Dense Multipath Components Research Articles

Dynamic V2V Channel Measurement and Modeling at Street Intersection Scenarios

Vehicular communication has been widely concerned by academia and industry. Wireless channel characterization and modeling are the foundation of communication systems. Compared with typical road scenarios such as urban and suburban areas, wireless channel characterization in intersections is a challenging task. In this paper, channel measurements at 5.9 GHz in street intersection scenarios are carried out and provide data for the characterization and modeling of time-varying vehicular channels. This paper proposes a double-slope path loss model, which can accurately reflect the signal propagation loss at intersections. Further, the time-varying spatial characteristics of multipath are extracted and analyzed, and the azimuth and elevation spread of arrival are statistically characterized. The influence of obstacles on multipath spatial characteristics in intersection scenarios is investigated. Then we investigate the spatial stationarity of channels and analyze the possible reasons for the differences in spatial stationarity of different scenarios. In addition, based on multipath extraction, we quantitatively analyze the energy of dense multipath components in different propagation scenarios. The research in this paper can enrich the investigation of vehicular channels and enable the analysis and design of vehicular communication systems.

Channel Propagation Characteristics for Massive Multiple-Input/Multiple-Output Systems in a Tunnel Environment [Measurements Corner

The effect of delay spread (DS), the specular multipath components (SMCs), and the impact of dense multipath components (DMCs) on multiple-input/multiple-output (MIMO) system performance in a tunnel environment are studied by considering a Richter’s maximum-likelihood (RiMAX)-based estimator. The path loss (PL), angular spread, interuser spatial correlation, and capacity of a massive MIMO framework are analyzed at the 3.5-GHz frequency band through a measurement campaign inside a subway tunnel to implement the latest 5G standards. The radio channel consists of a uniform rectangular array of 32 transmitting elements and a uniform cylindrical array of 64 receiving elements with horizontal and vertical polarizations. The power ratio of the DMCs is found to be distance dependent, as the DMCs and SMCs behave differently in tunnels. Moreover, the study shows that the channel capacity, angular spread, and DS are reduced as the distance between the transmitting and receiving antenna arrays increases, whereas the PL exponent increases with the distance. This research highlights the importance of considering spatial characteristics in 5G massive MIMO system models and provides guidelines to enhance the networks’ accuracy in underground mobile communications.

On the Contribution of Dense Multipath Components in an Intrawagon Environment for 5G mmW Massive MIMO Channels

In this letter, the dependence of the specular multipath components (SMC) and dense multipath components (DMC) to the interuser spatial correlation and sum-rate capacity of a massive multiuser multiple-input--multiple-output (MU-MIMO) setup is evaluated from measurements conducted inside an underground subway wagon at the 25–40 GHz candidate frequency bands for 5G systems. The radio channel consists in a 7 × 7 uniform rectangular array (URA) acting as access point for eight users uniformly distributed in the wagon. The DMC power ratio is observed to be distance- and frequency-dependent as the SMC and DMC exhibit different propagation mechanisms. Remarkably, it is reported that the interuser spatial correlation computed with DMC offers the best favorable propagation for a massive MIMO setup, whereas SMC contribute to the users correlation. Hence, correlation is found to be strongly dependent on the DMC ratio frequency characteristics. In addition, better interuser correlation and sum-rate capacity values are obtained as the frequency is increased. These results highlight the need to include DMC in 5G massive MIMO channel models and emulators to improve their accuracy at the system level.

Massive MIMO-Based Localization and Mapping Exploiting Phase Information of Multipath Components

In this paper, we present a robust multipath-based localization and mapping framework that exploits the phases of specular multipath components (MPCs) using a massive multiple-input multiple-output (MIMO) array at the base station. Utilizing the phase information related to the propagation distances of the MPCs enables the possibility of localization with extraordinary accuracy even with limited bandwidth. The specular MPC parameters along with the parameters of the noise and the dense multipath component (DMC) are tracked using an extended Kalman filter (EKF), which enables to preserve the distance-related phase changes of the MPC complex amplitudes. The DMC comprises all non-resolvable MPCs, which occur due to finite measurement aperture. The estimation of the DMC parameters enhances the estimation quality of the specular MPCs and, therefore, also the quality of localization and mapping. The estimated MPC propagation distances are subsequently used as input to a distance-based localization and mapping algorithm. This algorithm does not need prior knowledge about the surrounding environment and base station position. The performance is demonstrated with real radio-channel measurements using an antenna array with 128 ports at the base station side and a standard cellular signal bandwidth of 40MHz. The results show that the high accuracy localization is possible even with such a low bandwidth.

