Ultra-Wideband Wireless Channels - Estimation, Modeling and Material Characterization

Abstract

This licentiate thesis is focused on the characterization of ultra-wideband wireless

channels. The thesis presents results on ultra-wideband communications

as well as on the ultra-wideband characterization of materials.

The communications related work consisted in the measurement and modeling

of outdoor scenarios envisioned for infostation systems. By infostation,

we mean a communication system covering a small area, i.e., ranging up to 20

m, where mobile users can pass by or stop while receiving large amounts of

data in a short period of time. Considering the expected (but perhaps overly

optimistic) 480 Mbps for UWB systems, it should be possible to download a

complete DVD in roughly two minutes, which is something not realizable with

any of the current wireless technologies. Channel models, commonly based on

measurements, can be used to evaluate the performance of such systems. We

therefore, we started by performing measurements at one of the scenarios where

infostation systems can exist in the future, namely, petrol stations. The idealized

model, was one that could correctly describe the continuous evolution of

the channel impulse response for a moving user within the system’s range, and

therefore it was deemed necessary to track the multipath components defining

the impulse responses along a path of several meters. To solve this problem we

designed a novel high-resolution scatterer detection method, which is described

in Paper I, capable of tracking individual multipath components for a moving

user by identifying the originating point scatterers in a two dimensional geometrical

space. The same paper also gives insight on some properties of clusters

of scatterers, such as their direction-selective radiated power.

The scatterer detection method described in Paper I provided us with the

required tools to create the channel model described in Paper II. The proposed

channel model has a geometrical basis, i.e., each realization of the channel is

based on a virtual map containing point scatterers that contribute to the impulse

response by multipath components. Some of the particular characteristics

of the model include non-stationary effects, such as shadowing and cluster’s visibility

regions. At the end of Paper II, in a simple validation step, the output of the channel model showed a good match with the measured impulse responses.

The second part of our work, documented in Paper III, consisted on the dielectric

characterization of soil samples using microwave measurements. This

project was made in cooperation with the Department of Physical Geography

and Ecosystem Analysis at Lund University, which had been developing

research work on methane emissions from the wetlands in Zackenberg, Greenland.

In recent years, a lot of attention has been put into the understanding

of the methane emissions from soils, since methane is a greenhouse gas 20

times stronger than carbon dioxide. However, whereas the methane emissions

from natural soils are well documented, the reason behind this effect is an

open issue. The usage of microwave measurements to monitor soil samples,

aims to address this problem by capturing the sub-surface changes in the soil

during gas emissions. An experiment consisting on the monitoring of a soil

sample was performed, and a good correlation was found between the variations

of the microwave signals and the methane emissions. In addition, the soil

dielectric constant was calculated, and from that, the volumetric fractions of

the soil constituents which provided useful data for the elaboration of models

to describe the gas emission triggering mechanisms.

Based on this laboratory experiment, a complete soil monitoring system

was created and is at the time of writing running at Zackenberg, Greenland.

• author: Santos, Telmo
• supervisor: Andreas Molisch; Fredrik Tufvesson
• organization: Department of Electrical and Information Technology; Radio Systems-lup-obsolete (research group)
• publishing date: 2009
• type: Thesis
• publication status: published
• subject: Electrical Engineering, Electronic Engineering, Information Engineering
• keywords: Ultra-wideband, channel modeling, channel parameter estimation, material characterization, microwave measurements
• pages: 142 pages
• language: English
• LU publication?: yes
• id: 146da99f-0306-499a-b65e-b92629192841 (old id 1479808)
• date added to LUP: 2016-04-01 14:49:35
• date last changed: 2018-11-21 20:30:32