pass band signal
TRANSCRIPT
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Pass-band Data Transmission
Dr. Teerasit Kasetkasem
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Block Diagram
Functional model of pass-band data transmissionsystem.
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Signaling
Illustrative aveforms for t!e t!ree basic forms ofsignaling binary information. "a# $mplitude-s!ift keying."b# P!ase-s!ift keying. "c # Fre%uency-s!ift keying it!continuous p!ase.
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&!at do e ant to study'
&e are going to study and compare
different modulation tec!ni%ues in terms of
Probability of errors
Poer SpectrumBandidt! efficiency
B
Rb= ρ Bits(s()*
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+o!erent PSK
Binary P!ase S!ift Keying "BPSK#
+onsider t!e system it! , basis functions
and
( ) t f T t cb
π φ 2cos
21 =
( ) t f T t cb π φ 2sin
2
2 =
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BPSK
If e ant to fi t!at for bot! symbols " and /# t!e
transmitted energies are e%ual0 e !ave
φ/
φ,
s/
&e place s to minimi*e
probability of error
s
s
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BPSK
&e found t!at p!ase of s/
and s. are /1
degree difference. &e can rotate s/
and
s.
φ/
φ,
s/
s
2otate
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BPSK
&e observe t!at φ, !as not!ing to do it!
signals. )ence0 only one basis function is
sufficient to represent t!e signals
φ,
s/
s
φ/
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BPSK
Finally0 e !ave
( ) t f T
E t E t s c
b
bb π φ 2cos
2)(11 ==
( ) t f T
E t E t s c
b
bb π φ 2cos
2)(10 −=−=
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BPSK
Signal-space diagram for co!erent binary PSK system.
T!e aveforms depicting t!e transmitted signals s/"t # and
s,"t #0 displayed in t!e inserts0 assume nc = ,.
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BPSK
Probability of error calculation. In t!e case of
e%ually likely "Pr"m.#3Pr"m/##0 e !ave
=
=
0
0
erfc
2
1
2erfc
2
1
N
E
N
d P
b
ik e
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BPSK
Block diagrams for "a# binary PSK transmitter and "b#
co!erent binary PSK receiver.
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4uadrip!ase-S!ift Keying "4PSK#
( ) ( ) T t it f T
E t s ci <≤
−+= 0;
4122cos
2 π π
T is symbol duration
5 is signal energy per symbol
T!ere are 6 symbols for i 3 /0 ,0 70 and 6
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4PSK
( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) T t t i E t i E
t f T
i E t f T
i E t s cci
<≤
−−
−=
−−
−=
0;4
12sin4
12cos
2sin2
412sin2cos
2
412cos
21 φ π
φ π
π π
π π
&!ic! e can rite in vector format as
( )
( )
−−
−
=4
12sin4
12cos
π
π
i E
i E
is
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4PSK
i Input Dibit P!ase of4PSK
signaling
+oordinate of8essage point
si/ si,
/ /
, 7 /
6 //
4/π
4/3π
4/5π
4/7π
2/ E
2/ E
2/ E
2/ E
2/ E −
2/ E −2/ E −
2/ E −
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4PSK
φ,
φ/
s6
s/
s7
s,
"/#"#
"/# "//#
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4PSK signals
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4PSK
Block
diagrams of
"a# 4PSK
transmitter
and "b#co!erent
4PSK
receiver.
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4PSK9 5rror Probability 4PSK
+onsider signal
constellation
given in t!e
figure
φ,
φ/
s6
s/
s7
s,
"/#"#
"/# "//#
:6
:/
:7
:,
2/ E
2/ E
2/ E −
2/ E −
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4PSK
&e can treat 4PSK as t!e combination
of , independent BPSK over t!e interval
T3,Tb
since t!e first bit is transmitted by φ/ and
t!e second bit is transmitted by φ,.
Probability of error for eac! c!annel isgiven by
=
=′
00
12
2erf
2
1
2erfc
2
1
N
E c
N
d P
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4PSK
If symbol is to be received correctly bot! bits
must be received correctly.
