Experimental analysis of multidimensional radio channels

In this thesis new systems for radio channel measurements including space and polarization dimensions are developed for studying the radio propagation in wideband mobile communication systems. Multidimensional channel characterization is required for building channel models for new systems capable of exploiting the spatial nature of the channel. It also gives insight into the dominant propagation mechanisms in complex radio environments, where their prediction is difficult, such as urban and indoor environments. The measurement systems are based on the HUT/IDC wideband radio channel sounder, which was extended to enable real-time multiple output channel measurements at practical mobile speeds at frequencies up to 18 GHz. Two dual-polarized antenna arrays were constructed for 2 GHz, having suitable properties for characterizing the 3-D spatial radio channel at both ends of a mobile communication link. These implementations and their performance analysis are presented. The usefulness of the developed measurement systems is demonstrated by performing channel measurements at 2 GHz and analyzing the experimental data. Spatial channels of both the mobile and base stations are analyzed, as well as the double-directional channel that fully characterizes the propagation between two antennas. It is shown through sample results that spatial domain channel measurements can be used to gain knowledge on the dominant propagation mechanisms or verify the current assumptions. Also new statistical information about scatterer distribution at the mobile station in urban environment is presented based on extensive real-time measurements. The developed techniques and collected experimental data form a good basis for further comparison with existing deterministic propagation models and development of new spatial channel models.reviewe

Directional propagation channel estimation and analysis in urban environment with panoramic photography

International audienceThis article aims to provide readers with a physical understanding of the propagation channel that is complementary to mathematical channel modeling. It presents an analysis of the directional propagation channel based on radiophotos. Radiophotos are graphical objects where directions of arrival are superimposed on three-dimensional (3D) panoramic photographs.The interaction between electro magnetic waves and the environment is immediately identified with these representations. This paper focuses on the direction of arrival at mobile in an urban macrocell environment. The first radiophoto collection illustrates the major propagation phenomena such as reflection, diffraction, or street canyoning. The second collection illustrates typical propagation channel profiles that are classified according to delay, azimuth, and elevation spread values. The paper also describes an original panorama-based method for estimating noise level in the azimuth–elevation domain

Metal surface tolerant conformal low-profile plastic embedded antennas for automotive applications

