Showing papers in "Ad Hoc & Sensor Wireless Networks in 2005"

Maintaining Sensing Coverage and Connectivity in Large Sensor Networks.

Abstract: In this paper, we address the issues of maintaining sensing coverage and connectivity by keeping a minimum number of sensor nodes in the active mode in wireless sensor networks. We investigate the relationship between coverage and connectivity by solving the following two sub-problems. First, we prove that if the radio range is at least twice the sensing range, complete coverage of a convex area implies connectivity among the working set of nodes. Second, we derive, under the ideal case in which node density is sufficiently high, a set of optimality conditions under which a subset of working sensor nodes can be chosen for complete coverage. Based on the optimality conditions, we then devise a decentralized density control algorithm, Optimal Geographical Density Control (OGDC), for density control in large scale sensor networks. The OGDC algorithm is fully localized and can maintain coverage as well as connectivity, regardless of the relationship between the radio range and the sensing range. Ns-2 simulations show that OGDC outperforms existing density control algorithms [25, 26, 29] with respect to the number of working nodes needed and network lifetime (with up to 50% improvement), and achieves almost the same coverage as the algorithm with the best result.

Low-Interference Topology Control for Wireless Ad Hoc Networks.

Abstract: Topology control has been well studied in wireless ad hoc networks. However, only a few topology control methods take into account the low interference as a goal of the methods. Some researchers tried to reduce the interference by lowering node energy consumption (i.e. by reducing the transmission power) or by devising low degree topology controls, but none of those protocols can guarantee low interference. Recently, Burkhart et al. [?] proposed several methods to construct topologies whose maximum link interference is minimized while the topology is connected or is a spanner for Euclidean length. In this paper we give algorithms to construct a network topology for wireless ad hoc network such that the maximum (or average) link (or node) interference of the topology is either minimized or approximately minimized.

Computing connected dominated sets with multipoint relays

Abstract: Multipoint relays offer an optimized way of flooding packets in a radio network. However, this technique requires the last hop knowledge: to decide wether or not a flooding packet is retransmitted, a node needs to know from which node the packet was received. When considering broadcasting at IP level, this information may be difficult to obtain. We thus propose a scheme for computing an optimized connected dominating set from multipoint relays. This set allows to efficiently broadcast packets without the last hop information with performances close to multipoint relay flooding.

Adaptive Gateway Discovery Mechanisms to Enhance Internet Connectivity for Mobile Ad Hoc Networks.

Abstract: One of the key overhead components affecting the overall performance of hybrid ad hoc networks is the discovery and selection of Internet gateways. We develop an analytical model to evaluate existing proposals and we show that each of them is suited only for a limited range of network conditions. We propose and simulate two new adaptive gateway discovery algorithms (maximal source coverage and maximal benefit coverage) based on the dynamic adjustment of the scope of the gateway advertisement packets. Our results show that the adaptation capabilities of our proposed schemes allow them to outperform existing mechanisms over a variety of scenarios and mobility rates.

Duty Cycle Management in Sensor Networks Based on 802.15.4 Beacon Enabled MAC.

Abstract: The recent IEEE 802154 standard offers a promising platform for wireless sensor networks Among the main problems in many sensor network applications is the problem of ensuring the desired quality of service, expressed as the mean data rate obtained from a specific spatial area, while simultaneously maximizing the lifetime of the network In this work we consider the feasibility of duty cycle management as the vehicle to achieve these goals We consider the IEEE 802154 network in beacon enabled mode, and analyze its performance under two duty cycle management algorithms Both algorithms are fully distributed, ie, the nodes autonomously control their sleep period according to local information only In the first algorithm, the sleep period is a geometrically distributed random variable with a given mean value; in the second, the sleep period is inversely proportional to the most recent duration of the packet service time We model and evaluate both policies using the theory of discrete time Markov chains and M/G/1/K queues with vacations, where geometrically distributed sleep periods are modeled as server vacations We found that both policies are capable of achieving almost 100% reliability and less than 1% utilization under a wide range of packet arrival rates and network size

Lessons from an Ad hoc Network Test-Bed: Middleware and Routing Issues *

Abstract: Although MANET research has been ongoing for some time, there are relatively few experiences with real ad hoc networks. Instead, a large portion of protocol development is done in (often unrealistic) simulation settings only. In this paper we discuss lessons learned from our experimental work. Specifically, we present results for a fully functioning prototype implementing a p2p middleware (FreePastry) on top of a multihop ad hoc network based on 802.11b technology. Recently, for this technology, [GLNT04] pointed out the existence of an ad hoc horizon (2-3 hops and 10-20 nodes) after which the benefit of multi-hop ad hoc networking vanishes. All the experiments we performed fall inside this ad hoc horizon. The aim is to identify solutions for this realistic setting and to quantify the Quality of Service (QoS) the system is able to provide to the users. Our measurements pointed out that also in this limited setting, several problems still exist to construct efficient multi-hop ad hoc networks. Cross-layering seems to be an effective approach to fix some of the problems identified in our analysis.

Topology Control and Localization in Wireless Ad Hoc and Sensor Networks

Abstract: Over the last few years, novel architectures like ad-hoc and sensor networks have introduced new challenges in the way the communication infrastructure must be addressed Unlike traditional approaches, these architectures require the complete self-organization of nodes as well as the support of mobility A common problem encountered in such networks is the fundamental requirement of guaranteeing the connectivity between nodes A number of network functionality have then to be reassessed, where two components must receive particular attention: topology control and node localization In this paper, we survey the current state of the art for these domains and identify some open issues for future research and development

Health Care Sensor Networks - Architecture and Protocols.