)ence0 t!e average probability of correct
decision is given by&!ic! gives t!e probability of errors e%ual to
( ) 21 P P c ′−=
≈
−
=−=
0
0
2
0
2erfc
2
erfc
4
1
2
erfc1
N
E
N
E
N
E P P C e
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4PSK
Since one symbol of 4PSK consists of tobits0 e !ave E = ,E b.
T!e above probability is t!e error probabilityper symbol. T!e avg. probability of error per bit
&!ic! is eactly t!e same as BPSK .
( )
≈
0
erfcsymbol per N
E Pe b
( ) ( )
≈= 0erfc2
1
symbol per2
1
bit per N
E
Pe Pe
b
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BPSK vs 4PSK
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2Power spectrum density of BPSK vs. QPSK
Normalized frequency,fTb
N o r m a l i z e d P S D , S f / 2 E b
BPSK
QPSK
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4PSK
+onclusion4PSK is capable of transmitting data tice
as faster as BPSK it! t!e same energy per
bit.&e ill also learn in t!e future t!at 4PSK
!as !alf of t!e bandidt! of BPSK.
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;FFS5T 4PSK
φ,
φ/
s6
s/
s7
s,
"/#"#
"/# "//#
< degree s!ift in p!ase
/1 degree s!ift in p!ase
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;FFS5T 4PSK
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;FFS5T 4PSK
&!enever bot! bits are c!angedsimultaneously0 /1 degree p!ase-s!iftoccurs.
$t /1 p!ase-s!ift0 t!e amplitude of t!etransmitted signal c!anges very rapidlycosting amplitude fluctuation.
T!is signal may be distorted !en ispassed t!roug! t!e filter or nonlinearamplifier.
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;FFS5T 4PSK
0 1 2 3 4 5 6 7 8
-2
-1
0
1
2
0 1 2 3 4 5 6 7 8-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
;riginal Signal
Filtered signal
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;FFS5T 4PSK
To solve t!e amplitude fluctuation
problem0 e propose t!e offset 4PSK.
;ffset 4PSK delay t!e data in
%uadrature component by T(, seconds
"!alf of symbol#.
=o0 no ay t!at bot! bits can c!ange
at t!e same time.
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;FFS5T 4PSK
In t!e offset 4PSK0 t!e p!ase of t!e
signal can c!ange by ±< or degree
only !ile in t!e 4PSK t!e p!ase of t!e
signal can c!ange by ±/1 ±< or degree.
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0 1 2 3 4 5 6 7 8
-2
-1
0
1
2
0 1 2 3 4 5 6 7 8
-1
-0.5
0
0.5
1
0 1 2 3 4 5 6 7 8
-1
-0.5
0
0.5
1
;FFS5T 4PSK
0 1 2 3 4 5 6 7 8-2
-1
0
1
2
0 1 2 3 4 5 6 7 8-1
-0.5
0
0.5
1
0 1 2 3 4 5 6 7 8
-1
-0.5
0
0.5
1
/ /
/
/ / /
Inp!ase4PSK
4 p!ase
4PSK
4PSK
/ /
/
/ / /
Inp!ase
;ffset 4PSK
4 p!ase
;ffset 4PSK
;ffset 4PSK
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;ffset 4PSK
Possible pat!s for sitc!ing beteen t!e
message points in "a# 4PSK and "b# offset 4PSK.
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;FFS5T 4PSK
Bandidt!s of t!e offset 4PSK and t!e
regular 4PSK is t!e same.
From signal constellation e !ave t!at
&!ic! is eactly t!e same as t!e regular4PSK.
