MAXIMIZING LIFETIME OF POWERLIMITED NETWORK WITH ACTIVE MINIMUM SPANNING TREE AGGREGATION

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1 Published in he Proceedings of he 7 h Parallel and Disribued Compuing and Sysems, MAXIMIZING LIFETIME OF POWERLIMITED NETWORK WITH ACTIVE MINIMUM SPANNING TREE AGGREGATION Javed I. Khan and Asrar U. Haque Inerneworking and Media Communicaions Research Laboraories Deparmen of Mah & Compuer Science, Ken Sae Universiy 233 MSB, Ken, OH javed@ken.edu and ahaque@ken.edu ABSTRACT Recenly proposed Harness is a sysem level group communicaionware ha enables a large number of nodes o exchange programmable nework informaion using various communicaion paerns. I offers boh scalabiliy and versailiy in message communicaion beween a large se of nodes conneced via any nework. In his paper we show how he scalable message aggregaion offered by he Harness can be used o se up a group communicaion pahway for power limied ad hoc wireless nework. While, he harness can compue various paerns of communicaion in a disribued fashion and guide daa as per he paern, we show ha minimum spanning ree wih acive message aggregaion is one of he mos power efficien modes. In his paper we show how dramaically i can improve he nework life ime. KEY WORDS Power aware, Ad hoc wireless, sensor compuing.inroducion In his paper we propose a novel mechanism o maximize lifeime of an adhoc wireless nework by ensuring minimum energy ransmission (MET) wih acive daa aggregaion. Even hough, Heinzelman [] e al and Jae- Hwan e al [2] argue ha minimum energy rouing is no a feasible soluion since is nework pariioning ime [3] decrease due o overuse of some nodes which fall on he minimum energy ransmission (MET) roue, however, we show, in his paper ha his does no always hold, specifically whenever afer aggregaing daa he size of he daa does no increase significanly. More over, if daa aggregaion is no feasible, harness can deploy oher schemes for maximize lifeime wihou much effor. An ad hoc nework has limied power resources being operaed by sand-alone baery. Moreover, here can be oher consrains associaed wih QoS provisions like delay and bandwidh. Hence, maximizing he lifeime of a node and he nework as a whole is a challenging issue since nodes migh be responsible for no only in merely ransmiing is own colleced daa bu also in forwarding ohers daa. Chen e al [4] menioned characerisics a good power saving echnique which includes insuring delay and bandwidh equivalen o ha provided by a backbone ad hoc nework formed by all he nodes in he nework. A sensor nework requires scalable messaging among large number of nodes ofen conneced in an adhoc power consrain nework. Hence, he underlying echnique should be such ha he overhead, due o coordinaion among nodes, is as low as possible. Oherwise, nodes will use up is scarce power resource more in coordinaion raher han in collecing and forwarding daa. Moreover, he overlying proocol should no be burdened by any energy saving mechanism [5]. When in power safe mode a node can be eiher in wakeup or in sleep sae. The wake up can again be subdivided ino ransmiing, receiving, lisening, forwarding and any combinaion of hese. Recen research shows ha foremos power usage occurs due o being awake raher han lisening or receiving [5]. So in any scheme i is imporan o minimize he ime of wakeup sage in order o maximize he lifeime of he ad hoc nework. Moreover, Heinzelman e al have argued ha power expended o ransmi daa exponenially varies wih disance [,6]. Hence, whenever possible rouing a packe o he desinaion node, which can be a gaeway node or a base saion, via inermediae nodes (i.e. using muli-hop raher han direc ransmission o desinaion) saves energy. In addiion, Kulik e al [7] argue ha compuaion in a node is cheaper han ransmiing and receiving daa. Therefore, node level daa aggregaion in harness can save energy o a grea exend. A he same ime, aggregaed daa gives more useful informaion. In his paper we are presening a novel approach of harness ha can be used o maximize sleep phase of nodes preserving maximum delay and bandwidh using minimum spanning ree. Harness uses cos funcions shown o be effecive in maximizing lifeime of an ad hoc nework. Furher, i can reduce amoun of daa o be ransmied all over he nework. In remaining paper, we discussion relaed works in secion 2 followed by harness concep in secion 3. Then secion 4 illusraes he operaion of he harness in powerlimied nework. Finally, before concluding, in secion 5

