211 Internatonal Conference on Networkng, Sensng and Control Delft, the Netherlands, 11-13 Aprl 211 Long Lfetme Routng n Unrelable Wreless Sensor Networks Hamed Yousef, Mohammad Hossen Yeganeh, Al Movaghar Abstract Lfetme s the most mportant concern n wreless sensor networks due to lmted battery power of sensor nodes. In ths paper, we focus on desgnng an energyeffcent and energy-aware routng algorthm, LLR, to ncrease the operatonal lfetme of mult-hop wreless sensor networks n the presence of unrelable communcaton lnks. Our proposed protocol utlzes a parameter, Broadcastng Delay, n each node assocated wth the hop parameters passed by a route request packet to select long lfetme paths n the network. The key pont n Broadcastng Delay formulaton s that t ncludes both node and lnk specfc parameters. We use two dfferent scenaros: ether the lnk layer relablty or the transport layer relablty s mplemented. Smulaton results reveal that the proposed algorthm can outperform other exstng schemes n term of the network lfetme. I. INTRODUCTION ECENT advancement n wreless communcatons, R mcro-electroncs, and low power desgn shows gradually wde applcaton perspectve of Wreless Sensor Networks (WSNs) [1]. Consderng that communcaton costs (transmsson power) are usually more expensve than computng costs, Energy effcent routng algorthms are very mportant n mult-hop WSNs where the consttuent nodes have batteres wth lmted energy. Several energyaware routng protocols (e.g., [2]-[4]) defne the lnk cost based on the power requred to transmt a packet on t, and accordngly employ mnmum cost routng algorthms to determne the mnmum total transmsson energy route from a source to the destnaton. In many wreless ad-hoc scenaros, however, the metrc of actual nterest s the total operatonal network lfetme [5]-[15], not the transmsson energy of ndvdual packets. Through the energy aware routng mechansm, the resdual energy on each node s the bass of the routng decsons. The man objectve of these algorthms s to avod the extncton of nodes due to exhauston of ther battery power. However, none of the prevous papers have consdered the lossy property of the wreless lnks. They are often assumed to be relable. Ths s clearly too optmstc snce even under bengn condtons, wreless communcaton lnks are unrelable and often unpredctable due to varous factors lke fadng, nterference, mult-path effects, and collsons [16]-[18]. If a poor path s chosen for data delvery, loss rate wll be heavy and retransmssons wll cause extra energy consumpton, and consequently, less network lfetme. Furthermore, more traffc also yelds a hgher collson H. Yousef and A. Movaghar are wth the Department of Computer Engneerng, Sharf Unversty of Technology, IRAN (e-mal: hyousef@ce.sharf.edu, movaghar@sharf.edu). M.H. Yeganeh s wth the Department of Computer Engneerng, Scence and Research Branch, Islamc Azad Unversty, IRAN (e-mal: m.yeganeh@srbau.ac.r). probablty and delvery delay. [19]-[22] have shown why energy spent n potental retransmssons, s the proper metrc for relable, energy-effcent communcatons. In ths paper, we present a new energy-effcent and energy-aware route selecton algorthm called LLR (Long Lfetme Routng). Moreover, we show how power aware routng protocols must not only be based on node specfc parameters (e.g. resdual battery energy and the number of paths whch the node s common among), but also consder the lnk specfc parameters (e.g. lnk error rate and the packet transmsson energy for relable communcaton across the lnk) as well n each hop, to ncrease the operatonal lfetme of the network. To the best of our knowledge, t s the frst work addressng these goals n an ntegrated manner. To make a specal floodng mechansm, LLR combnes these four factors together n one parameter, Route Request Broadcastng Delay, defned as the nverse of the dealzed maxmum number of packets that can be transmtted n each hop by the transmttng node over the lnk. However, f a lot of mnmum-energy routes share a node, the node s battery wll be exhausted quckly. Therefore, LLR employs an energy reservaton scheme to sgnfcantly decrease the probablty of the common nodes selecton. We use two dfferent scenaros: ether the lnk layer relablty or the transport layer relablty s mplemented. Smulaton studes show how LLR leads to a longer network lfetme than alternatve suggested algorthms due to the optmal path selecton. The remander of the paper s organzed as follows. Secton II explans the proposed scheme and presents the specfcatons of LLR. Smulaton results are presented and dscussed n secton III. Fnally, Secton IV concludes our work and dscusses some future drectons. II. PROTOCOL