Encoding and Modulating

1
Chapter 5
Encoding and Modulating
2
Figure 5-1
Different Conversion Schemes
3
Figure 5-2
Digital to Digital Encoding
4
Figure 5-3
Types of Digital to Digital Encoding
5
Figure 5-4
Unipolar Encoding
Uses only one level of value. Problems - DC
component Synchronization
6
Figure 5-5
Types of Polar Encoding
Uses two levels of amplitude.
Ethernet LANs
Token Ring LANs
DC component is totally eliminated.
7
Figure 5-6
NRZ-L and NRZ-I Encoding
In NRZ-I the signal is inverted if a 1 is
encountered.
8
Figure 5-7
RZ Encoding

• Ensure synchronization
• Disadvantage more bandwidth

9
Figure 5-8
Manchester and Diff. Manchester Encoding
10
Figure 5-9
Types of Bipolar Encoding
Uses three levels positive, zero, and negative.
AMI Alternative mask version B8ZS Bipolar
8-zero substitution (North America) HDB3
High-density Bipolar 3 (Europe Japan)
11
Figure 5-10
Bipolar AMI Encoding
12
Figure 5-11
B8ZS Encoding
13
Figure 5-12
HDB3 Encoding
14
Figure 5-13
Solution to Example 5.1 (B8ZS)


Violation
15
Figure 5-14
Solution to Example 5.2


-
-
(No. of 1s substituted even)
(No. of 1s substituted odd)
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Figure 5-15
Analog to Digital Conversion
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Figure 5-16
PAM
Holding duration
Sampling point
18
Figure 5-17
Quantized PAM Signal
Quantization error
19
Figure 5-18
Quantizing Using Sign and Magnitude
20
Figure 5-19
PCM (Pulse Code Modulation)

• PCM is the sampling method used to digitize voice
  in T-line transmission in the North American
  telephone system.

21
Figure 5-20
From Analog Signal to PCM Digital Code
22
Figure 5-21
Nyquist Theorem
The sampling rate must be at least two times the
highest frequency of the original signal.
23
Figure 5-22
Digital-to-Analog Modulation
Carrier signal
Bit/baud rate
Ex.) Original data is digital gt Telephone wires
carry analog signals.
24
Figure 5-23
Types of Digital-to-Analog Modulation
Characteristics of carrier signals
ASK Amplitude Shift Keying FSK Frequency Shift
Keying PSK Phase Shift Keying QAM Quadrature
Amplitude Modulation
25
Figure 5-24
ASK

• Highly susceptible to noise interference.
• Frequency Phase Constant

Data rate No. of bits per second. Baud rate No.
of signal units per second.
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Figure 5-25
Baud Rate and Bandwidth in ASK

• BW (1d)?Nbaud
• BW Bandwidth
• Nbaud Baud rate No. of bits per second.
• d A factor related to the condition of the line.

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Figure 5-26
Solution to Example 5.10
No guard band
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Figure 5-27
FSK

• Avoids most of the noise problems of ASK.
• Peak amplitude Phase Constant
• Limiting factors Physical capabilities of the
  carrier.

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Figure 5-28
Baud Rate and Bandwidth in FSK
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Figure 5-29
PSK
- Peak amplitude Frequency Constant
31
Figure 5-30
PSK Constellation
32
Figure 5-31
4-PSK
33
Figure 5-32
4-PSK Characteristics
34
Figure 5-33
8-PSK Characteristics
35
Figure 5-34
Baud Rate and Bandwidth in PSK
36
Figure 5-35
4-QAM and 8-QAM Constellations
- Combining ASK PSK.
37
Figure 5-36
Time Domain for 8-QAM Signal
38
Figure 5-37
16-QAM Constellations
OSI recommendation
ITU-T recommendation (the great ration of phase
shift to amplitude)
39
Figure 5-38
Bit and Baud
40
Figure 5-39
Analog-to-Analog Modulation
41
Figure 5-40
Types of Analog-to-Analog Modulation
AM Amplitude modulation FM Frequency
modulation PM Phase modulation
42
Figure 5-41
Amplitude Modulation
43
Figure 5-42
AM Bandwidth
44
Figure 5-43
AM Band Allocation
FCC 10Khz for each AM station (Audio signal
5Khz)
45
Figure 5-44
Frequency Modulation
46
Figure 5-45
FM Bandwidth

• FCC 200Khz for each FM station to provide some
  room for guard bands (Stereo audio signal 15Khz)

47
Phase Modulation

• Peak amplitude and frequency of the carrier
  signal remain constant.
• The analysis and the modulated signal are similar
  to those of FM.

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Summary

• Digital-to-digital encoding
• Unipolar, Polar, Bipolar (NRZ, NRZ-L, NRZ-I, RZ,
  Biphase)
• Analog-to-digital conversion
• PCM
• Digital-to-analog modulation
• ASK, FSK, PSK, QAM
• Analog-to-analog modulation
• AM, FM, PM

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Figure 5-46
FM Band Allocation