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Mobile Computing, IEEE Transactions on

Issue 4 • Date April 2012

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Displaying Results 1 - 18 of 18
  • [Front cover]

    Page(s): c1
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    Freely Available from IEEE
  • [Cover 2]

    Page(s): c2
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    Freely Available from IEEE
  • Spectrum-Aware Mobility Management in Cognitive Radio Cellular Networks

    Page(s): 529 - 542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (939 KB) |  | HTML iconHTML  

    Cognitive radio (CR) networks have been proposed as a solution to both spectrum inefficiency and spectrum scarcity problems. However, they face several challenges based on the fluctuating nature of the available spectrum, making it more difficult to support seamless communications, especially in CR cellular networks. In this paper, a spectrum-aware mobility management scheme is proposed for CR cellular networks. First, a novel network architecture is introduced to mitigate heterogeneous spectrum availability. Based on this architecture, a unified mobility management framework is developed to support diverse mobility events in CR networks, which consists of spectrum mobility management, user mobility management, and intercell resource allocation. The spectrum mobility management scheme determines a target cell and spectrum band for CR users adaptively dependent on time-varying spectrum opportunities, leading to increase in cell capacity. In the user mobility management scheme, a mobile user selects a proper handoff mechanism so as to minimize a switching latency at the cell boundary by considering spatially heterogeneous spectrum availability. Intercell resource allocation helps to improve the performance of both mobility management schemes by efficiently sharing spectrum resources with multiple cells. Simulation results show that the proposed method can achieve better performance than conventional handoff schemes in terms of both cell capacity as well as mobility support in communications. View full abstract»

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  • Chip Error Pattern Analysis in IEEE 802.15.4

    Page(s): 543 - 552
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1344 KB) |  | HTML iconHTML  

    IEEE 802.15.4 standard specifies physical layer (PHY) and medium access control (MAC) sublayer protocols for low-rate and low-power communication applications. In this protocol, every 4-bit symbol is encoded into a sequence of 32 chips that are actually transmitted over the air. The 32 chips as a whole is also called a pseudonoise code (PN-Code). Due to complex channel conditions such as attenuation and interference, the transmitted PN-Code will often be received with some PN-Code chips corrupted. In this paper, we conduct a systematic analysis on these errors occurring at chip level. We find that there are notable error patterns corresponding to different cases. We then show that recognizing these patterns enables us to identify the channel condition in great details. We believe that understanding what happened to the transmission in our way can potentially bring benefit to channel coding, routing, and error correction protocol design. Finally, we propose Simple Rule, a simple yet effective method based on the chip error patterns to infer the link condition with an accuracy of over 96 percent in our evaluations. View full abstract»

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  • Energy-Efficient Strategies for Cooperative Multichannel MAC Protocols

    Page(s): 553 - 566
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    Distributed Information SHaring (DISH) is a new cooperative approach to designing multichannel MAC protocols. It aids nodes in their decision making processes by compensating for their missing information via information sharing through neighboring nodes. This approach was recently shown to significantly boost the throughput of multichannel MAC protocols. However, a critical issue for ad hoc communication devices, viz. energy efficiency, has yet to be addressed. In this paper, we address this issue by developing simple solutions that reduce the energy consumption without compromising the throughput performance and meanwhile maximize cost efficiency. We propose two energy-efficient strategies: in-situ energy conscious DISH, which uses existing nodes only, and altruistic DISH, which requires additional nodes called altruists. We compare five protocols with respect to these strategies and identify altruistic DISH to be the right choice in general: it 1) conserves 40-80 percent of energy, 2) maintains the throughput advantage, and 3) more than doubles the cost efficiency compared to protocols without this strategy. On the other hand, our study also shows that in-situ energy conscious DISH is suitable only in certain limited scenarios. View full abstract»

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  • Target Tracking in Wireless Sensor Networks Based on the Combination of KF and MLE Using Distance Measurements

    Page(s): 567 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (721 KB) |  | HTML iconHTML  

    A common technical difficulty in target tracking in a wireless sensor network is that individual homogeneous sensors only measure their distances to the target whereas the state of the target composes of its position and velocity in the Cartesian coordinates. That is, the senor measurements are nonlinear in the target state. Extended Kalman filtering is a commonly used method to deal with the nonlinearity, but this often leads to unsatisfactory or even unstable tracking performances. In this paper, we present a new target tracking approach which avoids the instability problem and offers superior tracking performances. We first propose an improved noise model which incorporates both additive noises and multiplicative noises in distance sensing. We then use a maximum likelihood estimator for prelocalization to remove the sensing nonlinearity before applying a standard Kalman filter. The advantages of the proposed approach are demonstrated via experimental and simulation results. View full abstract»

