126 Int. J. Ad Hoc and Ubiquitous Computing, Vol. 1, No. 3, Djamel Djenouri*

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1 126 Int. J. Ad Hoc and Ubqutous Coputng, Vol. 1, No. 3, 2006 New power-aware routng protocol for oble ad hoc networks Djael Djenour* Basc Software Laboratory, CERIST Center of Research, Algers, Algera E-al: *Correspondng author Nadjb Badache LSI, Coputer Scence Departent, USTHB Unversty, Algers, Algera E-al: Abstract: Snce devces used n wreless oble ad hoc networks are generally suppled wth lted autonoous resources, energy conservaton s one of the ost sgnfcant aspects n these networks. Recent studes show that the energy consued for routng data-packets n oble ad hoc networks can be sgnfcantly reduced copared wth the n-hop full-power routng protocols. One of the prosng echanss proposed n lterature to reduce the energy consupton s the transsson power control. In ths paper, we defne new routng etrcs to strke a balance between the requred power nsaton and batteres freshness consderaton. We also defne a new technque whch allows the dstrbuton of the routng task over nodes. Usng these etrcs and technques we derve fro DSR [2] a new power-aware and power-effcent routng protocol, whose perforance s analysed by sulaton n dfferent stuatons of oblty and network load. Keywords: wreless oble ad hoc network; routng protocol; power awareness; energy effcency; GloMoS sulaton. Reference to ths paper should be ade as follows: Djenour, D. and Badache, N. (2006) New power-aware routng protocol for oble ad hoc networks, Int. J. Ad Hoc and Ubqutous Coputng, Vol. 1, No. 3, pp Bographcal notes: Djael Djenour obtaned hs Engneerng Degree n Coputer Scence and hs Master s Degree n Coputer Scence fro the Unversty of Scence and Technology USTHB (Algers), respectvely n 2001 and He s currently a PhD student at USTHB and a Research Assstant at the CERIST centre of research n Algers. He works anly on ad hoc networkng, especally on the followng topcs: Securty, Power Manageent, Routng Protocols, MAC Protocols. Nadjb Badache obtaned the Engneer Degree n coputer scence fro Unversty of Constantne, Algera n 1978, and the Master Degree fro USTHB Unversty n In 1995, he joned The ADP research group at the IRISA nsttute n France, where he prepared a PhD Thess on causal orderng and fault tolerance n oble envronent. He obtaned hs PhD fro USTHB n He s currently a Professor at the coputer scence departent of USTHB, where he s also the head of the LSI laboratory. He s author of any papers, and he supervsed any thess and research projects. Hs research nterests are dstrbuted oble systes, oble ad hoc networks and securty. 1 Introducton For oblty and portablty constrants, devces used n oble ad hoc networks are generally suppled wth lghtweght, lted batteres. Moreover, each node acts as a router and relays packets ntated fro other nodes, whch adds extra tasks to these devces n addton to the executons of users applcatons. Therefore, power consupton becoes a very portant ssue n ths new envronent. Recent studes show that energy effcent routng protocols for ad hoc networks ay be desgned fro the exstng protocols, by addng new echanss and Copyrght 2006 Inderscence Enterprses Ltd.

2 New power-aware routng protocol for oble ad hoc networks 127 technques (Dosh and Brown, 2002b; Sngh et al., 1998), and that the reactve approach s ore adaptve than the proactve one (Brown et al., 2001; Badache et al., 2003). One of the prosng echanss proposed for reducng the energy consupton s the transsson power control, whch conssts of usng adaptve transsson powers accordng to the dstance separatng the transtter and the recever, nstead of usng a fxed full power. Dosh and Brown (2002a) have proposed an pleentaton of ths echans, where they have odfed DSR (Dynac Source Routng) (Johnson and Maltz, 1996) to obtan new power effcent versons. In Sngh et al. (1998), Sngh et al. have proposed general battery-aware etrcs whch can be used by routng protocols. However, all these etrcs do not take advantage of the power control usage. On the other hand, all DSR versons proposed n Dosh and Brown (2002a) do not consder nodes batteres states. Instead, routes are chosen by nsng the requred energy on the avalable routes, regardless of ether batteres states of nodes on the routes or states of the councaton channels, whch ay lead to an overuse of a nodes subset. Consequently, batteres of these nodes wll lose rapdly ther capactes before the others, resultng n a possble network partton. To ensure a long lfe to all nodes and to avod the network partton, we should take the batteres states nto account. We should also dstrbute the routng task over nodes, to avod overusng soe of the. In ths paper, we defne new etrcs ang at resolvng the tradeoff between the batteres freshness and the total requred power nsaton when selectng routes and defnng ther optalty. We also defne a new technque whch allows us to take advantage of all avalable routes, and dsperses the routng task over several nodes. Usng these etrcs and ths technque, we derve fro DSR a new power-aware and effcent protocol. The reander of ths paper s organsed as follows: we overvew n the Secton 2 the current route selecton strateges, focusng on ther drawbacks, followed n the Secton 3 by a presentaton of the new etrcs and the new technque we propose. Secton 4 s a presentaton of our protocol derved fro DSR. Sectons 5 and 6 are devoted to our protocol s perforance evaluaton. In the forer, we descrbe the sulaton envronent and n the latter, the results of our sulaton are presented. Fnally, Secton 7 concludes the