Showing papers in "Mobile Networks and Applications in 2005"

The coverage problem in a wireless sensor network

Abstract: One of the fundamental issues in sensor networks is the coverage problem, which reflects howwell a sensor network is monitored or tracked by sensors. In this paper, we formulate this problem as a decision problem, whose goal is to determine whether every point in the service area of the sensor network is covered by at least k sensors, where k is a given parameter. The sensing ranges of sensors can be unit disks or non-unit disks. We present polynomial-time algorithms, in terms of the number of sensors, that can be easily translated to distributed protocols. The result is a generalization of some earlier results where only k =1 is assumed. Applications of the result include determining insufficiently covered areas in a sensor network, enhancing fault-tolerant capability in hostile regions, and conserving energies of redundant sensors in a randomly deployed network. Our solutions can be easily translated to distributed protocols to solve the coverage problem.

MANTIS OS: an embedded multithreaded operating system for wireless micro sensor platforms

Abstract: The MANTIS MultimodAl system for NeTworks of In-situ wireless Sensors provides a new multithreaded cross-platform embedded operating system for wireless sensor networks. As sensor networks accommodate increasingly complex tasks such as compression/aggregation and signal processing, preemptive multithreading in the MANTIS sensor OS (MOS) enables micro sensor nodes to natively interleave complex tasks with time-sensitive tasks, thereby mitigating the bounded buffer producer-consumer problem. To achieve memory efficiency, MOS is implemented in a lightweight RAM footprint that fits in less than 500 bytes of memory, including kernel, scheduler, and network stack. To achieve energy efficiency, the MOS power-efficient scheduler sleeps the microcontroller after all active threads have called the MOS sleep() function, reducing current consumption to the µA range. A key MOS design feature is flexibility in the form of cross-platform support and testing across PCs, PDAs, and different micro sensor platforms. Another key MOS design feature is support for remote management of in-situ sensors via dynamic reprogramming and remote login.

Quorum-based asynchronous power-saving protocols for IEEE 802.11 ad hoc networks

Abstract: This paper investigates the power mode management problem for an IEEE 802.11-based mobile ad hoc network (MANET) that allows mobile hosts to tune to the power-saving (PS) mode. There are two major issues that need to be addressed in this problem: (a) wakeup prediction and (b) neighbor discovery. The former is to deliver buffered packets to a PS host at the right time when its radio is turned on. The latter is to monitor the environment change under a mobile environment. One costly, and not scalable, solution is to time-synchronize all hosts. Another possibility is to design asynchronous protocols as proposed by Tseng et al. in [25]. In this paper, we adopt the latter approach and correlate this problem to the quorum system concept. We identify a rotation closure property for quorum systems. It is shown that any quorum system that satisfies this property can be translated to an asynchronous power-saving protocol for MANETs. Thus, the result bridges the classical quorum system design problem in the area of distributed systems to the power mode management problem in the area of mobile ad hoc networks. We derive a lower bound for quorum sizes for any quorum system that satisfies the rotation closure property. We identify a group of quorum systems that are optimal or near optimal in terms of quorum sizes, which can be translated to efficient asynchronous power-saving protocols. We also propose a new e-torus quorum system, which can be translated to an adaptive protocol that allows designers to trade hosts' neighbor sensibility for power efficiency. Simulation experiments are conducted to evaluate and compare the proposed protocols.

Enhancing location privacy in wireless LAN through disposable interface identifiers: a quantitative analysis

Abstract: The recent proliferation of wireless local area networks (WLAN) has introduced new location privacy risks. An adversary controlling several access points could triangulate a client's position. In addition, interface identifiers uniquely identify each client, allowing tracking of location over time. We enhance location privacy through frequent disposal of a client's interface identifier. While not preventing triangulation per se, it protects against an adversary following a user's movements over time. Design challenges include selecting new interface identifiers, detecting address collisions at the MAC layer, and timing identifier switches to balance network disruptions against privacy protection. Using a modified authentication protocol, network operators can still control access to their network. An analysis of a public WLAN usage trace shows that disposing addresses before reassociation already yields significant privacy improvements.

