Low Duty Cycle, Energy-Efficient and Mobility-Based ...khaledelleithy.org/Journals/Low Duty Cycle.pdf · Low Duty Cycle, Energy-Efficient and Mobility-Based Boarder Node—MAC Hybrid

Low Duty Cycle, Energy-Efficient and Mobility-Based BoarderNode—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 is extremely important with the emergence ofwireless sensor networks (WSNs). The MAC protocol hasincreasingly been significant in advancing the performanceof WSNs. In this paper, a low duty cycle, energy-efficient andmobility-based Boarder Node Medium Access Control (BN-MAC) hybrid protocol is introduced for WSNs that controlsoverhearing, idle listening and congestion issues by preserv-ing energy over WSNs. BN-MAC leverages the features ofcontention and schedule-based MAC protocols. The conten-tion encompasses the novel semi-synchronous approach thathelps obtain faster access to the medium. The schedule-basedpart helps reduce the collision and overhearing problems.

The idle listening control (ILC) model is embedded withinthe BN-MAC that administers the nodes to go to sleep afterperforming their tasks to saves additional energy. The leastdistance smart neighboring search (LDSNS) model is used todetermine the shortest and most efficient path in a one-hopneighborhood.

Evaluation of the BN-MAC is conducted using networksimulator-2 (ns2), then its quality of service (QoS) parametersare compared with other known hybrid MAC protocols in-cluding X-MAC, Zebra medium access control (Z-MAC),mobility-aware SMAC (MS-MAC), advertisement-basedMAC (A-MAC), Adaptive Duty Cycle SMAC (ADC-SMAC) and Mobile Sensor (MobiSense) MAC protocols.

Keywords Wireless sensor networks .Mediumaccess controlprotocols . Energy efficiency .Mobility . Handlingmasscasualties

1 Introduction

Wireless Sensor Networks are considered one of the dominantresearch areas in recent years.WSNs consist of a large numberof sensor nodes with limited power, which gather and processdata from specific domains and return data back to specificlocations (e.g., disaster control centers and headquarters).With the emergence of low-cost sensing devices, WSNs havebeen proved to fit many applications such as environmentalmonitoring, industrial sectors, battlefield surveillance andconsumer applications [1]. WSNs are used to provide betterliving standards. Meanwhile, WSNs face many challengingissues such as insufficient coverage, scalability, lack of ro-bustness, uniformity, congestion, mobility and high energyconsumption [2]. Furthermore, limited battery life and severeoperating conditions are causes of node failure [3] that wasteenergy.

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 useof mobile devices inWSNs can offer flexibility, smartness andadaptability 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 energyconsumption.

MAC protocols specify how nodes share the channel forcommunication to improve the efficiency of WSNs. There aredifferent categories of MAC protocols introduced such as

A. Razaque (*) :K. M. ElleithyComputer Science and Engineering Department, University ofBridgeport, Bridgeport, CT, USAe-mail: [email protected]

K. M. Elleithye-mail: [email protected]

J Sign Process SystDOI 10.1007/s11265-014-0947-3

schedule-based, contention-based, mobility-aware, hybrid,cross-layer and real-time [9]. Meanwhile each MAC protocolis designed for a specific type of application [10]. Most of thewidely used MAC protocols are based on contention, whereaccess to the same communication channel by multiple sen-sors causes collisions.

A collision reduces the channel bandwidth and increasesenergy consumption. To conserve energy, schedule-basedMAC protocols were introduced to reduce idle listening byscheduling regular sleep intervals [11]. However, schedule-based MAC protocols are not accepted as a general standardbecause they are application-dependent, lack of mobility andof scalability support. Schedule-based MAC protocols facethe challenge of inconsistency in the physical layer and thesensor hardware. The change of topology is another issuecaused by insertion and deletion of wireless nodes [12, 13].

Hybrid MAC protocols were introduced by combining thecharacteristics of time division multiple access (TDMA) andcarrier sense multiple access CSMA in order to get higherenergy saving and flexibility. However, existing hybrid MACprotocols are not capable of providing mobility and networkadaptability support. These are some of the major issues thatneed to be addressed when designing a highly robust hybridMAC protocol. To address these concerns, a low duty cycle,energy-efficient and mobility-based Boarder Node MediumAccess Control hybrid protocol has been introduced. BN-MAC is designed to address the problems of existing hybridMAC protocols such as mobility and scalability. BN-MACalso addresses the problem of low power listening: reducingthe size of the preamble without the inclusion of a destinationaddress in each preamble and data packet. Further, BN-MACuses the automatic packet buffering and is compatible withpacketizing radios. In BN-MAC, the node gets completeaccess 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 asfollows. In Section 2, we present literature review of relatedtechniques. In section 3, we present the system model for theproposed work. In section 4, the BN-MAC protocol design ispresented. In section 5, the idle listening control model isexplained for handling the idle listening problem. In section6, the simulation setup and analysis of the results is discussed.In section 7, the discussion of results is presented, and section8 concludes the paper.

2 Review of Related Techniques

In this section, we examine some of the well-known hybridand mobility MAC protocols with their existing salient fea-tures and weak points. X-MAC is a hybrid-based low dutycycle 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 considersthat the target node is asleep. The transmitter node attempts tosend a short preamble again until the transmitter node reachesthe threshold value. In X-MAC, CSMA is performed beforepreamble packet transmission. Having received the preamble,the receiver has to wait for a short period to provide a chancefor other nodes if they want to send data packets. An advan-tage of X-MAC is minimization of energy consumption andlatency. In addition, idle listening at the receiver side andoverhearing at the neighboring nodes can be reduced.However, the gaps between series of preamble packets is aproblem 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 andCSMA techniques. In Z-MAC, CSMA builds the baselineand TDMA resolves the conflict. Z-MAC uses the owner slotidea. The nodes in Z-MAC use the novel flexible time-frameregulation 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 thenodes can compete for the channel for data transmission, butonly the allocated node gets the highest priority. Under thehigh competition conditions, the slot assignments decrease thecollisions. However, Z-MAC suffers latency problems due tothe use of a long preamble that increases the chance of strikingthe active period of the receiver. The nodes in Z-MAC arefixed to limit the network scalability. As a result, the mobilityand scalability support cannot be fully attained. Once a newnode intends to join the network, the setup phase must berepeated 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 processof synchronization is done using a broadcasting SYN packetat the start of the listening phase. A node first attempts tofollow a prevailing schedule while listening for a specificperiod of time. If no SYNC message is received, the nodesrandomly pick a time to go for sleep and instantly broadcaststhis information. However, if a node obtains different sched-ules, then that node picks one, but the nodes adopt bothschedules. MS-MAC uses border nodes that make a virtualcluster that may follow two or more different schedules. MS-MAC enables each node to determine the mobility and itslevel within its neighborhood. An advantage of MS-MAC isto handle different cluster schedules. MS-MAC can continuecommunication with the original neighbor while making anew virtual cluster. The synchronization can be adjusted withthe speed of the neighbor nodes. However, nodes get confusedby following different schedules that could lead to congestion

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and a waste of energy under a heavy traffic load. In addition,neighbor of the sensor node wastes a significant amount ofenergy even it is static.