≈
02erfc
N
E P e
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π(6-s!ifted 4PSK
Try to reduce amplitude fluctuation by
sitc!ing beteen , signal constellation
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π(6-s!ifted 4PSK
$s t!e result0
t!e p!ase of t!e
signal can be
c!anged in
order of ±π(6 or±7π(6
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π(6-s!ifted 4PSK
Since t!e p!ase of t!e net ill be varied in
order of ±π(6 and ±7π(60 e can designed t!e
differential π(6-s!ifted 4PSK as given belo
>ray-5ncoded Input Data P!ase +!ange in radians
?π(6
/
?7π(6// -7π(6
/ -π(6
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π(6-s!ifted 4PSK9///
Step Initialp!ase
Input Dibit P!asec!ange
Transmittedp!ase
/ π(6 π(6 π(,
, π(, / -π(6 π(6
7 π(6 / -π(6
6 / 7π(6 7π(6
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π(6-s!ifted 4PSK
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-2
0
2
QPSK
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-2
0
2
OFFSET QPSK
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-1
0
1
D OFFSET QPSK
/ / / /
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π(6-s!ifted 4PSK
Since e only measure t!e p!ase
different beteen ad@acent symbols0 no
p!ase information is necessary. )ence0
non-co!erent receiver can be used.
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Block diagram of t!e π (6-s!ifted D4PSK
detector.
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π(6-s!ifted 4PSK
Illustrating t!e
possibility of p!ase
angles rapping
around t!e positive
real ais.
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8-array PSK
$t a moment0 t!ere are 8 possible
symbol values being sent for 8 different
p!ase values0 ( ) M ii /12 π θ −=
( ) ( ) M ii M
t f T
E t s ci ,,2,1,1
22cos
2=
−+= π π
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8-array PSK
Signal-space diagram
for octap!ase-s!ift
keying "i.e.0 M = 1#. T!e
decision boundaries are
s!on as das!ed lines.
Signal-space diagram
illustrating t!e
application of t!e union
bound for octap!ase-
s!ift keying.
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8-array PSK
Probability of errors
( ) M E d d /sin21812 π ==∴
( ) 4 ;/sinerfc 0 ≥
≈ M M N
E
P e π
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8-ary PSK
0 5 10 15 20 25 3010-50
10-40
10-30
10-20
10-10
100
Eb /N0 dB
P r o b a b i l i t y o f S y m b o l e r r o r s
QPSK
8-ary PSK
16-ary PSK
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8-array PSK
Poer Spectra "8-array#
83,0 e !ave
( )
( ) M f T M E
Tf E f S
bb
PSK
22
2
2
logsinclog2
sinc2)(
=
=
( ) f T E f S bb BPSK 2sinc2)( =
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8-array PSK
Poer spectra of M -ary PSK
signals for 8 = ,0 60 1.
T bf
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8-array PSK
Bandidt! efficiency9
&e only consider t!e bandidt! of t!e main lobe
"or null-to-null bandidt!#
Bandidt! efficiency of 8-ary PSK is given by
M R
M T T B b
b 22 log2
log22 ===
M M R
R
B
R
b
bb22 log5.0log
2=== ρ
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8-ary 4$8
4$8 3 4uadrature $mplitude 8odulation
Bot! $mplitude and p!ase of carrier
c!ange according to t!e transmitted
symbol0 mi .
!ere ai and bi are integers.( ) ( ) ( ) T t t f bT
E
t f aT
E
t s cicii ≤<−= 0;2sin
2
2cos
2 00
π π
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8-ary 4$8
$gain0 e !ave
as t!e basis functions
( ) T t t f T
t c ≤<= 0;2cos2
1 π φ
( ) T t t f T
t cb
≤<= 02sin2
2 π φ
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8-ary 4$8
4$8 s%uare +onstellation)aving even number of bits per symbol0
denoted by ,n.
