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

Étude de la capacité de la liaison descendante d'un réseau cellulaire Mimo à large bande

RÉSUMÉ Ce travail cherche à évaluer la capacité du lien descendant d'un réseau cellulaire MIMO à large bande dans des environnements urbain et sous-urbain. De nombreuses études se sont déjà penchées sur les performances des liaisons MIMO point-à-point tandis que celles qui ont cherché à estimer les performances d'un réseau cellulaire ont posé plusieurs hypothèses qui limitent la portée de leurs résultats. Ce projet se distingue par la modélisation de la corrélation du canal induite par les caractéristiques spatiales des réseaux d'antenne et aussi par la modélisation de la corrélation des paramètres à grande échelle entre les stations de base. L'influence du nombre d'antennes à la station de base et à la station mobile ainsi que l'influence de l'espacement des antennes sont étudiées en employant le modèle de canal Spatial Channel Model proposé par le 3GPP et le modèle de Kronecker. La dégradation causée par un renvoi partiel des statistiques de l'interférence à la station de base a aussi été étudiée. Les résultats ont montré que l'espacement entre les antennes à la station de base doit être maintenu à au moins une longueur d'onde et l'espacement au récepteur à au moins un quart de longueur d'onde pour éviter une perte de capacité importante dans l'environnement urbain. Dans l'environnement sous-urbain, l'espacement à la station de base doit être doublé afin de compenser un étalement angulaire plus faible. Si les antennes sont suffisamment écartées, la capacité varie linéairement avec le nombre de degrés de liberté comme pour un canal de Rayleigh point-à-point. Cependant, les résultats ont aussi montré que les caractéristiques spatiales ont une influence qui varie en fonction de la position de la station mobile. Concernant l'influence de la connaissance de l'état du canal au transmetteur, ce travail a permis d'établir que la connaissance partielle des statistiques de l'interférence conduit à une dégradation de moins de 3% des performances versus une connaissance complète du canal au transmetteur. ----------ABSTRACT The purpose of this work is to estimate the downlink capacity of a wideband MIMO cellular network in an urban and suburban environment. Previous works on MIMO focused mostly on point-to-point links while others studied MIMO cellular network under site-specific conditions or unrealistic assumptions. This research project is novel because it takes in consideration the channel correlation induced by the spatial characteristics of the multi-antenna arrays and the inter-site correlation between large scale parameters in a cellular network setup. The influence of the number of antenna at the base station and at the mobile stations as well as the influence of the multi-antenna arrays spacing are evaluated by using the 3GPP Spatial Channel Model and the Kronecker model. Moreover, the degradation of the performances caused by a partial feedback of the interference statistics is also examined. The results showed that antenna spacing must be maintained over one carrier wavelength at the base station and over one fourth of a wavelength at the mobile station to avoid a large capacity penalty in an urban environment. In a suburban environment, the spacing at the base station must be increased to two wavelengths to compensate a smaller angle spread. If the antennas are sufficiently spaced, the cell capacity increases linearly with the number of degrees of freedom as with point-to-point links in an uncorrelated Rayleigh channel. However, the results also showed that the influence of spatial characteristics depends on the mobile station location in the cell. Regarding the impact of channel state information at the transmitter, the simulations suggest that interference covariance information at the transmitter has little influence on the performances