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在本文中,我们专注于为一类非线性离散时间随机系统设计粒子滤波器,在该系统中,多传感器测量可以随机或异步地延迟一个或两个采样周期。 在多传感器延迟的独立性假设下,通过使用一组独立的伯努利随机变量来构建异步延迟模型,以描述每个传感器的理想测量值与实际测量值之间的关系。 基于该模型,导出了一种新的粒子加权方案,并充分考虑了测量延迟。 通过将加权方案合并到粒子滤波框架中,我们为具有延迟测量的系统获得了一个新的滤波器。 通过两个数值示例证明了所提出的滤波器的性能。
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Regular paper
Particle filter for estimating multi-sensor systems using one- or two-step
delayed measurements
Junyi Zuo
a,1,
⇑
, Qing Guo
a,2
, Zhigang Ling
b,3
a
School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China
b
College of Electrical and Information Engineering, Hunan University, Changsha 410082, China
article info
Article history:
Received 12 April 2017
Accepted 21 August 2017
Keywords:
Particle filter
Nonlinear system
State estimation
Delayed measurement
abstract
In this paper, we focus on designing a particle filter for a class of nonlinear discrete-time stochastic sys-
tems, where the multi-sensor measurements can be randomly and asynchronously delayed by one- or
two- sampling periods. Under the independence assumption of multi-sensor delays, asynchronous delay
model is built by using a separate set of Bernoulli random variables to describe the relationship between
the ideal measurement and the actual measurement for each sensor. Based on the model, a new weight-
ing scheme for particles is derived with the measurement delay fully considered. By incorporating the
weighting scheme into the particle filtering framework, we obtain a new filter for systems with delayed
measurements. The performance of the proposed filter is demonstrated by two numerical examples.
Ó 2017 Elsevier GmbH. All rights reserved.
1. Introduction
In recent years, nonlinear filtering has been an active research
field and plays an important role in many applications (see, e.g.,
[1–4] and the references therein). The classical filtering methods
are based on the assumption that the measurements are available
in a real-time manner. However, in many actual applications such
as the communication networks with remote sensors, the received
measurements may undergo random delay due to the network
congestion. Hence, developing new nonlinear filters is urgently
demanded to tackle the problem of Random Measurement Delay
(RMD) [5].
Generally speaking, the filtering problems for systems with
measurement delay can be divided into two categories according
to whether the measurement data packets are time-stamped or
not. For time-stamped cases, it is exactly known when the current
received measurement is collected by a sensor, and many filters
have been developed in Kalman filtering framework [6,7] or parti-
cle filtering framework [8,9].
For no time stamp cases, the measurement delay is considered
to randomly arise with a certain probability and usually described
by a set of stochastic parameters obeying Bernoulli distribution.
Following this idea, in [10,11], a modified extended Kalman filter
and a modified unscented Kalman filter for nonlinear systems with
one- or Two-step RMD (TRMD) have been proposed based on the
first-order linearization and unscented transformation respec-
tively. Via Gaussian approximation of the one-step posterior pre-
dictive Probability Density Functions (PDFs) of state and delayed
measurement, a Modified Cubature Kalman Filter (MCKF) [12]
and the corresponding smoother [5] were proposed for nonlinear
systems with One-step RMD (ORMD).
These estimates were developed in Gaussian approximation
framework, where the distributions of state and measurement
are assumed to be Gaussian. However, due to the nonlinear prop-
agation of state, these distributions may be far away from Gaus-
sian, which leads to degraded performance [13].
Recently, Particle Filters (PFs) [14] have proven to be promising
alternatives to Gaussian approximation filters since they do not
have the limitation imposed by the Gaussian assumption, and
can yield optimal results asymptotically in the number of particles
[2,15]. Recently, taking into account the multi-step RMD, a modi-
fied PF was also proposed in [16]. The derivation of the filter is
based on an additional assumption, i.e., conditioned on the current
state, the current received actual measurement is independent of
the previous ones. Indeed, this assumption is true for no delay sys-
tems. However, it does not hold in the presence of measurement
delay, which brings a theoretical problem to the algorithm. In
http://dx.doi.org/10.1016/j.aeue.2017.08.037
1434-8411/Ó 2017 Elsevier GmbH. All rights reserved.
⇑
Corresponding author.
E-mail addresses: junyizuo@nwpu.edu.cn (J. Zuo), gq@nwpu.edu.cn (Q. Guo),
zgling@hnu.edu.cn (Z. Ling).
