Overview

Early satellite communication systems, primarily fixed and later mobile networks used the analog transmission technique. Although modern MSC networks are still using the analog technique, the rapid development of high-speed digital mobile equipment is fostering a trend toward completely digital MSC. This chapter includes techniques and technology that enable signals to be sent from one user to another and vice versa via satellites and LES.

There are several methods of modulation, multiplexing and multiple access techniques used in MSC and their reverse processes, with some overlapping. Modulation is the process by which the baseband signal in EM form can be impressed upon a carrier, so Phase (PM) and Frequency (FM) modulations are used heavily in satellite communications because of their positive ability to deal with nonlinear distortion, noise and interference. The amplitude of the PM and FM carrier is held constant, so there is no apparent change in the power level. Most nonlinear distortion is the result of amplitude variations on the carrier, while PM and FM is able to perform better in this environment than Amplitude Modulation (AM), so because of that problem there is a major limitation in directly using AM for MSC.

Multiplexing and multiple access require sharing the resources of the satellite. Facilities are shared based on spectrum assignment (frequencies), by time sharing (time domain) and by spatial separation (antenna beam and polarization). Theoretically, any method can be used for the transmission of analog and digital signals. In practice, frequency is easier used with analog...