83L L possible valuesDenoting M L =
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/A-4$8
[ ]
−−−−−−−−−−−−
−−
−−
=
)3,3()3,1()3,1()3,3(
)1,3()1,1()1,1()1,3()1,3()1,1()1,1()1,3(
)3,3()3,1()3,1()3,3(
, ii ba
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/A-4$8
-ary0 6-P$8
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/A-4$8
+alculation of Probability of errorsSince bot! basis functions are ort!ogonal0
e can treat t!e /A-4$8 as combination of
to 6-ary P$8 systems.For eac! system0 t!e probability of error is
given by
−=
−=′
0
0
0
11
2
11
N
E erfc
M N
d erfc
L P e
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/A-4$8
$ symbol ill be received correctly if data
transmitted on bot! 6-ary P$8 systems are
received correctly. )ence0 e !ave
Probability of symbol error is given by
( ) ( ) 21 ec P symbol P ′−=
( ) ( ) ( )
( ) eee
ece
P P P
P symbol P symbol P
′≈′−′+−=
′−−=−=
2211
111
2
2
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/A-4$8
)ence0 e !ave
But because average energy is given by
&e !ave
( )
−=
0
0112
N
E erfc
M symbol P e
( ) ( )
3
1212
22 0
2/
1
20 E M i
L
E E
L
iav
−=
−= ∑
=
( )( )
−
−=
012
3112
N M
E erfc
M symbol P av
e
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+o!erent FSK
FSK 3 fre%uency s!ift keying
+o!erent 3 receiver !ave information on
!ere t!e *ero p!ase of carrier.
&e can treat it as non-linear modulation
since information is put into t!e
fre%uency.
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Binary FSK
Transmitted signals are
!ere
( ) ( )
≤<
=
elsewere ,0
0,2cos2
bib
b
i
T t t f T
E
t sπ
2,1; =+= iT
in f b
ci
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Binary FSK
S/"t# represented symbol C/.
S,"t# represented symbol C.
T!is FSK is also knon as SundeEs FSK.It is continuous p!ase fre%uency-s!ift
keying "+PFSK#.
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Binary FSK
T!ere are to basis functions ritten as
$s a result0 t!e signal vectors are
( ) ( )
≤<
=
elsewere ,0
0,2cos2
bibi
T t t f T t
π φ
=
=
b
b
E
E 0 !n"
021 ss
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S
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BFSK
From t!e figure0 e !ave
In case of Pr"#3Pr"/#0 t!e probability of
error is given by
&e observe t!at at a given value of Pe0t!e BFSK system re%uires tice as muc!
poer as t!e BPSK system.
b E d 212 =
=
022
1
N
E erfc P b
e
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T2$=S8ITT52
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25+5I52
P S t l d it f BFSK
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Poer Spectral density of BFSK
+onsider t!e SundeEs FSK !ere f / and f , are different
by /(Tb. &e can rite
&e observe t!at in-p!ase component does not
depend on mi since
( )
( ) ( )t f T
t
T
E t f
T
t
T
E
T
t t f
T
E t s
cbb
bc
bb
b
bc
b
bi
π π
π π
π π
2sinsin2
2coscos2
2cos2
±−
±=
±=
=
±
bb
b
bb
b
T
t
T
E
T
t
T
E π π cos
2cos
2
P S t l d it f BFSK
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Poer Spectral density of BFSK
&e !ave
For t!e %uadrature component
( )
++
−=
=
bbb
b
bb
b BI
T f
T f
T
E
T
t
T
E F f S
2
1
2
1
2cos
22
δ δ π
)alf of t!e symbol poer
( )
±=
bb
b
T
t
T
E t g π sin
2 ( )
( )2222
2
14
cos8
−=
f T
f T T E S
b
bbb B
π
π
P S t l d it f BFSK
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Poer Spectral density of BFSK
Finally0 e obtain )()()( f S f S f S B BI B +=
P! T f BFSK
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P!ase Tree of BFSK
FSK signal is given by
$t t 3 0 e !ave
T!e p!ase of Signal is *ero.
