Advanced System Design of In-Building Wireless Communication Networks Using Ventilation Ducts

This thesis describes techniques to successfully design an IEEE 802.11g wireless system that uses ventilation ducts to distribute the signals throughout the building. To describe these techniques we present a wide array of measurements that have been performed on test duct networks, but setup in a laboratory and in buildings. We present trials of different duct modifications and antenna excitations we have tried, chronicling how to best install wireless local area network equipment in ventilation ducts. Using the installation techniques we developed, we present measurements of the pathloss through different duct networks in two dif ferent buildings in Stavanger and Oslo, Norway. Using our measurements we develop a model of propagation that predicts power levels inside a building based on only the duct locations. A rigorous calculation of propagation through the ducts would require detailed modeling of mode scattering at each component in the path. Since our goal was to develop reasonable prediction tools that do not require burdensome collection of detailed information about duct structure, we have chosen to develop an empirical model with parameters based on a physical understanding of the system. By describing this model and the accuracy of its use, we show that the model can be used reliably for designing a ventilation duct wireless distribution system. In fact, we present the design and performance of a building with a fully functional ventilation duct based IEEE 802.11g network. Our design covers a three story, 2000 square meter building. We fully characterize this design both with signal strength measurements and throughput performance measurements. As part of these measurements we present a simple technique for estimating the throughput present at particular locations in a building. In addition to describing how to design a ventilation duct based wireless system, we explore several techniques for improving channel statistics and capacity in such a system. We present a novel antenna array that can be used to excite two dif ferent, single modes in a common type of ventilation duct. We also present some antenna array diversity measurements that show diversity can be an ef fective technique for improving the performance of IEEE 802.11b communications transmitted through a ventilation duct. Further, we consider an extensive array of antenna array techniques utilizing time-reversal focusing methods. We first demonstrate that time-reversal can be used at microwave frequencies, something not known prior to this work. We then show that time-reversal focusing and time-reversal nulling techniques can be effective in ventilation ducts, though some techniques, antennas and duct configurations work better than others. We present the theoretical system capacity of some of these antenna and duct configurations. Lastly, as evidence that the time-reversal techniques are not just smoke and mirrors, we demonstrate both eigenvector diagonalization based MIMO and time-reversal based communications through ventilation duct channels. These demonstrations use actual frequency shift keying and IEEE 802.11g data transmissions to show that the techniques can substantively improve ventilation duct communications.