electrical communications systems ece.09.331 spring 2010
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
Electrical Electrical Communications SystemsCommunications Systems
ECE.09.331ECE.09.331 Spring 2010Spring 2010
Shreekanth MandayamECE Department
Rowan University
http://engineering.rowan.edu/~shreek/spring10/ecomms/
Lecture 7aLecture 7aMarch 2, 2010March 2, 2010
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
PlanPlan• Complex Envelope Representation
• Spectrum of a bandpass signal
• DSB-SC Modulation
• Costas Loop• QAM• SSB
Signals SystemsTime DomainComplex EnvelopeSpectrumPower
PerformanceTransmittersReceiversStandards
Modulation IndexEfficiencyBandwidthNoise
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
Complex Envelope RepresentationComplex 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
Modulatormessage: m(t)
carrier: c(t)
s(t): radio signal
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
Spectrum of a Bandpass Spectrum of a Bandpass SignalSignal
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
DSB-SC ModulationDSB-SC Modulation
Signals SystemsTime DomainComplex EnvelopeSpectrumPower
PerformanceTransmittersReceiversStandards
Modulation IndexEfficiencyBandwidthNoise
-B 0 +B
|M(f)|
f
-fc-B -fc -fc+B 0 fc-B fc fc+B
|S(f)|
f
Message Spectrum
DSB-SC Spectrum
Matlab Demo
http://engineering.rowan.edu/~shreek/spring10/ecomms/demos/dsbsc.m
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
DSB-SC: Coherent DetectorDSB-SC: Coherent Detector
ProductModulator
Aocos2fct
s(t)
LocalOscillator
BasebandLPF
v(t)(t)m~
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
Synchronous Coherent Synchronous Coherent Detection: Costas PLLDetection: Costas PLL
s(t)
v1(t) (t)m~ProductModulator
BasebandLPF
VCO LPF
-90o
Phase Shift
X
v2(t)
ProductModulator
BasebandLPF
v3(t)v4(t)
PhaseDiscriminator
I-Channel
Q-Channel
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
Quadrature Amplitude Quadrature Amplitude Modulation (QAM)Modulation (QAM)
ProductModulator
LocalOscillator
-90o
Phase Shift
ProductModulator
m1(t)
m2(t)
s(t) ProductModulator
LocalOscillator
-90o
Phase Shift
ProductModulator
LPF
LPF
(t)1m~
(t)2m~
Tx RxI-Channel
Q-Channel
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
Single Sideband (SSB) Single Sideband (SSB) ModulationModulation
• Recall: DSB-SC Spectrum
• USSB - Signal with zero-valued spectrum for |f| < fc
• LSSB - Signal with zero-valued spectrum for |f| > fc
-fc-B -fc -fc+B 0 fc-B fc fc+B
|S(f)|
f
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
The Hilbert TransformThe Hilbert Transform
-1
-0.5
0
0.5
1
1.5
0 1 2 3 4 5 6 7
time, t in sec
(t)w(t)w » t=0:0.1:2*pi;» w=sin(t);» plot(t,w)» holdCurrent plot held» H=hilbert(w);» plot(t,imag(H),'r');» xlabel('time, t in sec')
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
SSB GenerationSSB Generation
ProductModulator
Carrier -90o
Phase Shift
ProductModulator
-90o
Phase Shift
m(t)
s(t)
SidebandFilter
Carrier
ProductModulator
m(t) s(t)
Phasing Method
Filter Method
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
SSB Generation: SSB Generation: Weaver’s MethodWeaver’s Method
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
SummarySummary