A 2001 IBM manifesto observed that a looming software complexity crisis -caused by applications and environments that number into the tens of millions of lines of code - threatened to halt progress in computing. The manifesto noted the almost impossible difficulty of managing current and planned computing systems, which require integrating several heterogeneous environments into corporate-wide computing systems that extend into the Internet. Autonomic computing, perhaps the most attractive approach to solving this problem, creates systems that can manage themselves when given high-level objectives from administrators. Systems manage themselves according to an administrator's goals. New components integrate as effortlessly as a new cell establishes itself in the human body. These ideas are not science fiction, but elements of the grand challenge to create self-managing computing systems.

The vision of autonomic computing

Mobile ad hoc networks (MANETs) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self-organize into arbitrary and temporary, ‘‘ad-hoc’’ network topologies, allowing people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking concept is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad hoc paradigm. Recently, the introduction of new technologies such as the Bluetooth, IEEE 802.11 and Hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent evolutions have been generating a renewed and growing interest in the research and development of MANET. This paper attempts to provide a comprehensive overview of this dynamic field. It first explains the important role that mobile ad hoc networks play in the evolution of future wireless technologies. Then, it reviews the latest research activities in these areas, including a summary of MANETs characteristics, capabilities, applications, and design constraints. The paper concludes by presenting a set of challenges and problems requiring further research in the future. � 2003 Elsevier B.V. All rights reserved.

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Mobile ad hoc networking: imperatives and challenges

Topology Control (TC) is one of the most important techniques used in wireless ad hoc and sensor networks to reduce energy consumption (which is essential to extend the network operational time) and radio interference (with a positive effect on the network traffic carrying capacity). The goal of this technique is to control the topology of the graph representing the communication links between network nodes with the purpose of maintaining some global graph property (e.g., connectivity), while reducing energy consumption and/or interference that are strictly related to the nodes' transmitting range. In this article, we state several problems related to topology control in wireless ad hoc and sensor networks, and we survey state-of-the-art solutions which have been proposed to tackle them. We also outline several directions for further research which we hope will motivate researchers to undertake additional studies in this field.

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Topology Control in Wireless Ad Hoc and Sensor Networks

Mobile ad hoc networking has been an active research area for several years. How to stimulate cooperation among selfish mobile nodes, however, is not well addressed yet. In this paper, we propose Sprite, a simple, cheat-proof, credit-based system for stimulating cooperation among selfish nodes in mobile ad hoc networks. Our system provides incentive for mobile nodes to cooperate and report actions honestly. Compared with previous approaches, our system does not require any tamper-proof hardware at any node. Furthermore, we present a formal model of our system and prove its properties. Evaluations of a prototype implementation show that the overhead of our system is small. Simulations and analysis show that mobile nodes can cooperate and forward each other's messages, unless the resource of each node is extremely low.

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Sprite: a simple, cheat-proof, credit-based system for mobile ad-hoc networks

Gathering sensed information in an energy efficient manner is critical to operating the sensor network for a long period of time. The LEACH protocol presented by Heinzelman et al. (2000) is an elegant solution where clusters are formed to fuse data before transmitting to the base station. In this paper, we present an improved scheme, called PEGASIS (power-efficient gathering in sensor information systems), which is a near-optimal chain-based protocol that minimizes energy. In PEGASIS, each node communicates only with a close neighbor and takes turns transmitting to the base station, thus reducing the amount of energy spent per round. Simulation results show that PEGASIS performs better than LEACH. For many applications, in addition to minimizing energy, it is also important to consider the delay incurred in gathering sensed data. We capture this with the energy /spl times/ delay metric and present schemes that attempt to balance the energy and delay cost for data gathering from sensor networks. We present two new schemes to minimize energy /spl times/ delay using CDMA and non-CDMA sensor nodes. We compared the performance of direct, LEACH, and our schemes with respect to energy /spl times/ delay using extensive simulations for different network sizes. Results show that our schemes perform 80 or more times better than the direct scheme and also outperform the LEACH protocol.

