Angular dispersion of radio waves in mobile channels

Multi-antenna techniques are an important solution for significantly increasing the bandwidth efficiency of mobile wireless data transmission systems. Effective and reliable design of these multi-antenna systems requires thorough knowledge of radiowave propagation in the urban environment. The aim of the work presented in this thesis is to obtain a better physical understanding of radiowave propagation in mobile radio channels in order to provide a basis for the improvement of radiowave propagation prediction techniques for urban environments using knowledge from 3-D propagation experiments and simulations combined with space-wave modelling. In particular, the work focusses on: the development of an advanced 3-D mobile channel sounding system, obtaining propagation measurement data from mobile radio propagation experiments, the analysis of measured data and the modelling of angular dispersive scattering effects for the improvement of deterministic propagation prediction models. The first part of the study presents the design, implementation and verification of a wideband high-resolution measurement system for the characterisation of angular dispersion in mobile channels. The system uses complex impulse response data obtained from a novel 3-D tilted-cross switched antenna array as input to an improved version of 3-D Unitary ESPRIT. It is capable of characterising the delay and angular properties of physically-nonstationary radio channels at moderate urban speeds with high resolution in both azimuth and elevation. For the first time, omnidirectional video data that were captured during the measurements are used in combination with the measurement results to accurately identify and relate the received radio waves directly to the actual environment while moving through it. The second part of the study presents the results of experiments in which the highresolution measurement system, described in the first part, is used in several mobile outdoor experiments in different scenarios. The objective of these measurements was to gain more knowledge in order to improve the understanding of radiowave propagation. From these results the dispersive effects in the angular domain, caused by rough building surfaces and other irregular structures was paid particular attention. These effects not only influence the total amount of received power in dense urban environments, but can also have a large impact on the performance and deployment of multi-antenna systems. To improve the data representation and support further data analysis a hierarchical clustering method is presented that can successfully identify clusters of multipath signal components in multidimensional data. By using the data obtained from an omnidirectional video camera the clusters can be related directly to the environment and the scattering effects of specific objects can be isolated. These results are important in order to improve and calibrate deterministic propagation models. In the third part of the study a new method is presented to account for the angular dispersion caused by irregular surfaces in ray-tracing based propagation prediction models. The method is based on assigning an effective roughness to specific surfaces. Unlike the conventional reflection reduction factor for Gaussian surfaces, that only reduces the ray power, the new method also distributes power in the angular domain. The results of clustered measurement data are used to calibrated the model and show that this leads to improved channel representations that are better matched to the real-world channel behavior

On geometry-base statistical channel models for MIMO wireles communications

El uso de sistemas de comunicación de banda ancha de múltiple entradamúltiple salida (Multiple Input Multiple Output MIMO) es actualmente objeto de un interés considerable. Una razón para esto es el reciente desarrollo de sistemas de comunicación móvil de tercera generación (3G) y superiores, tales como la tecnología de banda ancha Wideband Code Division Multiple Access (WCDMA, por sus siglas en inglés), la cual proporciona canales de radio de 5 MHz de ancho de banda. Para el diseño y la simulación de estos sistemas de radio móviles que usan propagación inalámbrica MIMO (como Wideband-CDMA por ejemplo), necesitamos modelos de canal que provean la requerida información espacial y temporal necesaria para el estudio de tales sistemas, esto es, los parámetros básicos de modelado en los dominios del espacio y el tiempo. Como ejemplo podemos mencionar, el valor cuadrático medio de la dispersión del retardo (Delay spread DS) el cual está directamente relacionado a la capacidad de un sistema de comunicación específico y nos da una idea aproximada de la complejidad del receptor. En esta tesis, se propone un modelo basado en geometría con enfoque en grupos (clusters) y es utilizado para el análisis en los dominios del espacio y el tiempo para condiciones estacionarias, y para representar los perfiles de potencia-angulo-retardo (Power Delay Angle Profiles PDAPs) de los componentes multi-trayectoria en ambientes urbanos. Además, se han derivado soluciones en formas cerradas para las expresiones en el dominio del ángulo (espacial) y del tiempo. La investigación previa sobre el modelado de canales cubre una amplia variedad de aspectos en varios niveles de detalle, incluyendo análisis para condiciones no estacionarias. Sin embargo el trabajo presentado en la literatura no incluye las relaciones entre los grupos (cluster) físicos y los PDAPs. El modelo propuesto basado en grupos (clusters) puede ser usado para mejorar aún más el desempeño en condiciones estacionarias de los sistemas de comunicaciones móviles actuales y futuros tales como los sistemas de comunicación MIMO de banda ancha. En la tesis también se presenta un análisis en el dominio del ángulo (espacial) y del tiempo respectivamente, a través de las funciones densidad de probabilidad (PDF) de la dirección de llegada (Direction of Arrival DOA) y el tiempo de llegada (Time of Arrival TOA) para el modelo basado en grupos. A fin de evaluar las funciones de probabilidad teóricas derivadas, éstas han sido comparadas con resultados experimentales publicados en la literatura. La comparación con estos resultados experimentales muestran una buena concordancia, no obstante la técnica de modelado presentada en esta tesis se encuentra limitada a condiciones estacionarias del canal. La condición de no estacionariedad se ubica más allá del alcance de esta tesis, es decir, el modelo propuesto no incorpora el efecto Doppler en los análisis

