IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 60, NO. 11, NOVEMBER 2012 6041
be avoided and the Airy wavelet used in its place, reinforcing the con-
clusion of [9].
Of course, real-valued or non-analytic wavelets may be useful, par-
ticularly in the analysis of discontinuities [3], but for analyzing oscilla-
tory phenomena analytic wavelets are commonly favored. There may
be occasions when other members of the generalized Morse wavelet
family than the Airy wavelets would be more suitable. One instance
arises when the signal of interest may have a form corresponding to
one of the wavelet families; this is particularly true of the Gaussian
and Cauchy families which may provide useful models for time-local-
ized or “impulsive” events that themselves resemble wavelets. Another
common scenario is that oscillatory variability may exist close to the
Nyquist frequency, in which case one would like to sacrifice symmetry
of the wavelet for a more rapid high-frequency decay. Further inves-
tigation of the generalized Morse wavelet parameter space may yield
useful information regarding the properties and possible uses of an-
alytic wavelets, in particular, the relationship between the roles of the
parameters
and
as differentiation and “warping” operators explored
by [9], and the variations of the wavelet form.
A
PPENDIX
All software associated with this paper is distributed as a part
of a freely available MATLAB toolbox called JLAB, available at
http://www.jmlilly.net. The generalized Morse wavelets are imple-
mented with
morsewave, while various properties are computed in
the functions morseprops, morsefreq, morsederiv, mors-
espace, and morsebox. The wavelet transform wavetrans uses
the generalized Morse wavelets by default. Finally, makefigs_su-
perfamily generates all figures in this paper.
REFERENCES
[1] J. M. Lilly and S. C. Olhede, “On the analytic wavelet transform,” IEEE
Trans. Inf. Theory, vol. 56, no. 8, pp. 4135–4156, 2010.
[2] M. Holschneider, Wavelets: An Analysis Tool. Oxford, U.K.: Oxford
Univ. Press, 1995.
[3] S. Mallat, A Wavelet Tour of Signal Processing, 2nd ed. New York:
Academic, 1999.
[4] H. Knutsson, C.-F. Westin, and G. Granlund, “Local multiscale fre-
quency and bandwidth estimation,” in Proc. IEEE Int. Conf. Image
Process., Austin, TX, Nov. 1994, pp. 36–40.
[5] D. J. Field, “Relations between the statistics of natural images and the
response properties of cortical cells,” J. Opt. Soc. Amer. A, vol. 4, no.
12, pp. 2379–2394, 1987.
[6] I. Daubechies and T. Paul, “Time-frequency localisation operators: A
geometric phase space approach II. The use of dilations and transla-
tions,” Inverse Probl., vol. 4, pp. 661–80, 1988.
[7] M. Bayram and R. Baraniuk, “Multiple window time-varying
spectrum estimation,” in Nonlinear and Nonstationary Signal Pro-
cessing. Cambridge, U.K.: Cambridge Univ. Press, 2000, pp.
292–316.
[8] S. C. Olhede and A. T. Walden, “Generalized Morse wavelets,” IEEE
Trans. Signal Process., vol. 50, no. 11, pp. 2661–2670, 2002.
[9] J. M. Lilly and S. C. Olhede, “Higher-order properties of analytic
wavelets,” IEEE Trans. Signal Process., vol. 57, no. 1, pp. 146–160,
2009.
[10] P. Morse, “Diatomic molecules according to the wave mechanics II.
Vibrational levels,” Phys. Rev., vol. 34, pp. 57–64, 1929.
[11] E. W. Stacy, “A generalization of the gamma distribution,” Ann. Math.
Stat., vol. 33, no. 3, pp. 1187–1192, 1962.
[12] J. H. Lienhard and P. L. Meyer, “A physical basis for the generalized
gamma distribution,” Quart. Appl. Math., vol. 25, no. 3, pp. 330–334,
1967.
[13] S. Hegyi, “A powerful generalization of the NBD suggested by Peter
Carruthers,” in VIII International Workshop on Multiparticle Produc-
tion. Singapore: World Scientific, 1999, pp. 272–286.