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Data gathering algorithms in sensor networks using energy metrics

We study transmission strategies in a multiple-source, multiple-destination wireless network. Each source transmits packets that are intended for a particular destination. However, a transmitted packet can cause interference at other destinations. Our primary performance measure is throughput, which we define to be the average number of packets that are successfully received per intended destination per time slot. The sources are first divided into groups, based on the intended destination of their packets. In our parallel method, each group operates according to its own local protocol (e.g., TDMA), concurrently with and independently of the other groups. Our results show the impact of transmission schedules, channel fading, receiver noise, and other-user interference on network performance. We then show that, for given channel statistics and topology configurations, the network performance can be significantly improved when the groups in the network coordinate their transmissions according to an optimal schedule. Further, in many cases, even the use of randomly generated parallel schedules can provide considerably higher performance than traditional TDMA.

Parallel TDMA Scheduling for Multiple-Destination Wireless Networks

: The wireless networking environment presents formidable challenges to the study of broadcasting (one-to-all) and multicasting (one-to-many) problems, especially when energy-aware operation is required. To address the specific problem of energy-aware tree construction in wireless ad hoc networks, we have developed the Broadcast Incremental Power (BIP) and Multicast Incremental Power (MIP) algorithms. Our algorithms are based on a crosslayering approach in which tree structure and communication range are chosen jointly. We describe the similarities and differences between energy-limited and energy-efficient modes of operation, and we illustrate the impact of these overlapping (and sometimes conflicting) considerations on network operation. Examples of energy-limited applications include sensor networks and military networks in which soldiers batteries cannot be recharged during a mission. When such constraints are present, fundamental objectives include the maximization of a network's useful lifetime and the maximization of traffic volume that is delivered during this lifetime. Additionally, we extend our model to exploit the properties of directional antennas to obtain further performance improvement.

Energy-Aware Broadcasting and Multicasting in Wireless Ad Hoc Networks: A Cross-Layering Approach

Systems and method are provided for controlling the age of information, or information freshness, for remote status updating through the use of a packet deadline. In an embodiment, a packet deadline determines how long a packet is allowed to wait in a queue at the source before being transmitted, and, if the deadline expires, it is dropped from the system and never transmitted. This mechanism can control the flow of packets into the system, which can be used to control and optimize the age of information, thus providing a fresh status at a monitor.

Packet deadlines in a queue to control the age of information

We study cellular-like wireless networks in which the cells may overlap substantially, and a common channel is used for all cells. Thus, transmissions intended for one destination (or base station) can cause interference at neighboring destinations. We assume the use of a ?collision-channel? model, in which arbitrary communication and interference regions are associated with each destination. The interaction between such cells is best exemplified if the protocol of access in each cell is pure random access, i.e., Slotted Aloha. We derive a mathematical formula for the maximum achievable throughput for multiple-cell networks that satisfy a ?balance? condition, which is related to (but not as stringent as) symmetry. This formula implies that the throughput achieved in a cell is affected only by the degree of overlap with adjacent cells, i.e., a cell's throughput is not affected by transmissions that are outside of its interference region. Moreover, we show that, at the point of maximum throughput, the expected channel traffic is one packet per slot in each cell, an extension of the result obtained many years ago for single-destination networks.

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Random Access in Wireless Networks With Overlapping Cells

This paper discusses a networking concept referred to as multiple-ring architecture (MRA). In FDDI reliability applications, MRA is an attractive alternative to the popular dual homing architecture for the following reason. Unlike the requirement of several reliable concentrators needed in the dual homing architecture, the MRA only requires several routing interfaces at each backbone node (i.e., at each router node); different fiber cables and networks share the same set of routers, creating a set of highly fault tolerant networks of low overall cost and complexity.

Gam D. Nguyen

Papers

Parallel TDMA Scheduling for Multiple-Destination Wireless Networks

Energy-Aware Broadcasting and Multicasting in Wireless Ad Hoc Networks: A Cross-Layering Approach

Packet deadlines in a queue to control the age of information

Random Access in Wireless Networks With Overlapping Cells

Multiple-ring architecture and its FDDI applications