Mohammed Ali Hussain et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 2 (3), 2011,

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1 Energy Conservaion Techniques in Ad hoc Neworks Dr. Mohammed Ali Hussain 1, M.Ravi Sankar 2, Vijaya Kumar Volei 1,Y.Srinivasa Rao 3, Nalla Lovanjaneyulu 4 1 Dep.of Compuer Science & Engineering, Sri Sai Madhavi Insiue of Science & Technology, Rajahmundry, A.P., India. 2 Dep.of Compuer Science & Engineering, Vignan s Lara Insiue of Technology & Science, Gunur Dis., A.P., India. 3 Dep. of Compuer Science, Dravidian Universiy, Kuppam, Chioor Dis, A.P., India. 4 Dep.of Compuer Science, Akkineni Nageswara Rao College, Gudivada, Krishna Dis, A.P., India. Absrac - Energy is a limiing facor in he successful deploymen of ad hoc neworks since nodes are expeced o have lile poenial for recharging heir baeries. In his paper, we invesigae he energy coss of wireless communicaion and discuss he mechanisms used o reduce hese coss for communicaion in ad hoc neworks. We hen focus on specific MAC layer proocols can save energy by suspending he communicaion device during shor-erm idle periods in communicaion ha aim o reduce energy consumpion during boh acive communicaion and idle periods in communicaion. Keywords: Communicaion-ime energy, idle-ime energy, energy-aware rouing. I. INTRODUCTION The limied energy capaciy of mobile compuing devices has brough energy conservaion o he forefron of concerns for enabling mobile communicaions. This is a paricular concern for mobile ad hoc neworks where devices are expeced o be deployed for long periods of ime wih limied poenial for recharging baeries. Such expecaions demand he conservaion of energy in all componens of he mobile device o suppor improvemens in device lifeime [1] [2] [3]. In wireless neworks, here is a direc radeoff beween he amoun of daa an applicaion sends and he amoun of energy consumed by sending ha daa. Applicaion-level echniques can be used o reduce he amoun of daa o send, and so he amoun of energy consumed. However, once he applicaion decides o send some daa, i is up o he nework o ry o deliver i in an energy-efficien manner. To suppor energy-efficien communicaion in ad hoc neworks, i is necessary o consider energy consumpion a muliple layers in he nework proocol sack. A he nework layer, inelligen rouing proocols can minimize overhead and ensure he use of minimum energy roues [4] [5]. A he medium access conrol (MAC) layer, echniques can be used o reduce he energy consumed during daa ransmission and recepion [6] [7]. Addiionally, an inelligen MAC proocol can urn off he wireless communicaion device when he node is idle [8] [9]. Communicaion in ad hoc neworks necessarily drains he baeries of he paricipaing nodes, and evenually resuls in he failure of nodes due o lack of energy. Since he goal of an ad hoc nework is o suppor some desired communicaion, energy conservaion echniques mus consider he impac of specific node failures on effecive communicaion in he nework. A a high level, achieving he desired communicaion can be associaed wih a definiion of nework lifeime. Curren definiions of nework lifeime include: 1) he ime when he firs node failure occurs 2) he fracion of nodes wih non-zero energy as a funcion of ime [10] [11] [12], 3) he ime i akes he aggregae delivery rae o drop below a hreshold [13], or 4) he ime o a pariion in he nework. In he conex of any of hese definiions, i may also be useful o consider node prioriy in he definiion of lifeime. For example, he nework lifeime could be defined as he ime he firs high prioriy node fails. In general, one saic definiion of lifeime does no fi all neworks. In his paper, we presen approaches o energy conservaion ha minimize energy consumpion for communicaion in ad hoc neworks. However, hese approaches can be uned o suppor he desired communicaion and he definiion of nework lifeime as needed by he specific ad hoc nework. Energy conservaion can be achieved in one of wo ways: Saving energy during acive communicaion & Saving energy during idle imes in he communicaion. The firs arges he echniques used o suppor communicaion in an ad hoc nework and is ypically achieved hrough he use of energy-efficien MAC and rouing proocols. The second focuses on reducing he energy consumed when he node is idle and no paricipaing in communicaion by placing he node in a low-power sae. In his paper, we firs define he coss associaed wih communicaion in ad hoc neworks and hen discuss he use of communicaion-ime and idle-ime energy conservaion. II. ENERGY CONSUMPTION IN AD HOC NETWORKS In general here are hree componens o energy consumpion in ad hoc neworks. Firs, energy is consumed during he ransmission of individual packes. Second, energy is consumed while forwarding hose packes hrough he nework. And finally, energy is consumed by nodes ha are idle and no ransmiing or forwarding packes. To undersand how and when energy is consumed in ad hoc neworks, i is necessary o consider hese coss for daa packes forwarded hrough he nework and for conrol packes used o mainain he nework. To lay he groundwork for discussing energy efficien communicaion proocols in ad hoc neworks, we define hese coss for communicaion and inroduce energy-saving mechanisms used by many proocols. 1182

