TABLE OF CONTENTS Chapters 6 and 7 presented studies of the characteristics of fading based on envelope and phase. In this chapter, modulation schemes that can be used to counter the effects of multipath fading and time-delay spread in mobile-radio communication are discussed. In amplitude-modulated (AM) signaling, the information is contained in the envelope. During severe multipath fading, most of the amplitude information may be wiped out. One possible solution is to use a type of angle modulation. In FM signaling the noise or interference amplitude increases linearly with frequency; therefore the power spectrum of the noise will vary proportionately with the square of the frequency. This parabolic response on the power spectrum reflects the fact that input noise components that are close to the carrier frequency are suppressed.
Digital modulation techniques are also discussed in this chapter, and the difference in error rates between nonfading and fading cases is shown. Spread-spectrum modulation techniques are also discussed, since these modulation techniques have military as well as civilian applications. Finally, a new concept of using a modified SSB system is briefly introduced.