paper and suarses the future work. strategy s that t does not take nto account batteres states, whch ght result n an overuse of a nodes subset as shown n the followng exaple: We consder the statonary network represented n Fgure 1, where weghts represent the powers requred on the lnks. We assue there s a sesson between node s and node D 0, and another between s and D 1. And we assue that P 0 + P 2 < P 3 + P A. When usng ths strategy, node I 0 wll be used to route packets both for D 0 and D l, whle node I 1 wll not be used at all. Ths way, node I 0 ay lose ts battery capacty before the others; then, a soon network partton can take place (node D 0 wll not be reachable anyore). Ths partton would be avoded f node I 1 was used. Fgure 1 Statonary network 2.2 Routes contanng the freshest batteres The a of ths strategy s to select routes that contan the freshest batteres. For ths purpose, a cost representng the battery state s assocated wth each node and the route that nses the total su of these costs s consdered as the ost optal. In Sngh et al. (1998), a defnton of the cost functon proportonal to the battery voltage has been proposed. The cost of node s gven by: F (z ) = 1/(1 g(z )). Where z denotes the easured voltage (that gves a good ndcaton of the energy used thus far) and g(z ) (0 < g(z ) < 1) s the noralsed power (n percentage) consued for the voltage z. For a gven value of z, g(z ) can be obtaned fro the dscharge curve that features the battery (Gold, 1997). The ajor drawback of such a strategy s that t does not consder lnks costs, especally when batteres states are close to each other. In ths case, the shortest routes are selected regardless of ther costs, causng portant waste of energy. Ths etrc nses the dfference n energy consupton between nodes, but does not ensure long lfe for the batteres. In other words, t ensures that nodes rean alve together, but not for the longest perod. 2 Current route selecton strateges 2.1 Mnsng the total requred power Ths strategy needs the power control technque to be eployed, ts purpose s to nse the total requred power when sendng each packet. When usng the power control technque, a cost ay be assocated to each lnk as the power requred on t; the optal route s the one that nses the su of these costs. The proble wth ths 3 New power-aware routng strategy 3.1 Metrcs As llustrated n the prevous secton, each of the two power-aware strateges has a drawback. We thnk that both lnks costs and batteres states should be taken nto account when selectng routes. Therefore, a tradeoff between the batteres freshness and the requred power nsaton

3 128 D. Djenour and N. Badache should be overcoe when selectng routes. For ths purpose, we defne new etrcs on whch the routng s based. Frst, we assue wthout loss of generalty that the network s statonary, and we try to resolve the proble n a centralsed anner at a gven te t. Let (S, L, P, E) be a quadruple such as: S: Vertces set L: Arcs set, L = {(s, s j )/s S and s j S}, such that (S, L) s the graph representng the network topology at the te t. P: A functon whch assocates to each eleent (s, s j ) of L, a value n R (the real nubers set), called the weght of (s, s j ). E: A functon whch assocates to each eleent s fro S, a value n R, called the state of s. On a gven route C = I 0, I 1,, I n 1 we propose the followng etrc: n 2 M = α E( I ) + β P( I, I ). (1) c + 1 = 0 where α s the states rate, β s the lnks rate (α, β [0,1]), such that α + β = 1. The a s to choose the route C whch nses M c. The functon E should reflect batteres states, whle the functon P should reflect transsson power costs over lnks. Let E be the followng functon: Es ( ) = 1/(1 eng( s)), (2) where energy (s ) [0,1] s the rate of the energy consued by node s j. Ths functon s onotone n the nterval [0,1],.e., ore the node s consupton rate ncreases, the ore ts state value ncreases. For P, we propose the followng functon: Ps (, s) = 1/(1 PowRate( s, s)). (3) Such that, j j Pow( s, sj) PowRate( s, sj) =, MaxPow( s ) where Pow(s, s j ) [0,1] s the requred power over the lnk (s, s j ), MaxPow(s ) s the full power of the node s (the power that allows t to cover ts power range). Note that P ncreases wth PowerRate. When usng ths etrc (M c ), the ore α ncreases, the ore the routes contanng fresh batteres are favoured, and the ore t decreases, the ore routes that nse the total transsson energy cost are favoured. Hence, we propose the followng strategy. The ore the dfference between the nodes batteres states ncreases, the ore α should be ncreased. And the ore the nodes batteres states becoe closer, the ore t should be decreased. Ths way, batteres states are constantly well balanced whle consderng the total power when transttng data packets. Defnton 1: We defne the dfference between batteres states at the te t by: EngDff = ax( eng( s )) n( eng( s )). S S It s the dfference between the axu rate of the energy consued by the network s nodes and the nu one, note that Engdff [0,1]. It reans to fnd an ncreasng functon for α: α(engdff):[0,1] [0,1]. We propose the followng functons, where α 0 s an ntal value: F1 = (1 α ) EngDff + α 0 0 F2 = (1 α ) EngDff + α The two functons are onotone ncreasng n the nterval [0,1], but they dffer fro each other n ther way of ncreasng. The latter s ore ncreasng n the nterval [0,1] than the frst one. What s the way of ncreasng that gves ore effcency? Evaluatng the perforance of these two functons n a further secton ay provde an answer to ths queston. Usng equatons (1 3), we rewrte the etrc Opt c representng the optalty of the route C = I 0, I 1,, I