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Mobile Computing, IEEE Transactions on

Issue 7 • Date July 2007

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

    Page(s): c1
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  • [Inside front cover]

    Page(s): c2
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  • Connected Dominating Sets in Wireless Networks with Different Transmission Ranges

    Page(s): 721 - 730
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1041 KB) |  | HTML iconHTML  

    Since there is no fixed infrastructure or centralized management in wireless ad hoc networks, a Connected Dominating Set (CDS) has been proposed to serve as a virtual backbone. The CDS of a graph representing a network has a significant impact on the efficient design of routing protocols in wireless networks. This problem has been studied extensively in Unit Disk Graphs (UDG), in which all nodes have the same transmission ranges. However, in practice, the transmission ranges of all nodes are not necessarily equal. In this paper, we model a network as a disk graph and introduce the CDS problem in disk graphs. We present two efficient approximation algorithms to obtain a minimum CDS. The performance ratio of these algorithms is constant if the ratio of the maximum transmission range over the minimum transmission range in the network is bounded. These algorithms can be implemented as distributed algorithms. Furthermore, we show a size relationship between a maximal independent set and a CDS as well as a bound of the maximum number of independent neighbors of a node in disk graphs. The theoretical analysis and simulation results are also presented to verify our approaches. View full abstract»

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  • Performance Analysis of Handoff Techniques Based on Mobile IP, TCP-Migrate, and SIP

    Page(s): 731 - 747
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3337 KB) |  | HTML iconHTML  

    Mobility management protocols operating from different layers of the classical protocol stack (e.g., link, network, transport, and application layers) have been proposed in the last several years. These protocols achieve different handoff performance for different types of applications. In this paper, mobile applications are grouped into five different classes, class A through class E, based on their mobility management requirements. Analytical models are developed to investigate the handoff performance of the existing mobility management protocols for these application classes. The analysis shows that applications of a particular class experience different handoff performance when different mobility management protocols are used. Handoff performance comparisons of different mobility management protocols are carried out to decide on the suitable mobility management protocol for a particular application class. The results of mathematical analysis advocate the use of transport layer mobility management for class B and class C applications, mobile IP for non-real-time class D and class E applications, and session initiation protocol-based mobility management for real-time class D and class E applications. Moreover, through analytical modeling, the parameters that influence the handoff performance of mobility management protocols are identified. These parameters can be used to design new application-adaptive techniques to enhance the handoff performance of the existing mobility management protocols. View full abstract»

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  • On Searching Continuous k Nearest Neighbors in Wireless Data Broadcast Systems

    Page(s): 748 - 761
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3209 KB) |  | HTML iconHTML  

    A continuous nearest neighbor (CNN) search, which retrieves the nearest neighbors corresponding to every point in a given query line segment, is important for location-based services such as vehicular navigation and tourist guides. It is infeasible to answer a CNN search by issuing a traditional nearest neighbor query at every point of the line segment due to the large number of queries generated and the overhead on bandwidth. Algorithms have been proposed recently to support CNN search in the traditional client- server systems but not in the environment of wireless data broadcast, where uplink communication channels from mobile devices to the server are not available. In this paper, we develop a generalized search algorithm for continuous k-nearest neighbors based on Hilbert Curve Index in wireless data broadcast systems. A performance evaluation is conducted to compare the proposed search algorithms with an algorithm based on R-tree Air Index. The result shows that the Hilbert Curve Index-based algorithm is more energy efficient than the R-tree-based algorithm. View full abstract»

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  • Lexicographic Maxmin Fairness for Data Collection in Wireless Sensor Networks

    Page(s): 762 - 776
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1556 KB) |  | HTML iconHTML  

