1. Electrical Communications Systems ECE.09.433 Spring 2019
Lecture 11a April 9, 2019
Shreekanth Mandayam
ECE Department
Rowan University

2. Plan Data Processing & Data Communications
Communications Networks
Packet Switched Networks
OSI 7-Layer Protocol Architecture
TCP-IP Protocol Architecture
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

3. ECOMMS: Topics

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

5. Digital Communication Paradigms
Recall
Digital Communication Paradigms
Multiplexer
Message 2
Message 3
Message 1 1 2 3 S
Demultiplexer
Circuit Switching
Sync bits
Packet Switching
Header
bits
Packetizing
Message 2
Message 3
Message 1 1 H 2 3
Depacket-izing

6. Communications Networking
Router
Step 1:
Step 2:
Step 3:
……..
Protocol
Sender
Medium
Receiver
Message

7. A 3-Layer Protocol Architecture
File transfer application
Communications service module
Network access module
Files and file transfer commands
File transfer application
Communications service module
Network access module
Comm related messages
Comm network
Computer 1
Computer 2

8. ISO OSI 7-Layer Model 7 Application 6 5 Presentation 4 3 Session 2 1
Physical
Data Link
Network
Presentation
Session
Transport
Application 7 6 5 4 3 2 1
Please Do Not Touch Steve’s Pet Alligator

9. TCP-IP Protocol Architecture
Physical
Network Access
Internet
Transport
(host-to-host)
Application
TCP-IP
Application
Presentation
Session
Transport
Network
Data Link
Physical
OSI
Hardware
Firmware
Software
Operating
system
User
space

10. TCP-IP Operation Example
Network access protocol #1
Physical IP
TCP
Host A
App X
App Y
Network access protocol #2
Physical IP
TCP
Host B
App X
App Y
Port or
Service access point (SAP)
Logical connection (TCP)
Global network address
Subnetwork attachment point address
Logical connection
Router J IP
NAP1
NAP2
Network 1
Network 2

11. TCP-IP Protocol Packet
TCP header
IP header
Network header
User Data
Application
Byte Stream
TCP
Segment IP
Datagram
Network
Level
Packet

12. IP Header 0 4 8 16 19 31 20 octets Version IHL Type of Service
Version
IHL
Type of Service
Total Length
Identification
Flags
Fragment Offset
Time to Live
Protocol
Header Checksum
Source Address
Destination Address
Options + Padding
20 octets

13. Acknowledgement Number
TCP Header
Source Port
Destination Port
Sequence Number
Acknowledgement Number
Data Offset
Reserved
URG
ACK
PSH
RST
SYN
FIN
Window
Checksum
Urgent Pointer
Options + Padding
20 octets

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

15. 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!!!!!

16. Recall: Dig Comm Principle
Digital message
………
Digital
code
Analog
message
modulate AM
Sinusoidal carrier FM PM
AM & PM

17. Signal Vector Representation
s(t) = Ac(t) cos (2pfct + f(t))
fixed!!! Q S
Magnitude
Phase
0 degrees I
I-Q
Plane

18. Signal Changes: Representation in the IQ Plane
Phase
Change S1 S2 I Q
Magnitude
Change
I-Q Diagrams or
Constellations S1 S2 I Q
Magnitude
& Phase
Change
Frequency
Change
???

19. Binary Phase Shift Keying (BPSK)
s(t) = Ac cos(2pfct + f(t)) IQ
Diagram Q
p radians
f(t) 1
0 radians t I

20. 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

21. M-ary Phase Shift Keying (M-ary PSK)Q I
Octophase
I-Q
Constellation

22. M-ary Quadrature Amplitude Modulation (M-ary-QAM)
I-Q
Constellation

23. Summary