Dear Reader, Thank you for investing your time into this book devoted to the fascinating world of Digital Satellite Communications. This is an Edited book which possesses some peculiarities that we believe make it different from other books of the kind. In fact, this book is the result of the joint effort of some sixty co- Authors who took part to a common European Research Project, named SatNEx, i.e. the European Network of Excellence (NoE) in Satellite Communications. This NoE is an instrument funded by the European Commission under the sixth Framework Programme (FP6), within the thematic priority Mobile and Wireless Systems beyond 3G of the Information Society and Technology (1ST) area. In brief, the objectives of the SatNEx NoE are the integration of knowledge and facilities, the pursuit of jointly executed research, and the spreading of excellence beyond the boundary of the SatNEx community. Within SatNEx, several joint activities have been launched on different areas of interest; among these, the Flexwave ]omi activity has been devoted to the study of all aspects related to the physical layer of a satellite communication system. This book is the output of two years of collaboration among the Flexwave partners.