1954 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 33, NO. 10, MAY 15, 2015
An Improved Positioning Algorithm With High
Precision for Dual Mach–Zehnder Interferometry
Disturbance Sensing System
Qinnan Chen, Tiegen Liu, Kun Liu, Junfeng Jiang, Zhe Shen, Zhenyang Ding, Haofeng Hu, Xiangdong Huang,
Liang Pan, and Chunyu Ma
Abstract—An improved positioning algorithm for dual Mach–
Zehnder interferometry(DMZI)disturbancesensingsystemispro-
posed. We employ zero-crossing method, which can be computed
easily to extract the disturbance signal segment with maximum
zero-crossing rate. Meanwhile, we use general cross correlation
based on Wiener filtering and G
nn
subtraction weighting function
(WG-GCC) to estimate the time delay of the extracted signal, which
is robust to the correlated noise. Finally, we experimentally demon-
strate that the proposed positioning algorithm can greatly improve
the positioning accuracy with positioning error of ±20 m. Com-
pared with the traditional positioning algorithm, the positioning
error has been reduced by an order of magnitude. This algorithm
has a promising potential in real-time fence perimeter applications.
Index Terms—Distributed fiber-optic sensor, fence perimeter ap-
plication, general cross correlation, positioning algorithm, zero-
crossing rate.
I. INTRODUCTION
D
UAL Mach–Zehnder interferometry (DMZI) disturbance
sensing system is widely used in perimeter security mon-
itoring, pipeline leakage detection, submarine cable security
monitoring, and other applications [1]–[8] due to advantages of
high sensitivity, fast response, and simple structure [4]–[8]. It
can obtain disturbance position by applying time delay estima-
tion algorithm, which lies at the heart of positioning algorithm.
Currently, the most popular time delay estimation algorithm
is to do cross correlation between the two output signals [1]–[7].
It will bring a huge amount of computation thought it is easily
achieved, which influences real-time performance of the sens-
ing system and its positioning error is easily induced by diverse
noises of output signals [9]. In general, the noise sources which
Manuscript received August 17, 2014; revised November 28, 2014; accepted
January 18, 2015. Date of publication February 15, 2015; date of current version
March 16,2015. Thisworkwas supported in part by the National Basic Research
Program of China under Grant 2010CB327806, in part by National Instrument
Program under Grant 2013YQ030915, in part by the National Natural Science
Foundation of China under Grants 61475114, 61108070, 11004150, 61227011
and 61378043, and in part by the Tianjin Science and Technology Support Key
Project under Grant 11ZCKFGX01900. (Corresponding author: K. Liu.)
Q. Chen, T. Liu, K. Liu, J. Jiang, Z. Ding, H. Hu, L. Pan, and C. Ma are with
the College of Precision Instrument & Opto-electronics Engineering, Tianjin
University, Tianjin 300072, China (e-mail: beiyangkl@tju.edu.cn).
Z. Shen is with the Department of Electrical Engineering and Electronics,
University of Liverpool, Liverpool L69 3GJ, U.K. (e-mail: z.shen3@liv.ac.uk).
X. Huang is with the School of Electronic Information Engineering, Tianjin
University, Tianjin 300072, China (e-mail: xdhuang@tju.edu.cn).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JLT.2015.2394494
affect the positioning error include the frequency noise from the
laser source, the polarization noise and the environment noise.
The frequency noise and the polarization noise are ubiquitous
but can be reduced to some extent by compensating the length
difference between interferometer arms and dynamically ad-
justing the polarization state of the light in the interferometer,
respectively [4], [10]. The environment noise is negligible in
some cases such as submarine cable security monitoring, but
it is the major noise source in some applications such as fence
perimeter. Therefore, the main source of noise is not the same
in different applications.
As the aforementioned noises are difficult to eliminate, re-
searchers pay more attention to the positioning algorithms for
reducing noise. Xie et al. analyzed the positioning error of
DMZI sensor and proposed a positioning error reduction tech-
nique. They used a high-pass filter to reshape the original power
spectrum, and achieve a lower mean square error of the cross-
correlation based positioning algorithm [4], [6]. It is suitable for
submarine cable security application rather than fence perime-
ter application as the environment noise was neglected. Wu
et al. employed endpoint detection technologies such as dis-
crete wavelet to extract the effective signal segment at starting
point of disturbance before applying cross correlation [9], [11],
[12]. However, there is no obvious starting point when intrusion
occurs in fence perimeter application and the positioning error
of cross correlation based algorithm is easily affected by the
environment noise induced by slight vibration along the sensing
cable [10]. Although they obtained a certain degree of accuracy,
there is not enough in practical application.
We theoretically analyze the positioning error of the DMZI
sensing system by taking into account the environment noise.
Based on the theory, we proposed an improved positioning al-
gorithm with high precision for more general applications. As
far as we know, it is the first time to focus on the positioning
algorithm especially for fence perimeter application. Compared
with the traditional positioning algorithm, our method has some
improvements. First, we extract the signal segment with highest
zero-crossing rate, which has higher positioning accuracy in-
stead of endpoint extraction to estimate time delay. Moreover,
the signal extraction is based on zero-crossing technique, which
has advantages of easy implementation and high efficiency [13],
[14]. Furthermore, in order to remove the correlated noise,
general cross correlation based on Wiener filtering and G
nn
subtraction (WG-GCC) weighting function is used to estimate
the time delay [12], [15], [16]. We experimentally demonstrated
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