Algorithmic aspects of topology control problems for ad hoc networks

Abstract: Topology control problems are concerned with the assignment of power values to the nodes of an ad hoc network so that the power assignment leads to a graph topology satisfying some specified properties. This paper considers such problems under several optimization objectives, including minimizing the maximum power and minimizing the total power. A general approach leading to a polynomial algorithm is presented for minimizing maximum power for a class of graph properties called monotone properties. The difficulty of generalizing the approach to properties that are not monotone is discussed. Problems involving the minimization of total power are known to be NP-complete even for simple graph properties. A general approach that leads to an approximation algorithm for minimizing the total power for some monotone properties is presented. Using this approach, a new approximation algorithm for the problem of minimizing the total power for obtaining a 2-node-connected graph is developed. It is shown that this algorithm provides a constant performance guarantee. Experimental results from an implementation of the approximation algorithm are also presented.

Lightweight deployment-aware scheduling for wireless sensor networks

Abstract: Wireless sensor networks consist of a large number of tiny sensors that have only limited energy supply. One of the major challenges in constructing such networks is to maintain long network lifetime as well as sufficient sensing areas. To achieve this goal, a broadly-used method is to turn off redundant sensors. In this paper, the problem of estimating redundant sensing areas among neighbouring wireless sensors is analysed. We present simple methods to estimate the degree of redundancy without the knowledge of location or directional information. We also provide tight upper and lower bounds on the probability of complete redundancy and on the average partial redundancy. With random sensor deployment, our analysis shows that partial redundancy is more realistic for real applications, as complete redundancy is expensive, requiring up to 11 neighbouring sensors to provide a 90 percent chance of complete redundancy. Based on the analysis, we propose a scalable Lightweight Deployment-Aware Scheduling (LDAS) algorithm, which turns off redundant sensors without using accurate location information. Simulation study demonstrates that the LDAS algorithm can reduce network energy consumption and provide desired QoS requirement effectively.

Energy-balanced task allocation for collaborative processing in wireless sensor networks

Abstract: We propose an energy-balanced allocation of a real-time application onto a single-hop cluster of homogeneous sensor nodes connected with multiple wireless channels. An epoch-based application consisting of a set of communicating tasks is considered. Each sensor node is equipped with discrete dynamic voltage scaling (DVS). The time and energy costs of both computation and communication activities are considered. We propose both an Integer Linear Programming (ILP) formulation and a polynomial time 3-phase heuristic. Our simulation results show that for small scale problems (with ≤ 10 tasks), up to 5x lifetime improvement is achieved by the ILP-based approach, compared with the baseline where no DVS is used. Also, the 3-phase heuristic achieves up to 63% of the system lifetime obtained by the ILP-based approach. For large scale problems (with 60-100 tasks), up to 3.5x lifetime improvement can be achieved by the 3-phase heuristic. We also incorporate techniques for exploring the energy-latency tradeoffs of communication activities (such as modulation scaling), which leads to 10x lifetime improvement in our simulations. Simulations were further conducted for two real world problems - LU factorization and Fast Fourier Transformation (FFT). Compared with the baseline where neither DVS nor modulation scaling is used, we observed up to 8x lifetime improvement for the LU factorization algorithm and up to 9x improvement for FFT.

Dynamic bandwidth management in single-hop ad hoc wireless networks

Abstract: Distributed weighted fair scheduling schemes for Quality of Service (QoS) support in wireless local area networks have not yet become standard. Therefore, we propose an Admission Control and Dynamic Bandwidth Management scheme that provides fairness and a soft rate guarantee in the absence of distributed MAC-layer weighted fair scheduling. This scheme is especially suitable for smart- rooms where peer-to-peer multimedia transmissions need to adapt their transmission rates co-operatively. We present a mapping scheme to translate the bandwidth requirements of an application into its channel time requirements. The center piece of our scheme is a Bandwidth Manager, which allots each flow a share of the channel, depending on the flow's requirements relative to the requirements of other flows in the network. Admitted flows control their transmission rates so they only occupy the channel for the fraction of time allotted to them. Thus co-operation between flows is achieved and the channel time is fair shared. As the available channel capacity changes and the traffic characteristics of various flows change, the Bandwidth Manager dynamically re-allocates the channel access time to the individual flows. Our simulation experiments show that, at a very low cost and with high probability, every admitted flow in the network will receive at least its minimum requested share of the network bandwidth. We also present extensive testbed experiments with our scheme using a real-time audio streaming application running between Linux laptops equipped with standard IEEE 802.11 network cards.

