ENERGY EFFICIENT ROUTING PROTOCOLS FOR WIRELESS AD HOC NETWORKS A SURVEY

Transcription

1 K SANKAR: ENERGY EFFICIENT ROUTING PROTOCOLS FOR WIRELESS AD HOC NETWORKS A SURVEY ENERGY EFFICIENT ROUTING PROTOCOLS FOR WIRELESS AD HOC NETWORKS A SURVEY K. Sankar Department of Computer Scence and Engneerng, Sr Balaj Chockalngam Engneerng College, Inda E-mal: Shankar_24_1968@hotmal.com Abstract Reducng energy consumpton, prmarly wth the goal of extendng the lfetme of battery-powered devces, has emerged as a fundamental challenge n wreless communcaton. The performance of the medum access control (MAC) scheme not only has a farly sgnfcant end-result on the behavour of the routng approach employed, but also on the energy consumpton of the wreless network nterface card (NIC). We nvestgate the nadequaces of the MAC schemes desgned for ad hoc wreless networks n the context of power awareness heren. The topology changes due to uncontrollable factors such as node moblty, weather, nterference, nose, as well as on controllable parameters such as transmsson power and antenna drecton results n sgnfcant amount of energy loss. Controllng rapd topology changes by mnmzng the maxmum transmsson power used n ad hoc wreless networks, whle stll mantanng networks connectvty can prolong battery lfe and hence network lfetme consderably. In addton, we systematcally explore the potental energy consumpton ptfalls of non power-based and power based routng schemes. We suggest a thorough energy-based performance survey of energy aware routng protocols for wreless moble ad-hoc networks. We also present the statstcal performance metrcs measured by our smulatons. Keywords: Moble Ad Hoc Network; Energy Effcent Routng; Transmsson Power Control; Routng Protocols; Performance Metrcs 1. INTRODUCTION In wreless ad-hoc networks, the nonexstence of a centralzed authorty compounds the problem of medum access control. The centralzed medum access regulaton practces endeavoured by base statons n cellular networks have to be admnstered n a dstrbuted, and hence collaboratve, fashon by moble statons. Moble statons may compete smultaneously for medum access. Consequently, transmssons of packets from dstnct moble termnals are more vulnerable to overlap, eventually resultng n packet collsons and energy losses. In addton, the performance of the MAC scheme has an outstandng nfluence on the performance of the routng method employed and on the energy consumpton of the wreless network nterface card (NIC). Routng s one of the key ssues n MANETs due to ther hghly dynamc and dstrbuted nature. The on-demand routng algorthms ntate to fnd out the sutable route when a route s requested [1]. The pro-actve routng algorthm exchanges routng nformaton perodcally and generates the routng table n advance of route request [2]. These protocols select the routes based on the metrcs of mnmum hop count. The moble nodes n wreless ad-hoc networks are typcally battery powered and hence, energy effcent routng s of paramount sgnfcance n the desgn of such networks. Power falure of a wreless node not only affect the node tself radcally, but also ts capablty to forward packets on behalf of others and thus the overall network lfetme [3]. Many research efforts have been dedcated to extend the moble node battery capacty whch ncludes communcaton energy consumpton and Non communcaton energy consumpton. Durng communcaton, energy s consumed n ether nactve state of communcaton or actve communcaton states. The energy consumpton of actve communcaton s more sgnfcant than the others for hgh-traffc envronment. Energy effcent routng protocols are desgned to formulate energy effcent actve communcatons. Energy effcent actve communcatons prolong the network lfe tme. The network lfe tme s defned as the tme when a node runs out of ts own battery power for the frst tme [4, 5]. The energy effcent routng protocols should consder the power consumpton from the perspectves of both the network and the node. Ths paper s organzed as follows. Secton 2 brefs background of the paper. Secton 3 analyses the problems wth MAC protocol for ad-hoc networks and dscusses ther nadequaces n the context of power awareness. Sectons 4 and 5 bref the mpact of topology changes and transmsson power on energy conservaton. Secton 6 and 7 demonstrates a thorough comparatve study of routng schemes for ad-hoc networks Fnally, Secton 8 presents the conclusons. Recommendatons for power-effcent protocol desgn n ad-hoc networks are also dscussed. 