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

Diagnostic analysis of radio propagation in UMTS networks using high-resolution angle-of-arrival measurements

This work describes high-resolution propagation measurements performed as a diagnostic survey in an operational UMTS network. The results were obtained using the measurement system previously presented in. Measurements were performed in a dense urban environment in Amsterdam, the Netherlands. Results showed that the measurement approach can be used to create a setup that is similar to the actual network scenario, and that is capable of accurately identifying the dominant propagation effects while moving through the environment. The results are especially important for mobile-system operators, because they revealed some of the causes of inadequate propagation prediction. This underlined the limitations of propagation-prediction models currently used by most mobile-system operators, and the importance of accurate propagation information to obtain the optimal network configuration

Diagnostic analysis of radio propagation in UMTS networks using high-resolution angle-of-arrival measurements

This work describes high-resolution propagation measurements performed as a diagnostic survey in an operational UMTS network. The results were obtained using the measurement system previously presented in. Measurements were performed in a dense urban environment in Amsterdam, the Netherlands. Results showed that the measurement approach can be used to create a setup that is similar to the actual network scenario, and that is capable of accurately identifying the dominant propagation effects while moving through the environment. The results are especially important for mobile-system operators, because they revealed some of the causes of inadequate propagation prediction. This underlined the limitations of propagation-prediction models currently used by most mobile-system operators, and the importance of accurate propagation information to obtain the optimal network configuration

Angular dispersion of radio waves due to rough surface scattering in mobile channels

This paper describes the modelling of scattering caused by irregular surfaces as a basis for implementation in ray-tracing methods. An approach is presented in a first attempt to model the dispersive effects, caused by scattering on surfaces which have "random" irregularities, directly at the receiver. The method is based on assigning an effective stochastic roughness to a specific surface. The scattering effects caused by the surface roughness include the combined effects of both the surface irregularities and changes in material properties. The results of simulations and measurements show that the method can be used to model the dispersive effects of rough surface scattering in a manner similar to using the reflection reduction factor for Gaussian surfaces, except that the reduced power in the specular direction is distributed in the angular domain

Analysis of clustered multipath estimates in physically nonstationary radio channels

This paper presents the results of angle-delay measurements in physically nonstationary radio channels. The multidimensional estimation data are obtained using a recently developed 3-D high-resolution channel sounder. For a better analysis, a hierarchical whole clustering method is presented that organizes the multidimensional estimation data into clusters. Furthermore, estimation results are compared with results obtained from a 3-D deterministic propagation prediction tool. The clustering method proposed here was successfully applied to multi-dimensional estimation data. The results show that it is vital to cluster these data in order to be able to correctly interpret the measurement results. Compared to the measurements, a large number of multipath clusters are missing in the predictions. Furthermore, the multipath clusters obtained from the measurement data tend to have larger time and angular spreads than predicted