Existing routing protocols for mobile ad hoc networks assume that all nodes have the same radw tmnsmission range. In other words. the mobile ad hoc network has symmetric links, which means that two neighboring nodes A and B are within the transmission range of one another: However, since nodes consume battery power independently according to their computing and communication 1 4 there exist asymmetric links, which means that node A is within node B'
s transmission range, but not vice versa In this paper, two approaches are presented to suppon routing in the existence of asymmetric links: GAHA(GPS-based Hop-by-hop Acknowledgment) and GAPA(GPS-based Passive Acknowledgment) schemes. Both GAHA and GAPA can be applied to any routing protocols by utilizing GPS(Globa1 Positioning System) location information. Simulation results reveal that both GAHA and GAPA protocols cope well in the presence of asymmetric wireless links and nodes' mobility.
I. INTRODUCTIONRecently, research effort was focused on medium access control [lO,ll], routing[l-7.12], and transport[8,9] protocols for mobile ad hoc networks. Unlike traditional mobile networks where base stations and switches are wireconnected together to form the communication infrastructure and mobile nodes can access the network via their corresponding base-stations, nodes in a mobile ad hoc network can move freely and communicate with each other. Intermediate ad hoc nodes relay packets towards the destination node wirelessly. Due to the characteristics of mobile ad hoc networks, conventional network protocols proposed for fixed networks cannot be used.Existing routing protocols for mobile ad hoc networks can generally be categorized into two classes : (a) proactive, and (b) reactive. In proactive schemes[2, 121, nodes maintain their routing tables for all possible destinations irrespective of the need for routes. However, in reactive schemes [l,6], routes are acquired based ondemand manner by the source. Therefore, it does not have to main-'= wo& was suppmDsdia pm by Q Bnin -21 projar of Minisay of Emvrtios in pm by thc National Romch Lbormory project of Miuisuy of Science eod Tahmbgy. eod in pm by 4 e n c Y o f a t c m c a m , -0-7803-7244-
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