Wk3 Modulation

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Communication

Technologies

Modulation and Multiplexing

Week #3ICS620


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Overview

Frequency Spectrum

Modulation techniques Multiplexing--TDM vs FDM

Multiple Access Signal formats


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The Bands

VLF LF MF HF VHF UHF SHF EHF

Submillimeter

Range

ELF

3MHz 30MHz300MHz 3GHz 30GHz 300GHz

Far

Infra-

Red

300KHz30KHz 3THz

300mm

Radio Optical

3KHz

Near

Infra-

Red

700nm

1PetaHz

R

e

d

O

r

a

n

g

e

Y

e

l

l

o

w

G

r

e

e

n

B

l

u

e

I

n

d

i

g

o

V

i

o

l

e

t

600nm 400nm500nm

Ultraviolet

1ExaHz

X-Ray

1500nm


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Frequency Spectrum

Limited resource

Managed WARC

FCC

Bands


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Modulation Techniques

Amplitude Modulation

Frequency Modulation Phase Modulation

Pulse Modulation


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Amplitude Modulation

Uses a higher frequencycarrier

Most efficient use offrequency

Time and Frequency Domain Susceptible to Noise


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Most Efficient Use of

Frequency

Maximum frequency required

is: Twice baseband

Just baseband (specialconditions)


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Higher Frequency Carrier

Signal

Carrier

time

time


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Higher Frequency Carrier

Power Spectral Density

frequency

SignalCarrier

Baseband

watts


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Time Domain

Signal

Carrier

time

time


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Time Domain Continued

time


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Detection of Signal

time

time


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Frequency Domain

Unmodulated

frequency

SignalCarrier

Baseband

watts

Modulated

frequency

Signal

Carrier

Baseband

watts

Baseband


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Spectrum of AM signal


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Susceptible to Noise

time


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Carrier Signal

Oscillator

Information

Signal

Modulation

Device

Low-Power

Amplifier

Final Amplifier

Antenna

Simple block diagram of

AM modulation


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Single Sideband (SSB)

Variant of AM is single sideband (SSB) Sends only one sideband

Eliminates other sideband and carrier

Advantages Only half the bandwidth is required

Less power is required

Disadvantages Suppressed carrier cant be used for

synchronization purposes


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Frequency Modulation

Uses a higher frequency

carrier

Usually more bandwidth

Time and Frequency Domain

Resistant to some Noise


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Time Domain

Signal

Carrier

time

time


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Time Domain

time


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Frequency Domain

Unmodulated

frequency

SignalCarrier

Baseband

watts

Modulated

frequency

Signal

Carrier

watts


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Resistant to Some Noise

time


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Phase Modulation

Uses a higher frequencycarrier

Fairly efficient use offrequency

Time and Frequency Domain Used mainly for data

Ti D i


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Time Domain

(Instantaneous View)

Unmodulated Carrier

Modulated Carrier

Phase

Input


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Phase Shift Keying

Time Plot

0

O

90

O

180

O

270

O


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Pulse Modulation

Uses the sampling rate

PAM PDM, PWM

PPM PCM

S i h S li


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Starts with Sampling

Volts

time


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PAM

Volts

time

Pulse Amplitude Modulation


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PDM (a.k.a. PWM)

Volts

time

max = largest Positivemin = largest Negative

time

Pulse Duration Modulation (Pulse Width Modulation)


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PPM

Volts

time

max = largest Positive

min = largest Negative

time

Pulse Position Modulation


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Pulse Code Modulation

By quantizing the PAM pulse, originalsignal is only approximated

Leads to quantizing noise

Signal-to-noise ratio for quantizing noise

Thus, each additional bit increases SNR by6 dB, or a factor of 4

dB76.102.6dB76.12log20SNRdB nn


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PCM

Volts

time

time

01000 01000

8 8

-2

-9

-1

5

-7

10010 11001 10001 00101 10111

Pulse Code Modulation


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Multiplexing

Frequency Division

Multiplexing

Separate each basebandsignal into a discrete band

Uses AM-SSB/SC to positioneach baseband

F Di i i M lti l i


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Frequency Division Multiplexing1

2

3

4

frequency

frequency

frequency

frequency

frequency

1 2 3 4


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Multiplexing

Time Division Multiplexing

Separate each digitalbaseband into discrete time

slots

Cyclical in nature


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Time Division Multiplexing

1

2

3

4

Rotation Analogy


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FDMA


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FDMA

Frequency Division Multiple Access

F

requency

Time

Chan A

Chan B

Chan C

Chan D

TDMA


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TDMA

Time Division Multiple Access

F

requency

Time

Chan A

Chan B


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Summary

Frequency Spectrum

Modulation techniques--AM,

FM, Phase, and Pulse

Modulation

Multiplexing--TDM vs FDM

Wk3 Modulation

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