Gaussian sum filter of Markov jump non-linear
systems
ISSN 1751-9675
Received on 12th February 2014
Accepted on 28th October 2014
doi: 10.1049/iet-spr.2014.0066
www.ietdl.org
Li Wang
1,2
, Yan Liang
1,2
✉
, Xiaoxu Wang
1,2
, Linfeng Xu
1,2
1
School of Automation, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China
2
The Key Laboratory of Information Fusion Technology, Ministry of Education, Xi’an 710072, People’s Republic of China
✉ E-mail: liangyan@nwpu.edu.cn
Abstract: This pap er proposes a Gaussian sum filtering (GSF) framework for the state estimation of Markov jump non-
linear systems. Through presenting the Gaussian sum approximations about the model-con ditioned state posterior
probability density functions, a general GSF framework in the minimum mean square error sense is derived. The
minor Gaussian-set design is utilised to merge the Gaussian components at the beginning, which can effectively limi t
the computational requirements. Simulation result shows that the proposed algorithm demonstrates comparable
performance to the interacting multiple model particle filter with significantly reduced computational cost.
1 Introduction
Markov jump systems (MJSs) involve both time-evolving and
event-driven mechanisms, which have been widely accepted in
many fields such as target tracking [1, 2], seismic signal
processing [3], process monitoring and fault detection [4]. For the
state estimation problem of MJSs, the recursive optimal estimator
was derived in [5]. However, for most non-linear dynamical and
measurement models, an exact and recursive computation of the
state probability density functions (PDF) is intractable. Definitely,
one has to pursue suboptimal or approximate non-linear filters.
Much attention has been paid on the state estimation problem of
non-linear systems. Filtering of the MJSs can be divided into the
following two categories.
The first is the state estimation of Markov jump linear systems
(MJLSs), where multiple linear models are stochastically switched
according to a Markov chain. Since one has to match a filter to
each model, an exponentially increasing number of filters are
needed, which makes the optimal approach impractical [1]. Hence,
suboptimal techniques must be utilised to avoid the exponentially
increasing number of histories. A simple-minded suboptimal
technique is to keep the N histories with the largest probabilities
and normalise the probabilities. Another effective way is ‘merging’
used in GPB1 (generalised pseudo-Bayesian of order 1), GPB2
and IMM [1, 5, 6], in which the posterior PDFs can be represented
exactly by a sum of Gaussians. Learn from [5], the IMM estimator
can obtain the similar accuracy to GPB2, whereas its computation
burden is similar to that of GPB1.
The second is the state estimation of Markov jump non-linear
systems (MJNLSs), where each model is non-linear. One possible
scheme is to augment the state with mode and then apply the
particle filter (PF). However, it is computation-intensive by the
fact that the computation burden of PF increases significantly as
the state dimension increases. Another ad hoc scheme is that the
extended or unscented Kalman filter (EKF or UKF) is chosen as
the model-conditioned sub-filter in the IMM framework for mild
non-linearities [7, 8] or the particle filter (PF) for strong
non-linearities [9]. In [2], a multiple model particle filter was
presented for MJNLSs, which obtained superior performance to
the IMM algorithm using EKF. However, the particle cloud of this
filter can easily degenerate, especially around mode transitions. To
prevent the filter degenerating, a new particle filter for MJNLSs
was proposed in [10
], which we refer to as the interacting multiple
model particle filter (IMMPF). The number of particles per mode
in this filter is a parameter, which can be selected a priori by the
designer or online based on some adaptive scheme. This particle
filter for MJNLSs was illustrated more robust than the one in [2]
for the same number of particles. Further research was also carried
out in [11] for the case that the mode switching is state-dependent.
These above algorithms are very promising in accuracy for a class
of problems at the cost of heavy computation load.
For the state estimation of non-linear systems, a new possible
scheme is Gaussian or Gaussian sum approximation to the state
conditional PDF. The advantages are that it can effectively
approximate any PDF as closely as desired (in the L
1
norm) and
enable a more accurate representation of the non-linearities in the
dynamics and measurement models. The Gaussian sum filters
(GSF) was developed in [12], in which the conditional probability
density is approximated by a sum of Gaussians. Extensive
researches on GSF have been done in [13–17], which have
become popular in the target tracking community. A
Gaussian-sum based cubature Kalman filter (CKF) proposed in
[14] showed comparable performance to the PF with reduced
computational cost. However, it was found later that it lacks
robustness where a decrease in accuracy has been observed when
the threshold level for splitting the Gaussian components is very
low. In [15], modifications were made in the splitting and merging
procedure of the Gaussian components with improved robustness
compared with the algorithm in [14]. An adaptive GSF was
presented in [17] for non-linear tracking problems in high
dimensional data-starved environments such as space surveillance.
These algorithms demonstrate good performance for non-linear
systems.
In fact, Markov jump systems are stochastic non-linear systems. It
will result in a complicated non-linear estimation problem combined
with the non-linearity in system models. To the best of our
knowledge, up to the present, there has no research on GSF design
for the state estimation of MJNLSs. Motivated by the advantages
of the GSF, a GSF framework for MJNLSs based on the Gaussian
sum approximations is developed in this paper to obtain the
compromise of estimation accuracy and computational cost. The
procedure of this filter design includes the mixing and filtering
steps. In the mixing step, the Minor Gaussian-set design using
moment matching is utilised to control the number of Gaussian
components. The filtering step includes analytical computation and
Gaussian weighted integrals, thus the divided difference filter
(DDF) [18] based on the second-order Stirling’s interpolation is
chosen as the sub-filter. Simulation result shows that the proposed
GSF gives comparable performance to the IMMPF [10] with
significantly reduced computational cost.
IET Signal Processing
Research Article
IET Signal Process., 2015, Vol. 9, Iss. 4, pp. 335–340
335
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