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Mobile Computing, IEEE Transactions on

Issue 12 • Date Dec. 2013

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Displaying Results 1 - 17 of 17
  • Editorial and Changes to the Editorial Board

    Page(s): 2317 - 2321
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    Freely Available from IEEE
  • Radio-Frequency Tomography for Passive Indoor Multitarget Tracking

    Page(s): 2322 - 2333
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    Radio-frequency (RF) tomography is the method of tracking targets using received signal-strength (RSS) measurements for RF transmissions between multiple sensor nodes. When the targets are near the line-of-sight path between two nodes, they are more likely to cause substantial attenuation or amplification of the RF signal. In this paper, we develop a measurement model for multitarget tracking using RF tomography in indoor environments and apply it successfully for tracking up to three targets. We compare several multitarget tracking algorithms and examine performance in the two scenarios when the number of targets is 1) known and constant, and 2) unknown and time varying. We demonstrate successful tracking for experimental data collected from sensor networks deployed in three different indoor environments posing different tracking challenges. For the fixed number of targets, the best algorithm achieves a root-mean-squared error tracking accuracy of approximately 0.3 m for a single target, 0.7 m for two targets and 0.8 m for three targets. Tracking using our proposed model is more accurate than tracking using previously proposed observation models; more importantly, the model does not require the same degree of training. View full abstract»

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  • hJam: Attachment Transmission in WLANs

    Page(s): 2334 - 2345
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    Effective coordination can dramatically reduce radio interference and avoid packet collisions for multistation wireless local area networks (WLANs). Coordination itself needs consume communication resource and thus competes with data transmission for the limited wireless radio resources. In traditional approaches, control frames and data packets are transmitted in an alternate manner, which brings a great deal of coordination overhead. In this paper, we propose a new communication model where the control frames can be "attachedâ to the data transmission. Thus, control messages and data traffic can be transmitted simultaneously and consequently the channel utilization can be improved significantly. We implement the idea in OFDM-based WLANs called hJam, which fully explores the physical layer features of the OFDM modulation method and allows one data packet and a number of control messages to be transmitted together. hJam is implemented on the GNU Radio testbed consisting of eight USRP2 nodes. We also conduct comprehensive simulations and the experimental results show that hJam can improve the WLANs efficiency by up to 200 percent compared with the existing 802.11 family protocols. View full abstract»

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  • Utilizing Massive Spatiotemporal Samples for Efficient and Accurate Trajectory Prediction

    Page(s): 2346 - 2359
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    Trajectory prediction is widespread in mobile computing, and helps support wireless network operation, location-based services, and applications in pervasive computing. However, most prediction methods are based on very coarse geometric information such as visited base transceiver stations, which cover tens of kilometers. These approaches undermine the prediction accuracy, and thus restrict the variety of application. Recently, due to the advance and dissemination of mobile positioning technology, accurate location tracking has become prevalent. The prediction methods based on precise spatiotemporal information are then possible. Although the prediction accuracy can be raised, a massive amount of data gets involved, which is undoubtedly a huge impact on network bandwidth usage. Therefore, employing fine spatiotemporal information in an accurate prediction must be efficient. However, this problem is not addressed in many prediction methods. Consequently, this paper proposes a novel prediction framework that utilizes massive spatiotemporal samples efficiently. This is achieved by identifying and extracting the information that is beneficial to accurate prediction from the samples. The proposed prediction framework circumvents high bandwidth consumption while maintaining high accuracy and being feasible. The experiments in this study examine the performance of the proposed prediction framework. The results show that it outperforms other popular approaches. View full abstract»

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  • Local Differential Perturbations: Location Privacy under Approximate Knowledge Attackers

