TABLE OF CONTENTS In earlier chapters, we provided a guide to the design of communications receivers in accordance with the present state of the art. Page constraints have made it necessary to limit coverage in some areas, and at best, a book represents the situation at the time the manuscript was prepared. In this chapter, we touch on related areas of receiver design that we have not been able to cover in depth previously. In particular, we discuss three areas:
Expanded digital implementation of receiver functions
Spread-spectrum receivers
The use of system simulation in design
The development of advanced integrated circuits has made digital logic functions relatively cheap and reliable, allowing complete microprocessor systems to be built on a single chip. This has led to the widespread replacement of analog circuits in communications receivers with digital-processing circuits. Techniques for performing filtering, frequency changing, demodulation, error correction, and many other functions have been developed, and have been touched upon in earlier chapters.
Digital processing has a number of inherent advantages over analog processing. Greater accuracy and stability frees digital circuits from the drifts caused by temperature, humidity, pressure, and supply voltage changes. The possibility of long-time storage of signal samples makes repeated processing of the same data for more accurate detection and demodulation feasible. The economy of small-size but large-scale digital implementation makes practical optimum detection and decoding techniques that were once only theorists' dreams.
While there are many advantages to digital processing,...
