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Mobile Computing, IEEE Transactions on

Issue 10 • Date Oct. 2009

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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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  • Continuous Monitoring of Spatial Queries in Wireless Broadcast Environments

    Page(s): 1297 - 1311
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3340 KB) |  | HTML iconHTML  

    Wireless data broadcast is a promising technique for information dissemination that leverages the computational capabilities of the mobile devices in order to enhance the scalability of the system. Under this environment, the data are continuously broadcast by the server, interleaved with some indexing information for query processing. Clients may then tune in the broadcast channel and process their queries locally without contacting the server. Previous work on spatial query processing for wireless broadcast systems has only considered snapshot queries over static data. In this paper, we propose an air indexing framework that 1) outperforms the existing (i.e., snapshot) techniques in terms of energy consumption while achieving low access latency and 2) constitutes the first method supporting efficient processing of continuous spatial queries over moving objects. View full abstract»

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  • Mobility Management Approaches for Mobile IP Networks: Performance Comparison and Use Recommendations

    Page(s): 1312 - 1325
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1474 KB) |  | HTML iconHTML  

    In wireless networks, efficient management of mobility is a crucial issue to support mobile users. The mobile Internet protocol (MIP) has been proposed to support global mobility in IP networks. Several mobility management strategies have been proposed which aim reducing the signaling traffic related to the Mobile Terminals (MTs) registration with the Home Agents (HAs) whenever their Care-of-Addresses (CoAs) change. They use different foreign agents (FAs) and Gateway FAs (GFAs) hierarchies to concentrate the registration processes. For high-mobility MTs, the Hierarchical MIP (HMIP) and Dynamic HMIP (DHMIP) strategies localize the registration in FAs and GFAs, yielding to high-mobility signaling. The Multicast HMIP strategy limits the registration processes in the GFAs. For high-mobility MTs, it provides lowest mobility signaling delay compared to the HMIP and DHMIP approaches. However, it is resource consuming strategy unless for frequent MT mobility. Hence, we propose an analytic model to evaluate the mean signaling delay and the mean bandwidth per call according to the type of MT mobility. In our analysis, the MHMIP outperforms the DHMIP and MIP strategies in almost all the studied cases. The main contribution of this paper is the analytic model that allows the mobility management approaches performance evaluation. View full abstract»

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  • The Beacon Movement Detection Problem in Wireless Sensor Networks for Localization Applications

    Page(s): 1326 - 1338
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3103 KB) |  | HTML iconHTML  

    Localization is a critical issue in wireless sensor networks. In most localization systems, beacons are being placed as references to determine the positions of objects or events appearing in the sensing field. The underlying assumption is that beacons are always reliable. In this work, we define a new beacon movement detection (BMD) problem. Assuming that there are unnoticed changes of locations of some beacons in the system, this problem concerns how to automatically monitor such situations and identify such unreliable beacons based on the mutual observations among beacons only. Existence of such unreliable beacons may affect the localization accuracy. After identifying such beacons, we can remove them from the localization engine. Four BMD schemes are proposed to solve the BMD problem. Then, we evaluate how these solutions can improve the accuracy of localization systems in case there are unnoticed movements of some beacons. Simulation results show that our solutions can capture most of the unnoticed beacon movement events and thus can significantly alleviate the degradation of such events. View full abstract»

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  • MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

    Page(s): 1339 - 1352
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2524 KB) |  | HTML iconHTML  

    Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN). View full abstract»

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  • Analysis of Enhanced Collision Avoidance Scheme Proposed for IEEE 802.11e-Enhanced Distributed Channel Access Protocol

    Page(s): 1353 - 1367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2661 KB) |  | HTML iconHTML  

    In enhanced distributed channel access (EDCA) protocol, small contention window (CW) sizes are used for frequent channel access by high-priority traffic (such as voice). But these small CW sizes, which may be suboptimal for a given network scenario, can introduce more packet collisions, and thereby, reduce overall throughput. This paper proposes enhanced collision avoidance (ECA) scheme for AC_VO access category queues present in EDCA protocol. The proposed ECA scheme alleviates intensive collisions between AC_VO queues to improve voice throughput under the same suboptimal yet necessary (small size) CW restrictions. The proposed ECA scheme is studied in detail using Markov chain numerical analysis and simulations carried out in NS-2 network simulator. The performance of ECA scheme is compared with original (legacy) EDCA protocol in both voice and multimedia scenarios. Also mixed scenarios containing legacy EDCA and ECA stations are presented to study their coexistence. Comparisons reveal that ECA scheme improves voice throughput performance without seriously degrading the throughput of other traffic types. View full abstract»

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  • A Novel Scheduled Power Saving Mechanism for 802.11 Wireless LANs

