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Mobile Computing, IEEE Transactions on

Issue 11 • Date Nov. 2012

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

    Page(s): c1
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    Freely Available from IEEE
  • [Inside front cover]

    Page(s): c2
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  • Optimal Hop Distance and Power Control for a Single Cell, Dense, Ad Hoc Wireless Network

    Page(s): 1601 - 1612
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    We consider a dense, ad hoc wireless network, confined to a small region. The wireless network is operated as a single cell, i.e., only one successful transmission is supported at a time. Data packets are sent between source-destination pairs by multihop relaying. We assume that nodes self-organize into a multihop network such that all hops are of length d meters, where d is a design parameter. There is a contention-based multiaccess scheme, and it is assumed that every node always has data to send, either originated from it or a transit packet (saturation assumption). In this scenario, we seek to maximize a measure of the transport capacity of the network (measured in bit-meters per second) over power controls (in a fading environment) and over the hop distance d, subject to an average power constraint. We first motivate that for a dense collection of nodes confined to a small region, single cell operation is efficient for single user decoding transceivers. Then, operating the dense ad hoc wireless network (described above) as a single cell, we study the hop length and power control that maximizes the transport capacity for a given network power constraint. More specifically, for a fading channel and for a fixed transmission time strategy (akin to the IEEE 802.11 TXOP), we find that there exists an intrinsic aggregate bit rate (Theta_{opt} bits per second, depending on the contention mechanism and the channel fading characteristics) carried by the network, when operating at the optimal hop length and power control. The optimal transport capacity is of the form d_{opt}(bar{P_t}) times Theta_{opt} with d_{opt} scaling as bar{P_t}^{{1over eta}}, where bar{P_t} is the available time average transmit power and eta is the path loss exponent. Under certain conditions on the fading distribution, we then provide a simple characterization of the optimal operating point. Simulation results are provided comparing the performance of the optimal strategy derived here w- th some simple strategies for operating the network. View full abstract»

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  • Indoor Location Estimation with Reduced Calibration Exploiting Unlabeled Data via Hybrid Generative/Discriminative Learning

    Page(s): 1613 - 1626
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    For indoor location estimation based on wireless local area networks fingerprinting, how to reduce the offline calibration effort while maintaining high location estimation accuracy is of major concern. In this paper, a hybrid generative/discriminative semi-supervised learning algorithm is proposed that utilizes a large number of unlabeled samples to supplement a small number of labeled samples. This hybrid method allows us to combine the modeling power and flexibility of generative models with the superior performance of discriminative approaches. Other related issues, such as learning efficiency enhancement and distribution estimation smoothing, are also discussed. Extensive experimental results show that our proposed method can effectively reduce the calibration effort and exhibit superior performance in terms of localization accuracy and robustness. View full abstract»

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  • Multicast Capacity Scaling Laws for Multihop Cognitive Networks

    Page(s): 1627 - 1639
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    In this paper, we study multicast capacity for cognitive networks. We consider the cognitive network model consisting of two overlapping ad hoc networks, called the primary ad hoc network (PaN) and secondary ad hoc network (SaN), respectively. PaN and SaN operate on the same space and spectrum. For PaN (or SaN, respectively), we assume that primary (or secondary, respectively) nodes are placed according to a Poisson point process of intensity n (or m, respectively) over a unit square region. We randomly choose ns (or ms, respectively) nodes as the sources of multicast sessions in PaN (or SaN, respectively), and for each primary source vp (or secondary source vs, respectively), we pick uniformly at random nd primary nodes (or md secondary nodes, respectively) as the destinations of vp (or vs, respectively). Above all, we assume that PaN can adopt the optimal protocol in terms of the throughput. Our main work is to design the multicast strategy for SaN by which the optimal throughput can be achieved, without any negative impact on the throughput for PaN in order sense. Depending on nd and n, we choose the optimal one for PaN from two strategies called percolation strategy and connectivity strategy, respectively. Subsequently, we design the corresponding throughput-optimal strategy for SaN. We derive the regimes in terms of n, nd, m, and md in which the upper bounds on multicast capacities for PaN and SaN can be achieved simultaneously. Unicast and broadcast capacities for the cognitive network can be derived by our results as the special cases by letting nd = 1 (or md = 1) and nd = n - 1 (or md = m - 1), respectively, which enhances the generality of this work. View full abstract»