n 1 connectng node I 0 to node I n 1 as follows: n 2 α 1 α Opt c = +, 1 eng( I ) 1 Pow( I, I ) / MaxPow( I ) (4) = where: α = F1 or α = F2. The optal path corresponds to the nu value of Opt c. At te t, Pow(s, s j ) value s known for each lnk, the value of eng(s ) s known for each node, thus both EngDff and α can be coputed. Thus, the optal path connectng any par of nodes at the nstant t can be coputed (usng Djkstra algorth for nstance). In te, values of eng(s ) change, the coputaton of paraeters and routes ust consequently be done agan. Usng ths approach, node I 0 of the prevous exaple wll not be used all along the sessons between node s and nodes D 0 and D 1. Because when I 0 starts consung ts battery capacty for routng packets, E(I 0 ) ncreases, and the route (s, I 0, D 1 ) becoes less optal than (s, I 1, D 1 ), hence the last one wll be used for routng packets to D 1. Ths way, a soon network partton s avoded. Thus far we have proposed new etrcs that have been explaned usng a centralsed soluton. It s obvous that n practce, no node can have an accurate vew of the network topology. Stll, these etrcs can be eployed by any dstrbuted routng protocol, as we wll see n the next secton. 3.2 New data dspersal technque Many reactve routng protocols, such as DSR (Johnson and Maltz, 1996), are ultroutes,.e., after a route dscovery, any routes ay be found. But n DSR, just one route (consdered to be the optal) aong the avalable ones s chosen. All the others are consdered only as alternatves, and they are not used untl the optal route fals. Data dspersal had been frst proposed n dstrbuted systes for securty and load balancng as by Rabn (1989). In Rabn s algorth, largely used n

4 New power-aware routng protocol for oble ad hoc networks 129 lterature, addtonal redundancy s added to data packets and the sae aount of data s sent on each route. We thnk that ths strategy could be projected to our context, and eployed n order to explot a axu nuber of the avalable routes, thereby dspersng data load over a axu nuber of nodes. But route optalty should be consdered n such a way to transt ore packets on the ost optal routes. To apply data dspersal whle consderng routes optalty, we suggest a echans analogous to the one used by schedulers of operatng systes (such as UNIX). Routes are analogous to queues, packets to processes, and the routng protocol to the scheduler. Let nbrpaths be the nuber of routes avalable that relay a source node s to a destnaton D. We assue that these routes are ordered accordng to ther optalty (route 0 s the ost optal one). And let nbrpackets be the nuber of packets to be sent, stored n a buffer. In order to use the axu nuber of routes and to use optal routes ore than the less optal ones, we propose to transt on each route, the followng nuber of packets: nbrpaths 1 2 nbrpaquets nbrpaquets = nbrpaths, (5) 2 1 where [] denotes the upper nteger part. Thereby, on the frst route, node s sends the: 2 nbrpaths 1 nbrpaquets nbrpaths 2 1 frst packets. On the next, t sends the followng: 2 nbrpaths 2 nbrpaquets nbrpaths 2 1 and so on, tll all the packets are transtted. Ths way alost all the routes wll be used and the nuber of packets sent on each route s approxately twce as uch as the nuber of packets sent on the next route ( + 1). 4 The protocol The protocol we propose s derved fro DSR whch s a dstrbuted reactve protocol based on the source routng concept. In ths secton, we frst gve an overvew on DSR; then we wll present the an odfcatons that we have added to ths protocol. In the thrd subsecton, we wll present our protocol n ore detal and dscuss the operaton that we have added. 4.1 DSR (Dynac Source Routng) DSR (Johnson and Maltz, 1996) s a reactve protocol based on the source route approach. The prncple of ths approach s that the whole route s chosen by the source, and s put wthn the header of each data packet transtted, n the IP optons. Each node keeps n ts cache, the source routes that t learns. When t needs to send a packet, t frst checks ts cache; f t fnds a route to the correspondng destnaton then t uses t, otherwse t launches a route dscovery by broadcastng a request (RREQ) packet through the network. When recevng the RREQ, a node seeks a route n ts cache for the RREQ s destnaton; f t fnds such a route, t sends a route reply (RREP) packet to the source, and f no approprate route exsts, then t adds ts address to the request packet and contnues the broadcastng. When a node detects a route falure, t sends a route error (RER) packet to the source that uses ths lnk, then ths one wll ether choose another route or apply agan, the route dscovery process f t has no other route to the destnaton n ts cache. A detaled presentaton of DSR s avalable n Johnson and Maltz (1996). 4.2 Man odfcatons We anly add to DSR, the followng: Ipleentaton of the power control technque. The requred powers are coputed on each lnk durng the route dscovery procedure, as n Dosh and Brown (2002a). On each lnk, the transtter of a RREQ puts the transsson power n the RREQ s header, then the recever retreves ths value that t uses along wth the recepton power whch t gets fro ts rado, and the approprate envronent s propagaton odel, to copute the requred power. Consder energy state. For ths purpose, we assue that each node s able to deterne ts consued energy rate. Ths can be acheved by pleentng a botto level echans, allowng nodes to deterne ther battery voltage. When gettng ts battery voltage, the node can deduce ts energy consued rate fro the battery dscharge curve (Brown et al., 2001; Gold, 1997). Moreover, each node should