Abstract: Wireless sensor networks consist of a large number of tiny devices capable of executing sensing, data processing and communication tasks and as such can be applied in numerous user scenarios Various military, security and environment monitoring applications are the most frequent examples Another area that can also significantly benefit from advanced features of this technology is health-care monitoring In contrast to the conventional, face-to-face oriented health-care systems organized around health-care centers, the new health-care paradigm presented in this paper relies on personal mobile health-care solutions that utilize ad-hoc networking principles and wireless communication technologies to provide continuous and unobtrusive health monitoring regardless of patient’s or caregiver’s location and activity Health-care sensors worn by patients are controlled by user’s communication device (for example mobile phone) that automatically recognizes the sensors’ functions and establishes required communication links In this paper, architecture of such systems is proposed and discussed A flexible XML based communication protocol that supports various types of sensors is also presented The concept of distributed, peer-to-peer, health care systems is also discussed

Race-Free Resource Allocation for QoS Support in Wireless Networks

Abstract: Routing protocols are an essential part of the efficient design of mobile ad hoc networks (MANETs). Existing routing protocols such as DSR, AODV, and TORA are based on a best effort strategy [21,22]. However, in order for MANETs to be practical for more demanding real time applications such as multimedia, providing a certain needed level of quality of service becomes an essential component in the communication protocol design [2, 11–14, 24, 25]. QoS routing protocols provide the capability of finding a path between two nodes which satisfies the application layer’s minimum bandwidth requirements. Previous papers addressed this issue for different communication environments such as TDMA (Time Division Multiple Access) [7,8,15,16] and CDMA (Code Division Multiple Access)-over-TDMA [3,17,18]. While most of these models are generally more practical and less expensive, they impose on the designer the constraint of the hidden terminal and exposed terminal problems. The paper by Liao and Tseng [15] addressed these issues and provided a TDMA-based bandwidth reservation protocol for QoS routing in MANETs. However, this protocol does not account for the race condition which can become more significant with increased node mobility, network density and higher traffic loads. This race condition is also a limitation of other QoS routing protocols [7, 8]. This paper addresses this issue and provides a protocol which enables the network to cope with this and other related problems such as parallel reservation. We also provide increased optimizations which significantly enhance the throughput and efficiency of the QoS routing protocol.

Adaptive Path Energy Conserving Routing in MANETs.

Abstract: The specific features of mobile ad hoc networks (MANETs) impose new requirements for routing protocols. The aim of this paper is to present an approach that enhances routing performance by integrating ad hoc related characteristics. We propose a loop-free adaptive path energy conserving scheme which attempts to minimize both routing and storage overhead in order to efficiently provide robustness to host mobility, adaptability to wireless channel fluctuations and optimization of network resources use in large-scale networks. The strength of our scheme, based on source routing approach, named Energy Conserving Dynamic Source Routing (EC-DSR), is to handle network state related constraints such as node’s energy consumption, links’ availability and paths’ quality. The performance of the proposed scheme is evaluated via simulation and is compared to DSR protocol. Better results are obtained with EC-DSR in terms of control overhead. Furthermore, EC-DSR shows significant improvements in delay and forwarding efficiency for large scalable networks.

A Dichotomized Rendezvous Algorithm for Mesh Bluetooth Scatternets

Abstract: A Bluetooth scatternet is formed by sharing some nodes (bridges) among piconets in a time division multiplex basis. Effective coordination of these bridge nodes is crucial for the smooth operation of a scatternet. In this paper, a distributed, two-phase RP scheduling algorithm called Dichotomized Rendezvous Point algorithm (DRP) is presented to address this problem. DRP makes the assumption that a mesh scatternet is mainly S/S bridge based (with small amount of M/S bridges to connect masters at three hops). The scatternet configuration is further simplified to allow a bridge to be shared by only two piconets, which leads to an easily scalable solution for very large scatternets since the scatternetwide coordination problem can be avoided. A suboptimal RP schedule is generated at the scatternet formation time, while it is adjusted to improve the capacity of bridge nodes later on as per flow basis. The algorithm is implemented on our newly developed Bluetooth simulator under the ns-2 framework. The performance is obtained for various traffic conditions.

OSCAR - An Opportunistic Call Admission Protocol for LEO Satellite Networks.

Abstract: The main contribution of this work is to propose OSCAR - an opportunistic call admission protocol that provides a simple and robust solution to call admission and handoff management in LEO satellite networks. One of the features that sets OSCAR apart from existing protocols is that it avoids the overhead of reserving resources for users in a series of spotbeams along predicted user trajectories. Instead, OSCAR relies on a novel opportunistic bandwidth allocation mechanism that is very simple and efficient and does not involve maintaining complicated data structures or making expensive reservations. Extensive simulation results have shown that OSCAR achieves results comparable to those of Q-Win: it features very low call dropping probability, thus providing for reliable handoff of on-going calls, low call blocking probability for new call requests, and high bandwidth utilization.

A Class-Based EDF Scheduling for Bluetooth Piconet.

Abstract: An electronic source synthesizer that employs frequency modulation. Wave-form data of both a fundamental wave and a modulated wave are stored in a RAM as 6-bit digital data. A sine wave signal is produced by modulation wave frequency data and the wave-form data from the RAM. The sine wave signal is multiplied with amplitude data of the modulation wave to obtain the modulation index data (J(t)). The frequency data (wc) of the fundamental wave and the modulation index data are multiplied. A result of the multiplication provides a read out address of the RAM for storing the wave-form data of the fundamental wave, thereby changing the read out speed of the RAM. The digital data read out from the RAM is converted to an analog sound signal by a D/A converter. Amplitude data (A) of the fundamental wave is pulse-width modulated, and the digital data from the RAM is gated by the modulated pulse. Thus the output of the D/A converter is activated and, forms a sound signal represented by the equation e=A sin J(t) wct.