OVERVIEW AND PROPERTIES LLR s a dstrbuted algorthm that provdes a robust transmsson envronment based on the energy-effcent and energy-aware routng and energy-reservaton mechansms at the network layer. The algorthm comprses: Path Dscovery stage, Path Reservaton stage and Data Transmsson stage. However, the man dea of LLR protocol s to combne the broadcastng speed wth four factors together to make a specal floodng mechansm for the selecton of long lfetme paths. All these factors are mxed and ntegrated nto the noton of Broadcastng Delay. As the routng decson s made based on these factors, n the next secton we wll explan them and wll formally defne how to calculate the value of Broadcastng Delay n two dfferent operatng models: 978-1-4244-9573-3/11/$26. 211 IEEE 457
a) Hop-by-Hop Retransmssons (HBH): where each ndvdual lnk provdes relable forwardng to the next hop usng localzed packet retransmssons. b) End-to-End Retransmssons (E2E): where the ndvdual lnks do not provde lnk-layer retransmssons and error recovery but relable packet transfer s acheved only va retransmssons ntated by the source node. A. Calculaton of Broadcastng Delay As descrbed earler, Route Request Broadcastng Delay n each ntermedate node s a key parameter to make decson durng the routng. It contans four factors whch are relevant to the resdual node energy, the transmsson energy on the lnk, lnk error rate, and the number of paths whch the node s common among. To formulate the Broadcastng Delay, Consder a smple path P= v 1, v 2,, v N from a source node S (v 1 ) to destnaton node D (v N ) consstng of N-1 ntermedate nodes ndexed as 2,, N. Moreover, let us assume that B s the resdual battery power at a certan nstance of tme at node, E,+1 s the transmsson energy consumed n node to transmt a packet over lnk (,+ to node +1, and ler,+1 s the packet error probablty assocated wth lnk (,+. Here,,, where d s the dstance between the recever and the transmtter and α s a technology specfc constant. When a lnk layer relablty (Hop-by-Hop Retransmsson) s mplemented, the expected number of transmssons (ncludng retransmssons as necessary) to relably transmt a sngle packet across lnk (,+ s calculated by. Hence, the expected energy, requrement to relably transmt a packet across the lnk s gven by,, and t s calculated,, by for path P. Therefore, the, maxmum number of packets that node can forward over the lnk (,+ s clearly. However, t s possble, that node s common among k other paths and therefore t consumes some energy, E con, for relable data transmsson on output lnks assocated wth those paths, where k 1 E, + 1( m) Econ() = ( m= (1 ler, + 1( m) ) Accordngly, we can defne a node-lnk Metrc, Ablty () for the hop count as: B Ablty() = (2) Econ () + E lnk (, + Fnally Route Request Broadcastng Delay (B Delay) n each ntermedate node s calculated by: 1 Econ() + Elnk (, + BDelayHBH () = = Ablty() B k 1 E, 1 ( m) E (3) +, + 1 + m= (1 ler, + 1 ( m) ) (1 ler, + BDelayHBH () = B When a transport layer relablty (End-to-End Retransmsson) s mplemented, the expected number of transmssons (ncludng retransmssons as necessary) to relably transmt a sngle packet across lnk (,+ s. Hence, the expected energy requrement to, relably transmt a packet across the lnk s gven by,, and for path P s calculated,,, by. Therefore, the maxmum number of packets that node can forward over the lnk (,+ s clearly. However, t s possble that the, node s common n k other paths and therefore t consumes some energy, E con, for relable data transmsson on output lnks assocated wth those paths. E con () = E k 1, + 1( m) (4) hop( m) 1 m= (1 lerj, j+ 1( m) ) j= where hop(m) s the number of hops n path m. Accordngly, we can defne a node-lnk Metrc, Ablty () for the hop count as: B Ablty () = (5) Econ() + E lnk (, + Fnally, Route Request Broadcastng Delay (B Delay) n each ntermedate node s calculated by: 1 Econ () + Elnk (, + BDelayE2E() = = Ablty () B k 1 E, + 1 ( m) E, + 1 + hop( m) 1 N 1 m= (1 ler, 1( )) (1 j, j j j m ler + + j= j= BDelayE2E() = B (6) The key pont n these formulatons s that the Broadcastng Delay ncludes both two node specfc parameters and two lnk specfc parameters. By ncreasng ler,+1, the Broadcastng Delay value wll ncrease. Thus, by factorng the ndvdual lnk error probabltes n the Broadcastng Delay, our algorthm avods ncludng poor qualty lnks n the eventual transmsson path, even f such lnks apparently ncur lower transmsson costs. Therefore the man advantage of usng ths parameter s a hgher qualty path selecton whch causes reducton of retransmssons, reducton of energy consumpton and prolongaton of the network lfetme. By decreasng B, the Broadcastng Delay value wll ncrease. Thus the selecton probablty of one node wth lttle resdual energy wll decrease. It maxmzes the total number of packets that may be deally transmtted over network paths. Moreover, by provdng a more stable transmsson envronment, LLR can reduce packet loss due to the frequent path breakdowns. Consequently, path requests wll be reduced. Thus, more energy can be used to forward data, nstead of beng wasted on consecutve path dscoveres. By ncreasng E,+1, the Broadcastng Delay value wll ncrease. Thus the selecton probablty of one lnk wth hgh energy consumpton wll decrease. Usng ths parameter can 978-1-4244-9573-3/11/$26. 211 IEEE 458
