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									      WSN Based Data Collection Framework and Protocols for Disaster
                    Mitigation and Rescue Operation

                                    Suman Saha , Mitsuji Matsumoto
                                  GITS, Waseda University, Tokyo, Japan.
                               suman@asagi.waseda.jp, mmatsumoto@waseda.jp

              Rapid development of Wireless Sensor Network (WSN) expedites the movement
              of ubiquitous computing. Though people can deploy this WSN for disaster
              mitigation and rescue operation after disaster, very few research works of WSN
              consider about disaster management system. None of the existing works considers
              one of the major effects of disaster such as some base stations might be collapsed
              or unreachable due to catastrophe. Considering this deficiency, in this paper, a data
              collection framework for disaster mitigation is demonstrated. This proposed
              framework is designed based on large-scale hybrid networks of cellular networks
              and WSNs. Considering the some base stations might be collapsed or unreachable
              during or after disaster, in this framework, ARSs are deployed on the border
              regions of every cell of cellular system. Sensor nodes of the corresponding cell
              disseminate their data to the ARSs and ARSs route the received data to non-
              collapsed base stations or nearby ARSs. In addition, in order to disseminate data
              from WSN to ARSs, in this paper, a protocol for disaster mitigation is proposed.
              This proposed protocol is a clustering and angular based routing protocol. Based
              on sensor node residual energy and node centrality, cluster head selection is
              performed. Simulation results prove that the performance of proposed protocol in
              the proposed framework outperforms those of LEACH and PEGASIS protocol.
              Though at first ARS is mentioned in [5], in this paper, the ARS placement strategy
              is updated and this update is justified by the simulation results. Furthermore, a
              small-scale data collection framework is proposed for rescue operation system
              after disaster. The proposed framework for rescue operation considers that rescue
              operators or first responders use some portable devices named cnode to collect
              data from some particular disaster areas for rescue operation. During rescue
              operation, cnode disseminates task over the sensor nodes of the disaster area by
              directional antenna to inform the sensor nodes to send their sense data to the cnode.
              For energy efficient and lower delay based data routing from these sensor nodes to
              cnode, in this paper, a protocol for rescue operation is proposed. Performance
              evaluation results prove that the performance of proposed rescue operation
              protocol in proposed framework outperforms that of SENDROM [1].

              Keywords: Wireless Sensor Network(WSN), Cellular network, ARS(Adhoc Relay
              Station), Clustering, Routing.

1   INTRODUCTION                                           Communications Commission) has required to
                                                           cellular systems the role for locating the position of a
     Our disaster management system is not so              terminal [10]. To satisfy the requirement, several
efficient comparing with our rapid development in          technologies have been studied such as the Global
communication system. Current communication                Positioning System (GPS) and so on [10], [11], [12].
systems could meet disaster management needs               However, no system has been demonstrated to
sufficiently, as long as communication services are        overcome the requirement.
uninterrupted. However, when these infrastructures              Lots of research works ([2], [3]) use cellular
break down, the pipeline for essential information is      network as a data gateway to convey data from
cut. A famous example of such a situation occurred         disaster location. But almost in every case, after a
immediately after the Kobe earthquake in 1995 and          catastrophe, rescuers cannot communicate with
the attack on the World Trade Center (WTC) in New          survivors due to destruction in an established cellular
York on September 11, 2001. The FCC (Federal               network. Main reason is collapsed or unreachable

