CPETECET 355

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CPET/ECET 355

• 4. Digital Transmission
• Data Communications and Networking
• Fall 2004
• Professor Paul I-Hai Lin
• Electrical and Computer Engineering Technology
• Indiana University-Purdue University Fort Wayne
• www.ecet.ipfw.edu/lin

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4.1 Line Encoding

• A process converting binary data, a sequence of
  bits, to a digital signal
• Binary data data, text, numbers, graphical
  images, audio, and video
• Some characteristics Signal levels, bit rate, dc
  components, self-synchronization

From p. 85, Figure 4.1 of Data Communications and
Networking, Forouzan, McGrawHill
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4.1 Line Encoding (cont.)

• Signal Level vs. Data Level

Three signal levels, 2 data levels
From p. 86, Figure 4.2 of Data Communications and
Networking, Forouzan, McGrawHill
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4.1 Line Encoding (cont.)

• Pulse Rate vs. Bit Rate
• Pulse Rate
• Number of pulses per second
• A pulse is the min amount of time required to
  send a symbol
• Bit Rate
• Number of bits per second
• BitRate PulseRate x Log2L
• Level of signal 2, BitRate PulseRate
• Level of signal 4, BitRate 2 x PulseRate
• Example 1 2 Find Bit rate
• If - Pulse rate 1000 pulses/sec, L 2, 1000 bps
• If - Pulse rate 1000 pulses/sec, L 4, 2000 bps

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4.1 Line Encoding (cont.)

• DC Components (undesirable)
• Cannot passing through a transformer
• Unnecessary energy on the line

From p. 87, Figure 4.3 of Data Communications and
Networking, Forouzan, McGrawHill
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4.1 Line Encoding (cont.)

• Self-Synchronization (desirable)
• For correctly interpret signal
• Sending 10110001 receiving 110111000011

Figure 4.4 Lack of Synchronization, From p. 88,
Data Communications and Networking, Forouzan,
McGrawHill
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4.1 Line Encoding (cont.)

• Line Coding Schemes
• Unipolar
• Simple and primitive
• One voltage level
• Two problems DC component Lack of
  synchronization
• Polar
• Two signal levels positive negative
• Eliminate DC component
• Biploar
• Three signal levels positive, zero, and negative

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4.1 Line Encoding (cont.)

• Unipolar Encoding

Figure 4.6 Unipolar Encoding, From p. 89, Data
Communications and Networking, Forouzan,
McGrawHill
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4.1 Line Encoding (cont.)

• Polar Encoding
• NRZ Non Return to Zero
• RZ Return to Zero
• Manchester
• Differential Manchester

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4.1 Line Encoding (cont.)

• NRZ Non Return to Zero
• NRZ-L
• 0 positive 1 negative
• Sync. Problem if long string of 0s or 1s is
  encountered
• NRZ-I
• the signal is inverted if a 1 is encountered
• A long string of 0s still cause sync. problem

Figure 4.8 NRZ-L and NRZ-I Encoding, From p. 91,
Data Communications and Networking, Forouzan,
McGrawHill
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4.1 Line Encoding (cont.)

• RZ Return to Zero
• Uses three values positive, zero, negative
• Ensure Sync a signal change for each bit
• Main disadvantage use more bandwidth

Figure 4.9 RZ Encoding, From p. 91, Data
Communications and Networking, Forouzan,
McGrawHill
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4.1 Line Encoding (cont.)

• Manchester Encoding
• Uses two level signal values positive, negative
• Sync Inversion at the middle of each bit
• Zero High -gt Low One Low -gt High

Figure 4.10 Manchester Encoding, From p. 92,
Data Communications and Networking, Forouzan,
McGrawHill
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4.1 Line Encoding (cont.)

• Differential Manchester Encoding
• Uses two level signal values positive, negative
• Sync Inversion at the middle of each bit
• Zero A transition One No transition

Figure 4.10 Differential Manchester Encoding,
From p. 93, Data Communications and Networking,
Forouzan, McGrawHill
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4.1 Line Encoding (cont.)

• Biploar Encoding
• Uses three level signal values positive, zero,
  negative
• 0 Zero level 1 Alternating positive and
  negative voltages
• AMI Alternate Mark Inversion
• BnZS Bipolar n-zero Substitution

Figure 4.12 Bipolar AMI Encoding, From p. 94,
Data Communications and Networking, Forouzan,
McGrawHill
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4.2 Block Encoding

• Improve performance
• Ensure synchronization through redundancy bits
• Block Encoding Schemes
• 4B/5B 4-bit data encoded into 5-bit code
• 8B/10B 8-bit data encoded into 10-bit code
• 8b/6T 8-bit data encoded into 6-symbol code

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4.2 Block Encoding (cont.)