1
Contributions: carried out the study design, the analysis and interpretation of
data, drafted the manuscript and developed the simulation code.
2
Contributions: participated in the study design and the simulation code
development.
3
Contributions: participated in the data analysis and manuscript revision.
Int. J. Electron. Commun. (AEÜ) 82 (2017) 265–271
Contents lists available at ScienceDirect
International Journal of Electronics and
Communications (AEÜ)
journal homepage: www.elsevier.com/locate/aeue
addition, the filter is only suitable for single sensor systems or
multi-sensor systems but with synchronous delay. In fact, multi-
sensor asynchronous delay is more common in practice since mea-
surements from different sensors may take different transmission
links and consequently have different delay steps. In this paper, a
more elaborate PF is developed to address the problem of RMD
with delay steps no more than 2. The filter no longer suffers from
the theoretical problems in [16] and can be used for systems with
multi-sensor asynchronous delay.
2. Problem formulation
Consider the following multi-sensor nonlinear dynamic system
x
t
¼ f
t
ðx
t1
Þþw
t1
ð1Þ
z
t;k
¼ h
t;k
ðx
t
Þþ
v
t;k
; k ¼ 1; 2; ...; K ð2Þ
where x
t
is the n-dimensional state vector with known initial distri-
bution pðx
0
Þ, z
t;k
is the m
k
-dimensional ideal measurement collected
by the k-th sensor at time t, w
t
p
w
ðÞ and
v
t;k
p
v
;k
ðÞ denote the
white process noise and measurement noise respectively. The sys-
tem function f
t
ðÞ and measurement function h
t;k
ðÞ, as well as the
PDFs p
w
ðÞ and p
v
;k
ðÞ, are known a priori. Define z
t
to be the mea-
surement set of the K sensors, i.e., let z
t
¼½z
t;1
; z
t;2
; ...; z
t;K
T
.
The multi-sensor asynchronous RMD model with the maximum
possible delay step being 2 can be formulated as
y
t;k
¼
z
t;k
; t ¼ 1; 2
P
2
d¼0
c
d
t;k
z
td;k
; t > 2
(
; k ¼ 1; 2; ...; K ð3Þ
where y
t;k
is the current received actual measurement collected by
the k-th sensor, d is the delay step,
c
d
t;k
; d ¼ 0; 1; 2 are Bernoulli ran-
dom variables taking the value of 1 if y
t;k
is delayed by d sampling
periods. Define y
t
¼½y
t;1
; y
t;2
; ...; y
t;K
T
to be the actual measurement
set of the K sensors.
Define
c
t;k
¼½
c
0
t;k
;
c
1
t;k
;
c
2
t;k
T
. For any given t and k, the state space
of
c
t;k
consists of 3 column vectors f
c
d
t;k
g
2
d¼0
.In
c
d
t;k
, the ðd þ 1Þ-th
element
c
d
t;k
takes the value of 1, while others take 0. For example,
c
1
t;k
¼½0; 1; 0
T
. Random vector
c
t;k
obeys the known discrete
distribution
pð
c
t;k
¼
c
d
t;k
Þ¼p
d
t;k
; d ¼ 0; 1; 2 ð4Þ
where p
d
t;k
P 0 and
P
2
d¼0
p
d
t;k
¼ 1. The random event c
t;k
¼ c
d
t;k
indi-
cates that, for the k-th sensor, the current received measurement
y
t;k
is delayed by d sampling periods. It is assumed that c
t
1
;k
is inde-
pendent of
c
t
2
;k
when t
1
– t
2
, and c
t;k
1
is independent of c
t;k
2
when
k
1
– k
2
. We further assume the mutual independence of x
0
,
fw
t
; t P 0g, f
v
t;k
; t > 0g
K
k¼1
and fc
t;k
; t > 0g
K
k¼1
.
For the case of K ¼ 2, the dynamic system given by (1)–(3) can
be illustrated by Fig. 1. Our aim is to recursively estimate x
t
based
on all available measurements y
1:t
¼fy
s
g
t
s
¼1
:
Remark 1. The ORMD model can be regarded as the special case of
model (3). Indeed, if p
2
t;k
0; for all k ¼ 1; 2; ...; K, then model (3)
reduces to ORMD model.
Remark 2. The RMD model given by (3) poses a great challenge to
estimators due to the degraded quality of received measurements.