Mit der rasanten Zunahme drahtloser Dienste und dem Einsatz von Antennendiversitätstechniken zur Erzielung höherer Datenraten oder Dienstzuverlässigkeit ist die Zahl der in Pkw zu installierenden Antennen nicht mehr unbedeutend und nimmt weiter zu. Gleichzeitig wird es immer schwieriger, geeignete Montageplätze für diese Antennen zu finden, da die Zahl der Montageplätze im Auto nicht parallel zur Zahl der zu installierenden Antennen gewachsen ist; Autos sind nach wie vor meist Metallkästen, mit einigen wenigen Kunststoffteilen und Glasscheiben die die Integration von Antennen ermöglichen. Die meisten dieser Teile wurden bereits zu diesem Zweck verwendet, die B-Säulen-Kunststoffabdeckungen wurden jedoch bisher nicht für die Antennenintegration berücksichtigt. In dieser Arbeit werden nicht nur die Vorteile der B-Säulen-Kunststoffabdeckungen als Antenneneinbauort gegenüber anderen Orten hervorgehoben, sondern auch die damit verbundenen Herausforderungen untersucht, insbesondere der begrenzte Platz für die Antennenintegration und die unmittelbare Nähe der eingebauten Antenne zum Metallchassis des Fahrzeugs. Letzteres führt zu einer starken elektromagnetischen Kopplung zwischen der Antenne und der Fahrzeugkarosserie, was sich auf die Antenneneigenschaften wie Impedanzanpassung und realisierten Gewinn auswirkt. In den folgenden Kapiteln werden die zugrundeliegenden Entwurfsprinzipien, die Theorie und die Messungen neuartiger, flacher, konformer und metalloberflächentoleranter Mobilfunkantennen vorgestellt, nämlich die Einzelband-Di-Patch-Antenne und eine koplanar gestapelte, mit Mikrostreifenleitungen gekoppelte Multibandantenne, die die oben genannten Herausforderungen adressieren und überwinden. Zusätzlich wird in der zweiten Hälfte dieser Arbeit eine high impedance surface basierte Dipolantennenlösung vorgestellt. Die Simulations- und Messergebnisse der nicht integrierten und der integrierten Versionen der vorgestellten Antennen, einschließlich der LTE-MIMO-Datenratenmessungen, die im vorletzten Kapitel vorgestellt werden, sprechen nicht nur für die Eignung dieser Antennen für flache, metallnahe Oberflächenanwendungen im Allgemeinen, sondern zeigen auch, dass die B-Säulen- Kunststoffabdeckungen einen sehr geeigneten neuen Antennenintegrationsort für mobile Kommunikationsanwendungen im Automobil darstellen.With a rapid increase in the number of wireless services, and the utilization of antenna diversity techniques to achieve enhanced data rates or service reliability, the number of antennas that need to be installed in passenger cars is not insignificant any more, and only sees a rising trend. At the same time, finding suitable mounting locations for these antennas has become ever more challenging, because the number of such locations on a car has not grown parallelly to the number of antennas that need to be installed; cars are still mostly metal boxes, with a few plastic parts and the glass windows that allow for antenna integration. While most of these parts have already been utilized for embedding antennas, the plastic parts that were overlooked till now were the B-column plastic covers. In addition to highlighting the advantages of using the B-column plastic covers as an antenna embedding location over other locations, this work takes a comprehensive look into the challenges associated with the same, specifically the limited space for antenna integration and the close proximity of the embedded antenna to the car metal chassis. The latter introduces a strong electro- magnetic coupling between the antenna and the car body, consequently impacting antenna properties like impedance matching and realized gain. The upcoming chapters present the underlying design principles, theory, and measurements of novel, low-profile, conformal and metal surface tolerant mobile communications antennas, namely, the single band di-patch antenna and a co-planar stacked microstrip line coupled multi-band antenna, that suitably address and overcome the aforementioned challenges. Additionally, a high impedance surface based dipole antenna solution is also presented in the later half of this thesis. The simulation and measurement results of the bare and the integrated versions of the presented antennas, including LTE-MIMO data rate measurements presented in the penultimate chapter, not only speak for the suitability of these antennas for low-profile, close-to-metal surface applications in general, but also show that the B-column plastic covers present a highly suitable new antenna integration location for automotive mobile communications applications

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

Characterization, modeling and simulation of the MIMO propagation channel

International audienceThis article deals with several aspects relative to the MIMO propagation channel. Based on simulations and/or measurements, different approaches are used to model the propagation channel. These models are useful for the MIMO system design. Several studies are performed in order to realize realistic simulation of MIMO channel. Different measurement techniques are used in characterizing the propagation channel in various environments. Measurement campaigns made in different situations have been analyzed to obtain the relevant statistical parameters of the channel. Simulation of MIMO channel is then presented. Measurement and simulation results provide an evaluation of the capacity of MIMO channel. Obtained results show feasibility in the integration of MIMO techniques in practical wireless communication systems.Cet article traite de plusieurs aspects relatifs au canal de propagation MIMO. Différentes approches, basées sur des simulations et des mesures, utilisées pour modéliser le canal sont d’abord présentées. Ensuite, les différentes techniques de mesure utilisées dans le but de caractériser le canal de propagation dans divers milieux sont décrites. Des campagnes de mesures effectuées dans différents environnements sont analysées pour obtenir les paramètres statistiques du canal. Quelques problématiques liées à la simulation du canal MIMO sont évoquées notamment en lien avec une simulation réaliste dans des milieux complexes. Les résultats obtenus, en simulation comme en mesure, permettent une évaluation de la capacité du canal MIMO. Ces résultats permettent de discuter de l’intégration des techniques MIMO dans des systèmes de communication sans fil