                    Ubiquitous Computing and Communication Journal                                               1
base stations. Best example of this is 2004 Nigata       future study.
earthquake in Japan. To overcome these deficiencies,
wireless sensor network can be deployed to make          2   PREVIOUS WORKS
communications among rescuers and survivors. In
addition, before disaster emergency workers need              Few research works are for disaster management
varieties of sensing data, as an instance, which can     ([1], [2], [3], [4], [14]). In [1], based on state-of the-
be applicable in case of tsunami. Because most cases     art technologies, sensor network architecture is
earthquakes in the ocean areas precede tsunamis. If      developed for rescuer operation after disaster. But
emergency workers can get the data of these              the data dissemination technique is not efficient
earthquakes earlier, according to significant of the     because of overall delayed route establishment time
earthquake they can evacuate or warn the people of       and energy inefficiency. Although a protocol of ad
coastal region. For data collection from ocean, Under    hoc sensor network for disaster management is
Water Sensor Network (hereafter, it is denoted as        presented in [4] along with its energy efficiency,
UWSN) should be considered. Links in underwater          which achieved by the combination of a low power
networks are usually based on acoustics wireless         mode algorithm and a power aware routing strategy,
communications [6]. The unique characteristics of        this network is not viable for real world
the underwater acoustic communication channel,           implementation and its sensor prototype is
such as limited bandwidth capacity and high              expensive. In [2], a location aware distributed sensor
propagation delays [6], require very efficient and       networks is presented, but there is no mention about
reliable data communication protocols. These             hybrid network interface such like sensor and
limitations make a gap between UWSN and                  cellular network interface. Though [3] is defined on
terrestrial wireless sensor network.                     a hybrid of sensor and cellular network, it does not
     In this paper, the disaster management system is    consider collapsed or unreachable base stations. In
divided into two subsystems: disaster mitigation and     [2], clustering method does not regard energy
rescue operation. Here disaster mitigation subsystem     efficiency, while in [3], routing and access protocol
stands for a large-scale heterogeneous system of         for sensor network is not energy efficient though it
WSN, Cellular networks and Ad hoc Relay Station          can be easily deployable in a cellular network
(ARS)s networks that can be used for 24 hours            without considering collapsed base stations.
disaster surveillances, while rescue operation can            In this paper, the proposed protocol for disaster
work in a small area for rescue operation after          mitigation is a cluster-based protocol. Among the
disaster. Considering both of these subsystems of        distributed cluster-based sensor networks protocols,
disaster management system, a data collection            LEACH [9] is very popular. But clustering technique
                                                         used in LEACH wastes energy in terms of long run.
framework is proposed in this paper. In addition,
                                                         In LEACH, when clusters are created, each node of n
based on energy efficiency and lower delay,
                                                         autonomously decides if it will be a cluster head for
protocols for data collection from disaster areas for
                                                         the next round. The selection is stochastically: each
disaster mitigation and rescue operation are proposed.   node determines a random number between 0 and 1.
Here proposed data collection framework for disaster     If this number is lower than a threshold T(n), the
mitigation considers collapsed or unreachable base       node becomes a cluster head. T(n) is determined
stations, which was not regarded as a significant area   according to the equation
in previous works [2], [3], [4]. So in this framework,
static ARSs [5] are placed in bordering areas of cells                                       P                 (1)
                                                                      T   (n ) =
for conveying data from collapsed base station areas                                       ⎛        1 ⎞
                                                                                   1 − P × ⎜ r m od   ⎟
to their nearest base stations. Details motivations of                                     ⎝        P ⎠
proposed works are discussed in section 2. Though in
proposed framework, UWSN framework is                    for nodes that have not been cluster head in the last
considered for ocean data collection, proposed WSN       1/P rounds, otherwise T(n) is zero. Here P is an a
protocols are only for terrestrial WSN. For UWSN,        priori determined number that determines the
delay sensitive routing protocol [6] might be a good     average number of cluster heads during a round, r is
choice.                                                  the number of the current round. Using this
     The remainder of the paper is structured as         algorithm, each node will be a cluster head exactly
follows. Section 2 will discuss related works and        once within 1/P rounds. But in long run, there may
their drawbacks briefly. We present a data collection    be lots of cluster heads in a densely small zone or
framework in section 3. Section 4 presents our           there are no cluster heads in a large area of network.
proposed protocol for disaster mitigation along with     So cluster formation is not uniformly distributed over
its performance evaluation. The proposed protocol        the network. Another point LEACH considers the
for rescue operation and its performance evaluation      number of times the node has been a cluster head up
is proposed in section 5. In section 6, we conclude      to current round but not energy status of node. For
the paper and highlight the possible avenues for         long run, energy is one of the main factors of every

