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Low Duty Cycle, Energy-Efficient and Mobility-Based Boarder
Node—MAC Hybrid Protocol for Wireless Sensor Networks
Abdul Razaque &Khaled M. Elleithy
Received: 16 September 2013 /Revised: 12 July 2014 /Accepted: 20 August 2014
#Springer Science+Business Media New York 2014
Abstract The need for an efficient medium access control
(MAC) protocol isextremely important with the emergence of
wireless sensor networks (WSNs). The MAC protocol has
increasingly been significant in advancing the performance
of WSNs. In this paper, a low duty cycle, energy-efficient and
mobility-based Boarder Node Medium Access Control (BN-
MAC) hybrid protocol is introduced for WSNs that controls
overhearing, idle listening and congestion issues by preserv-
ing energy over WSNs. BN-MAC leverages the features of
contention and schedule-based MAC protocols. The conten-
tion encompasses the novel semi-synchronous approach that
helps obtain faster access to the medium. The schedule-based
part helps reduce the collision and overhearing problems.
The idle listening control (ILC) model is embedded within
the BN-MAC that administers the nodes to go to sleep after
performing their tasks to saves additional energy. The least
distance smart neighboring search (LDSNS) model is used to
determine the shortest and most efficient path in a one-hop
neighborhood.
Evaluation of the BN-MAC is conducted using network
simulator-2 (ns2), then its quality of service (QoS) parameters
are compared with other known hybrid MAC protocols in-
cluding X-MAC, Zebra medium access control (Z-MAC),
mobility-aware SMAC (MS-MAC), advertisement-based
MAC (A-MAC), Adaptive Duty Cycle SMAC (ADC-
SMAC) and Mobile Sensor (MobiSense) MAC protocols.
Keywords Wireless sensor networks .Medium access control
protocols .Energy efficiency .Mobility .Handling mass
casualties
1 Introduction
Wireless Sensor Networks are considered one of the dominant
research areas in recent years. WSNs consist of a large number
of sensor nodes with limited power, which gather and process
data from specific domains and return data back to specific
locations (e.g., disaster control centers and headquarters).
With the emergence of low-cost sensing devices, WSNs have
been proved to fit many applications such as environmental
monitoring, industrial sectors, battlefield surveillance and
consumer applications [1]. WSNs are used to provide better
living standards. Meanwhile, WSNs face many challenging
issues such as insufficient coverage, scalability, lack of ro-
bustness, uniformity, congestion, mobility and high energy
consumption [2]. Furthermore, limited battery life and severe
operating conditions are causes of node failure [3]thatwaste
energy.
Significant research has been conducted in WSNs to main-
tain high standards of communication, especially coverage,
but the issue of high energy consumption is still not sufficient-
ly resolved [4]. With the exploitation of a mobile infrastruc-
ture, a larger area is covered, compared to an infrastructure-
based network using the same number of sensors [5]. The use
of mobile devices in WSNs can offer flexibility, smartness and
adaptability to connect dynamically to any environment [6–8].
Furthermore, developments in sensor technology and its ma-
turity level can improve the quality and cause less energy
consumption.
MAC protocols specify how nodes share the channel for
communication to improve the efficiency of WSNs. There are
different categories of MAC protocols introduced such as
A. Razaque (*):K. M. Elleithy
Computer Science and Engineering Department, University of
Bridgeport, Bridgeport, CT, USA
e-mail: arazaque@my.bridgeport.edu
K. M. Elleithy
e-mail: elleithy@bridgeport.edu
J Sign Process Syst
DOI 10.1007/s11265-014-0947-3
schedule-based, contention-based, mobility-aware, hybrid,
cross-layer and real-time [9]. Meanwhile each MAC protocol
is designed for a specific type of application [10]. Most of the
widely used MAC protocols are based on contention, where
access to the same communication channel by multiple sen-
sors causes collisions.
A collision reduces the channel bandwidth and increases
energy consumption. To conserve energy, schedule-based
MAC protocols were introduced to reduce idle listening by
scheduling regular sleep intervals [11]. However, schedule-
based MAC protocols are not accepted as a general standard
because they are application-dependent, lack of mobility and
of scalability support. Schedule-based MAC protocols face
the challenge of inconsistency in the physical layer and the
sensor hardware. The change of topology is another issue
caused by insertion and deletion of wireless nodes [12,13].
Hybrid MAC protocols were introduced by combining the
characteristics of time division multiple access (TDMA) and
carrier sense multiple access CSMA in order to get higher
energy saving and flexibility. However, existing hybrid MAC
protocols are not capable of providing mobility and network
adaptability support. These are some of the major issues that
need to be addressed when designing a highly robust hybrid
MAC protocol. To address these concerns, a low duty cycle,
energy-efficient and mobility-based Boarder Node Medium
Access Control hybrid protocol has been introduced. BN-
MAC is designed to address the problems of existing hybrid
MAC protocols such as mobility and scalability. BN-MAC
also addresses the problem of low power listening: reducing
the size of the preamble without the inclusion of a destination
address in each preamble and data packet. Further, BN-MAC
uses the automatic packet buffering and is compatible with
packetizing radios. In BN-MAC, the node gets complete
access to its owner slot, similar to TDMA-based approaches.
The rest of the slots are accessed through the CSMA approach.
The remaining portions of this paper are organized as
follows. In Section 2, we present literature review of related
techniques. In section 3, we present the system model for the
proposed work. In section 4, the BN-MAC protocol design is
presented. In section 5, the idle listening control model is
explained for handling the idle listening problem. In section
6, the simulation setup and analysis of the results is discussed.
In section 7, the discussion of results is presented, and section
8 concludes the paper.
2 Review of Related Techniques
In this section, we examine some of the well-known hybrid
and mobility MAC protocols with their existing salient fea-
tures and weak points. X-MAC is a hybrid-based low duty
cycle MAC protocol based on short preambles [14]. In X-
MAC, the transmitter sends a short preamble. If the transmitter
does not get acknowledgment, the transmitter node considers
that the target node is asleep. The transmitter node attempts to
send a short preamble again until the transmitter node reaches
the threshold value. In X-MAC, CSMA is performed before
preamble packet transmission. Having received the preamble,
the receiver has to wait for a short period to provide a chance
for other nodes if they want to send data packets. An advan-
tage of X-MAC is minimization of energy consumption and
latency. In addition, idle listening at the receiver side and
overhearing at the neighboring nodes can be reduced.
However, the gaps between series of preamble packets is a
problem that can be considered as idle listening. As a result,
the goal of preserving the energy remains unfulfilled.
The Z-MAC incorporates both features of TDMA and
CSMA techniques. In Z-MAC, CSMA builds the baseline
and TDMA resolves the conflict. Z-MAC uses the owner slot
idea. The nodes in Z-MAC use the novel flexible time-frame
regulation without global synchronization. Nodes, however,
require the operating global clock synchronization when set-
ting up the phase, which is considered a complicated process.
As a result, nodes consume significant energy resources. Z-
MAC also introduces a node highest priority scheme. All the
nodes can compete for the channel for data transmission, but
only the allocated node gets the highest priority. Under the
high competition conditions, the slot assignments decrease the
collisions. However, Z-MAC suffers latency problems due to
the use of a long preamble that increases the chance of striking
the active period of the receiver. The nodes in Z-MAC are
fixed to limit the network scalability. As a result, the mobility
and scalability support cannot be fully attained. Once a new
node intends to join the network, the setup phase must be
repeated several times, which decreases throughput and con-
sumes additional energy.
The mobility-aware MAC protocol for sensor networks
(MS-MAC) [15] is introduced as an extension of SMAC.
MS-MAC uses coordinated sleep/listen duty cycles and peri-
odically synchronizes the schedule of the nodes. The process
of synchronization is done using a broadcasting SYN packet
at the start of the listening phase. A node first attempts to
follow a prevailing schedule while listening for a specific
period of time. If no SYNC message is received, the nodes
randomly pick a time to go for sleep and instantly broadcasts
this information. However, if a node obtains different sched-
ules, then that node picks one, but the nodes adopt both
schedules. MS-MAC uses border nodes that make a virtual
cluster that may follow two or more different schedules. MS-
MAC enables each node to determine the mobility and its
level within its neighborhood. An advantage of MS-MAC is
to handle different cluster schedules. MS-MAC can continue
communication with the original neighbor while making a
new virtual cluster. The synchronization can be adjusted with
the speed of the neighbor nodes. However, nodes get confused
by following different schedules that could lead to congestion
J Sign Process Syst
and a waste of energy under a heavy traffic load. In addition,
neighbor of the sensor node wastes a significant amount of
energy even it is static.
