EE 418 Project 2: Key Distribution in Wireless Sensor Networks
EE 6332, Spring, 2014 Wireless Communication
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Transcript of EE 6332, Spring, 2014 Wireless Communication
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EE 6332, Spring, 2017
Wireless Communication
Zhu Han
Department of Electrical and Computer Engineering
Class 12
Feb. 27th, 2017
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Outline (Chapter 5.2-5.4)Outline (Chapter 5.2-5.4) Geometric representation of modulation signals
Linear modulation– BPSK, DPSK; QPSK, offset QPSK, /4 QPSK
Constant envelope modulation– BFSK, MSK, GMSK
Combined linear and constant envelope modulation– MPSK
– QAM
– MFSK
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Analog Modulation: PAM, PWM, PPM, PCMAnalog Modulation: PAM, PWM, PPM, PCM
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Geometric Representation of Modulation SignalGeometric Representation of Modulation Signal
Digital Modulation involves– Choosing a particular signal waveform for transmission for a
particular symbol or signal
– For M possible signals, the set of all signal waveforms are:
For binary modulation, each bit is mapped to a signal from a set of signal set S that has two signals
We can view the elements of S as points in vector space
)}(),...,(),({ 21 tststsS M
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Geometric Representation of Modulation SignalGeometric Representation of Modulation Signal Vector space
– We can represented the elements of S as linear combination of basis signals.
– The number of basis signals are the dimension of the vector space.
– Basis signals are orthogonal to each-other.
– Each basis is normalized to have unit energy:
signal. basis theis )(
1)(2
thi
i
it
dttE
0)()(
)()(1
dttt
tsts
ji
N
jjiji
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ExampleExample
)(),(
)2cos(2
)(
)2cos(2
)(
)2cos(2
)(
11
1
2
1
tEtES
tfT
t
tfT
Ets
tfT
Ets
bb
cb
cb
b
cb
b
b
b
T t 0
T t 0
bE bE
Q
I
The basis signal
Two signal waveforms to be used for transmission
Constellation Diagram Dimension = 1
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Constellation DiagramConstellation Diagram
Properties of Modulation Scheme can be inferred from Constellation Diagram– Bandwidth occupied by the modulation increases as the
dimension of the modulated signal increases
– Bandwidth occupied by the modulation decreases as the signal points per dimension increases (getting more dense)
– Probability of bit error is proportional to the distance between the closest points in the constellation.
Bit error decreases as the distance increases (sparse).
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Concept of a constellation diagramConcept of a constellation diagram
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Example of samples of matched filter output Example of samples of matched filter output for some bandpass modulation schemesfor some bandpass modulation schemes
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Linear Modulation TechniquesLinear Modulation Techniques
Classify digital modulation techniques as: – Linear
The amplitude of the transmitted signal varies linearly with the modulating digital signal, m(t).
They usually do not have constant envelope. More spectral efficient. Poor power efficiency
– Non-linear
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Binary Phase Shift KeyingBinary Phase Shift Keying
Use alternative sine wave phase to encode bits– Phases are separated by 180 degrees.
– Simple to implement, inefficient use of bandwidth.
– Very robust, used extensively in satellite communication.
Q
0State
1 State
0binary
1binary
)2cos()(
)2cos()(
2
1
ccc
ccc
fAts
fAts
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BPSK ExampleBPSK Example
Data
Carrier
Carrier+
BPSK waveform
1 1 0 1 0 1
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BPSK Virtue of pulse shapingBPSK Virtue of pulse shaping
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BPSK Coherent demodulatorBPSK Coherent demodulator
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Differential PSK encodingDifferential PSK encoding
Differential BPSK– 0 = same phase as last signal element
– 1 = 180º shift from last signal element
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EE 542/452 Spring 2008EE 552/452 Spring 2007
DPSK modulation and demodulationDPSK modulation and demodulation
3dB loss
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Quadrature Phase Shift KeyingQuadrature Phase Shift Keying
Multilevel Modulation Technique: 2 bits per symbol
More spectrally efficient, more complex receiver.