lead to provdng the path wth mnmum energy consumpton and consequently prolongaton of the network lfetme. By ncreasng E con, the Broadcastng Delay value and consequently the selecton probablty of the common nodes wll decrease. Moreover, the network operatonal tme maxmzes by balancng the energy dranng rates among nodes. However, selectng common nodes can accelerate paths breakdowns and lead to lower path lfetme, more path dscovery, and consequently wastage of network resources. The reducton of packet loss nduced by buffer overflow and the reducton of the end to end packet transmsson delay are other man advantages of usng ths parameter. However, among several paths arrvng n one node, we are nterested n a path wth mnmum error rate and energy consumpton on ts lnks, maxmum battery power on ts nodes, and mnmum number of common nodes wth other paths. All of these factors that extremely mpress network lfetme are consdered n Broadcast Delay formulaton. Thus, one path wth lower value of Route Request Broadcastng Delay on ts nodes ndcates a better path. B. Path Dscovery Stage The process starts at the snk by broadcastng a route request packet (label) to ts neghbors. Ths stage s ntated when the snk receves an nterest that carres an unknown source, or when the already establshed path s broken. A label carres the nformaton of the source, one ndex, and a route table onto whch ntermedate nodes pggyback ther IDs. The label ndex ncreases one unt n each new path dscovery stage. We suppose that there s one tmer n each node for every source node. When an ntermedate node receves a label, t does not broadcast t to ts neghbors mmedately. Before sendng the label out, several actons must be undertaken. Thereafter, the node decdes to transmt or dscard the label accordng to the algorthm shown n Fg. 1. The labels are flooded throughout the network untl they reach the source node. The source wats untl expraton of ts tmer. Thereafter, the path dscovery stage fnshes. It should be noted that there may be many potental label paths from the snk to the source. However, we are nterested n one optmal (long lfetme) establshed path towards the source. Therefore, the source only selects one label whch has been receved wth mnmum path Broadcastng Delay. C. Path Reservaton Stage LLR tres to ensure an equtable dstrbuton of transmsson costs among the consttuent nodes. Ths s realzed through path reservaton. Path reservaton s manly concerned wth energy. After the source retreves the canddate-path from the label, t wll generate a path reservaton packet and uncast t along the retreved path toward the snk. Every node on ths path wll ncrease ts E con by E lnk. The path reservaton s a key element of the Route Request Broadcastng Delay. It can prevent too many paths from sharng a few nodes. Once a node s reserved, ts Broadcastng Delay becomes longer (B Delay ncreases), and so another path can potentally bypass ths node to use other nodes wth lower Broadcastng Delay. Ths also can reduce the effects of a broken node. If the broken node s only on one path, then only one new path dscovery s employed. 1:If (label ndex already has been cached n the node) 2: The receved label s dscarded; 3:Else{ 4: B Delay s calculated as n (3,6); 5: If (t s the frst tme the node receves ths ndex) 6: Node tmer s scheduled to B Delay; 7: Else f (B Delay < tmer value){ 8: Node tmer s rescheduled to B Delay; 9: The prevous receved label s dscarded; } 1: Else 11: The receved label s dscarded; 12: Steps 4-11 can be repeated for ths label receved from dfferent paths untl expraton of the node tmer; 13: The label ndex s cached n the node; 14: The node ID s added to the label route table; 15: The label s transmtted to neghbor nodes; } Fg. 1. The routng decson algorthm n each ntermedate node However, f k paths share ths node, then there wll be k new attempts for the path dscovery. The procedure of path reservaton ends once the snk receves the path reservaton packet. D. Data Transmsson Stage LLR provdes relable packet