                    Ubiquitous Computing and Communication Journal                                               2
sensor node with limited energy battery.                      Fig.1 depicts our considered network model.
     Among the distributed techniques, Power             Right side of the figure presents UWSN framework.
Efficient Gathering in Sensor Information Systems        Here we count the UWSN, because we can collect
(PEGASIS), a chain-based routing protocol, further       the data of earthquakes, which are originated in
enhances network lifetime among same class               ocean-areas; and in ocean-areas, sometimes tsunamis
techniques by increasing local collaboration among       follow the earthquakes. Due to lots of challenges of
sensor nodes [15]. In PEGASIS, nodes are organized       UWSN such as overall infrastructure and
into a chain using a greedy algorithm so that each       communication, it is different from terrestrial WSN.
node transmits to and receives from only one of its      In this paper, the proposed WSN protocol is only for
neighbors. In each round, a randomly chosen node         terrestrial WSN. Here, we consider that the delay
from the chain will transmit the aggregated data to
                                                         sensitive routing protocol [6] is the routing protocol
the base station, thus reducing the per round energy
                                                         of our UWSN.
expenditure compared to LEACH. But average delay
                                                              Left side of Fig. 1 presents a combined view of
per round makes PEGASIS an ineligible to disaster
                                                         data collection framework of terrestrial WSN, which
mitigation technique.
                                                         is used for disaster mitigation and rescue operation.
     Form the discussion of the related works it is
                                                         For disaster mitigation, data dissemination network
evident that until now there is no large scale WSN
                                                         architecture is defined based on a hybrid model,
and cellular network based hybrid disaster mitigation
                                                         whose heterogeneity is confirmed by sensor, ARSs
network system, which can consider collapsed or
                                                         and cellular network. Deployed sensor nodes for
unreachable base stations. Normally used disaster
                                                         forming sensor networks and to collect information
management system runs for a short time and for a
                                                         from surrounding areas, and hybrid network, referred
small scale, so this does not have to consider energy
                                                         as an access network, hereafter, which combines a
scarcity of the sensor network. This type of system is
                                                         cellular network and ad hoc relay station (ARS) [5]
designed based on only lower data transmission
                                                         networks. We also initiate some concentric circular
delay. Due to rapid development of ubiquitous
                                                         zones in each cell for facilitating routing, which is
computing, we can deploy a large-scale disaster
                                                         called zoning. For better illustration of disaster
mitigation network that will track disaster
                                                         mitigation architecture, we present the Fig. 2. This
information for a long time. But in this case, energy
                                                         figure is presented with a cellular system with 7 cells,
efficiency and lower data delay should be considered
                                                         where some base stations are collapsed or
in together. To the best of my knowledge, in this
                                                         unreachable. In [5], author discusses the number of
paper, two major factors: energy efficiency and
                                                         ARSs needed to cover the entire system, and
lower data delay are considered in together for the
                                                         proposes a seed growing approach for the case only a
first time for the two proposed protocols of disaster
                                                         limited number of ARSs are available. Seed ARS is
mitigation and rescue operation. Furthermore, the
                                                         placed on each pair of shared edges along the border
proposed framework can be easily deployed in real
                                                         between two cells. According to [5], Fig. 3 depicts a
world cellular network. So, in the proposed
                                                         cellular system with 19 cells, where major
protocols’ part only WSN protocols are considered.
                                                         classification of cell is two: boundary cell and non-
Some researchers have studied a hybrid network for
                                                         boundary cell. But in Fig. 2, our network framework
cellular systems [5], [13], [16], [17]. The objectives
                                                         puts ARS in every edge without considering whether
of those systems are to achieve high speed, high
                                                         it is a shared edge or non-shared edge. In order to
capacity and wide area coverage by way of multi-
                                                         increase lifetime of sensor networks, we maintain
hopping. In [5], ad hoc relay station (ARS) is
                                                         every cell as a non-boundary cell. For performance
presented with its way of placement and various air
                                                         study, in section 4, we divide boundary cell class into
interfaces, though in this paper ARS placement
                                                         two subclasses: boundary cell with two non-shared
strategy is updated.
                                                         edges and boundary cell with three non-shared edges.
                                                         As an example, in Fig. 3, cell 1 is a boundary cell
                                                         with three non-shared edges, where cell 2 and cell 5
                                                         are boundary cell with two non-shared edges and
    We have already mentioned, our framework of
                                                         non-boundary cell respectively. In section 4, by
disaster management system consists of two
                                                         evaluating performances of the protocol with respect
subsystems: disaster mitigation and rescue operation.    to above-mentioned three kinds of cell, we justify
Former one is a general monitoring system for            that we have to consider every cell as a non-
disasters’ tracking. For instance, the first sign of     boundary cell. A WSN protocol for this proposed
tsunamis is earthquakes in the ocean-areas. If we        disaster mitigation architecture is developed in
know about these earthquakes in real time, we can        section 4. In this paper, we assume that every ARS
evacuate the residents of tsunami prone areas before     supports two types of interface: ad hoc relay
the tsunamis taking effect on those areas. Latter        interface and cellular interface. By ad hoc interface,
subsystem is for rescue purpose after disaster.          ARS can communicate with other ARSs and sensor
                                                         networks. ARS uses cellular interface to

                    Ubiquitous Computing and Communication Journal                                             3
communicate with base stations of cellular network.                  integrator. Section 5 presents a protocol for this
                                                                     proposed rescue operation architecture.


                                                      Onshore sink

                                                                                                         Surface station
            Base Station     Ad hoc Relay Station (ARS)
            Zoning           Sensor Network Node
                                                                                          Underwater sensor nodes
                             Sensor Network Node

                                          Figure 1: Network model

                                                                                                                      Non-shared Edge
                                                                                     1                                A pair of Shared Edge
                                                                                2            3
                                                                         4           5             6                  ARS
                                                                                7           8
                                                                         9           10           11
                                                                                                                      Boundary Cell
                                                                               12           13
                                                                         14          15           16
                                                                               17           18
                                                                                     19                               Non-Boundary Cell

    Base Station              Ad hoc Relay Station (ARS)
                                                                               Figure 3: Cellular network with 19 cells
    Collapsed Base Station    Sensor Network Node

                                                                     4        DISASTER MITIGATION
   Figure 2: A 7 cell-model for disaster mitigation
                                                                          One of the major advances in the field of
     For rescue operation, rescue workers or first
                                                                     surveillance technology is the deployment of
responders work for rescue purpose using portable
                                                                     distributed WSN. This has provided a means to
data collectors named cnode and mobile access
                                                                     monitor areas, which are either unreachable or
points. When cnode queries the sensor nodes, they
                                                                     hostile to human existence. So for disaster mitigation,
switch from idle mode to active mode and start
                                                                     WSN might be a strong medium of disaster data
reporting the sensed data to the cnode. Sensor nodes
                                                                     dissemination. In pervious section, we have
of rescue operation are different from those of
                                                                     presented a framework for this and now in this
disaster mitigation. RFID sensor can be used as
                                                                     section, we present a protocol for this WSN along
location tracking interrogator for rescue operations
                                                                     with its performance evaluation.
[7]. Non-battery RFID tags or passive RFID tags are
ubiquitously placed along roadsides and function as
                                                                     4.1     WSN Protocol For Mitigation
information-storage units. Information such as
                                                                          Mainly based on energy efficiency and
location of refuges and safety assessments of
                                                                     considering some base stations are unreachable, here
damaged buildings is remotely downloaded for the
                                                                     we propose a protocol for terrestrial WSN that is
tags by the RFID integrators or sensors. The
                                                                     applicable for disaster mitigation purpose.
maximum communication distance between the
                                                                        4.1.1 Addressing scheme
passive or non-battery RFID tag and the interrogator
                                                                          The addressing scheme in traditional networks is
is roughly 1.5 meters. Battery-driven RFIDS can
                                                                     fixed x-y coordinate address. But in our proposed
extend the communication distance with the
                                                                     protocol, the addressing format is <Location ID,