Speck MAC [16] is another hybrid MAC protocol that is a
deviation from the B-MAC protocol. Speck MAC integrates
destination address and superfluous transmission of short
packets. The first goal of Speck-MAC is to reduce the trans-
mission energy, and the second is to decrease the significant
overhearing problem during a heavy traffic situation. Speck-
MAC is also efficient during the transmission of unicast
packets. However, Speck-MAC experiences the problem of
extra consumption of energy by sending wake-up frames even
though frames are already received by the receiver Wake-Up
[17]. Speck-MAC also suffers due to the excess latency prob-
lem. Speck MAC is not supported for real-time communica-
tion and mobility
The mobility-aware MAC (MA-MAC) protocol is pro-
posed in [18] as an extension of XMAC. MA-MAC enables
a node to extend sleep time and switch on radio when the
packets are arriving. MA-MAC covers two scenarios: static
and mobility. In the static scenario, the performance of MA-
MAC is similar to X-MAC. MA-MAC divides the preamble
into several strobes to send an early acknowledgment packet
to preserve energy. In the mobility scenario, MA-MAC uses a
seamless handover to relay the data to a new node before the
collapse of the link. During mobility, if a transmitter notices
that the distance of the receiving node exceeds the first thresh-
old, the transmitter starts to discover an intermediate neighbor
node. To do this task, the transmitter broadcasts a data mes-
sage in which handover requests are included. If the transmit-
ter receives one acknowledgment packet from a new node,
then the transmitter directs the data transmission to the newly
discovered node. An advantage of MA-MAC is handling the
mobility in time, and relay nodes are discovered during data
transmission. However, MA-MAC has a weakness because
MA-MAC depends on the network density and the schedule
of nodes. Further, in MA-MAC, it is also hard to maintain two
threshold values.
ADC-SMAC [19] is a hybrid MAC protocol that is an
improved version of S-MAC [20]. ADC-SMAC adds two
additional features to S-MAC. First, the node calculates the
energy consumption rate of the forwarding node and an aver-
age sleep delay at the time of sending the synchronized
packets. ADC-SMAC also adjusts the duty cycle according
to the network conditions and broadcasts the new schedule to
the neighbor nodes. Hence, ADC-SMAC reduces the energy
consumption, but it increases the latency and it is difficult to
manage the network scalability. In addition, ADC-SMAC is
not fully robust in mobility conditions.
MobiSense is a cross-layer mobility-based MAC protocol
that combines MAC and the network layer to perpetuate
energy efficient data communication within a micro-mobility
scenario. Inthe scenario, the nodes are structured into clusters,
in which stationary nodes perform as cluster heads. The non-
cluster head nodes interchange data packets between cluster
head nodes [21]. MobiSense implements multi-channel data
communications to increase throughput and simplify the net-
work management. The goal of MobiSense is to decrease the
intervention between the clusters and to permit the cluster-
heads to schedule traffic dynamically. MobiSense manages a
super-frame using synchronized slots, transmission slots,
downlink and uplink, discovery slots and data admission
mini-slots. The cluster heads send synchronized data packets
at the start of each frame to notify mobile nodes about changes
in downlink and uplink data transmission. The strength of
MobiSense is to obtain quick network discovery information.
MobiSense also confirms fast admission and rapid network
convergence. However, MobiSense experiences the problem
of managing the multi-channel. As a result, the node mobility
is difficult to handle in time and therefore causes the
collisions.
The low-power real-time medium access control (LPRT-
MAC) protocol is proposed in [22] for actuation and wireless
systems. LPRT-MAC consists of an infrastructure-based star
topology. The stations communicate with base stations direct-
ly. The LPRT-MAC includes a super frame that is divided into
mini slots and is used for transmission with the base station.
LPRT-MAC reduces power consumption and coordinates
with the channel. The beauty of LPRT-MAC is handling
overhead by using the star topology. However, LPRT-MAC
is limited and not suitable for large multi-hop wireless sensor
networks. As a result, the topological change causes the
additional energy consumption, and the nodes reduce the
throughput. LPRT-MAC is also not suitable for mobility
scenarios.
Mobility-aware and energy-efficient MAC (ME-MAC) is
proposed in [23]. ME-MAC possesses almost similar features
to MMAC-SW [24]. ME-MAC inherits the features from
TDMA and CSMA and dynamically adjusts the frame size
as discussed in [24]. ME-MAC consists of the prediction
model that depends on the accuracy of the localization mech-
anism. ME-MAC also uses order-autoregressive that helps to
predict the current mobility state. The ME-MAC protocol
achieves its task through two phases: a data transfer phase
and a clustering phase. An advantage of this protocol is to
reduce delay to improve the packet delivery rate. However,
ME-MAC suffers due to network adaptability.
Based on the survey, we demonstrate that existing Z-MAC,
ADC-SMAC, X-MAC, LPRT-MAC, and Speck-MAC hybrid
MAC protocols attempt to be energy efficient but experience a
problem in mobility conditions. Mobility based MAC proto-
cols such as MobiSense, ME-MAC, MS-MAC, MA-MAC
are good candidates in mobility conditions. However, they
experience a problem due to network density, management of
multi-channels and following the dual schedule in the net-
work. Finally, we conclude that these protocols are designed
J Sign Process Syst
as application-specific. In this paper, we introduce the BN-
MAC protocol that handles network scalability, mobility, and
improves the real time communications. Additionally, BN-
MAC reduces the idle listening overhearing and improves
the throughput. The BN-MAC can also be used for multiple
WSN application areas.
3 System Model
The emergence of the latest wireless sensing technology helps
address the several shortcomings related to wired-sensors.
Wired sensor technology is generally used in emergency
rooms and hospitals to monitor the patients [25]. The heap
of wires is attached to a patient, which makes patients uncom-
fortable. As a result, their mobility is restricted, and increased
anxiety is observed in the patients. The increased anxiety level
is also difficult for the staff to handle. When patients are
moved from one unit to another, the sensors need to be
removed and reattached, which is considered a cumbersome
process. The wireless sensor networks should be mobility-
aware to help reduce both the jumble of wires and patient
concerns. There are already existing triage protocols for han-
dling emergency medical services [26]. The performance of
these protocols can be degraded due to the state of mobility
and increasing numbers of casualties.
There is a need to augment the evaluation of the mass-
casualty during increased mobility and scalability to report the
triage levels of several victims automatically. To handle such a
situation, we have simulated a WSN health scenario that
tracks the indoor patients who are examined by local practi-
tioners and remote practitioners. Further, outdoor casualties
and movements of victims are monitored and reported to the
control room to take immediate measures for reducing the
number of casualties, as depicted in Fig. 1. The simulated
WSN health scenario consists of different regions, and each
region is controlled by a Boarder Node (BN). From another
perspective, the WSNs experience the problems and limita-
tions due to mobility and scalability [27].
Therefore, the energy-efficient MAC protocol will be able
to reduce such problems to some extent. We have therefore
deployed the BN-MAC protocol in this scenario to handle the
mobility and scalability to reduce the number of casualties in a
mass disaster area. One of the major goals for deploying the
BN-MAC is to reduce energy consumption while maintaining
a high degree of scalability, mobility and collision avoidance.
The sensor nodes are deployed in different regions to monitor
the different types of activities. The deployed sensor nodes are
static and mobile and can move to any region. Whenever a
node leaves one region, then it needs to join another adjacent
region based on activities assigned to the node. To maintain
the smooth data exchange and efficient use of the bandwidth,
the bidirectional end-to-end reliability is mandatory in WSN
[28]. End-to-end reliability is accomplished when each event
is reported to the BN, and every task of the BN is delivered to
the sensing field effectively. The lack of bidirectional reliabil-
ity weakens event detection and provides inappropriate data
collection. We achieve end-to-end reliability using a new
bidirectional reliable transport mechanism that uses a short
preamble ACK/NACK control packet between the BN and
important sensor nodes. In this scenario, the necessary nodes
are chosen applying the weighted-greedy algorithm
1
based on
the residual energy of the sensor node. When congestion
occurs, unimportant sensor nodes receive an alarm signal from
important nodes. As a result, the unimportant sensor nodes
stop reporting the events to adjust unnecessary traffic.
The sensor nodes communicate with each other using short
range and one-hop communication rather than long range
communication to preserve energy. The message forwarding
process is done with intra- and inter-communications. The
intra-communication process is done within regions using
semi-synchronous features.
The semi-synchronous
2
process consists of scheduled and
contention-based approaches. The contention-based feature
uses asynchronous communication to find the availability of
the channel for communication, whereas schedule-based helps
fix the schedule of the nodes for sending and receiving the
data within the regions. Single-hop communication has little
edge over multi-hop communication [29]. Multi-hop commu-
nication increases the latency because each node stores and
forwards the packets. If the transmission consists of many
hops, the transmission consumes more energy while
forwarding packets, and the situation can even be worse if
the packet size is larger.