delvery for uncast transmsson. It uses two dfferent operatng models n dfferent scenaros: a) Hop-by-Hop Retransmssons (HBH) b) End-to-End Retransmssons (E2E) Reserved energy for a path wll not be released unless the path s broken when one or more node/lnk falures occur on the reserved path. The falure s detected by the sender when t does not receve any ACK from the recever wthn a tme out perod after a fxed number of attempts. In the event of a path falure, an error report wll be generated and broadcast to both termnals of the broken path. The reserved energy, E lnk, n the ntermedate nodes wll be released, and the old path wll be removed from the route table of the termnals. Also, the snk wll start a new path dscovery once t receves ths error report packet. III. PERFORMANCE ANALYSIS In ths secton, we evaluate the performance of our algorthm va smulaton. We mplemented a smulaton framework usng OMNeT++, an object-orented dscrete event network smulator [23]. Here, we compare the performance of 7 dfferent routng schemes. 1. Our proposed algorthm, LLR, n whch long lfetme paths are selected based on both two node specfc parameters and two lnk specfc parameters. 2. Mn-hop routng as the conventonal energyunaware Internet routng algorthm. 3. Smple energy-aware routng protocol consderng only the remanng energy levels of the nodes n route dscovery. 4. Smple energy-effcent routng algorthm selectng the route based on only the mnmum total transmsson power. 978-1-4244-9573-3/11/$26. 211 IEEE 459
5. Smple energy-aware energy-effcent routng protocol whch takes nto account both total energy cost and resdual energy when selectng the next hop, wthout consderng the lnk relablty. 6. Relable energy-effcent routng whch selects the path correspondng to the mnmum packet transmsson energy for relable communcaton, wthout consderng the battery power of ndvdual nodes. 7. Relable energy-aware routng n whch the cost assocated wth each hop s a functon of the lnk error rate and resdual battery energy. A. Smulaton Model The same network setup s used to compare the routng schemes. Table I summarzes the network characterstcs. We used a traffc scenaro, where four source nodes at the upsde left of the terran send perodc data to the snk at the downsde rght. Each ntermedate node s equpped wth a total amount of energy.5 J (node wth mnmum energy) or 1.5 J (node wth normal energy) at the begnnng of the smulaton. We have dvded up all the lnks nto two categores: one wth a normal error rate 2%, and the other wth a hgh value of 3%. The percentage of network lnks wth hgh error rate s consdered 1% over smulatons. If a packet loss occurs for any reason durng the transmsson, t wll be retransmtted untl t s delvered successfully to the snk. TABLE I. NETWORK CHARACTERISTICS Smulaton Area (Terran) 5 5 m 2 Number of Nodes 1 Node Deployment Rado Range Bandwdth Data Packet Sze Route Request Packet sze Unform 2 m 2 kb/sec 5 B We use the followng metrcs to evaluate the performance of LLR and compare the results wth the tradtonal schemes. Lfetme: The network lfetme s defned as the smallest tme that t takes for at least one node n the network to dran ts energy [7]-[9]. Total Energy Consumpton: The total energy expended by all nodes. B. Smulaton Results We run the smulaton by varyng several parameters, ncludng data rate, the percentage of network nodes wth mnmum energy, and tme. Smulaton results are obtaned from 1 runs and results are averaged over the runs (wth a 9% confdence level and 1% confdence ntervals). Fgures 4 and 5 llustrate the network lfetme when varyng the data rate from 2 to 1 n HBH and E2E manner, respectvely. Here, the percentage of network nodes wth mnmum energy s set to 5%. Obvously, the network lfetme decreases wth the ncrease n the data rate. We can see that, as expected, the mn-hop algorthm performs the worst, snce t not only fals to balance the workload among the ntermedate nodes, but also uses large dstance hops and 5 B consequently larger transmsson energy. Furthermore, the plots effectvely demonstrate the superor performance of algorthms 7 and 6 over the 3 and 4 as a result of selectng the low-error lnks and consequently, smaller energy expendture on packet re-transmssons. Moreover, the scheme 5 outperforms 3 and 4 by takng nto account both resdual battery energy and packet transmsson energy n node capacty measure. However, we can clearly see that the LLR expectedly performs better than the others. In contrast to other schemes, not only does LRR consder the node specfc parameters (e.g. resdual battery energy and the number of paths whch the node s common among), but also the lnk specfc parameters (e.g. lnk error rate and the packet transmsson energy for relable communcaton across the lnk) as well, to ncrease the operatonal network lfetme. Even f the resdual battery energy and effectve transmsson energy for a sngle packet are dentcal on all hops, LLR performs better by selectng the path wth mnmum number common nodes usng a path reservaton mechansm and preventng quckly exhauston of common nodes. In E2E retransmsson model, the results are generally smlar to the case of HBH retransmsson, except that the performance of HBH s better especally n the case of the schemes whch consder relablty n route dscovery. Ths can be explaned by the effect of the number of retransmssons on energy expendture and consequently, the network lfetme. Snce any lost packet must be retransmtted from the source node n E2E manner that causes more energy consumpton on ntermedate nodes. Lfe-tme (s) Lfe-tme (s) 9 8 7 6 5 4 3 2 1 8 9 1 11 9 8 7 6 5 4 3 2 1 Data Rate Fg. 2. Lfetme vs. Data Rate (HBH) 8 9 1 11 Data Rate Fg. 3. Lfetme vs. Data Rate (E2E) 978-1-4244-9573-3/11/$26. 211 IEEE 46
To study better, next we show how varyng the percentage of network nodes wth mnmum energy from 1% to 5% affects the network performance,.e., the network lfetme when the data rate s set to 2 packets per second (see Fg. 4, 5). Once agan, t can be seen that the LLR algorthm present better lfetme than other routng protocols. Fgures 6 and 7 plot total energy consumpton for the schemes n dfferent tme when the smulaton duraton s 2 seconds. In these scenaros, the data rate and the percentage of network nodes wth mnmum energy are set to 2 and 5%, respectvely. Whereas the LLR algorthm obvously results n maxmum network lfetme, we can clearly see that the Relable energy-effcent routng results n the lowest total energy consumpton among all the routng schemes. Lfe-tme (s) Lfe-tme (s) Total Energy Consumpton (J) 14 12 1 8 6 4 2 % 1% 2% 3% 4% 5% Fg. 4. Lfetme vs. percentage of nodes wth mnmum energy (HBH) 12 1 Fg. 5. Lfetme vs. percentage of nodes wth mnmum energy (E2E) 6 5 4 3 2 1 8 6 4 2 Percentage of Network Nodes wth Mnmum Energy % 1% 2% 3% 4% 5% Percentage of Network Nodes wth Mnmum Energy 2 4 6 8 1 12 14 16 18 2 Tme (s) Fg. 6. Total energy consumpton vs. percentage of nodes wth mnmum energy (HBH) Fg. 7. Total energy consumpton vs. percentage of nodes wth mnmum energy (E2E) As expected, especally n a harsh envronment characterzed by extremely poor channel condtons, E2E manner wll cause more energy consumpton on ntermedate nodes because the lost packets must be retransmtted from the source nodes whch t causes more energy consumpton on ntermedate nodes. Moreover, from the experments made, t can be concluded that power-aware routng protocols must not only be based on the node specfc parameters but also consder the lnk specfc parameters to prolong the operatonal network lfetme. IV. CONCLUSION In ths paper, we have presented a new power-aware algorthm for energy-effcent routng that ncreases the lfetme of mult-hop WSNs. In contrast to conventonal power-aware algorthms, LLR dentfes the capacty of a hop not only based on the resdual battery energy and the number of paths sharng the assocated node, but also the expected energy spent n relably forwardng a packet on t. Our smulaton experments confrm that LLR outperforms other tradtonal routng schemes. The algorthm could be modfed to take nto account some aspects that have not been addressed n ths work, and that can be nterestng subject of future research. For nstance, studyng a deadlne-aware long lfetme algorthm can be consdered as a future work. [1] [2] [3] [4] [5] [6] Total Energy Consumpton (J) 8 7 6 5 4 3 2 1 2 4 6 8 1 12 14 16 18 2 Tme (s) REFERENCES I.F. Akyldz, W. Su, Y. Sankarasubramanam, and E. Cayrc, A Survey on Sensor Networks, IEEE Communcaton Mag., pp. 12-114, 22. S. Sngh and C.S. Raghavendra, PAMAS-Power Aware Mult- Access Protocol wth Sgnalng for Ad Hoc Networks, ACM Communcaton Revew, 1998. J.M. Zhang, L.F. Gu, and L.M. Wang, Relable Transmsson Method Wth Energy-Awareness for Wreless Sensor Networks, Internatonal Journal of Computer Scence and Network Securty (IJCSNS), Vol. 6, 26. A. Srnvas and E. Modano, Fndng Mnmum Energy Dsjont Paths n Wreless Ad-Hoc Networks, Wreless Networks, Vol. 11, pp. 41-417, 25. J. Park and S. Sahn, An Onlne Heurstc for Maxmum Lfetme Routng n Wreless Sensor Networks, IEEE Transactons on Computers, Vol. 55, No. 8, pp. 148-156, 26. R. Shah and J. Rabaey, Energy Aware Routng for Low Energy Ad Hoc Sensor Networks, n Proc. WCNC 2, Vol. 1, pp. 35-355, 22. 978-1-4244-9573-3/11/$26. 211 IEEE 461
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