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Mobile Computing, IEEE Transactions on

Issue 8 • Date Aug. 2010

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Displaying Results 1 - 14 of 14
  • [Front cover]

    Publication Year: 2010 , Page(s): c1
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  • [Inside front cover]

    Publication Year: 2010 , Page(s): c2
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  • Providing Service Guarantees in 802.11e EDCA WLANs with Legacy Stations

    Publication Year: 2010 , Page(s): 1057 - 1071
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1946 KB) |  | HTML iconHTML  

    Although the EDCA access mechanism of the 802.11e standard supports legacy DCF stations, the presence of DCF stations in the WLAN jeopardizes the provisioning of the service guarantees committed to the EDCA stations. The reason is that DCF stations compete with Contention Windows (CWs) that are predefined and cannot be modified, and as a result, the impact of the DCF stations on the service received by the EDCA stations cannot be controlled. In this paper, we address the problem of providing throughput guarantees to EDCA stations in a WLAN in which EDCA and DCF stations coexist. To this aim, we propose a technique that, implemented at the Access Point (AP), mitigates the impact of DCF stations on EDCA by skipping with a certain probability the Ack reply to a frame from a DCF station. When missing the Ack, the DCF station increases its CW, and thus, our technique allows us to have some control over the CWs of the legacy DCF stations. In our approach, the probability of skipping an Ack frame is dynamically adjusted by means of an adaptive algorithm. This algorithm is based on a widely used controller from classical control theory, namely a Proportional Controller. In order to find an adequate configuration of the controller, we conduct a control-theoretic analysis of the system. Simulation results show that the proposed approach is effective in providing throughput guarantees to EDCA stations in presence of DCF stations. View full abstract»

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  • SAMAC: A Cross-Layer Communication Protocol for Sensor Networks with Sectored Antennas

    Publication Year: 2010 , Page(s): 1072 - 1088
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3375 KB) |  | HTML iconHTML  

    Wireless sensor networks have been used to gather data and information in many diverse application settings. The capacity of such networks remains a fundamental obstacle toward the adaptation of sensor network systems for advanced applications that require higher data rates and throughput. In this paper, we explore potential benefits of integrating directional antennas into wireless sensor networks. While the usage of directional antennas has been investigated in the past for ad hoc networks, their usage in sensor networks bring both opportunities as well as challenges. In this paper, Sectored-Antenna Medium Access Control (SAMAC), an integrated cross-layer protocol that provides the communication mechanisms for sensor network to fully utilize sectored antennas, is introduced. Simulation studies show that SAMAC delivers high energy efficiency and predictable delay performance with graceful degradation in performance with increased load. View full abstract»

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  • Achieving Guaranteed Anonymity in GPS Traces via Uncertainty-Aware Path Cloaking

    Publication Year: 2010 , Page(s): 1089 - 1107
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4319 KB) |  | HTML iconHTML  

    The integration of Global Positioning System (GPS) receivers and sensors into mobile devices has enabled collaborative sensing applications, which monitor the dynamics of environments through opportunistic collection of data from many users' devices. One example that motivates this paper is a probe-vehicle-based automotive traffic monitoring system, which estimates traffic congestion from GPS velocity measurements reported from many drivers. This paper considers the problem of achieving guaranteed anonymity in a locational data set that includes location traces from many users, while maintaining high data accuracy. We consider two methods to reidentify anonymous location traces, target tracking, and home identification, and observe that known privacy algorithms cannot achieve high application accuracy requirements or fail to provide privacy guarantees for drivers in low-density areas. To overcome these challenges, we derive a novel time-to-confusion criterion to characterize privacy in a locational data set and propose a disclosure control algorithm (called uncertainty-aware path cloaking algorithm) that selectively reveals GPS samples to limit the maximum time-to-confusion for all vehicles. Through trace-driven simulations using real GPS traces from 312 vehicles, we demonstrate that this algorithm effectively limits tracking risks, in particular, by eliminating tracking outliers. It also achieves significant data accuracy improvements compared to known algorithms. We then present two enhancements to the algorithm. First, it also addresses the home identification risk by reducing location information revealed at the start and end of trips. Second, it also considers heading information reported by users in the tracking model. This version can thus protect users who are moving in dense areas but in a different direction from the majority. View full abstract»

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  • A Better Approximation Algorithm for Computing Connected Dominating Sets in Unit Ball Graphs

    Publication Year: 2010 , Page(s): 1108 - 1118
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1531 KB) |  | HTML iconHTML  

