurements and RT show general agreement.

A Spatially Aware Channel Model for Body-to-Body Communications

This paper presents the results of an experimental-based body-to-body (B2B) channel characterization in an indoor environment at 2.4 GHz in the Industrial, Scientific and Medical band. The peculiarity of B2B channels suggests the extension of classical stochastic models toward one that is aware of the reciprocal position and orientation of the bodies wearing the terminals to include the effects of body shadowing. To reach this goal, three on-body antenna positions (head, belt, and wrist) and multiple human mobility scenarios have been investigated in the measurements. The characterization of these channels shows that not only channel gain is affected by mutual body orientation, but also short and long term fading are. Exploiting this characterization, we are able to derive a comprehensive channel model whose components and parameters directly depend on the mutual body position in terms of distance and orientation.

Correlation-based radio localization in an indoor environment

We investigate the feasibility of using correlation-based methods for estimating the spatial location of distributed receiving nodes in an indoor environment. Our algorithms do not assume any knowledge regarding the transmitter locations or the transmitted signal, but do assume that there are ambient signal sources whose location and properties are, however, not known. The motivation for this kind of node localization is to avoid interaction between nodes. It is most useful in non-line-of-sight propagation environments, where there is a lot of scattering. Correlation-based node localization is able to exploit an abundance of bandwidth of ambient signals, as well as the features of the scattering environment. The key idea is to compute pairwise cross correlations of the signals received at the nodes and use them to estimate the travel time between these nodes. By doing this for all pairs of receivers, we can construct an approximate map of their location using multidimensional scaling methods. We test this localization algorithm in a cubicle-style office environment based on both ray-tracing simulations, and measurement data from a radio measurement campaign using the Stanford broadband channel sounder. Contrary to what is seen in other applications of cross-correlation methods, the strongly scattering nature of the indoor environment complicates distance estimation. However, using statistical methods, the rich multipath environment can be turned partially into an advantage by enhancing ambient signal diversity and therefore making distance estimation more robust. The main result is that with our correlation-based statistical estimation procedure applied to the real data, assisted by multidimensional scaling, we were able to compute spatial antenna locations with an average error of about 2 m and pairwise distance estimates with an average error of 1.84 m. The theoretical resolution limit for the distance estimates is 1.25 m.

Short term fading spatial dependence in indoor body-to-body communications

This paper presents the preliminary results of Body to Body (B2B) channel characterization, based on an extensive measurement campaign in an indoor environment in the ISM 2.4 GHz band. The peculiarity of B2B channels suggests the extension of classical stochastic models towards one that is aware of the position and mutual orientation of the bodies wearing the terminals. To reach this goal, three on-body antenna positions (head, belt and wrist) and multiple human mobility scenarios have been investigated in the measurements. In this work we focus on the spatial dependent characterization of short term fading and, specifically, on its dependence on mutual body orientation, concluding that, to have a reliable model, it is necessary to take into account this spatial dependence.

Low-complexity sub-band divided ray tracing for UWB indoor channels

Ray tracing has been extensively used to simulate indoor channel characteristics. For an ultra-wideband system, the channel characteristics vary significantly over the entire bandwidth. To cope with this, sub-band divided RT has been proposed by dividing the frequency of interest into multiple subbands and superposing the RT results at the individual center frequency of each subband. Thus, the computational complexity is directly proportional to the number of subbands. In this paper, we propose a mathematical method to significantly reduce the computational complexity of the sub-band divided RT, making it almost independent of the number of subbands. It is important to note that, based on our approach, not only the determination of the rays reaching a give location is made only once, but also the electromagnetic calculation of the received signal is not needed to perform repeatedly. The accuracy of low-complexity subband divided RT algorithm is verified through a measurement campaign.

Parameterization of a Polarimetric Diffuse Scattering Model in Indoor Environments

Diffuse or dense multipath components play an important role in determining the polarization behavior of wireless transmission channels. In this communication, we parametrize a polarimetric diffuse scattering model in two indoor environments. Our method relies on the empirical extraction of dense multipaths by means of a high resolution algorithm and on the investigation of the properties of this diffuse component. The analysis reveals that diffuse scattering significantly depolarizes the impinging wave in indoor scenarios, yielding cross-polar discrimination values close to 0 dB.

A Ray Based Method to Evaluate Scattering by Vegetation Elements

Contributions from trees may represent an important part of wireless communication channels in outdoor environments. For this reason, a simple ray-based model for scattering by tree branches has been developed and implemented in a pre-existent ray-tracing tool. In addition to the new rays created by scattering, an empirical attenuation model has also been implemented. Simulations have been validated with measurements in a campus scenario where several trees where present alongside the propagation environment. Received power results show an increase in accuracy when accounting for trees.