have a vew on the energy states of the other nodes. To ensure ths, we suggest that t should pggyback the energy state nforaton nto control packets, especally nto reply packets and E_state packets that we present hereafter. Addng E_state packet. Each node has a global vew of other nodes energy states. To get a better vew (especally about neghbours), we propose that each node broadcasts n ts neghbourhood, a specal packet called E_state, whch carres the current energy state of the sender. Ths sall packet s sent each te the energy consued rate changes wth a certan rate. For nstance, f we fx ths rate at 25%, each node sends 3 packets; the frst upon consung 25%, the second upon consung 50%, and the last one upon consung 75% of the total battery capacty. Ths adds an overhead of coplexty 3 n packets transsson durng the whole network lfe, where n s the nodes nuber. Generally speakng, f the rate s 1/x then the cost s (x 1) n packets transsson. We note that t

5 130 D. Djenour and N. Badache ay be nterestng to ncrease ths rate when batteres capactes decrease, because the energy state nforaton becoes ore and ore portant when the batteres lose ther capactes. But ncreasng ths rate, however, requres ore overhead and poses a tradeoff between the nforaton freshness and the overhead. Routes are stored n each node s cache accordng to our etrc Opt c presented prevously (forula 4). Packets forat odfcaton. In order to pleent our technque and etrcs, we add soe odfcatons to packets forat. Manly, each feld of the record part should contan, n addton to the IP address of a node, the current energy state of the node (E ), and the power to use on the lnk relayng t to the next hope. Addng the possblty to dscover ore routes. When a node receves a request that t has already receved, contrary to DSR, t ay contnue relayng t f ths request has followed a dfferent route fro the one followed by the frst receved request. Ths depends on the ALLROUTES flag that we add to the request. Although ths technque allows dscoverng uch ore routes than the standard DSR, t results n ore overhead, especally when connectvty ncreases. We wll test ths technque s perforance n the next secton. Route antenance odfcaton. Moblty ay ake a power used on a lnk nsuffcent, wthout causng the lnk falure. Ths occurs when nodes forng the lnk ove away fro each other, whle keepng the dstance between the less than ther power range. Therefore, a echans allowng dscovery of new sutable power s requred. We suggest proceedng as follows: When a packet fals to pass through a lnk and the MAC layer protocol of the sender turns t back to the routng protocol, the last protocol tres to resend the packet usng the full power, by pagng t back to what we call a drected request, a specal request packet whch dffers fro the ordnary request n the fact that t s sent to a unque node (the upstrea node of the approprate lnk), nstead of beng propagated. Moreover, the sender updates ts varables n order to teporally avod sendng packets va ths lnk. If the upstrea receves the packet, t reples wth a antenance reply packet. Otherwse, after a gven teout, the sender s MAC protocol turns back the drected request to ts routng protocol, then ths latter detects the lnk falure. To dstrbute the routng load over a axu nuber of nodes, and to beneft fro the avalable routes n the cache, we propose to use our data dspersal technque presented prevously. 4.3 Protocol descrpton and verfcaton In the followng, we descrbe the algorth executed by each node, and we analyse and verfy the operatons added to DSR, relyng on the correctness and the stablty of DSR. Our protocol can be suarsed by the followng events: Havng packets to send Ths local event s trggered when a node has one or ore data packets to send to any destnaton. If the node has any routes to the destnaton then t can send the packets, usng our data dspersal technque prevously presented. However, f the node has no route to the approprate destnaton, then t launches a route request (f no request to the destnaton has recently been launched). When the node fnds no route to the destnaton, t reacts exactly as n DSR. The only dfference appears when the node has ore than one route to the destnaton. In ths case t uses alost all these routes, contrary to DSR where just the shortest one s used. Ths s equvalent to the data dspersal technque (Rabn, 1989) already proposed for securty and load balancng as n dstrbuted systes, but our protocol, however, does not add any redundancy, and consders routes optalty when selectng the nuber of packets to be transtted on each route. The stablty of ths operaton depends on the stablty of each transsson on each route, whch s dentcal to DSR. Note that dspersng data packets causes no proble, snce data n packets based networks (to whch ad hoc networks belong) usually follow dfferent routes and the upper protocols (TCP/UDP) reorder the. Recevng a route request packet (RREQ) When a node receves a request packet, and f t s a ater of a drected request, then t coputes the new power requred and sends a reply. Otherwse, f the request s an ordnary one and the node s not ts fnal destnaton, then t coputes the requred power on the prevous lnk, adds ths coputed value along wth ts current battery state to the RREQ, and contnues ts broadcast as n DSR. If the node s the RREQ s destnaton, t sends back a RREP exactly lke n DSR; t just adds to each feld of the source route dscovered, the power-aware nforaton coputed and collected along the route dscovery process. The drected request does not exst n the standard DSR; we have added t n order to antan unbroken lnks on whch the power used becoes nsuffcent because of nodes oblty. Ths operaton does not affect the protocol correctness; when sendng a drected. RREQ, f the destnaton s stll n the sender s power range, then t reples and provdes the new requred power, thereby the forwardng contnues lke n DSR. On the other hand, f the lnk s broken then the sender wll not receve any reply, and after a teout t wll react for the lnk broken detecton as n DSR. However, the pact of these operatons s the possble rse of the latency that wll be nvestgated later n the sulaton. The power-aware nforaton addton nto RREQs ncreases the overhead, whch causes ore energy consupton, but provdes portant energy gan later when transttng data packets. The sulaton results whch we present n the