    A Virtual Backbone (VB) of a wireless network is a subset of nodes such that only VB nodes are responsible for routing-related tasks. Since a smaller VB causes less overhead, size is the primary quality factor of VB. Frequently, Unit Disk Graphs (UDGs) are used to model 2D homogeneous wireless networks, and the problem of finding minimum VBs in the networks is abstracted as Minimum Connected Dominating Set (MCDS) problem in UDGs. In some applications, the altitude of nodes can be hugely different and UDG cannot abstract the networks accurately. Then, Unit Ball Graph (UBG) can replace UDG. In this paper, we study how to construct quality CDSs in UBGs in distributed environments. We first give an improved upper bound of the number of independent nodes in a UBG, and use this result to analyze the Performance Ratio (PR) of our new centralized algorithm C-CDS-UBG, which computes CDSs in UBGs. Next, we propose a distributed algorithm D-CDS-UBG originated from C-CDS-UBG and analyze its message and time complexities. Our theoretical analysis shows that the PR of D-CDS-UBG is 14.937, which is better than current best, 22. Our simulations also show that D-CDS-UBG outperforms the competitor, on average. View full abstract»

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  • Optimal Jamming Attack Strategies and Network Defense Policies in Wireless Sensor Networks

    Publication Year: 2010 , Page(s): 1119 - 1133
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1639 KB) |  | HTML iconHTML  

    We consider a scenario where a sophisticated jammer jams an area in which a single-channel random-access-based wireless sensor network operates. The jammer controls the probability of jamming and the transmission range in order to cause maximal damage to the network in terms of corrupted communication links. The jammer action ceases when it is detected by the network (namely by a monitoring node), and a notification message is transferred out of the jammed region. The jammer is detected by employing an optimal detection test based on the percentage of incurred collisions. On the other hand, the network defends itself by computing the channel access probability to minimize the jamming detection plus notification time. The necessary knowledge of the jammer in order to optimize its benefit consists of knowledge about the network channel access probability and the number of neighbors of the monitor node. Accordingly, the network needs to know the jamming probability of the jammer. We study the idealized case of perfect knowledge by both the jammer and the network about the strategy of each other and the case where the jammer and the network lack this knowledge. The latter is captured by formulating and solving optimization problems where the attacker and the network respond optimally to the worst-case or the average-case strategies of the other party. We also take into account potential energy constraints of the jammer and the network. We extend the problem to the case of multiple observers and adaptable jamming transmission range and propose a meaningful heuristic algorithm for an efficient jamming strategy. Our results provide valuable insights about the structure of the jamming problem and associated defense mechanisms and demonstrate the impact of knowledge as well as adoption of sophisticated strategies on achieving desirable performance. View full abstract»

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  • On the Performance Bounds of Practical Wireless Network Coding

    Publication Year: 2010 , Page(s): 1134 - 1146
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2025 KB) |  | HTML iconHTML  

    Network coding is an attracting technology that has been shown to be able to improve the throughput of wireless networks. However, there still lacks fundamental understanding on how network coding works under realistic scenarios. In this paper, we examine the performance of a recently proposed network coding system under a realistic wireless physical layer and practical random access mechanisms. We propose a key performance measure called “encoding number”-the number of packets that can be encoded via network coding in each transmission. We provide an upper bound on the encoding number for the general coding topology, and derive the average encoding number and system throughput for a general class of random access mechanisms. Based on the practical coding system, we also derive a tighter upper bound on the throughput gain for a general wireless network. Our results are of fundamental value for coding-related MAC/Routing protocol design and analysis. View full abstract»

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  • Controlled Wi-Fi Sharing in Cities: A Decentralized Approach Relying on Indirect Reciprocity

    Publication Year: 2010 , Page(s): 1147 - 1160
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2333 KB) |  | HTML iconHTML  

    In densely populated cities, Wi-Fi networks-private or otherwise-are ubiquitous. We focus on the provision of citywide broadband communication capability to mobile users through private Wi-Fi networks that are in range but belong to others. We form a club that relies on indirect reciprocity: Members participate in the club and provide free Wi-Fi access to other members in order to enjoy the same benefit when they are away from their own Wi-Fi network. Our club scheme does not require registration with an authority and does not rely on centrally issued club identities: Members create their own identities (public-private key pairs) and receive signed digital receipts when they provide Wi-Fi service to other members. These receipts form a distributed receipt graph, parts of which are used as input to an indirect reciprocity algorithm that classifies club members according to their contribution. We show that our algorithm can sustain cooperation within the club and is robust to attacks by free-riders. We implement and evaluate our proposed club algorithms on commodity Wi-Fi routers and dual-mode cellular/Wi-Fi phones. Because we anticipate that Wi-Fi telephony will be a popular club application, we present and evaluate a secure and decentralized architecture for citywide voice (and multimedia) communications that is compatible with our club both from an architectural as well as an incentives perspective. View full abstract»