Two times more bandwidth efficient than BPSK
Q
11 State
00 State 10 State
01 State
Phase of Carrier: /4, 2/4, 5/4, 7/4
ts
42cos
tfA c 11
4
32cos
tfA c
4
32cos
tfA c
42cos
tfA c
01
00
10
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4 different waveforms4 different waveforms
-1.5-1
-0.50
0.51
1.5
0 0.2 0.4 0.6 0.8 1 -1.5-1
-0.50
0.51
1.5
0 0.2 0.4 0.6 0.8 1
-1.5-1
-0.50
0.51
1.5
0 0.2 0.4 0.6 0.8 1 -1.5-1
-0.50
0.51
1.5
0 0.2 0.4 0.6 0.8 1
11 01
0010
cos+sin -cos+sin
cos-sin -cos-sin
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QPSK ExampleQPSK Example
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QPSK Virtue of pulse shapingQPSK Virtue of pulse shaping
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QPSK modulationQPSK modulation
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QPSK receiverQPSK receiver
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Differential CoherentDifferential Coherent DBPSK
3dB loss
QPSK BER, the same as BPSK
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Offset QPSK waveformsOffset QPSK waveforms
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Offset OQPSKOffset OQPSK
QPSK can have 180 degree jump, amplitude fluctuation
By offsetting the timing of the odd and even bits by one bit-period, or half a symbol-period, the in-phase and quadrature components will never change at the same time.
90 degree jump
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Pi/4 QPSK signalingPi/4 QPSK signaling
135 degree
Non-coherent
detection
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MSK modulationMSK modulation
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Minimum Shift Keying spectraMinimum Shift Keying spectra
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GMSK spectral shapingGMSK spectral shaping
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GMSK spectra shapingGMSK spectra shaping
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8-PSK Signal Constellation8-PSK Signal Constellation
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Pulse Shaped M-PSKPulse Shaped M-PSK
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QAM – Quadrature Amplitude ModulationQAM – Quadrature Amplitude Modulation
Modulation technique used in the cable/video networking world
Instead of a single signal change representing only 1 bps – multiple bits can be represented buy a single signal change
Combination of phase shifting and amplitude shifting (8 phases, 2 amplitudes)
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QAMQAM QAM
– As an example of QAM, 12 different phases are combined with two different amplitudes
– Since only 4 phase angles have 2 different amplitudes, there are a total of 16 combinations
– With 16 signal combinations, each baud equals 4 bits of information (2 ^ 4 = 16)
– Combine ASK and PSK such that each signal corresponds to multiple bits
– More phases than amplitudes– Minimum bandwidth requirement
same as ASK or PSK
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16-QAM Signal Constellation16-QAM Signal Constellation
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Constant Envelope ModulationConstant Envelope Modulation
Amplitude of the carrier is constant, regardless of the variation in the modulating signal– Better immunity to fluctuations due to fading.
– Better random noise immunity
– Power efficient
They occupy larger bandwidth
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Frequency Shift Keying (FSK)Frequency Shift Keying (FSK)
The frequency of the carrier is changed according to the message state (high (1) or low (0)).
One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency modulation)
0)(bit Tt0
1)(bit Tt0
b
b
tffAts
tffAts
c
c
)22cos()(
)22cos()(
2
1
Continues FSK
))(22cos()(
))(2cos()(
t
fc
c
dxxmktfAts
tfAts
Integral of m(x) is continues.
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FSK BandwidthFSK Bandwidth Limiting factor: Physical capabilities of the carrier Not susceptible to noise as much as ASK
Applications– On voice-grade lines, used up to 1200bps– Used for high-frequency (3 to 30 MHz) radio transmission– used at higher frequencies on LANs that use coaxial cable
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Multiple Frequency-Shift Keying (MFSK)Multiple Frequency-Shift Keying (MFSK) More than two frequencies are used
More bandwidth efficient but more susceptible to error
f i = f c + (2i – 1 – M)f d
f c = the carrier frequency f d = the difference frequency M = number of different signal elements = 2 L
L = number of bits per signal element
tfAts ii 2cos Mi 1
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QAM vs. MFSKQAM vs. MFSK
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Comparison of Digital ModulationComparison of Digital Modulation
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Modulation SummaryModulation Summary
Phase Shift Keying is often used, as it provides a highly bandwidth efficient modulation scheme.
QPSK, modulation is very robust, but requires some form of linear amplification. OQPSK and p/4-QPSK can be implemented, and reduce the envelope variations of the signal.
High level M-ary schemes (such as 64-QAM) are very bandwidth efficient, but more susceptible to noise and require linear amplification.
Constant envelope schemes (such as GMSK) can be employed since an efficient, non-linear amplifier can be used.
Coherent reception provides better performance than differential, but requires a more complex receiver.