Communication Technologies Modulation and Multiplexing

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Communication TechnologiesModulation and
Multiplexing

• Week 3

ICS 620
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Overview

• Frequency Spectrum
• Modulation techniques
• Multiplexing--TDM vs FDM
• Multiple Access
• Signal formats

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The Bands
3MHz
30MHz
300MHz
3GHz
30GHz
300GHz
300KHz
30KHz
3THz
3KHz
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
ELF
Far Infra- Red
Submillimeter Range
Radio
Optical
300mm
1500nm
1PetaHz
1ExaHz
Near Infra- Red
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
Ultraviolet
X-Ray
700nm
600nm
400nm
500nm
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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 frequency carrier
• Most efficient use of frequency
• Time and Frequency Domain
• Susceptible to Noise

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Most Efficient Use of Frequency

• Maximum frequency required is
• Twice baseband
• Just baseband (special conditions)

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Higher Frequency Carrier
Signal
time
Carrier
time
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Higher Frequency Carrier
Power Spectral Density
watts
Carrier
Signal
frequency
Baseband
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Time Domain
Signal
time
Carrier
time
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Time Domain Continued
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Detection of Signal
time
time
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Frequency Domain
Unmodulated
watts
Carrier
Signal
frequency
Baseband
watts
Modulated
Carrier
Signal
frequency
Baseband
Baseband
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Spectrum of AM signal
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Susceptible to Noise
time
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Antenna
Carrier Signal Oscillator
Low-Power Amplifier
Final Amplifier
Information Signal
Modulation Device
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
time
Carrier
time
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Time Domain
time
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Frequency Domain
Unmodulated
watts
Carrier
Signal
frequency
Baseband
watts
Modulated
Carrier
Signal
frequency
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Resistant to Some Noise
time
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Phase Modulation

• Uses a higher frequency carrier
• Fairly efficient use of frequency
• Time and Frequency Domain
• Used mainly for data

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Time Domain (Instantaneous View)
Unmodulated Carrier
Modulated Carrier
Phase Input
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Phase Shift Keying
0O
90O
180O
270O
Time Plot
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Pulse Modulation

• Uses the sampling rate
• PAM
• PDM, PWM
• PPM
• PCM

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Starts with Sampling
Volts
time
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PAM
Pulse Amplitude Modulation
Volts
time
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PDM (a.k.a. PWM)
Pulse Duration Modulation (Pulse Width Modulation)
Volts
time
time
min largest Negative
max largest Positive
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PPM
Pulse Position Modulation
Volts
time
time
min largest Negative
max largest Positive
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Pulse Code Modulation

• By quantizing the PAM pulse, original signal is
  only approximated
• Leads to quantizing noise
• Signal-to-noise ratio for quantizing noise
• Thus, each additional bit increases SNR by 6 dB,
  or a factor of 4

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PCM
Pulse Code Modulation
8
8
Volts
5
-1
time
-2
-7
-9
10001
00101
10111
01000
01000
10010
11001
time
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Multiplexing

• Frequency Division Multiplexing
• Separate each baseband signal into a discrete
  band
• Uses AM-SSB/SC to position each baseband

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Frequency Division Multiplexing
1
frequency
2
frequency
3
frequency
4
frequency
3
4
1
2
frequency
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Multiplexing

• Time Division Multiplexing
• Separate each digital baseband into discrete time
  slots
• Cyclical in nature

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Time Division Multiplexing
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2
3
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Rotation Analogy
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FDMA

• Frequency Division Multiple Access

Chan D
Chan C
Frequency
Chan B
Chan A
Time
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TDMA

• Time Division Multiple Access

Chan B
Frequency
Chan A
Time
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CDMA

• Code Division Multiple Access

Code
Frequency
Time
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Summary

• Frequency Spectrum
• Modulation techniques--AM, FM, Phase, and Pulse
  Modulation
• Multiplexing--TDM vs FDM