2 Published in he Proceedings of he 7 h Parallel and Disribued Compuing and Sysems, we share empirical resuls depicing he performance of he proposed harness sysem. 2.Relaed Work Some rouing algorihms [8,9,0] in mobile wireless neworks uses shores-pah rouing where he number of hops is he pah lengh. However, [,2,3,4,5] argue ha he opimum rouing in wireless and mobile neworking wih minimum energy consrain, is a variaion of spanning ree problem raher han shores pah. Chang and Tassiullas [2] uses soluions for maximum flow (for a single power level) and linear programming (for muliple power levels) o disribue wireless raffic among various pahs so ha baeries of he nodes drainou in a uniform way in order o maximize lifeime of a nework. Chalermek e al [5] uses greedy incremenal ree (GIT) for daa aggregaion and energy saving. In SPAN [4], coordinaors are eleced periodically by roaion, which are awake while oher non-coordinaor nodes remain in power saving mode. Chalermek e al [6] refers he problem of aggregaing daa wih minimum cos as se-cover problem. SPIN [7] uses mea-daa o find similariy beween daa in order o aggregae sensor daa. Our approach is similar o SPIN in he way daa each node needs o know abou is singe hop neighbors. However, in SPIN he here is no provision o pu a node ino sleep sae when i is no aking par in daa collecion or daa forwarding. Several researches in sensor neworking area are recenly invesigaing means for scalable daa aggregaion [7]. In [8] aggregaion is done based on Cener a Neares Source (CNS), Shores Pah Tree, or Greedy Incremenal Tree (GIT). PEGASIS [9] creaes a chain pah beween nework of sensors o gaher and fuse daa as daa passes over he chain. Then fused daa is sen o base saion by one of he randomly chosen sensors locaed in he chain. LEACH [] is a cluser-based proocol using daa fusion. Younis e al [20] used muliple clusers headed by nonenergy-consrain gaeway nodes for increasing lifeime of a sensor nework. Gaeway nodes se he roue along wih ransmission ime for oher nodes in he cluser. Feeny [2] proposes an asynchronous power save proocol based on sleep/wakeup cycle. [5] observes ha he foremos energy expendiure of a node is due o being awake. Hence, wheher a node is sending or receiving is no he dominan facor. Therefore, o maximize lifeime of a node i should spend in sleep sae as much as possible. Feeny [5] uses he facs ha if all nodes are awaken half of he ime hen here are overlapping awakeperiods irrespecive of phase difference beween any wo nodes. However, his principle of nodes being awake half of he cycle causes he limiaion ha even if he inerval needed o send daa from one node o oher node does no require half of he cycle sill nodes will be awake more hen half of he cycle causing wasage of scarce power resource. 3.Harness Approach We are exploring an experimenal dynamic mechanism for sae informaion polling and propagaion inside nework wih similar embedded informaion synhesizers, which seems o be boh scalable and versaile[2,22]. In his paper, we explain he applicaion of he harness in ad hoc nework o maximize is lifeime of ad hoc nework by using he minimal spanning ree. There is an added cos of compuaion. However, he power cos of compuaion is order of magniude less han he power cos of communicaion [5]. Thus, as we will show he sensor compuaion significanly reduces he power wase. 3.. Harness Archiecure The harness is in charge for iniiaing, propagaing and responding o a series of well-coordinaed messages beween he nodes in a nework. The harness once insalled in nework nodes, can ac in hree roles-- session iniiaor, sae synhesizer, and erminals. The iniiaor acs as he communicaion agen in he nework layer for he applicaion ha acually requires he informaion. The synhesizer propagaes he sae requess and processes he reurning saes from he erminals. The harness conrols he communicaion paern and hus deals wih he efficiency of messaging. Harness sysem acceps a