Speck MAC [16] is another hybrid MAC protocol that is adeviation from the B-MAC protocol. Speck MAC integratesdestination address and superfluous transmission of shortpackets. The first goal of Speck-MAC is to reduce the trans-mission energy, and the second is to decrease the significantoverhearing problem during a heavy traffic situation. Speck-MAC is also efficient during the transmission of unicastpackets. However, Speck-MAC experiences the problem ofextra consumption of energy by sending wake-up frames eventhough 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 enablesa node to extend sleep time and switch on radio when thepackets are arriving. MA-MAC covers two scenarios: staticand mobility. In the static scenario, the performance of MA-MAC is similar to X-MAC. MA-MAC divides the preambleinto several strobes to send an early acknowledgment packetto preserve energy. In the mobility scenario, MA-MAC uses aseamless handover to relay the data to a new node before thecollapse of the link. During mobility, if a transmitter noticesthat the distance of the receiving node exceeds the first thresh-old, the transmitter starts to discover an intermediate neighbornode. 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 newlydiscovered node. An advantage of MA-MAC is handling themobility in time, and relay nodes are discovered during datatransmission. However, MA-MAC has a weakness becauseMA-MAC depends on the network density and the scheduleof nodes. Further, in MA-MAC, it is also hard to maintain twothreshold values.

ADC-SMAC [19] is a hybrid MAC protocol that is animproved version of S-MAC [20]. ADC-SMAC adds twoadditional features to S-MAC. First, the node calculates theenergy consumption rate of the forwarding node and an aver-age sleep delay at the time of sending the synchronizedpackets. ADC-SMAC also adjusts the duty cycle accordingto the network conditions and broadcasts the new schedule tothe neighbor nodes. Hence, ADC-SMAC reduces the energyconsumption, but it increases the latency and it is difficult tomanage the network scalability. In addition, ADC-SMAC isnot fully robust in mobility conditions.

MobiSense is a cross-layer mobility-based MAC protocolthat combines MAC and the network layer to perpetuateenergy efficient data communication within a micro-mobilityscenario. In the scenario, the nodes are structured into clusters,

in which stationary nodes perform as cluster heads. The non-cluster head nodes interchange data packets between clusterhead nodes [21]. MobiSense implements multi-channel datacommunications to increase throughput and simplify the net-work management. The goal of MobiSense is to decrease theintervention between the clusters and to permit the cluster-heads to schedule traffic dynamically. MobiSense manages asuper-frame using synchronized slots, transmission slots,downlink and uplink, discovery slots and data admissionmini-slots. The cluster heads send synchronized data packetsat the start of each frame to notify mobile nodes about changesin downlink and uplink data transmission. The strength ofMobiSense is to obtain quick network discovery information.MobiSense also confirms fast admission and rapid networkconvergence. However, MobiSense experiences the problemof managing the multi-channel. As a result, the node mobilityis difficult to handle in time and therefore causes thecollisions.

The low-power real-time medium access control (LPRT-MAC) protocol is proposed in [22] for actuation and wirelesssystems. LPRT-MAC consists of an infrastructure-based startopology. The stations communicate with base stations direct-ly. The LPRT-MAC includes a super frame that is divided intomini slots and is used for transmission with the base station.LPRT-MAC reduces power consumption and coordinateswith the channel. The beauty of LPRT-MAC is handlingoverhead by using the star topology. However, LPRT-MACis limited and not suitable for large multi-hop wireless sensornetworks. As a result, the topological change causes theadditional energy consumption, and the nodes reduce thethroughput. LPRT-MAC is also not suitable for mobilityscenarios.

Mobility-aware and energy-efficient MAC (ME-MAC) isproposed in [23]. ME-MAC possesses almost similar featuresto MMAC-SW [24]. ME-MAC inherits the features fromTDMA and CSMA and dynamically adjusts the frame sizeas discussed in [24]. ME-MAC consists of the predictionmodel that depends on the accuracy of the localization mech-anism. ME-MAC also uses order-autoregressive that helps topredict the current mobility state. The ME-MAC protocolachieves its task through two phases: a data transfer phaseand a clustering phase. An advantage of this protocol is toreduce 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 hybridMAC protocols attempt to be energy efficient but experience aproblem in mobility conditions. Mobility based MAC proto-cols such as MobiSense, ME-MAC, MS-MAC, MA-MACare good candidates in mobility conditions. However, theyexperience a problem due to network density, management ofmulti-channels and following the dual schedule in the net-work. Finally, we conclude that these protocols are designed

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as application-specific. In this paper, we introduce the BN-MAC protocol that handles network scalability, mobility, andimproves the real time communications. Additionally, BN-MAC reduces the idle listening overhearing and improvesthe throughput. The BN-MAC can also be used for multipleWSN application areas.

3 System Model

The emergence of the latest wireless sensing technology helpsaddress the several shortcomings related to wired-sensors.Wired sensor technology is generally used in emergencyrooms and hospitals to monitor the patients [25]. The heapof wires is attached to a patient, which makes patients uncom-fortable. As a result, their mobility is restricted, and increasedanxiety is observed in the patients. The increased anxiety levelis also difficult for the staff to handle. When patients aremoved from one unit to another, the sensors need to beremoved and reattached, which is considered a cumbersomeprocess. The wireless sensor networks should be mobility-aware to help reduce both the jumble of wires and patientconcerns. There are already existing triage protocols for han-dling emergency medical services [26]. The performance ofthese protocols can be degraded due to the state of mobilityand increasing numbers of casualties.

There is a need to augment the evaluation of the mass-casualty during increased mobility and scalability to report thetriage levels of several victims automatically. To handle such asituation, we have simulated a WSN health scenario thattracks the indoor patients who are examined by local practi-tioners and remote practitioners. Further, outdoor casualtiesand movements of victims are monitored and reported to thecontrol room to take immediate measures for reducing thenumber of casualties, as depicted in Fig. 1. The simulatedWSN health scenario consists of different regions, and eachregion is controlled by a Boarder Node (BN). From anotherperspective, the WSNs experience the problems and limita-tions due to mobility and scalability [27].

Therefore, the energy-efficient MAC protocol will be ableto reduce such problems to some extent. We have thereforedeployed the BN-MAC protocol in this scenario to handle themobility and scalability to reduce the number of casualties in amass disaster area. One of the major goals for deploying theBN-MAC is to reduce energy consumption while maintaininga high degree of scalability, mobility and collision avoidance.The sensor nodes are deployed in different regions to monitorthe different types of activities. The deployed sensor nodes arestatic and mobile and can move to any region. Whenever anode leaves one region, then it needs to join another adjacentregion based on activities assigned to the node. To maintainthe 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 eventis reported to the BN, and every task of the BN is delivered tothe sensing field effectively. The lack of bidirectional reliabil-ity weakens event detection and provides inappropriate datacollection. We achieve end-to-end reliability using a newbidirectional reliable transport mechanism that uses a shortpreamble ACK/NACK control packet between the BN andimportant sensor nodes. In this scenario, the necessary nodesare chosen applying the weighted-greedy algorithm1 based onthe residual energy of the sensor node. When congestionoccurs, unimportant sensor nodes receive an alarm signal fromimportant nodes. As a result, the unimportant sensor nodesstop reporting the events to adjust unnecessary traffic.