( )
±=
bc
b
b
T
t t f
T
E t s
π π 2cos
2
( ) ( )0cos20
02cos2
0b
b
bc
b
b
T
E
T f
T
E s =
±=
π π
P! T f BFSK
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P!ase Tree of BFSK
$t t 3 Tb0 e !ave
&e observe t!at p!ase c!anges by ±π afterone symbol "Tb seconds#. -π for symbol C/
and ?π for symbol C
&e can dra t!e p!ase trellis as
( ) ( )π π
π ±=
±= cos
22cos
2
b
b
b
bbc
b
bb
T
E
T
T T f
T
E T s
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8i i S!ift k i "8SK#
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8inimum-S!ift keying "8SK#
8SK tries to s!ift t!e p!ase after one
symbol to @ust !alf of SundeEs FSK
system. T!e transmitted signal is given
by
( ) ( )[ ]
( )[ ]
( )[ ]
+
+
=+= #0#for02cos2
#1#for02cos2
2cos2
2
1
θ π
θ π
θ π
t f T
E
t f T
E
t t f T
E t s
b
b
b
b
cb
b
8SK
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8SK
&!ere
;bserve t!at
( ) ( ) t T
!t
b
π θ θ ±= 0
bc
bc
T
! f f
T
! f f
2!n"
221 −=+=
( )212
1 f f f c +=
8SK
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8SK
h 3 T b"f /-f ,# is called Cdeviation ratio.
For SundeEs FSK0 h 3 /.
For 8SK0 h 3 .G.
h cannot be any smaller because t!eort!ogonality beteen cos",πf /t # and cos",πf ,t #
is still !eld for h H .G.
;rt!ogonality guarantees t!at bot! signal illnot interfere eac! ot!er in detection process.
8SK
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8SK
P!ase trellis diagram for 8SK signal ///
8SK
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8SK
Signal s"t# of 8SK can be decomposed
into
!ere
( ) ( )[ ]
( )[ ] ( ) ( )[ ] ( )
( ) ( ) ( ) ( )t f t st f t s
t f t T
E t f t
T
E
t t f
T
E t s
cc I
cb
bc
b
b
c
b
b
π π
π θ π θ
θ π
2sin2cos
2sinsin2
2coscos2
2cos2
−=
−=
+=
( ) ( ) bb
T t t T
t ≤<±= 0;2
0 π
θ θ
8SK
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8SK
Symbol θ "# θ "Tb#
/
π(,
π -π(,
-π(,
ππ(,
8SK
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8SK
For t!e interval T b H t ≤ 0 e !ave
etEs note !ere t!at t!e ± for t!e interval-T bHt ≤ and H t ≤T b may not be t!e same.
&e kno t!at
( ) ( ) 0;2
0 ≤<−±= t T t T
t bb
π θ θ
( ) ( )[ ] ( )[ ]
=
±
bbb T
t
T
t
T
t
2sin0sin
2cos0cos
20cos
π θ
π θ
π θ
8SK
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8SK
Since θ"# can be eit!er or π depending ont!e past !istory. &e !ave
C? for θ"# 3 and C- for θ"# 3 π)ence0 e !ave
( ) ( )[ ]
±=
=
±
bbb T
t
T
t
T
t
2
cos
2
cos0cos
2
0cos π π
θ π
θ
bbbb
b I T t T
T
t
T
E t s ≤<−
±= ;
2cos
2)(
π
8SK
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8SK
Similarly e can rite
for H t ≤T b and T b H t ≤,T b. =ote t!e C? and C-may be different beteen t!ese intervals.
Furt!ermore0 e !ave t!at θ "T b# can be ±π(,
depending on t!e past !istory.
( ) ( ) ( )bb
b T t T
T t −±=2
π θ θ
8SK
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8SK
)ence0 e !ave
e !ave t!at θ "T b# can be ±π(, depending
on t!e past !istory.
