karp @ eecs.harvard.edu We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the po-sitions of touters and a packer's destination to make packet for-warding decisions. GPSR makes greedy forwarding decisions us-ing only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks.

Abstract — The topology of wireless multihop ad hoc networks can be controlled by varying the transmission power of each node. We propose a simple distributed algorithm where each node makes local decisions about its transmission power and these local decisions collectively guarantee global connectivity. Specifically, based on the directional information, a node grows it transmission power until it finds a neighbor node in every direction. The resulting network topology increases network lifetime by reducing transmission power and reduces traffic interference by having low node degrees. Moreover, we show that the routes in the multihop network are efficient in power consumption. We give an approximation scheme in which the power consumption of each route can be made arbitrarily close to the optimal by carefully choosing the parameters. Simulation results demonstrate significant performance improvements. I.

Abstract—Many ad hoc routing protocols are based on some variant of flooding. Despite various optimizations, many routing messa ges are propagated unnecessarily. We propose a gossiping-based approa ch, where each node forwards a message with some probability, to reduce the ov erhead of the routing protocols. Gossiping exhibits bimodal behavio r in sufficiently large networks: in some executions, the gossip dies out quic kly and hardly any node gets the message; in the remaining executions, a sub stantial fraction of the nodes gets the message. The fraction of execution s in which most nodes get the message depends on the gossiping probability a nd the topology of the network. In the networks we have considered, using g ossiping probability between 0.6 and 0.8 suffices to ensure that almost every node gets the message in almost every execution. For large networ ks, this simple gossiping protocol uses up to 35 % fewer messages than flood ing, with improved performance. Gossiping can also be combined with va rious optimizations of flooding to yield further benefits. Simulations show that adding gossiping to AODV results in significant performance improv ement, even in networks as small as 150 nodes. We expect that the improvemen t should be even more significant in larger networks. I.

und the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's iii scalability on densely deployed wireless networks. iv Contents 1 Introduction 1 1.1 Metrics for Evaluating Routing Scalability . . . . . . . . . . . . . . . . . . 3 1.2 Traditional Shortest-Path Algorithms . . . . . . . . . . . . . . . . . . . . . 4 1.3 Ad-Hoc Routing Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Techniques for Routing Scalability . . . . . . . . . . . . . . . . . . . . . . 7 1.5 Applica

The topology of a wireless multi-hop network can be controlled by varying the transmission power at each node. In this paper, we give a detailed analysis of a cone-based distributed topology control algorithm. This algorithm does not assume that nodes have GPS information available; rather it depends only on directional information. Roughly speaking, the basic idea of the algorithm is that a node u transmits with the minimum power p u,# required to ensure that in every cone of degree # around u, there is some node that u can reach with power p u,# . We show that taking # = 5#/6 is a necessary and su#cient condition to guarantee that network connectivity is preserved. More precisely, if there is a path from s to t when every node communicates at maximum power then, if # 5#/6, there is still a path in the smallest symmetric graph G # containing all edges (u, v) such that u can communicate with v using power p u,# . On the other hand, if # > 5#/6, # This is a revised and extended version of "Analysis of a cone-based topology control algorithm for wireless multi-hop networks", which appeared in Proceedings of ACM Principles of Distributed Computing (PODC), 2001, and includes results from "Distributed topology control for power e#cient operation in multihop wireless ad hoc networks", by R. Wattenhofer, L. Li, P. Bahl, and Y. M. Wang, which appeared in Proceedings of IEEE INFOCOM, 2001.

In the context of multi-hop wireless networks, various topology control algorithms have been proposed to adapt the transmission range of nodes based on local information while maintaining a connected topology. These algorithms are particularly suited for deployment in sensor networks which typically consist of energy constrained sensors. Sensor nodes should support power adaptation in order to use the benefits of topology control for energy conservation. In this paper, we design a framework for evaluating the performance of topology control algorithms using overall network throughput, and total energy consumption per packet delivered, as the metrics. Our goal is to identify the scenarios in which topology control improves the network performance. We supplement our analysis with ns2 simulations using the conebased topology control algorithm [10, 19]. Based on our analysis and simulations, we find that link layer retransmissions are essential with topology control to avoid throughput degradation due to increase in number of hops in lightly loaded networks. In heavily loaded networks, the throughput can be improved by a factor up to k 2,where k is the average factor of reduction in transmission range using topology control. Studies of energy consumption reveal that improvements of up to k 4 can be obtained using topology control. However, these improvements decrease as the traffic pattern shifts from local (few hop connections) to non-local (hop lengths of the order of the diameter of the network). These results can be used to guide the deployment of topology control algorithms in sensor networks.

