Electrical communications systems ece 09 331 spring 2010
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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/


Electrical communications systems ece 09 331 spring 2010

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


Ssb generation weaver s method
SSB Generation: Weaver’s Method