The sensor nodes communicate with each other using shortrange and one-hop communication rather than long rangecommunication to preserve energy. The message forwardingprocess is done with intra- and inter-communications. Theintra-communication process is done within regions usingsemi-synchronous features.

The semi-synchronous2 process consists of scheduled andcontention-based approaches. The contention-based featureuses asynchronous communication to find the availability ofthe channel for communication, whereas schedule-based helpsfix the schedule of the nodes for sending and receiving thedata within the regions. Single-hop communication has littleedge over multi-hop communication [29]. Multi-hop commu-nication increases the latency because each node stores andforwards the packets. If the transmission consists of manyhops, the transmission consumes more energy whileforwarding packets, and the situation can even be worse ifthe packet size is larger.

The sensor nodes inside the region that monitor differentevents and forward the collected data to BN node are staticand mobile. Each BN forwards the information obtained fromsensor nodes using inter-communication to the base station.Each base station further forwards the information to “controlroom” using the IP network. The LDSNS model [30] is alsoused to help find the efficient shortest path. As a result, thesensor node uses Anycast communication3for maintaining theload balancing to save additional energy.

In this scenario, different events occur simultaneously suchas indoor patient reporting, outdoor casualties reporting to the

1 A weighted greedy algorithm: It can be considered as backtrackingalgorithmwhere each decision point “the best” selection is already knownand accordingly can be chosen without having to think over any of thesubstitute.2 Semi-synchronous: This feature is desirable for decreasing latency andenergy consumption for several WSN application areas to improve thethroughput.3 Anycast communication: It is message mechanism that only sendscontrol message to the nearest node within the group of possible receiversor may pick several nodes with subject to condition.

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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 handlingthe faster recovery process. In the scenario, the PT mobilityrouting model is incorporated.

PT encompasses two important features; packet generationrate and the pheromone sensitivity [30] to handle the task ofobserving the rescue events and maintaining a faster recoveryprocess. Furthermore, most recent WSN applications in thearea of surveillance and monitoring also require mobility andscalability. Currently, surveillance and monitoring applica-tions cover multiple scenarios ranging from vigilance of trav-elers to moving aircraft. Without mobility and scalabilitysupport, it is not possible to cover the whole surveillanceprocess.

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.

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For several applications, low duty cycling MAC protocolsare superior to other approaches in the context of latency,energy consumption, mobility, scalability and throughput. Inaddition, contention partly based on the semi-synchronousapproach helps obtain faster access to the medium [31, 32].BN-MAC continues a shorter awake period while maintaininghigh throughput and low latency. The schedule-based part ishelpful for those applications that require loose latencies. Forthese motives, BN-MAC builds upon the grounds provided byhybrid low duty cycled MAC protocols.

BN-MAC is designed to address the problems of existinghybrid 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 thedestination address in each preamble and data packets.Further, BN-MAC uses the automatic packet buffering andcompatibility with packetizing radios. In BN-MAC, the nodegets complete access to its owner slot similar to TDMA-basedapproaches. The rest of the slots are accessed through theCSMA approach. This approach reserves the energy andreduces the collisions. In addition, BN-MAC eliminates idlelistening using the ILC model to obtain a considerable energysaving. BN-MAC allots contention-free slot exchange to im-prove the network scalability dynamically even under heavytraffic 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 theshort preamble (SP)4 without inclusion of the destinationaddress. Before sending the short preamble, the LDSNS mod-el is used to sort out the one-hop shortest path nodes. Thus, theshort preamblemessage is Anycasted to the particular nodes atone-hop neighbors. When the particular node wakes up ac-cording to its schedule and samples the medium, if the nodefinds the short preamble message, then the node sends a clear-to send (CTS) packet. When the sender receives the CTScontrol packet, the sender sends the data to the particular nodeat the one-hop destination. The particular node adopts thesame method for the next second hop. This process is said tobe intra process. Finally, the data are delivered to the lastdestination node (BN).

BN either forwards using the IP networks to the controlroom (base station) given in Fig. 1 or sends to an adjacent BN.When the BN intends to send received data to an adjacent BN,the BN sends the RTSmessage. Once an adjacent BN receivesthe RTS, the BN responds with the CTS. When the lastdestination node (BN) receives the CTS, it sends theBoarder Node Inter Frame (BNIF) that is data received

through intra-communication. Once data are delivered to anadjacent BN, the BN acknowledges. BN-MAC consists of thefollowing phases: Selection of one-hop neighbor node andslot allocation, intra-semi-synchronous communication, inter-synchronous communication and boarder node selectionprocess.

4.1 Selection of One-Hop Neighbor Node and Slot Allocation

A one-hop discovery operation runs during the setup processuntil the topology changes. The benefit of this approach is tostabilize the initial costs while achieving efficient energy andsuperior throughput during intra- and inter-transmission. Evenif the topology changes constantly, that does not affect theone-hop neighbor nodes too much because BN-MAC doesnot deal with all one-hop neighbor nodes and does not evenmaintain the schedule with all one-hop neighbor nodes. Oneof supporting models in BN-MAC is LDSNS that helps findthe shortest efficient path. Through this model, each one-hopneighbor node keeps the updates of two nodes available at theone-hop neighbor. One is the principal node and the other isthe backup node.

The principal node is used for forwarding and receiving thedata to the next one-hop neighbor node. In case of movementof the principal one-hop neighbor node, the backup neighbornode is considered the principal node, and then another nodeis chosen as the backup node. Similarly, in case of mobility ofthe backup node prior to movement of the principal node, thesame method is applied for finding the backup node. Whenboth major and backup node leaves the one-hop neighborhoodat the same time, they inform the respective one-hop neighbornodes prior to moving. The moving node incorporates a flagsignal in the last sent data packet that indicates that the node isabout to leave. This feature lets the node adjust the mobility.BN-MAC uses a very promising time scheduler that helps notto exceed the assigned slot more than a one-hop neighbor. BN-MAC also uses a localized time slot without disturbing thetime 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 allone-hop neighbor nodes but synchronizes only with a partic-ular node (either the principal or the backup node) using theLDSNSmodel. The communication process starts with carriersensing (CS). After this process, the node sends a short pre-amble message to alert the particular node, especially theprincipal node. In case of mobility and power failure of theprincipal node, SP is sent to the backup node. Thus, each nodekeeps the information of the two nodes at the one-hop neigh-bor destination. When the SP is received, then the noderesponds 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 ison its way. In addition, it is also first portion of the Physical layerConvergence Protocol/Procedure (PLCP) Protocol Data Unit (PDU).The short preamble lets the receiver to get the wireless signal andcoordinate itself with the transmitter.

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data. Thus, the identical process is used for the next hop untilthe packet is delivered to the BN. This process helps reducethe overhead. The benefit of using a lower duty cycle protocolis to keep the receiver and the sender decoupled. A shortpreamble that MAC protocols prefer over a long preambleenabled MAC protocols to operate by the low power dutycycle mechanism.

The existing lower power listening (LPL) protocol uses along preamble and experiences the overhearing problem. As aresult, additional energy is consumed at non-targeted re-ceivers. The LPL protocol also introduces extra latency ateach hop [32]. In the long preamble technique, the node needsto wait until the long preamble is received. This approachconsumes excess energy at both the sender and the receiversides.

