TABLE OF CONTENTS In the next few years digital transmission techniques are going to spread throughout national and international satellite networks. The introduction of digital earth station satellite systems creates new problems of connection with terrestrial networks; since many of these are analog systems, provision has to be made for analog-to-digital conversion.
In this chapter analog-to-digital (A/D) and digital-to-analog (D/A) conversion techniques of audio, television, and frequency-division-multiplexed (FDM) signals are reviewed. Due to the relatively long propagation delay of satellite systems, the effect of voice echo is annoying to the user. For this reason, recently developed echo suppression and cancellation subsystems are described in Section 2.4. Afterward, we study a technique known as digital speech interpolation (DSI) and show that modern DSI equipment doubles the capacity of the transmission system. The last two sections of this chapter deal with digital noninterpolated interface (DNI) systems and energy dispersal (scrambling) techniques. An important function of DNI systems is to provide a means to interface between two digital links which might be on different continents and have plesiochronous operation of reference clocks (they have the same nominal frequency, but are independent within a frequency tolerance). DNI systems also remove the effects of the variations of propagation time of the satellite link. The digital energy dispersal equipment reduces the variations in the transmitted power spectrum, irrespective of any patterns in the information pulse train.
Signal processing and multiplexing is a large...
