Electrical Communications Systems 0909.331.01 Spring 2005

1
Electrical Communications Systems0909.331.01
Spring 2005
Lecture 11bApril 20, 2005

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

2
Plan

• Digital Bandpass Communications
• M-ary PSK and M-ary QAM
• Different ways of looking at a digitally
  modulated signal
• Data Processing Data Communications
• Communications Networks
• Packet Switched Networks
• OSI 7-Layer Protocol Architecture
• TCP-IP Protocol Architecture
• Broadcast Transmitters and Receivers
• AM Broadcast Transmitter
• Class-C Amp Collector Modulator
• TRF Receiver
• Superheterodyne Receiver

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ECOMMS Topics
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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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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
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Different ways of looking at a digitally
modulated signal
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Time Frequency Domain View
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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Frequency Power View
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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I-Q Constellation Diagram
Matlab Demo qpsk.m
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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Eye Diagram
Matlab gtgteyediagram
Reproduced from http//www.tm.agilent.com/tmo/Not
es/pdf/5965-7160E.pdf
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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 Communication Paradigms
Recall
Circuit Switching
Sync bits
Packet Switching
Header bits
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Communications Networking
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A 3-Layer Protocol Architecture
Files and file transfer commands
File transfer application
Communications service module
Network access module
File transfer application
Communications service module
Network access module
Comm related messages
Comm network
Computer 1
Computer 2
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ISO OSI 7-Layer Model
Please Do Not Touch Steves Pet Alligator
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TCP-IP Protocol Architecture
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TCP-IP Operation Example
Port or Service access point (SAP)
Logical connection (TCP)
Global network address
Subnetwork attachment point address
Logical connection
Router J
IP IP
NAP1 NAP2
Network 1
Network 2
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TCP-IP Protocol Packet
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IP Header
0 4 8
16 19
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Version IHL Type of Service Total Length Total Length
Identification Identification Identification Flags Fragment Offset
Time to Live Time to Live Protocol Header Checksum Header Checksum
Source Address Source Address Source Address Source Address Source Address
Destination Address Destination Address Destination Address Destination Address Destination Address
Options Padding Options Padding Options Padding Options Padding Options Padding
20 octets
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TCP Header
0 4 10
16
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Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port
Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number
Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number
Data Offset Reserved URG ACK PSH RST SYN FIN Window
Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer
Options Padding Options Padding Options Padding Options Padding Options Padding Options Padding Options Padding Options Padding Options Padding
20 octets
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ECOMMS Topics
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AM Broadcast Transmitter
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Amplifier Classification
Class B
Class A
Class C
Class AB
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BJT Collector Modulator
Output Characteristics
Circuit
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BJT Collector Modulator
Operation
Circuit
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AM Receiver

• Purpose
• Demodulate received signal
• Requirements
• Carrier frequency tuning
• Filtering
• Amplification

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Tuning Circuits
Series Tuned Circuit
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Series Tuned Circuit
function f,Aresonance(f0,Q) ECOMMS Spring 00
Class Demo S. Mandayam, ECE Dept., Rowan
University To illustrate series resonance and
Q-factor close all defining frequency
axis ff0-f0/20.1f0f0/2 calculating relative
response y(f/f0)-(f0./f) A20log10(1./(1(yQ).
2).0.5) plot(f-f0,A)grid on xlabel('Shift
from resonant frequency in Hz') ylabel('Relative
Response in dB') title('Series Tuning Circuit')
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Tuning Circuits
Parallel Tuned Circuit
I

r
V
C
L
-
Active Tuned Circuits?
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Tuned Radio Frequency (TRF) Receiver
Active Tuning Circuit
Detector Circuit
Bandpass Filter
Baseband Audio Amp
Local Oscillator
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Heterodyning
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Superheterodyne Receiver
fm
fm
fIF
fIF
RF Amplifier H1(f)
IF Amplifier H2(f)
Audio Amp
Mixer
Detector
fRF or fc
Local Oscillator
fLO
Common tuning
Downconversion fIF fRF - fLO
Upconversion fIF fRF fLO
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Summary