2. RELATED WORK Man emphass of research on routng protocols n wreless ad Hoc networks has been the energy effcency, delvery of packets, network performance and network lfetme. There has been very less amount of work have done on energy effcent routng schemes, though t s very mportant aspect n route dscovery, route selecton, route mantenance and performance of protocol. Major mpact on energy awareness needs a more detaled revew of MAC scheme adopted for transcever, transmsson power control to mantan network topology, choce of routng protocols and routng algorthms. Some study has been done n ths context and presented s a bref revew of them. 3. IEEE MAC PROTOCOL AND ENERGY EFFICIENCY The IEEE protocol s wdely used n wreless ad hoc networks. It s based on carrer sense multple access (CSMA) technque wth addtonal collson avodance (CA) feature. When a node has data to transmt, t frst senses the medum. If t 542

2 ISSN: (ONLINE) ICTACT JOURNAL ON COMMUNICATION TECHNOLOGY, JUNE 2012, VOLUME: 03, ISSUE: 02 fnds the medum dle, the node wats for a random back off perod as a result of the CA feature. Durng ths perod, f the channel becomes busy, the node freezes ts counter untl the medum becomes dle agan. When the counter runs out, RTS/CTS handshake takes place followed by data transmsson. Medum access control (MAC) s a serous problem n ad hoc networks. Snce ad hoc networks are wreless and moble networks, ther MAC protocols need more sophstcated methods n order to solve ssues lke the hdden termnal and the exposed node problems [7]. However, were proposed for fully connected wreless networks and do not perform well n mult hop ad hoc networks [8]. In [6], the authors found the followng problems mplanted n the MAC layer: TCP nstablty - The nteractons between dfferent nodes carryng TCP-data and TCP-ACK traffc causes throughput of only one TCP connecton exstng n the network tme and agan reachng zero or was near zero. The hdden termnal stmulates collson and the exposed termnal prevents the ntermedate node from sendng a CTS message. Hence, the node obstructed reachng ts neghbour. The lnk s repeatedly broken n the mddle of the route and usng smaller maxmum wndow sze can dmnsh or clear ths problem. Neghborng Node One-hop unfarness: If two TCP connectons exst n the network, one sesson may be entrely shut down and have no opportunty to restart n some crcumstances even f t starts much earler. Ths problem cannot be decphered by balancng the wndow sze. Incompatblty between two TCP sessons: Two TCP sessons cannot coexst n the network at the same tme, and the turnover tme s totally random, whch s brought about by the exposed node problem. It cannot be solved by adjustng TCP parameters. [9] Proposes an adaptve RTS/CTS mechansm to reduce the unfarness caused by IEEE In an adaptve RTS/CTS scheme, a node wll turn off RTS/CTS when the number of watng for CTS tmeout events exceeds a threshold. The countng number s updated n a sldng wndow fashon. The smulaton results show that ths adaptve mechansm can sgnfcantly mprove the farness both for UDP and TCP transmsson. [10] Explores the RTS/CTS ssue even further. At frst CTS/RTS may cause a blockng problem, as llustrated n Fg.1 [10]. Node B s sendng packets to node A. Node C receves both RTS and CTS, so t wll stop transmttng. If at ths tme node D sends RTS to node C, node C cannot reply wth CTS, fnally node D wll enter the exponental backoff mode. In ths