Service composition for mobile environments

Abstract: Service Composition, that is, the development of customized services by discovering, integrating and executing existing services has received a lot of attention in the last couple of years with respect to wired-infrastructure or Internet web services. With the advancement in the wireless technology and rapid deployment of mobile devices, we envision that in the near future wirelessly connected mobile devices in a given vicinity will also provide services that can be leveraged in the composition process. This is particularly true of what have been described as "pervasive computing" environments. However, wired-infrastructure based service composition architectures are not designed to consider the various factors like mobility, device heterogeneity, resource variability and reliability in a mobile environment. In this paper, we describe the issues related to service composition in mobile environments and evaluate criteria for judging protocols that enable such composition. We present a distributed architecture and associated protocols for service composition in mobile environments that take into consideration mobility, dynamic changing service topology and device resources. The composition protocols are based on distributed brokerage mechanisms and utilize a distributed service discovery process over ad-hoc network connectivity. We present simulation results of our protocols, and compare them with a centralized service composition protocol traditionally used for wired-infrastructure environments. The results show that our approach clearly outperforms the existing centralized approaches, and that our protocols are able to adapt and better utilize the changing service topology and resources in a mobile environment.

Scheduling sleeping nodes in high density cluster-based sensor networks

Abstract: In order to conserve battery power in very dense sensor networks, some sensor nodes may be put into the sleep state while other sensor nodes remain active for the sensing and communication tasks. In this paper, we study the node sleep scheduling problem in the context of clustered sensor networks. We propose and analyze the Linear Distance-based Scheduling (LDS) technique for sleeping in each cluster. The LDS scheme selects a sensor node to sleep with higher probability when it is farther away from the cluster head. We analyze the energy consumption, the sensing coverage property, and the network lifetime of the proposed LDS scheme. The performance of the LDS scheme is compared with that of the conventional Randomized Scheduling (RS) scheme. It is shown that the LDS scheme yields more energy savings while maintaining a similar sensing coverage as the RS scheme for sensor clusters. Therefore, the LDS scheme results in a longer network lifetime than the RS scheme.

Training a wireless sensor network

Abstract: The networks considered in this paper consist of tiny energy-constrained commodity sensors massively deployed, along with one or more sink nodes providing interface to the outside world. Our contribution is to propose a scalable energy-efficient training protocol for nodes that are initially anonymous, asynchronous and unaware of their location. Our training protocol imposes a flexible and intuitive coordinate system onto the deployment area and partitions the anonymous nodes into clusters where data can be gathered from the environment and synthesized under local control. An important by-product of the training protocol is a simple and natural data fusion protocol as well as an energy-efficient protocol for routing data from clusters to the sink node. Being energy-efficient, our training protocol can be run on either a scheduled or ad-hoc basis to provide robustness and dynamic reconfiguration. We also outline a way of making the training protocol secure by using a parameterized variant of frequency hopping.

Throughput analysis and admission control for IEEE 802.11a

Abstract: We propose a new Markov model for the distributed coordination function (DCF) of IEEE 80211 The model incorporates carrier sense, non-saturated traffic and SNR, for both basic and RTS/CTS access mechanisms Analysis of the model shows that the throughput first increases, and then decreases with the number of active stations, suggesting the need for an admission control mechanismWe introduce such a mechanism, which tries to maximize the throughput while maintaining a fair allocation The maximum achievable throughput is tracked by the mechanism as the number of active stations increases An extensive performance analysis shows that the mechanism provides significant improvements

