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An ad hoc network may be logically represented as a set of clusters. The clusterheads form a d-hop dominating set. Each node is at most d hops from a clusterhead. Clusterheads form a virtual backbone and may be used to route packets for nodes in their cluster. Previous heuristics restricted themselves to 1-hop clusters. We show that the minimum d-hop dominating set problem is NP-complete. Then we present a heuristic to form d-clusters in a wireless ad hoc network. Nodes are assumed to have non-deterministic mobility pattern. Clusters are formed by diffusing node identities along the wireless links. When the heuristic terminates, a node either becomes a clusterhead, or is at most d wireless hops away from its clusterhead. The value of d is a parameter of the heuristic. The heuristic can be run either at regular intervals, or whenever the network configuration changes. One of the features of the heuristic is that it tends to re-elect existing clusterheads even when the network configurat...

Most of the routing algorithms for ad-hoc networks assume that all wireless links are bidirectional. In reality, some links may be unidirectional. The presence of such links can jeopardize the performance of the existing routing algorithms. In this paper we show that routing protocols that account for unidirectional links will require nodes to exchange O(n 2 ) information with each other, where n is the number of nodes in the network. We also present modifications to distance vector based routing algorithms to make them work in ad-hoc networks with unidirectional links. 1 Introduction The mobility pattern of the nodes in an ad-hoc network is often non-deterministic. Hence, the network topology is always in a flux. There has been a significant amount of effort towards developing routing algorithms for such networks. These algorithms can be classified into (a) cluster-based algorithms, and (b) flat algorithms. In cluster-based algorithms [1, 2, 5, 6], at regular intervals, a sub...

Bandwidth and power constraints are the main concerns in current wireless networks because multihop, ad hoc mobile wireless networks rely on each node in the network to act as a router and packet forwarder. This dependency places bandwidth, power, and computation demands on mobile hosts which must be taken into account when choosing the best routing protocol. In recent years, protocols that build routes based "on demand" have been proposed. The major goal of on-demand routing protocols is to minimize control traffic overhead. In this paper, we perform a simulation and performance study on some routing protocols for ad hoc networks. Distributed Bellman-Ford, a traditional table-driven routing algorithm, is simulated to evaluate its performance in multihop wireless networks. In addition, two on-demand routing protocols (Dynamic Source Routing and Associativity-Based Routing) with distinctive route selection algorithms are simulated in a common environment to quantitatively measure and co...

Ad hoc networks consist of a set of identical nodes that move freely and independently and communicate with other node via wireless links. Such networks may be logically represented as a set of clusters by grouping together nodes that are in close proximity with one another. Clusterheads form a virtual backbone and may be used to route packets for nodes in their cluster. Nodes are assumed to have non-deterministic mobility pattern. Clusters are formed by diffusing node identities along the wireless links. Different heuristics employ different policies to elect clusterheads. Several of these policies are biased in favor of some nodes. As a result, these nodes shoulder greater responsibility and may deplete their energy faster, causing them to drop out of the network. Therefore, there is a need for load-balancing among clusterheads to allow all nodes the opportunity to serve as a clusterhead. We propose a loadbalancing heuristic to extend the life of a clusterhead to the maximum budget b...

In mobile computing systems the network con guration changes due to node mobility. This paper identi es the issues a group communication service has to take into account in order to handle node mobility. These include the need to identify the location of a node, and the ability to cope with inaccuracies in the determination of a group membership. A multi-level architecture for group communication in mobile systems is presented. This architecture contains a synchronous proximity layer protocol to determine the set of mobile nodes in the proximity of a given node in the network. This information is used by a three-round group membership protocol for construction of groups used bymobile applications. As an example, the architecture is specialized to solve the channel allocation problem. 1.

Abstract — 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).

The digital information revolution has brought about profound changes in our society and our lives. The many advantages of digital information have also generated new challenges and new opportunities for innovation. This thesis discusses the issues regarding multimedia data hiding and its application to multimedia security and communication, addressing both theoretical and practical aspects, and tackling both design and attack problems. In the fundamental part, we identify a few key elements of data hiding through a layered structure. Data hiding is modeled as a communication problem where the embedded data is the signal to be transmitted. Various embedding mechanisms target different robustness-capacity tradeoffs. We study this tradeoff for two major categories of embedding mechanisms. In addition, we have found that the un-evenly distributed embedding capacity brings difficulty in data hiding. We propose a comprehensive solution to this problem, addressing the considerations for choosing constant or variable embedding rate and enhancing the performance for each case.

Ad hoc networks are gaining increasing popularity in recent years because of their ease of deployment. No wired base station or infrastructure is supported, and each host communicasts one another via packet radios. In ad hoc networks, routing protocols are challenged with establishing and maintaining multihop routes in the face of mobility, bandwidth limitation and power constraints. In this dissertation, we study the routing strategies for ad hoc networks. On-demand routing protocols and table-driven algorithms are analyzed and compared against each other. Our study shows that on-demand protocols are better suited for mobile networks because they generate less control overhead and manage the mobility in a more efficient manner. Simulation experiments also indicate that providing multiple routes is beneficial in increasing the robustness against mobility.

Reliable multicast schemes often cannot scale to large receiver sets due to the problems of state explosion and message implosion. In this paper we propose Erasure Correcting Scalable Reliable Multicast, ECSRM. ECSRM is based on the SRM framework proposed by Floyd et. al., which utilizes NACK suppression to reduce message implosion. ECSRM makes a number of modifications to SRM to addressed enhanced scalability and rate control. Most notably, instead of resending lost packets, erasure-correcting encoded packets are sent in response to NACK messages. Introduction There are many instances in which it is desirable to deliver the same data to a number of receivers across a network. Popular "push" technology is focused on distributing news articles, stock quotes and the like to many subscribers. Other examples of applications that can utilize multipoint communication included multi-party video-conferencing, software updates, and multiplayer gaming. IP multicast is an excellent means of tra...