The sensor nodes inside the region that monitor different
events and forward the collected data to BN node are static
and mobile. Each BN forwards the information obtained from
sensor nodes using inter-communication to the base station.
Each base station further forwards the information to “control
room”using the IP network. The LDSNS model [30]isalso
used to help find the efficient shortest path. As a result, the
sensor node uses Anycast communication
3
for maintaining the
load balancing to save additional energy.
In this scenario, different events occur simultaneously such
as indoor patient reporting, outdoor casualties reporting to the
1
A weighted greedy algorithm: It can be considered as backtracking
algorithm where each decision point “the best”selection is already known
and accordingly can be chosen without having to think over any of the
substitute.
2
Semi-synchronous: This feature is desirable for decreasing latency and
energy consumption for several WSN application areas to improve the
throughput.
3
Anycast communication: It is message mechanism that only sends
control message to the nearest node within the group of possible receivers
or may pick several nodes with subject to condition.
J Sign Process Syst
designated specific location (control room), rescuing the vic-
tims from the area of mass destruction, detecting the move-
ment of victims, monitoring the rescue activities and handling
the faster recovery process. In the scenario, the PT mobility
routing model is incorporated.
PT encompasses two important features; packet generation
rate and the pheromone sensitivity [30] to handle the task of
observing the rescue events and maintaining a faster recovery
process. Furthermore, most recent WSN applications in the
area of surveillance and monitoring also require mobility and
scalability. Currently, surveillance and monitoring applica-
tions cover multiple scenarios ranging from vigilance of trav-
elers to moving aircraft. Without mobility and scalability
support, it is not possible to cover the whole surveillance
process.
4 BN-MAC Protocol Design
The design goals of the BN-MAC protocol for low duty-
cycled WSNs are:
&Energy efficiency,
&Handling the scalability,
&Low latency for data,
&Mobility support,
&High data throughput,
&Reducing idle listening,
&Controlling the overhearing and congestion in the net-
work, and
&Compatibility with all types of packetizing and digital
radios,
Figure 1 The Hospital scenario that involves Indoor and outdoor mass-casualties handling process.
J Sign Process Syst
For several applications, low duty cycling MAC protocols
are superior to other approaches in the context of latency,
energy consumption, mobility, scalability and throughput. In
addition, contention partly based on the semi-synchronous
approach helps obtain faster access to the medium [31,32].
BN-MAC continues a shorter awake period while maintaining
high throughput and low latency. The schedule-based part is
helpful for those applications that require loose latencies. For
these motives, BN-MAC builds upon the grounds provided by
hybrid low duty cycled MAC protocols.
BN-MAC is designed to address the problems of existing
hybrid MAC protocols such as mobility and scalability. BN-
MAC also addresses the problem of low power listening:
reducing the size of the preamble without inclusion of the
destination address in each preamble and data packets.
Further, BN-MAC uses the automatic packet buffering and
compatibility with packetizing radios. In BN-MAC, the node
gets complete access to its owner slot similar to TDMA-based
approaches. The rest of the slots are accessed through the
CSMA approach. This approach reserves the energy and
reduces the collisions. In addition, BN-MAC eliminates idle
listening using the ILC model to obtain a considerable energy
saving. BN-MAC allots contention-free slot exchange to im-
prove the network scalability dynamically even under heavy
traffic load.
A visual representation of BN-MAC is shown in Fig. 2.
When a node has to send data, that node first senses the carrier.
If the node finds the carrier free, then the node transmits the
short preamble (SP)
4
without inclusion of the destination
address. Before sending the short preamble, the LDSNS mod-
el is used to sort out the one-hop shortest path nodes. Thus, the
short preamble message is Anycasted to the particularnodes at
one-hop neighbors. When the particular node wakes up ac-
cording to its schedule and samples the medium, if the node
finds the short preamble message, then the node sends a clear-
to send (CTS) packet. When the sender receives the CTS
control packet, the sender sends the data to the particular node
at the one-hop destination. The particular node adopts the
same method for the next second hop. This process is said to
be intra process. Finally, the data are delivered to the last
destination node (BN).
BN either forwards using the IP networks to the control
room (base station) given in Fig. 1or sends to an adjacent BN.
When the BN intends to send received data to an adjacent BN,
the BN sends the RTS message. Once an adjacent BN receives
the RTS, the BN responds with the CTS. When the last
destination node (BN) receives the CTS, it sends the
Boarder Node Inter Frame (BNIF) that is data received
through intra-communication. Once data are delivered to an
adjacent BN, the BN acknowledges. BN-MAC consists of the
following phases: Selection of one-hop neighbor node and
slot allocation, intra-semi-synchronous communication, inter-
synchronous communication and boarder node selection
process.
4.1 Selection of One-Hop Neighbor Node and Slot Allocation
A one-hop discovery operation runs during the setup process
until the topology changes. The benefit of this approach is to
stabilize the initial costs while achieving efficient energy and
superior throughput during intra- and inter-transmission. Even
if the topology changes constantly, that does not affect the
one-hop neighbor nodes too much because BN-MAC does
not deal with all one-hop neighbor nodes and does not even
maintain the schedule with all one-hop neighbor nodes. One
of supporting models in BN-MAC is LDSNS that helps find
the shortest efficient path. Through this model, each one-hop
neighbor node keeps the updates of two nodes available at the
one-hop neighbor. One is the principal node and the other is
the backup node.
The principal node is used for forwarding and receiving the
data to the next one-hop neighbor node. In case of movement
of the principal one-hop neighbor node, the backup neighbor
node is considered the principal node, and then another node
is chosen as the backup node. Similarly, in case of mobility of
the backup node prior to movement of the principal node, the
same method is applied for finding the backup node. When
both major and backup node leaves the one-hop neighborhood
at the same time, they inform the respective one-hop neighbor
nodes prior to moving. The moving node incorporates a flag
signal in the last sent data packet that indicates that the node is
about to leave. This feature lets the node adjust the mobility.
BN-MAC uses a very promising time scheduler that helps not
to exceed the assigned slot more than a one-hop neighbor. BN-
MAC also uses a localized time slot without disturbing the
time slots of existing nodes.
4.2 Intra-semi-synchronized Communication
This phase covers region-wise communication based on intra-
semi-synchronization. Each node initially gets the list of all
one-hop neighbor nodes but synchronizes only with a partic-
ular node (either the principal or the backup node) using the
LDSNS model. The communication process starts with carrier
sensing (CS). After this process, the node sends a short pre-
amble message to alert the particular node, especially the
principal node. In case of mobility and power failure of the
principal node, SP is sent to the backup node. Thus, each node
keeps the information of the two nodes at the one-hop neigh-
bor destination. When the SP is received, then the node
responds to the sender. In the next step, the sender sends the
4
Short preamble: It is used to make the receiver to be ready that data is
on its way. In addition, it is also first portion of the Physical layer
Convergence Protocol/Procedure (PLCP) Protocol Data Unit (PDU).
The short preamble lets the receiver to get the wireless signal and
coordinate itself with the transmitter.
J Sign Process Syst
data. Thus, the identical process is used for the next hop until
the packet is delivered to the BN. This process helps reduce
the overhead. The benefit of using a lower duty cycle protocol
is to keep the receiver and the sender decoupled. A short
preamble that MAC protocols prefer over a long preamble
enabled MAC protocols to operate by the low power duty
cycle mechanism.
The existing lower power listening (LPL) protocol uses a
long preamble and experiences the overhearing problem. As a
result, additional energy is consumed at non-targeted re-
ceivers. The LPL protocol also introduces extra latency at
each hop [32]. In the long preamble technique, the node needs
to wait until the long preamble is received. This approach
consumes excess energy at both the sender and the receiver
sides.
In X-MAC, the destination address is incorporated into
each preamble that increases the size of preamble packet.
Additionally, each node checks the preamble packets broad-
cast on the network because the sensor nodes are not intelli-
gent. If the node is not the intended recipient, then that node
goes to sleep. If the preamble packet is discarded by a non-
intended node, then there is no chance for a short preamble
packet to be delivered to the destined node. If the node is not
the intended recipient receiver, even if it checks and ignores
the preamble packet, this process also causes energy waste. If
the node is the intended recipient, it remains awake for the
subsequent data packets. Further, X-MAC is based purely on
an asynchronous mechanism, and it does not have the sched-
ule of the neighbors. As a result, the node consumes excess
energy while waiting on the medium for the traffic.