    Page(s): 2360 - 2372
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    Location privacy research has received wide attention in the past few years owing to the growing popularity of location-based applications, and the skepticism thereof on the collection of location information. A large section of this research is directed toward mechanisms based on location obfuscation enforced using cloaking regions. The primary motivation for this engagement comes from the relatively well-researched area of database privacy. Researchers in this sibling domain have indicated multiple times that any notion of privacy is incomplete without explicit statements on the capabilities of an adversary. As a result, we have started to see some efforts to categorize the various forms of background knowledge that an adversary may possess in the context of location privacy. Along this line, we consider some preliminary forms of attacker knowledge, and explore what implication does a certain form of knowledge has on location privacy. Continuing on, we extend our insights to a form of adversarial knowledge related to the geographic uncertainty that the adversary has in correctly locating a user. We empirically demonstrate that the use of cloaking regions can adversely impact the preservation of privacy in the presence of such approximate location knowledge, and demonstrate how perturbation-based mechanisms can instead provide a well-balanced tradeoff between privacy and service accuracy. View full abstract»

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  • A Tracking System for Wireless Embedded Nodes Using Time-of-Flight Ranging

    Page(s): 2373 - 2385
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    In this work, we present the design, development, and evaluation of a real-time target tracking system for wireless embedded nodes, capable of effectively tracking manoeuvring targets. The proposed tracking system is designed to operate solely on range measurements obtained with the use of a two-way time-of-flight method without the need for additional hardware being incorporated in the nodes. To address the challenge of coping with manoeuvring targets, the tracking problem is formulated as a dynamical estimation problem where an adaptive multiple-model approach is employed to represent the motion pattern of manoeuvring targets. The ranging observations are produced in real time and used as inputs to a particle filter algorithm that produces the estimates of the target's kinematic variables. Simulations are provided to assess the effect of several factors on the system's performance. Ultimately, the entire system is implemented on commercially available hardware and tested in an outdoor deployment. A total of 25 experiments demonstrate an average RMS accuracy of 2.6 m for position and 1.9 m/s for velocity, in a 15 m × 15 m area. Such performance, which is additionally confirmed from simulation results, reveals the potential of the proposed range-only system in application scenarios where real-time tracking of mobile targets is needed. View full abstract»

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  • Background Subtraction for Online Calibration of Baseline RSS in RF Sensing Networks

    Page(s): 2386 - 2398
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    Radio frequency (RF) sensing networks are a class of wireless sensor networks (WSNs) which use RF signals to accomplish tasks such as passive device-free localization and tracking. The algorithms used for these tasks usually require access to measurements of baseline received signal strength (RSS) on each link. However, it is often impossible to collect this calibration data (measurements collected during an offline calibration period when the region of interest is empty of targets). We propose adapting background subtraction methods from the field of computer vision to estimate baseline RSS values from measurements taken while the system is online and obstructions may be present. This is done by forming an analogy between the intensity of a background pixel in an image and the baseline RSS value of a WSN link and then translating the concepts of temporal similarity, spatial similarity, and spatial ergodicity, which underlie specific background subtraction algorithms to WSNs. Using experimental data, we show that these techniques are capable of estimating baseline RSS values with enough accuracy that RF tomographic tracking can be carried out in a variety of different environments without the need for a calibration period. View full abstract»

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  • GMTC: A Generalized Commit Approach for Hybrid Mobile Environments