Joint range extension and localization for low‐power wide‐area network

This paper introduces Snipe, a novel system offering joint localization and range extensions for Low‐power wide‐area networks (LPWANs). Although LPWAN systems such as Long Range (LoRa) are designed to achieve high communication range with low energy consumption, they suffer from fading in obstructed environments with dense multipath components, and their localization system is sub‐par in terms of accuracy. In this work, Multiple‐Input Multiple‐Output techniques are leveraged to achieve a higher signal‐to‐noise ratio at both the end device and the gateway while providing an opportunistic accurate radar‐based system for localization with limited additional cost.

On Modeling of Dense Multipath Component for Indoor Massive MIMO Channels

Elaborate channel modeling is an essential prerequisite for design, testing, and improvement of the massive multiple-input–multiple-output (MIMO) system. In this letter, dense multipath component (DMC) modeling for massive MIMO channels is presented based on measurement campaigns in three different indoor scenarios. The parameters for DMC are extracted by applying a RiMAX-based estimator. The distance-dependence and the variance behaviors of the DMC parameters across the large-scale array are analyzed and modeled. Moreover, the model validation is performed by using an empirical cluster-based massive MIMO channel model. Entropy capacity, condition number, channel ellipticity, and root-mean-square delay spread, which reflect the spatial structure and multipath richness of the channel, are used as the validation metrics. The validation shows that the incorporation of DMC can significantly improve the accuracy of channel modeling.

An extension of the RiMAX multipath estimation algorithm for ultra-wideband channel modeling

This work presents an extension of the high-resolution RiMAX multipath estimation algorithm, enabling the analysis of frequency-dependent propagation parameters for ultra-wideband (UWB) channel modeling. Since RiMAX is a narrowband algorithm, it does not account for the frequency-dependency of the radio channel or the environment. As such, the impact of certain materials in which these systems operate can no longer be considered constant with respect to frequency, preventing an accurate estimation of multipath parameters for UWB communication. In order to track both the specular and dense multipath components (SMC and DMC) over frequency, an extension to the RiMAX algorithm was developed that can process UWB measurement data. The advantage of our approach is that geometrical propagation parameters do not appear or disappear from one sub-band onto the next. The UWB-RiMAX algorithm makes it possible to re-evaluate common radio channel parameters for DMC in the wideband scenario, and to extend the well-known deterministic propagation model comprising of SMC alone, towards a more hybrid model containing the stochastic contributions from the DMC’s distributed diffuse scattering as well.Our algorithm was tested with synthetic radio channel models in an indoor environment, which show that our algorithm can match up to 99% of the SMC parameters according to the multipath component distance (MCD) metric and that the DMC reverberation time known from the theory of room electromagnetics can be estimated on average with an error margin of less than 2 ns throughout the UWB frequency band. We also present some preliminary results in an indoor environment, which indicate a strong presence of DMC and thus diffuse scattering. The DMC power represents up to 50% of the total measured power for the lower UWB frequencies and reduces to around 30% for the higher UWB frequencies.

Measurement‐based analysis of specular and dense multipath components at 94 GHz in an indoor environment

In this study, the authors present a measurement-based analysis of the indoor radio channel characteristics of both the specular and dense multipath components [specular part of the channel (SMC) and diffuse part of the channel] at 94 GHz within a 3 GHz bandwidth. On the basis of an investigation of the frequency stationarity of this band, they have selected multiple sub-bands to perform their evaluation. A method is developed that allowed for the estimation of the specular propagation paths, after which the remainder is regarded as the diffuse spectrum. Radio channel characteristics such as the path loss, root-mean-square delay spread, and the SMC ratio have been calculated as a function of transmitter–receiver distance, and in the different sub-bands. On the basis of the diffuse spectrum, the behaviour of the reverberation time is analysed for the first time in the 94 GHz band.

