Presenter: Hong Wen-Chih 2015/8/11. Outline Introduction Definition of fractional fourier transform...
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Transcript of Presenter: Hong Wen-Chih 2015/8/11. Outline Introduction Definition of fractional fourier transform...
OutlineIntroduction Definition of fractional fourier transformLinear canonical transformImplementation of FRFT/LCT
The Direct ComputationDFT-like MethodChirp Convolution Method
Discrete fractional fourier transformConclusion and future work
112/04/19 2
IntroductionDefinition of fourier transform:
Definition of inverse fourier transform:
1
2j wtF e f t dt
1
2j wtf t e F dt
112/04/19 3
Introduction In time-frequency representation
Fourier transform: rotation π/2+2k πInverse fourier transform: rotation -π/2+2k πParity operator: rotation –π+2k πIdentity operator: rotation 2k π
And what if angle is not multiple of π/2 ?
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Introduction
t
v
u
( , )u v( , )t w
Time-frequency plane and a set of coordinates
rotated by angle α relative to the original coordinates
.
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Fractional Fourier Transform Generalization of FTuse to represent FRFTThe properties of FRFT:
Zero rotation:Consistency with Fourier transform:Additivity of rotations: 2π rotation:
Note: do four times FT will equal to do nothing
0F I/2F F
F F F 2F I
F
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Fractional Fourier Transform Definition:
Note: when α is multiple of π, FRFTs degenerate into parity and identity operator
( ) ( ) ( , )F u x t K t u dt
2 2
cot cot csc2 21 cot( )
2
u tj j jutje x t e e dt
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Linear Canonical Transform Generalization of FRFTDefinition:
when b≠0
when b=0a constraint: must be satisfied.
2 2
2 2( , , , )
1( ) ( )
2
jd j jau ut tb b b
a b c dF u e e e f t dtj b
2
2( ,0, , ) ( ) ( )
jcd u
a c dF u d e f du
1ad bc
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Linear Canonical Transform Additivity property:
where
Reversibility property:
where
tfOtfOO hgfeF
dcbaF
dcbaF
),,,(),,,(),,,( 11112222
2 2 1 1
2 2 1 1
a b a be f
c d c dg h
tftfOO dcbaF
acbdF ),,,(),,,(
d b a bI
c a c d
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Linear Canonical Transform Special cases of LCT:
{a, b, c, d} = {0, 1, 1, 0}: {a, b, c, d} = {0, 1, 1, 0}: {a, b, c, d} = {cos, sin, sin, cos}:
{a, b, c, d} = {1, z/2, 0, 1}: LCT becomes the 1-D Fresnel transform
{a, b, c, d} = {1, 0, , 1} : LCT becomes the chirp multiplication operation
{a, b, c, d} = {, 0, 0, 1}: LCT becomes the scaling operation.
)()()0,1,1,0( tfFTjtfOF
)()()0,1,1,0( FIFTjFOF
tfOetfO Fj
F 2/1)cos,sin,sin,(cos
112/04/19 10
Implementation of FRFT/LCTConventional Fourier transform
Clear physical meaningfast algorithm (FFT)Complexity : (N/2)log2N
LCT and FRFTThe Direct ComputationDFT-like MethodChirp Convolution Method
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Implementation of FRFT/LCTThe Direct Computationdirectly sample input and output
2 2
2 2( , , , )
12
u d ut t aj j jb b b
a b c dY u e e e x t dtj b
2 2 2 2
2
1
2 2( , , , )
12
u u t tm d mn n anj j jb b b
a b c d u t tn n
Y m e e e x nj b
t u
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Implementation of FRFT/LCTThe Direct Computation
Easy to designNo constraint expect forDrawbacks
lose many of the important propertiesnot be unitary no additivity Not be reversible lack of closed form properties
applications are very limited
1ad bc
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Implementation of FRFT/LCTChirp Convolution Method
Sample input and output as and
tp uq2 2
2 2( , , , )
1( ) ( )
2
jd j jau ut tb b b
a b c dF u e e e f t dtj b
2 2 2 2
2 2( , , , )
1( ) ( )
2
u u t tj d j j aMq p q pb b b
a b c d u tp M
F q e e e f pj b
M
Mpt
pb
ajpq
b
jq
b
dj
udcba pfbj
qFttuu eee22222 1
2
1
2,,, 2
1
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Implementation of FRFT/LCTChirp Convolution Methodimplement by
2 chirp multiplications 1 chirp convolution
complexity 2P (required for 2 chirp multiplications) + Plog2P (required
for 2 DFTs) Plog2P (P = 2M+1 = the number of sampling points)
Note: 1 chirp convolution needs to 2DFTs
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Implementation of FRFT/LCTDFT-like Method
constraint on the product of t and u
(chirp multi.) (FT) (scaling) (chirp multi.)
