A Reactive Location Service for Mobile Ad Hoc Networks

We present and analyze a reactive location service RLS for mobile ad hoc networks. RLS provides a mobile node in a wireless ad-hoc network with the means to inquire the current geographical position of another node on-demand and can be used as a building block for location-based routing. We provide a comparison of RLS to an ideal omniscient location service as well as to the complex Grid Location Service (GLS). In addition, we compare the performance of greedy location-based routing in combination with RLS to the performance of a non-location-based ad hoc routing approach, namely Dynamic Source Routing (DSR). DSR was chosen for the comparison since RLS can be considered an adaptation of DSR\'s route discovery mechanisms to the location-based domain. We also introduce and study possible optimizations for RLS, in particular caching, random re-broadcast jitter, and re-broadcast suppression. The quantitative results of our NS-2 simulation study show a very good perform! ance of RLS combined with greedy routing, outperforming GLS and DSR for scenarios with high mobility and high node density

Beaconless Position-Based Routing for Mobile Ad-Hoc Networks

Existing position-based unicast routing algorithms, where packets are forwarded in the geographic direction of the destination, require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. The transmission of beacons and the storage of neighbor information consumes resources. Due to mobility, collected neighbor information can quickly get outdated which in turn can lead to packet drops. In this paper, we propose a mechanism to perform position-based forwarding without the help of beacons or the maintenance of neighbor tables. In our contention-based forwarding scheme(CBF) the next hop is selected through a distributed contention process using biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy routing approach by means of simulation with ns-2. Our results demonstrate that CBF is a promising strategy for position-based routing

A Comparison of Routing Strategies for Vehicular Ad Hoc Networks

On this paper we investigate the use of ad-hoc routing algorithms for the exchange of data between vehicles. There are two main aspects that are of interest in this context: the specific characteristics of ad-hoc networks formed by vehicles and the applicability of existing ad-hoc routing schemes to networks that display these characteristics. In order to address both aspects we generate realistic vehicular movement patterns of highway traffic scenarios using a well validated traffic simulation tool. Based on these patterns we show that the characteristics of vehicular ad-hoc networks are quite different from the frequently used random waypoint model. We then proceed to evaluate the performance of a reactive ad-hoc routing protocol (DSR) and of a position-based approach (greedy forwarding as done in GPSR) in combination with a simple reactive location service. Our analysis suggests that for vehicular networks where communication spans more than 2 or 3 hops position-! based ad-hoc routing has significant advantages over reactive non-position-based approaches both in the number of successfully delivered packets and in routing overhead

A Simulation Study of a Location Service for Position-Based Routing in Mobile Ad Hoc Networks

Position-based routing in a mobile ad hoc network requires geographic addresses. Thus, a node that wants to send a packet to some target node has to know the target's (approximate) current position. In order to provide each node's position to the other network nodes, a distributed location service has to be used. J. Li et al. recently put forward a promising approach called the Grid Location Service' (GLS). In this paper we provide some analyses and evaluations of GLS by means of simulation with ns-2 beyond the results of the original paper. We present quantitative results with respect to location query failure rate and bandwidth consumption. We analyze in detail why queries failed and how the query failure rate can be decreased for scenarios with a low density of nodes

Dissidents and God-Talk in the Johannine Epistles

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