In a typical wireless mobile ad hoc network (MANET) using a shared communication medium, every node receives or overhears every data transmission occurring in its vicinity. However, this technique is not applicable when a power saving mechanism (PSM) such as the one specified in IEEE 802.11 is employed, where a packet advertisement period is separated from the actual data transmission period. When a node receives an advertised packet that is not destined to itself, it switches to a low-power state during the data transmission period, and thus, conserves power. However, since some MANET routing protocols such as Dynamic Source Routing (DSR) collect route information via overhearing, they would suffer if they are used with the IEEE 802.11 PSM. Allowing no overhearing may critically deteriorate the performance of the underlying routing protocol, while unconditional overhearing may offset the advantage of using PSM. This paper proposes a new communication mechanism, called RandomCast or Rcast, via which a sender can specify the desired level of overhearing in addition to the intended receiver. Therefore, it is possible that only a random set of nodes overhear and collect route information for future use. Rcast improves not only the energy efficiency, but also the energy balance among the nodes, without significantly affecting the routing efficiency. Extensive simulation using the ns-2 network simulator shows that Rcast is highly energy-efficient compared to the original IEEE 802.11 PSM and On-Demand Power Management (ODPM) protocol in terms of total energy consumption

Asymmetric links are common in wireless networks for a variety of physical, logical, operational, and legal considerations. An asymmetric link supports uni-directional communication between a pair of mobile stations and requires a set of relay stations for the transmission of packets in the other direction. We introduce a MAC layer protocol for wireless networks with Asymmetric links (AMAC).TheMAC layer protocol requires fewer nodes to maintain silence during a transmission exchange than the protocols proposed in [1, 2]. We present a set of concepts and metrics characterizing the ability of a medium access control protocol to silence nodes which could cause collisions.

Abstract — Recently, researchers have discovered that many of social, natural and biological networks are characterized by scale-free power-law connectivity distribution and a few densely populated nodes, known as hubs. We envision that wireless communication or sensor networks are directly deployed over such real-world networks to facilitate communication among participating entities. Here nodes move in such a way that they exhibit scale-free connectivity distribution at any instance, which cannot be modeled by most of the prior mobility models such as random waypoint (RWP) mobility model. This paper proposes clustered mobility model (CMM), which facilitates in forming hubs in a network satisfying the scale-free property. We call this a scale-free wireless network (SFWN). In CMM, it is possible to control the degree of node concentration or non-homogeneity to easily assess the strengths and weaknesses of the scale-free phenomena. To the best of the authors ’ knowledge, there has been no such mobility model reported in the literature and we believe the proposed CMM can be usefully used to investigate the properties of the SFWNs that are likely to occur in a real deployment of wireless multihop and sensor networks. Another important feature of CMM is that it does not possess any unintended spatial and temporal characteristics found in other mobility models such as RWP. Finally, to highlight the difference between a SFWN and a conventional wireless network, extensive simulation study has been conducted to measure network capacities at the physical, link and network layers. Index Terms — Connectivity distribution, mobility model, network capacity, random waypoint mobility, scale-free wireless networks. I.

Abstract — In this paper we discuss time-parallel simulation of wireless ad hoc networks. Such systems are rarely amenable to analytical modelling due to the complexity of the models involved. Thus, to obtain a quantitative evaluation of such models we often resort to simulation. Yet, current simulation techniques do not allow us to study systems consisting of thousands of nodes for extended periods of time. We introduce the notion of perturbation of measurements and present a layer-by-layer analysis of the impact of perturbations on the functioning of the wireless network. This model allows us to predict the accuracy of the simulation for several measures of performance through an analysis of the protocols involved at the various layers. We also present an implementation of time-parallel simulation based on iterative extension of the warmup period. In a series of experiments, we find good concordance between the predicted findings and the results of the simulations. I.