electrical communications systems ece.09.331 spring 2009

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Electrical Electrical Communications SystemsCommunications Systems

ECE.09.331ECE.09.331 Spring 2009Spring 2009

Shreekanth MandayamECE Department

Rowan University

http://engineering.rowan.edu/~shreek/spring09/ecomms/

Lecture 12aLecture 12aApril 14, 2009April 14, 2009


Plan• 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)


ECOMMS: Topics

Probability

Inform ation

Entropy

Channel Capacity

Discrete

Pow er & Energy Signals

Continuous Fourier Transform

Discrete Fourier Transform

Baseband and Bandpass Signals

Com plex Envelope

Gaussian Noise & SNR

Random VariablesNoise Calculations

Continuous

Signals

AMSw itching M odulator

Envelop Detector

DSB-S CProduct M odulatorCoherent Detector

Costas Loop

SSBW eaver's MethodPhasing M ethod

Frequency M ethod

Frequency & Phase M odulationNarrowband/WidebandVCO & Slope Detector

PLL

Analog

Source EncodingHuffm an codes

Error-control EncodingHam m ing Codes

Sam plingPAM

QuantizationPCM

Line Encoding

Tim e Division M uxT1 (DS1) Standards

Packet Sw itchingEthernet

ISO 7-Layer Protocol

BasebandCODEC

ASKPSKFSK

BPSK

QPSK

M -ary PSK

QAM

BandpassM ODEM

DigitalDigital Com m Transceiver

Systems

Electrical Comm unication Systems


Digital Communications Transceiver

Anti-aliasingFilter

DataEncryption

Encoder

SourceEncoder

ErrorControlEncoder

Channel/Line

Encoder

Modulator

MU

X

AudioAmp

SourceDecoder

DataEncryption

Decoder

ErrorControlDecoder

Equalization /DecisionCircuits

Demod-ulatorD

EM

UX

Reconstruction/DAC

ADC

CODEC MODEM

Analog o/p

Mu

ltip

le a

cces

s ch

ann

el

Analog i/p

Sampling Quantization


Pulse Code Modulation (PCM)

• Standard for all digital communications

Sample &Hold Quantize Encode

AnalogSignal

DigitalBitstream

PCMPAM


Pulse Amplitude Modulation: Flat-top Sampling

-0.5 0 0.5 1 1.5 2 2.5 3 3.5 4-6

-4

-2

0

2

4

6

8

time

AnalogPAM

Matlab Demo: pam.m


Quantization

Uniform Non-Uniform

Mid-rise Mid-tread -Law A-Law

• Mid-rise• Mid-tread

• Mid-rise• Mid-tread

Matlab Demos: quantization.mpcm.m

Matlab Demos: companding.mpcm_mucompand.mpcm_mucompand2.mpcm_acompand.mpcm_acompand2.m



Anti-aliasingFilter

DataEncryption

Encoder

SourceEncoder

ErrorControlEncoder

Channel/Line

Encoder

Modulator

MU

X

AudioAmp

SourceDecoder

DataEncryption

Decoder

ErrorControlDecoder


Demod-ulatorD

EM

UX

Reconstruction/DAC

ADC

CODEC MODEM

Analog o/p

Mu

ltip

le a

cces

s ch

ann

el

Analog i/p



Time Division Multiplexing

Message 1

Message 2

Message N

Quantize&

EncodeChannel

Message 1

Message 2

Message N

Decode

LPF

LPF

LPF


T1-Line TDM Format

F

Channel 1

1 8765432

Channel 2

1 8765432

Channel 24

1 8765432

1 Frame = (24 Channels + F) = 125 s

193 bits

Frame Sync BitEven Frames: 0 0 1 1 1 0Odd Frames: 1 0 1 0 1 0

Every Sixth FrameLSB (8th bit) is a Signaling bit

Bipolar R-Z Line Encoding


North American TDMA Hierarchy

1st

MUX

1

24

64 kbs1 VFDS-0

1

2

DS-4274.176 Mbs4032 VF

5th

MUX

1

6

DS-344.736 Mbs672 VF

4th

MUX

1

7

DS-26.312 Mbs96 VF

3rd

MUX

1

4

DS-11.44 Mbs24 VF

2nd

MUX

DS-5560.160 Mbs8064 VF

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



Anti-aliasingFilter

DataEncryption

Encoder

SourceEncoder

ErrorControlEncoder

Channel/Line

Encoder

Modulator

MU

X

AudioAmp

SourceDecoder

DataEncryption

Decoder

ErrorControlDecoder


Demod-ulatorD

EM

UX

Reconstruction/DAC

ADC

CODEC MODEM

Analog o/p

Mu

ltip

le a

cces

s ch

ann

el

Analog i/p



Line Encoding

Couch, p. 157 Couch, p. 162


ECOMMS: Topics

Probability

Inform ation

Entropy

Channel Capacity

Discrete

Pow er & Energy Signals

Continuous Fourier Transform

Discrete Fourier Transform

Baseband and Bandpass Signals

Com plex Envelope

Gaussian Noise & SNR

Random VariablesNoise Calculations

Continuous

Signals

AMSw itching M odulator

Envelop Detector

DSB-S CProduct M odulatorCoherent Detector

Costas Loop

SSBW eaver's MethodPhasing M ethod

Frequency M ethod

Frequency & Phase M odulationNarrowband/WidebandVCO & Slope Detector

PLL

Analog

Source EncodingHuffm an codes

Error-control EncodingHam m ing Codes

Sam plingPAM

QuantizationPCM

Line Encoding

Tim e Division M uxT1 (DS1) Standards

Packet Sw itchingEthernet

ISO 7-Layer Protocol

BasebandCODEC

ASKPSKFSK

BPSK

QPSK

M -ary PSK

QAM

BandpassM ODEM

DigitalDigital Com m Transceiver

Systems

Electrical Comm unication Systems



Anti-aliasingFilter

DataEncryption

Encoder

SourceEncoder

ErrorControlEncoder

Channel/Line

Encoder

Modulator

MU

X

AudioAmp

SourceDecoder

DataEncryption

Decoder

ErrorControlDecoder


Demod-ulatorD

EM

UX

Reconstruction/DAC

ADC

CODEC MODEM

Analog o/p

Mu

ltip

le a

cces

s ch

ann

el

Analog i/p



Digital Bandpass Communications

• Why digital modulation?

Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf


Industry Trends



Applications



Digital Modulation

Carrier signal: Ac cos (2fct +)

Modulation: m(t)

Modulated signal: Ac (t) cos (2fc(t) t +(t))

Vary Vary Vary amplitude frequency phase

Variations are discrete!!!!!

m(t); discrete


Recall: Dig Comm Principle

1 0 1 0………1 1

0 0

Analog message

Digitalcode

Digital message

Sinusoidal carrier

modulate

AM

FM

PM

AM &PM

1 0 1 0


Signal Vector Representation

PhaseM

agnit

ude

S

0 degreesI

Q

I-QPlane

s(t) = Ac(t) cos (2fct +(t))

fixed!!!fixed!!!


Signal Changes:Representation in the IQ Plane

S1

S2 I

QMagnitudeChange

S1

S2

I

Q

PhaseChange

S1

S2

I

QMagnitude& PhaseChange

FrequencyChange

???

I-Q Diagrams or

Constellations


Binary Phase Shift Keying (BPSK)

I

Q

1 0

IQ Diagram

t

(t)

0 radians

radians

s(t) = Ac cos(2fct + (t))


SummarySummary

electrical communications systems ece.09.331 spring 2009

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