    The ad hoc deployment of a sensor network causes unpredictable patterns of connectivity and varied node density, resulting in uneven bandwidth provisioning on the forwarding paths. When congestion happens, some sensors may have to reduce their data rates. It is an interesting but difficult problem to determine which sensors must reduce rates and how much they should reduce. This paper attempts to answer a fundamental question about congestion resolution: What are the maximum rates at which the individual sensors can produce data without causing congestion in the network and unfairness among the peers? We define the maxmin optimal rate assignment problem in a sensor network, where all possible forwarding paths are considered. We provide an iterative linear programming solution, which finds the maxmin optimal rate assignment and a forwarding schedule that implements the assignment in a low-rate sensor network. We prove that there is one and only one such assignment for a given configuration of the sensor network. We also study the variants of the maxmin fairness problem in sensor networks. View full abstract»

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  • Sprinkler: A Reliable and Energy Efficient Data Dissemination Service for Extreme Scale Wireless Networks of Embedded Devices

    Page(s): 777 - 789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1936 KB) |  | HTML iconHTML  

    We present Sprinkler, a reliable data dissemination service for wireless embedded devices which are constrained in energy, processing speed, and memory. Sprinkler embeds a virtual grid over the network whereby it can locally compute a connected dominating set of the devices to avoid redundant transmissions and a transmission schedule to avoid collisions. Sprinkler transmits O(1) times the optimum number of packets in O(1) of the optimum latency; its time complexity is O(1). Sprinkler is tolerant to fail-stop and state corruption faults. Thus, Sprinkler is suitable for resource-constrained wireless embedded devices. We evaluate the performance of Sprinkler in terms of the number of packet transmissions and the latency, both in an outdoor and indoor environment. The outdoor evaluation is based on data from project ExScal, which deployed 203 extreme scale stargazer (XSS). Our indoor evaluation is based on an implementation in the Kansei testbed, which houses 210 XSSs whose transmission power is controllable to even low ranges. We compare Sprinkler with the existing reliable data dissemination services, analytically or using simulations also. Our evaluations show that Sprinkler is not only energy efficient as compared to existing schemes, but also has less latency. Further, the energy consumption of nodes and the latency grows linearly as a function of newly added nodes as the network grows larger. View full abstract»

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  • Mathematical Evaluation of Environmental Monitoring Estimation Error through Energy-Efficient Wireless Sensor Networks

    Page(s): 790 - 802
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1307 KB) |  | HTML iconHTML  

    In this paper, the estimation of a scalar field over a bidimensional scenario (e.g., the atmospheric pressure in a wide area) through a self-organizing wireless sensor network (WSN) with energy constraints is investigated. The sensor devices (denoted as nodes) are randomly distributed; they transmit samples to a supervisor by using a clustered network. This paper provides a mathematical framework to analyze the interdependent aspects of WSN communication protocol and signal processing design. Channel modelling and connectivity issues, multiple access control and routing, and the role of distributed digital signal processing (DDSP) techniques are accounted for. The possibility that nodes perform DDSP is studied through a distributed compression technique based on signal resampling. The DDSP impact on network energy efficiency is compared through a novel mathematical approach to the case where the processing is performed entirely by the supervisor. The trade-off between energy conservation (i.e., network lifetime) and estimation error is discussed and a design criterion is proposed as well. Comparison to simulation outcomes validates the model. As an example result, the required node density is found as a trade-off between estimation quality and network lifetime for different system parameters and scalar field characteristics. It is shown that both the DDSP technique and the MAC protocol choice have a relevant impact on the performance of a WSN. View full abstract»

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  • Quality of Service and Capacity in Constrained Intermittent-Connectivity Networks

    Page(s): 803 - 814
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1720 KB) |  | HTML iconHTML  

    In an intermittent-connectivity network, there rarely exists a connected path between a source node and its destination. These networks arise frequently when each node has a limited transmission range, such as a communication network between separated villages or a surveillance network with a large geographical span. One method of addressing the low connectivity of the network uses redundancy. A node generates and stores data; upon reaching the communication range of another node, it replicates the data to it. Multiple copies of the packet decrease the time to offload the data to the destination, but increase the energy and storage used in the system. In this paper, we quantify the resource-delay trade-off and the throughput capacity for intermittent-connectivity networks with quality of service restrictions such as limited communication bandwidth. Many routing protocols have been proposed for these intermittent-connectivity networks. Using the shared wireless infostation model as an example strategy, we mathematically represent the intermittent-connectivity network and adjust the model to include a quality of service constraint. By completely defining a mathematical model, we allow network designers control over system performance through the adjustment of allocated resources such as communication bandwidth, fraction of time a node spends in sleep mode, or required reliability of packet offloading. View full abstract»

