Showing papers by "Gam D. Nguyen published in 2002"

Energy-efficient broadcast and multicast trees in wireless networks

Abstract: The wireless networking environment presents formidable challenges to the study of broadcasting and multicasting problems. In this paper we focus on the problem of multicast tree construction, and we introduce and evaluate algorithms for tree construction in infrastructureless, all-wireless applications. The performance metric used to evaluate broadcast and multicast trees is energy-efficiency. We develop the Broadcast Incremental Power (BIP) algorithm, and adapt it to multicast operation by introducing the Multicast Incremental Power (MIP) algorithm. These algorithms exploit the broadcast nature of the wireless communication environment, and address the need for energy-efficient operation. We demonstrate that our algorithms provide better performance than algorithms that have been developed for the link-based, wired environment.

Energy-aware wireless networking with directional antennas: the case of session-based broadcasting and multicasting

Abstract: We consider ad hoc wireless networks that use directional antennas and have limited energy resources. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance, We observe significant improvement with respect to the omnidirectional case, in terms of both energy efficiency and network lifetime. Additionally, we show that further substantial increase in the network's lifetime can be achieved by incorporating a simple measure of a node's residual energy into the node's cost function.

Energy-limited wireless networking with directional antennas: the case of session-based multicasting

Abstract: We consider ad hoc wireless networks that use directional antennas and have limited energy resources. The performance objectives of such networks depend largely on the application. However, a robust performance measure is the total traffic volume that the network can deliver when all nodes are equipped with a finite and non-renewable amount of energy. We show that the network's lifetime can be extended significantly by incorporating a simple measure of a node's residual energy into the node's cost function. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance. We observe significant improvement with respect to the omnidirectional case.

The energy efficiency of distributed algorithms for broadcasting in ad hoc networks

Abstract: The broadcast incremental power (BIP) algorithm is a centralized heuristic for the construction of energy-efficient broadcast trees in wireless networks. We discuss the issues associated with the development of distributed algorithms for broadcast tree construction, and develop and evaluate several versions of distributed BIP (Dist-BIP). We compare the performance of these schemes with that of both centralized BIP and minimum-cost spanning tree (MST) algorithm.

Distributed algorithms for energy-efficient broadcasting in ad hoc networks

Abstract: Previously, we developed the broadcast incremental power (BIP) algorithm (Wieselthier, J.E. et al., Proc. IEEE INFOCOM 2000, p.585-94, 2000; Mobile Networks and Applications (MONET), vol.7, no.6, 2002), which is a centralized heuristic for energy-efficient broadcasting of source-initiated session-based traffic in wireless networks. This algorithm, which exploits the characteristics of the wireless channel, was shown to perform better than adaptations of conventional algorithms that were originally developed for wired networks. However, as a consequence of its centralized nature, it is "expensive" in terms of both communication and computation requirements. We now develop two distributed versions of BIP, and compare their performance to that of centralized BIP and to an algorithm based on the minimum-cost spanning tree formulation.

Energy-Efficient Multicasting of Session Traffic in Bandwidth- and Transceiver-Limited Wireless Networks

Abstract: In this paper, we address the impact of resource limitations on the operation and performance of the broadcasting and multicasting schemes developed for infrastructureless wireless networks in our earlier studies. These schemes, which provide energy-efficient operation for source-initiated session traffic, were previously studied without fully accounting for such limitations. We discuss the “node-based” nature of the all-wireless medium, and demonstrate that improved performance can be obtained when such properties are exploited by networking algorithms. Our broadcast and multicast algorithms involve the joint choice of transmitter power and tree construction, and thus depart from the conventional approach that makes design choices at each layer separately. We indicate how the impact of limited frequency resources can be addressed. Alternative schemes are developed for frequency assignment, and their performance is compared under different levels of traffic load, while also incorporating the impact of limited transceiver resources. The performance results include the comparison of our algorithms to alternative “link-based” algorithms for broadcasting and multicasting.

Application of optimization techniques to a nonlinear problem of communication network design with nonlinear constraints

Abstract: Nonlinear optimization under nonlinear constraints is usually difficult. However, standard ad-hoc search techniques may work successfully in some cases. Here, we consider an augmented Lagrangian formulation, and we develop a "projection heuristic" that "guides" the iterative search toward the optimum. We demonstrate the effectiveness of this approach by applying it to the problem of maximizing a circuit-switched communication network's throughput under quality-of-service (QoS) constraints by means of choosing the input offered load. This problem is useful for "sizing" the network capacity. Performance results using several versions of the algorithm demonstrate its robustness, in terms of its accuracy and convergence properties.

The effect of discrete power levels on energy-efficient wireless broadcast in ad hoc networks

Abstract: We take initial steps toward developing energy-efficient broadcast algorithms for ad hoc wireless networks that operate under changing connectivity conditions. Such algorithms need to be distributed. To be distributed these algorithms need to probe neighboring nodes to determine possible connectivities at different power levels. We proceed toward this goal by revisiting and modifying previously obtained broadcast algorithms that were centralized and in which the exact levels of minimally necessary RF power to reach neighboring nodes could be determined. Instead, we now constrain RF power to take values from a finite discrete set, and evaluate the impact on algorithm performance. We then discuss further modifications for distributed operation.

Circuit-switched “network capacity” under QoS constraints

Abstract: Usually the network-throughput maximization problem for constant-bit-rate (CBR) circuit-switched traffic is posed for a fixed offered load profile. Then choices of routes and of admission control policies are sought to achieve maximum throughput (usually under QoS constraints). However, similarly to the notion of channel “capacity,” it is also of interest to determine the “network capacity;” i.e., for a given network we would like to know the maximum throughput it can deliver (again subject to specified QoS constraints) if the appropriate traffic load is supplied. Thus, in addition to determining routes and admission controls, we would like to specify the vector of offered loads between each source/destination pair that “achieves capacity.” Since the combined problem of choosing all three parameters (i.e., offered load, admission control, and routing) is too complex to address, we consider here only the optimal determination of offered load for given routing and admission control policies. We provide an off-line algorithm, which is based on Lagrangian techniques that perform robustly in this rigorously formulated nonlinear optimization problem with nonlinear constraints. We demonstrate that significant improvement is obtained, as compared with simple uniform loading schemes, and that fairness mechanisms can be incorporated with little loss in overall throughput.