In X-MAC, the destination address is incorporated intoeach 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 nodegoes to sleep. If the preamble packet is discarded by a non-intended node, then there is no chance for a short preamblepacket to be delivered to the destined node. If the node is not

the intended recipient receiver, even if it checks and ignoresthe preamble packet, this process also causes energy waste. Ifthe node is the intended recipient, it remains awake for thesubsequent data packets. Further, X-MAC is based purely onan asynchronous mechanism, and it does not have the sched-ule of the neighbors. As a result, the node consumes excessenergy 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 improvementin the throughput. It also saves energy and is preferable forseveral applications. When multiple nodes communicate withthe same neighbor node, BN-MAC uses a slotted contentionwindow to handle the congestion and emitting problem. Thenodes select the slots randomly in the contention window. Asa 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 thepacket 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 radiosuch 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

TXCS

SP

CTS

TIME

ACKNOWLEDGEMENTINTRA DATA FRAME CARRIER

SENSING

SHORT PREAMBLE

RX

IDF

RSP

WAKE-UP

SP

BOARDERNODE (TX)

RTS

CS

TIME

TIME

TIME

BOARDERNODE INTER FRAME CLEAR-TO-SEND REQUEST-TO-SEND

BNIF

ACK

ABP

AUTOMATICBUBBERPACKET

RTS PROCESS

SP

IDF

CTS

BNIF

BNIF

TIMECTS

CTS WAITTIME

RECEIVED SHORTPREAMBLE

BOARDERNODE (RX)

Figure 2 BN-MAC messagemechanism process.

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accurate for the traditional long preamble LPL. Additionally,the short preamble packets are also compatible with all radiosusing bit streaming interfaces, including the CC1000 that isavailable in the MICA2 mote. Another key advantage of BN-MAC is an automatic buffering capability that also savesenergy and increases the lifetime of the network. We heredemonstrate 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 automaticpacket buffering process that also reduces the wake up timeand increases the lifetime of the network. In the automaticbuffering process, the node uses a promiscuous mode 5thatenables the node to listen to all ongoing data traffic andcoordinates, if requested. Furthermore, the node saves a copyof the packet that is received regardless of the intended desti-nation of the data packet until the receipt of the packet isacknowledged by the destination node. Such buffering re-quires a relay that is used under the saturated conditionsbecause each node is able to cooperate in sending data packetsto other buffers.

As mentioned above, a short preamble improves the net-work lifetime by consuming less power. Let us determine theenergy consumed for carrier sensing and sending a shortpreamble.

The energy consumed for carrier sensing is ‘γ’, the checktime is ‘δ’, and the average energy consumed for carriersensing is ‘Δр’.

Δр ¼ γδ

ð1Þ

The energy consumed for the short preamble ‘Esp’ consistsof an average energy consumed for carrier sensing ‘Δc’ andthe consumed energy for synchronization is ‘Esyn’.

Esp ¼ Δp � 2Esyn � Cdrift ð2Þ

We use clock drift, ‘Cdrift’, that is consumed time forsynchronization, and ‘2Esyn’ is the energy consumed by thetransmitter and the receiver for the synchronization. The nodethat transmits its clock at the one-hop neighbor during intra-communication is called the source node, and the node thatreceives the clock at the one-hop neighborhood is called theparticular node (principal or backup node). The synchronizednodes send a short preamble before sending data withoutusing the target address because a short preamble is sent toparticular nodes (principal or backup node) at the one-hopneighbor that reduces the energy consumption.

Let us assume that the source and the particular nodeconsume 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 thestored schedule. Thus, the source node and the particular nodeconsume the energy that can be obtained as follows:

β ¼Xj¼0

m

SjΔφ:μ*Δv2ð Þ * Δр* 2Esyn* Cdrift

� �Δt

ð3Þ

This is the energy consumed by the source node.

δ ¼Xj¼0

m

SjΔφ:μ*Δv2ð Þ * Δр* 2Esyn* Cdrift

� �Δt

þ Δр* Esyn* Cdrift

� �Δt

ð4Þ

This is energy consumed by the particular node (principalor backup node) that is available at one-hop destination.

where ‘c’ is the starting point of the short preamble, ‘n’ isthe ending point of the short preamble, ‘Sj’ is the shortpreamble, ‘Δφ’is the size of the preamble, ′μ ′ is the natureof the location, ′Δv2 ′ is the short preamble speed, and’ ′Δt ′ isthe total time spent for sending the short preamble. BN-MACcan explicitly find out the energy consumed for a short pre-amble prior to sending the data. BN-MAC has an edge overlow-duty-cycle long-preamble-enabled MAC protocols andX-MAC.

4.3 Inter-synchronized Communication

We have already discussed that BN-MAC is introduced forWSNs consisting of different regions. The previous sectionhighlights how to access the channel and forward the datainside regions. This section explains how to set the scheduleswithin regions and outside regions. Each region of the WSNcontains a Boarder Node. The inter-synchronized transmis-sion schedule is done from one region to other regions. TheBoarder Node receives intra data packets within the regionand forwards the data packets to outside the region. TheBoarder Nodes of each region follow a schedule-basedmethod.

The Boarder Node first broadcasts three ‘hello’ messagesto warn the region nodes to be ready for getting the BoarderNode indication signal (BNIS). BN does not wait to receive anacknowledgment from all region nodes. If the BN gets a singleacknowledgment from one region node, the BN assumes thatthe ‘hello’message is delivered successfully. We have alreadydiscussed that neighbor nodes exchange the schedule. Thus, ifany node is unable to receive the ‘hello’message, the neighbornode informs other nodes at the time of exchanging theschedule. In this way, each node of the region knows theschedule of the BN. BNIS consists of the current time, thenext 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 slotsbetween the source and the destination and describes therelated offset time. Once the Boarder Node announces the

5 Promiscuous mode: It causes the controller to permit all traffic ratherthan allowing only the frames. Promiscuous mode is also used to detectnetwork connectivity problems.

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schedules for the nodes of the region, all of the nodes areresponsible for following the given schedule.

The announcement of the schedule gives the permission tothe region nodes to send and receive intra data messagesduring the distribution time. After sending the intra datatransmission, nodes go to sleep automatically, as explainedin Section 5. Once the node is not scheduled for exchangingthe message, that node remains asleep during the whole dis-tribution time. At the end of the scheduled time of the regionnodes, the Boarder Node synchronizes with another BoarderNode 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 aschedule-slot for next scheduled distribution time.

The nodes remain active only during BNIS and other thanBNIS time, the nodes remain in the sleep state that causes theenergy saving. In addition, the automatic feature of going tosleep after performing the task causes control of the idlelistening 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 carriersensing. Carrier sensing makes it possible to forward themessage of request-to-send (RTS). In response, the BN willget a clear-to-send (CTS) message from the BN of the otherregion shown in Fig. 4.

There is no hidden terminal problem in BN-MAC becauseBNs of all regions are synchronized with adjacent regions.

The network is divided into several regions. The scheme isvery simple, and each BN just tracks the schedule of neighborBNs.