Modeling the Power Angular Profile of Dense Multipath Components Using Multiple Clusters

In this paper, the power angular profile (PAP) of the dense multipath components (DMCs) was analyzed and characterized based on a channel sounding measurement campaign at 11 GHz in an indoor environment. The specular multipath components (SMCs) were estimated with the SAGE algorithm, and the RiMAX framework was applied for the estimation of the DMC in both the time-delay and the angular domain. After careful inspection of the spectrum of the residual signal components in the angular domain, we found that the DMC should be modeled by taking into account multiple angular clusters at different angles, to better characterize the diffuse scattering between transmitter and receiver, originating from multiple reflections in an environment. Therefore, we propose to extend the maximum likelihood estimation of the angular DMC parameters in the RiMAX framework so that the PAP of the DMC can be modeled with a multimodal von Mises distribution. We also validate our proposed method with the results of the measured channel sounding data.

Dense Multipath Component Characteristics in 11-GHz-Band Indoor Environments

In the next-generation mobile communication system, the higher frequency bands from C-band to V-band are expected to be utilized because it has the potential to improve network capacity drastically by the available wideband spectrum. Since the characteristics of reflected and scattered radio waves from surrounding environments in those bands are thought to be quite different than at lower frequencies, the clarification of its influence on the multiple-input multiple-output (MIMO) transmission performance is a critical issue. In this paper, we focused on the characteristics of diffuse scattering in X-band, and conducted the MIMO channel measurements in indoor environments in the 11-GHz band. The frequency, angular, and polarization domain dense multipath component (DMC) propagation parameters were jointly estimated by using the RiMAX-based estimator. The measurement result showed the existence of significant DMC, which is thought to have originated from the floor, the ceiling as well as the walls. The angular spreads of the DMC tended to increase, and their decay factor tended to decrease as the room size decreased. It is also shown that the existence of DMC significantly affected the eigenvalue structure of the MIMO channel, which defines the MIMO transmission performance. The result is expected to be utilized for novel MIMO channel modeling in X-band that includes the DMC contribution.

Capacity analysis of an IEEE 802.11n system in a residential house based on estimated specular and dense multipath components

This study analyses the multiple-input multiple-output (MIMO) capacity in a residential house. The capacity calculation is based on physical radio channels estimated from channel sounding measurements. Both specular and dense multipath components are estimated from the channel sounding data with the RiMAX maximum-likelihood algorithm. In particular, the capacity analysis is made for a 2x2 IEEE 802.11n MIMO system that conforms to the legacy mode of the standard and operates in the 2.4GHz ISM band. The contribution of dense multipath to the channel capacity is quantified by calculating the capacity of radio channels for which the dense multipath is ignored and only the specular multipath is retained. It is found that ignoring dense multipath underestimates the capacity on average by 1.1, 9.1, and 37.8% for line-of-sight, obstructed line-of-sight, and non-line-of-sight situations, respectively.

Two Novel Space-Time Coding Techniques Designed for UWB MISO Systems Based on Wavelet Transform.

In this paper two novel space-time coding multi-input single-output (STC MISO) schemes, designed especially for Ultra-Wideband (UWB) systems, are introduced. The proposed schemes are referred to as wavelet space-time coding (WSTC) schemes. The WSTC schemes are based on two types of multiplexing, spatial and wavelet domain multiplexing. In WSTC schemes, four symbols are transmitted on the same UWB transmission pulse with the same bandwidth, symbol duration, and number of transmitting antennas of the conventional STC MISO scheme. The used mother wavelet (MW) is selected to be highly correlated with transmitted pulse shape and such that the multiplexed signal has almost the same spectral characteristics as those of the original UWB pulse. The two WSTC techniques increase the data rate to four times that of the conventional STC. The first WSTC scheme increases the data rate with a simple combination process. The second scheme achieves the increase in the data rate with a less complex receiver and better performance than the first scheme due to the spatial diversity introduced by the structure of its transmitter and receiver. The two schemes use Rake receivers to collect the energy in the dense multipath channel components. The simulation results show that the proposed WSTC schemes have better performance than the conventional scheme in addition to increasing the data rate to four times that of the conventional STC scheme.