                       Ubiquitous Computing and Communication Journal                                                                   4
Node Type ID>. The Location ID identifies the                  over, a new cluster head is selected in the respective
location of a node that conducts sensing activities in         cluster based on residual energy of sensor nodes and
a specified region of the network. Locations of these          node centrality of that cluster (i.e. sub-area). Every
nodes are recorded in terms of polar co-ordinates (r,          node transmits a message containing the information
θ) with respect to the base station as origin of the           about weighted summation of its residual energy and
coordinate system (0,0). Based on r value, each node           node centrality to its neighbors along with the node
falls in one of the logical zones, which are concentric.       address and sub-area identification number. In Eq.
Also, every sensor node keeps records of its polar             (4), Ci represents the weighted summation of its
co-ordinates (ri, θi) with respect to i-th ARS, where i        residual energy and node centrality of ith
= 1,2,…,6. Protocol is applicable to stationary sensor
nodes and a stationary base station. The                                                             1− γ
                                                                                    Ci = γ Ei +                                (4)
implementation can be extended to mobile and ad                                                       di
hoc networks with GPS enabling of the nodes, which
is an added expenditure. In that case, it is assumed           node. In this equation, a constant γ is introduced to
that the base station keeps up-to-date information on          weight the residual energy and node centrality,
the location of all the nodes in the network with the          whose value is 0.7. A node i, receiving the Cj
help of GPS. Each node within the cluster is further           information of all other nodes j, compares its Ci with
provided with a Node Type ID that describes the                Cj of all other nodes j in the same sub-area (i.e.
functionality of the sensor such as seismic sensing,           cluster). If its Ci is less than Cj of other nodes j of
thermal sensing, RFID sensing and so on.                       same sub-area, then it can detect the node having the
   4.1.2 Clustering and scheduling                             maximum Cj from the received information, and
     The proposed disaster mitigation protocol is a            elect the corresponding j as the cluster head. Thus
cluster-based protocol. For facilitating clustering and        the node having maximum Cj becomes the cluster
routing of the protocol, each cell is divided into some        head for the particular sub-area. After being a new
concentric zones, what is already mentioned in                 cluster head, the cluster head updates the routing
chapter 3. Each zone area is divided into some sub             tables of its nearby clusters and the cluster itself. Fig.
areas. Each sub-area has unique identification                 4 represents the way of update the route. By
number. Every sensor node within this sub-area uses            broadcasting the route discovery message with its
this identification number along with its own address          sub area identification, new cluster head informs the
for communication purpose.                                     nearby clusters that the cluster, which is representing
     Each sub-area stands for a cluster, while a sensor        the corresponding sub area, has changed its head. As
node acts as a cluster head for the respective cluster.        a consequence, every nearby cluster updates its
Cluster head selection is based on two properties that         routing table information for the corresponding
are residual energy and node centrality of the nodes           cluster. When the new cluster head receives polar
of a cluster. Node centrality- a value that classifies         coordinates from nearby clusters, it calculates the
the nodes based on how central the node is to the              minimum angular deviation in shorter distance with
cluster. To find node centrality, every node keeps
the records of distances to the other nodes of
                                                                Algorithm Update_Route()
respective cluster and calculates the reciprocal of
sum of the squared distances of others node of the              // All the distance and angle (in radians) measured
cluster. Since the transmission energy is proportional          // with respect to nearest ARS of initiating cluster head
to d2, the higher value of the node centrality, the                    r0 ← new cluster head radial distance;
lower the amount of energy required by other nodes                    θ0 ← new cluster head polar angle;
                                                                      // Transmit signal with E such that (Q≤E<2Q)
to transmit data to that node as a cluster head. For                  Broadcast_Route_Discovering_Message ( );
elaboration, see Eq. (2) and Eq. (3), where SN is the                // receiving heads response with their polar
set of sensor nodes of the Nth sub area (i.e. cluster).              // coordinates with respect to respective
                                                                    // ARS as acknowledgement.
                                                                      r1, r2,….., rn ← radial distances of responding heads.
                  di =      ∑             d i2, j        (2)          θ1, θ2,….., θn ← polar angles of responding heads.
                         j ∈{ S N − i }                               Receive_Co-ordinates((r1,θ1),(r2,θ2),…,( rn,θn));
                                                                      // calculation of minimum angular deviation with
                 Node Centrality of node i =             (3)          //respect to all i node, where ri < r0
                                                    di                Calculate_Minima((|θ0-θ1|),( |θ0-θ2|),…,(|θ0-θn|));
                                                                      // return polar co-ordinate of next head (with
    Every cluster head maintains a routing table,                     // respect to respective ARS)
                                                                      retrun (r, θ)
which keeps the location information of nearby                  }
cluster-heads’ locations in polar coordinates. When
energy level Ei of a sensor node i (who is acting as a
cluster head) reaches a threshold level or interval            Figure 4: Algorithm for next head selection of
time between two consecutive clustering process is             routing