Put /2
1/
01
0
0/1
01
10
1/
01
bab
b
bddc
ba
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Implementation of FRFT/LCTDFT-like Method Chirp multiplication:
Scaling:
Fourier transform:
Chirp multiplication:
tfbjattf 2/exp 21
2
22 1
abj t
f t f bb teb t bf
dttfeuF tuj
j
23 2
1
uFbjduuF 32
4 2/exp
112/04/19 17
Implementation of FRFT/LCTDFT-like Method
For 3rd step
Sample the input t and output u as pt and qu
Put /2
dttfeuF tuj
j
23 2
1
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Implementation of FRFT/LCTDFT-like Method
Complexity 2 M-points multiplication operations 1 DFT 2P (two multiplication operations) + (P/2)log2P (one DFT)
(P/2)log2P
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Implementation of FRFT/LCTCompare
Complexity Chirp convolution method: Plog2P (2-DFT)
DFT-like Method: (P/2)log2P (1-DFT)
DFT: (P/2)log2P (1-DFT)
trade-off: chirp. Method: sampling interval is FREE to choice
DFT-like method: some constraint for the sampling
intervals Put /2
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Discrete fractional fourier transformDirect form of DFRFTImproved sampling type DFRFTLinear combination type DFRFTEigenvectors decomposition type DFRFTGroup theory type DFRFTImpulse train type DFRFTClosed form DFRFT
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Discrete fractional fourier transform
Direct form of DFRFTsimplest way sampling the continuous FRFT and computing it
directly
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Discrete fractional fourier transformImproved sampling type DFRFTBy Ozaktas, ArikanSample the continuous FRFT properlySimilar to the continuous caseFast algorithm
Kernel will not be orthogonal and additiveMany constraints
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Discrete fractional fourier transformLinear combination type DFRFTBy Santhanam, McClellan
Four bases: DFT IDFT Identity Time reverse
nFAnfAnFAnfAnF 3210
4
1
2
4
1
k
kqj
q eA
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Discrete fractional fourier transformLinear combination type DFRFT
transform matrix is orthogonaladditivity propertyreversibility property
very similar to the conventional DFT or the identity operation
lose the important characteristic of ‘fractionalization’
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Discrete fractional fourier transformLinear combination type DFRFTDFRFT of the rectangle window function for various angles : (top left) α= 0:01, (top right) α = 0:05, (middle left) α = 0:2, (middle right) α = 0:4, (bottom left) α =π/4, (bottom right) α =π/2.
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Discrete fractional fourier transformEigenvectors decomposition type DFRFT
DFT : F=Fr – j Fi
Search eigenvectors set for N-points DFT
t tr iF U U U U
( ) tr iF U U
( ) tr iF U U
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Discrete fractional fourier transformEigenvectors decomposition type DFRFT
Good in removing chirp noiseBy Pei, Tseng, Yeh, Shyucf. : DRHT can be H Fr Fi
T1N
T1
Τ0
1N10
d
d
d
dddF
)1(00
0
0
001
Nj
j
e
e
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Discrete fractional fourier transformEigenvectors decomposition type DFRFTDFRFT of the rectangle window function for various angles : (top left) α= 0:01, (top right) α = 0:05, (middle left) α = 0:2, (middle right) α = 0:4, (bottom left) α =π/4, (bottom right) α =π/2
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Discrete fractional fourier transformGroup theory type DFRFTBy Richman, Parks
Multiplication of DFT and the periodic chirps Rotation property on the Wigner distribution Additivity and reversible property
Some specified angles Number of points N is prime
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Discrete fractional fourier transformImpulse train type DFRFT By Arikan, Kutay, Ozaktas, Akdemir
special case of the continuous FRFTf(t) is a periodic, equal spaced impulse trainN = 2 , tanα = L/Mmany properties of the FRFT exists
many constraints not be defined for all values of
0 5 10 15 20 25-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
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Discrete fractional fourier transformClosed form DFRFTBy Pei, Ding
further improvement of the sampling type of DFRFTTwo types
digital implementing of the continuous FRFT practical applications about digital signal
processing
112/04/19 33
Discrete fractional fourier transformType I Closed form DFRFT
Sample input f(t) and output Fa(u)
Then
Matrix form:
tnfny Δ umFmY Δαα
N
Nn
tnj
tumnjum
j
nyeetj
mY e2222 Δαcot
2ΔΔαcscΔαcot
2α Δ
π2
αcot1
N
Nn