    Page(s): 2399 - 2411
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    Mobile environments increasingly require distributed atomic transactions to support the growing diversity of financial, gaming, social networking and many other applications. The underlying mobile infrastructure is correspondingly evolving with increasingly diverse wired and wireless elements and also with increasing exposure to a variety of operational perturbations at the mobile elements and communication levels. Consequently, the challenge is not only in providing efficient nonblocking mobile commit (as a fundamental basis behind consistent mobile transactions) but to also provide efficient perturbation-resilient atomic commit in the heterogeneous mobile space. The contribution of this paper is in developing a perturbation-resilient mobile commit protocol that efficiently provides for and preserves strict atomicity for transactional applications. The protocol does not necessarily require access to the powerful communication/computation elements of the wired infrastructure during transaction execution. However, in case access to a wired network becomes possible, it then adapts to utilize this to 1) increase the resilience to network perturbations achieving higher commit rates, and 2) reduce the wireless message overhead and the blocking of transaction participants leading to higher transactions throughput. In contrast, existing solutions are often tailored either for 1) infrastructure-based mobile environments, or 2) infrastructure-less ad hoc networks. To our knowledge, there is no existing commit protocol that can adapt across diverse infrastructure communication modes. The proposed perturbation-resilient generalized mobile transaction commit (GMTC) protocol represents the first atomic commit protocol for hybrid mobile environments which 1) takes advantage of accessing infrastructures, by choosing reliable infrastructure nodes for coordination of transactions and for replication of commit data of mobile participants to tolerate network disconnections, and 2) to- erates network partitioning and delivers best-effort resultsâin terms of transaction commit rate, message complexity, and commit/abort decision time (latency)âif the access to wired infrastructure is unavailable. The protocol performance simulations (covering transaction commit rate, message complexity, and commit/abort decision time) demonstrate the effectiveness of the developed protocol in generalized mobile environments. View full abstract»

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  • Frequency Domain Packet Scheduling with Stability Analysis for 3GPP LTE Uplink

    Page(s): 2412 - 2426
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    In this paper, we investigate the Frequency Domain Packet Scheduling (FDPS) problem for 3GPP Long Term Evolution (LTE) Uplink (UL). Instead of studying a specific scheduling policy, we provide a unified approach to tackle this issue. First, we formalize a general LTE UL FDPS problem, which is suitable for various scheduling policies. Then, we prove that the problem is MAX SNP-hard, which implies that approximation algorithms with constant approximation ratios are the best that we can hope for. Therefore, we design two approximation algorithms, both of which have polynomial runtime. The first algorithm is based on a simple greedy method. The second one is based on the Local Ratio (L-R) technique and it can approximately solve the LTE UL FDPS problem with an approximation ratio of 2. To further analyze the stability of the 2-approximation L-R algorithm, we derive a specific FDPS problem, which incorporates the queue length and channel quality information. We utilize the Lyapunov Drift to prove the L-R algorithm is stable for any (ω00)-admissible LTE UL systems. The simulation results indicate good performance of the L-R scheduler. View full abstract»

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  • Network Selection and Resource Allocation Games for Wireless Access Networks

    Page(s): 2427 - 2440
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    Wireless access networks are often characterized by the interaction of different end users, communication technologies, and network operators. This paper analyzes the dynamics among these "actorsâ by focusing on the processes of wireless network selection, where end users may choose among multiple available access networks to get connectivity, and resource allocation, where network operators may set their radio resources to provide connectivity. The interaction among end users is modeled as a noncooperative congestion game, where players (end users) selfishly select the access network that minimizes their perceived selection cost. A method based on mathematical programming is proposed to find Nash equilibria and characterize their optimality under three cost functions, which are representative of different technological scenarios. System level simulations are then used to evaluate the actual throughput and fairness of the equilibrium points. The interaction among end users and network operators is then assessed through a two-stage multileader/multifollower game, where network operators (leaders) play in the first stage by properly setting the radio resources to maximize their users, and end users (followers) play in the second stage the aforementioned network selection game. The existence of exact and approximated subgame perfect Nash equilibria of the two-stage game is thoroughly assessed and numerical results are provided on the "qualityâ of such equilibria. View full abstract»

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  • Byzantine Fault-Tolerant Consensus in Wireless Ad Hoc Networks