The BN-MAC asynchronous duty cycle feature that re-
duces the latency and overhead that causes the improvement
in the throughput. It also saves energy and is preferable for
several applications. When multiple nodes communicate with
the same neighbor node, BN-MAC uses a slotted contention
window to handle the congestion and emitting problem. The
nodes select the slots randomly in the contention window. As
a result, the winner of the slot gets the medium for communi-
cation and therefore provides a collision free medium. BN-
MAC also uses randomization and sampling that avoid the
packet loss, in case of the selection of same slots.
The characteristic of BN-MAC is that it can be incorporat-
ed with all types of radios, including any packetizing radio
such as the CC2420 feature of TelosB motes and MICAz.
CC2500 and XBe, are able to send a series of short packets.
Such a unique advantage through packetizing radios is not
TX CS
SP
CTS
TIME
ACKNOWLEDGEMENT
INTRADATAFRAME CARRIER
SENSING
SHORT PREAMBLE
RX
IDF
RSP
WAKE-UP
SP
BOARDER
NODE (TX)
RTS
CS
TIME
TIME
TIME
BOARDER
NODE INTER FRAME CLEAR-TO-SEND REQUEST-TO-SEND
BNIF
ACK
ABP
AUTOMATIC
BUBBER
PACKET
RTS PROCESS
SP
IDF
CTS
BNIF
BNIF
TIME
CTS
CTS WAIT
TIME
RECEIVED SHORT
PREAMBLE
BOARDER
NODE (RX)
Figure 2 BN-MAC message
mechanism process.
J Sign Process Syst
accurate for the traditional long preamble LPL. Additionally,
the short preamble packets are also compatible with all radios
using bit streaming interfaces, including the CC1000 that is
available in the MICA2 mote. Another key advantage of BN-
MAC is an automatic buffering capability that also saves
energy and increases the lifetime of the network. We here
demonstrate the process of long preamble (LPL), short pre-
amble (X-MAC) and BN-MAC in Fig. 3.
We have already discussed that BN-MAC has an automatic
packet buffering process that also reduces the wake up time
and increases the lifetime of the network. In the automatic
buffering process, the node uses a promiscuous mode
5
that
enables the node to listen to all ongoing data traffic and
coordinates, if requested. Furthermore, the node saves a copy
of the packet that is received regardless of the intended desti-
nation of the data packet until the receipt of the packet is
acknowledged by the destination node. Such buffering re-
quires a relay that is used under the saturated conditions
because each node is able to cooperate in sending data packets
to other buffers.
As mentioned above, a short preamble improves the net-
work lifetime by consuming less power. Let us determine the
energy consumed for carrier sensing and sending a short
preamble.
The energy consumed for carrier sensing is ‘γ’,the check
time is ‘δ’,and the average energy consumed for carrier
sensing is ‘Δр’.
Δр¼γ
δð1Þ
The energy consumed for the short preamble ‘Esp’consists
of an average energy consumed for carrier sensing ‘Δc’and
the consumed energy for synchronization is ‘Esyn’.
Esp ¼Δp2Esyn Cdrift ð2Þ
We use clock drift, ‘Cdrift’,that is consumed time for
synchronization, and ‘2E
syn
’is the energy consumed by the
transmitter and the receiver for the synchronization. The node
that transmits its clock at the one-hop neighbor during intra-
communication is called the source node, and the node that
receives the clock at the one-hop neighborhood is called the
particular node (principal or backup node). The synchronized
nodes send a short preamble before sending data without
using the target address because a short preamble is sent to
particular nodes (principal or backup node) at the one-hop
neighbor that reduces the energy consumption.
Let us assume that the source and the particular node
consume energy for one work cycle that is ‘β’and ‘δ’,respec-
tively. The average short preamble reception time could be
reduced because the particular node wakes up based on the
stored schedule. Thus, the source node and the particular node
consume the energy that can be obtained as follows:
β¼X
j¼0
m
Sj Δφ:μ*Δv2
ðÞ*Δр*2Esyn*Cdrift
Δt
ð3Þ
This is the energy consumed by the source node.
δ¼X
j¼0
m
Sj Δφ:μ*Δv2
ðÞ*Δр*2Esyn*Cdrift
Δt
þΔр*Esyn*Cdrift
Δt
ð4Þ
This is energy consumed by the particular node (principal
or backup node) that is available at one-hop destination.
where ‘c’is the starting point of the short preamble, ‘n’is
the ending point of the short preamble, ‘Sj’is the short
preamble, ‘Δφ’is the size of the preamble,′μ′is the nature
of the location, ′Δv
2
′is the short preamble speed, and’′Δ
t
′is
the total time spent for sending the short preamble. BN-MAC
can explicitly find out the energy consumed for a short pre-
amble prior to sending the data. BN-MAC has an edge over
low-duty-cycle long-preamble-enabled MAC protocols and
X-MAC.
4.3 Inter-synchronized Communication
We have already discussed that BN-MAC is introduced for
WSNs consisting of different regions. The previous section
highlights how to access the channel and forward the data
inside regions. This section explains how to set the schedules
within regions and outside regions. Each region of the WSN
contains a Boarder Node. The inter-synchronized transmis-
sion schedule is done from one region to other regions. The
Boarder Node receives intra data packets within the region
and forwards the data packets to outside the region. The
Boarder Nodes of each region follow a schedule-based
method.
The Boarder Node first broadcasts three ‘hello’messages
to warn the region nodes to be ready for getting the Boarder
Node indication signal (BNIS). BN does not wait to receive an
acknowledgment from all region nodes. If the BN gets a single
acknowledgment from one region node, the BN assumes that
the ‘hello’message is delivered successfully. We have already
discussed that neighbor nodes exchange the schedule. Thus, if
any node is unable to receive the ‘hello’message, the neighbor
node informs other nodes at the time of exchanging the
schedule. In this way, each node of the region knows the
schedule of the BN. BNIS consists of the current time, the
next distribution time, the next collection time and the sched-
ule for getting intra data packets from the nodes of the region.
BNIS has also the responsibility to exchange traffic slots
between the source and the destination and describes the
related offset time. Once the Boarder Node announces the
5
Promiscuous mode: It causes the controller to permit all traffic rather
than allowing only the frames. Promiscuous mode is also used to detect
network connectivity problems.
J Sign Process Syst
schedules for the nodes of the region, all of the nodes are
responsible for following the given schedule.
The announcement of the schedule gives the permission to
the region nodes to send and receive intra data messages
during the distribution time. After sending the intra data
transmission, nodes go to sleep automatically, as explained
in Section 5. Once the node is not scheduled for exchanging
the message, that node remains asleep during the whole dis-
tribution time. At the end of the scheduled time of the region
nodes, the Boarder Node synchronizes with another Boarder
Node of the region to exchange the inter-synchronous sched-
ule to send the data. When the contention period starts again,
only one node with a data exchange responsibility requests a
schedule-slot for next scheduled distribution time.
The nodes remain active only during BNIS and other than
BNIS time, the nodes remain in the sleep state that causes the
energy saving. In addition, the automatic feature of going to
sleep after performing the task causes control of the idle
listening time of the region. When the BN intends to commu-
nicate with an adjacent BN of the region, the BN starts with
the inter-synchronized transmission schedule by using carrier
sensing. Carrier sensing makes it possible to forward the
message of request-to-send (RTS). In response, the BN will
get a clear-to-send (CTS) message from the BN of the other
region shown in Fig. 4.
There is no hidden terminal problem in BN-MAC because
BNs of all regions are synchronized with adjacent regions.
The network is divided into several regions. The scheme is
very simple, and each BN just tracks the schedule of neighbor
BNs.
4.4 Boarder Node Selection Process
The Boarder Node is selected periodically using the dynamic
Boarder Node selection process (DBNSP) model that chooses
the Boarder Node based on residual energy, signal strength
and memory allocation resources. The energy level of the BN
is decided based on Table 1using DBNSP and level of energy
information (LEI). The function of LEI is to announce the
level of energy for each node, and DBNSP decides to declare
LONG PREAMBLE
TARGET ADDRESS
IN PACKET HEADER
DATA
TRANSMIT
TX (LPL)
RX (LPL)
TIME
EXTENDED WAIT TIME
RX WAKE UP TIME
DATA
RECEIVE TIME
SP
BP
LISTEN TIME FOR BUFFER PACKETS
SHORT PREAMBLE WITH
TARGET ADDRESS
TE-
ACK
DATA
TRANSMIT
TX (X-MAC)
RX WAKE UP
RE-
ACK
DATA
RECEIVE
BP
ENERGY AND
TIME SAVE AT
TX & RX
RX (X-MAC)
RX WAKE UP TIME
TE-
ACK
DATA
TRANSMIT
SHORT PREAMBLE WITHOUT
TARGET ADDRESS
TX (BN-
MAC)
RX (BN-
MAC) RX
S- W
RE-
ACK
DATA
RECEIVE
ABP
ENERGY AND TIME
SAVE AT TX & RX
ABP
AUTOMATIC
BUFFER PACKET
RE-ACK
RECEIVER EARLY
ACKNOWLEDGEMENT
TE-ACK
SHORT
PREAMBLE
TRANSMITTER EARLY
ACKNOWLEDGEMENT
SP
RX WAKE
UP TIME
TIME
TIME
TIME
TIME
SP
SP
SP SPSP
BP
BUFFER
PACKET
Figure 3 Comparison of
timeline of duty cycle MAC
protocols.