• Block Encoding

Figure 4.15 Block Encoding, From p. 95, Data
Communications and Networking, Forouzan,
McGrawHill
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4.2 Block Encoding (cont.)

• 4B/5B Block Substitution
• Better Sync Error detection
• 16 groups -gt 32 groups
• No more than 3 consecutive 0s

Figure 4.16 Substitution in Block Encoding, From
p. 95, Data Communications and Networking,
Forouzan, McGrawHill
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4.2 Block Encoding (cont.)

• 4B/5B Encoding Table

Table 4.1 4B/5B Encoding, From p. 97, Data
Communications and Networking, Forouzan,
McGrawHill
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4.2 Block Encoding (cont.)

• 4B/5B Encoding Table

Table 4.1 4B/5B Encoding, From p. 97, Data
Communications and Networking, Forouzan,
McGrawHill
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4.2 Block Encoding (cont.)

• 8B/6T Encoding
• 28 256 possibilities
• 36 729 six-symbol ternary signal

Figure 4.17 Example of 8B/6T Encoding, From p.
98, Data Communications and Networking, Forouzan,
McGrawHill
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4.3 Sampling

• Pulse Amplitude Modulation (PAM)
• Sample Hold circuit
• Pulse Code Modulation (PCM)
• Quantized PAM
• Sampling Rate
• Nyquist theorem
• How many bit per sample

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4.3 Sampling (cont.)

• PAM

Figure 4.18 PAM, From p. 99, Data Communications
and Networking, Forouzan, McGrawHill
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4.3 Sampling (cont.)

• Quantized PAM Signal

Figure 4.19 Quantized PAM Signal, From p. 100,
Data Communications and Networking, Forouzan,
McGrawHill
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4.3 Sampling (cont.)

• Quantization, sign magnitude

Figure 4.20 Quantizing by using sign and
magnitude, From p. 100, Data Communications and
Networking, Forouzan, McGrawHill
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4.3 Sampling (cont.)

• PCM

Figure 4.21 PCM, From p. 101, Data
Communications and Networking, Forouzan,
McGrawHill
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4.3 Sampling (cont.)

• PCM

Figure 4.22 From analog signal to PCM digital
code, From p. 101, Data Communications and
Networking, Forouzan, McGrawHill
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4.3 Sampling (cont.)
x Hz 2 x samples

• Nyquist Theorem
• Sampling rate must be at least 2 times the
  highest frequency

½ x
Figure 4.23 Nyquist Theorem, From p. 102, Data
Communications and Networking, Forouzan,
McGrawHill
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4.3 Sampling (cont.)

• Examples
• Q1 What sampling rate is needed for a signal
  with a bandwidth of 10 KHz (1KHz to 11KHz)
• A1 Sampling rate 2 x 11 KHz 22,000 samples
  per second

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4.3 Sampling (cont.)

• Examples
• Q2 A signal is sampled. Each sample requires at
  least 12 levels of precision (0 to 5 and 0 to
  -5). How many bits should be sent for each
  sample?
• A2 4-bit
• 1-bit for sign
• 3-bit for magnitude (8-levels)

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4.3 Sampling (cont.)

• Examples
• Q3 We want to digitize the human voice. What is
  the bit rate, assuming 8-bits per sample?
• A3 BW of Human voice 0-4000 Hz
• Sampling rate 4000 x 2 8000 samples/sec
• Bit rate
• 8000 sample/sec x 8 bit/sample
• 64,000 bps

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4.4 Transmission Mode

• Parallel
• Serial
• Synchronous
• Asynchronous

Figure 4.25 Parallel transmission, From p. 104,
Data Communications and Networking, Forouzan,
McGrawHill
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4.4 Transmission Mode

• Serial Transmission

Figure 4.26 Serial transmission, From p. 105,
Data Communications and Networking, Forouzan,
McGrawHill
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4.4 Transmission Mode

• Serial - Asynchronous

Figure 4.27Asynchronlus transmission, From p.
106, Data Communications and Networking,
Forouzan, McGrawHill
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4.4 Transmission Mode

• Serial - Synchronous

Figure 4.28 Synchronlus transmission, From p.
107, Data Communications and Networking,
Forouzan, McGrawHill
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Summary
Questions?