Post on 11-Apr-2017
978-1-4577-0351-5/11/$26.00 c 2011 IEEE
Recycled ID Assignment for Relocation of Hopping Sensors
Moonseong Kim
Information and Communications Examination Bureau
Korean Intellectual Property Office
Daejeon, 302-701, Korea
Email: moonseong@kipo.go.kr
Matt W. Mutka
Department of Computer Science and Engineering
Michigan State University
East Lansing, MI 48824, USA
Email: mutka@cse.msu.edu
Abstract—Redundant mobile sensors might be moved inorder to cover sensing holes or replace power-exhausted sen-sors. Within rugged terrains, the use of hopping sensors maybe more suitable than wheeled mobile sensors. Since WSNcommunication is data-centric, globally unique ID allocationthat is used for MANETs is usually not applicable for WSNs. Arecent study classifies the locally unique ID allocation schemefor WSNs into two representative types: a proactive and areactive scheme. In the reactive scheme, energy preservationis improved because ID conflict resolution is delayed untildata communication is needed. Although a typical reactive IDassignment scheme is used, local uniqueness cannot be guar-anteed if hopping sensors are relocated. In order to overcomethe weakness, we propose the recycled ID assignment schemefor relocation of hopping sensors. Simulation results show thatthe proposed recycled ID assignment scheme outperforms thetypical reactive scheme for relocation of hopping sensors.
Keywords-wireless sensor netowrks; hopping sensors; reloca-tion of sensors; sensing holes; ID assignment;
I. INTRODUCTION AND PREVIOUS WORK
Redundant sensors are scattered initially over the entire
field using a well planned deployment; thus, if a sensing
hole is detected, a relocation of mobile sensors is needed
to recover the sensing hole. That is, mobile sensor nodes
could move to a specific emergent area, or replace energy-
exhausted sensor nodes. Recently, the discussion of reloca-
tion of hopping sensors has been further accelerated by [1]-
[3]. However, there is no research to support ID assignment
for the efficient communication after some hopping sensors
move to the desired areas. As a matter of course, the research
for supporting hopping sensor mobility could consider a
Mobile Ad-hoc NETwork (MANET). However, although a
WSN is similar to a MANET, because both are multi-hop
wireless communication, they are different in terms of data
communication architectures. Generally, a MANET is an
IP-based network; thus, every node has to need a globally
unique ID such as an IP address, and any node can try to
connect with any other node for initiating communication.
Unlike a MANET that is address-centric, the communi-
cation for a WSN is usually data-centric. Actually, a com-
munication of WSN is interested in the location and the re-
quested/collected data, but does not care about the address of
a sensor node. In addition, if all data is encapsulated within
a TCP/UDP/IP packet, it wastes energy and bandwidth,
since the payload length in the data packet is usually small.
Thus, customized network protocols may be adopted to save
the communication overhead and energy consumption. For
example, Directed Diffusion (DD [4]) might be considered
a representative reactive dissemination protocol for WSNs
instead of IP-based data communications. In order to collect
the desired data, a sink node first broadcasts an Interest
message that could be flooded to the entire network. Every
relay node records the upstream node as the next hop that
is back toward the sink. After the desired data is found out
at a source node and some paths are built, a reply message
is sent back from the source to the sink along the reverse
paths. Finally, the sink node can select a suitable path using
Reinforce and can unicast. One of the assumptions in DD is
that every node has a locally unique ID instead of a globally
unique ID.
Although there are many auto-configuration algorithms
proposed for ID assignment in MANETs, the goal of an
assignment is globally unique; hence, it is not appropriate for
ID assignment for WSNs. The authors of [5] propose the use
of Huffman coded address, called proactive ID assignment,
for locally unique ID assignment for WSNs. The size of
the proposed ID is not fixed and is usually less than that
of a fixed address format. Even if the use of a Huffman
coded ID decreases the average address field length, the
authors admit that there is no benefit in a practical dense
WSN. Moreover, a priori Huffman code table may not be
optimal, the Huffman code table must be stored in the
memory of the sensor node during all its lifetime, and it
would be much easier for designers to allocate the fixed-
length. Hence, the authors of [6] propose the use of fixed-
length address assignment, called reactive ID assignment, for
locally unique ID assignment for WSNs. They prove that the
proposed reactive ID assignment outperforms the proactive
one. However, since there is frequent movement of sensors
in hopping sensor networks, the conflict probability may be
high when the locally unique ID assignment is considered. In
this paper, therefore, we address the ID assignment problem
for hopping sensor networks.
The remainder of this paper is organized as follows.
Section II presents details of the proposed scheme. Section
III evaluates our proposal by employing a simulation; and
finally, Section IV concludes this paper.
II. ID ASSIGNMENT FOR HOPPING SENSOR NETWORKS
In this section, we discuss the ID assignment policy to
resolve the ID conflicts occurred when the hopping sensors
are relocated. In general, there are three types of hopping
strategies, , direct, relayed, and cascaded hopping [2].
Cluster heads are assumed to be capable of jumping high
and have redundant energy. The cluster heads cooperate
with each other in order to cover and maintain the entire
WSN. After a hopping sensor is appointed as a cluster
head, the cluster head can broadcast to its neighbor hopping
sensors included to the cluster. If it does not receive an Ack
message from its neighbor, then the cluster may be a sensing
hole; otherwise, the neighbor hopping sensors can send the
Ack message to the cluster head using jumping as high as
possible.