Low power downlink MAC protocols for infrastructure wireless sensor networks

Abstract: This paper addresses low power medium access control (MAC) protocols for the downlink channel of infrastructure wireless sensor networks. Access points are assumed to be energy unconstrained. The trade-off between the power consumption of the sensor nodes and the transmission delay is analyzed, focusing on low traffic. We describe WiseMAC (Wireless Sensor MAC), a new protocol for the downlink of infrastructure wireless sensor networks. Another original contribution is the presentation and analysis of PTIP (Periodic Terminal Initiated Polling). Here, polling is used in the reversed direction as compared to common polling protocols. WiseMAC and PTIP are compared with PSM (Power Save Mode), the power save protocol used in both the IEEE 802.11 and IEEE 802.15.4 ZigBee standards. Analytical expressions are derived for the power consumption and the transmission delay for each protocol, as a function of the wakeup period. It is shown that WiseMAC provides, with low bit rate radio transceivers, a significantly lower power consumption than PSM. Although less energy efficient than WiseMAC and PSM, it is shown that PTIP can, thanks to its implementation simplicity, become attractive for applications tolerating large transmission delays.

Comparing energy-saving MAC protocols for wireless sensor networks

Abstract: Applications for wireless sensor networks have notably different characteristics and requirements from standard WLAN applications. Low energy consumption is the most important consideration. The low message rate that is typical for sensor network applications and the relaxed latency requirements allow for significant reductions in energy consumption of the radio. In this article we study the energy saved by two MAC protocols optimized for wireless sensor networks, S-MAC and T-MAC, in comparison to standard CSMA/CA, We also report on the effects of low-power listening, a physical layer optimization, in combination with these MAC protocols. The comparison is based on extensive simulation driven by traffic that varies over time and location; sensor nodes are inactive unless they observe some physical event, or send status updates to the sink node providing the connection to the wired world. T-MAC in combination with low-power listening saves most energy, but can not handle the same peak loads as CSMA/CA and S-MAC.

Maximizing lifetime for data aggregation in wireless sensor networks

Abstract: This paper studies energy efficient routing for data aggregation in wireless sensor networks. Our goal is to maximize the lifetime of the network, given the energy constraint on each sensor node. Using linear programming (LP) formulation, we model this problem as a multicommodity flow problem, where a commodity represents the data generated from a sensor node and delivered to a base station. A fast approximate algorithm is presented, which is able to compute (1-e)-approximation to the optimal lifetime for any e > 0. Then along this baseline, we further study several advanced topics. First, we design an algorithm, which utilizes the unique characteristic of data aggregation, and is proved to reduce the running time of the fastest existing algorithm by a factor of K, K being the number of commodities. Second, we extend our algorithm to accommodate the same problem in the setting of multiple base stations, and study its impact on network lifetime improvement. All algorithms are evaluated through both solid theoretical analysis and extensive simulation results.

(UWB) 2 : uncoordinated, wireless, baseborn medium access for UWB communication networks

Abstract: A MAC protocol for Ultra Wide Band (UWB) radio networks named (UWB)2 is proposed. The algorithm exploits typical features of impulse radio such as large processing gain, and is conceived in conjunction with a synchronization strategy which foresees the presence of a synchronization sequence in each transmitted packet. (UWB)2 adopts a pure Aloha approach; Performance analysis of the synchronization tracking mechanism showed in fact that under the preliminary simplistic hypothesis of an AWGN channel, and for a sufficient number of pulses in the synchronization sequence, a fairly high probability of successful synchronization can be achieved, even in the presence of several users and Multi User Interference (MUI). The multiple access scheme is based on the combination of a common control channel provided by a common Time Hopping (TH) code with dedicated data channels associated to transmitter specific TH codes.Results obtained by simulation indicate that (UWB)2 can be successfully applied when the number of users spans from a few tens to about one hundred, for data rates ranging from a few thousands to a few hundreds of bits per second. Network throughput was above 99.8% in all considered simulation settings. Such achievement confirms that (UWB)2 is a suitable and straightforward solution for large networks of terminals using impulse radio for transmission at low bit rates.

