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

Electrical Electrical Communications SystemsCommunications Systems

0909.331.010909.331.01 Spring 2005Spring 2005

Shreekanth MandayamECE Department

Rowan University

http://engineering.rowan.edu/~shreek/spring05/ecomms/

Lecture 11aLecture 11aApril 19, 2005April 19, 2005

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

PlanPlan• 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

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

ECOMMS: TopicsECOMMS: 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

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

Digital Communications TransceiverDigital 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

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

Digital Bandpass Digital Bandpass CommunicationsCommunications

• Why digital modulation?

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

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

Industry TrendsIndustry Trends

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

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

ApplicationsApplications

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

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

Digital ModulationDigital 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

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

Recall: Dig Comm PrincipleRecall: 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

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

Signal Vector RepresentationSignal Vector Representation

PhaseM

agnit

ude

S

0 degreesI

Q

I-QPlane

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

fixed!!!fixed!!!

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

Signal Changes:Signal Changes:Representation in the IQ PlaneRepresentation in the IQ Plane

S1

S2 I

QMagnitudeChange

S1

S2

I

Q

PhaseChange

S1

S2

I

QMagnitude& PhaseChange

FrequencyChange

???

I-Q Diagrams or

Constellations

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

Binary Phase Shift Keying Binary Phase Shift Keying (BPSK)(BPSK)

I

Q

1 0

IQ Diagram

t

(t)

0 radians

radians

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

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

Quadrature Phase Shift KeyingQuadrature Phase Shift Keying(QPSK)(QPSK)

I

Q

11

IQ Diagrams(t) = Ac cos(2fct + (t))

t

(t)

01

10

00

00

10

01

11

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

M-ary Phase Shift KeyingM-ary Phase Shift Keying(M-ary PSK)(M-ary PSK)

I

Q

Octophase I-Q

Constellation

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

M-ary Quadrature Amplitude ModulationM-ary Quadrature Amplitude Modulation(M-ary-QAM)(M-ary-QAM)

I

Q

16 QAMI-Q

Constellation

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

Different ways of looking at Different ways of looking at a digitally modulated signala digitally modulated signal

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

Time & Frequency Domain ViewTime & Frequency Domain View

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

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

Frequency & Power ViewFrequency & Power View

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

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

I-Q Constellation DiagramI-Q Constellation Diagram

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

Matlab Demo:qpsk.m

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

Eye DiagramEye Diagram

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

Matlab:>>eyediagram