VSAT Networks ویرایش دوم

Книга посвящена сетям спутниковой связи построенным с применением терминалов с малой апертурой антенны (VSAT). Сети спутниковой связи состоят из нескольких элементов – Центральных управляющих станций, удаленных абонентских станций, геостационарных спутников (для сетей спутниковой связи работающих в ФСС (фиксированных сетях связи) сетях). Данное издание будет очень полезно для людей работающих в отрасли и студентов “спутниковых” специальностей.Доп. информация: Satellites for communication services have evolved quite significantly in size and power since the launch of the first commercial satellites in 1965. This has permitted a consequent reduction in the size of earth stations, and hence their cost, with a consequent increase in number. Small stations, with antennas in the order of 1.2–1.8 rn, have become very popular under the acronym VSAT, which stands for ’Very Small Aperture Terminals’. Such stations can easily be installed at the customer’s premises and, considering the inherent capability of a satellite to collect and broadcast signals over large areas, are being widely used to support a large range of services. Examples are broadcast and distribution services for data, image, audio and video, collection and monitoring for data, image
and video, two-way interactive services for computer transactions, data base inquiry, internet access and voice communications. The trend towards deregulation, which started in the United States, and progressed in other regions of the world, has triggered the success of VSAT networks for corporate applications. This illustrates that technology is not the only key to success. Indeed, VSAT networks have been installed and operated only in those regions of the world where demand existed for the kind of services that VSAT technology could support in a cost effective way, and also where the regulatory framework was supportive.
This book on VSAT networks aims at introducing the reader to the important issues of services, economics and regulatory aspects. It is also intended to give detailed technical insight on networking and radiofrequency link aspects, therefore addressing the specific features of VSAT networks at the three lower layers of the OSI Reference Layer Model for data communications. From my experience in teaching, I felt I should proceed from the general to the particular.
Therefore, Chapter 1 can be considered as an introduction to the subject, with rather descriptive contents on VSAT network configurations, services, operational and regulatory aspects. The more intrigued reader can then explore the subsequent chapters.
Chapter 2 deals with those aspects of satellite orbit and technology which influence the operation and performance of VSAT networks.
Chapter 3 details the operational aspects which are important to the customer. Installation problems are presented, and a list of potential concerns to the customer is explored. Hopefully, this chapter will not be perceived as discouraging, but on the contrary as a friendly guide for avoiding misfortunes, and getting the best from a VSAT network. The next two chapters are for technique oriented readers. Actually, I thought this would be a piece of cake for my students, and a reference text for network design engineers.
Chapter 4 deals with networking. It introduces traffic characterisation, and discusses network and link layers protocols of the OSI Reference Layer Model, as used in VSAT networks. It also presents simple analysis tools for the dimensioning of VSAT networks from traffic demand and user specifications in terms of blocking probability and response time.
Chapter 5 covers the physical layer, providing the basic radio frequency link analysis, and presenting the parameters that condition link quality and availability. An important aspect discussed here is interference, as a result of the small size of the VSAT antenna, and its related large beamwidth. Appendices are provided for the benefit of those readers who may lack some background and have no time or opportunity to refer to other sources.
The second edition of this book takes into account my experience while using the first edition as a support for my lectures. It incorporates some theoretical developments that were missing in the first edition, which constitute useful tools for the dimensioning and the performance evaluation of VSAT networks. In particular, Chapter 4 provides a more detailed treatment on how to evaluate blocking probability and expands on the information transfer delay analysis of the first edition. This second edition also underplays the regulatory aspects, as during the seven year interval between this second edition and the first, many administrations have simplified and harmonised their regulatory framework. I felt this topic was not perhaps as important as it used to be.
I would like to take this opportunity to thank all the students I have taught, at the Ecole Nationale Sup´erieure des T´el´ecommunications, the University of Surrey, CEI-Europe and other places, who, by raising questions, asking for details and bringing in their comments, have helped me to organise the material presented here.
G´erard Maral, Professor.