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Electrical Communications Systems ECE.09.331 Spring 2010. Lecture 7a March 2, 2010. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring10/ecomms/. Signals Systems. Modulation Index Efficiency Bandwidth Noise.

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electrical communications systems ece 09 331 spring 2010

Electrical Communications SystemsECE.09.331Spring 2010

Lecture 7aMarch 2, 2010

Shreekanth Mandayam

ECE Department

Rowan University

http://engineering.rowan.edu/~shreek/spring10/ecomms/

slide2

Signals Systems

Modulation

Index

Efficiency

Bandwidth

Noise

Performance

Transmitters

Receivers

Standards

Time Domain

Complex Envelope

Spectrum

Power

Plan
  • Complex Envelope Representation
    • Spectrum of a bandpass signal
  • DSB-SC Modulation
  • Costas Loop
  • QAM
  • SSB
complex envelope representation

message: m(t)

carrier: c(t)

Modulator

s(t): radio signal

Complex Envelope Representation
  • We want a common mathematical representation for
      • information transfer from baseband to bandpass
      • any bandpass signal
      • any time of modulation
      • signal/noise and signal+noise
dsb sc modulation

|M(f)|

-B 0+B

Signals Systems

Modulation

Index

Efficiency

Bandwidth

Noise

Performance

Transmitters

Receivers

Standards

Time Domain

Complex Envelope

Spectrum

Power

DSB-SC Modulation

Message Spectrum

Matlab Demo

http://engineering.rowan.edu/~shreek/spring10/ecomms/demos/dsbsc.m

f

DSB-SC Spectrum

|S(f)|

-fc-B -fc -fc+B 0fc-B fc fc+B

f

dsb sc coherent detector
DSB-SC: Coherent Detector

Product

Modulator

Baseband

LPF

v(t)

s(t)

Aocos2pfct

Local

Oscillator

synchronous coherent detection costas pll

v1(t)

Product

Modulator

Baseband

LPF

v3(t)

v4(t)

VCO

LPF

X

s(t)

-90o

Phase Shift

Phase

Discriminator

Product

Modulator

Baseband

LPF

v2(t)

Synchronous Coherent Detection: Costas PLL

I-Channel

Q-Channel

quadrature amplitude modulation qam

Product

Modulator

S

s(t)

m1(t)

LPF

Product

Modulator

Local

Oscillator

Local

Oscillator

-90o

Phase Shift

-90o

Phase Shift

Product

Modulator

LPF

m2(t)

Product

Modulator

Quadrature Amplitude Modulation (QAM)

Rx

Tx

I-Channel

Q-Channel

single sideband ssb modulation

|S(f)|

-fc-B -fc -fc+B 0fc-B fc fc+B

f

Single Sideband (SSB) Modulation
  • Recall: DSB-SC Spectrum
  • USSB - Signal with zero-valued spectrum for |f| < fc
  • LSSB - Signal with zero-valued spectrum for |f| > fc
the hilbert transform

1.5

1

0.5

0

-0.5

-1

0

1

2

3

4

5

6

7

time, t in sec

The Hilbert Transform

» t=0:0.1:2*pi;

» w=sin(t);

» plot(t,w)

» hold

Current plot held

» H=hilbert(w);

» plot(t,imag(H),\'r\');

» xlabel(\'time, t in sec\')

ssb generation

Product

Modulator

S

s(t)

m(t)

Product

Modulator

-90o

Phase Shift

Sideband

Filter

Product

Modulator

m(t)

s(t)

Carrier

-90o

Phase Shift

Carrier

SSB Generation

Phasing Method

Filter Method

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