J Sign Process Syst
the Boarder Node. We categorize the level of energy into six
levels as given in Table 1.
When the energy level of an already working BN goes
down, the shift of responsibility from one BN to another BN is
accomplished by using the election flag bit (EFB). The EFB
specifies the process of immediate BN election. To reduce the
overhead of shifting the responsibility of one BN to another
BN, BN-MAC uses a proactive method to decide the next BN
based on computing the contention time for election using the
available energy, the signal strength and the memory alloca-
tion resources.
The DBNSP model helps determine the energy of each
node in each region to select the BN. Each sensor node
determines its residual energy after completing some rounds
of detecting the events. This residual energy decides whether
the node should be considered as a candidate to become a BN
or not. The nodes detect the BN in its region based on multiple
processes of WSNs using multiple rounds. The benefit of this
model is to give enough options to each node to be declared
BN based on set criteria. The process of choosing the BN
consists of several steps. First, the base station broadcasts a
short preamble in the network. In response, each node calcu-
lates its distance from the base station based on the signal
strength. The node that receives a short preamble with high
radio frequency becomes a candidate BN.
Each node waits for another node to get an alert to compare
its memory allocation, residual energy and radio range. If no
alert is received by another node, that node is selected
dynamically as the BN. The selected BN sends a multicasting
message to its neighbor nodes to let them know about its
selection as the new BN for future communication. We deter-
mine the residual energy of each node in each region. Let us
assume that single-hop communication is used among sensor
nodes to detect events and to transmit the information. Each
node forwards data ‘d’at distance ‘r’within region ‘R’and
located at the N*N area of WSN. We determine the residual
energy of two types of nodes: the BN and the Non-Boarder
Node (NBNs) that can be expressed as follows.
Erd;rðÞ¼d*Eradio
fþd*Eamp
N2
2πRoð5Þ
where ′E
r
′is the total residual energy consumed by all
nodes, ′E
radio
′is the energy consumption of the radio and ′
E
amp
′is the energy used for amplifying the radio signal.
HELLO
TX
(BN)
BNIS
HELLOHELLO ACK
RX
REGION
NODE
TIME
TIME
RX (BN)
RX (BN)
OF OTHER
REGION
TIME
TIME
CTS
EITHER SLEEP OR
AWAKE
ACK
RECEIVER IS BUSY WITH BN DURING THIS TIME
BN OF OTHER REGION IS BUSY EITHER WITH REGION NODE OR
ADJACENT BOARDER NODE
ACK
ACKNOWLEDGEMENT CLEAR-
TO-SEND
RTS
REQUEST-
TO-SEND
ABP
AUTOMATIC
BUFFER
PACKET
BNIS
BOARDER NODE
INDICATION
SIGNAL
BNIF
BOARDER
NODE INTER
FRAME
ACK
DATA
TX
REGION
NODE
DATA
R-
HELLO
ABP R-HELLO
RECEIVED
HELLO
CTS RTS BNIF
TRANSMITTER OF BN IS BUSY WITH REGION
NODE DURING THIS TIME
Figure 4 Inter-synchronized
transmission schedule with region
node and Boarder Nodes.
Tabl e 1 showing the
sensor node distribution
energy level.
Energy Level Sensor Voltage level
Very High 3.3 to 3.7 V
High 3.0 to 3.3 V
High Moderate 2.7 to 3.0 V
Moderate 2.4 to 2.7 V
Low 2.1 to 2.4 V
Lowest < 2.0
J Sign Process Syst
Thus, Eq. (5) shows the residual energy consumed by BN
and NBNs. It is calculated after performing their respective
monitoring process for assigned task.
Here, we are interested in determining the residual energy
of BN in two cases.
a. When the BN forwards information to an adjacent region
or the base station.
b. When BN transmits and receives the information among
the non-boarder nodes.
Thus, the residual energy of BN is calculated in Eq. (6)
when performing the task with adjacent BN or base station
Erd;rðÞ¼d*Eradio
fþd*Emhrnoð6Þ
where ′E
mh
′is the multi-hop fading channel.
We also determine the energy consumed by the BN when
communicating with NBNs for receiving the data that can be
expressed as:
ERX dðÞ¼d*Eradio
N
C−1
ð7Þ
where ‘E
RX(d)
′is the energy consumed for receiving the
data packets and ‘N’is the number of sensor nodes.
BN also consumes energy in scheduling with the BNs of
adjacent regions.
ERX dðÞ¼d*Eschd
N
C−1
ð8Þ
BN requires three types of short preamble messages by
setting initial phase that include ′E
schd
′shows the energy
consumed for scheduling, ′P
adv
′is for the advertisement and
′P
syn
′is for synchronization. Thus, consumed energy of BN
canbecomputedasfollows:
EBN ¼ETXPadv ;rðÞþERXPadv
ðÞþETXPsyn ;r
þERXPsyn
þETXPj;r
þERXPj
ð9Þ
From Eq. (9), we deduce the energy consumed by the BN
during the initial setting up process.
ENBN ¼ETXPadv ;rðÞþERXPadv
ðÞþETXPsyn ;r
þERXPsyn þd
*Eradio ð10Þ
After the initial phase setting, BN and NBN nodes start to
send data. On completion of the event monitoring process, the
final residual energy, the memory allocation and the signal
strength decide the selection of the next BN. The residual
energy of BN can be calculated by Eq. (11).
EBN ¼Edf−CHN þhERXdsþ1ðÞ−ERXds
ðÞ
þERXdsþ1ðÞþETXdsþ1ðÞETXds
ðÞ
þETXdsþ1ðÞ ð11Þ
Based on Eq. (11), it is decided whether BN should con-
tinue working as BN or not. Similarly, we can determine the
residual energy of NBN that can be calculated as follow.
ENBN ¼ETXd;rðÞþ½ds*Eradio þETXdsþ1;r
þETXdsþn;rðÞ
þERXds*Eradio þERXdsþ1;r
þERXdsþn;rðÞ
ð12Þ
ð12Þ
where ′d
s
′represents the size of data to be transmitted in
each data packet, and ′n′shows the number of packets trans-
mitted and received by NBN. Based on Eqs. (11)and(12), the
new BN is selected.
5IdleListeningControlModel
In many applications, nodes remain mostly in idle in the WSN
for longer periods of time if no sensing event occurs. The pace
of the data delivery rate remains low during this mode, but it is
not a good practice to keep the nodes listening all the time. In a
previous section, we have discussed the BN-MAC mecha-
nism, but in this section, our aim is to preserve more energy by
reducing the idle listening time of the nodes by letting the
nodes go into either sleep or an active state, if they are
scheduled to receive and transmit data. This process is done
through the ILC model. When the sensor nodes are active
(ON) without doing anything, they are costing both time delay
and energy [33]. The costs can be justified if energy is saved
with the [Off] mode. We set a threshold value for idle and
‘OFF’modes to save energy.
Idletime ≤t off ð13Þ
The total idle time can be computed by Eq. (13). Assume ′
CE
idle
′is consumed energy during idle time; M
idle
(t) is the
minimum time required for sensors to remain in an idle state;
E
idle
/
on
is the energy consumed during the ‘idle’or ‘ON’state,
and ′CS
idle
/
off
’is the energy required to change state from (idle
to off).
Idletime ¼CEidle*Midle tðÞþ Eidle =on *CSidle=off ð14Þ
J Sign Process Syst
Idle time must always be less than or equal to ‘OFF’time
because nodes consume energy during idle time (listening)
without doing anything.
Tot al ‘OFF’time can be calculated by Eq. (15). Assume ′
E
off
′is the preserved energy during ‘OFF’time, ′M
off
(t)′is the
minimum time required for sensors to remain in the idle state
and ′CS
off
/
on
′is the energy required for going from the ‘OFF’
state to the ‘ON’state.
toff ¼PEoff *Moff tðÞþ CSoff =on ð15Þ
Assume that ′M
off
(t)′is the time that sensors stay in the
‘OFF’state (higher than the idle state, as already proved) and
given in Eq. (16). Thus, Eq. (13) can be satisfied by substitut-
ing the remaining values.