                      Ubiquitous Computing and Communication Journal                                                            5
the nearest ARS. The method of communication              here, during disaster some base stations may be
between the nodes under one particular cluster head       collapsed. So data sending from initiating cluster
and the cluster head is same as that of the LEACH.        head to the nearest ARS is done through multi-
     Radio interference caused by neighboring             hoping by cluster heads. After receiving data, ARS
clusters that could impede the operation of any given     sends data to one of its neighboring base stations if
cluster. This protocol makes use of code–division         one of these two is not collapsed. If both base
multiple access (CDMA) codes to counteract this           stations are collapsed, ARS sends data to the nearest
problem. Each cluster is assigned a spreading code        ARS. Routing protocols of ARSs and base stations
that the nodes in the cluster use to distinguish their    discussed in [5] might be the best choice for
data transmission from those of nodes in the              proposed framework and disaster mitigation data
neighboring clusters.                                     dissemination from ARSs to base stations. For
   4.1.3 Routing                                          integrated networks with heterogeneous technologies
     After clustering and scheduling, cluster nodes       such as cellular and ad hoc relaying, [5] describes the
send their data to the cluster head based on scheduled    proposed signaling and routing protocols for iCAR to
slots. Once data from all sensor nodes have been          establish and release bandwidth guaranteed
received, the cluster head performs data fusion on the    connections possibly involving ARS relaying. Such
collected data, and reduces the amount of raw data        protocols aim to addressing the QoS need of IP based
that needs to send to the nearest ARS. In general,        real time applications.
data is routed to the base station by single hop or by
multi hop. But here, to reduce average energy                                                      Base
dissipation of sensor nodes and consider unreachable                                                Cluster
or collapsed base stations, data is routed to the
nearest ARSs rather than base stations. And energy is
distributed over the sensor network by keeping
multi-hop routing from cluster head to the nearest
     During routing, cluster head node forward its
data to a neighbor cluster head that is selected
applying the algorithm presented in Fig. 4. After
forwarding data to selected cluster head, the sensor                                                   Radial
node listens to that head to ensure that it repeats the
data packet i.e. implicit acknowledgement. If the
packet is not repeated, this indicates a transmission
failure. A transmission failure invokes route update
process (i.e. Fig. 4). Sometimes, a node fails to                    Figure 5: Data routing outline
forward data to none of its neighbors or it does not
have any negihbor within its transmission range.          4.2     Performance Evaluation
Usually this occurs when the node observes a void              To evaluate the performance of the proposed
region between itself and the destination ARS. At         protocol, using C programming language a
this situation, it broadcast the sensed data with the     simulation program is developed based on proposed
maximum transmission power. It is already                 framework. Though here the performances of the
mentioned due to severe disaster some base stations       protocol are studied in two ways: based on 3 types of
can be collapsed. So unreachable or collapsed base        cell and comparing with others protocols such as
stations have to be considered during developing          LEACH, PEGASIS; in both cases main evaluation
data routing technique for disaster management. In        metric is system life.
this proposed protocol, clusters send data to ARSs           4.2.1 Based on 3 Types of Cell
and then ARSs send data to the base stations                   To evaluate the performance of the proposed
considering their status: collapsed or not. If the base   protocol, the proposed protocol is simulated and
station of respective cell is collapsed, in that case     compared its performance regarding three different
ARSs send their data to a live base station or ARSs.      types of cell: non- boundary cell, boundary cell with
During disaster, any ARS may be collapsed. But            2 non-shared edges, and boundary cell with 3 non-
there is little chance to collapse all ARSs of a cell.    shared edges, which are briefly discussed with Fig. 3.
Only one ARS is enough to convey data from sensor         Here performance metrics are average energy
network of a cell to a base station.                      dissipation, successful data delivery and number of
     Fig. 5 shows data routing outline, how data is       live nodes. In a cell, 500 sensor nodes are uniformly
routed from data source cluster head to ARS. This         distributed with center-located base station and
outline is a modified version of [2], where authors       energy level of each node is assigned initially 5 Joule.
consider that data from cluster head is routed to base    Here the simulation area is kept small regarding
station through multi hoping by cluster heads. But        general sensor network simulation technique and