scenaro, node C need not be ether a hdden node or an exposed node as Fg.1 shows, because t can receve both RTS and CTS. In the current mplementaton of the RTS/CTS mechansm, when a node receved an RTS packet not addressed to t, t s requred to stop transmttng. Fg.1. Node Blockng Problem In the blockng problem scenaro, these nodes neghborng to the blocked node may be falsely blocked, and even worse, the false blockng may spread through the network untl some event lke the packet drop breaks ths knd of pseudo-deadlock. [10] Proposes a soluton to the false blockng problem. The basc dea s RTS valdaton: when a node hears RTS, whch s not addressed to t, t wll defer a certan amount of tme to check f there are really data packets n transmsson. If the medum s stll dle, whch means that false blockng may happen, t wll not defer any more. The smulaton results show these solutons can sgnfcantly mprove the battery lfe and throughput. 4. TOPOLOGY CONTROL AND ENERGY EFFICIENCY The topology of a mult-hop wreless network s a set of relatonshps between node pars that are lnked drectly or va mult-hops. Transmsson power, node moblty, sgnal attenuaton, nose, clmate condtons and drecton of antenna stmulate rapd topology changes n wreless ad-hoc networks. Almost all the studes focus on structurng a desred topology by fne-tunng the transmsson power. Topology control of ad-hoc networks preserves the network capacty, consderably mproves the end-to-end packet delay, and lowers the node falure rates. For nstance, f the topology s too sparse, routng requests may be delberately obstructed due to the network parttonng. Furthermore, end-to-end delays may be very hgh. On the other hand, f the topology s too dense, nodes may run out of ther energy quckly and may escalate nterference among them. Networks that do not employ topology control are lkely to be n one of these modes, whch results n short battery lfe of nodes, and/or poor connectvty. 5. TRANSMISSION POWER CONTROL AND ENERGY EFFICIENCY Many studes on topology control am to mnmze the maxmum transmsson power used n ad hoc wreless networks, whle stll mantanng network's connectvty. For statc networks, optmal centralzed algorthms were proposed. The basc nterpretaton of the algorthms s to add lnks one by one n non-decreasng order accordng to ther dstance. For moble networks, two dstrbuted heurstcs called the neghbor reducton protocol and the neghbor addton protocol are used to adjust node transmsson powers n response to topology changes. If a route update reveals that a lnk falure has occurred such that the network s no longer connected, the approprate 543

3 K SANKAR: ENERGY EFFICIENT ROUTING PROTOCOLS FOR WIRELESS AD HOC NETWORKS A SURVEY nodes ncrease ther transmsson power untl t s connected. Ths technque reles heavly on routng protocol performance, because changes n network connectvty can ntate further routng updates and hence more energy loss. 6. ROUTING PROTOCOLS AND ENERGY EFFICIENCY IN AD-HOC NETWORKS A moble Ad-Hoc network s a co-operatve network of wreless nodes that communcate over a wreless medum. Topology changes of the wreless nodes n the network are rapd, and these networks are self-confgurng n nature requrng de-centralzed control and admnstraton. Such networks do not surmse all the nodes to be n the drect transmsson range of each other. Hence, these networks requre hghly specalzed routng protocols that sgnfcantly contrbute self-startng behavor. Energy constraned nodes, low channel bandwdth, node moblty, hgh channel error rates, and channel varablty are some of the lmtatons n an Ad-Hoc network. Under these condtons, exstng wred network routng protocols would fal or perform poorly. Thus, Ad-Hoc networks necesstate specal routng protocols. Ad Hoc routng protocols are convenently categorzed based on the way route tables are constructed, mantaned, and updated [11]. Fg.2 shows the broad classfcaton of MANET routng protocols. Proactve Routng Protocols Reactve