Neurocomputing 71 (2008) 1669–1679
Morphologically constrained ICA for extracting weak
temporally correlated signals
Zhi-Lin Zhang
a,b,
a
School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
b
Department of Computer Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Received 10 March 2006; received in revised form 9 October 2006; accepted 11 April 2007
Communicated by H. Valpola
Available online 24 April 2007
Abstract
Recently the constrained ICA (cICA) algorithm has been widely applied to many applications. But a crucial problem to the algorithm
is how to design a reference signal in advance, which should be closely related to the desired source signal. If the desired source signal is
very weak in mixed signals and there is no enough a priori information about it, the reference signal is difficult to design. With some
detailed discussions on the cICA algorithm, the paper proposes a second-order statistics based approach to reliably find suitable
reference signals for weak temporally correlated source signals. Simulations on synthetic data and real-world data have shown its validity
and usefulness.
r 2007 Elsevier B.V. All rights reserved.
Keywords: Constrained independent component analysis (cICA); Blind source extraction (BSE); Blind source separation (BSS); Reference signal;
Temporally correlated signal
1. Introduction
Temporally correlated signals widely exist in various
fields, such as biomedical engineering [3,6,8,9,19,21] and
financial time series an alysis [7]. These signals are often
‘‘interesting’’ and important to us. For example, in
abnormal EEG analysis the quasi-periodic complex re-
sulted from periodic synchronous discharge is of impor-
tance to determine whether or not the subject suffers from
subacute sclerosing panencephalitis (SSPE) or other
diseases. In the non-invasive extraction of fetal electro-
cardiogram (FECG) [8,19,21], the FECG, which provides
information about fetal maturity, position of the fetus and
multiple pregnancies, also can be regarded as a quasi-
periodic signal.
Unfortunately, these valuable temporally correlated
source signals and other unwanted source signals are often
mixed in observed signals and often contaminated by noise.
To obtain the desired source signals, one powerful
technique is the blind source separation (BSS) [4,7], which
simultaneously separates all of the source signals. How-
ever, in many applications the number of sensors is often
large, which may result in heavy computational load and
cost lots of time, while the ‘‘interesting’’ source signals (the
desired ones) are few. For exampl e, in EEG or MEG we
obtain typically more than 64 sensor signals but only
several source signals (e.g. the periodically evoked brain
potentials) are considered interesting, and the rest are
considered to be interfering noise. For such applications it
is essential to develop reliable, robust and effective learning
algorithms whi ch enable us to extract only a small number
of temporally correlated source signals that are potentially
interesting and contain useful information [4,9,20–22].
The co nstrained ICA (cICA ) (also called ICA with
reference) [10–14] is a good can didate for extracting several
source signals from a large number of observed signals.
ARTICLE IN PRESS
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doi:10.1016/j.neucom.2007.04.004
Corresponding author at: School of Computer Science and Engineer-
ing, University of Electronic Science and Technology of China, Chengdu
610054, China.
E-mail address: zlzhang@uestc.edu.cn.