1. Electrical Communications Systems ECE.09.331 Spring 2008
Lecture 11b April 9, 2008
Shreekanth Mandayam
ECE Department
Rowan University

2. Plan Pulse Amplitude Modulation Digital Bandpass Communications
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)

3. ECOMMS: Topics

4. 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

5. Pulse Code Modulation (PCM)
Standard for all digital communications
Analog
Signal
Sample &
Hold
Digital
Bitstream
Quantize
Encode
PAM
PCM

6. Pulse Amplitude Modulation: Flat-top Sampling
-0.5
0.5 1
1.5 2
2.5 3
3.5 4 -6 -4 -2 6 8
time
Analog
PAM
Matlab Demo: pam.m

7. 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_mucompand2.m
pcm_acompand.m
pcm_acompand2.m

8. 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

9. Time Division Multiplexing
Message 1
Quantize
&
Encode
Message 2
Channel
Message N
Message 1
LPF
Decode
Message 2
LPF
Message N
LPF

10. T1-Line TDM Format 1 Frame = (24 Channels + F) = 125 ms Channel 1 1 87 6 5 4 3 2
Channel 2 1 8 7 6 5 4 3 2
Channel 24 1 8 7 6 5 4 3 2 F
193 bits
Frame Sync Bit
Even Frames:
Odd Frames:
Every Sixth Frame
LSB (8th bit) is a Signaling bit
Bipolar R-Z Line Encoding

11. North American TDMA Hierarchy
64 kbs
1 VF
DS-0 1 1 7
DS-2
6.312 Mbs
96 VF
3rd M U X 1 6
DS-3
Mbs
672 VF
4th M U X 1 2
DS-4
Mbs
4032 VF
5th M U X 1 4
DS-1
1.44 Mbs
24 VF
2nd M U X
1st M U X 24
DS-5
Mbs
8064 VF
Figure 3-40, p. 207 in Couch
Table 3-8, p. 208 in Couch
Table 3-9, p. 209 in Couch

12. 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

13. Line Encoding
Couch, p. 162
Couch, p. 157

14. ECOMMS: Topics

15. 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

16. Digital Bandpass Communications
Why digital modulation?
Reproduced from:

17. Industry Trends
Reproduced from:

18. Applications
Reproduced from:

19. 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!!!!!

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

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

22. 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
???

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

24. Summary