intruders in different scenarios. In order to detect an
intruder, Onur et al. proposed the probabilistic detection
model with false alarm rate in [22].
Compared with traditional omni-directional sensors,
directional sensors provide much richer information of the
environment in the forms of images or sounds and hence
promise a huge potential in applications [2, 6]. Almost
existing works about DSNs considered the sensing model of
directional sensor as a sector, which is also the boolean
sensing model [10]. Yildiz et al. [28] investigated the problem
of determining optimal camera placement to achieve angular
coverage continuously over a given region. Some deployment
strategies for satisfying given coverage probability require-
ments with sectorial sensing models were designed in [19].
Most of existing works focused on considering the sensing
model for DSNs as a deterministic sensing model, ignoring
extraction the probabilistic factors. Then, more practical
factors for DSNs should be considered to better complete the
DSNs. Especially, Ahmed et al. [1] investigated the coverage
issues in wireless sensor networks based on probabilistic
sensing model and proposed a probabilistic coverage algo-
rithm to compute the coverage probability. The assumption is
valid for certain kind of sensors, which include the acoustic
sensor as a directional sensor. However, they only introduce
the sensor’s characteristics of signal propagation. Hence, in
this paper, we propose different sensing models for DSNs,
which consider more probabilistic factors.
3 Sensing models
In this section, the sensing models for DSNs are discussed.
Based on the deterministic sector sensing model, we first
study two more realistic probabilistic sensing models,
which are called exponential decay probabilistic sensing
model and fault-tolerant probabilistic sensing model,
respectively. Then, a hybrid probabilistic sensing model for
DSNs is proposed by combining the above sensing models.
3.1 Deterministic sensing model
The commonly-used deterministic sector sensing model sim-
plifies the coverage problem. Almost all the previous works
have been considered the sector sensing model for DSNs.
As depicted in Fig. 2(a), the deterministic sensing area
of directional sensor is sector-shaped region, which can be
denoted by 4-tuple ðS; R; h
f
; v
!
Þ. S is the location coordi-
nate in a two-dimension plane, and it also denotes the
directional sensor. R points out the maximum sensing
radius. h
f
indicates sensing offset angle which equals to the
half of the vertex angle of sector. Note that the omni-
directional sensing model is a special case of the deter-
ministic directional sensing model when h
f
¼ p. v
!
is a
unit vector, and denotes the viewing angle, which repre-
sents the orientation of a directional sensor.
It can be determined whether a point x is covered by the
directional sensor S or not by the following:
Sx
jj
R ð1Þ
Sx
!
v
!
Sx
!
cos h
f
ð2Þ
In other words, the deterministic sensing model for DSNs
can be described by:
pðxÞ¼
0; ðd [ RÞ_ h
b
[ h
f
;
1; ðd RÞ^ h
b
h
f
:
ð3Þ
where d and h
b
are the euclidean distance between x and
S and the offset angle between Sx
!
and orientation of
directional sensor, respectively.
3.2 Exponential decay probabilistic sensing model
Probabilistic sensing models assume that the sensing prob-
ability is a decreasing function of the sensing distance.
Actually, Sensors typically perform the sensing task proba-
bilistic—for two main reasons: (i) The signal propagation
from a target to a sensor follows a probabilistic model [1].
The probability of detection of a target by a sensor decreases
exponentially with increase in distance between the target
and sensor. (ii) Especially for underwater acoustic sensors,
the signal roughly decays based on the path loss log normal
shadowing model by blocking effect of water.
As shown in Fig. 2(b), the exponential decay proba-
bilistic sensing model for DSNs can be defined by 5-tuple
Fig. 2 Sensing models for DSNs: a deterministic sensing model;
b exponential decay probabilistic sensing model; c fault-tolerant
probabilistic sensing model; d hybrid probabilistic sensing model
Wireless Netw (2019) 25:355–365 357
123