6 New power-aware routng protocol for oble ad hoc networks 131 next secton wll check whether the gan s ore portant than the cost. Recevng a route reply packet (RREP) When a node receves a antenance reply packet, t updates ts cache, resends awatng packets for ths antenance, and sends a route error back to each node whch s usng the antaned lnk. Otherwse, f the reply type s not antenance, the recever reacts as n DSR. Resendng awatng packets s analogous to salvagng packets after a lnk break n the standard DSR (Johnson and Maltz, 1996). The only dfference s that when salvagng after a lnk break, the packets wll be transtted on a new dscovered route, but n our case they wll be transtted on the sae route usng a new up to date power on the current hop. Sendng a route error packet to nodes currently usng the antaned lnk has the purpose of nforng these nodes about the actual requred power on the lnk n queston, whch would be useful at these node for routes selecton. The only pact of ths procedure s the ncreasng overhead. Recevng a data packet to forward Ths event s trggered when a node receves a data packet for whch t s not ts fnal destnaton but an nteredate router. If the next hop of the routng header was recently broken then the node sends an error packet to the source. If the lnk s watng for antenance then the node puts the packet n a watng queue. Otherwse, f the lnk s supposed to be relable, the router contnues forwardng the packet lke n DSR, but usng the power specfed n the source header nstead of usng the full power. The only consderable dfference fro DSR s when the lnk s watng for antenance; n ths case packets are delayed. All the possble subsequent operatons n ths case have been already dscussed. Recevng a lnk error essage It s a local event trggered by the MAC protocol when the node fals to relay a packet to ts next hop. If the packet returned s a drected request, then the node detects a lnk falure. Otherwse, t supposes that the power used over the lnk s not suffcent anyore, so t tres to antan ths lnk by sendng a drected request. Recevng a route error packet (RER) Error packets can be launched ether because of a lnk falure or because the power requred on a lnk changes, accordng to the cost feld value, a feld we add to the RER packet. If the cost feld value s, then t s a atter of a lnk falure and the node reacts as n DSR. Otherwse, t just updates ts cache by takng nto consderaton the new power value and t norally contnues forwardng the RER packet. Sgnfcant change of energy state Ths local event takes place each te the energy state of the node changes sgnfcantly wth a certan threshold, as descrbed before. When the event s trggered, the node broadcasts to ts neghbours, an E_state packet, n order to nfor the about ts new energy state. Ths adds overhead but, note that ths addtonal overhead s lted, snce the E_state packet s of oderate sze, and t s not forwarded beyond the transtter s neghbourhood. As llustrated before, the threshold energy change confgured for E_state transsson affects the overhead, as well as the power-aware nforaton freshness essental for selectng routes. In our sulaton, we fxed ths value at 10%. That s, each node sends an E_state packet each te t consues 10% of ts battery power. Recevng E_state When a node receves an E_state packet, t updates the paraeters used to copute routes, and ts cache as well. 5 Perforance evaluaton To evaluate our protocol s perforance, we drve a sulaton study usng GloMoS (Zeng et al., 1998), to whch we add any extensons, such as the pleentaton of our protocol. Fro our protocol we derve four versons by varyng the paraeter ALL_ROUTES and the functon α; then we copare the to the standard DSR avalable n GloMoS whch we consder as a benchark. As t wll be llustrated later n the next secton, our protocol shows portant proveents n power consupton whle keepng acceptable delays. We note our protocol DSRPA as DSR Power-Aware, and ts versons as follows: DSRPA0: ALL_ROUTES paraeter s dsabled, and α = F1 DSRPA1: ALL_ROUTES paraeter s enabled, and α = F1 DSRPA2: ALL_ROUTES paraeter s dsabled, and α = F2 DSRPA3: ALL_ROUTES paraeter s enabled, and α = F Sulaton envronent We sulate a network of ten nodes ovng around n a area durng 900 seconds. Each node has a power range of 150, and oves accordng to the rando way pont odel (Badache et al., 2003; Broch et al., 1998). Table 1 suarses the sulaton set up. Table 1 Sulaton set up No. of nodes 10 Sulaton te 900 s Terran Power range 150 Moblty pattern Rando way pont Propagaton pattern Free space MAC protocol IEEE Applcaton protocol CBR

