Wk3 Modulation Basic
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Communication Technologies Modulation and Multiplexing Week #3 ICS 620
Overview • • • • •
Frequency Spectrum Modulation techniques Multiplexing--TDM vs FDM Multiple Access Signal formats
The Bands ELF VLF
LF
MF
HF VHF UHF SHF EHF Radio
Submillimeter Range
3KHz 30KHz 300KHz 3MHz 30MHz300MHz 3GHz 30GHz 300GHz 3THz Far InfraRed Optical 300 m 1500nm 1PetaHz
Near InfraRed
R e d
700nm
1ExaHz O r a n g e
Y e l l o w
600nm
G r e e n
B l u e 500nm
I n d i g o
V i o l e t
Ultraviolet
400nm
X-Ray
Frequency Spectrum • •
Limited resource Managed • WARC • FCC
•
Bands
Modulation Techniques • • • •
Amplitude Modulation Frequency Modulation Phase Modulation Pulse Modulation
Amplitude Modulation • • • •
Uses a higher frequency carrier Most efficient use of frequency Time and Frequency Domain Susceptible to Noise
Most Efficient Use of Frequency •
Maximum frequency required is: • Twice baseband • Just baseband (special conditions)
Higher Frequency Carrier Signal
time
Carrier
time
Higher Frequency Carrier Power Spectral Density watts
Signal
Carrier
frequency Baseband
Time Domain Signal
time
Carrier
time
Time Domain Continued
time
Detection of Signal
time
time
Frequency Domain Unmodulated
watts
Carrier
Signal
frequency Baseband
watts
Modulated
Carrier Signal
frequency Baseband
Baseband
Spectrum of AM signal
Susceptible to Noise
time
Antenna Carrier Signal Oscillator
Low-Power Amplifier
Information Signal
Modulation Device
Final Amplifier
Simple block diagram of AM modulation
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 can’t be used for synchronization purposes
Frequency Modulation • • • •
Uses a higher frequency carrier Usually more bandwidth Time and Frequency Domain Resistant to some Noise
Time Domain Signal
time
Carrier
time
Time Domain
time
Frequency Domain Unmodulated
watts
Carrier
Signal
frequency Baseband
watts
Modulated
Carrier Signal
frequency
Resistant to Some Noise
time
Phase Modulation • • • •
Uses a higher frequency carrier Fairly efficient use of frequency Time and Frequency Domain Used mainly for data
Time Domain (Instantaneous View) Unmodulated Carrier
Modulated Carrier Phase Input
Phase Shift Keying 0O
90O
180O
Time Plot
270O
Pulse Modulation • • • • •
Uses the sampling rate PAM PDM, PWM PPM PCM
Starts with Sampling
Volts time
PAM Pulse Amplitude Modulation
Volts time
PDM (a.k.a. PWM) Pulse Duration Modulation (Pulse Width Modulation)
Volts time
time max = largest Positive
min = largest Negative
PPM Pulse Position Modulation
Volts time
time max = largest Positive
min = largest Negative
Pulse Code Modulation By quantizing the PAM pulse, original signal is only approximated ■ Leads to quantizing noise ■ Signal-to-noise ratio for quantizing noise ■
SNR dB = 20 log 2 + 1.76 dB = 6.02n + 1.76 dB n
■
Thus, each additional bit increases SNR by 6 dB, or a factor of 4
PCM Pulse Code Modulation
Volts
8
8 5 -1
-2 -9
time -7
01000 01000 10010 11001 10001 00101 10111
time
Multiplexing ■ Frequency
Division Multiplexing –Separate each baseband signal into a discrete band –Uses AM-SSB/SC to position each baseband
Frequency Division Multiplexing 1 frequency 2 frequency 3 4
frequency frequency
1
2
3
4 frequency
Multiplexing •
Time Division Multiplexing • Separate each digital baseband into discrete time slots • Cyclical in nature
Time Division Multiplexing 1 2 3 4
Rotation Analogy
FDMA Frequency Division Multiple Access
Frequency
Chan D
Chan C Chan B Chan A
Time
TDMA
Frequency
Time Division Multiple Access
Chan B
Chan A
Time
CDMA Code Division Multiple Access
Code
eq
Fr y nc
ue Time
Summary • •
•
Frequency Spectrum Modulation techniques--AM, FM, Phase, and Pulse Modulation Multiplexing--TDM vs FDM
