The minimum-energy multicast tree problem aims to construct a multicast tree rooted at the source node and spanning all the destination nodes such that the sum of transmission power at non-leaf nodes is minimized. However, aggressive power assignment at non-leaf nodes, although conserving more energy, results in multicast trees that suffer from higher hop count and jeopardizes delay-sensitive applications, signifying a clear tradeoff between energy efficiency and delay. This article formulates these issues as a constrained Steiner tree problem, and describes a distributed constrained Steiner tree algorithm, which jointly conserves energy and bounds delay for multicast routing in ad hoc networks. In particular, the proposed algorithm concurrently constructs a constrained Steiner tree, performs transmission power assignment at non-leaf nodes, and strives to minimize the sum of transmission power of non-leaf nodes, subject to the given maximum hop count constraint. Simulation results validate the effectiveness and reveal the characteristics of the proposed algorithm.

For mobile ad hoc networks, network-wide broadcast is a critical network layer function supporting route discovery and maintenance in many unicast and multicast protocols. A number of broadcast schemes have been proposed; however, almost all of them assume the usage of omnidirectional antennas and focus on broadcast overhead in terms of the number of forwarding nodes. Directional antennas have narrow beams and can potentially reduce broadcast overhead in terms of the ratio of the number of received duplicate packets to the number of nodes that receive broadcast packets. In this paper, we propose to map probability-based directional and omnidirectional broadcast to bond and site percolation, respectively, and describe a collection of directional antenna-based broadcast schemes for mobile ad hoc networks. A thorough and comparative simulation study is conducted to demonstrate the efficiency of the proposed schemes.

Mobile access points with long range communication capability may be deployed in mobile ad hoc networks to bridge (e.g. via airborne units) network partitions. In this paper, we address the problem of continuously navigating mobile access points to proper locations within their respective partitions such that certain network performance metrics are optimized, and refer to this problem as trajectory control. We present several trajectory control algorithms with different assumptions on locationing capabilities to achieve the objectives of reducing hop count and reducing overhead. Our proposed algorithms are more practical than existing centralized algorithms and make fewer assumptions on locationing capabilities. Simulation results demonstrate the effectiveness of the proposed algorithms.

The paper describes a distributed energy-conserving multicast routing protocol, termed ECMANSI, which makes use of the biological metaphor of swarm intelligence to create the multicast structure. ECMANSI adopts a core-based approach by establishing connectivity among the group members through a designated core node. Each node explores a better path with lesser transmission power to the core, which results in an energy efficient multicast structure. Results from extensive simulations have validated the efficiency of the protocol.

We propose a quorum-based approach to facilitating match-making (content-based routing) service for wireless mesh networks. Given a wireless mesh network, mesh nodes first autonomously select a set of backbone nodes via a backbone selection protocol. These backbone nodes then participate in a symmetric coterie construction process to create a quorum system. A quorum system has the property that the interaction of every two quorums is not empty and the union of all quorums results in the set of all backbone nodes. By using these two properties, the approach facilitates a match-making service that matches producer nodes' advertisements and consumer nodes' subscriptions at intersecting nodes between quorums.

The topology of an ad hoc network has a significant impact on its performance in that a dense topology may induce high interference and low capacity, while a sparse topology is vulnerable to link failure and network partitioning. Topology control aims to maintain a topology that optimizes network performance while minimizing energy consumption. Existing topology control algorithms utilize either a purely centralized or a purely distributed approach. A centralized approach, although able to achieve strong connectivity (k-connectivity for k /spl ges/ 2), suffers from scalability problems. In contrast, a distributed approach, although scalable, lacks strong connectivity guarantees. We propose a hybrid topology control framework, cluster-based topology control (CLTC) that achieves both scalability and strong connectivity. By varying the algorithms utilized in each of the three phases of the framework, a variety of optimization objectives and topological properties can be achieved. In this paper, we present the CLTC framework; describe topology control algorithms based on CLTC and prove that k-connectivity is achieved using those algorithms; analyze the message complexity of an implementation of CLTC, namely, CLTC-A, and present simulation studies that evaluate the effectiveness of CLTC-A for a range of networks.

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented.

Future Earth and space science missions are envisioned to be implemented using a flexible, distributed architecture consisting of a constellation of dynamically deployed or configured satellites that are networked together into an integrated information system. These satellites form an ad hoc network characterised by a frequently changing topology and potentially sparse and intermittent connectivity, which pose unique challenges to routing. We propose interrogation-based relay routing for ad hoc satellite networks, where the satellites interrogate each other to learn more about network topology and nodal capacity to make intelligent routing decisions. Simulations have been conducted to study the effects of satellite density and orbital patterns on throughput and delivery ratio.

This paper describes an adaptive multicast mechanism for ad hoc networks. The multicast mechanism adopts a two-tier architecture with an adaptive backbone infrastructure to integrate the effectiveness of the flooding scheme and the efficiency of the tree-based scheme for different network conditions. Coverage of a backbone node is not limited to a single hop, but is automatically adjusted according to the mobility status of each local area. Multicast capability is then provided via the construction of rendezvous-based multicast trees in the local group level and a mesh structure over the backbone level, providing both efficiency in static areas and robustness in dynamic areas. Performance evaluations are also presented.

Topology control for ad hoc networks aims to increase effective network capacity and conserve energy. Most proposed algorithms assume the use of isotropic antennas and thus only adjust the transmission power of each node. We propose a distributed topology control mechanism for ad hoc networks with directional antennas that adjusts antenna pattern (direction) in addition to transmission power. Simulation studies have been conducted to demonstrate the effectiveness of the approach, as well as to investigate its benefits and impacts on application layer performance.

Ad hoc networks are fundamentally different from wireline networks due to the following peculiarities. Ad hoc networks are autonomously formed with a large number of heterogeneous nodes (ranging in complexity from sensors to palmtops and fully functional laptops and routers) without the aid of any pre-existing communication infrastructure. Therefore, tasks are distributed over and carried out by groups of collaborating nodes. In addition, the nodes run on battery. They will have to be power-conscious to conserve energy, and the functions offered by a node will depend on its available power level and capability. Furthermore, their topology can be highly dynamic due to autonomous mobility of nodes and physical characteristics of wireless links. Energy constraints, varying wireless communication bandwidth and quality, and node mobility result in networks becoming partitioned more frequently. These make managing ad hoc networks significantly more challenging than managing wireline networks. We propose the Guerrilla Management Architecture to satisfy the survivability, adaptability, autonomy, economy, heterogeneity, and scalability requirements in managing ad hoc networks. Success in addressing these research issues will lead to robust deployment of ad hoc networks and their effective network operations and efficient resource utilization. The Guerrilla management architecture builds on the following model and mechanisms to address these specific management requirements.

As sensor nodes are embedded into physical environments and becoming integral parts of our daily lives, sensor networks will become the important nerve systems that monitor and actuate our physical environments. We define the process of monitoring the status of a sensor network and figuring out the problematic sensor nodes sensor network diagnosis. However, the high sensor node-to-manager ratio makes it extremely difficult to pay special attention to any individual node. In addition, the response implosion problem, which occurs when a high volume of incoming replies triggered by diagnosis queries cause the central diagnosing node to become a bottleneck, is one major obstacle to be overcome. We describe approaches to addressing the response implosion problem in sensor network diagnosis. We also present simulation experiments on the performance of these approaches, and discuss presentation schemes for diagnostic results.