                     Ubiquitous Computing and Communication Journal                                                 6
sensor network readers can get an idea easily from                         data messages than other types of cell. Non-
the following simulation results. Eventually, the                          boundary cell offers improvements in data delivery
radius of cell is 50 meter. Data packet size of sensor                     by factor of 12 percent and 49 percent over boundary
node is 1 kilobit. Number of operation is divided into                     cell with 2 non-shared edges and boundary cell with
rounds like LEACH protocol, and the number of                              3 non-shared edges respectively.
rounds is 2500. In analysis, radio model of [9] is
used that has already been discussed briefly in
section 4.1.1.
     In Fig. 6, the plot shows the total number of live                                                                               5

                                                                             Average energy dissipation (Joule)
nodes that remain alive over the number of rounds of                                                                         4.5
activity for proposed protocol regarding three types                                                                                  4
of cell. With non-boundary cell, 486 nodes out of
500 remain alive after the end of the simulation,
while corresponding numbers for boundary cell with
2 non-shared edges and boundary cell with 3 non-                                                                             2.5

shared edges are 341 and 125 respectively.                                                                                            2

Eventually performance of non-boundary cell                                                                                  1.5
justifies the update of ARS placement in chapter 3.                                                                                   1
     The improvement of gained through non-                                                                                  0.5
boundary cell is further exemplified by the average
energy dissipation graph in Fig. 7, which shows the                                                                                       0            500         1000      1500     2000    2500
average energy dissipation of the protocols under                                                                                                             Number of rounds
study over the number of rounds of operation. The
plot clearly portraits that non-boundary cell has a
much more desirable energy expenditure curve than                          Figure 7: Average energy dissipation over the
those of others. After 2500 rounds, 4% energy                              number of rounds of operation
remained in boundary cell with 3 non-shared edges
and 21% energy remained in boundary cell with 2
non-shared edges , while in non-boundary cell,
remaining energy is 50% of the initial network                                                                                        1200000
                                                                                                   Number of data messages received



                          450                                                                                                             400000
   Number of live nodes

                                                                                                                                                   0         500      1000     1500    2000   2500
                                                                                                                                                                   Number of rounds
                                0   500     1000    1500     2000   2500
                                                                           Figure 8: Total number of data messages received at
                                          Number of rounds                 the ARSs over the number of rounds

                                                                              4.2.2 Comparison with PEGASIS and LEACH
Figure 6: Number of live nodes over the number of                               In this section, the performance of the proposed
rounds of operation.                                                       protocol is compared with those of PEGASIS and
                                                                           LEACH protocol. Simulation environment is same as
     Next the number of data messages received by                          section 4.2.1 except cell radius and number of
the sink (i.e. ARS) for three types of cells is analyzed.                  deployed sensor nodes. Here cell radius is 500 meter
Fig. 8 shows the total number of data messages                             (i.e. ten times bigger than previous environment).
received by the sink over the number of rounds of                          Like       previous       simulation     environment,
activity. The plot clearly illustrates the effectiveness                   circumscribed hexagon is a regular hexagon.
of non-boundary cell in delivering significantly more                      Eventually the diagonals’ intersection of the hexagon

                                          Ubiquitous Computing and Communication Journal                                                                                                             7
divides the hexagon into 6 equal areas. 1200 sensor                                                                      PEGASIS     LEACH      Proposed Protocol
nodes are uniformly distributed over these 6 areas.

                                                                                           Number of rounds
     Fig. 9 presents the node death percentage over                                                           2500

the number of rounds of operation for the PEGASIS,                                                            2000

LEACH and proposed protocol. With proposed                                                                    1500

protocol all nodes remain alive till 1498 rounds,                                                             1000
while in PEGASIS and LEACH, all nodes remain
alive till 1005 and 498 rounds. After 1502 rounds,                                                                   0         20        40   60        80          100
there is no live node in PEGASIS, while proposed
                                                                                                                             Energy consumption percentage
protocol can maintain the system up to 2019 rounds.
Although 75% nodes with LEACH method dies
within 1000 rounds due to direct transmission, few
closer nodes of ARS can communicate up to round                                      Figure 10: Energy consumption percentage over the
1902.                                                                                number of rounds of operation.
     Energy consumption percentage of the protocols
under study is demonstrated in Fig. 10, where
proposed protocol presents most desirable energy                                     Table 1: Average time for a round.
curve for the proposed framework. In LEACH, 50 %
energy of initial energy of the whole network is                                           Protocol                            PEGASIS        LEACH          Proposed
consumed by the 630 rounds of operation, while the                                                                                                           Protocol
corresponding round’s number in PEGASIS and
proposed protocol are 855 and 1190. Though [42]                                            Average                                  24          2.5                 4.1
presents that PEGASIS is a protocol, whose energy                                         time for a
consumption rate is near to optimal, these results                                       round (sec.)
contradict with that because energy consumption rate
depends not only technique but also coverage areas.                                  5        RESCUE OPERATION
     The further improvement of proposed protocol
over PEGASIS is exhibited by computing average                                           For rescue operation, we assume, multiple
round time, which is present in Table 1. Due to                                      sensors are deployed in each room of a building or in
making chain among the nodes, PEGASIS takes                                          localized areas. These sensors may be several types
huge time to complete a round, while proposed                                        such like RFID tag location sensor, high temperature
technique saves time by not doing cluster head                                       sensor in the fire, and distortion sensor of the
selection for every round, which is executed after                                   building. In the event a disaster happens, assuming
interval time between two consecutive clustering                                     survivors are trapped in rubble, sensor nodes located
process or if current cluster head i energy level Ei                                 near the survivors may detect them. After detecting
reaches to threshold level. Though here LEACH                                        survivors’ information or other necessary
performs better than proposed protocol because of                                    information, sensor nodes have to disseminate their
LEACH’s direct transmissions from cluster heads, in                                  data to cnode in an energy efficient way.
real world LEACH implementation in a large
network will not viable. The performance of                                          5.1    WSN Protocol for Rescue
proposed protocol can be easily improved by adding                                        In this section, mainly based on energy
more ARSs in every cell of proposed data collection                                  efficiency and lower delay, we propose a WSN
framework.                                                                           protocol only for rescue operation.
                                                                                       5.1.1 Addressing scheme
                                                                                          This node addressing scheme is similar to the
                                 PEGASIS        LEACH      Proposed Protocol
                                                                                     scheme that described in section 4.1.1., where the
                                                                                     addressing format is <Location ID, Node Type ID>.
   Number of rounds

