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C h a p t e r
AM, FM, AND DIGITAL
MODULATED SYSTEMS
CHAPTER OBJECTIVES
• Amplitude modulation and single sideband
• Frequency and phase modulation
• Digital audio broadcasting
• Digitally modulated signals (OOK, BPSK, FSK, MSK, MPSK, QAM,
QPSK, p>4QPSK, and OFDM)
• Spread spectrum and CDMA systems
This chapter is concerned with the bandpass techniques of amplitude modulation (AM), singlesideband
(SSB), phase modulation (PM), and frequency modulation (FM); and with the digital
modulation techniques of on–off keying (OOK), binary phase-shift keying (BPSK), frequencyshift
keying (FSK), quadrature phase-shift keying (QPSK), quadrature amplitude modulation
(QAM) and orthogonal frequency-division multiplexing (OFDM). All of these bandpass signaling
techniques consist of modulating an analog or digital baseband signal onto a carrier. This approach
was first introduced in Sec. 4–2. In particular, the modulated bandpass signal can be described by
s(t) = Re{g(t) jv ct }
(5–1)
where v c = 2p
f c and f c is the carrier frequency. The desired type of modulated signal, s(t), is
obtained by selecting the appropriate modulation mapping function g[m(t)] of Table 4–1,
where m(t) is the analog or digital baseband signal.
The voltage (or current) spectrum of the bandpass signal is
S(f) = 1 2 [G(f - f c) + G*(-f -f c )]
(5–2a)
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