se of plug-ins, which deermines he conen of hese messages, and how hey are propagaed and aggregaed a he juncion poins Messaging The harness sysem is designed o operae wih a novel reques-reply-updae messaging scheme. I has hree ypes of messages reques, reply and updae. The session iniiaor decides how ofen a reques is generaed. The reques messages are sen o he erminals if hey are immediaely conneced, or o synhesizers for furher downsream propagaion. A synhesizer upon receiving a reques, propagaes he query by generaing a new reques message o he down-sream nodes. However, a he same ime i migh also generae an immediae reply for he requesor. The replies from synhesizers may conain curren local sae and/or pas remoe saes. The reply migh also be used o acknowledge receip of a reques indicaing ha he receiver will generae reques furher down-sream. The erminal nodes send replies o heir respecive requesors. The erminal reply conains locally rerieved curren saes. The erminals or updae iniiaors iniiaes reurn rip of informaion by generaing updae messages. In he reurn rip of informaion, he synhesizer nodes aggregae he informaion and a each sage generae updae messages for heir requesors. Once a node receives all or specific number of updae messages

3 Published in he Proceedings of he 7 h Parallel and Disribued Compuing and Sysems, from is immediae down-sream nodes or on imeou, i updaes he nework local sae variables and generaes a new updae message. The updae message conains a synhesized summary of informaion calculaed from all is immediae downsream nodes. In essence, he requesreply phase allows collecion of local immediae saes. Toal Energy Spend (J) Minimum Transmission Energy Toal Energy Spend In New ork vs Hops w ih varying BF E elec =50nJ/bi,ε amp =00pJ/bi/m 2,k=2000,r=0m E+32 E+28 E+24 E+20 E+6 E+2 E Number of Hops BF=2 BF=8 BF=32 BF=64 BF=28 Figure : Toal Energy Spend for MTE The reply mechanism allows immediae probing ino curren local saes and pas synhesized remoe saes, while he updae message rerieves aggregaed laes remoe saes Sae Composiion Harness sysem acceps a se of six-plug-ins which are called reques generaor, reply generaor, updae generaor, reques aggregaor, reply aggregaor, and updae aggregaor. These modules ogeher deermine he conen of hese messages, and how hey are aggregaed a he juncion poins. They work via a virual slae. A copy of which is mainained in each of he nodes. The reques generaor specifies he reques message describing he fields i wans from he slae of is down-sream node. Reply aggregaor (or updae aggregaors) in a similar fashion is invoked each ime a reply (or updae) is received by he harness. They perform domain specific processing of he reply message fields and similarly updae heir own slae variables. The updae generaor sends he slae variables synhesized by he updae aggregaors o he upsream node. S S j j Toal Energy Spen (J) Figure 2: Toal Energy Spend for DT A he hear of he composiion abiliy is he ransfer funcions of he inermediae synhesizers. The reques and updae phase can be represened by equaions: r r i, j, j j, j, k = Φ( Ε( Q ), M, S ) and Q = F ( S ) Direc Transmission Toal Energy Spend In New ork vs Hops w ih varying BF E elec =50nJ/bi,ε amp =00pJ/bi/m 2,k=2000,r=0m E+32 E+28 E+24 E+20 E+6 E+2 E s, k j j = Ψ( F( P j ), M, S Number of Hops BF=2 BF=8 BF=32 BF=64 BF=28 ), and P s = E( S, i, j,_ j Here S is he local slae sae a even ime a node j, E r is he reques receiving filer (RRF), M is he local nework sae (such as MIB variable), F r is he reques forwarding filer (RFF). Q i,j,- is he arrived reques from paren i, o node j and Q -,j,k is he propagaed requess o children k. E s is he updae forwarding filer (UFF), F s is he updae receiving filer (URF). P -,j,k is he arrived updae from child k, and P i,j,- is he propagaed updae o paren i. While he filers deermined he informaion propagaion rules, composiion funcions Φ() and Ψ () ogeher deermine he message conen. 4.Harness for Maximizing Lifeime of Ad Hoc Nework There is a general rend o use eiher shores pah or variaions of spanning ree in adhoc sensor nework. The cos funcion differs depending on he crieria ha are sressed in a specific applicaion. In his paper we are assuming ha he nodes are saic during each phase of harness execuion. A command node [23] uses he daa colleced by he ad hoc nework. The cos funcion defined in [20] is used. The programmabiliy of he harness for MST is defind in [22]. Heinzelman e al showed ha even direced ransmission (DT) ouperforms MET []. Here, we show if daa aggregaion is possible a inermediae nodes hen MTE can maximize lifeime of ad hoc nework. Given E elec =50nJ/bi, ε amp =00 pj/bi/m 2, number of bis k=2000, ) 2