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  • Distributed Throughput Maximization in Wireless Networks via Random Power Allocation

    Page(s): 577 - 590
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    We develop a distributed throughput-optimal power allocation algorithm in wireless networks. The study of this problem has been limited due to the nonconvexity of the underlying optimization problems that prohibits an efficient solution even in a centralized setting. By generalizing the randomization framework originally proposed for input queued switches to SINR rate-based interference model, we characterize the throughput-optimality conditions that enable efficient and distributed implementation. Using gossiping algorithm, we develop a distributed power allocation algorithm that satisfies the optimality conditions, thereby achieving (nearly) 100 percent throughput. We illustrate the performance of our power allocation solution through numerical simulation. View full abstract»

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  • Maximum Entropy Principle-Based Algorithm for Simultaneous Resource Location and Multihop Routing in Multiagent Networks

    Page(s): 591 - 602
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (766 KB) |  | HTML iconHTML  

    This paper presents a framework that develops algorithms for solving combined locational and multihop routing optimization problems. The objective is to determine resource node locations in a multiagent network and to specify the multihop routes from each agent to a common destination through a network of resource nodes that minimize total communication cost. These problems are computationally complex (NP-hard) where the cost functions are riddled with multiple minima. Algorithms based on Maximum Entropy Principle, which guarantee local minima and are heuristically designed to seek the global minimum are presented. These algorithms accommodate practical constraints on resource nodes as well as on the routing network architectures. Simulation results show that the multihop routes and resource locations allocated by these algorithms achieve lower costs (as low as 47 percent) than those algorithms where resource locational optimization is done without multihop routing or where the locational and routing optimization objectives are separated. The enabling feature of these algorithms is accommodating problems with resource constraints which is demonstrated through simulations. View full abstract»

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  • Improving QoS in High-Speed Mobility Using Bandwidth Maps

    Page(s): 603 - 617
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    It is widely evidenced that location has a significant influence on the actual bandwidth that can be expected from Wireless Wide Area Networks (WWANs), e.g., 3G. Because a fast-moving vehicle continuously changes its location, vehicular mobile computing is confronted with the possibility of significant variations in available network bandwidth. While it is difficult for providers to eliminate bandwidth disparity over a large service area, it may be possible to map network bandwidth to the road network through repeated measurements. In this paper, we report results of an extensive measurement campaign to demonstrate the viability of such bandwidth maps. We show how bandwidth maps can be interfaced with adaptive multimedia servers and the emerging vehicular communication systems that use on-board mobile routers to deliver Internet services to the passengers. Using simulation experiments driven by our measurement data, we quantify the improvement in Quality of Service (QoS) that can be achieved by taking advantage of the geographical knowledge of bandwidth provided by the bandwidth maps. We find that our approach reduces the frequency of disruptions in perceived QoS for both audio and video applications in high-speed vehicular mobility by several orders of magnitude. View full abstract»

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  • A Statistical Mechanics-Based Framework to Analyze Ad Hoc Networks with Random Access

    Page(s): 618 - 630
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (741 KB) |  | HTML iconHTML  

    Characterizing the performance of ad hoc networks is one of the most intricate open challenges; conventional ideas based on information-theoretic techniques and inequalities have not yet been able to successfully tackle this problem in its generality. Motivated thus, we promote the totally asymmetric simple exclusion process (TASEP), a particle flow model in statistical mechanics, as a useful analytical tool to study ad hoc networks with random access. Employing the TASEP framework, we first investigate the average end-to-end delay and throughput performance of a linear multihop flow of packets. Additionally, we analytically derive the distribution of delays incurred by packets at each node, as well as the joint distributions of the delays across adjacent hops along the flow. We then consider more complex wireless network models comprising intersecting flows, and propose the partial mean-field approximation (PMFA), a method that helps tightly approximate the throughput performance of the system. We finally demonstrate via a simple example that the PMFA procedure is quite general in that it may be used to accurately evaluate the performance of ad hoc networks with arbitrary topologies. View full abstract»

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  • Coverage Verification without Location Information

    Page(s): 631 - 643
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    Wireless sensor networks (WSNs) have recently emerged as a prominent technology for environmental monitoring and hazardous event detection. Yet, their success depends considerably on their ability to ensure reliable event detection. Such guarantees can be provided only if the target field monitored by a WSN does not contain coverage holes that are not monitored by any sensor. Currently, the coverage hole detection solutions require accurate knowledge of the sensors locations, which cannot be easily obtained, or they cannot provide guarantees on the coverage quality. In this study, we address the challenge of designing an accurate k-coverage verification scheme, without using location information, for a predefined k ≥ 1. To this end, we present two efficient, distributed, and localized k-coverage verification schemes with proven guarantees on their coverage detection quality. Our simulations show that the schemes accurately detect coverage holes of various sizes. View full abstract»