Comparison and evaluation of multiple objective genetic algorithms for the antenna placement problem

Abstract: The antenna placement problem, or cell planning problem, involves locating and configuring infrastructure for cellular wireless networks. From candidate site locations, a set needs to be selected against objectives relating to issues such as financial cost and service provision. This is an NP-hard optimization problem and consequently heuristic approaches are necessary for large problem instances. In this study, we use a greedy algorithm to select and configure base station locations. The performance of this greedy approach is dependent on the order in which the candidate sites are considered. We compare the ability of four state-of-the-art multiple objective genetic algorithms to find an optimal ordering of potential base stations. Results and discussion on the performance of the algorithms are provided.

Training a wireless sensor network

Abstract: The networks considered in this paper consist of tiny energy-constrained commodity sensors massively deployed, along with one or more sink nodes providing interface to the outside world. Our contri...

Ad hoc multicast routing algorithm with swarm intelligence

Abstract: Swarm intelligence refers to complex behaviors that arise from very simple individual behaviors and interactions, which is often observed in nature, especially among social insects such as ants. Although each individual (an ant) has little intelligence and simply follows basic rules using local information obtained from the environment, such as ant's pheromone trail laying and following behavior, globally optimized behaviors, such as finding a shortest path, emerge when they work collectively as a group. In this paper, we apply this biologically inspired metaphor to the multicast routing problem in mobile ad hoc networks. Our proposed multicast protocol adapts a core-based approach which establishes multicast connectivity among members through a designated node (core). An initial multicast connection can be rapidly setup by having the core flood the network with an announcement so that nodes on the reverse paths to the core will be requested by group members to serve as forwarding nodes. In addition, each member who is not the core periodically deploys a small packet that behaves like an ant to opportunistically explore different paths to the core. This exploration mechanism enables the protocol to discover new forwarding nodes that yield lower total forwarding costs, where cost is abstract and can be used to represent any metric to suit the application. Simulations have been conducted to demonstrate the performance of the proposed approach and to compare it with certain existing multicast protocols.

Towards designing a trusted routing solution in mobile ad hoc networks

Abstract: Designing a trusted and secure routing solution in an untrustworthy scenario is always a challenging problem. Lack of physical security and low trust levels among nodes in an ad hoc network demands a secure end-to-end route free of any malicious entity. This is particularly challenging when malicious nodes collude with one another to disrupt the network operation. In this paper we have designed a secure routing solution to find an end-to-end route free of malicious nodes with collaborative effort from the neighbors. We have also extended the solution to secure the network against colluding malicious nodes, which, to the best of our knowledge, is the first such solution proposed. We have also proposed a framework for computing and distributing trusts that can be used with out trusted routing protocol. Our proposed framework is unique and different from the other schemes in that it tries to analyze the psychology of the attacker and quantifies the behavior in the computational model. Extensive simulation has been carried out to evaluate the design of our protocol.

Maximizing network lifetime of broadcasting over wireless stationary ad hoc networks

Abstract: We investigate the problem of extending the network lifetime of a single broadcast session over wireless stationary ad hoc networks where the hosts are not mobile. We define the network lifetime as the time from network initialization to the first node failure due to battery depletion. We provide through graph theoretic approaches a polynomial-time globally optimal solution, a variant of the minimum spanning tree (MST), to the problem of maximizing the static network lifetime. We make use of this solution to develop a periodic tree update strategy for effective load balancing and show that a significant gain in network lifetime over the optimal static network lifetime can be achieved. We provide extensive comparative simulation studies on parameters such as update interval and control overhead and investigate their impact on the network lifetime. The simulation results are also compared with an upper bound to the network lifetime.

Wireless hotspots: current challenges and future directions

Abstract: In recent years, wireless Interact service providers (WISPs) have established Wi-Fi hotspots in increasing numbers at public venues, providing local coverage to traveling users and empowering them with the ability to access email, Web, and other Internet applications on the move. In this paper, we observe that while the mobile computing landscape has changed both in terms of number and type of hotspot venues, there are several technological and deployment challenges remaining before hotspots can become an ubiquitous infrastructure. These challenges include authentication, security, coverage, management, location services, billing, and interoperability. We discuss existing research, the work of standards bodies, and the experience of commercial hotspot providers in these areas, and then describe compelling open research questions that remain.

