Journal of Systems Engineering and Electronics
Vol. 26, No. 1, Februar y 2015, pp.32–37
Efficient hybrid method for time reversal
superresolution imaging
Xiaohua Wang
*
, Wei Gao, and Bingzhong W ang
School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
Abstract:
An efficient hybrid time reve rsal (TR) imaging method
based on signal subspace and noise subspace is proposed for
electromagnetic superresolution detecting and imaging. First, the
locations of targets are estimated by the transmitting-mode decom-
position of the TR operator (DORT) method employing the signal
subspace. Then, the TR multiple signal classification (TR-MUSIC)
method employing the noise subspace is used in the estimated
target area to get the superresolution imaging of targets. Two
examples with homogeneous and inhomogeneous background
mediums are considered, respectively. The results show that the
proposed hybrid method has advantages in CPU time and memory
cost because of the combination of rough and fine imaging.
Keyw ords: time reversal (TR), decomposition of the time-reversal
operator (DORT) method, multiple signal classification (MUSIC)
method, superresolution, imaging.
DOI: 10.1109/JSEE.2015.00005
1. Introduction
The time reversal (TR) technique has attracted a lot of
attention for its spatial- temporal focusing characteristics
in domains such as imaging, communication, location,
and nondestructive evaluation. In the imaging domain, ge-
nerally, TR imaging techniques can be divided into two
categories: wave back propagation methods and TR ope-
rator methods. The TR mirror method (TRM) [1,2] and the
iterative TR method (ITRM) [3,4] are b ased on wave back
propagation. However, they cannot focus on weaker targets
in the situation of multiple objects because of the spatial
focusing characteristics of TR electromagnetic waves. To
overcome this fatal flaw, some improved methods based
on the deco mposition of the TR operator (TRO) are de-
veloped, such as [5,6]. These methods, definedbythe
Manuscript received March 17, 2014.
*Corresponding author.
This work was supported by the National Natural Science Foundation
of China (61301271; 61331007), the Specialized Research Fund for
the Doctoral Program of Higher Education of China (20110185120008;
20120185130001), and the Fundamental Research Funds for Central Uni-
versities (ZYGX2012J043).
multistatic response (MSR) matrix, can be classified as the
decomposition of the time reversal operator (DORT) me-
thods [7 – 10] and time reversal multiple signal classifica-
tion (TR-MUSIC) methods [11 – 13]. Among these meth-
ods, the transmitting-mode electromagnetic TR-MUSIC
method was investigated f or surveillance in wireless sen-
sor network (WSN) by employing the pseudo-spectrum de-
duced from the Maxwell equations [13]. Compared with
the echo-mode TRO imaging methods, the transmitting-
mode TRO methods can get more accurate locations
and higher resolutions. Additionally, the performances of
TRO-based imaging techniques under clutter or additive
noise were investigated in [12 – 14].
Throughout the existing imaging methods based on the
TR technique, time domain methods have the properties
of statistical stability [15], but they cost more comput-
ing resource. The central frequency TR-MUSIC method
could get the superresolution results without considering
the efficiency [14], but this method cannot provide a sta-
ble image of the point-like targets under high-level clutter
and noise. The DORT method is more robust than the TR-
MUSIC method under high-level clutter or noise, but it can
only give low resolution results.
Therefore, the efficiency and memory cost of the TRO-
based superresolution imaging method will be concen-
trated on. An efficient hybrid TRO-based imaging method
will be proposed, which is especially suitable for the tar-
gets whose sizes and separation are less than the diffrac-
tion limit. Under the assumption of transmitting-mode, the
DORT method using signal subspace is employed to pro-
vide a primary estimation of the target area. Then, the TR-
MUSIC method using noise subspace is employed to pro-
vide superresolution imaging of the targets.
2. Hybrid TR imaging method
Suppose the analytical model is composed of a transmitter
array Tx (located at α
t
), M small anisotropic spheres as
the targets (located at m
i
, i =1, 2,...,M), and a receiver
array Rx (located at α
r
). In addition, the transmitter and