Dual-polarized spatial-temporal propagation measurement and modeling in uma o2i scenario at 3.5 GHz

Outdoor-to-indoor (O2I) coverage in urban areas by using the sub-6 GHz (sub-6G) band is important in the fifth generation (5G) mobile communication system. The spatial-temporal propagation characteristics in different polarizations in the 5G spectrum are crucial for the network coverage. In this paper, we measured the urban macrocell (UMa) O2I channels at 3.5 GHz in the space, time, and polarization domains simultaneously. The channel sounder utilized two ±45° polarized antenna arrays. The transmitter (TX) was placed on the rooftop of a five-storey building to emulate a base station and the receiver (RX) was moved in the corridors on different floors in another building to emulate user equipments (UEs). We obtained the small-scale parameters of excess delay, power, and azimuth/elevation of arrival (AoA/EoA) of individual multipath components (MPCs), the propagation profiles of azimuth/elevation power spectrum (APS/EPS) and power delay profile (PDP), and the large-scale parameters including azimuth/elevation spread of arrival (ASA/ESA) and delay spread (DS). Based on the measurement results, we propose the lifted-superposed Laplace distribution (LS-Laplace) function and lifted-superposed normal distribution (LS-Normal) function to model the APS and EPS, respectively, and a three-phase model for the PDP. We find that the ASA and ESA follow the lognormal distribution and the DS has a Rayleigh distribution. We also reveal the impact of surrounding environments and polarization on the channel propagation profiles and statistical characteristics. The measurement results and channel models in this paper provide reference for the design and deployment of the 5G system to exploit the spatial and polarization diversities in the UMa O2I scenario.This work was supported in part by the National Natural Science Foundation of China under Grant 61571370, Grant 61601365, and Grant 61801388, in part by the Key Research Program and Industrial Innovation Chain Project of Shaanxi Province under Grant 2019ZDLGY07-10, Grant 2019JQ-253, and Grant 2019JM-345, and in part by the China Postdoctoral Science Foundation under Grant BX20180262, Grant BX20190287, Grant 2018M641020, and Grant 2018M641019.Scopu