Figure 1. An example of relocation of hopping sensors between aconsumer and supplier
Here, we assume that the cluster head detects the sensing
hole through self-verification, and then the cluster head of
the sensing hole is called the consumer. The consumer
broadcasts the Interest message, including the number of
required sensors, to its neighbor cluster heads like the DD
paradigm. In order to communicate and avoid ID conflict
with each cluster head, the mentioned reactive ID assign-
ment [6] could be applied. After the candidate paths are
constructed between the consumer and some suppliers, the
consumer could choose one or more suitable suppliers,
as shown in Fig. 1. After the requested hopping sensors
are completely moved to the neighbor cluster, each moved
hopping sensor must first try to communicate with the
current cluster head. They are also able to communicate with
each other hopping sensor with/without jumping, , multi-
hop communication. Here, first and most importantly, the
resolution to avoid ID conflict is needed; thus, the reactive
ID assignment is also used.
The proposed address format is as follows briefly:
Random number for communication between clusters
Random number for intra communication . Let be
the address format. For instance, if the hopping sensors are
in the same cluster, then all of the sensors’ addresses are
same. To satisfy 1-hop uniqueness as address uniqueness
among direct neighbor clusters, the range of should be
greater than 3 bits ( 6=2.58), as shown in Fig. 1, if
the cluster model is considered as a hexagon. Moreover, to
satisfy 2-hop uniqueness, the range of should be greater
than 5 bits ( 18=4.16). Finally, the range of should
be greater than , where is the average number of
hopping sensors per each cluster initially deployed, , the
density of hopping sensor nodes per a cluster.
(a) The typical reactive ID assignment
(b) The proposed recycled ID assignment
Figure 2. Scenarios for description of the recycled scheme reactivescheme under relayed movement
Fig. 2 shows a simple scenario to compare with the previ-
ous reactive scheme for relocation of hopping sensors under
relayed movement. The cluster head is currently recording
the addresses of inner hopping sensors. As illustrated in
Fig. 2 (a), there is a duplicated ID after a hopping sensor
is moved. According to the typical reactive ID assignment
scheme, a resolve process may be started. On the other
hand, we generally use relayed or cascaded movement for
relocation of hopping sensors. This means that the number
of incoming hopping sensors is likely more than or equal to
the number of outgoing hopping sensors. Therefore, if the
cluster head can keep the addresses of outgoing hopping
sensors and reallocate the ones to the incoming hopping
sensors, then the overall overhead and the spent time could
be reduced, as described in Fig. 2 (b). However, there is
possibility that a sensor cannot move out. Since the proposed
recycled ID allocation is applied, there must be an ID
conflict. In order to resolve the problem, the failure sensor
should regenerate its address properly.
III. PERFORMANCE EVALUATION
We analyze some numerical results that can be used for
comparing the performance of the proposed recycled ID
assignment and the typical reactive ID assignment schemes.
We simulate them in perspective of the impact of ID conflict
after the requested hopping sensors are relocated. Hence, for
simplicity, we do not take into account the current cluster
address of . We assume that the size of is set
to 6 bits, =64; therefore, the number of hopping sensors
initially deployed per each cluster could be assumed to 30
and 40. Each ID is randomly and distinctly chosen for each
hopping sensor initially.
0 10 20 30 40 50
0
10
20
30
40
50
60
Number of incoming hopping sensors (%)
Reactive ID assignmentRecycled ID assignment
Figure 3. Communication overhead in terms of the number of incomingsensors
0 10 20 30 40 50
0
20
40
60
80
100
120
140
Number of incoming hopping sensors (%)
Reactive ID assignment w. pf=0.0
Reactive ID assignment w. pf=0.2
Reactive ID assignment w. pf=0.8
Recycled ID assignment w. pf=0.0
Recycled ID assignment w. pf=0.2
Recycled ID assignment w. pf=0.8
Figure 4. Communication overhead for the case of relocation failure
Fig. 3 shows the total number of packets sent, as the
requested hopping sensors migrate to the new cluster. 30
hopping sensors initially deployed per each cluster. The x-
axis represents the number of incoming hopping sensors. For
instance, 10% means that 3 hopping sensors (30 10%=3)
are requested from the direct neighbor cluster. As might be
expected, the advantage of using the proposed recycled ID
assignment versus the typical reactive ID assignment can be
clearly seen in these graphs.
In Fig. 4, we take into account that means the probabil-
ity of failure when the hopping sensor moves out under the
relayed hopping environment. Here, the number of hopping
sensors initially deployed per a cluster is 40. We easily note
that the recycled ID assignment scheme outperforms the
typical reactive scheme as the failure probability increases.
As a result, in rugged terrains, the hopping sensor is suitable;
and the proposed recycled ID assignment scheme is also
appropriate for communications.
IV. CONCLUSION
Mobile sensors are able to move to a specific emer-
gent area, or replace power-exhausted sensors. The use
of hopping sensors is more adaptable to the rugged area
than wheeled mobile sensors. Since the communication for
WSNs is data-centric, it is sufficient to assign locally unique
IDs for WSNs. In this paper, we have studied about the
ID assignment problem for relocation of hopping sensors.
Actually, under the relayed or cascaded movement for the
relocation, the number of incoming hopping sensors may
be more than or equal to the number of outgoing hopping
sensors. Therefore, if the addresses of outgoing hopping
sensors are recycled for the incoming hopping sensors, then
the overall overhead can be reduced. We have proved that the
performance of the proposed recycled ID assignment scheme
is superior to the typical reactive scheme for relocation of
hopping sensors.
ACKNOWLEDGMENT
This research was supported in part by NSF (USA) Grants
No. OCI-0753362 and CNS-0721441.
REFERENCES
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