0195136047.pdf

648 SIGNAL PROCESSING

x 1 (t)

x 2 (t)

x 3 (t)

x 1 (t)

x 2 (t)

x 3 (t)

Master

oscillator

Frequency

synthesizer

Transmission

medium

Input

signals

(a)

(b)

LPF

LPF

LPF

SSB

mod

SSB

mod

SSB

mod

Σ

64 kHz

68 kHz

72 kHz

Frequency

synthesizer

Output

signals

BPF

BPF

BPF

BPF

Demod

Demod

Demod

60-kHz pilot

Pilot

60–64 kHz

64–68 kHz

68–72 kHz

64 kHz

60-kHz pilot

68 kHz

72 kHz

f , kHz

(^060646872)
Figure 14.2.8(a)Simple FDM system.(b)Typical spectrum of multiplexed signal with pilot.
multiplexing. Integrated switching circuits have made the TDM implementation much simpler
than FDM.
EXAMPLE 14.2.2
Find the transmission bandwidth required of a data telemetry system that is to handle three different
signals with bandwidthsW 1 =1 kHz,W 2 =2 kHz, andW 3 =3 kHz, by employing:
(a) FDM with DSB subcarrier modulation.
(b) TDM with pulse durationD=Ts/6.
Solution
(a)B≥ 2 W 1 + 2 W 2 + 2 W 3 =12kHz.
(b)fs≥ 2 W 3 =6 kHz, soB≥ 1 /D= 6 fs≥36 kHz.