Polarimetric Distance-Dependent Models For Large Hall Scenarios

A comprehensive polarimetric distance-dependent model of the power delay profile (PDP) and path gain is proposed. The model includes both specular multipath components (SMCs) and dense multipath components (DMC), the latter being modeled with an exponential and power law. The parameters of the model were estimated from polarimetric measurements of a large hall radio channel under line-of-sight (LOS) conditions at 1.3 GHz with a dedicated procedure. The validity and robustness of the proposed approach are provided by the good agreement between the polarimetric data and models for the investigated transmitter–receiver distance range. Furthermore, the description of the radio channel with path loss models is discussed for cases where the DMC is included, and a two-step method to compute the path loss characteristics directly from the measured data is developed. The results of this contribution highlight the fact that a complete polarimetric description of all propagation mechanisms and related path loss models is desired to design faithful polarimetric radio channel models.

Polarization Properties of Specular and Dense Multipath Components in a Large Industrial Hall

This paper presents a comprehensive analysis of the polarization characteristics of specular and dense multipath components (SMC and DMC) in a large industrial hall based on frequency-domain channel sounding experiments at 1.3 GHz with 22-MHz bandwidth. Twenty-nine positions were measured under line-of-sight (LOS) and obstructed LOS (OLOS) scenarios. The RiMAX maximum-likelihood estimator is used to extract the full-polarimetric SMC and DMC from the measurement data by taking into account the polarimetric radiating patterns of the dual-polarized antennas. Cross-polar discrimination (XPD) and copolar ratio (CPR) values are presented from the measured and de-embedded channels, as well as the polarimetric delay and angular spread distributions. Strong de-embedded SMC depolarization is obtained for the horizontal polarization in OLOS scenarios. Additionally, DMC depolarization is observed to be weaker than previously reported for indoor environments but constant across LOS/OLOS, polarization, and distance. The results also show that the copolar (cross-polar) DMC power to total channel power ratio is equal to 15% (40%) for LOS and 40% (60%) for OLOS and that this ratio does not correlate significantly with transmitter-receiver distance. Finally, the validity of the room electromagnetics theory was confirmed for transmitter-receiver distances larger than 15 m with no significant difference between polarized subchannels.

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.

Experimental Analysis of Dense Multipath Components in an Industrial Environment

This work presents an analysis of dense multipath components (DMC) in an industrial workshop. Radio channel sounding was performed with a vector network analyzer and virtual antenna arrays. The specular and dense multipath components were estimated with the RiMAX algorithm. The DMC covariance structure of the RiMAX data model was validated. Two DMC parameters were studied: the distribution of radio channel power between specular and dense multipath, and the DMC reverberation time. The DMC power accounted for 23% to 70% of the total channel power. A significant difference between DMC powers in line-of-sight and nonline-of-sight was observed, which can be largely attributed to the power of the line-of-sight multipath component. In agreement with room electromagnetics theory, the DMC reverberation time was found to be nearly constant. Overall, DMC in the industrial workshop is more important than in office environments: it occupies a fraction of the total channel power that is 4% to 13% larger. The industrial environment absorbs on average 29% of the electromagnetic energy compared to 45%-51% for office environments in literature: this results in a larger reverberation time in the former environment. These findings are explained by the highly cluttered and metallic nature of the workshop.

Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations - including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor - as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.

The COST 2100 MIMO channel model

The COST 2100 channel model is a geometry- based stochastic channel model (GSCM) that can reproduce the stochastic properties of MIMO channels over time, frequency, and space. In contrast to other popular GSCMs, the COST 2100 approach is generic and flexible, making it suitable to model multi-user or distributed MIMO scenarios. In this article a concise overview of the COST 2100 channel model is presented. Main concepts are described, together with useful implementation guidelines. Recent developments, including dense multipath components, polarization, and multi-link aspects, are also discussed.

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.