4 Published in he Proceedings of he 7 h Parallel and Disribued Compuing and Sysems, disance beween each node r=0m, and for simpliciy assuming a balanced ree wih branching facor, b, and deph, d, energy spend in MTE: Toal Energy Spend (J) E+32 E+28 E+24 E+20 E+6 E+2 E Shores Pah Transmission Toal Energy Spend In New ork vs Hops w ih varying BF E elec =50nJ/bi,ε amp =00pJ/bi/m 2,k=2000,r=0m Number of Hops BF=2 BF=8 BF=32 BF=64 BF=28 Figure 3: Toal Energy Spend for SPT E MTE = (b d+ )/(b-)*(e elec *k + ε amp * k*r 2 )+(b d+ )/(b- )*(E elec *k). Figures, 2, and 3 approximae he oal energy dissipaed for SPT, MET, and DT. MET has lowes dissipaed energy. Table - shows for differen probing dephs he amoun of dissipaed for branchingfacor of 28. Table : E MTE, E SPT, and E DT For BF=28 Deph MTE SPT DT E+ 3.35E+.3E E E E E E+9 3.8E E+24.47E E E E E+30 The cos of sending daa packe via a pah is he accumulaed cos of all he links raversed. Younis e al [20] proposed seven cos facors associaed wih a link while ha is used in ransmiing a packe opimizing delay which resrics overuse of any specific node o increase ime of nework pariioning. The cos facors aken ino consideraions are: communicaion cos (CF 0 ), energy sock (CF ), energy consumpion rae (CF 2 ), relay enabling cos (CF 3 ), sensing cos (CF 4 ), maximum connecion per relay (CF 5 ), propagaion delay (CF 6 ) and queuing cos (CF 7 ). Toal cos incurred raversing a link beween i and j is: c 0 *(disance ij ) l +c *f(energy j )+c 2 /T j +c 3 +c 4 +c 5 +c 6 *(disanc e ij )+c 7 *load. Here, c 0 is he weighing consan and l depends on environmen. Funcion f favors baery wih higher remaining power. c 2 is anoher weighing consan T j is he expeced ime for node j o reach minimum accepable energy hreshold. c 3 is he relaying cos. c 4 is he consan added if he node is sensing. c 5 conrols numbers of nodes associaed wih a node by adding exra cos when a node reaches pre-assigned number. c 6 favors closer node while he facor c 7 *load helps o avoid dropping or delaying daa packes. Whenever daa aggregaion is possible, MET (minimal energy ransmission) gives oal nework wide energy expended o be minimal in each round of daa collecion. Heinzelman e al and ohers argue [,20] ha minimum energy rouing is no a feasible soluion since is nework pariioning ime [3] decreases due o over use of some nodes which fall on he minimum energy ransmission (MET) roue. However, if daa can be aggregaed [7] hen daa is no forwarded for every daa packe received; raher only once in one updae phase a node forwards an aggregaed daa packe. Moreover, he power dissipaed from a node depends on how long a node is in wakeup sae. Using he cos funcion menioned, we can impose an upper bound on number of nodes associaed wih a node. Thus, overuse of any specific node does no occur even if a node falls in MTE roue. Hence, he nodes dissipae energy a a uniform rae improving neworkpariioning ime. 5.Simulaion Resuls We have performed saisical simulaion o projec he performance of he harness sysem under various consrains. The performance depends on he characerisics of he programmable componens (complexiy of he plug-ins, message size ec.) as well as on he nework (such as bandwidh, probing deph, number of nodes ec.) and plaform characerisics (link laency, messaging delay, ec) 5.. Link Laency Link laency is generally one of he mos disinguishing aspecs of a nework environmen for applicaion involving small daa. The firs simulaion resul, presened in Figure 4, shows he effec of link laency on he updae delay for sessions wih various probing dephs (d=4-7). In his simulaion we assume ha message size of firs reques message is 00 byes. Here he reques generaion, updae generaion and aggregaion is 2 ms each, he reques aggregaion, reply generaion and aggregaion is 0.5 ms each, and he bandwidh is 56 kbps. We assume he probabiliy of imeou is.0005 and average branching facor is 3 and imeou facor is 2τ where τ is he link laency. Updae delay, in seconds, is drawn in he verical axis while link laency, in seconds, is on he horizonal axis. As he graph shows, when he probing deph is relaively low, less han 5 ms, updae delay remains below sec. A large nework-- as large as of deph 7, can be probed wih his sysem wihin his ime bound if he link laency is small. The graph also shows ha a nework