Hybrd OLSR DSDV AOD DSR TORA ZRP V Fg.2. Classfcaton of Routng Protocols Table.1. Comparson of several routng protocols Protocol Reference Cost Metrc Power Aware Source Routng (PSR) [14] Mnmum Dran Rate (MDR) [15] Mn-Max Battery Cost Routng (MMBCR) Mnmal Battery Cost Routng (MBCR) n er mn er F R t RBP DR max 1 [16] R j t eroute _ j c D j 1 1 [16] R j c 0 Pj Mchal and Ephremdes [17], j RWp W P max t e E E o j R j Max. Network Lfe Tme Mn. Energy Consumpton 6.1. PROACTIVE (TABLE-DRIVEN) ROUTING PROTOCOLS. In proactve routng, each node has one or more tables that contan the latest nformaton regardng the routes to any node n the network. Each node has the next hop for reachng to a node/subnet and the cost of ths route. Varous table-drven protocols dffer n the way the nformaton about change n topology s propagated through all nodes n the network. The two knds of table updatng n proactve protocols are the perodc update and the trggered update [12]. In perodc update, each node perodcally broadcasts ts table n the network. Each node just arrvng n the network receves that table. In trggered update, as soon as a node detects a change n ts neghborhood node, t broadcasts entres n ts routng table that have been changed. Examples of ths class of Ad Hoc routng protocols are the Destnaton-Sequenced Dstance-Vector (DSDV) [2] and the Wreless Routng Protocol (WRP) [13]. Proactve routng tends to waste bandwdth and power n the network because of the need to broadcast the routng tables/updates. Furthermore, as the number of nodes n the MANET ncreases, the sze of the table wll ncrease; ths can become a problem, n and of tself. In addton, t needs to control traffc for contnual update of stale route entres. Unlke the Internet, an Ad-Hoc network may contan moble nodes, and therefore lnks are contnuously broken and re-establshed. 6.2 REACTIVE (ON-DEMAND) ROUTING PROTOCOLS Reactve routng protocols take a sluggsh approach to routng. They do not mantan or constantly update ther route tables wth the latest network topology changes. Instead, when a source node wants to transmt a message, t floods a query nto the network to dscover the route to the destnaton. Ths dscovery packet s called the Route Request (RREQ) packet, and the mechansm s termed Route Dscovery. The destnaton reples wth a Route Reply (RREP) packet. As a result, the source dynamcally fnds the route to the destnaton. Dscovered route s mantaned untl the destnaton node becomes unreachable or 544

4 ISSN: (ONLINE) ICTACT JOURNAL ON COMMUNICATION TECHNOLOGY, JUNE 2012, VOLUME: 03, ISSUE: 02 untl the route s no longer needed. Ths class of protocol dffer n handlng cache routes, and n the way route dscoveres and route reples are handled. Reactve protocols are generally consdered effcent when the route dscovery s employed rather nfrequently n comparson wth the data transfer. Although the network topology changes dynamcally, the network traffc caused by the route dscovery process s low compared to the total communcaton bandwdth. Table.2. Comparson of several routng protocols Propertes AODV DSR DSDV TORA /IMEP Reactve Yes Yes No Yes Multple Routes No Yes No Yes Power Conservaton No No No No Undrectonal Lnk Support No Yes No No Multcast Yes No No No Perodc Broadcast Yes No Yes Yes Examples of Reactve routng protocols are the Dynamc Source Routng (DSR) [9, 1], the Ad Hoc on-demand Dstance Vector Routng (AODV) [18] and the Temporally-Ordered Routng Algorthm (TORA) [19]. Snce the route to destnaton wll have to be acqured just before communcaton begns, the latency perod for most applcatons s lkely to ncrease drastcally. 6.3 HYBRID ROUTING PROTOCOLS Both the proactve and reactve protocols work well for networks wth a relatvely small number of nodes. As the number of nodes ncreases, hybrd protocols are used to attan hgher performance. The key dea s to use a reactve routng procedure at the global network level whle operatng a proactve routng procedure n a node s local neghbourhood. Zone Routng Protocol (ZRP) [9] s an example of the hybrd routng protocols. Table.2 presents a comprehensve comparson of varous routng protocols propertes for the wreless ad-hoc networks. 