Moff tðÞ≥0;PEoff −CEidle
*CSidle=off
hi
ð16Þ
The purpose of the ILC model is to bring the sensors into
the sleep mode, if no data are being delivered. We infer and
generalize from Eqs. (13)and(16) that the operating mode of
sensors can automatically be set up. Let us assume α(alpha)
and β(beta) for active (ON) and sleep (OFF), respectively.
The automatic change of transitions can be justified if Eq. (17)
is satisfied.
CSa≥max h0;CEon þCEidle−PEoff
*CSαβ ð17Þ
where ′CE
on
′is the energy consumed during the active
mode, and ′CS
αβ
′is the consumption of energy from going
active (ON) to Sleep (OFF) mode that is a negligible amount
of energy. Thus ′CS
a
′is greater than or equal to the amount of
energy consumed in the active mode, preserved energy in the
sleep mode and energy consumed for change of transition to
ON/OFF mode.
Therefore, in our case, we have preserved 93.6 % of the
energy by letting sensors to go into sleep rather than remaining
in idle mode. We have just wasted 6.4 % of the energy. The
total preserved energy in sleep and idle modes is shown in
Fig. 5. The consumption and preservation processes are ob-
served when the node finishes the monitoring process and
continues sensing the medium. Such a situation wastes addi-
tional energy in the idle listening process. With the incorpo-
ration of the ILC model, nodes are forced not to stay in idle
listening. This model restricts additional waste of energy.
Similarly, we have calculated the total energy consumed in
the monitoring process and idle listening and also shown
preserved energy using ILC in Fig. 6. Without this model,
energy could not be saved while showing in Fig. 6.Hence,
nodes only consumed 220 J/C during the entire process. If the
nodes should have been in the active as well as the listening
states without use of ILC, then nodes could consume a total
energy of 1806 joules/coulombs. The energy measuring pro-
cess is done using two metrics: Relative Standard Deviation
(RSD)
6
and Gini coefficient.
7
As a result, we are able to
determine the reduced amount of energy.
The BN and the scheduled nodes are active during the
compilation time. In the case of an empty network, BN takes
the same timeout as the GMAC nodes [34] takefor sensingthe
traffic of the network during both distribution and collection
time while the rest of the nodes remain in the sleep state. In
BN-MAC, we spend 832 μs to send a 14-byte BNIS message,
which produces 0.3 % duty cycle in the frame of 1 s. Further,
BN-MAC consumes less energy using a 14-byte BNIS.
6 Simulation Setup and Result Analysis
We have simulated a realistic health scenario that covers
indoor and outdoor casualties using ns-2.35-RC7 on Ubuntu
13.10 operating system. In this scenario, different activities
are performed, which involves indoor patient monitoring ex-
amined by local and remote practitioners. In addition, casual-
ties and movement of victims in the outdoor environment are
monitored. All activities are reported to the control room. The
scenario reflects the real WSNs environment. The obtained
simulation results are quite convincing and identical to realis-
tic experimental results.
The wireless sensor network is disseminated into different
regions as depicted in Fig. 1to collect faster data with low
latency. We have set one BN in each region. The BN forwards
the collected information of its region to either the BN of the
adjacent region or the control room. We have simulated dif-
ferent realistic scenarios: mobility and static. The main goal of
simulation is to handle the hospital emergency situation con-
suming less energy with faster data delivery. We evaluate the
performance of the BN-MAC protocol and compare with
known hybrid and mobility MAC protocols: Z-MAC, X-
MAC, MS-MAC, A-MAC, ADC-SMAC, and MobiSense.
The similar parameters have been used for all MAC protocols
for simulation.
The simulation scenario consists of 180 nodes with a
transmission radius of 30 m. The nodes are randomly placed
in uniform fashion in the area of 400 * 400 square meters. The
network is divided into equal 100 m × 100 m regions. The
initial energy of the nodes is set 3.7J. The bandwidth of the
node is 50 kb/s, and maximum power consumption for each
6
Relative Standard Deviation (RSD): It is the absolute value for
deviation of coefficient and defined as a percentage. It is also
commonly used when doing quality assurance.
7
Gini coefficient: It is an inequality distribution measure that is
expressed as the ratio with values between 0 and 1.
J Sign Process Syst
sensor is set 16mW. Sensing and idle modes have 12mW and
0.5mW, respectively, but in our case, there is no idle mode.
Sensors go to either active or sleep mode. Each sensor is
capable of broadcasting the data at power intensity ranging
from -20 dBm to 12 dBm.
The total simulation time is 35 min, and the pause time is
set to 30 s for phase initialization at the start of the simulation.
The results demonstrate an average of 15 simulation runs. The
energy consumption pertaining to different radio modes and
simulation parameters is summed up in Table 2.
We collected several results but use the following metrics
to demonstrate the performance of the BN-MAC and other
competing MAC protocols in the health scenario.
&Throughput performance of BN-MAC, Z-MAC, X-MAC,
MS-MAC, A-MAC, ADC-SMAC and MobiSense in stat-
ic and mobility situations.
&Network coverage efficiency and lifetime in static and
mobility situation.
&Latency of BN-MAC, Z-MAC, X-MAC, MS-MAC, A-
MAC, ADC-SMAC and MobiSense in static and mobility
situation.
6.1 Throughput Performance
We analyze the throughput efficiency of BN-MAC and other
competing hybrid MAC protocols: X-MAC, Z-MAC, MS-
MAC, A-MAC, ADC-SMAC and Mobisense in Figs. 7and 8.
We used static and mobility scenarios for determining the
throughput based on the varying number of transmitting
nodes. In Fig. 7, we set 30 % of the nodes to be mobile,
including transmitting nodes throughout the simulation. In the
given scenario of the hospital for disaster recovery, indoor
patients, outdoor victims and movement of local and remote
practitioners is 30 % mobile. We have noticed that BN-MAC
and other competing MAC protocols initially produce an
average throughput of 450 to 500 Kbits/s, but when the
number of transmitting nodes increases, then performance of
BN-MAC slightly decreases as compared with other MAC
protocols.
BN-MAC reduces the throughput from 500 Kbits/s to 400
Kbits/s by using 1 transmitter to 18 transmitter nodes, whereas
others decrease throughput from 475Kbits/s to 260 Kbits/s
with the same number of transmitters. A-MAC and ADC-
SMAC are highly affected with increased number of
transmitters. BN-MAC is superior to other competing
MAC protocols and achieves 12.5 to 37.5 % higher
throughput in the mobility scenario. This mobility anal-
ysis is based on two methodologies: analysis based on
synthetic traces and analysis based on real-world traces
as discussed in [35].
In Fig. 8, all nodes are stationary. Similarly, BN-MAC and
other competing MAC protocols produce throughput. They
initially get from 462 Kbits/s to 500 Kbits/s at 1 transmitter
when the number of transmitters increases, then the through-
put performance of all MAC protocols starts reducing. We
have observed that an increase in the number of transmitters
also causes a decrease in throughput even though the nodes
are static. Once again, BN-MAC also outperforms other MAC
protocols in the static scenario, and BN-MAC achieves 15 to
40.25 % higher throughput. Mobisense and ADC-SMAC are
highly affected in the static scenario because they are specially
designed for handling the mobility of nodes. The simulation
results demonstrate that BN-MAC is the superior choice for
several WSN applications.
0510152025
30 35
0.2 0.4 0.6 0.8 1
Simulation time in minutes
Total Energy Consumption/preservation in%
Consumption in
idle mode
0
Preservation in
Sleep mode
Figure 5 Total percentage (%) of energy preserved in sleep mode VS
consumed in idle mode.
0510152025
30 35
300 600 900 1200 1500
Simulation time in minutes
Total Energy in joules/ coulomb
Consumption
in idle mood
0
Preservation in
Sleep mode
Consumption in
active mode
Figure 6 Consumption of energy in active and idle modes VS preserved
energy in idle mode using IDL model.
J Sign Process Syst
6.2 Network Coverage Efficiency and Lifetime
We validate network coverage performance of BN-MAC
using static and mobility nodes. We have scaled the
network coverage scenarios for handling the monitoring
activities of a hospital including the recovery of mass
victims. We have conducted several tests while
deploying from 1 to 180 sensor nodes. In Figs. 9and
10, we have created a mobility scenario covering 25%
and 50 % mobility of the nodes, respectively. The
mobility of the nodes is set from 0–9m/s.
