A Modified AOMDV Routing Protocol forMaritime Inter-ship CommunicationDaeseung Yoo, Gwangja Jin

and Byungtae JangElectronics and Telecommunications

Research InstituteRepublic of Korea

Email: {ooseyds.gjjin.jbt}@etri.re.kr

Abstract-In maritime communication, QoS problem causedby routing is very important. In this paper, we propose amethod based on AOMDV protocol providing a route recoverymechanism when a link breaks in an active route to reduce lostpackets. The results show that the proposed method can reducepacket loss ratio and delay time compared with the AOMDV.

Index Terms-Ad-hoc network, Maritime communication,AOMDV routing protocol, Local repair.

I. INTRODUCTION

Nowadays, communication between ships is based onsystems such as UHF and VHF radios for communicationnear port waters and satellite communication for long-range.In this paper, we propose a method based on the AOMDVrouting protocol [1] for inter-ship communication near portwater. But ad-hoc network (AN) [2] mode has some seriousproblems, such as ensuring QoS. In the ad-hoc network, theend-to-end packet delivery ratio depends on the recovery pathwhen one link breaks and the number of hops. A modifiedAOMDV protocol uses a single mechanism to recover theroute for ship-to-ship communication. This method will solvethe packet loss problem. In addition, data packets will betransferred to the destination node with an acceptable delaytime.

II. M-AOMDV SOLUTION

In an Ad-hoc network using AOMDV routing protocol isshown in figure 1. Source node S is transmitting data todestination node D, node F detected that link F-J is broken [3].Node F will start a processing "local repair" [4] to discovernew route to destination node by generating RREQ packetwith that destination if it has not other route to D. If node Fcannot receive any RREP packet, node F will transmit a RRERpacket for this destination. Therefore, data packets are cachedat node F and if source node S must restart route discoverythese data will be deleted. On the other hand, S does newroute discovery, it will increase data transferring delay time.We propose modified AOMDV local repair mechanism asfollows:

Le Thanh Tuan, Soonghwan RoKongju National University

275 Budae-dong, Cheonan-siChungnam, Republic of Korea

Email: [tuanltc roshj Okongju.ac.kr

Fig. 1. Local repair process of AOMDV routing protocol

1) Multipath routing: have multi routes for one destinationin routing table at each node. Each routes group for onedestination is shown as table 1.

TABLE IROUTING TABLE ENTRY FOR DESTINATION D AT NODE F

Destination Destination Next Hop PrioritySeq. No hop count Notice

D 2 J 1 Main routeD 2 G 2 Sub routeD 2 0 3 Sub route

2) In figure 1, a link breaks in the active route i.e. F-J link.If in the routing table of the intermediate node F hasother sub routes to destination D, it will select the routewith the lowest hop count and send data via this route. Ifit has no sub-route to D, node F does not send any RRERpacket. Instead, it tries to reach node D via another hop.It searches again for a node from its neighbors to reachto node D. It finds node X and starts sending packetsvia X to D (1) as in figure 2.

3) If, after step 2, the node F cannot search a new route toD, it will transmit a RRER packet to the source node Svia node E. If the routing table of node S has anothersub-route to D, S will select this sub-route and startsending packets via this route (2), as in figure 2. If Shas only one route to D, it will restart route discoveryfor this destination.

978-1-4577-1268-5/11/$26.00 2011 IEEE 605 ICTC 2011

Fig. 2. Route recovery process at F

III. SHIP MOVEMENT PATTERNThis section details the analysis of the mobility pattern

of ships near port. We have extensively analyzed theAIS(Automatic Identification System) data [5] to determinethe mobility pattern of ships traveling along the shorelinearea near the Pusan port in South Korea. Besides aiding inthe dimensioning of the network, the mobility pattern willalso be used in the maritime ad-hoc network simulator thatwe used to apply the proposed method to network topology,as in figure 3.