2 2.1 Poin-o-Poin Communicaion The basis for all communicaion in ad hoc neworks is he poin-o-poin communicaion beween wo nodes. A each node, communicaion impacs energy consumpion in wo ways. Firs, he wireless communicaion device consumes some base energy when i is acivaed and idle (see Table 1. Noe ha specificaions for mos curren wireless devices do no provide a differeniaion beween idle and receive coss). Second, he ac of ransmiing a packe from one node o anoher consumes energy a boh nodes. The ransmi power level a he sender (see Table 1). Recepion energy depends on he base recepion coss in he wireless card. The amoun of ime needed for he packe ransfer deermines he amoun of ime he card mus be acive, and so direcly deermines he energy consumed by he base card coss for boh ransmission and recepion. This ime is deermined by wo facors: he conrol overhead from packe ransmission and he rae a which he packe is ransmied. The per-packe conrol overhead is deermined by he mechanisms of he medium access conrol (MAC) proocol. Depending on he chosen proocol, some energy may be consumed due o channel access or conenion resoluion. For example, in IEEE [8], he sender ransmis an RTS (ready o send) message o inform he receiver of he sender s inenions. The receiver replies wih a CTS (clear o send) message o inform he sender ha he channel is available a he receiver. The energy consumed for conenion resoluion includes he ransmission and recepion of he wo messages. Addiionally, he nodes may spend some ime waiing unil he RTS can be sen and so consume energy lisening o he channel. In his chaper, we focus on he use of RTS/CTS-based proocols. While i has been shown ha such proocols may no be opimal for hroughpu [14], here is no widely acceped alernaive for communicaion in mobile ad hoc neworks. Card Cisco Airone 350 Socke Low Power SDIO Transmi Power Levels 100,50,30,20,5 mw Max 25 mw Table 1. Transmi power levels for seleced wireless cards wih power conrol capabiliies. Card Raes IEEE b.g 11,5.5,2,1 Mbps IEEE a.g 54,48,36,24,18,12,9,6 Mbps Mica2 Moes 12 Mbps Table 2. Transmi raes for seleced wireless card ypes. Once channel access and conenion resoluion have deermined ha a packe may be sen, many wireless nework cards provide muliple raes a which he daa can be ransmied, which deermines he ime needed o send he daa (See Table 2). The specific ransmission rae used is deermined by a number of facors, including he signal-onoise raio (SNR) and he arge reliabiliy of he ransmission [5] [15]. In general, he signal srengh a he receiver, which deermines he SNR, varies direcly wih he sender s ransmi power level and varies inversely wih he disance beween he sender and he receiver. This relaionship can be formulaed as: ReceiveSignal x TransmiPower/Disance n where he pah loss exponen n varies from 2 o 6 [16], alhough is mos commonly used as 2 or 4. For he receiver o correcly receive he packe, he SNR mus be over a cerain hreshold. As long as he receive SNR is mainained above his hreshold, he ransmi power level a he sender can be reduced, direcly reducing energy consumpion a he sender. The adapaion of he sender s ransmi power level is called power conrol and is he main ool used o conserve energy during acive communicaion. For he remainder of his chaper, we use power level o mean ransmi power level. Finally, energy is consumed o compensae for los packes, generally via some number of reransmissions of he los packes. While reliabiliy is generally he domain of he ranspor layer, he MAC layer in mos wireless devices compensaes for some packe failure by reransmiing he packe up o some reransmi limi number of imes before considering he packe los. For curren energy conserving proocols, his cos is only considered by proocols ha aim o avoid low qualiy channels and so avoid needing o reransmi packes. 