The BN-MAC has achieved 95.8% and 95.2 % net-
work coverage with 25% and 50 % mobility, respective-
ly, whereas Z-MAC, A-MAC, ADC-SMAC, X-MAC,
MobiSense and MS-MAC get 70.5–83 % network cov-
erage when 25 % sensor nodes are mobile, as shown in
Fig. 9. When mobility increases up to 50 %, then
competing MAC protocols get 68–78.5 % network cov-
erage performance using 180 sensor nodes, as shown in
Fig. 10. We have established 18 sessions in both sce-
narios simultaneously to determine the exact behavior of
the network using highly congested traffic. We observe
that ADC-SMAC, A-MAC and MS-MAC are signifi-
cantly affected due to mobility. In addition, BN-MAC
has obtained the same network coverage with 113–120
sensor nodes as other MAC protocols get with 180
sensor nodes.
Based on simulation results, we demonstrate that
mobility brings a trivial change in the network coverage
by using the BN-MAC protocol. In addition, we have
also validated that the duration of the simulation (either
increases or decreases) does not affect the efficiency of
BN-MAC. In Fig. 11,wehaveshownthenetwork
coverage of BN-MAC and other MAC protocols based
on the static scenario. Similarly, BN-MAC has a slight
Tabl e 2 Summarized simulation parameters for proposed scenario hos-
pital to involve indoor monitoring and outdoor handling of mass
casualties.
Name of parameters Description
Transmission Range 30 m
Type of sensors BT node sensors
Sensing Range of node 12 m
Initial energy of node 3.7 J
Bandwidth of node 50 Kb/s
Number of sensors 180 BT node rev-3
Size of network 400 * 400 square meters
Size of each region 100 * 100 square meters
Packet transmission rate 40 Packets/s
Data Packet size 256 bytes
Simulation time 40 min
Initial pause time 30 s
T
x
energy 16 mW
R
x
energy 12 mW,
Power intensity -20 dBm to 12 dBm.
Sink location in each region (46, 50)
MAC protocol BN-MAC,Z-MAC,X-MAC, MS-MAC,
A-MAC, ADC-SMAC and MobiSense
Type of protocols Hybrid protocols
Deployed models ILC model
Mobility 0 m/s to 9 m/s
Routing Protocol Pheromone termite
a
a
Pheromone termite: It provides routing support and based on two
important features: Pheromone sensitivity and packet generation rate.
This model also helps in the detection power (emitted signal) that node
uses to communicate with other nodes. In addition, packet generation rate
informs the node to handle variable number of packet generation rate and
adopt the network condition.
Figure 7 Throughput at heavy traffic load using mobility.
Figure 8 Throughput at heavy traffic load using static nodes.
J Sign Process Syst
advantage over other competing MAC protocols because
BN-MAC gets 99.1 % network coverage with 180 sen-
sor nodes. Other MAC protocols obtain 89–96.5 %
network coverage. We have also validated that BN-
MAC is a better choice in the static scenario, showing
that BN-MAC prolongs the network lifetime.
We also hereby determine the minimum number of sensor
nodes required to cover whole area of the network (400 ×
400 m
2
).
Smin ¼2Arπ
3πR218ðÞ
where ′S
min
′is the minimum number of sensor nodes
required to cover the entire network area, ‘A’is the entire
network area, ‘R’is the total distance of the network, and r
is the sensing range of the sensor nodes.
We assume that the sensing range is smaller than the whole
monitoring area.
Thus, Smin
Smax can be the maximum number of sensor nodes
required to cover the ‘R’total distance.
Lemma 1: Smin
Smax is an upper bound on ‘R’,S
min
is a lower
bound and ‘N
i
’is the number of sensors in the network, where
Smin ¼2Arπ
3πR219ðÞ
Proof: Let the upper bound be linear on ‘R’with
the maximum number of sensors (total number of
sensors) as ′S
max
′, whereas the lower bound on ‘N
i
is
invariant with ′S
min
′.In addition, these bounds are not
considered tight as long as they do not consider the
transmission radius ‘T
r
’of the sensors. However, we
need a better heuristic solution to follow these bounds
closely irrespective of changes that occur in the pa-
rameters of the network. Hence, the lifetime of the
network should be linear with ′S
min
′,and ‘N
i
’will be
constant with ′S
max
′.
Based on the simulation, we also determine the network
lifetime consists of 400 × 400 m
2
shown in Table 3using BN-
MAC and other protocols.
In Fig. 12, we show the lifetime of the WSN based
on a different number of sensor nodes. BN-MAC gets
a higher lifetime than other MAC protocols. The other
MAC protocols are less capable of utilizing energy
efficiently to get an improved network lifetime with
the increased size of the nodes. BN-MAC possesses
the capability of maintaining the traffic and reducing
the WSN ideal listening time. The nodes using BN-
MAC die after 472 days compared with other MAC
protocols, where nodes die between 373–438 days. A-
MAC behaves worse, and all nodes die in 373 days.
BN-MAC gets 7.2–20.97 % additional network
lifetime.
6.3 Latency
In this section, we introduce the latency by using BN-
MAC and other competing MAC protocols. We measure
the latency in terms of how much time one packet takes
to travel from sender to destination point. In addition,
we measure and display different types of latencies,
including propagation delay, transmission delay, router
delay and storage delay. In addition, these four types of
delays are collectively shown in Figs. 13 and 14.We
also used the mobility and the static scenario for deter-
mining the latency. In Fig. 13, the latency is shown at
0 20 40 60 80 100 120 140 160 180
10
20
30
40
50
60
70
80
90
100
COVERAGE EFFICIENCY %
NUMBER OF SENSOR NODES
0
BN-MAC
X-MAC
MS-MAC
A-MAC
MobiSense
ADC-SMAC
Z-MAC
Figure 9 Coverage efficiency at 25 % mobility of nodes.
Figure 10 Coverage efficiency at 50 % mobility of nodes.
J Sign Process Syst
the different mobility rates. We observe in Fig. 13 that,
based on the simulation, when mobility increases, the
latency also increases. BN-MAC gets 0.015–0.06 s of
latency at 0–9m/sspeedwith50%mobility(number
of moving nodes), whereas other competing MAC pro-
tocols show higher latency, namely, 0.0156–0.17 s, at
the same mobility rates. A-MAC produces higher laten-
cy than other MAC protocols. BN-MAC achieves 4–
183.33 % less latency than other MAC protocols. We
validate that BN-MAC can be used for different types
of applications for faster delivery of data.
In Fig. 14, we show the latency of BN-MAC and other
competing MAC protocols based on the static scenario. In this
scenario, latency covers propagation delay, transmission de-
lay, router delay and storage delay. We use a different packet
generation interval on the x-axis. We observe that BN-MAC
outperforms all other MAC protocols because BN-MAC gets
0.015–0.016 s latency from 0 to 18 packet generation inter-
vals. Other MAC protocols also experience the problem due to
the increase of packet generating rates.
The average latency for other MAC protocols is counted as
0.015–0.034 with similar packet generating rates. The BN-
MAC gets 6.25–106.25 % less latency when nodes are sta-
tionary. We conclude that mobility is the factor affecting
performance, especially when mobile sensors move randomly.
Mobility is a key parameter for performance analysis, espe-
cially in massive multi-user virtual environments (MMVEs)
[35]. BN-MAC has the capability to manage its timeframe, the
number of random access frames, and the rate of transfer
frames in the static and mobility scenarios, but the average
delay remains almost stable with Z-MAC, X-MAC and other
MAC protocols, which exhibit higher latency and reduced
throughput.
Figure 11 Coverage efficiency when all nodes are static.
Tabl e 3 Network life of MAC protocols.
MAC protocol Name No traffic Unicast Frame Inter Frame
Z-MAC 308 356 167
X-MAC 325 348 166
A-MAC 235 303 133
MS-MAC 327 386 172
ADC-SMAC 330 403 177
MobiSense 354 400 192
BN-MAC 411 456 231
Figure 12 Lifetime of MAC protocols using different number of
sensors.
Figure 13 Average packet delay at different mobility rates.
J Sign Process Syst
7 Discussion of Results
Energy has been a challenge and will also remain a
future challenge for efficient deployment of WSNs, be-
cause advancement in battery technology has been slow
compared with growth of processing power and com-
munication data rates. We need special emphasis on
improvement of energy-efficient operation. To overcome
this challenge, hybrid MAC protocols have been intro-
duced to prolong network lifetime. The hybrid MAC
protocols get higher energy savings, flexibility and bet-
ter scalability. In this section, we discuss and compare
the merits and demerits of BN-MAC and competing
hybrid MAC protocols.