4.4 Boarder Node Selection Process

The Boarder Node is selected periodically using the dynamicBoarder Node selection process (DBNSP) model that choosesthe Boarder Node based on residual energy, signal strengthand memory allocation resources. The energy level of the BNis decided based on Table 1 using DBNSP and level of energyinformation (LEI). The function of LEI is to announce thelevel of energy for each node, and DBNSP decides to declare

LONG PREAMBLE

TARGET ADDRESSIN PACKET HEADER

DATATRANSMITTX (LPL)

RX (LPL)

TIME

EXTENDED WAIT TIME

RX WAKE UP TIME

DATARECEIVE TIME

SP

BP

LISTEN TIME FOR BUFFER PACKETS

SHORT PREAMBLE WITHTARGET ADDRESS

TE-ACK

DATATRANSMITTX (X-MAC)

RX WAKE UPRE-ACK

DATARECEIVE BP

ENERGY ANDTIME SAVE AT

TX & RX

RX (X-MAC)

RX WAKE UP TIME

TE-ACK

DATATRANSMIT

SHORT PREAMBLE WITHOUTTARGET ADDRESS

TX (BN-MAC)

RX (BN-MAC) RX

S- W

RE-ACK

DATARECEIVE ABP

ENERGY AND TIMESAVE AT TX & RX

ABP

AUTOMATICBUFFER PACKET

RE-ACK

RECEIVER EARLYACKNOWLEDGEMENT

TE-ACK

SHORTPREAMBLE

TRANSMITTER EARLYACKNOWLEDGEMENT

SP

RX WAKEUP TIME

TIME

TIME

TIME

TIME

SPSP

SP SPSP

BP

BUFFERPACKET

Figure 3 Comparison oftimeline of duty cycle MACprotocols.

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the Boarder Node. We categorize the level of energy into sixlevels as given in Table 1.

When the energy level of an already working BN goesdown, the shift of responsibility from one BN to another BN isaccomplished by using the election flag bit (EFB). The EFBspecifies the process of immediate BN election. To reduce theoverhead of shifting the responsibility of one BN to anotherBN, BN-MAC uses a proactive method to decide the next BNbased on computing the contention time for election using theavailable energy, the signal strength and the memory alloca-tion resources.

The DBNSP model helps determine the energy of eachnode in each region to select the BN. Each sensor nodedetermines its residual energy after completing some roundsof detecting the events. This residual energy decides whetherthe node should be considered as a candidate to become a BNor not. The nodes detect the BN in its region based onmultipleprocesses of WSNs using multiple rounds. The benefit of thismodel is to give enough options to each node to be declaredBN based on set criteria. The process of choosing the BNconsists of several steps. First, the base station broadcasts ashort preamble in the network. In response, each node calcu-lates its distance from the base station based on the signalstrength. The node that receives a short preamble with highradio frequency becomes a candidate BN.

Each node waits for another node to get an alert to compareits memory allocation, residual energy and radio range. If noalert is received by another node, that node is selected

dynamically as the BN. The selected BN sends a multicastingmessage to its neighbor nodes to let them know about itsselection as the new BN for future communication. We deter-mine the residual energy of each node in each region. Let usassume that single-hop communication is used among sensornodes to detect events and to transmit the information. Eachnode forwards data ‘d’ at distance ‘r’ within region ‘R’ andlocated at the N*N area of WSN. We determine the residualenergy of two types of nodes: the BN and the Non-BoarderNode (NBNs) that can be expressed as follows.

Er d; rð Þ ¼ d*Eradiof þ d*EampN2

2πR

oð5Þ

where ′Er ′ is the total residual energy consumed by allnodes, ′Eradio ′ is the energy consumption of the radio and ′Eamp ′ is the energy used for amplifying the radio signal.

HELLOTX(BN)

BNISHELLOHELLO ACK

RXREGIONNODE

TIME

TIME

RX (BN)

RX (BN)OF OTHERREGION

TIME

TIMECTS

EITHER SLEEP ORAWAKE

ACK

RECEIVER IS BUSY WITH BN DURING THIS TIME

BN OF OTHER REGION IS BUSY EITHER WITH REGION NODE ORADJACENT BOARDER NODE

ACK

ACKNOWLEDGEMENT CLEAR-TO-SEND

RTS

REQUEST-TO-SEND

ABP

AUTOMATICBUFFERPACKET

BNIS

BOARDER NODEINDICATION

SIGNAL

BNIF

BOARDERNODE INTER

FRAME

ACK

DATA

TXREGIONNODE

DATA

R-HELLO

ABP R-HELLO

RECEIVEDHELLO

CTS RTS BNIF

TRANSMITTER OF BN IS BUSY WITH REGIONNODE DURING THIS TIME

Figure 4 Inter-synchronizedtransmission schedule with regionnode and Boarder Nodes.

Table 1 showing thesensor node distributionenergy 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

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Thus, Eq. (5) shows the residual energy consumed by BNand NBNs. It is calculated after performing their respectivemonitoring process for assigned task.

Here, we are interested in determining the residual energyof BN in two cases.

a. When the BN forwards information to an adjacent regionor the base station.

b. When BN transmits and receives the information amongthe non-boarder nodes.

Thus, the residual energy of BN is calculated in Eq. (6)when performing the task with adjacent BN or base station

Er d; rð Þ ¼ d*Eradiof þ d*Emhrno

ð6Þ

where ′Emh′ 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 beexpressed as:

ERX dð Þ¼ d* EradioN

C−1

� �ð7Þ

where ‘ERX(d) ′ is the energy consumed for receiving thedata packets and ‘N’ is the number of sensor nodes.

BN also consumes energy in scheduling with the BNs ofadjacent regions.

ERX dð Þ¼ d* EschdN

C−1

� �ð8Þ

BN requires three types of short preamble messages bysetting initial phase that include ′Eschd ′ shows the energyconsumed for scheduling, ′Padv ′ is for the advertisement and′Psyn ′ is for synchronization. Thus, consumed energy of BNcan be computed as follows:

EBN ¼ ETX Padv ; rð Þ þ ERX Padvð Þ þ ETX Psyn ; r� �

þ ERX Psyn

� �þ ETX P j ; r� �þ ERX P j

� � ð9Þ

From Eq. (9), we deduce the energy consumed by the BNduring the initial setting up process.

ENBN ¼ ETX Padv ; rð Þ þ ERX Padvð Þ þ ETX Psyn ; r� �

þ ERX Psyn þ d� �

* Eradio ð10Þ

After the initial phase setting, BN and NBN nodes start tosend data. On completion of the event monitoring process, thefinal residual energy, the memory allocation and the signal

strength decide the selection of the next BN. The residualenergy of BN can be calculated by Eq. (11).

EBN ¼ Ed f −CHN þhERX ds þ 1ð Þ− ERX dsð Þ

þ ERX ds þ 1ð Þ þ ETX ds þ 1ð Þ ETX dsð Þþ ETX ds þ 1ð Þ ð11Þ

Based on Eq. (11), it is decided whether BN should con-tinue working as BN or not. Similarly, we can determine theresidual energy of NBN that can be calculated as follow.