                      2000                                                           But here node does not need to keep the record of its
                      1500                                                           polar-coordinate with respect to ARSs.
                      1000                                                             5.1.2 Routing
                      500                                                                 Two major issues are associated with this
                        0                                                            proposed routing process, namely task dissemination
                             0         20        40      60         80         100
                                                                                     and data dissemination.
                                            Node death percentage                         Task Dissemination: For rescue purpose, cnode
                                                                                     collects data from sensor nodes of disaster areas.
                                                                                     This data collection is similar to a query based data
Figure 9: Node death percentage over the number of                                   collection, which is denoted as task based data
rounds of operation.                                                                 collection. At the beginning, cnode broadcasts a task
                                                                                     message over the sensor nodes of a particular area.

                                             Ubiquitous Computing and Communication Journal                                                                               8
Due to directional antennas in cnodes, sensor nodes        individual task id. It only selects a next hop on the
in specific sections of the disaster area are invoked in   following condition:
sensing system. In the task message, cnode includes              -cnode changes its coordinate position.
its polar coordinate regarding base station as its               -transmission failure.
origin. We assume, during task dissemination cnode         After forwarding data to selected next hop, the
and sensor nodes are located in same cell of a             sensor node listens to that hop to ensure that it
cellular system; and cnode has GPS facility though         repeats     the    data      packet    i.e.   implicit
here we consider that sensor nodes do not have this        acknowledgement. If the packet is not repeated, this
facility. In addition, here considered sensor nodes are    indicates a transmission failure. A transmission
stationary. For mobile sensor nodes, we can add GPS        failure invokes next hope selection process.
facility with the sensor nodes, and in that case cost      Sometimes, a node fails to forward data to none of its
will be expanded. After receiving the broadcasting         neighbors or it does not have any negihbor within its
message from the cnode with particular task id and         transmission range. Usually this occurs when the
polar coordinate, every sensor node updates its polar      node observes a void region between itself and the
coordinate regarding current cnode as its origin. For      destination cnode. At this situation, it broadcast the
instance, in Fig. 11, a sensor node S, whose polar         sensed data with the maximum transmission power.
coordinate is (rs, θs) with respect to base station        Fig. 12 depicts data routing outline.
O(0,0), calculates its polar coordinate with respect to
current cnode C(rc, θc) and that would be (CS,                                                   Radial Distance

                                                                                                 Actual Distance
                                        S (rs,θs)

           C (rc,θc)                D                              Cnode                    Sensor node

      O (0,0)                                                           Figure 12: Routing outline

Figure 11: Polar coordinate calculation of sensor          5.2     Performance Evaluation
node S with respect to current cnode C.                         To evaluate the performance of the proposed
                                                           protocol of rescue network architecture, we simulate
    Data Dissemination: At the end of the task             the protocol and compare its performance with that
dissemination, every sensor node in the specific area      of SENDROM [1] architecture. Performance is
that is covered by directional antenna of cnode            measured by system lifetime, initial route
senses data. The sensed data should be forwarded to        establishment delay and recovery delay. Throughout
the cnode that broadcast the task. Here we use a           the simulation, we consider 50 nodes are uniformly
multi-hoping technique for forwarding the sensed           distributed in area of 160×160 meters and cnode is
data. For selecting the next hop, we use similar           located on one of the corners. Operation is divided
algorithm that is presented in Fig. 4. But here all        into number of events. Each individual task id
polar coordinates of sensor nodes are computed with        represents individual event. Radio model used in [8]
respect to task initiating cnode. This is an angular       is used for energy computation, where the power
deviation updated algorithm of [2]. Here a sensor          dissipation is 35 mW in idle mode, 395 mW in
node selects its next hop based on minimum angular         receive mode and 660mW in transmit mode. The
deviation on the way to the cnode. A sensor node           data transmission rate is set to 1.6 Mbps.
broadcasts a route discovery message to its                     In Fig. 13, the plot shows remaining total energy
neighbors. After receiving the route discovery             of the network over the number of events of activity
message, the neighbors who already received the            for our proposed protocol and SENDROM. After 35
task message from the particular cnode send their          events, with proposed protocol, remaining total
polar coordinates (where cnode is regarded as origin)      energy is 73 percentage of initial total energy of the
to route discovery message initiating sensor node.         network, while corresponding percentage for
And then the route discovery message initiating
                                                           SENDROM is 47. Proposed protocol offers
sensor node finds the minimum angular distance next
                                                           improvements in energy conservation by factor of
hop from the receiving polar coordinates of its
                                                           156 percent over SENDROM. In SENDROM, cnode
neighbors and updates its routing record. A sensor
node does not select a new next hop for every              includes every node of the network during route
                                                           establishment phase. But some of these nodes that