X-MAC is a hybrid low duty cycle protocol based on
short preambles with a target address. An advantage of
X-MAC is to minimize energy consumption and latency.
Idle listening at the receiver side and overhearing at
neighboring nodes can be reduced. However, the gaps
between series of preamble packets is the problem that
can be considered as idle listening by other nodes, and
they start to send their preamble packets.
The mechanism of Z-MAC supports multi-hop topology,
and nodes are fixed on their positions. The global time syn-
chronization is used to synchronize the nodes, and slots are
assigned for nodes but not fixed.
The fixed nodes limit the scalability of WSNs. If new nodes
are joined, that will be harder to set up the network phase.
During the mobility, nodes with Z-MAC are unable to receive
and send the data packets. A-MAC, based on a collision-free
and non-overhearing mechanism, is designed for surveillance
and monitoring applications. The major advantage of A-MAC
is to notify the nodes in advance. However, A-MAC faces a
little idle listening and a packet overhead problem. As a result,
it consumes enough energy due to the advertisement.
MobiSense is a cross-layer MAC protocol that com-
bines MAC and network layers to accomplish energy
efficient data communication in the micro-mobility sce-
nario. However, Mobisense experiences the problem due
to managing the multi-channel and mobility in time that
causes the collision. As a result, nodes reduce through-
put and increase the latency. ADC-SMAC improves two
features of S-MAC: node utilization and sleeping delay.
The advantage of ADC-SMAC is to introduce flexible
duty cycles for nodes. However, ADC-SMAC is not
suitable for controlling idle listening and overhead is-
sues. MS-MAC has introduced coordinated sleep/listen
duty cycles and synchronizes the schedule of nodes
periodically. MS-MAC enables each node to determine
the mobility and its level within its neighborhood.
However, nodes get confused to follow different sched-
ules that could lead to congestion and waste of energy
under a heavy traffic load.
The limitations of existing hybrid MAC protocols,
create the platform for new hybrid MAC protocol to
fulfill the remaining issues. Thus, BN-MAC protocol is
introduced with features of a low duty cycle using the
semi-synchronization approach. The beauty of the BN-
MAC protocol is dynamic election of BN based on
memory allocation, signal strength and residual energy,
making an improvement in the network lifetime. The
Figure 14 Average packet delay when sensor nodes are static.
Tabl e 4 Characteristics and Comparison of Hybrid Medium Access Control (MAC) Protocols.
Name of MAC Protocol Throughput Residual energy Mobility Latency Scalability Life of Network Real time Support
A-MAC Low Low No High Good Moderate No
ADC-SMAC Moderate Low No Moderate Good Moderate Yes
MobiSense Moderate Moderate Yes Moderate Good Moderate No
BN-MAC High High Yes Low Good High Yes
MS-MAC Moderate Moderate Marginal support High Weak Moderate No
Z-MAC Moderate High No Moderate Weak Moderate May be/May be not
X-MAC Moderate Moderate Marginal Support Moderate Good Moderate Yes
J Sign Process Syst
LDSNS model is used, adding extra energy saving
based on a one-hop neighbor search. The LDSNS model
finds the shortest efficient path that makes it more
attractive. Thus, there is a trivial chance of failure of
the one-hop path; if the one-hop path fails, then the
second best one-hop path is chosen for intra-data com-
munication using PT model. BN-MAC possesses a
promising time schedule because the assigned slot is
not exceeded more than the one-hop neighborhood.
BN-MAC performs localized time slot allocation without
changing time slots of already existing nodes, reducing the
latency and overhead with less chance of breaking the routes
in WSN. The ILC model is an energy efficient model that fully
supports consumption of less energy because the nodes auto-
matically go to the sleep state after completing their monitor-
ing process. These features make BN-MAC as good candidate
for multiple WSN application areas. Further, based on simu-
lation, we have characterized the BN-MAC and other com-
peting MAC protocols given in Table 4to show their strength
and the weaknesses.
8 Conclusions
This paper introduces a low duty cycle, energy-efficient
and mobility-based Boarder Node - MAC hybrid proto-
col for wireless sensor networks. The mechanism of
BN-MAC demonstrates low latency, reduces the energy
consumption, handles the mobility and scalability, and
maximizes the throughput. BN-MAC leverages the fea-
tures of contention and schedule-based MAC protocols.
The contention part especially consists of a semi-
synchronous approach that helps getting faster access
to the medium. The schedule-based part is helpful for
those applications that require loose latencies. For these
motives, BN-MAC builds upon the grounds provided by
hybrid low duty cycled MAC protocols.
In addition, BN-MAC eliminates idle listening by
using the ILC model to provide considerable energy
saving. BN-MAC allots contention-free slot exchange
dynamically to improve the network scalability even
under a heavy traffic load. The several stationary and
mobility scenarios that cover the health monitoring pro-
cess are simulated. In the scenarios, we track the indoor
patients who are examined by local practitioners and
remote practitioners. Furthermore, outdoor casualties
and movements of victims are monitored and reported
to the control room to take immediate measures for
reducing the number of casualties.
To demonstrate the soundness of the proposed BN-
MAC, we reported some interesting results by using
ns2.35-RC7. We have compared BN-MAC with known
low duty cycle protocols (X-MAC, and also compared
with hybrid and mobility MAC protocols), Z-MAC,
MS-MAC, A-MAC, ADC-SMAC, and MobiSense over
WSNs. Simulation results demonstrate that BN-MAC
has achieved 12.5–37.5%and15–40.25 % higher
throughput than other competing MAC protocols in
mobility and static scenarios, respectively.
BN-MAC has also outperformed other MAC proto-
cols in latency and network coverage. BN-MAC gets
4.00–183.33 % and 6.25–106.25 % less latency as
compared with other MAC protocols in mobility and
static situations respectively. Network coverage of BN-
MAC is higher (that is, approximately 99.1 %) as
compared with other MAC protocols that get 89–
96.5 %. In addition, BN-MAC gets 7.2–20.97 % addi-
tional network lifetime. Based on the outcomes, we
argue that BN-MAC can also be good candidate for
multiple applications to achieve faster delivery of data
with low latency. In the future, we plan to simulate
different WSN applicationareasusingBN-MACand
other MAC protocols.
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J Sign Process Syst
Abdul Razaque is Editor-in-
Chief for International Jour-
nal for Engineering and
Technology (IJET), Singa-
pore and also associated with
Computer Science and Engi-
neering Department, Univer-
sity of Bridgeport, USA. He
holds fellowship form Higher
Education Commission
(HEC) Pakistan, and Com-
mon Wealth, UK. He served
as Head of computer science
department in Model colleges
setup Islamabad, Pakistan
from 2002 to 2009. He also led several projects as project
Director for promoting the trend of information technology
(IT) in Pakistan funded by United Nation organization (UNO)
and World Bank during 2005 to 2008. He is currently active
researcher of wireless and Mobile communication (WMC) lab-
oratory, UB, USA. Abdul Razaque has also been working as
Chair, Strategic Planning Committee for IEEE SAC Region-1.
USA and Relational Officer for IEEE SAC Region-1 for Eu-
rope, Africa and Middle-East. Abdul Razaque has chaired more
than dozen of highly reputed international conferences and also
delivered his lectures as Keynote Speaker. His research inter-
ests include the wireless sensor networks, design and develop-
ment of learning environments, TCP/IP protocols, multimedia
applications and ambient intelligence.
Dr. Elleithy is the Associate Vice
President of Graduate Studies and
Research at the University of
Bridgeport. He is a professor of
Computer Science and Engineer-
ing. He has research interests are
in the areas of wireless sensor net-
works, mobile communications,
network security, quantum comput-
ing, and formal approaches for de-
sign and verification. He has pub-
lished more than two hundreds re-
search papers in international
journals and conferences in his
areas of expertise. Dr. Elleithy has
more than 25 years of teaching experience. His teaching evaluations are
distinguished in all the universities he joined. He supervised hundreds of
senior projects, MS theses and Ph.D. dissertations. He supervised several
Ph.D. students. He developed and introduced many new undergraduate/
graduate courses. He also developed new teaching / research laboratories in
his area of expertise. Dr. Elleithy is the editor or co-editor for 12 books by
Springer. He is a member of technical program committees of many interna-
tional conferences as recognition of his research qualifications. He served as a
guest editor for several International Journals. He was the chairman for the
International Conference on Industrial Electronics, Technology & Automa-
tion, IETA 2001, 19-21 December 2001, Cairo –Egypt. Also, he is the
General Chair of the 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013
International Joint Conferences on Computer, Information, and Systems
Sciences, and Engineering virtual conferences.
J Sign Process Syst