( ) ( )
( )[ ] ( )
( )[ ] ( )
( )[ ] ( )[ ]
−±
−=
−±
−=
−±
22sincos
22cossin
2sincos
2cossin
2sin
π π θ π π θ
π θ
π θ
π θ
bb
bb
b
bb
b
bb
b
bb
T t T
T t T
T
T t T
T
T t T
T
T t T
( ) ( )
±=
−±=
−±
bbb
bb
T
t
T
t
T
T t T
2sin
22cos
2sin
π π π π θ
8SK
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8SK
)ence0 e !ave
C? for θ"T b# 3 ?π(, and C- for θ"T b# 3 -π(,T!e basis functions c!ange to
bbb
b T t
T
t
T
E t s 20;
2sin
2)( ≤<
±=
π
( ) ( ) bc
bb
T t t f T
t
T t ≤<
= 0;2cos
2cos
21 π
π φ
( ) ( ) bcbb
T t t f T
t
T t ≤<
= 0;2sin
2sin
22 π
π φ
8SK
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8SK
&e rite 8SK signal as
&!ere and
( ) ( )[ ] ( ) ( )[ ] ( )
( )[ ] ( ) ( )[ ] ( )
( )[ ] ( )[ ]
)()(
)(sin$)(0cos$
2sin
2
sinsin
2
2cos
2
cos0cos
2
2sinsin2
2coscos2
2211
2 b1 b
t st s
t T t
t f T
t
T T
E
t f T
t
T
E
t f t T
E t f t
T
E t s
b
cb
bb
b
cbb
b
cb
bc
b
b
φ φ
φ θ φ θ
π
π
θ π
π
θ
π θ π θ
+=
−=
−
=
−=
( )[ ]0cos1 θ b E s = ( )[ ]bb T E s θ sin2 −=
8SK
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8SK
Symbol θ "# s/ θ "Tb# s,
/
π(,
π -π(,
-π(,
ππ(,
b E
b E
b E
b E
b E −
b E −
b E −
b E −
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=
02
1
N
E erfc P b
e
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P!ase9 π(, π π π(, -π(,π(,
8SK
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8SK
&e observe t!at 8SK is in fact t!e4PSK !aving t!e pulse s!ape
Block diagrams for transmitter and
receiver are given in t!e net to slides.
bT
t
2cos
π
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∫bT
dttt )()( φ
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∫ −
=bT
dt t t " " )()( 11 φ
∫ =bT
dt t t " "
2
022 )()( φ
4
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.5
1
1.5
2
2.5
3
3.5
Normalized Frequency, fTb
N o r m a l i z e d P S D ,
S ( f ) / E b
MSK
BPSK
QPSK
8SK
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8SK
Probability of error of 8SK system is e%ual toBPSK and 4PSK
T!is due to t!e fact t!at 8SK observes t!e
signal for to symbol intervals !ereas FSKonly observes for single signal interval.
Bandidt! of 8SK system is GJ larger t!an
4PSK.
( ) 2
222 11%
2cos32)(
−=
f T
f T E f S
b
bb MSK
π
π
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
=onco!erent implies t!at p!ase information isnot available to t!e receiver.
$s a result0 *ero p!ase of t!e receiver canmean any p!ase of t!e transmitter.
$ny modulation tec!ni%ues t!at transmitsinformation t!roug! t!e p!ase cannot be usedin nonco!erent receivers.
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
cos",πft#
sin",πft#
2eceiver
cos",πft#sin",πft#
Transmitter
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
It is impossible to dra t!e signal constellationsince e do not kno !ere t!e aes are.
)oever0 e can still determine t!e distance
of t!e eac! signal constellation from t!e origin. $s a result0 t!e modulation tec!ni%ues t!at put
information in t!e amplitude can be detected.
FSK uses t!e amplitude of signals in to
different fre%uencies. )ence non-co!erent
receivers can be employed.
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
+onsider t!e BFSK system !ere tofre%uencies f / and f , are used to represented
to C/ and C.
T!e transmitted signal is given by
Problem is t!at θ is unknon to t!e receiver.For t!e co!erent receiver0 θ is precisely knon
by receiver.
( ) bi T t it f T
E t s ≤<=+= 0,2,1;2cos
2)( θ π
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
Furt!ermore0 e !ave
To get rid of t!e p!ase information "θ#0 e use
t!e amplitude
( )
( ) ( ) ( ) ( )
)()(
2sinsin2
2coscos2
2cos2
)(
2211 t st s
t f T
E t f
T
E
t f T
E t s
ii
ii
i
φ φ
π θ π θ
θ π
+=
+=
+=
( ) ( ) ( ) E E E s st s ii =+=+= θ θ 2222
21 sincos
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
&!ere
T!e amplitude of t!e received signal
∫ ∫ =⇒=T T
i dt t t " "dt t t s s
011
011 )()()()( φ φ
∫ ∫ =⇒=
T T
i dt t t " "dt t t s s0
220
22 )()()()( φ φ
( ) ( )
2/12
0
2
0
2sin)(2cos)(
+
= ∫ ∫ T
iT
ii dt t f t "dt t f t "l π π
4uadrature 2eceiver using
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g
correlators
4uadrature 2eceiver using 8atc!ed
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g
Filter
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
Decision rule9 et if l i & l k for all k . Foreamples0 decide if l 1 & l 2
T!is decision rule suggests t!at if t!e envelop"amplitude# of t!e received signal described in
term of cos(2π f 1t ) is greater t!an t!e envelop of
t!e received signal described in term of
cos(2π f 2t ), e say s1(t ) w!s sent.