                       Ubiquitous Computing and Communication Journal                                              9
waste their energy for route establishment are not                                                                                                             SENDROM           Proposed Protocol

                                                                                                          Total number of failing nodes
used for data dissemination. In addition, angular
distance data dissemination technique of proposed
protocol invigorates the energy conservation process                                                                                      10

of the network.                                                                                                                           8
     The improvement of life system through                                                                                               6
proposed protocol is further exemplified by the
number of failing nodes in Fig. 14, which shows the
total number of failing nodes of the protocols under
study over the number of events of operation. The                                                                                         0
                                                                                                                                               0       5       10      15   20         25       30      35
plot clearly portraits that proposed protocol has a
                                                                                                                                                              Number of events
much more desirable failing nodes curve than that of
other. After 35 events, one-fourth nodes are failed to
communicate in SENDROM, while in proposed
protocol, this number is 5% of the total nodes.                                               Figure 14: The number of nodes failed due to energy
     Next we analyze the number of events                                                     depletion
transmitted to sink (e.g. cnode) for the SENDROM                                                                                                               SENDROM           Proposed Protocol
and our proposed protocol. Fig. 15 shows the total                                                                                        35

                                                                                              Total number events transmitted
number of events transmitted to the sink over the                                                                                         30
number of events of activity. The plot clearly
illustrates the effectiveness of proposed protocol in
delivering significantly more events than its                                                            to sink                          20

counterpart. Proposed protocol offers improvement                                                                                         15
in event delivery by factor of 135 percent over
SENDROM.                                                                                                                                  10

     Fig. 16 represents the route establishment delay                                                                                      5
and route recovery delay of the protocols under study.
Though route establishment delay and route recovery                                                                                             0       5      10      15   20          25       30     35
delay are defined in the SENDROM system, in                                                                                                                     Number of events
proposed protocol, route establishment is not similar
to SENDROM. In SENDROM, cnode initiates route                                                 Figure 15: The number of events reported to the
establishment process and the process is completed                                            network
for all nodes of the network by flooding the route
message. But in proposed protocol, this process is
not done in together. A node selects its next hop only
when it needs to that (see details in section 5.1.2).
                                                                                              Time (Sec)

For comparison purpose, in proposed protocol, we
define that total time for first time next hop selection
is denoted as route establishment time. When first
time selected next hop cannot forward data or
communicate, route update is needed; and the total
time to update route is denoted as route recovery                                                                                                      SENDROM                    Proposed Protocol
                                                                                                                                               Route establishment delay         Route Recovery delay
                                                 SENDROM        Proposed Protocol
   Remaining total energy of the

                                                                                              Figure 16: Route establishment and route recovery
        network (*100%)

                                   0.6                                                        delay
                                   0.2                                                        6                                   CONCLUSION
                                         0   5    10       15   20      25          30   35
                                                                                                   In this paper, we present a framework for
                                                 Number of events                             disaster mitigation and rescue operation that can be
                                                                                              easily implemented in real world communication
                                                                                              system. Though current real world communication
                                                                                              system does not support various effects of disasters
Figure 13: The energy available in the network                                                or catastrophes, while our proposed system removes

                                                  Ubiquitous Computing and Communication Journal                                                                                                             10
those drawbacks. In addition, here we present                    Transactions on Networking, pp. 2-16,
protocols for sensor networks, which are based on                February,2003.
proposed framework, consider energy efficiency of         [9]    W. B. Heinzelman, A. P. Chandrakasan, and H.
                                                                 Balakrishnan,         “An      Application-Specific
the sensor nodes strongly along with lower route                 Protocol Architecture for Wireless Microsensor
establishment delay. We update the ARS placement                 Networks,” IEEE Trans. Wireless Commun.,
of actual ARS placement in [5]. The simulation                   vol. 1, no. 4, , pp. 660–70, Oct. 2002.
results justify this update. In future, our future        [10]   Jeffrey H. Reed, Kevin J. Krizman, Brian D.
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avenue is to develop a semantic query based protocol             Overview of the Challenges and Progress in
for disaster management.                                         Meeting the E-911 Requirement for Location
                                                                 Service", IEEE Communications Magazine, no.4
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                      Ubiquitous Computing and Communication Journal                                             11

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