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On-demand Rout<strong>in</strong>g <strong>in</strong> MANETs:The Impact of a Realistic Physical Layer ModelLiang Q<strong>in</strong> and Thomas KunzCarleton University, Ottawa, Ont., Canada K1S 5B6{lq<strong>in</strong>,tkunz}@sce.carleton.caAbstract. Most simulations and performance comparisons of mobile ad hocnetwork rout<strong>in</strong>g protocols are based on a simplistic and idealistic physical layermodel. In real applications, there are different k<strong>in</strong>ds of noise or <strong>in</strong>terference thatimpact the signal power. We use a shadow<strong>in</strong>g propagation model <strong>in</strong> our simulationevaluation of two on-demand rout<strong>in</strong>g protocols: AODV and DSR. Becauseof signal power fluctuation, active routes will break, which causes significantthroughput degradation and longer packet delay. In this paper, we analyze theimpact of a shadow<strong>in</strong>g model on the performance of these two rout<strong>in</strong>g protocols.Then we set a new signal power threshold dur<strong>in</strong>g the route discoveryprocess so that only those l<strong>in</strong>ks with strong enough signal power will be chosen;we also reduce some control messages for DSR. The simulation resultsshow significant <strong>in</strong>creases <strong>in</strong> packet delivery ratio and decreases <strong>in</strong> packet latencyfor both protocols.1 IntroductionA mobile ad hoc network (MANET) is an <strong>in</strong>frastructure-less network. Because theradio transmission range is limited and mobile nodes are free to move randomly, theroutes are subject to frequent failure. Dozens of rout<strong>in</strong>g protocols for MANET havebeen proposed, for example, Dest<strong>in</strong>ation-Sequenced Distance-Vector Rout<strong>in</strong>g(DSDV)[1], Temporally-Ordered Rout<strong>in</strong>g Algorithm (TORA) [2], Dynamic SourceRout<strong>in</strong>g protocol (DSR)[3], Signal Stability-Based Adaptive Rout<strong>in</strong>g (SSA) [4], andAd-hoc On-Demand Distance Vector Rout<strong>in</strong>g (AODV)[5]. Performance evaluationsand comparisons between several rout<strong>in</strong>g protocols have been published <strong>in</strong> [6][7]. Butthese evaluations are based on simulations us<strong>in</strong>g a two-ray ground propagation model.In real applications, the path between transmitter and receiver can be l<strong>in</strong>e-of-sight, orobstructed <strong>by</strong> physical obstacles between them, thus the signal strength on the receivernot only depends on the distance, but also on the environment. At the timewhen this research began, few simulations tried to use different propagation models toevaluate rout<strong>in</strong>g protocol performance, and most rout<strong>in</strong>g protocols assume that packetloss over a l<strong>in</strong>k <strong>in</strong>dicates a l<strong>in</strong>k breakage due to node mobility. Takai [8] presentssimulation results us<strong>in</strong>g free space, Rayleigh and SIRCIM (Simulation of IndoorRadio Channel Impulse Response Models with Impulse Noise) propagation models <strong>in</strong>a 130m <strong>by</strong> 130m area with 20 mobile nodes. Goff [9] proposes some ways to verifywhether the signal fluctuation is caused <strong>by</strong> channel fad<strong>in</strong>g.This paper concentrates on the impact of a shadow<strong>in</strong>g propagation model on theperformance of two on-demand rout<strong>in</strong>g protocols: AODV and DSR. Simulations ofS. Pierre, M. Barbeau, and E. Kranakis (Eds.): ADHOC-NOW 2003, LNCS <strong>2865</strong>, pp. 37–48, 2003.© Spr<strong>in</strong>ger-Verlag Berl<strong>in</strong> Heidelberg 2003

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