    Page(s): 2441 - 2454
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    Wireless ad hoc networks, due to their inherent unreliability, pose significant challenges to the task of achieving tight coordination among nodes. The failure of some nodes and momentary breakdown of communications, either of accidental or malicious nature, should not result in the failure of the entire system. This paper presents an asynchronous Byzantine consensus protocol-called Turquois-specifically designed for resource-constrained wireless ad hoc networks. The key to its efficiency is the fact that it tolerates dynamic message omissions, which allows an efficient utilization of the wireless broadcasting medium. The protocol also refrains from computationally expensive public-key cryptographic during its normal operation. The protocol is safe despite the arbitrary failure of f <; n/3 nodes from a total of n nodes, and unrestricted message omissions. Progress is ensured in rounds where the number of omissions is σ ≤ [n-t/2] (n - k - t) + k - 2, where k is the number of nodes required to terminate and t ≤ f is the number of nodes that are actually faulty. These characteristics make Turquois the first consensus protocol that simultaneously circumvents the FLP and the Santoro-Widmayer impossibility results, which is achieved through randomization. Finally, the protocol was prototyped and subject to a comparative performance evaluation against two well-known Byzantine fault-tolerant consensus protocols. The results show that, due to its design, Turquois outperforms the other protocols by more than an order of magnitude as the number of nodes in the system increases. View full abstract»

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  • A Scalable and Accurate Nonsaturated IEEE 802.11e EDCA Model for an Arbitrary Buffer Size

    Page(s): 2455 - 2469
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    IEEE 802.11e EDCA induces service differentiation by appropriate joint tuning of four adjustable contention parameters. Existing and emerging work has devoted considerable attention to the nonsaturated performance of EDCA networks due to the difficulty of predicting the joint influence of the four parameters. However, most existing nonsaturated EDCA models adopt complex extensions of a Markov-chain approach. In sharp contrast, this paper invokes an extension of a renewal-reward approach. Our extension has the following unparalleled advantages: good scalability, ease of understanding, fast computation speed, high accuracy, models joint differentiation of all four parameters, captures the impact of an arbitrary buffer size, and predicts a wide range of performance indicators including the buffer overflow probability and the MAC access delay distribution. Our nonsaturated EDCA model is a nontrivial augmentation of our previously proposed nonsaturated DCF model. Our results indicate that if we accurately model the nonsaturated collision probability, the same formulas used for the saturated performance descriptors can produce accurate results for nonsaturated operation, and therefore it is unnecessary to construct specific formulas for nonsaturated performance descriptors, as done in previous work. To illustrate the utility of our model, we also develop an admission control policy based on the proposed EDCA model for a CWmin-differentiation system. Simulations validate that this policy enables the system to run slightly below a critical point, beyond which the system performance deteriorates drastically. View full abstract»

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  • Throughput Optimal Switching in Multichannel WLANs

    Page(s): 2470 - 2482
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    We observe that in a multichannel wireless system, an opportunistic channel/spectrum access scheme that solely focuses on channel quality sensing measured by received SNR may induce users to use channels that, while providing better signals, are more congested. Ultimately the notion of channel quality should include both the signal quality and the level of congestion, and a good multichannel access scheme should take both into account in deciding which channel to use and when. Motivated by this, we focus on the congestion aspect and examine what type of dynamic channel switching schemes may result in the best system throughput performance. Specifically, we derive the stability region of a multiuser multichannel WLAN system and determine the throughput optimal channel switching scheme within a certain class of schemes. We also empirically examine the impact of considering congestion in addition to signal quality in making channel selection decisions. View full abstract»

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  • Analysis of Individual Pair and Aggregate Intercontact Times in Heterogeneous Opportunistic Networks

