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One of the main design issues for a sensor network is conservation of the energy available at each sensor node. We propose to deploy multiple, mobile base stations to prolong the lifetime of the sensor network. We split the lifetime of the sensor network into equal periods of time known as rounds. Base stations are relocated at the start of a round. Our method uses an integer linear program to determine new locations for the base stations and a flow-based routing protocol to ensure energy efficient routing during each round. We propose four metrics and evaluate our solution using these metrics. Based on the simulation results we show that employing multiple, mobile base stations in accordance with the solution given by our schemes would significantly increase the lifetime of the sensor network.

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d hoc networks consist of a set of mobile hosts communicating among themselves using wireless links, without the use of any other communication support facilities (e.g., base stations). They are also called mobile radio networks or multihop wireless networks. Two mobile hosts (MHs) are said to be within range and neighbors of each other if each can receive the other's transmission. Every MH behaves in a cooperative fashion by acting as a router, allowing packets destined to other MHs to pass through it.The topology of an ad hoc network changes every time an MH's movement results in the establishment of new wireless links (an MH moves within range of another) or link disconnections (an MH moves out of range of another which was within its range). The rate of topology change is dependent on the extent of mobility and transmission range of the hosts. Routes are heavily dependent on the relative location of MHs. Hence, routes may be repeatedly invalidated in an unpredictable and arbitrary fashion due to the mobility of hosts. The mobility of a single node may affect several routes that pass through it.In this article, we consider the problem of maintaining reliable end-to-end communication in ad hoc networks, similar to that provided by TCP over the Internet. It is desirable to use TCP directly even in ad hoc networks in order to provide seamless portability to applications like file transfer, e-mail, and Web browsers written using standard TCP libraries.Hence, it is of interest to study the behavior of TCP in the context of ad hoc networks and evaluate the effect of dynamic topology on TCP performance. Our studies and simulation results indicate that as a result of frequent and unpredictable route disruptions, TCP's performance is substantially degraded. We propose a feedback mechanism for overcoming this problem. Simulation experiments show that the use of feedback mechanisms along with TCP can result in substantial performance improvements.The rest of the article is organized as follows. We describe existing work in related areas. We describe the ad hoc network model and assumptions. We discuss the behavior of TCP in ad hoc networks and explain the proposed approach for improving TCP performance. The simulation model, experiments, and observations are presented and discussed, followed by conclusions. Related WorkThe dynamic nature of topology in ad hoc networks poses many interesting problems in the domain of routing protocols. As a result, ad hoc networks have been studied extensively in the context of routing (i.e., at the network layer). In these networks, it is necessary to have a routing protocol that:• Quickly provides relatively stable, loop-free routes • Adapts to the mobility of the network Conventional protocols like link state and distance vector do not match these requirements because they do not converge quickly enough or scale well as mobility increases. A number of alternative protocols have been proposed, including a dynamic sequenced distance vector (DSDV) AbstractAd hoc networks are completel...

We consider the problem of link scheduling in a sensor network employing a TDMA MAC protocol. Our link scheduling algorithm involves two phases. In the first phase, we assign a color to each edge in the network such that no two edges incident on the same node are assigned the same color. We propose a distributed edge coloring algorithm that needs at most (δ+1) colors, where δ is the maximum degree of the graph. To the best of our knowledge, this is the first distributed algorithm that can edge color a graph with at most (δ + 1) colors. In the second phase, we map each color to a unique timeslot and attempt to identify a direction of transmission along each edge such that the hidden terminal and the exposed terminal problems are avoided. Next, considering topologies for which a feasible solution does not exist, we obtain a direction of transmission for each edge using additional timeslots, if necessary. Finally, we show that reversing the direction of transmission along every edge leads to another feasible direction of transmission. Using both the transmission assignments we obtain a TDMA MAC schedule which enables two-way communication between every pair of neighbors. For acyclic topologies, we show that at most 2(δ + 1) timeslots are required. Through simulations we show that for sparse graphs with cycles the number of timeslots assigned is close to 2(δ + 1).