7 132 D. Djenour and N. Badache Table 1 Sulaton set up (contnued) Receved request lst entry te out 30 s Replayng fro cache No Mnu te separatng two requests 10 s Te separatng two transssons of a 500 s request Estate sendng fracton 10% Faled lnks lst entry te out 1 s 5.2 Metrcs of coparson Our purpose s to nse the energy consupton and axse the battery lfe te of all nodes, so that the network partton wll be avoded as long as possble. Intutvely, ths eans axsng the average battery lfe te and nsng the battery lfe te dfference between nodes. A protocol s consdered ore power-effcent than another f t causes less energy consupton, ore average battery lfe te, and less battery lfe te dfference. By ntroducng new routng etrcs, our protocol adds ore councaton and coputaton overhead, thus ore energy consupton. The easureents of the energy consupton allow us to check whether the energy gan provded fro our protocol s hgher than the energy consupton caused by ts overhead. Moreover, ths overhead ay ncrease the latency. To nvestgate ths pact, the end to end delay s also ncluded as a etrc of coparson n our sulaton. Our sulaton study ncludes the followng etrcs of coparson: Consued energy The energy coputaton n GloMoS s based on NCR Wavelan rado odel (Lucent technologes, 2000). Node s consued energy (Power_consued ) s coputed usng the followng forula: PC = TD ( RRR RSR) Rx + TD ( RTR ( p p ) RSR) Tx + RSR ( R R ) off on where TD: packet sze/bandwdth + ST. ST: 192 cro second. RTR(RadoTransssonRate) = 3/second, RRR(RadoReceptonRate) = 1.48/second, RSR(RadoSleepRate) = 0.18/second. R on : the rado turnng on te (sulaton start te). R off : the rado turnng off te (sulaton end te). P: the transsson power. p ax : the axu full power, t s 72,321 Whr n our sulatons, whch s the power allowng to cover the 150 power range. Tx: The set of transtted packets. Rx: The set of receved packets. ax (6) In other words, PC s the su of: the power consued for transttng all packets, the power consued for recevng all packets, and the power consued durng the te when the rado s n the dle ode. Snce the last part of forula 7 (RSR (R off R on )) s equvalent to the power consued n the dle ode for the whole sulaton te, the equvalent consued energy n the dle ode durng receptons and transssons has been subtracted n TD RSR and TD RSR. the frst two sus ( Rx Tx ) Thus, the forula (6) can be rewrtten as: PC = TD RRR + TD RTR p/ p ax Rx + RSR ( Roff Ron ) TD RSR TD RSR. Tx Tx Rx The frst two sus represent, together, the energy consued for councaton; the forer represents the total energy consued n recepton, whereas the latter s the total energy consued n transsson. The reander of the forula s the energy consued by the rado when t s n the dle ode, whch s unaffected by the routng protocol but can be reduced f soe rado anageent technque s eployed by the MAC protocol (Rakhatov et al., 2002). In our case, however, the power consued n the dle ode s always the sae regardless of the protocols; hence we do not consder t. Our frst etrc of coparson s the consued energy for councaton, t s the two frst sus of the prevous forula averaged to ake an average etrc on nodes nuber (), and s gven by: E co TD RRR + TD RTR p/ p (7) Rx Tx ax. (8) I = 1 = Ths etrc can be dvded nto two parts: the recepton average energy, and the transsson average energy; they are respectvely gven by: E E RX TD RRR = (9) I= 1 Rx TD RTR p / p ax TX =. (10) I= 1 Tx Average battery lfe te It s the average battery dscharge te, that s, the average te when nodes batteres are dscharged; t s gven by: BL = BL /. (11) avg I = 1 BL : s the dscharge te of the battery of node, we also call t the battery lfe te of node.

8 New power-aware routng protocol for oble ad hoc networks 133 Battery lfe te dfference It s the dfference between the axu battery lfe te and the nu one, forally speakng: BLdf = BL BL ax( ) n ( ). (12) = 1 = 1 The perforance regardng ths etrc wll be acheved by nsng t. Thus, a protocol s ore energy effcent than another f t ncreases the average battery lfe te and decreases ths etrc. End to end delay Ths well-known etrc s the average te separatng the data packets transsson fro source nodes and ther arrvng at destnatons. If we note ths etrc by delay, then: delay delay = pr pr such that: pr s the set of packets receved by all the destnaton nodes, pr s the nuber of the receved packets and delay s the transfer delay of packet, where: delay = packet arrval te packet transsson te. We wll nvestgate the pact of our protocol s coputaton and councaton overhead on ths etrc. 5.3 Sulaton stages We evaluate our protocol s perforance by coparng t to DSR n dfferent network loads, batteres charge, and oblty stuatons. In order to nvestgate the oblty pact on our soluton, we use along our sulaton, three knds of oblty: ob0 whch s a statonary stuaton (no oblty), ob1 whch s a edu oblty, the nodes average speed s 0.5 /s resultng n an average lnk change (Badache et al., 2003) of 8.00, and fnally the hgh oblty ob2, resulted fro an average speed 1 /s whch s portant vs a vs the sulaton scenaros, snce t causes an average lnk change of The network load s generated by two CBR sessons that last for the whole sulaton te, one between nodes 0 and 9 and the other between 6 and 7. The packet sze s antaned at 1 kb all along our sulaton, and we vary the sender s CBR load (throughput) by changng the te separatng two transssons; the loads used are 1 kb/s, 2 kb/s, 3 kb/s, 4 kb/s and 5 kb/s. We assue that all the nodes have the sae ntal battery charge. Durng the perforance evaluaton vs. the load, t s fxed to 300 Whr when easurng the energy and the end to end delay (ths value avods any dscharge durng the 10 nutes of sulaton), and ths paraeter s fxed at 160 Whr when easurng the other etrcs to cause dscharge durng the sulaton te. Durng the easureents vs. the battery capacty, the batteres charge s changed fro 40 Whr to 200 Whr. However, these values are far fro the real batteres charges (Rakhatov et al., 2002) whch requre uch ore sulaton te and thus, very powerful equpent. These last easureents (vs. the battery charge) llustrate the pact of the battery charge on the protocol perforance. All the etrcs presented n the prevous sectons are easured n the dfferent stuatons of oblty, network load, and battery capacty, resultng n 225 scenaros (executons). 