Modeling and characterization of urban radio channels for mobile communications

Results of this thesis contribute in modeling and characterization of radio channels for future mobile communications. The results are presented mainly in three parts: a) modeling of propagation mechanisms, b) methodology of developing a propagation model, c) characterization of urban radio channel. One of the main propagation physical phenomena that have an important role in diverting signals to non line of sight scenarios is the diffraction process. This thesis proposes diffraction coefficients that have better agreement with finite difference time domain solution and rigorous diffraction theory than the coefficient commonly used in propagation predictions for mobile communications. The importance of diffuse scattering has also been investigated and showed that this physical process may have a key role in urban propagation, with a particular impact on the delay spread and angular spread of the signal at the receiver. This thesis proposes wideband propagation models for main and perpendicular streets of urban street grids. The propagation models are ray-based and are given in explicit mathematical expressions. Each ray is characterized in terms of its amplitude, delay, and angle of arrival, angle of departure for vertical and horizontal polarizations. Each of these characteristics is given in a closed mathematical form. Having wideband propagation model in explicit expression makes its implementation easy and computation fast. Secondary source modeling approach for perpendicular streets has also been introduced in this thesis. The last part of the thesis deals with characterization of urban radio channels for extracting parameters that help in successful design of mobile communication systems. Knowledge of channel characteristics enables reaching optimum trade off between system performance and complexity. This thesis analyzes measurement results at 2 GHz to extract channel parameters in terms of Rake finger characteristics in order to get information that helps to optimize Rake receiver design for enhanced-IMT2000 systems. Finger life distance has also been investigated for both micro- and small cell scenarios. This part of the thesis also presents orthogonality factor of radio channel for W-CDMA downlink at different bandwidths. Characterization of dispersion metrics in delay and angular domains for microcellular channels is also presented at different base station antenna heights. A measure of (dis-) similarity between multipath components in terms of separation distance in delay and angular domains is introduced by the concept of distance function, which is a step toward in development of algorithm extraction and analysis multipath clustering. In summary, the significant contributions of the thesis are in three parts. 1) Development of new diffraction coefficients and corrections of limitations of existing one for accurate propagation predictions for mobile communications. 2) Development of wideband propagation models for urban street grid. The novelty of the model is the development in explicit mathematical expressions. The developed models can be used to study propagation problem in microcellular urban street grids. 3) Presenting channel parameters that will help in the design of future mobile communication systems (enhanced-IMT2000), like number of active fingers, finger life distance, and orthogonality factors for different bandwidths. In addition, a technique based on multipath separation distance is proposed as a step toward in development of algorithms for extraction and analysis of multipath clusters.reviewe

Millimeter wave and UWB propagation for high throughput indoor communications

Millimeter-wave systems at 60 GHz and ultra-wideband (UWB) systems in the microwave range of 3-10 GHz have been received with great interest for their high data rate wireless communications. In design, test and optimization of future wireless systems, channel models featuring the relevant characteristics of radiowave propagation are required. Furthermore, detailed understanding of the propagation channel and its interaction with system, creates insights into possible solutions. In this work, both theoretical (ray-tracing) and statistical models of the 60 GHz and UWB channels are studied. Propagation characteristics of the 60 GHz and UWB indoor channels are also compared for providing useful information on design of radio systems. More specifically, based on real-time channel sounder measurements performed in the 60 GHz band, propagation mechanisms including person blocking effect are concluded. Ray-based models in LOS and NLOS indoor corridors are proposed. Multipath power distributions in the 60 GHz band are studied first time. Moreover, propagation interdependencies of path loss, shadowing, number of paths, Rice K-factor and cross polarization discrimination (XPD) with channel delay spread are established. In the UWB propagation channel, frequency- and bandwidth- dependencies are investigated. Multipath and clustering propagation characteristics are analyzed. A new cluster model is proposed and compared with the classical Saleh-Valenzuela model for gaining more understanding of channel general properties. Finally, the performance and capacities of the 60 GHz UWB and MIMO (multiple-in and multiple-out) systems are analyzed for providing reliable parameters for system design and useful information for standardization groups

A Centralized Energy Management System for Wireless Sensor Networks

This document presents the Centralized Energy Management System (CEMS), a dynamic fault-tolerant reclustering protocol for wireless sensor networks. CEMS reconfigures a homogeneous network both periodically and in response to critical events (e.g. cluster head death). A global TDMA schedule prevents costly retransmissions due to collision, and a genetic algorithm running on the base station computes cluster assignments in concert with a head selection algorithm. CEMS\u27 performance is compared to the LEACH-C protocol in both normal and failure-prone conditions, with an emphasis on each protocol\u27s ability to recover from unexpected loss of cluster heads

Geometry-based Radio Channel Characterization and Modeling: Parameterization, Implementation and Validation