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  • Scalable Activity-Travel Pattern Monitoring Framework for Large-Scale City Environment

    Page(s): 644 - 662
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    In this paper, we introduce Activity Travel Pattern (ATP) monitoring in a large-scale city environment. ATP represents where city residents and vehicles stay and how they travel around in a complex megacity. Monitoring ATP will incubate new types of value-added services such as predictive mobile advertisement, demand forecasting for urban stores, and adaptive transportation scheduling. To enable ATP monitoring, we develop ActraMon, a high-performanceATP monitoring framework. As a first step, ActraMon provides a simple but effective computational model of ATP and a declarative query language facilitating effective specification of various ATP monitoring queries. More important, ActraMon employs the shared staging architecture and highly efficient processing techniques, which address the scalability challenges caused by massive location updates, a number of ATP monitoring queries and processing complexity of ATP monitoring. Finally, we demonstrate the extensive performance study of ActraMon using realistic city-wide ATP workloads. View full abstract»

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  • Cooperative Download in Vehicular Environments

    Page(s): 663 - 678
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2521 KB) |  | HTML iconHTML  

    We consider a complex (i.e., nonlinear) road scenario where users aboard vehicles equipped with communication interfaces are interested in downloading large files from road-side Access Points (APs). We investigate the possibility of exploiting opportunistic encounters among mobile nodes so to augment the transfer rate experienced by vehicular downloaders. To that end, we devise solutions for the selection of carriers and data chunks at the APs, and evaluate them in real-world road topologies, under different AP deployment strategies. Through extensive simulations, we show that carry&forward transfers can significantly increase the download rate of vehicular users in urban/suburban environments, and that such a result holds throughout diverse mobility scenarios, AP placements and network loads. View full abstract»

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  • Understanding the Interaction between Packet Forwarding and Channel Access in Multihop Wireless Networks

    Page(s): 679 - 691
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    We proposed an analytical model to study the interplay between medium access control (MAC) and packet forwarding disciplines in multihop wireless networks. The model jointly considers the channel access procedure and the active portions of the topology, which is determined by packet forwarding discipline. The model allows the computation of per-node performance metrics for any given network topology and the combination of specific MAC protocols and packet forwarding methods. As an example of the applicability of our modeling framework, the analytical model is used to study the performance of multihop wireless networks using a contention-based MAC protocol (the IEEE 802.11 distributed coordination function) and a schedule-based MAC protocol (NAMA), together with different packet forwarding schemes in multihop networks. The analytical results derived from the model are validated with discrete-event simulations in Qualnet; the analytical results are shown to be very close to those attained by simulations. View full abstract»

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  • Risk-Aware Distributed Beacon Scheduling for Tree-Based ZigBee Wireless Networks

    Page(s): 692 - 703
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    In a tree-based ZigBee network, ZigBee routers (ZRs) must schedule their beacon transmission time to avoid beacon collisions. The beacon schedule determines packet delivery latency from the end devices to the ZigBee coordinator at the root of the tree. Traditionally, beacon schedules are chosen such that a ZR does not reuse the beacon slots already claimed by its neighbors, or the neighbors of its neighbors. We observe, however, that beacon slots can be reused judiciously, especially when the risk of beacon collision caused by such reuse is low. The advantage of such reuse is that packet delivery latency can be reduced. We formalize our observation by proposing a node-pair classification scheme. Based on this scheme, we can easily assess the risk of slot reuse by a node pair. If the risk is high, slot reuse is disallowed; otherwise, slot reuse is allowed. This forms the essence of our ZigBee-compatible, distributed, risk-aware, probabilistic beacon scheduling algorithm. Simulation results show that on average the proposed algorithm produces a latency only 24 percent of that with conventional method, at the cost of 12 percent reduction in the fraction of associated nodes. View full abstract»

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  • Correction to “Geometry and Motion-Based Positioning Algorithms for Mobile Tracking in NLOS Environments”

    Page(s): 704
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    In the above-cited article, which appeared in the IEEE Transactions on Mobile Computing, vol. 11, no. 2, pp. 254-263, February 2012, the authors wish to clarify that the authors listed in reference [10] are incorrect. View full abstract»

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  • [Inside back cover]

    Page(s): c3
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    Freely Available from IEEE
  • [Cover 4]

    Page(s): c4
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    Freely Available from IEEE

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