nynmFmY ,αα
M
Mm
N
Nk
kykmFnmFny ,, αα
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Discrete fractional fourier transformType I Closed form DFRFT
Constraint:
M
Mm
N
Nk
tuknmjtnk
j
kyt ee ΔΔαcsc
Δαcot2
2 222
αsinπ2
Δ
M
Mm
N
Nk
kykmFnmFny ,, αα
12/αsinπ2ΔΔ MStu
112/04/19 35
Discrete fractional fourier transformType I Closed form DFRFT
and
choose S = sgn(sin) = 1
2222 Δαcot
212
π2Δαcot
2α Δ
π2
αcot1,
tnj
M
mnSjum
j
eeetjnmF
M
Mm
N
Nk
kykmFnmF ,, αα nytM
2Δ
αsin)αsgn(sinπ2
12
2222 Δαcot
212
π2)αsin(sgnΔαcot
2α 12
αcos)αsin(sgnαsin,
tnj
M
mnjum
j
eeeM
jnmF
112/04/19 36
Discrete fractional fourier transformType I Closed form DFRFT
when 2D+(0, ), D is integer (i.e., sin > 0)
when 2D+(, 0), D is integer (i.e., sin < 0)
2 2 2 22π
cot α Δ cot α Δ2 2 1 2
α
sin α cosα
2 1
j n m jNm u j n tM
n N
jF m y n
Me e e
2 2 2 22π
cot α Δ cot α Δ2 2 1 2
α
sin α cos α
2 1
j n m jNm u j n tM
n N
jF m y n
Me e e
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Discrete fractional fourier transformType I Closed form DFRFT
Some properties 1 2 and 3 Conjugation property: if y(n) is real 4 No additivity property 5 When is small, and also become very small 6 Complexity
mnFnmF uttu ,, Δ,Δ,αΔ,Δ,α
α α πF m F m 2F m F m
F m F m
t u
22 ( / 2) logP P P
112/04/19 38
Discrete fractional fourier transformType II Closed form DFRFT
Derive from transform matrix of the DLCT of type 1 Type I has too many parameters Simplify the type I Set p = (d/b)u2, q = (a/b)t2
22
212
)sgn(2
2),( 12
1,
nqj
M
mnbjmp
j
qp eeeM
nmF
112/04/19 39
Discrete fractional fourier transformType II Closed form DFRFT
from tu = 2|b|/(2M+1), we find
a, d : any real value No constraint for p, q, and p, q can be any real value. 3 parameters p, q, b without any constraint, Free dimension of 3 (in fact near to 2)
adMqp 2)12/(2
112/04/19 40
Discrete fractional fourier transform Type II Closed form DFRFT
p=0: DLCT becomes a CHIRP multiplication operation followed by a DFT
q=0: DLCT becomes a DFT followed by a chirp multiplication
p=q: F(p,p,s)(m,n) will be a symmetry matrix (i.e., F(p,p,s)
(m,n) = F(p,p,s)(n,m))
112/04/19 41
Discrete fractional fourier transform Type II Closed form DFRFT
2P+(P/2)log2P
No additive propertyConvertible
112/04/19 42
Discrete fractional fourier transformThe relations between the DLCT of type 2 and its
special cases
DFRFT of type 2 p = q, s = 1
DFRFT of type 1 p = cotu2, q = cott2, s = sgn(sin)
DLCT of type 1 p = d/bu2, q = a/bt2, s = sgn(b)
DFT, IDFT p = q = 0, s = 1 for DFT, s = 1 for DFT
112/04/19 43
Discrete fractional fourier transformComparison of Closed Form DFRFT and DLCT
with Other Types of DFRFTDirectly Improved Linear Eigenfxs. Group Impulse Proposed
Reversible *
Closed form
Similarity
Complexity P2 Plog2P+
2P
P2/2 Plog2P+
2P
Plog2P+
2P +2P
FFT 2 FFT 1 FFT 2 FFT 2 FFT 1 FFT
Constraints Less Middle Unable Less Much Much Less
All orders
Properties Less Middle Middle Less Many Many Many
Adv./Cvt. No Convt. Additive Additive Additive Additive Convt.
DSP
PP
2log2
PP
2log2
112/04/19 44
Conclusions and future work
Generalization of the Fourier transformApplications of the conventional FT can also be the
applications of FRFT and LCTMore flexibleUseful tools for signal processing
112/04/19 45
References [1] V. Namias , ‘The fractional order Fourier transform and its
application to quantum mechanics’, J. Inst. Maths Applies. vol. 25, p. 241-265, 1980.
[2] L. B. Almeida, ‘The fractional Fourier transform and time-frequency representations’. IEEE Trans. Signal Processing, vol. 42, no. 11, p. 3084-3091, Nov. 1994.
[3] J. J. Ding, Research of Fractional Fourier Transform and Linear Canonical Transform, Ph. D thesis, National Taiwan Univ., Taipei, Taiwan, R.O.C, 1997
[4] H. M. Ozaktas, Z. Zalevsky, and M. A. Kutay, The Fractional Fourier Transform with Applications in Optics and Signal Processing, 1st Ed., John Wiley & Sons, New York, 2000.
112/04/19 46
References[5] S. C. Pei, C. C. Tseng, M. H. Yeh, and J. J. Shyu,’ Discrete
fractional Hartley and Fourier transform’, IEEE Trans Circ Syst II, vol. 45, no. 6, p. 665–675, Jun. 1998.
[6] H. M. Ozaktas, O. Arikan, ‘Digital computation of the fractional Fourier transform’, IEEE Trans. On Signal Proc., vol. 44, no. 9, p.2141-2150, Sep. 1996.
[7] B. Santhanam and J. H. McClellan, “The DRFT—A rotation in time frequency space,” in Proc. ICASSP, May 1995, pp. 921–924.
[8] J. H. McClellan and T. W. Parks, “Eigenvalue and eigenvector decomposition of the discrete Fourier transform,” IEEE Trans. Audio Electroacoust., vol. AU-20, pp. 66–74, Mar. 1972.
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