ENBN ¼ ETX d; rð Þ þ ½ ds*Eradio þ ETX

�ds þ 1; r

� �þ ETX ds þ n; rð Þ

þ ERX ds*Eradio þ ERX

�ds þ 1; r

� �þ ERX ds þ n; rð Þ�

ð12Þð12Þ

where ′ds ′ represents the size of data to be transmitted ineach data packet, and ′n ′ shows the number of packets trans-mitted and received by NBN. Based on Eqs. (11) and (12), thenew BN is selected.

5 Idle Listening Control Model

In many applications, nodes remain mostly in idle in theWSNfor longer periods of time if no sensing event occurs. The paceof the data delivery rate remains low during this mode, but it isnot a good practice to keep the nodes listening all the time. In aprevious section, we have discussed the BN-MAC mecha-nism, but in this section, our aim is to preserve more energy byreducing the idle listening time of the nodes by letting thenodes go into either sleep or an active state, if they arescheduled to receive and transmit data. This process is donethrough the ILC model. When the sensor nodes are active(ON) without doing anything, they are costing both time delayand energy [33]. The costs can be justified if energy is savedwith 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 ′CEidle ′ is consumed energy during idle time; Midle(t) is theminimum time required for sensors to remain in an idle state;Eidle/on is the energy consumed during the ‘idle’ or ‘ON’ state,and ′CSidle/off’ is the energy required to change state from (idleto off).

Idletime ¼ CEidle*Midle tð Þ þ Eidle=on *CSidle=off ð14Þ

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Idle time must always be less than or equal to ‘OFF’ timebecause nodes consume energy during idle time (listening)without doing anything.

Total ‘OFF’ time can be calculated by Eq. (15). Assume ′Eoff ′ is the preserved energy during ‘OFF’ time, ′Moff(t) ′ is theminimum time required for sensors to remain in the idle stateand ′CSoff/on ′ is the energy required for going from the ‘OFF’state to the ‘ON’ state.

t off ¼ PEoff *Moff tð Þ þ CSoff =on ð15Þ

Assume that ′Moff(t) ′ is the time that sensors stay in the‘OFF’ state (higher than the idle state, as already proved) andgiven in Eq. (16). Thus, Eq. (13) can be satisfied by substitut-ing the remaining values.

Moff tð Þ≥ 0; PEoff − CEidle

� �* CSidle=off

h � ið16Þ

The purpose of the ILC model is to bring the sensors intothe sleep mode, if no data are being delivered. We infer andgeneralize from Eqs. (13) and (16) that the operating mode ofsensors 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 ≥maxh0;�

CEon þ CEidle− PEoff

� �* CSαβ ð17Þ

where ′CEon′ is the energy consumed during the activemode, and ′CSαβ ′ is the consumption of energy from goingactive (ON) to Sleep (OFF) mode that is a negligible amountof energy. Thus ′CSa ′ is greater than or equal to the amount ofenergy consumed in the active mode, preserved energy in thesleep mode and energy consumed for change of transition toON/OFF mode.

Therefore, in our case, we have preserved 93.6 % of theenergy by letting sensors to go into sleep rather than remainingin idle mode. We have just wasted 6.4 % of the energy. Thetotal preserved energy in sleep and idle modes is shown inFig. 5. The consumption and preservation processes are ob-served when the node finishes the monitoring process andcontinues 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 idlelistening. This model restricts additional waste of energy.

Similarly, we have calculated the total energy consumed inthe monitoring process and idle listening and also shownpreserved 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 thenodes should have been in the active as well as the listeningstates without use of ILC, then nodes could consume a totalenergy 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 todetermine the reduced amount of energy.

The BN and the scheduled nodes are active during thecompilation time. In the case of an empty network, BN takesthe same timeout as the GMACnodes [34] take for sensing thetraffic of the network during both distribution and collectiontime while the rest of the nodes remain in the sleep state. InBN-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 coversindoor and outdoor casualties using ns-2.35-RC7 on Ubuntu13.10 operating system. In this scenario, different activitiesare 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 aremonitored. All activities are reported to the control room. Thescenario reflects the real WSNs environment. The obtainedsimulation results are quite convincing and identical to realis-tic experimental results.

The wireless sensor network is disseminated into differentregions as depicted in Fig. 1 to collect faster data with lowlatency. We have set one BN in each region. The BN forwardsthe collected information of its region to either the BN of theadjacent region or the control room. We have simulated dif-ferent realistic scenarios: mobility and static. The main goal ofsimulation is to handle the hospital emergency situation con-suming less energy with faster data delivery. We evaluate theperformance of the BN-MAC protocol and compare withknown 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 protocolsfor simulation.

The simulation scenario consists of 180 nodes with atransmission radius of 30 m. The nodes are randomly placedin uniform fashion in the area of 400 * 400 square meters. Thenetwork is divided into equal 100 m × 100 m regions. Theinitial energy of the nodes is set 3.7J. The bandwidth of thenode is 50 kb/s, and maximum power consumption for each

6 Relative Standard Deviation (RSD): It is the absolute value fordeviation of coefficient and defined as a percentage. It is alsocommonly used when doing quality assurance.7 Gini coefficient: It is an inequality distribution measure that isexpressed as the ratio with values between 0 and 1.

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http://en.wikipedia.org/wiki/Absolute_value%23Absolute%20value

http://en.wikipedia.org/wiki/Coefficient_of_variation%23Coefficient%20of%20variation

sensor is set 16mW. Sensing and idle modes have 12mW and0.5mW, respectively, but in our case, there is no idle mode.Sensors go to either active or sleep mode. Each sensor iscapable of broadcasting the data at power intensity rangingfrom -20 dBm to 12 dBm.

The total simulation time is 35 min, and the pause time isset to 30 s for phase initialization at the start of the simulation.The results demonstrate an average of 15 simulation runs. Theenergy consumption pertaining to different radio modes andsimulation parameters is summed up in Table 2.

We collected several results but use the following metricsto demonstrate the performance of the BN-MAC and othercompeting 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 andmobility situation.

& Latency of BN-MAC, Z-MAC, X-MAC, MS-MAC, A-MAC, ADC-SMAC andMobiSense in static and mobilitysituation.

6.1 Throughput Performance

We analyze the throughput efficiency of BN-MAC and othercompeting hybrid MAC protocols: X-MAC, Z-MAC, MS-MAC, A-MAC, ADC-SMAC andMobisense in Figs. 7 and 8.We used static and mobility scenarios for determining thethroughput based on the varying number of transmittingnodes. In Fig. 7, we set 30 % of the nodes to be mobile,including transmitting nodes throughout the simulation. In thegiven scenario of the hospital for disaster recovery, indoorpatients, outdoor victims and movement of local and remotepractitioners is 30 % mobile. We have noticed that BN-MACand other competing MAC protocols initially produce anaverage throughput of 450 to 500 Kbits/s, but when thenumber of transmitting nodes increases, then performance ofBN-MAC slightly decreases as compared with other MACprotocols.

BN-MAC reduces the throughput from 500 Kbits/s to 400Kbits/s by using 1 transmitter to 18 transmitter nodes, whereasothers decrease throughput from 475Kbits/s to 260 Kbits/swith the same number of transmitters. A-MAC and ADC-SMAC are highly affected with increased number oftransmitters. BN-MAC is superior to other competingMAC protocols and achieves 12.5 to 37.5 % higherthroughput in the mobility scenario. This mobility anal-ysis is based on two methodologies: analysis based onsynthetic traces and analysis based on real-world tracesas discussed in [35].