Tree based broadcast in ad hoc networks

Abstract: Although broadcasting using tree structure established in a network is a well known and widely used technique, it is typically claimed to be inappropriate for ad hoc networks, being the maintained tree very sensitive to network changes. On the contrary this paper presents an efficient tree based broadcasting scheme, which is reliable and stable even in case of the ever changing network structure of the ad hoc networks.To achieve this, first, a novel method is presented to maintain a spanning tree in an ad hoc network in a fully distributed, on-line and asynchronous way. Once the tree is established the broadcast itself is performed based on this tree. Some further improvements on the basic algorithm are also presented that reduce the resource requirements even more, increase the stability of the tree, enable the mobility of the nodes to be taken into account and make the method more configurable.As it is shown by simulation, the obtained broadcast scheme is stable, reliable and it uses small amount of resources: the acyclic structure of the broadcast tree ensures that the nodes get the broadcast messages only once, so the broadcast needs little bandwidth and the nodes need not store the recent broadcast messages, reducing the computational and memory requirements.As a byproduct a technique is proposed to measure the mobility of the nodes. This technique needs no additional GPS device or any geographical information but it is based on the stability of the links of the node.

Secure authentication system for public WLAN roaming

Abstract: A serious challenge for seamless roaming between independent wireless LANs (WLANs) is how best to confederate the various WLAN service providers, each having different trust relationships with individuals and each supporting their own authentication schemes, which may vary from one provider to the next. We have designed and implemented a comprehensive single sign-on (SSO) authentication architecture that confederates WLAN service providers through trusted identity providers. Users select the appropriate SSO authentication scheme from the authentication capabilities announced by the WLAN service provider, and can block the exposure of their privacy information while roaming. In addition, we have developed a compound Layer 2 and Web authentication scheme that ensures cryptographically protected access while preserving pre-existing public WLAN payment models. Our experimental results, obtained from our prototype system, show that the total authentication delay is about 2 seconds in the worst case. This time is dominated primarily by our use of industry-standard XML-based protocols, yet is still small enough for practical use.

Efficient and robust protocols for local detection and propagation in smart dust networks

Abstract: Smart Dust is a set of a vast number of ultra-small fully autonomous computing and communication devices, with very restricted energy and computing capabilities, that co-operate to quickly and efficiently accomplish a large sensing task. Smart Dust can be very useful in practice, i.e., in the local detection of a remote crucial event and the propagation of data reporting its realization. In this work we make an effort towards the research on smart dust from an algorithmic point of view. We first provide a simple but realistic model for smart dust and present an interesting problem, which is how to propagate efficiently information on an event detected locally. Then we present various smart dust protocols for local detection and propagation that are simple enough to be implemented on real smart dust systems, and perform, under some simplifying assumptions, a rigorous average case analysis of their efficiency and energy consumption (and their interplay). This analysis leads to concrete results showing that our protocols are very efficient and robust. We also validate the analytical results by extensive experiments.

Wireless LANs: from WarChalking to open access networks

Abstract: This work discusses the evolution of W-LANs from their current status of wireless termination of LAN services to a possible global infrastructure where the access networks become open to multiple operators and a vehicle of a win-win scenario, where both users and operators benefit from the new network architecture. The idea of Open Access Networks (OANs) can go beyond wireless HotSpots and be generalized to a generic shared access infrastructure that fosters service operators competition and drastically reduces the cost of last mile coverage.The general concept of Open Access Networks is detailed, highlighting its difference with the more traditional model of vertical integration of the access network into the global service. About the OANs development, it is shown how to support the quick and smooth evolution of the infrastructure toward a widespread and reliable communication support.Business models are discussed by mentioning the different actors, the market organization and the different organization forms.The final part of the paper is devoted to technical challenges such as access control, security, privacy, roaming, resource exploitation and service differentiation. As an example of how to tackle these problems, we discuss a pricing technique devoted to resource management and billing support.In addition we present a simulation on how the OAN concept can speed-up the deployment of broadband access in a real case.