    Page(s): 1368 - 1383
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    Power conservation is a general concern for mobile computing and communication. In this paper, we investigate the performance of the current 802.11 power saving mechanism (unscheduled PSM) and identify that background network traffic can have a significant impact on the power consumption of mobile stations. To improve power efficiency, a novel scheduled PSM protocol based on time slicing is proposed in this paper. The protocol adopts the mechanism of time division, schedules the access point to deliver pending data at designated time slices, and adaptively adjusts the power state of the mobile stations. The proposed scheme is near theoretical optimal for power saving. It greatly reduces the effect of background traffic, minimizes the station idle time, and maximizes its energy utilization. Comprehensive analysis and simulations are conducted to evaluate the new protocol. The results show that the new protocol provides significant energy saving over the unscheduled PSM, particularly in circumstances where multiple traffic streams coexist in a network. Moreover, it achieves the saving at the cost of only a slight degradation of the one-way-delay performance. View full abstract»

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  • DRAND: Distributed Randomized TDMA Scheduling for Wireless Ad Hoc Networks

    Page(s): 1384 - 1396
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2208 KB) |  | HTML iconHTML  

    This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(delta) time and message complexity where delta is the maximum size of a two-hop neighborhood in a wireless network while message complexity remains O(delta), assuming that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh networks and wireless sensor networks. We implement the algorithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced. We further evaluate the effect of the time-varying nature of wireless links on the conflict-free property of DRAND-assigned time slots. This experiment is conducted on a 55-node testbed consisting of the more recent MicaZ sensor nodes. View full abstract»

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  • Exploiting Contact Spatial Dependency for Opportunistic Message Forwarding

    Page(s): 1397 - 1411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2059 KB) |  | HTML iconHTML  

    The movement of real users often follows patterns that can be characterized by certain statistical metrics of the contacts. Such metrics are useful for routing decisions, especially in sparse mobile ad hoc networks where node connectivity is opportunistic and messages are delivered using store-carry-forward routing. Past analysis on real-world data traces indicates that human behaviors affect the node contact pattern and spatial dependency exists among mobile nodes. A new metric called the expected dependent delay that characterizes the expected delay of a contact dependent on the previous hop is proposed. It characterizes the spatial dependency between neighboring contact pairs and reflects the regularity in node movement. In sparse opportunistic mobile ad hoc networks, a good approximation of the expected delay of a multihop path can be derived as the sum of the expected delay of the first hop and the expected dependent delays of later hops. We apply the proposed path-delay estimation to end-to-end routing. Simulation results show that compared with routing schemes that consider only the delivery probability or the expected delay, the proposed scheme can reduce the message delay significantly, when the network is sufficiently sparse and the spatial dependency is quantitatively constant over time. Moreover, the proposed method is tractable and can be easily implemented in combination with other routing techniques such as multipath routing and per-contact routing. View full abstract»

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  • MDPF: Minimum Distance Packet Forwarding for Search Applications in Mobile Ad Hoc Networks

    Page(s): 1412 - 1426
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4531 KB) |  | HTML iconHTML  

    This paper introduces a message forwarding algorithm for search applications within mobile ad hoc networks that is based on the concept of selecting the nearest node from a set of designated nodes. The algorithm, which is called Minimum Distance Packet Forwarding (MDPF), uses routing information to select the node with the minimum distance. The goal of the proposed algorithm is to minimize the average number of hops taken to reach the node that holds the desired data. Numerical analysis and experimental evaluations using the network simulation software ns2 were performed to derive the lower and upper bounds of the confidence interval for the mean hop count between the source node of the data request, on one hand, and the node that holds the desired data and the last node in the set of search nodes, on the other hand. In the experimental evaluation, the performance of MDPF was compared to that of Random Packet Forwarding (RPF) and Minimal Spanning Tree Forwarding (MSTF). The results agreed with the numerical analysis results and demonstrated that MDPF offers significant hop count savings and smaller delays when compared to RPF and MSTF. View full abstract»

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  • On the Relevance of Node Isolation to the K-Connectivity of Wireless Optical Sensor Networks

    Page(s): 1427 - 1440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2872 KB) |  | HTML iconHTML  

    In designing wireless multihop sensor networks, determining system parameters that guarantee a reasonably connected network is crucial. In this paper, we investigate node isolation in wireless optical sensor networks (WOSNs) as a topology attribute for network connectivity. Our results pertain to WOSNs modeled as random-scaled sector graphs that employ directional broad-beamed free space optics for point-to-point communication. We derive a generalized analytical expression relating the probability that no node is isolated to the physical layer parameters of node density, transmitter radius, and angular beam width. Through simulations, we demonstrate that for probability values close to 1, dense networks, and increasing beam width, the probability that the WOSN is connected is tightly upper bounded by the probability that no isolated node exists. In addition, our study demonstrates conditions for probabilistic K-connectivity guarantees and provides empirical insights on the impact of clustering on connectivity by employing simulations to validate analytical derivations. Our analysis provides a methodology of practical importance to choosing physical layer parameter values for effective network level design. View full abstract»

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  • TMC Information for authors

    Page(s): c3
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    Freely Available from IEEE
  • [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