Overview • • • • •
Frequency Spectrum Modulation techniques Multiplexing--TDM vs FDM Multiple Access Signal formats
The Bands ELF VLF
LF
MF
HF VHF UHF SHF EHF Radio
Submillimeter Range
3KHz 30KHz 300KHz 3MHz 30MHz300MHz 3GHz 30GHz 300GHz 3THz Far InfraRed Optical 300 m 1500nm 1PetaHz
Near InfraRed
R e d
700nm
1ExaHz O r a n g e
Y e l l o w
600nm
G r e e n
B l u e 500nm
I n d i g o
V i o l e t
Ultraviolet
400nm
X-Ray
Frequency Spectrum • •
Limited resource Managed • WARC • FCC
•
Bands
Modulation Techniques • • • •
Amplitude Modulation Frequency Modulation Phase Modulation Pulse Modulation
Amplitude Modulation • • • •
Uses a higher frequency carrier Most efficient use of frequency Time and Frequency Domain Susceptible to Noise
Most Efficient Use of Frequency •
Maximum frequency required is: • Twice baseband • Just baseband (special conditions)
Higher Frequency Carrier Signal
time
Carrier
time
Higher Frequency Carrier Power Spectral Density watts
Signal
Carrier
frequency Baseband
Time Domain Signal
time
Carrier
time
Time Domain Continued
time
Detection of Signal
time
time
Frequency Domain Unmodulated
watts
Carrier
Signal
frequency Baseband
watts
Modulated
Carrier Signal
frequency Baseband
Baseband
Spectrum of AM signal
Susceptible to Noise
time
Antenna Carrier Signal Oscillator
Low-Power Amplifier
Information Signal
Modulation Device
Final Amplifier
Simple block diagram of AM modulation
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 can’t be used for synchronization purposes
Frequency Modulation • • • •
Uses a higher frequency carrier Usually more bandwidth Time and Frequency Domain Resistant to some Noise
Time Domain Signal
time
Carrier
time
Time Domain
time
Frequency Domain Unmodulated
watts
Carrier
Signal
frequency Baseband
watts
Modulated
Carrier Signal
frequency
Resistant to Some Noise
time
Phase Modulation • • • •
Uses a higher frequency carrier Fairly efficient use of frequency Time and Frequency Domain Used mainly for data
Time Domain (Instantaneous View) Unmodulated Carrier
Modulated Carrier Phase Input
Phase Shift Keying 0O
90O
180O
Time Plot
270O
Pulse Modulation • • • • •
Uses the sampling rate PAM PDM, PWM PPM PCM
Starts with Sampling
Volts time
PAM Pulse Amplitude Modulation
Volts time
PDM (a.k.a. PWM) Pulse Duration Modulation (Pulse Width Modulation)
Volts time
time max = largest Positive
min = largest Negative
PPM Pulse Position Modulation
Volts time
time max = largest Positive
min = largest Negative
Pulse Code Modulation By quantizing the PAM pulse, original signal is only approximated ■ Leads to quantizing noise ■ Signal-to-noise ratio for quantizing noise ■
SNR dB = 20 log 2 + 1.76 dB = 6.02n + 1.76 dB n
■
Thus, each additional bit increases SNR by 6 dB, or a factor of 4
PCM Pulse Code Modulation
Volts
8
8 5 -1
-2 -9
time -7
01000 01000 10010 11001 10001 00101 10111
time
Multiplexing ■ Frequency
Division Multiplexing –Separate each baseband signal into a discrete band –Uses AM-SSB/SC to position each baseband
Frequency Division Multiplexing 1 frequency 2 frequency 3 4
frequency frequency
1
2
3
4 frequency
Multiplexing •
Time Division Multiplexing • Separate each digital baseband into discrete time slots • Cyclical in nature
Time Division Multiplexing 1 2 3 4
Rotation Analogy
FDMA Frequency Division Multiple Access
Frequency
Chan D
Chan C Chan B Chan A
Time
TDMA
Frequency
Time Division Multiple Access
Chan B
Chan A
Time
CDMA Code Division Multiple Access
Code
eq
Fr y nc
ue Time
Summary • •
•
Frequency Spectrum Modulation techniques--AM, FM, Phase, and Pulse Modulation Multiplexing--TDM vs FDM
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