6 Sulaton results 6.1 Consued energy The hstogras A, C, and E of Fgure 2 show the DSR consued energy and those of each DSRPA versons vs. the throughput n the dfferent obltes (ob0, ob1 and ob2). The other dagras; B, D and F represent the energy consupton of DSR and that of the best verson of our protocol; they clearly llustrate the dfference between DSR and our new protocols. We reark fro the dagra A that all the versons of DSRPA consue far less energy than DSR, and they have alost the sae consupton. But for oblty ob2, the versons that use the ALLROUTES opton (DSRPA1 and DSRPA3) consue slghtly ore energy than the others. However, all DSRPA s versons outperfor DSR n all stuatons. Fro the dagras B, D and F, we can see that the dfference between DSR and DSRPA decreases wth oblty, but t ncreases wth the throughput even for hgh oblty (ob2). DSRPA ensures an portant gan n the energy consupton, especally when the throughput (the network load) ncreases. In the followng, we wll nvestgate ths gan by analysng the two parts of ths etrc (transsson and recepton energy). Fgure 2 Consued councaton energy

9 134 D. Djenour and N. Badache Transsson energy. Dagras representng the transsson energy have alost the sae fors as the prevous ones, thus they are otted due to space ltaton. However, we rearked soe dfferences: the dfference between DSR and DSRPA s ore portant especally for ob2 the versons that use ALL_ROUTES opton do not consue ore energy for transssons than the others. Recepton energy. We reark that the plots n dagras A and B of Fgure 3 have alost the sae fors as the correspondng ones of Fgure 2. Nevertheless, for the oblty ob2, and contrary to the prevous plots, we reark that before the debt 4 kb/s, DSR consues slghtly less energy than DSRPA, and DSRPA becoes a lttle bt ore effcent for the hghest load (5 kb/s). On the one hand, unlke DSRPA, DSR uses the proscuous ode; thereby nodes receve all packets that they overhear when they are n the deal ode, whch explans the DSRPA s gan. On the other hand, oblty causes ore overhead for antanng routes n DSRPA that uses adaptable powers. As we have sad, nodes oblty ay renders powers used on lnks nsuffcent wthout breakng these lnks down, whch causes extra antenance only to DSRPA but not to DSR. Ths overhead for antenance explans the dfference n favour of DSR n the frst part of the dagra C. We pont out that because the extra antenance overhead has been largely copensated by the gan provded fro the power control technque and fro the etrc used to select routes ths DSR s outperforng was not observed ether n the transsson energy part or n the total councaton energy. The hstogras are not represented, snce they have qute the sae fors as those of Fgure 2. The nor extra consupton of versons that use the ALLROUTES opton s due to the wde propagaton of requests. 6.2 Average battery lfe te On dagras A, C, and E of Fgure 4, we present the average battery lfe te vs. the throughput. The sae etrc s represented vs. the battery ntal charge on the other dagras. The hstogras representng the DSRPA s versons are otted snce all these versons have all but the sae values. We can clearly see that DSRPA s always ore effcent than DSR, and that the dfference between DSR and DSRPA ncreases wth the network load and the battery charge, but t slghtly decreases wth the oblty. The DSRPA s gan s due to the energy consupton gan analysed prevously. Fgure 4 Average lfe te Fgure 3 Consued recepton energy 6.3 Battery lfe te dfference Dagras B, D and F of Fgure 5 llustrate how the dfference between DSR and DSRPA wth respect to the battery lfe te dfference s portant. It ncreases wth the load and also wth the oblty, contrary to the other etrcs. Ths perforance s anly due to our etrcs that are battery state aware, and also to our new technque that allows us to dsperse the network charge over the avalable routes. Fro dagras A, C and E, we can see that DSRPA3 has often the best perforance (the nu dfference); the other versons are close to each other. Hence, the functon F2 and the ALL_ROUTES opton nse the battery lfe te dfference whle keepng the average battery lfe

10 New power-aware routng protocol for oble ad hoc networks 135 te good enough. But note that the choce of the ALL_ROUTES opton ust depend on the network connectvty. When the connectvty s hgh, ths opton causes a lot of requests broadcastng, resultng n ore energy consupton. Fgure 5 Battery lfe te dfference vs. throughput the lnk antenance procedure due to nodes oblty whch affects only DSRPA due to the power control use. However, the dfference s nor and unaffected by the oblty or the load ncrease. We also ot representng the delay vs. the ntal battery capacty, snce we rearked that the delay was unnfluenced by ths paraeter. Fgure 6 Battery lfe te dfference vs. Battery s charge Fgure 7 End to end delay vs. load Fgure 6 shows the dfference between DSRPA and DSR on the battery lfe te dfference vs. the ntal battery charge. The plot A s onotone, ncreasng upon the charge 80 Whr, where B s ncreasng up to the charge 120, then t becoes stable. The last one shows an portant ncreasng fro charges 80 to 160, and t s nearly stable out of ths nterval. Generally speakng, the dfference between DSRPA and DSR wth respect to the battery lfe te dfference ncreases wth the ntal battery charge, and t s very portant for the hgh charges (160 Whr an 200 Whr) copared wth the low ones (40 Whr and 80 Whr). 