imm ='1' mm =
=onco!erent 8atc!ed Filter
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=onco!erent 8atc!ed Filter
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
+onsider t!e output of matc!ed filter ofcos(2π f it ).
( ) ( )[ ] ( )[ ]∫ +−=−∗=T
ii d t T f "t T f t "t y
0
2cos)(2cos)( τ τ π τ π
[ ] ( )
[ ] ( )
2sin)()(2in
2cos)()(2cos)(
0
0
∫
∫
−
−=
T
ii
T
ii
d f "t T f s
d f "t T f t y
τ τ π τ π
τ τ π τ π
=onco!erent ;rt!ogonal 8odulation
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=onco!erent ;rt!ogonal 8odulation
5nvelope at t3T is
&!ic! is eactly t!e same as in
correlator receiver
( ) ( )
2/12
0
2
0
2cos)(2cos)(
+
=
∫ ∫
T
i
T
ii d f "d f "l τ τ π τ τ τ π τ
>enerali*ed binary receiver for nonco!erent ort!ogonal
modulation
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modulation.
4uadrature receiver e%uivalent to eit!er one of t!e to
matc!ed filters in part
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matc!ed filters in part
=onco!erent ;rt!ogonal 8odulation
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g
Probability of 5rrors
−=
02
ep
2
1
N
E P e
=onco!erent9 BFSK
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=onco!erent9 BFSK
For BFSK0 e !ave
( ) ( )
≤<=
elsewere ; 0
0;2cos2
bib
bi
T t t f T
E
t s π
=onco!erent9 BFSK
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o co e e S
=onco!erent9 BFSK
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Probability of 5rrors
−=
02
ep2
1
N
E P b
e
DPSK
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Differential PSK Instead of finding t!e p!ase of t!e signal on
t!e interval 0*t ≤T b$ +is receier "etermines te
p!se "ifference between !"-!cent time inter!ls. f /1 is sent, te p!se will rem!in te s!me
f /0 is sent, te p!se will c!nge 180 "egree.
DPSK
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;r e !ave
and
( )
( )
≤<
≤<
=
bbcb
b
bcb
b
T t T t f T
E
T t t f T
E
t s
2;2cos2
20;2cos2
)(1
π
π
( )
( )
≤<+
≤<
=
bbcb
b
bc
b
b
T t T t f T
E
T t t f
T
E
t s
2;2cos2
20;2cos
2)(2
π π
π
DPSK
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In t!is case0 e !ave T 2T b !n" E 2 E b
ence, te prob!bility of error is gien by
−= 0ep2
1
N
E
P
b
e
DPSK9 Transmitter
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11 −− ⊕= k k k k k d bd bd
DPSK
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bk L / / / /
d k 1
L/ / / / /
Differentialencoded d k L
/ / / / /
TransmittedP!ase
π π π π π
DPSK9 2eceiver
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DPSK9 2eceiver
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From t!e block diagram0 e !ave t!at t!edecision rule as
If t!e p!ase of signal is unc!anged "send C/#t!e sign "C? or C-# of bot! "i and " sol" notc!nge. ence, te l (x) sol" be positie.
If t!e p!ase of signal is unc!anged "send C#t!e sign "C? or C-/# of bot! "i and " sol"c!nge. ence, te l (x) sol" be neg!tie.
( ) 0
1s!y
0s!y
1010 <>
+= I I " " " "l x
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