In Fig. 8, all nodes are stationary. Similarly, BN-MAC andother competing MAC protocols produce throughput. Theyinitially get from 462 Kbits/s to 500 Kbits/s at 1 transmitterwhen the number of transmitters increases, then the through-put performance of all MAC protocols starts reducing. Wehave observed that an increase in the number of transmittersalso causes a decrease in throughput even though the nodesare static. Once again, BN-MAC also outperforms other MACprotocols in the static scenario, and BN-MAC achieves 15 to40.25 % higher throughput. Mobisense and ADC-SMAC arehighly affected in the static scenario because they are speciallydesigned for handling the mobility of nodes. The simulationresults demonstrate that BN-MAC is the superior choice forseveral WSN applications.

0 5 10 15 20 25 30 35

0.2

0.4

0.6

0.8

1

Simulation time in minutes

TotalE

nergyCon

sumption /pr

eserva

ti oni n

%

Consumption inidle mode

0

Preservation inSleep mode

Figure 5 Total percentage (%) of energy preserved in sleep mode VSconsumed in idle mode.

0 5 10 15 20 25 30 35

300

600

900

1200

1500

Simulation time in minutes

TotalE

nerg

yin

joules

/cou

lomb Consumption

in idle mood

0

Preservation inSleep mode

Consumption inactive mode

Figure 6 Consumption of energy in active and idle modes VS preservedenergy in idle mode using IDL model.

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6.2 Network Coverage Efficiency and Lifetime

We validate network coverage performance of BN-MACusing static and mobility nodes. We have scaled thenetwork coverage scenarios for handling the monitoringactivities of a hospital including the recovery of massvictims. We have conducted several tests whiledeploying from 1 to 180 sensor nodes. In Figs. 9 and10, we have created a mobility scenario covering 25%and 50 % mobility of the nodes, respectively. Themobility of the nodes is set from 0–9 m/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 inFig. 9. When mobility increases up to 50 %, thencompeting MAC protocols get 68–78.5 % network cov-erage performance using 180 sensor nodes, as shown inFig. 10. We have established 18 sessions in both sce-narios simultaneously to determine the exact behavior ofthe network using highly congested traffic. We observethat ADC-SMAC, A-MAC and MS-MAC are signifi-cantly affected due to mobility. In addition, BN-MAChas obtained the same network coverage with 113–120sensor nodes as other MAC protocols get with 180sensor nodes.

Based on simulation results, we demonstrate thatmobility brings a trivial change in the network coverageby using the BN-MAC protocol. In addition, we havealso validated that the duration of the simulation (eitherincreases or decreases) does not affect the efficiency ofBN-MAC. In Fig. 11, we have shown the networkcoverage of BN-MAC and other MAC protocols basedon the static scenario. Similarly, BN-MAC has a slight

Table 2 Summarized simulation parameters for proposed scenario hos-pital to involve indoor monitoring and outdoor handling of masscasualties.

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

Tx energy 16 mW

Rx 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 termitea

a Pheromone termite: It provides routing support and based on twoimportant features: Pheromone sensitivity and packet generation rate.This model also helps in the detection power (emitted signal) that nodeuses to communicate with other nodes. In addition, packet generation rateinforms the node to handle variable number of packet generation rate andadopt the network condition.

Figure 7 Throughput at heavy traffic load using mobility.

Figure 8 Throughput at heavy traffic load using static nodes.

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advantage over other competing MAC protocols becauseBN-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, showingthat BN-MAC prolongs the network lifetime.

We also hereby determine the minimum number of sensornodes required to cover whole area of the network (400 ×400 m2).

Smin ¼ 2Arπ

3πR2 18ð Þ

where ′Smin ′ is the minimum number of sensor nodesrequired to cover the entire network area, ‘A’ is the entire

network area, ‘R’ is the total distance of the network, and ris the sensing range of the sensor nodes.

We assume that the sensing range is smaller than the wholemonitoring area.

Thus, SminSmax

can be the maximum number of sensor nodes

required to cover the ‘R’ total distance.Lemma 1: Smin

Smaxis an upper bound on ‘R’, Smin is a lower

bound and ‘Ni’ is the number of sensors in the network, where

Smin ¼ 2Arπ

3πR2 19ð Þ

Proof: Let the upper bound be linear on ‘R’ withthe maximum number of sensors (total number ofsensors) as ′Smax ′, whereas the lower bound on ‘Ni isinvariant with ′Smin ′. In addition, these bounds are notconsidered tight as long as they do not consider thetransmission radius ‘Tr’ of the sensors. However, weneed a better heuristic solution to follow these boundsclosely irrespective of changes that occur in the pa-rameters of the network. Hence, the lifetime of thenetwork should be linear with ′Smin ′, and ‘Ni’ will beconstant with ′Smax ′.

Based on the simulation, we also determine the networklifetime consists of 400 × 400 m2 shown in Table 3 using BN-MAC and other protocols.

In Fig. 12, we show the lifetime of the WSN basedon a different number of sensor nodes. BN-MAC getsa higher lifetime than other MAC protocols. The otherMAC protocols are less capable of utilizing energyefficiently to get an improved network lifetime withthe increased size of the nodes. BN-MAC possessesthe capability of maintaining the traffic and reducingthe WSN ideal listening time. The nodes using BN-MAC die after 472 days compared with other MACprotocols, 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 networklifetime.

6.3 Latency

In this section, we introduce the latency by using BN-MAC and other competing MAC protocols. We measurethe latency in terms of how much time one packet takesto travel from sender to destination point. In addition,we measure and display different types of latencies,including propagation delay, transmission delay, routerdelay and storage delay. In addition, these four types ofdelays are collectively shown in Figs. 13 and 14. Wealso 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

100CO

VERA

GEEF

FICIEN

CY%

NUMBER OF SENSOR NODES

0

BN-MAC

X-MACMS-MACA-MACMobiSenseADC-SMAC

Z-MAC

Figure 9 Coverage efficiency at 25 % mobility of nodes.

Figure 10 Coverage efficiency at 50 % mobility of nodes.

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the different mobility rates. We observe in Fig. 13 that,based on the simulation, when mobility increases, thelatency also increases. BN-MAC gets 0.015–0.06 s oflatency at 0–9 m/s speed with 50 % mobility ( numberof moving nodes), whereas other competing MAC pro-tocols show higher latency, namely, 0.0156–0.17 s, atthe 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. Wevalidate that BN-MAC can be used for different typesof applications for faster delivery of data.

In Fig. 14, we show the latency of BN-MAC and othercompetingMAC protocols based on the static scenario. In thisscenario, latency covers propagation delay, transmission de-lay, router delay and storage delay. We use a different packetgeneration interval on the x-axis. We observe that BN-MACoutperforms all other MAC protocols because BN-MAC gets0.015–0.016 s latency from 0 to 18 packet generation inter-vals. OtherMAC protocols also experience the problem due tothe increase of packet generating rates.

The average latency for other MAC protocols is counted as0.015–0.034 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 affectingperformance, especially whenmobile 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, thenumber of random access frames, and the rate of transferframes in the static and mobility scenarios, but the averagedelay remains almost stable with Z-MAC, X-MAC and otherMAC protocols, which exhibit higher latency and reducedthroughput.

