Communication Fundamentals

The Hong Kong Polytechnic University

EIE331: Communication Fundamentals

File name: eie331 03am.pdf

CONTINUOUS-WAVE MODULATION SCHEMES:
AMPLITUDE MODULATION (AM)
• Double sideband amplitude modulation (DSB)
• Frequency spectrum and power relationships of the AM signal
• Modifications of amplitude modulation:
– Double sideband – suppressed carrier (DSB–SC)
– Vestigial sideband modulation (VSB)
– Single sideband modulation (SSB)
• Frequency-division multiplexing (FDM)
´
G´za KOLUMBAN — Dept. of Electronic and Information Engineering e 1

The Hong Kong Polytechnic University

EIE331: Communication Fundamentals

References for amplitude modulation:
Haykin: Sections 3.1–3.7, pp. 121–151
Sections 3.9, pp. 152–154
Lecture notes
Tutorial notes
Remark: Implementation and operation of
• envelope detector
• coherent detector will be discussed at the tutorial lecture.

´
G´za KOLUMBAN — Dept. of Electronic and Information Engineering e 2

The Hong Kong Polytechnic University

EIE331: Communication Fundamentals

CONTINUOUS-WAVE MODULATION
Continuous-wave (CW) modulation means that some characteristic of a sinusoidal carrier is varied in accordance with the message (modulating) signal.
Sinusoidal carrier: c(t) = a(t) cos[θi(t)] = a(t) cos[ωc(t)t + φc(t)] where ωc(t) = 2πfc(t)
1
i (t) where a(t), θi(t) and fi(t) = 2π dθdt are the instantaneous amplitude, phase and frequency, respectively, of the carrier

Varied characteristic:
• Amplitude ⇒ amplitude modulation (AM)
• Phase ⇒ phase modulation (PM)
• Frequency ⇒ frequency modulation (FM)
´
G´za KOLUMBAN — Dept. of Electronic and Information Engineering e 3

The Hong Kong Polytechnic University

EIE331: Communication Fundamentals

Reasons of modulation:
• Match the signal to the channel characteristics and increase the efficiency of information transmission.
Example: radio communications • Shift the frequency band occupied by the message signal.