electrical communications systems ece.09.331 spring 2009
DESCRIPTION
Electrical Communications Systems ECE.09.331 Spring 2009. Lecture 7a March 3, 2009. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring09/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 2009Spring 2009
Shreekanth MandayamECE DepartmentRowan University
http://engineering.rowan.edu/~shreek/spring09/ecomms/
Lecture 7aLecture 7aMarch 3, 2009March 3, 2009
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
PlanPlan• 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 E nvelope
G aussian 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 & P hase M odulationNarrow band/W idebandVCO & Slope Detector
P LL
Analog
Source EncodingHuffm an codes
E rror-control EncodingHamm ing Codes
Sam plingPAM
Q uantizationPCM
Line Encoding
Tim e Divis ion M uxT1 (DS 1) S tandards
Packet Sw itchingEthernet
ISO 7-Layer Protocol
BasebandCO DE C
ASKPSKFSK
BPSK
Q PSK
M -ary PSK
Q AM
BandpassM O DEM
DigitalDigita l Com m Transceiver
Systems
Electrical Comm unication Systems
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
DSB-SC ModulationDSB-SC ModulationSignals Systems
Time 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 Demohttp://engineering.rowan.edu/~shreek/spring09/ecomms/demos/dsbsc.m
S. Mandayam/ ECOMMS/ECE Dept./Rowan University
DSB-SC: Balanced DSB-SC: Balanced ModulatorModulator
AMAccos2fct
m(t)
AM-Accos2fct
-m(t)
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)Product
ModulatorBaseband
LPF
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
ProductModulatorm(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