6.4 End to end delay Fgure 7 shows the end to end delay of data packets vs. the network load n dfferent obltes. We rearked that all the versons of our protocol have always alost the sae values, thus we ot hstogras representng these versons. As llustrated n plots of dagras A, B, and C of Fgure 7, representng respectvely, obltes ob0, ob1 and ob2, the delay of our protocol s too close to that of DSR n all stuatons. Nevertheless, the DSR s delay s a bt lower than that of DSRPA. Ths s anly due to the coputaton and councaton overhead added by our protocol to exchange power-aware nforaton, and to 7 Conclusons and future work One of the prosng technques proposed n lterature to reduce the energy consupton n ad hoc networks s the power transsson control. When usng ths technque, the obvous etrc for route selecton s to nse the total power requred, but ths choce ay cause an overuse of a nodes subset and resultng n a network partton. To avod such a proble, batteres states should be consdered when selectng routes. In ths paper, we have defned new power-aware etrcs and a new technque that can be pleented wth any routng protocol. The proposed etrcs represent both powers requred on lnks and batteres states of nodes. The technque we have defned s analogous to a polcy used by operatng syste schedulers; t as to dsperse the network nforaton load over as any nodes as possble, whle consderng ther optalty. Basng on

11 136 D. Djenour and N. Badache these etrcs, technques, and DSR, we have presented a new power-aware routng protocol, whose purpose s to allow nodes to stay alve together as long as possble. Our protocol s perforance has been evaluated by sulaton n dfferent stuatons of oblty and network load. We have defned two knds of coparson etrcs; the frst represents the energy consupton, whereas the second represents the battery lfe te. The last knd ncludes two etrcs: the average battery lfe te and the battery lfe te dfference. Ths last one s not related to the consued energy (the fst etrc) at all. We have also easured the end to end delay, and nvestgated the pact of the overhead ntroduced by our protocol s operatons on ths portant QoS (Qualty of Servce) etrc. An effcent protocol ust both ncrease the average battery lfe te (by decreasng the consued energy), and decrease the battery lfe te dfference, wthout affectng the end to end delay. The results of our sulaton show portant proveents copared wth the DSR benchark, especally for hgh load stuatons, whle keepng the end to end delay too close to the one of DSR. The second functon (F2) for the paraeter α shows slghtly better effcency as well as the ALL_ROUTES paraeter. But as for the last one, t ust be treated carefully n hgh connected networks. The proposed protocol reles on the cooperaton and the wellbehavng of nodes. However, n soe applcatons, naely the self-organsed ad hoc networks applcatons where nodes do not belong to a sngle authorty and do not pursue a coon goal, a node s unwllng to spend ts energy on routng packets for other nodes, and ay tend to be selfsh. As a perspectve, we plan to study ths eergent proble. Acknowledgeents Many thanks are due to the anonyous revewers for ther coents that have consderably helped us provng the frst verson of the paper. References Badache, N., Djenour, D. and Dehab, A. (2003) Moblty pact on oble ad hoc networks, ACS/IEEE Conference Proceedng, Tuns, Tunsa. Broch, J., Maltz, D.A., Hu, Y-C. and Jetcheva, J. (1998) A perforance coparson of ult-hop wreless ad hoc network routng protocols, The Fourth Annual ACM/IEEE Internatonal Conference on Moble Coputng and Networkng, Dallas, TX, USA, pp Brown, T., Dosh, S. and Zhang, Q. (2001) Optal power aware routng n a wreless ad hoc network, IEEE LANMAN 2001 Workshop Proceedngs, pp Dosh, S. and Brown, T. (2002a) Mnu energy routng schees for a wreless ad hoc network, The 21st IEEE Annual Jont Conference on Coputer Councatons and Networkng (INFOCOM 02), New York, USA. Dosh, S. and Brown, T. (2002b) Desgn consderatons for an on-deand nu energy routng protocol for a wreless ad hoc network, Internatonal Conference on Councatons (ICC 02), New York, USA. Gold, S. (1997) A PSPICE acroodel for lthu-on batteres, The 12th Annual Battery Conference on Applcatons and Advances, Calforna State Unversty, Long Beach, CA, USA. Johnson, D.B. and Maltz, D.A. (1996) Dynac source routng n ad hoc wreless networks, n Ielnskand, T. and Korth, H. (Eds.): Moble Coputng, Kluwer Acadec Publshers, Vol. 353, Chapter 5, pp Lucent technologes (2000) WAVELAN product specfcaton, Rabn, M.O. (1989) Effcent dspersal of nforaton for securty, load balancng, and fault tolerance, Journal of ACM, Vol. 36, No. 2, pp Rakhatov, D., Vrudhula, S. and Wallach, D.A. (2002) Battery lfete predcton for energy-aware coputng, Internatonal Syposu on Low Power Electrcs and Desgn, Monterey, Calforna, USA, pp Sngh, S., Woo, M. and Raghavendra, C.S. (1998) Power-aware routng n oble ad hoc networks, Proceedngs of the Fourth Annual ACM/IEEE Internatonal Conference on Moble Coputng and Networkng, Dallas, Texas, USA, pp Zeng, X., Bagroda, R. and Gerla, M. (1998) GloMoS: a lbrary for the parallel sulaton of large-scale wreless networks, The 12th Workshop on Parallel and dstrbuted Sulaton, PADS 98, Banff, Alberta, Canada, pp