2.2 End-o-End Communicaion End-o-end communicaion in ad hoc neworks is suppored by all nodes paricipaing in roue mainenance and daa forwarding. Therefore, nework wide energy consumpion includes any conrol overhead from rouing proocols, including roue seup, mainenance and recovery, as well as he impac of he chosen roues on he energy consumed a he inermediae nodes o forward daa o he receiver. The choice of a specific roue is deermined by he merics used in he rouing proocol. Iniial proocols use hop coun as a primary meric [17] [18], alhough delay ofen implicily impacs roue choices [19]. More recen proocols sugges he use of exended merics such as signal srengh [20], sabiliy [21] and load [22], all of which impac performance and so implicily impac energy consumpion [23]. Energy can also be used explicily o choose roues ha minimize energy consumpion [24] or avoid nodes wih limied energy resources [25]. Addiionally, when a roue breaks, i is essenial o use energy-efficien mechanisms o find a new roue, avoiding a reflooding of he nework whenever possible. A he nework layer, energy-efficien rouing proocols combine hese echniques wih power conrol for addiional energy conservaion during acive communicaion. III. ENERGY CONSERVATION APPROACHES Once all of hese coss are undersood, wo mechanisms affec energy consumpion: Communicaion Time Energy Conservaion and Energy Aware Rouing. If hese mechanisms are no used wisely, he overall effec could be an increase in energy consumpion or reduced communicaion in he nework. 3.1 Communicaion-Time Energy Conservaion The goal of communicaion-ime energy conservaion is o reduce he amoun of energy used by individual nodes as well as by he aggregaion of all nodes o ransmi daa hrough he ad hoc nework. Two componens deermine he cos of communicaion in he nework. Firs, direc node-o- 1183

3 node ransmissions consume energy based on he power level of he node, he amoun of daa sen and he rae a which i is sen. The amoun of daa is deermined by he applicaion and he rae is deermined by he characerisics of he communicaion channel. Alhough he ransmission rae can also be adaped by he sender [26], we do no consider such rae conrol in his chaper. However, he power level can be conrolled by he node o reduce energy consumpion. Such power conrol mus be performed in a careful manner since i can direcly affec he qualiy and quaniy of communicaion in he nework. Second, energy is consumed a every node ha forwards daa hrough he nework. Such coss can be minimized using energy-aware rouing proocols. This secion firs discusses he use of power conrol and is impac on communicaion in ad hoc neworks. We hen presen power conrol proocols and energy-aware rouing proocols ha aim o minimize energy consumpion for communicaion in he nework. 3.2 Energy-Aware Rouing Rouing proocols for ad hoc neworks generally use hop coun as he rouing meric, which does no necessarily minimize he energy o roue a packe [27]. Energy-aware rouing addresses his problem by finding energy-efficien roues for communicaion. A he nework layer, rouing algorihms should selec roues ha minimize he oal power needed o forward packes hrough he nework, so-called minimum energy rouing. However, minimum energy rouing may no be opimal from he poin of view of nework lifeime and long-erm conneciviy, leading o energy depleion of nodes along frequenly used roues and causing nework pariions. Therefore, rouing algorihms should evenly disribue forwarding duies among nodes o preven any one node from being overused (i.e., capaciyaware rouing). Hybrid proocols explore he combinaion of minimum energy rouing and capaciy-aware rouing o achieve energy efficien communicaion while mainaining nework lifeime. IV. MINIMUM ENERGY ROUTING The rouing meric used by minimum energy rouing is he per-hop minimum power level P (i, j) needed for node i o reach node j The oal power level for roue r, P r, is he sum of all power levels P (i, j) along he roue: D-1 P r = Σ P (ni, ni+1), where nodes n O and n D are he source and desinaion, respecively. Minimum oal ransmission power rouing (MTPR) [24] [28] finds a minimal power roue such ha: P s = minp r, rєa where A is he se of all possible roues. Based on a given minimum energy opology ha defines he maximum power level for all nodes, MTPR finds he minimum energy roues opimizing he power level for each hop. In conras, PARO [5] is a minimum energy rouing proocol ad hoc neworks ha discovers minimum energy roues on demand. PARO assumes ha all nodes are locaed wihin direc ransmission range of each oher and ha a source node iniially uses he hreshold power level o reach he desinaion. Each node capable of receiving he packe deermines if i should inervene and forward he packe o he desinaion iself o reduce he energy needed o ransmi he packe. Alhough, PARO is designed for one-hop ad hoc neworks, he opimizaion can be used by any pair of communicaing