Radio Wave Propagation in Metal Train Compartments

Abstract

Wireless sensor networks are being deployed extensively to collect sensory data in various environments under different conditions. A wireless sensor network consists of multiple nodes, each with the ability to communicate using radio waves. The characteristics of the radio link between nodes are largely influenced by their environment. For instance, a radio link between two nodes with obstructed line-of-sight behaves more erratic than one that is not obstructed. This thesis focuses primarily on the characteristics of radio wave propagation in metal train compartments from a Computer Science standpoint. It means that the electrical aspects of this subject are not discussed in detail. In this work, we focus mainly on matters such as transmission output power, signal strength, preamble length, and packet reception rate. Various tests were performed throughout the length of the project. The purpose of the tests was to gain insights on the characteristics of radio wave propagation under various circumstances. We examine the effect exerted on radio wave propagation by varying transmission output power, antenna orientation, and antenna position. The characteristics reported in this thesis are signal strength, preamble length, and packet reception rate. The tests were carried out in an open field and in metal train compartments. The open field tests were used to create benchmark data for which data from metal train compartments could be compared with. The tests have led to several important findings. They show that radio links could be established within metal train compartments and even between two compartments. The latter seems to contradict rational belief that radio waves cannot propagate from one train compartment to the other, because of the metallic structure. Furthermore, there are some indications that antenna orientation may greatly influence radio wave propagations in compartments for low transmission output powers. This thesis also examines the preamble length. It finds that the preamble length could potentially be reduced to two bytes without affecting packet reception rates. And finally, the results show that higher transmission output power leads to greater packet reception rates and stronger received signal strengths, regardless of the environment. These and other findings are discussed in detail in the remainder of this thesis.