Electrical Communications Systems 0909.331.01 Spring 2005

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Electrical Communications Systems0909.331.01
Spring 2005
Lecture 10aApril 11, 2005

• Shreekanth Mandayam
• ECE Department
• Rowan University
• http//engineering.rowan.edu/shreek/spring05/ecom
  ms/

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Plan

• Digital Communications
• Digital Baseband Communications
• Error Correction Coding
• Hamming Code
• Pulse Amplitude Modulation
• Sampling
• Quantization
• TDM Standards
• T1 (DS-1) Line
• North American TDMA Hierarchy

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ECOMMS Topics
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(7, 4) Hamming Code

• Single error detection and correction code
• Hamming distance, d 3
• Fits into a general category of coding techniques
  called BCH codes
• Employs a
• Code Generator Matrix
• Syndrome Decoding Technique

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(7, 4) Hamming Code
Encoding
Parity bits
Code Generator

Info bits
Code word
Decoding
Parity Check
Received code word
Error position indicator
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(7, 4) Hamming Code
Code Generator Matrix
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Hamming Encoder
Info bits
Parity bits
P3 I4 ? I2 ? I1 P2 I4 ? I3 ? I1 P1 I4 ? I3
? I2
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Syndrome Decoding
Parity Check Matrix
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Hamming Decoder
Received code word
Error Position Indicator



s3 R7 ? R5 ? R4 ? R3 s2 R7 ? R6 ? R4 ? R2 s1
R7 ? R6 ? R5 ? R1
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Hamming Decoder
Error position indicator (syndrome) s
Error Position, e
No error







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ECOMMS Topics
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Digital Communications Transceiver
Anti- aliasing Filter
Data Encryption Encoder
Error Control Encoder
Channel/ Line Encoder
Source Encoder
Sampling
Quantization
Modulator
MUX
ADC
Analog i/p
CODEC
MODEM
Multiple access channel
Analog o/p
Data Encryption Decoder
Error Control Decoder
Audio Amp
Source Decoder
Reconstruction/ DAC
Equalization / Decision Circuits
Demod-ulator
DEMUX
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Pulse Code Modulation (PCM)

• Standard for all digital communications

Analog Signal
Sample Hold
Digital Bitstream
Quantize
Encode
PAM
PCM
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Pulse Modulation

• Pulse Amplitude Modulation (PAM) A ? m(t)
• Pulse Time Modulation (PTM) Td ? m(t)
• Pulse Width Modulation (PWM) T ? m(t)

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Pulse Amplitude Modulation Flat-top Sampling
Matlab Demo pam.m
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Quantization
Uniform Non-Uniform
m-Law A-Law
Mid-rise Mid-tread
Matlab Demos quantization.m pcm.m

• Mid-rise
• Mid-tread

• Mid-rise
• Mid-tread

Matlab Demos companding.m pcm_mucompand.m pcm_mu
compand2.m pcm_acompand.m pcm_acompand2.m
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Digital Communications Transceiver
Anti- aliasing Filter
Data Encryption Encoder
Error Control Encoder
Channel/ Line Encoder
Source Encoder
Sampling
Quantization
Modulator
MUX
ADC
Analog i/p
CODEC
MODEM
Multiple access channel
Analog o/p
Data Encryption Decoder
Error Control Decoder
Audio Amp
Source Decoder
Reconstruction/ DAC
Equalization / Decision Circuits
Demod-ulator
DEMUX
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Time Division Multiplexing
Message 1
Quantize Encode
Message 2
Channel
Message N
Message 1
LPF
Message 2
LPF
Message N
LPF
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T1-Line TDM Format
1 Frame (24 Channels F) 125 ms
F
193 bits
Frame Sync Bit Even Frames 0 0 1 1 1 0 Odd
Frames 1 0 1 0 1 0 Every Sixth Frame LSB (8th
bit) is a Signaling bit Bipolar R-Z Line Encoding
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North American TDMA Hierarchy
64 kbs 1 VF DS-0
1st M U X
DS-5 560.160 Mbs 8064 VF

• Figure 3-40, p. 207 in Couch
• Table 3-8, p. 208 in Couch
• Table 3-9, p. 209 in Couch

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Summary