[14] M. J. Zhang, J. R. Russell, and R. S. Tsay, “A nonlinear autoregressive
conditional duration model with applications to financial transaction
data,” J. Econometrics, vol. 104, pp. 179–207, 2001, 2001.
[15] N. C. Sagias, G. K. Karagiannidis, P. T. Mathiopoulos, and T.
A. Tsiftsis, “On the performance analysis of equal-gain diversity
receivers over generalized gamma fading channels,” IEEE Trans.
Wireless Commun., vol. 5, no. 10, pp. 2967–2975, 2006.
[16] M. D. Yacoub, “The
0
distribution: A physical fading model for
the Stacy distribution,” IEEE Trans. Veh. Technol., vol. 56, no. 1, pp.
27–34, 2007.
Sampling and Reconstruction of Signals in Function Spaces
Associated With the Linear Canonical Transform
Jun Shi, Xiaoping Liu, Xuejun Sha, and Naitong Zhang
Abstract—The linear canonical transform (LCT) has been shown to be
useful and powerful in signal processing, optics, etc. Many results of this
transform are already known, including sampling theory. Most existing
sampling theories of the LCT consider the class of bandlimited signals.
However, in the real world, many analog signals arising in engineering ap-
plications are non-bandlimited.
In this correspondence, we propose a sampling and reconstruction
strategy for a class of function spaces associated with the LCT, which
can provide a suitable and realistic model for real applications. First,
we introduce definitions of semi- and fully-discrete convolutions for the
LCT. Then, we derive necessary and sufficient conditions pertaining to the
LCT, under which integer shifts of a chirp-modulated function generate a
Riesz basis for the function spaces. By applying the results, we present a
more comprehensive sampling theory for the LCT in the function spaces,
and further, a sampling theorem which recovers a signal from its own
samples in the function spaces is established. Moreover, some sampling
theorems for shift-invariant spaces and some existing sampling theories
for bandlimited signals associated with the Fourier transform (FT), the
fractional FT, or the LCT are noted as special cases of the derived results.
Finally, some potential applications of the derived theory are presented.
Index Terms—Convolution theorem, function spaces, linear canonical
transform, sampling and reconstruction.
I. I
NTRODUCTION
The linear canonical transform (LCT) [1], [2] is a four-parameter
class of linear integral transforms, which includes the classical Fourier
transform (FT), the fractional Fourier transform (FRFT), the Fresnel
transform, as well as certain other transforms among its members.
Serving as a useful and powerful analyzing tool, the LCT has received
much attention in many fields, including quantum mechanics [1],
optics [3], communications [4], signal and image processing [5]–[18],
etc. For more details of the LCT, see [2], [3].
Manuscript received February 05, 2012; revised June 08, 2012; accepted July
13, 2012. Date of publication July 31, 2012; date of current version October 09,
2012. The associate editor coordinating the review of this manuscript and ap-
proving it for publication was Prof. Namrata Vaswani. This work was completed
in part while J. Shi was the Department of Electrical and Computer Engineering,
University of Delaware. The work was supported in part by the National Nat-
ural Science Foundation of China under Grant 61171110 and the Short-Term
Overseas Visiting Scholar Program of Harbin Institute of Technology.
J. Shi was with the Department of Electrical and Computer Engineering, Uni-
versity of Delaware, Newark, DE 19716 USA. He is now with the Communi-
cation Research Center, Harbin Institute of Technology, Harbin 150001, China
(e-mail: j.shi@hit.edu.cn).
X. Liu, and X. Sha are with the Communication Research Center, Harbin
Institute of Technology, Harbin 150001, China (e-mail: xp.liu@hit.edu.cn;
shaxuejun@hit.edu.cn).
N. Zhang is with the Communication Research Center, Harbin Institute
of Technology, Harbin 150001, China, and also with the Shenzhen Graduate
School, Harbin Institute of Technology, Shenzhen 518055, China (e-mail:
ntzhang@hit.edu.cn).
Digital Object Identifier 10.1109/TSP.2012.2210887
1053-587X/$31.00 © 2012 IEEE