5 Published in he Proceedings of he 7 h Parallel and Disribued Compuing and Sysems, wih larger laency can sill avoid he imeou and mainain performance scalabiliy if he deph is small. As he link delay becomes larger, he effec of inermediae imeous a deeper probes becomes prominen. As can be observed, in he exreme end, a deph 7 nework showing abou 300 ms delay can sill be probed in abou 0 second wih he sysem. Updae Delay (s) Updae Delay vs Link Laency for various Probing Deph Link Laency (s) Figure 4: Updae Delay 5.2. Scalabiliy The nex experimen depics scalabiliy of he harness. For his experimen we sudied he average ime o probe very large neworks. We assumed a nework of deph 7 and le he branching facor a each node vary from 2-9. Figure 5 plos he updae ime experienced by nework of various sizes. For comparison we also show he number of nodes ha can be probed for each case (he righ y axis and he bars show he number of nodes for each BF). We repeaed he simulaion for various link laencies. As can be seen abou a million nodes can be probed in abou 20 seconds. Wih 0 fold increase in he number of nodes probed he increase of updae delay is only second. Such scalabiliy and he associaed programmabiliy of he probing ask can make his echnology a poenial ool for acceleraing in collecing daa in sensor neworks. 6.Conclusions The key o he sysem s scalabiliy and versailiy are he embedded aggregaors. Since local sae dependen aggregaion is performed inside a nework, i reduces communicaion and hus enhances he sysem s scalabiliy. Aggregaors also provide he abiliy o compue nework relaive deep composie saisics, enhancing he versailiy of is abiliy o collec nework saes. Harness offers boh scalabiliy and versailiy in message communicaion beween a large se of nodes conneced via any nework. In his paper we show how he scalable message aggregaion offered by he Harness can be used o se up a group communicaion pahway for power limied ad hoc wireless nework. While, he harness can disribuedly compue various paerns of communicaion and guide daa as per he paern, he resuls show ha minimum spanning ree wih acive message aggregaion is one of he mos power efficien Updae Delay (s) Updae Delay and Number of Nodes vs Branching Facor Average Branching Facor Figure 5: Updae Delay and Number of Nodes modes. In his paper we show how dramaically i can improve he nework life ime. The scope of his paper does no permi discussion on implemenaion. I is non-rivial neverheless can be realized a user space as deamons. Embedded implemenaion can cu down some overhead and will be criical for sub-second range probing cycles. Implemenaion on some form of acive plaform can furher faciliae maers such as remoe deploymen, and seamless secured execuion of he plug-ins. The harness plug-ins require very limied form of programmabiliy compared o general acive ne proposal. The proposed harness is perhaps one of hose cases where provisioning even very low-grade programmabiliy can be highly rewarding. The harness increases sae visibiliy of nework. In effec i faciliaes high pay off smar opimizaions for numerous applicaions, which are no possible oday due o he black box naure of curren nework. Ineresingly, such a nework layer uiliy is no only crucial for building a new generaion of nework aware applicaions bu i is also vial for many of he curren problems of differen ypes of neworks, ineresingly, many of which are arguably arifacs of he opaciy of curren nework design. Currenly, we are exploring is acive nework based simulaion. The work is being suppored by he DARPA acive nework Research Gran F NODE NUMBER OF NODES

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