The propagation channel determines the fundamental basis of wireless communications, as well as the actual performance of practical systems. Therefore, having good channel models is a prerequisite for developing the next generation wireless systems. This thesis first investigates one of the main channel model building blocks, namely clusters. To understand the concept of clusters and channel characterization precisely, a measurement based ray launching tool has been implemented (Paper I). Clusters and their physical interpretation are studied by using the implemented ray launching tool (Paper II). Also, this thesis studies the COST 2100 channel model, which is a geometry-based channel model using the concept of clusters. A complete parameter set for the outdoor sub-urban scenario is extracted and validated for the COST 2100 channel model (Paper III). This thesis offers valuable insights on multi-link channel modeling, where it will be widely used in the next generation wireless systems (Paper IV and Paper V). In addition, positioning and localization by using the phase information of multi-path components, which are estimated and tracked from the radio channels, are investigated in this thesis (Paper VI). Clusters are extensively used in geometry-based stochastic channel models, such as the COST 2100 and WINNER II channel models. In order to gain a better understanding of the properties of clusters, thus the characteristics of wireless channels, a measurement based ray launching tool has been implemented for outdoor scenarios in Paper I. With this ray launching tool, we visualize the most likely propagation paths together with the measured channel and a detail floor plan of the measured environment. The measurement based ray launching tool offers valuable insights of the interacting physical scatterers of the propagation paths and provides a good interpretation of propagation paths. It shows significant advantages for further channel analysis and modeling, e.g., multi-link channel modeling. \par The properties of clusters depend on how clusters are identified. Generally speaking, there are two kinds of clusters: parameter based clusters are characterized with the parameters of the associated multi-path components; physical clusters are determined based on the interacting physical scatterers of the multi-path components. It is still an open issue on how the physical clusters behave compared to the parameter based clusters and therefore we analyze this in more detail in Paper II. In addition, based on the concept of physical clusters, we extract modeling parameters for the COST 2100 channel model with sub-urban and urban micro-cell measurements. Further, we validate these parameters with the current COST 2100 channel model MATLAB implementation. The COST 2100 channel model is one of the best candidates for the next generation wireless systems. Researchers have made efforts to extract the parameters in an indoor scenario, but the parameterization of outdoor scenarios is missing. Paper III fills this blank, where, first, cluster parameters and cluster time-variant properties are obtained from the 300~MHz measurements by using a joint clustering and tracking algorithm. Parameterization of the COST 2100 channel model for single-link outdoor MIMO communication at 300~MHz is conducted in Paper III. In addition, validation of the channel model is performed for the considered scenario by comparing simulated and measured delay spreads, spatial correlations, singular value distributions and antenna correlations. Channel modeling for multi-link MIMO systems plays an important role for the developing of the next generation wireless systems. In general, it is essential to capture the correlations between multi-link as well as their correlation statistics. In Paper IV, correlation between large-scale parameters for a macro cell scenario at 2.6 GHz has been analyzed. It has been found that the parameters of different links can be correlated even if the base stations are far away from each other. When both base stations were in the same direction compared to the movement, the large-scale parameters of the different links had a tendency to be positively correlated, but slightly negatively correlated when the base stations were located in different directions compared to the movement of the mobile terminal. Paper IV focuses more on multi-site investigations, and paper V gives valuable insights for multi-user scenarios. In the COST 2100 channel model, common clusters are proposed for multi-link channel modeling. Therefore, shared scatterers among the different links are investigated in paper V, which reflects the physical existence of common clusters. We observe that, as the MS separation distance is increasing, the number of common clusters is decreasing and the cross-correlation between multiple links is decreasing as well. Multi-link MIMO simulations are also performed using the COST 2100 channel model and the parameters of the extracted common clusters are detailed in paper V. It has been demonstrated that the common clusters can represent multi-link properties well with respect to inter-link correlation and sum rate capacity. Positioning has attracted a lot of attention both in the industry and academia during the past decades. In Paper VI, positioning with accuracy down to centimeters has been demonstrated, where the phase information of multi-path components from the measured channels is used. First of all, an extended Kalman filter is implemented to process the channel data, and the phases of a number of MPCs are tracked. The tracked phases are converted into relative distance measures. Position estimates are obtained with a method based on so called structure-of-motion. In Paper VI, circular movements have been successfully tracked with a root-mean-square error around 4 cm when using a bandwidth of 40 MHz. It has been demonstrated that phase based positioning is a promising technique for positioning with accuracy down to centimeters when using a standard cellular bandwidth. In summary, this thesis has made efforts for the implementation of the COST 2100 channel model, including providing model parameters and validating such parameters, investigating multi-link channel properties, and suggesting implementations of the channel model. The thesis also has made contributions to the tools and algorithms that can be used for general channel characterizations, i.e., clustering algorithm, ray launching tool, EKF algorithm. In addition, this thesis work is the first to propose a practical positioning method by utilizing the distance estimated from the phases of the tracked multi-path components and showed a preliminary and promising result