TABLE OF CONTENTS Analog transmission is characterized by processing performed on the baseband signal before and after modulation in order to improve the quality of the link. The carrier can support only one or few channels for the transmission of baseband signals. In the case of a carrier transmitted from the station representing only a single user channel, this is Single Channel Per Carrier (SCPC) transmission. On the other hand, if the carrier represents a number of multiplexed users, it is designated Multiple Channel Per Carrier (MCPC) and use several channels is Frequency Division Multiplexing (FDM) transfer.
A signal needs to be impressed on an RF carrier for transmission through the satellite and for this purpose uses a process known as modulation. The objective of any communications is to transmit the modulated carrier to Rx as reliably as possible, so that the demodulated signals can be satisfactorily recovered. In analog transmission systems, the information waveform in the form of voice, data or video signal are modulated directly from the source onto the carrier at the modulator of Tx, by using methods of Amplitude (AM), Frequency (FM) and Phase Modulation (PM). Frequency and phase modulation are used most widely for direct analog transmission in satellite communications, while amplitude modulation is a process used indirectly in the satellite link.
Modulation may also be used at very low frequencies, like the more common and various forms of Phase Shift Keying (PSK). In addition, modulation is often done on a carrier with an RF...
