Resource Management in Satellite Networks part 4. This book provides significant knowledge on innovative radio resource management schemes for satellite communication systems that exploit lower layer adaptivity and the knowledge of layer 3 IP QoS support and transport layer behavior. The book integrates competencies considering all the parts of system design: propagation aspects, radio resource management, access protocols, network protocols, transport layer protocols, and more, to cover both broadband and mobile satellite systems | Chapter 1 INTRODUCTION TO SATELLITE COMMUNICATIONS 7 of significant signal impairment in the presence of bad wheatear conditions . rain . A transponder is a receiver-transmitter unit on a communication satellite. It receives a signal from the Earth uplink manages it and retransmits it back to Earth at a different frequency downlink . A satellite has several transponders in its payload. Two different types of transponders can be distinguished as follows Bent-pipe transponder . the transponder acts as a simple repeater . On board the signal is simply amplified and retransmitted but there is no improvement in the signal-to-noise ratio since also background noise is amplified. Regenerating transponder a transponder demodulates and decodes the received signal thus performing signal recovery before retransmitting it. Since at some point base-band signals are available other activities are also possible such as routing and beam-switching in case of multi-beam satellite antenna . Satellites with regenerating transponders and on board processing capabilities can also employ Inter-Satellite Links ISLs with other satellites of the same constellation thus permitting the routing of the signal in the sky. It is important to provide here some interesting data for current state-of-the-art GEO satellites. The Astra 1H satellite has 32 transponders with 24 32 MHz bandwidth total bandwidth of 1 GHz . Each transponder has a traffic capacity of 25-30 Mbit s. The AmerHis satellite 51 transponders has a hybrid payload with 4 channels each with 36 MHz for a total capacity of 174 Mbit s. Moreover there is a DVB-RCS transponder that can manage up to 64 carriers each with Mbit s and a DVB-S transponder with a capacity of 54 Mbit s see the following Section for more details on DVB-RCS and DVB-S systems. Tables and below provide a survey of some satellite communication systems that are currently operational or planned 8 9 for the definition of the different access .