We focus on analyzing the distributions of inter-arrivaltimes and speeds of all ships crossing a given liner line onthe surface of the Earth. There is no obvious difference in theship arrival patterns from both directions. The total numbersof ships heading east-north and west-south in 24-hour periodsare 102 and 119, respectively. And the speeds of all ships areroughly 5-20 knots (2.5m1s-15m/s).

IV. PERFORMANCE EVALUATIONUsing NS2 [6], we evaluate the performance of Modified-

AOMDV (M-AOMDV) protocol. Also, we used ad-hoc net-work mode in mobile WiMAX environment [7] [8] to simulateproposed method [9].

A. Simulation scenarioIn our simulation as in figure 3, ship 12 wants to connect to

base station 2 (BS2). It starts route discovery with destinationBS2 on the mainland. After route discovery, routes to destina-tion BS2 is saved at ship 12 and intermediate ships (ISs). Thescenario is illustrated below: When ship 12 is transmittingdata to BS2 via route (12-9-5-3-1), we will gradually turnoff different IS node, off-IS, such as node (3), (4), (5) andevaluate performance result of this simulation. In simulationCBR traffic was used.

B. Result of performance evaluationIn order to evaluate the M-AOMDV performance, we

increased number of off-ISs from 1 to 7 in simulationscenario in which there are 20 ISs nodes. We measured thepacket loss rate of communication between ships farthest fromport and BS2 in comparison with that of AOMDV routingprotocol. Also, we evaluated the relationship between averageend-to-end delay and moving speed of the nodes (ships).

Fig. 3. Simulation scenario for M-AOMDV

Fig. 4. Packet loss rate vs. Number of off-ISs

Fig. 5. The relationship between speed and time delay

Figure 4 shows that when there are fewer intermediateships, the packet loss rate will increase. However, we cansee that our method has lower packet loss ratio than that ofAOMDV.

From figure 5, we can see that the delay of the AOMDVprotocol is longer than M-AOMDV, and the delay of thesetwo protocols are basically consistent with the fluctuating ofthe speed. The link repair mechanism of M-AOMDV canreduce delays, to a certain extent, by requesting routing toforward data packets as soon as possible in order to completelink repair to the destination node when the node detects that

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the link has been interrupted.

V. CONCLUSIONIn this paper, we proposed modified AOMDV local repair

process. We evaluated the proposed protocol and comparedperformances with those of AOMDV protocol. The resultsshow that M-AOMDV reduces average delay and packet lossratio. Also, this proposed method increases the potential forthe ad-hoc network mode to be applied to ship networks onshoreline areas.

VI. ACKNOWLEDGMENTThis work was supported by the IT R&D program of

MKE. [1OMC9910, Development of Solution for Ship SafetyNavigation based Maritime Ad-hoc Network]

REFERENCES

[1] Abolhasan, M., Wysocki, T., and Dutkiewicz, E., "A review of routingprotocols for mobile ad hoc networks," Ad Hoc Networks 2, pp. 1-22(2004).

[2] Stamatios V. Kartalopoulos, "Mobile Ad-hoc Networking", the Instituteof Electrical and Electronics Engineers, 2004.

[3] YuHua Yuan, HuiMin Chen, and Min Jia, "An Optimized Ad-hoc On-demand Multipath Distance Vector(AOMDV) Routing Protocol", 2005Asia-Pacific Conference on Communications, Perth, Western Australia, 3- 5 October 2005.

[4] Perkins, C., Belding-Royer, E., and Das, S., "Ad hoc On-DemandDistance Vector (AODV) routing," rfc3561.txt (2003).

[5] http://www.marinetraffic.comlais/[6] The Network Simulator - ns-2, http://www.isLedulnsnamlns[7] Application Working Group (AWG), WiMAX Forum and National Insti-

tute of Standards and Technology (NIST), "Simulator NS-2 MAC+PHYAdd-on for WiMAX (IEEE 802.16)", Aug 2008.

[8] WiMAX Forum, "WiMAX TM system Evaluation Methodology version2.1", July, 2008.

[9] http://code.google.comlp/ns2- wimax-awg

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