nodes, which allows exending PARO o muli-hop neworks. Given his definiion of minimal power rouing, boh MTPR and PARO favor roues wih more hops (i.e., more shorer hops vs. fewer longer hops). Since he power level, and so he ransmission energy consumpion, depends on disance (proporional o d n ), he energy consumed using many shor hops may be less han he energy consumed using fewer longer hops [5] [15].However, he more nodes involved in rouing, he greaer he end-o-end delay. Addiionally, a roue consising of more hops is likely o be unsable due o he higher probabiliy of he movemen or failure of inermediae nodes. Furhermore, boh proocols ignore he energy consumed a he relay nodes o receive he packes. Based on hese observaions, he roues found by MTPR and PARO may no be efficien. To overcome hese problems, he energy consumed when receiving he packe should be included ino he rouing meric [29] [30], which is likely o resul in he use of shorer roues. An even more accurae meric should include he oal energy consumed in reliably delivering he message o is desinaion (e.g., he energy cos of link-layer reransmissions). In paricular, i is essenial o avoid links wih relaively high error raes o reduce he energy consumed o reliably ransmi packes. 4.1 Capaciy-Aware Rouing Assuming all nodes in he nework are equally imporan, no node should be used for rouing more ofen han oher nodes. However, if many minimum energy roues all go hough a specific node, he baery of his node is drained quickly and evenually he node dies. Therefore, he remaining baery capaciy of a node should be used o define a rouing meric ha capures he expeced lifeime of a node, and so, he lifeime of he nework. Given c i, he baery capaciy of node i a he funcion f i (c i) capures he cos o forward packes for a node i This cos can be defined as he inverse of he remaining baery capaciy and modeled as [25] [31]: 1 f i (c i ) =, C i The baery cos meric for roue r a ime, R r, can hen be deermined as: R r = maxf i (c i ), iєr Therefore, he desired capaciy-aware roue s, where A is he se of all possible roues saisfies: R s = min { R r r Є A}, I mus be noed ha he choice of 1 f i (c i ) = _, C i does no consider he effec of he raffic load on he node baery capaciy. To his end, drain rae is proposed as a meric o measure he energy dissipaion rae a a given node 1184

4 [32]. The Minimum Drain Rae (MDR) algorihm deermines he baery cos meric of roue r, R r, as: R r = min c i, iєr DrainRae i and capaciy-aware roue saisfies: R s = max { R r r Є A }, Incorporaing he baery cos ino he rouing proocol prevens a node from being overused. However, here is no guaranee ha minimum energy roues are found by he rouing proocol. Therefore, capaciy-aware rouing may consume more energy o roue raffic, which can reduce he lifeime of he nework. V. HYBRID SOLUTIONS (MINIMUM ENERGY/MAXIMUM CAPACITY) Hybrid soluions ry o find minimum energy roues while maximizing he lifeime of he nework. To his end, Condiional Max-Min Baery Capaciy Rouing (CMMBCR) [29] follows minimum energy rouing as long as some roues beween he source and he desinaion have sufficien remaining baery capaciy (i.e., above a cerain hreshold). The baery capaciy of a roue r, R c r, is: R r c = minc i, iєr and minimum energy rouing is followed as long as: R c r δ for any r Є A, If all roues are below he energy hreshold capaciy-aware rouing is used o deermine he roue o choose. The benefi of such an approach comes from he fac ha capaciy-aware rouing is only used when criical nodes in he nework have low baery levels. The efficiency of he CMMBCR depends on he energy hreshold δ However, i is no sraighforward how o deermine The Condiional Minimum Drain Rae (CMDR) proocol [32] limis roue choices for MTPR o roues only conaining nodes wih a lifeime higher han a given hreshold (i.e., c i γ,) DrainRae i If no such roue exiss, CMDR swiches o he MDR scheme. To overcome he difficuly of selecing a value for δ in CMMBCR, CMDR uses γ which is an absolue ime value based on he curren raffic condiions. The max-min Z. P min algorihm [15] minimizes energy consumpion P min, and maximizes he minimum residual energy of he nodes. If he minimum energy roue has energy consumpion roues wih higher minimum residual energy can be used as long as he energy consumpion is less han Z. P min he Z-facor, similar o CMDR, is compued based on he minimum lifeime of he nodes. All hree of he above algorihms find minimum energy roues when nodes have sufficien residual energy and swich o capaciy-aware rouing as he baery capaciy of he nodes decreases or he lifeime decreases beyond a predefined hreshold. In conras, he cos meric of a link (i,j) can