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  • Maximizing the Lifetime of a Barrier of Wireless Sensors

    Publication Year: 2010 , Page(s): 1161 - 1172
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1849 KB) |  | HTML iconHTML  

    To make a network last beyond the lifetime of an individual sensor node, redundant nodes must be deployed. What sleep-wake-up schedule can then be used for individual nodes so that the redundancy is appropriately exploited to maximize the network lifetime? We develop optimal solutions to both problems for the case when wireless sensor nodes are deployed to form an impenetrable barrier for detecting movements. In addition to being provably optimal, our algorithms work for nondisk sensing regions and heterogeneous sensing regions. Further, we provide an optimal solution for the more difficult case when the lifetimes of individual nodes are not equal. Developing optimal algorithms for both homogeneous and heterogeneous lifetimes allows us to obtain, by simulation, several interesting results. We show that even when an optimal number of sensor nodes has been deployed randomly, statistical redundancy can be exploited to extend the network lifetime by up to seven times. We also use simulation to show that the assumption of homogeneous lifetime can result in severe loss (two-thirds) of the network lifetime. Although these results are specifically for barrier coverage, they provide an indication of behavior for other coverage models. View full abstract»

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  • Decentralized QoS-Aware Checkpointing Arrangement in Mobile Grid Computing

    Publication Year: 2010 , Page(s): 1173 - 1186
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1663 KB) |  | HTML iconHTML  

    This paper deals with decentralized, QoS-aware middleware for checkpointing arrangement in Mobile Grid (MoG) computing systems. Checkpointing is more crucial in MoG systems than in their conventional wired counterparts due to host mobility, dynamicity, less reliable wireless links, frequent disconnections, and variations in mobile systems. We've determined the globally optimal checkpoint arrangement to be NP-complete and so consider Reliability Driven (ReD) middleware, employing decentralized QoS-aware heuristics, to construct superior checkpointing arrangements efficiently. With ReD, an MH (mobile host) simply sends its checkpointed data to one selected neighboring MH, and also serves as a stable point of storage for checkpointed data received from a single approved neighboring MH. ReD works to maximize the probability of checkpointed data recovery during job execution, increasing the likelihood that a distributed application, executed on the MoG, completes without sustaining an unrecoverable failure. It allows collaborative services to be offered practically and autonomously by the MoG. Simulations and actual testbed implementation show ReD's favorable recovery probabilities with respect to Random Checkpointing Arrangement (RCA) middleware, a QoS-blind comparison protocol producing random arbitrary checkpointing arrangements. View full abstract»

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  • Maximizing Rewards in Wireless Networks with Energy and Timing Constraints for Periodic Data Streams

    Publication Year: 2010 , Page(s): 1187 - 1200
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2064 KB) |  | HTML iconHTML  

    Power efficiency is an important design issue in mobile devices with limited power supplies. In this paper, we study a reward-based packet scheduling problem in wireless environments. We consider a general scenario in which a transmitter communicates with multiple receivers periodically. To guarantee timely transmission of data, each packet is associated with a delay constraint. The periodic data streams have different importance levels, power functions, and levels of data sizes. The more data a transmitter delivers, the more rewards it obtains. Our objective is to develop schemes that selectively transmit data streams of different data sizes at different transmission rates so that the system reward can be maximized under given time and energy constraints. We show that the problem is NP-hard and develop a dynamic programming algorithm for the optimal solution in pseudopolynomial time. A fast polynomial-time heuristic approach based on clustering of states in state space is presented to achieve close approximation. Simulation results demonstrate the effectiveness of the optimal solution and show that the proposed polynomial-time approach can achieve near-optimal results. Both approaches make a significant improvement over other approaches adapted from existing studies at a marginal runtime overhead. View full abstract»

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  • TMC Information for authors

    Publication Year: 2010 , Page(s): c3
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 2010 , Page(s): c4
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Aims & Scope

Mobile Computing, as proposed in this Transactions, focuses on the key technical issues related to (a) architectures, (b) support services, (c) algorithm/protocol design and analysis, (d) mobile environments, (e) mobile communication systems, (f) applications, and (g) emerging technologies.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Prasant Mohapatra
Interim Vice-Provost and CIO
Professor, Dept. Computer Science
University of California, Davis, USA
pmohapatra@ucdavis.edu