6.4 ENERGY EFFICIENCY OF TABLE-RIVEN vs. SOURCE-INITIATED PROTOCOLS Table-drven protocols have the overhead of route updates wth no consderaton to the frequency of forwardng packets that take place n the Ad-Hoc network. The routng nformaton s constantly propagated wthn the network. Wth on-demand protocols, routng nformaton s exchanged only when the source wshes to send some nformaton to the destnaton and has no nformaton about the destnaton n ts route cache. On the other hand, snce routng nformaton s constantly propagated and updated n table-drven protocols, nformaton about a partcular source-destnaton route s always avalable regardless of whether or not ths nformaton s requred. Ths feature leads to sgnfcant sgnallng overhead and power consumpton. Snce both battery and bandwdth are scarce resources n Ad-Hoc networks, ths becomes a serous lmtaton. Table.1 presents some of the metrcs for power-aware routng that addresses maxmzng the lfetme of wreless networks and mnmzng power consumpton for packet delvery. From the dscusson of table-based protocols provded n Secton 6.1 and on-demand protocols demonstrated n Secton 6.2, table-based protocols ncur sgnfcantly hgh routng overhead and hence lead to ncrease the energy consumpton compared to the ondemand protocols. 7. SIMULATION RESULTS Followng are the smulaton results of our work wth a network smulator. Fg.3 and Fg.4 shows the amount of data dropped of the three routng protocols when appled n a moble 15-node and 30-node network topology. Low data drop shows that both DSR and TORA routng protocols mantan many routes to the same destnaton. Fg.3. Data dropped wth 15 Nodes Fg.4. Data dropped wth 30 Nodes The packet can stll be delvered to ts destnaton, n the event of a lnk falure. On the other hand, AODV keeps only one route to a destnaton and therefore, a lnk falure must ntate route dscovery to the destnaton node. Whle the route dscovery process s underway, an ncreasng number of nodes are beng dropped. 545

5 K SANKAR: ENERGY EFFICIENT ROUTING PROTOCOLS FOR WIRELESS AD HOC NETWORKS A SURVEY general, TORA routng protocol performed moderately because the TORA routng protocol does not scale well wth relatvely large networks, and t s desgned for networks wth moble nodes movng at a moderate speed. Fg.5. Delay for 15 Nodes TORA routng protocol has the lowest level of data dropped (bts / second) followed by DSR, whch s almost near the performance of TORA protocol. AODV has the greatest level of data dropped because t does not support several routes for destnaton nodes as DSR and TORA routng protocols do. Therefore, wth node moblty, a lot of routes wll be broken, and some packets wll be dropped untl the route s redscovered. Fg.5 presents the delay encountered by the three routng protocols durng the smulaton perod n a 15-node moble topology. DSR routng protocol encounters most of the delay durng the smulaton than AODV and TORA. As the number of mobles s ncreasng DSR protocol performs worst than AODV and TORA as shown n Fg.6. Fg.7. Throughput 15 Nodes 8. CONCLUSION Fg.8. Throughput 30 Nodes Fg.6. Delay for 30 Nodes Fg.7 and Fg.8 represents the throughput of the routng protocols across the smulaton tme. As shown AODV experences the lowest throughput snce, t requres dscoverng the route to the destnaton, especally n a moble network. However, packets can be easly delvered n the case of DSR and TORA, as more than one route to the destnaton present ether n route tables of TORA or n the cache of DSR. In The performance of three source-ntated routng protocols that are AODV, DSR and TORA routng protocols were closely examned. Even f energy effcency s not the desgn targets of these routng protocols, each routng protocol behaved n a dfferent way wth energy aware metrcs. Ths s due to the route dscovery and mantenance mechansms of the routng protocols. The smulaton results revealed that TORA exceeds AODV and DSR n energy per packet consumpton. The network lfetme of TORA s also better than DSR and AODV. Ths ndcates that less energy consumpton does not prolong the network lfetme by tself. So, t s an ndcaton that energy effcent routng protocols must nclude battery energy level aware load balancng. Each routng protocol exhbted better performance n specfc scenaros and metrcs. In general, TORA 546

