TABLE OF CONTENTS The information transmitted over an RF communications link consist in signals conveyed from one user to another via telephone, video telephone, via facsimile, telex, data, packets, radio and PC terminals and via television cameras and receivers. Such signals are called baseband signals, which consist in basic electrical impulses carried by the radio path of a satellite or via other communication networks. If the baseband signal is analog, the voltage which represents it can take any value within a given range but if the signal is digital, the voltage takes discrete values within a given range.
The type of baseband signals are determined by the communication requirements of the final users and the nature of the network. The main types of baseband used in MSS are voice (Tel), Fax and Tlx signals on Tel channels, then data, video and image signals. The baseband signals of mobile broadcast satellite services consist in direct TV (television) and sound transmissions, while in a broadband wireless or satellite service baseband the signal is IT Internet and multimedia, such as data, video retrieval and image transfer.
Each of these radio signals has to be arranged in a form suitable for transmission over some physical layer (air or wire) and such a technique is called baseband signal processing. The modified baseband signal is then superimposed onto a higher frequency carrier wave, when the signal modulates the carrier to a value suitable for propagation over the many different transmission links, such as radio, satellite, etc.