be chosen o represen boh he ransmission power cos of he link and he iniial and residual energy of node i [4] [31]. Specifically, link cos, can be compued as [4]: Cos i,j = eα(c i) -β (c o i) θ, Equaion.1 where is he energy used o ransmi and receive on he link, c i, is he curren capaciy of node i,c o i is he iniial capaciy of node i and and γ, β and θ are non-negaive weighs. The link cos funcion compued in his fashion emphasizes he energy expendiure erm when nodes have high baery capaciy. As he residual energy of he nodes decreases, he baery capaciy erm is more emphasized. To avoid depleion of nodes along common minimum energy roues, anoher approach is o occasionally use subopimal roues [33]. Basically, possible roues beween a source and desinaion are used wih a probabiliy based on he energy meric in Equaion.1 VI. IDLE-TIME ENERGY CONSERVATION Effecive idle-ime energy conservaion necessarily spans all layers of he communicaion proocol sack. Each layer has access o differen ypes of informaion abou he communicaion in he nework, and hus, uses differen mechanisms o suppor energy conservaion. MAC layer proocols can save energy by suspending he communicaion device during shor-erm idle periods in communicaion (i.e., operae in a power-save mode). Such fine-grained conrol requires inegraed knowledge of ransiions beween device suspend and resume in he MAC proocol o insure he communicaing nodes are boh awake. 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Energy aware rouing for low energy ad hoc sensor neworks. In IEEE Wireless Communicaions of Neworking Conference (WCNC), AUTHORS PROFILE Dr. Mohammed Ali Hussain M.Tech., Ph.D., He received his Ph.D. degree in Compuer Science from Magadh Universiy, India in He is doing Pos- Docoral degree in Compuer Science & Engineering from Acharya Nagarjuna Universiy, Gunur, Andhra Pradesh, India. He is currenly working as Professor & Head, Deparmen of CSE & IT a Sri Sai Madhavi Insiue of Science & Technology, Mallampudi, Rajahmundry, Andhra Pradesh, India. His research ineress are Web Designing, E-Commerce and Wireless Neworks. He has published large number of papers in differen Naional & Inernaional Conferences and Inernaional journals. He also served as a Program Commiee (PC) Member for many Inernaional Conferences. He is a presen Edior in Chief for Inernaional Journal of Research and Reviews in Ad hoc Neworks (IJRRAN) and Ediorial Board Member for Inernaional Journal of Compuer Technology and Applicaions (IJCTA), Inernaional Journal of Compuer Trends and Technology (IJCTT), Inernaional Journal of Sensor Neworks and Daa Communicaions (IJSNDC), Journal of Engineering and Compuer Innovaions (JECI) and Technical reviewer of many Inernaional journals. He is a member of Inernaional Associaion of Engineers, IACSIT and ISTE. M Ravi Sankar received he M.Tech degree in Compuer Science & Engineering in He is currenly pursuing Ph.D. in Compuer Science & Engineering a Acharya Nagarjuna Universiy, Gunur Disric., A.P., India. He has 11 plus years of experience in hree repued Engineering colleges affiliaed o JNTU. He has discharged duies as Head of Deparmen for MCA in LBRCE, Mylavaram, A.P., India. Since July 2010, he has been wih VIGNAN's LARA Insiue of Technology & Science, where he is currenly an Associae professor in he deparmen of Compuer Science & Engineering. He is a Life Member of ISTE. Vijaya Kumar Volei received M.Tech degree in Compuer Science & Engineering from JNTU(H),India in he year He is currenly an Associae Professor in he Deparmen of Compuer Science & Engineering in Sri Sai Madhavi Insiue of Science & Technology, Rajahmundry, A.P., India. He had career in IT Indusry for 4 years and serving various Engineering Insiues for he las 5 years. His ineresed areas are Nework Securiy and Daa Mining. Y. Srinivasa Rao M.Tech(I.T) from Vignan Universiy, India and a presen he is pursuing his Ph.D. in Compuer Science a Dravidian Universiy, Kuppam under he guidance of Dr. Md. Ali Hussain. His research ineress are Wireless Neworks wih specializaion in Qualiy of Service (QoS) Wireless MAC Proocol using Nework Load Adapaion. His Area of Ineres are Wireless Neworks and Mobile Neworks. Nalla Lovanjaneyulu received MCA degree from Allahabad Agriculural Insiue Deemed Universiy. He received M.Phil in Compuer Science from Annamalai Universiy. He is pursuing Ph.D. Compuer Science from Dravidian Univerisy, Kuppam, Chioor Dis. A.P., India. He is currenly working as Lecurer in Deparmen of Compuer Science in Akkineni Nageswara Rao College, Gudivada, Krishna Dis, A.P., India. His Area of Ineres are Communicaion Neworks, Wireless LANs & Ad-Hoc Neworks. 1186