6 ISSN: (ONLINE) ICTACT JOURNAL ON COMMUNICATION TECHNOLOGY, JUNE 2012, VOLUME: 03, ISSUE: 02 outperforms n the majorty of scenaros and metrcs. Hence we conclude that TORA s more energy-effcent than DSR and AODV wth better performance. REFERENCES [1] D. B. Johnson, D. A. Maltz and Yh-Chun Hu, The Dynamc Source Routng Protocol (DSR) for Moble Ad Hoc Networks for IPv4, Internet Request for Comments RFC 4728, [2] C. Perkns, P. Bhagwat, Hghly dynamc Destnaton- Sequenced Dstance-Vector routng (DSDV) for moble computers, Proceedngs of the Conference on Communcatons archtectures, protocols and applcatons, pp , [3] Chansu Yu, Ben Lee Hee and Yong Youn, Energy Effcent routng protocols for moble ad-hoc networks, Wreless Communcatons and Moble Computng, Vol. 3, No. 8, pp , [4] Q. L, J. Aslam and D. Rus, Onlne Power-aware Routng n Wreless Ad-Hoc Networks, Proceedngs of the 7 th Internatonal Conference on Moble Computng and Networkng, pp , [5] Sunsook Jung, Nsar Hundewale and Alex Zelkovsky, Energy effcency of load balancng n MANET routng protocols, Sxth Internatonal Conference on Internatonal Workshop on Self-Assemblng Wreless Networks, pp , [6] IEEE Standards Department, Wreless LAN Medum Access Control (MAC) and Physcal Layer (PHY) Specfcatons, IEEE Standard , [7] Elzabeth M. Royer, Sung Ju Lee and Charles E. Perkns, The Effects of MAC Protocols on Adhoc Network Communcaton, IEEE Wreless Communcatons and Networkng Conference, Vol. 2, pp , [8] Svetlana Radosavac, S. Wu and C. Bonnet, Adaptve power-aware metrc n moble Ad hoc networks, XVIII World Telecommuncatons Congress, [9] X. L. Huang and B. Bensaou, On max-mn farness and schedulng n wreless adhoc networks: analytcal framework and mplementaton, Proceedngs of the 2 nd ACM Internatonal Symposum on Moble Ad-Hoc Networkng and Computng, pp , [10] A.Tsertou and D. I. Laurenson, Insghts nto the hdden node problem, Proceedngs of the 2006 Internatonal Conference on Wreless Communcatons and Moble Computng, pp , [11] Jharna Chokhawala and Albert M. K. Cheng, Optmzng Power Aware Routng n Moble Ad Hoc Networks, Real- Tme and Embedded Technology and Applcatons Symposum, [12] C. E. Perkns, Ad-Hoc Networkng, Addson Wesley, [13] S. Murthy and J.J. Garca-Luna-Aceves, An Effcent Routng Protocol for Wreless Networks, Moble Networks and Applcatons Specal ssue: Routng n Moble Communcaton Networks, Vol. 1, No. 2, pp , [14] M. Malek, K. Dantu, and M. Pedram, Power Aware Source Routng Protocol for Moble Ad Hoc Networks, Proceedngs of Internatonal Symposum on Low Power Electroncs and Desgn, pp , [15] D. Km, Garca-Luna-Aceves J.J, Obraczka K, Cano J.C and Manzon P, Power-aware Routng Based on the Energy Dran Rate for Moble Ad Hoc Networks, Proceedngs of 11 th Internatonal Conference on Computer Communcatons and Networks, pp , [16] C.K. Toh, Maxmum Battery Lfe Routng to Support Ubqutous Moble Computng n Wreless Ad Hoc Networks, IEEE Communcatons Magazne, Vol. 39, No. 6, pp , [17] A.Mchal and A. Ephremdes, Energy Effcent Routng for Connecton-orented Traffc n Wreless Ad-Hoc Networks, Moble Networks and Applcatons, Vol. 8, No. 5, pp , [18] C.E. Perkns and E. M. Royer, Ad Hoc on-demand Dstance Vector (AODV) Routng, Proceedngs of the 2 nd IEEE Workshop on Moble Computng Systems and Applcatons, pp , [19] V.D. Park and S. Corson, Temporally-Ordered Routng Algorthm (TORA) Verson 1 Functonal Specfcaton, IETF, Internet Draft: draft-etf-manet-tora-spec-04.txt,