Compared with z
1:t
, the actual measurement sequence y
1:t
not only
is out-of-sequence, but also suffers from measurement random
missing. It is easy to prove that the ideal measurement z
t;k
, t > 2
is absent from the actual measurement sequence with probability
P
miss
¼ð1 p
0
t;k
Þð1 p
1
tþ1;k
Þð1 p
2
tþ2;k
Þ: Specially, if the delay proba-
bilities are time-invariant, i.e. they can be represented by
p
0
t;k
¼ p
0
k
; p
1
t;k
¼ p
1
k
and p
2
t;k
¼ p
2
k
; then P
miss
reaches the maximum
value 8/27 at the point p
0
k
¼ p
1
k
¼ p
2
k
¼ 1=3.
3. Particle filter for systems with multi-sensor TRMD
In PF, the joint PDF pðx
0:t
jy
1:t
Þ is usually approximated by a set of
weighted particle-trajectories as follows
pðx
0:t
jy
1:t
Þ
X
N
i¼1
p
i
t
dðx
0:t
x
i
0:t
Þð5Þ
where dðÞ is the Dirac delta function, x
i
0:t
¼fx
i
0
; x
i
1
; ...; x
i
t
g is the i-th
particle-trajectory drawn from a pre-selected importance density
function qðx
0:t
jz
1:t
Þ and assigned a normalized weight according to
p
i
t
/
pðx
i
0:t
jy
1:t
Þ
qðx
i
0:t
jy
1:t
Þ
ð6Þ
Here, / stands for ‘proportional to’.
Assume that the weighted particle-trajectory set fx
i
0:t1
;
p
i
t1
g
N
i¼1
is available. When y
t
arrives, a new set fx
i
0:t
;
p
i
t
g
N
i¼1
is required to
approximate pðx
0:t
jy
1:t
Þ, where x
i
0:t
qðx
0:t
jy
1:t
Þ. Usually, qðx
0:t
jy
1:t
Þ
is chosen to factorize such that
qðx
0:t
jy
1:t
Þ¼qðx
t
jx
0:t1
; y
1:t
Þqðx
0:t1
jy
1:t1
Þð7Þ
Then x
i
0:t
can be obtained by augmenting the existing particle-
trajectory x
i
0:t1
qðx
0:t1
jy
1:t1
Þ with the new state
x
i
t
qðx
t
jx
i
0:t1
; y
1:t
Þ: By using the Bayes’ rule, we have
pðx
0:t
jy
1:t
Þ¼
pðy
t
jx
0:t
; y
1:t1
Þpðx
t
jx
0:t1
; y
1:t1
Þpðx
0:t1
jy
1:t1
Þ
pðy
t
jy
1:t1
Þ
/ pðy
t
jx
0:t
; y
1:t1
Þpðx
t
jx
t1
Þpðx
0:t1
jy
1:t1
Þð8Þ
If we choose qðx
t
jx
0:t1
; y
1:t
Þ¼ pðx
t
jx
t1
Þ, and perform resam-
pling at each filter cycle just like the Standard PF (SPF) [14], then
by substituting (7) and (8) into (6), the weight equation can be
simplified as
p
i
t
/ pðy
t
jx
i
0:t
; y
1:t1
Þ¼pðy
t
jx
i
t2:t
; y
1:t1
Þð9Þ
The equality in (9) comes from the fact that, conditioned on
x
i
t2:t
, y
t
does not depend on x
i
0:t3
.
In [16,17], an additional assumption, i.e., y
t
does not depend on
y
1:t1
, is made, which leads to a further simplified weight equation
3,1t
z
2,1t
z
1,1t
z
2t
x
1t
x
3t
x
Hidden states
Ideal
measurements
of sensor 1
3,1t
y
2,1t
y
1,1t
y
Actual
measurements
of sensor 1
0
,1t
p
,1t
z
t
x
,1t
y
1
()+
tt
fw
,1 ,1
()+
tt
hv
1
,1t
p
2
,1t
p
3,2t
z
2,2t
z
1,2t
z
,2t
z
3,2t
y
2,2t
y
1,2t
y
,2t
y
Ideal
measurements
of sensor 2
Actual
measurements
of sensor 2
0
,2t
p
1
,2t
p
2
,2t
p
,2 ,2
()+
tt
hv
Fig. 1. Two-sensor asynchronous delay model with maximum possible delay step
being 2.
266 J. Zuo et al. / Int. J. Electron. Commun. (AEÜ) 82 (2017) 265–271
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