    Page(s): 2483 - 2495
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    Foundational work in the area of opportunistic networks has shown that the distribution of intercontact times between pairs of nodes has a key impact on the network properties, for example, in terms of convergence of forwarding protocols. Specifically, forwarding protocols may yield infinite expected delay if the intercontact time distributions present a particularly heavy tail. While these results hold for the distributions of intercontact times between individual pairs, most of the literature uses the aggregate distribution, i.e., the distribution obtained by considering the samples from all pairs together, to characterize the properties of opportunistic networks. In this paper, we provide an analytical framework that can be used to check when this approach is correct and when it is not, and we apply it to a number of relevant cases. We show that the aggregate distribution can be way different from the distributions of individual pair intercontact times. Therefore, using the former to characterize properties that depend on the latter is not correct in general, although this is correct in some cases. We substantiate this finding by analyzing the most representative distributions characterizing real opportunistic networks that can be obtained from reference traces. We review key cases for opportunistic networking, where the aggregate intercontact time distribution presents a heavy tail with or without exponential cutoff. We show that, when individual pairs follow Pareto distributions, the aggregate distribution consistently presents a heavy tail. However, heavy tail aggregate distributions can also emerge in networks where individual pair intercontact times are not heavy tailed, for example, exponential or Pareto with exponential cutoff distributions. We show that an exponential cutoff in the aggregate appears when the average intercontact times of individual pairs are finite. Finally, we discuss how to use our analytical model to know whether collecting aggregate - nformation about intercontact times is sufficient or not, to decideâin practiceâwhich type of routing protocols to use. View full abstract»

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  • Threshold Constraints on Symmetric Key Extraction from Rician Fading Estimates

    Page(s): 2496 - 2506
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    Symmetric key establishment using reciprocal quantization of channel estimates in wireless Rician fading environments is considered. The quantization bits from channel-phase and channel-amplitude are treated as the output of a random number generator. We determine threshold constraints on the required minimal distance of the legitimate communicating parties from a passive eavesdropper, and determine threshold constraints on maximal key establishing rates. The analysis makes use of widely accepted statistical test suites applied to the generated bit streams along with a lemma we define and prove. For distance analysis, the minimal required distance from the eavesdropper to maintain perfect secrecy during key establishment is derived. For key establishing rates, the maximal rates are derived while ensuring the generated bits streams pass the statistical test suites. The work results in generic and clear threshold requirements on distance and rates as function of the Rician factor and quantization bit for any transmission frequency. Clear thresholds are useful for systems operating in a-priori known or estimated propagation environments. In addition, we address the effect of imperfect channel reciprocity on key agreement. Results show practical systems can operate under reciprocal and secure conditions, and that channel-phase estimates perform better than channel-amplitude estimates. View full abstract»

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  • Unilateral Wakeup for Mobile Ad Hoc Networks with Group Mobility

    Page(s): 2507 - 2517
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    Asynchronous wakeup schemes have been proposed for ad hoc networks to increase the energy efficiency of wireless communication. The basic idea is to allow a node to sleep when it is idle, and wakeup periodically to check if there are pending transmissions. In this paper, we examine the applicability of asynchronous wakeup schemes to the Mobile Ad Hoc NETworks (MANETs). We discover that, although it is desirable to have nodes with lower mobility to sleep more in reaction to the less-changing link states, in practice this is prohibited due to an unwanted tradeoff between the energy saving and in-time link discovery. All nodes in a network must stay awake frequently based on their highest possible moving speed to avoid network partition. To address this problem, we propose a new wakeup scheme, named Unilateral- (Uni-) scheme, for MANETs that allows nodes with slower moving speed to sleep more without losing the network connectivity. The Uni-scheme supports both the entity mobility and group mobility of nodes, thus has broad applicability. Theoretical analysis and simulation are conducted and show that the Uni-scheme can render significant energy saving as compared with the previous arts. View full abstract»

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  • Efficient Aggregation Scheduling in Multihop Wireless Sensor Networks with SINR Constraints

    Page(s): 2518 - 2528
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    We study delay-efficient data aggregation scheduling in wireless sensor networks subject to signal to interference-plus-noise ratio (SINR) constraints. We construct a routing tree and propose two scheduling algorithms that can generate collision-free link schedules for data aggregation. We prove that the delay of each algorithm is O(R + Δ) time slots, where R and Δ are respectively the graph radius and the maximum node degree in a reduced communication graph of the original network; the proposed algorithms are asymptotically optimum on delay in random wireless sensor networks. We evaluate the performances of the proposed algorithms and the simulation results corroborate our theoretical analysis. View full abstract»

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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