A comparison of different modulation techniques performances in an underground multiuser communications scenario

Abstract

The potential use of typical commercial communication systems with ultra high frequencies for the underground emergency/military situations will be investigated, as commercial systems have already a fully developed market that makes them cheap and reliable. The possible usage of broadband techniques like CDMA in the direct sequence will be studied because most commercial communication systems have already been designed to support multiple users, as the underground propagation has many possible applications. The performances of both modulation techniques are evaluated from the point of view of the quality of the signals, power spectral density and the effect that the propagation medium has on the transmitted signals such that the best modulation technique is determined. The 16QAM and QPSK modulations (two of the most popular modulation techniques in the terrestrial wireless system) are compared in a scenario where a number of underground sources share the same physical channel (and antenna) - the receiver is placed at the ground level so the generated signals must propagate through the dielectric layer in order to reach it. The transmitted power, electric and magnetic fields as well as occupied bandwidth are also calculated.