Figure 11 Coverage efficiency when all nodes are static.

Table 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 ofsensors.

Figure 13 Average packet delay at different mobility rates.

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7 Discussion of Results

Energy has been a challenge and will also remain afuture challenge for efficient deployment of WSNs, be-cause advancement in battery technology has been slowcompared with growth of processing power and com-munication data rates. We need special emphasis onimprovement of energy-efficient operation. To overcomethis challenge, hybrid MAC protocols have been intro-duced to prolong network lifetime. The hybrid MACprotocols get higher energy savings, flexibility and bet-ter scalability. In this section, we discuss and comparethe merits and demerits of BN-MAC and competinghybrid MAC protocols.

X-MAC is a hybrid low duty cycle protocol based onshort preambles with a target address. An advantage ofX-MAC is to minimize energy consumption and latency.Idle listening at the receiver side and overhearing atneighboring nodes can be reduced. However, the gapsbetween series of preamble packets is the problem that

can be considered as idle listening by other nodes, andthey 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 areassigned for nodes but not fixed.

The fixed nodes limit the scalability ofWSNs. If new nodesare joined, that will be harder to set up the network phase.During the mobility, nodes with Z-MAC are unable to receiveand send the data packets. A-MAC, based on a collision-freeand non-overhearing mechanism, is designed for surveillanceand monitoring applications. The major advantage of A-MACis to notify the nodes in advance. However, A-MAC faces alittle 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 energyefficient data communication in the micro-mobility sce-nario. However, Mobisense experiences the problem dueto managing the multi-channel and mobility in time thatcauses the collision. As a result, nodes reduce through-put and increase the latency. ADC-SMAC improves twofeatures of S-MAC: node utilization and sleeping delay.The advantage of ADC-SMAC is to introduce flexibleduty cycles for nodes. However, ADC-SMAC is notsuitable for controlling idle listening and overhead is-sues. MS-MAC has introduced coordinated sleep/listenduty cycles and synchronizes the schedule of nodesperiodically. MS-MAC enables each node to determinethe mobility and its level within its neighborhood.However, nodes get confused to follow different sched-ules that could lead to congestion and waste of energyunder a heavy traffic load.

The limitations of existing hybrid MAC protocols,create the platform for new hybrid MAC protocol tofulfill the remaining issues. Thus, BN-MAC protocol isintroduced with features of a low duty cycle using thesemi-synchronization approach. The beauty of the BN-MAC protocol is dynamic election of BN based onmemory allocation, signal strength and residual energy,making an improvement in the network lifetime. The

Figure 14 Average packet delay when sensor nodes are static.

Table 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 savingbased on a one-hop neighbor search. The LDSNS modelfinds the shortest efficient path that makes it moreattractive. Thus, there is a trivial chance of failure ofthe one-hop path; if the one-hop path fails, then thesecond best one-hop path is chosen for intra-data com-munication using PT model. BN-MAC possesses apromising time schedule because the assigned slot isnot exceeded more than the one-hop neighborhood.

BN-MAC performs localized time slot allocation withoutchanging time slots of already existing nodes, reducing thelatency and overhead with less chance of breaking the routesinWSN. The ILCmodel is an energy efficient model that fullysupports 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 candidatefor multiple WSN application areas. Further, based on simu-lation, we have characterized the BN-MAC and other com-peting MAC protocols given in Table 4 to show their strengthand the weaknesses.

8 Conclusions

This paper introduces a low duty cycle, energy-efficientand mobility-based Boarder Node - MAC hybrid proto-col for wireless sensor networks. The mechanism ofBN-MAC demonstrates low latency, reduces the energyconsumption, handles the mobility and scalability, andmaximizes 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 accessto the medium. The schedule-based part is helpful forthose applications that require loose latencies. For thesemotives, BN-MAC builds upon the grounds provided byhybrid low duty cycled MAC protocols.

In addition, BN-MAC eliminates idle listening byusing the ILC model to provide considerable energysaving. BN-MAC allots contention-free slot exchangedynamically to improve the network scalability evenunder a heavy traffic load. The several stationary andmobility scenarios that cover the health monitoring pro-cess are simulated. In the scenarios, we track the indoorpatients who are examined by local practitioners andremote practitioners. Furthermore, outdoor casualtiesand movements of victims are monitored and reportedto the control room to take immediate measures forreducing 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 knownlow duty cycle protocols (X-MAC, and also comparedwith hybrid and mobility MAC protocols), Z-MAC,MS-MAC, A-MAC, ADC-SMAC, and MobiSense overWSNs. Simulation results demonstrate that BN-MAChas achieved 12.5–37.5 % and 15–40.25 % higherthroughput than other competing MAC protocols inmobility and static scenarios, respectively.

BN-MAC has also outperformed other MAC proto-cols in latency and network coverage. BN-MAC gets4.00–183.33 % and 6.25–106.25 % less latency ascompared with other MAC protocols in mobility andstatic situations respectively. Network coverage of BN-MAC is higher (that is, approximately 99.1 %) ascompared 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, weargue that BN-MAC can also be good candidate formultiple applications to achieve faster delivery of datawith low latency. In the future, we plan to simulatedifferent WSN application areas using BN-MAC andother MAC protocols.

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Abdul Razaque is Editor-in-Chief for International Jour-na l f o r Eng inee r i ng andTechnology (IJET), Singa-pore and also associated withComputer Science and Engi-neering Department, Univer-sity of Bridgeport, USA. Heholds fellowship form HigherE d u c a t i o n C omm i s s i o n(HEC) Pakistan, and Com-mon Wealth, UK. He servedas Head of computer sciencedepartment in Model collegessetup Islamabad, Pakistan

from 2002 to 2009. He also led several projects as projectDirector 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 activeresearcher of wireless and Mobile communication (WMC) lab-oratory, UB, USA. Abdul Razaque has also been working asChair, 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 morethan dozen of highly reputed international conferences and alsodelivered his lectures as Keynote Speaker. His research inter-ests include the wireless sensor networks, design and develop-ment of learning environments, TCP/IP protocols, multimediaapplications and ambient intelligence.

Dr. Elleithy is the Associate VicePresident of Graduate Studies andResearch at the University ofBridgeport. He is a professor ofComputer Science and Engineer-ing. He has research interests arein 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 internationaljournals and conferences in hisareas of expertise. Dr. Elleithy has

more than 25 years of teaching experience. His teaching evaluations aredistinguished in all the universities he joined. He supervised hundreds ofsenior projects, MS theses and Ph.D. dissertations. He supervised severalPh.D. students. He developed and introduced many new undergraduate/graduate courses. He also developed new teaching / research laboratories inhis area of expertise. Dr. Elleithy is the editor or co-editor for 12 books bySpringer. He is a member of technical program committees of many interna-tional conferences as recognition of his research qualifications. He served as aguest editor for several International Journals. He was the chairman for theInternational Conference on Industrial Electronics, Technology & Automa-tion, IETA 2001, 19-21 December 2001, Cairo – Egypt. Also, he is theGeneral Chair of the 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013International Joint Conferences on Computer, Information, and SystemsSciences, and Engineering virtual conferences.

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