Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Material Type: Notes; Class: Wireless Communications; Subject: Electrical & Computer Engr; University: Villanova University; Term: Unknown 1989;
Typology: Study notes
1 / 80
This page cannot be seen from the preview
Don't miss anything!
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Yimin Zhang, Ph.D.
Department of Electrical & Computer Engineering
Villanova University
http://yiminzhang.com/ECE
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Concept of ModulationPower and Spectral EfficiencyPulse ShapingDigital Modulations
Linear – BPSK, QPSK, DPSK, OQPSK,
π
Nonlinear – FSK, MSK, GMSKM-ary ASK, M-ary PSK, M-ary FSK
Coherent and Noncoherent Detection
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Amplitude modulation
Angle modulation
(Frequency & phase modulations)
Amplitude shift keying (ASK)Frequency shift keying (FSK)
Phase shift keying (PSK)
Quadrature amplitude
modulation (QAM)
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
AM and FM signalsproduced by a single tone.( a
) Carrier wave. ( b
) Sinusoidal modulating signal.( c
) Amplitude-modulated signal.( d
) Frequency-modulated signal.
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
AM signal can be represented as
)
2
cos( )] (
(^1) [
) (
t f t m A t s c
c
AM
π
=
For a sinusoidal modulating signalthe modulation index is given by
m^ c
c
m
π
The spectrum of an AM signal can be show to be
c
c
c
c
c
AM
δ
δ
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
1
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
The two most important classes of angle modulation are frequencymodulation and phase modulation
Frequency modulation (FM) can be represented as
=
=
t ∫ ∞− f
c
c
c
c
FM
d m k t f A t t f A t S
η η π π θ π ) (
2
2
cos
)] (
2
cos[
) (
c^
f^
Phase modulation (PM) can be represented as
)] (
2
cos[
) (
t m k t f A t S
c
c
PM
θ
π
=
θ
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Direct method^ ¾
The carrier frequency is directly
varied in accordance with the inputmodulating signal.
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Slope Detector
Zero-crossing Detector - PLL for FM Detection - Quadrature Detection
Yimin Zhang, Villanova University
Yimin Zhang, Villanova University
In digital wireless communication systems, the message(modulating signal) is represented as a time sequence of symbolsor pulses.
-^
Each symbol has
m
finite states
Example
m
Each symbol represents^ n
bits of information n
= log
m 2
bits/symbol
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Performance of modulation is often measured by
power efficiency
The ability of a modulation technique to preserve the fidelity ofthe digital message at low power levels.Expressed in
/ b
0
(ratio of signal energy per bit to noise
power spectral density) required at the receiver output for acertain error probability.
bandwidth efficiency
The ability of modulation scheme to accommodate data withina limited bandwidth.Expressed as the ratio of throughput data rate per Hz.
p
bps/Hz
R B
B^
=
B η η
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
Examples :For US digital cellular standard,
= 48.6 kbps
RF bandwidth = 30 KHzFor SNR = 20 dB
= 30000 * log
= 30000 * log
(1 + 100) = 199.75 kbps 2
For GSM standard,
= 270.833 kbps
= 1.99 Mbps
for
S/N = 30 dB
Yimin Zhang, Villanova University
ECE 8708 Wireless Communications : Modulation Techniques
The
power spectral density
(PSD) of a random signal
w
( t
is define
as
∞ →
f
W
f
p
T
T
w
2 ) (
lim ) (
elsewhere
T t T t w t w f W
T
