Electrical Communications Systems 0909.331.01 Spring 2005

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Electrical Communications Systems0909.331.01
Spring 2005
Lecture 10bApril 13, 2005

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

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Plan

• Digital Baseband Communications
• Pulse Amplitude Modulation
• Sampling
• Quantization
• TDM Standards
• T1 (DS-1) Line
• North American TDMA Hierarchy
• Line Encoding
• Digital Bandpass Communications
• Why digital modulation?
• Digital Modulation Introduction (ASK, FSK, PSK)
• Binary Phase Shift Keying (BPSK)
• Quadrature Phase Shift Keying (QPSK)
• M-ary PSK and M-ary QAM

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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 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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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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Line Encoding
Couch, p. 162
Couch, p. 157
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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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Digital Bandpass Communications

• Why digital modulation?

Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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Industry Trends
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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Applications
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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Digital Modulation
Carrier signal Ac cos (2pfct f) Modulation
m(t) Modulated signal Ac
(t) cos (2pfc(t) t f(t))
? m(t) discrete
Vary Vary Vary amplitude
frequency phase
Variations are discrete!!!!!
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Recall Dig Comm Principle
Digital message
1 1
1 0 1 0
0 0
Digital code
Analog message
modulate
1 0 1 0
Sinusoidal carrier
AM
FM
PM
AM PM
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Signal Vector Representation
s(t) Ac(t) cos (2pfct f(t))
fixed!!!
Q
S
Magnitude
Phase
0 degrees
I
I-Q Plane
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Signal ChangesRepresentation in the IQ Plane
I-Q Diagrams or Constellations
Frequency Change
???
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Binary Phase Shift Keying (BPSK)
s(t) Ac cos(2pfct f(t))
IQ Diagram
Q
p radians
f(t)
1
0
0 radians
t
I
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Quadrature Phase Shift Keying(QPSK)
IQ Diagram
s(t) Ac cos(2pfct f(t))
Q
3p/4
01
11
10
f(t)
p/4
00
p/4
t
I
10
-p/4
11
01
00
-3p/4
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M-ary Phase Shift Keying(M-ary PSK)
Q
I
Octophase I-Q Constellation
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M-ary Quadrature Amplitude Modulation(M-ary-QAM)
Q
I
16 QAM I-Q Constellation