Algorithmic aspects of the time synchronization problem in large-scale sensor networks

Abstract: We study the time synchronization problem for large-scale wireless sensor networks in the high-density regime. Our interest in this problem arises from a sensor networking application, where a large number of power-constrained radio transmitters coordinate their access to a Gaussian multiple access channel to cooperate in generating a waveform stronger than any individual node would be able to generate. In a companion paper to this one, we study theoretical aspects of a time synchronization mechanism that is optimal in the limit of asymptotically high network densities. In this work we summarize those results, and explore practical implementation issues of that mechanism in the context of networks with large, but finite, numbers of nodes. Through simulations, we find that the synchronization mechanism performs very well for finite (and relatively small) networks, maintaining tight clock synchronization indefinitely.

Localized algorithms for energy efficient topology in wireless ad hoc networks

Abstract: Topology control in wireless ad hoc networks is to select a subgraph of the communication graph (when all nodes use their maximum transmission range) with some properties for energy conservation. In this paper, we propose two novel localized topology control methods for homogeneous wireless ad hoc networks.Our first method constructs a structure with the following attractive properties: power efficient, bounded node degree, and planar. Its power stretch factor is at most ρ=1/1-(2sin π/k)β, and each node only has to maintain at most k + 5 neighbors where the integer k > 6 is an adjustable parameter, and β is a real constant between 2 and 5 depending on the wireless transmission environment. It can be constructed and maintained locally and dynamically. Moreover, by assuming that the node ID and its position can be represented in O(log n) bits each for a wireless network of n nodes, we show that the structure can be constructed using at most 24n messages, where each message is O(log n) bits.Our second method improves the degree bound to k, relaxes the theoretical power spanning ratio to ρ = √2β/1-(2√2sin π/k)β, where k > 8 is an adjustable parameter, and keeps all other properties. We show that the second structure can be constructed using at most 3n messages, where each message has size of O (log n) bits.We also experimentally evaluate the performance of these new energy efficient network topologies. The theoretical results are corroborated by the simulations: these structures are more efficient in practice, compared with other known structures used in wireless ad hoc networks and are easier to construct. In addition, the power assignment based on our new structures shows low energy cost and small interference at each wireless node.

Enforcing cooperative resource sharing in untrusted P2P computing environments

Abstract: Peer-to-Peer (P2P) computing is widely recognized as a promising paradigm for building next generation distributed applications. However, the autonomous, heterogeneous, and decentralized nature of participating peers introduces the following challenge for resource staring: how to make peers profitable in the untrusted P2P environment? To address the problem, we present a self-policing and distributed approach by combining two models: PET, a personalized trust model, and M-CUBE, a multiple-currency based economic model, to lay a foundation for resource sharing in untrusted P2P computing environments. PET is a flexible trust model that can adapt to different requirements, and provides the solid support for the currency management in M-CUBE. M-CUBE provides a novel self-policing and quality-aware framework for the sharing of multiple resources, including both homogeneous and heterogeneous resources. We evaluate the efficacy and performance of this approach in the context of a real application, a peer-to-peer Web server sharing. Our results show that our approach is flexible enough to adapt to different situations and effective to make the system profitable, especially for systems with large scale.

Energy-efficient data caching and prefetching for mobile devices based on utility

Abstract: In mobile computing environments, vital resources like battery power and wireless channel bandwidth impose significant challenges in ubiquitous information access. In this paper, we propose a novel energy and bandwidth efficient data caching mechanism, called GreedyDual Least Utility (GD-LU), that enhances dynamic data availability while maintaining consistency. The proposed utility-based caching mechanism considers several characteristics of mobile distributed systems, such as connection-disconnection, mobility handoff, data update and user request patterns to achieve significant energy savings in mobile devices. We develop an analytical model for energy consumption of mobile devices in a dynamic data environment. Based on the utility function derived from the analytical model, we propose algorithms for cache replacement and passive prefetching of data objects. Our comprehensive simulation experiments demonstrate that the proposed caching mechanism achieves more than 10% energy saving and near-optimal performance tradeoff between access latency and energy consumption.