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  • Bandwidth Sharing Schemes for Multimedia Traffic in the IEEE 802.11e Contention-Based WLANs

    Page(s): 815 - 831
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    Bandwidth allocation schemes have been well studied for mobile cellular networks. However, there is no study about this aspect reported for IEEE 802.11 contention-based distributed wireless LANs. In cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the contrary, bandwidth allocation in contention- based distributed wireless LANs is extremely challenging due to its contention-based nature, packet-based network, and the most important aspect: only one channel is available, competed for by an unknown number of stations. As a consequence, guaranteeing bandwidth and allocating bandwidth are both challenging issues. In this paper, we address these difficult issues. We propose and study nine bandwidth allocation schemes, called sharing schemes, with guaranteed Quality of Service (QoS) for integrated voice/video/data traffic in IEEE 802.11e contention-based distributed wireless LANs. A guard period is proposed to prevent bandwidth allocation from overprovisioning and is for best-effort data traffic. Our study and analysis show that the guard period is a key concept for QoS guarantees in a contention-based channel. The proposed schemes are compared and evaluated via extensive simulations. View full abstract»

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  • Data Dissemination with Ring-Based Index for Wireless Sensor Networks

    Page(s): 832 - 847
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    In wireless sensor networks, sensor nodes are capable of not only measuring real world phenomena, but also storing, processing, and transferring these measurements. Many techniques have been proposed for disseminating sensing data. However, most of them are not efficient in the scenarios where a huge amount of sensing data are generated, but only a small portion of them are queried. In this paper, we first propose an index-based data dissemination scheme to address the problem. With this scheme, sensing data are collected, processed, and stored at the nodes close to the detecting nodes, and the location information of these storing nodes is pushed to some index nodes, which act as the rendezvous points for sinks and sources. To address the issues of fault tolerance and load balance, we extend the scheme with an adaptive ring-based index (ARI) technique in which the index nodes for one event type form a ring surrounding the location which is determined by the event type, and the ring can be dynamically reconfigured. Considering that frequently updating or querying index nodes may cause high overhead, we also propose a lazy index updating (LIU) mechanism and a lazy index querying (LIQ) mechanism to reduce the overhead. Analysis and simulations are conducted to evaluate the performance of the proposed scheme. The results show that the proposed scheme outperforms the external storage-based scheme, the DCS scheme, and the local storage-based schemes with flood-response style. The results also show that using ARI can tolerate clustering failures and achieve load balance and using LIU (LIQ) can further improve the system performance. is pushed to some index nodes, View full abstract»

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  • A Framework for Transaction-Level Quality of Service for M-Commerce Applications

    Page(s): 848 - 864
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4331 KB) |  | HTML iconHTML  

    In the emerging wireless Internet environment involving m-commerce and other mobile applications, an increasing number of users are likely to adopt mobile transactions. These transactions may have very diverse requirements and some of them may require a significant amount of network resources and/or bounded delays. One of many unique characteristics of transactions involving a financial value is the criticality of its completion. The unique requirements of mobile transactions necessitate the introduction of new metrics for quality-of-service. So far, most of the quality-of-service research in wireless networks has focused on call or connection- level QoS. In this paper, we propose a framework to support QoS requirements of mobile transactions by resource allocation at the connection level, transaction level, and a combination of connection and transaction levels. To measure the QoS effectiveness of mobile transactions, two new metrics, transaction completion probability and transaction response time, are introduced. Simulation and analytical models are used for computing different metrics for transaction performance under varying network and traffic conditions. The results show that the balanced transaction and connection level resource allocation can improve the probability of transactions completion and resource utilization. This improvement is at the cost of slightly increased processing overload, which is dependent on both the group size and number of transactions during a connection. View full abstract»

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  • TMC Information for authors

    Page(s): c3
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  • [Back cover]

    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