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  • Enhanced Fast Base Station Switching

    Page(s): 1640 - 1651
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    IEEE 802.16-2009 specifies two fast handover mechanisms, fast base station switching and macro diversity handover, to streamline communication for a mobile station (MS). Both operate with a diversity set that lists base stations among which an MS can move its connection readily. In view that an unduly chosen diversity set may cause prohibitive cost, we provide means to prevent the diversity set from including base stations that are less likely to serve the MS in the near future. Inspired from the working-set model, our approach develops predictive handover using numerical extrapolation to accommodate temporal locality of the MS. While a joint entry-replacement strategy is exercised to evict least-preferred entries in the diversity set, its capacity is reviewed and tuned periodically allowing for reasonable space demand. Simulation results show that our approach, compared with the counterpart scheme, reduces handover executions by over 48 percent, handover delay by over 51 percent, and diversity-set space requirement by up to 17.9 percent on average. As another salient strength, our approach conforms fully to the standard, keeping current protocols on the MS side operable without modification. Qualitative and quantitative performance discussions indicate the usefulness of our approach in pragmatic settings. View full abstract»

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  • Exploiting Spatial, Frequency, and Multiuser Diversity in 3GPP LTE Cellular Networks

    Page(s): 1652 - 1665
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    This paper addresses the problem of frequency domain packet scheduling (FDPS) incorporating spatial division multiplexing (SDM) multiple input multiple output (MIMO) techniques on the 3GPP Long-Term Evolution (LTE) downlink. We impose the LTE MIMO constraint of selecting only one MIMO mode (spatial multiplexing or transmit diversity) per user per transmission time interval (TTI). First, we address the optimal MIMO mode selection (multiplexing or diversity) per user in each TTI in order to maximize the proportional fair (PF) criterion adapted to the additional frequency and spatial domains. We prove that both single-user (SU-) and multi-user (MU-) MIMO FDPS problems under the LTE requirement are NP-hard. We therefore develop two types of approximation algorithms (ones with full channel feedback and the others with partial channel feedback), all of which guarantee provable performance bounds for both SU- and MU-MIMO cases. Based on 3GPP LTE system model simulations, our approximation algorithms that take into account both spatial and frequency diversity gains outperform the exact algorithms that do not exploit the potential spatial diversity gain. Moreover, the approximation algorithms with partial channel feedback achieve comparable performance (with only 1-6 percent performance degradation) to the ones with full channel feedback, while significantly reducing the channel feedback overhead by nearly 50 percent. View full abstract»

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  • Admission and Eviction Control of Cognitive Radio Users at Wi-Fi 2.0 Hotspots

    Page(s): 1666 - 1677
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    Cognitive radio (CR)-based Wi-Fi 2.0 hotspots are introduced as an attractive application of dynamic spectrum access (DSA), at which a wireless service provider (WSP) leases licensed channels via secondary market and offers Internet access to CR-enabled customers by opportunistically utilizing the leased spectrum. The CR users access the channels only when they are temporarily unoccupied by their legacy users, and pay a usage charge according to the WSP's pricing policy. In this paper, we study the profit maximization problem of a WSP by deriving the (sub)optimal control of admission (at CR user arrivals) and eviction (upon return of the legacy users) of CR users. We formulate the problem as a semi-Markov decision process (SMDP) with two quality-of-service (QoS) constraints on arrival-blocking and service-dropping probabilities, which is solved by the linear programming techniques. Using an extensive numerical analysis, we show that the derived policy achieves up to 22.5-44 percent more profit than simple complete-sharing algorithms in the tested scenarios. In addition, we evaluate the impact of the number of leased channels and pricing on the achieved profit, and study the tradeoffs between the two QoS constraints. View full abstract»

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  • Cross-Layer Optimization of Correlated Data Gathering in Wireless Sensor Networks

    Page(s): 1678 - 1691
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    We consider the problem of gathering correlated sensor data by a single sink node in a wireless sensor network. We assume that the sensor nodes are energy constrained and design efficient distributed protocols to maximize the network lifetime. Many existing approaches focus on optimizing the routing layer only, but in fact the routing strategy is often coupled with power control in the physical layer and link access in the MAC layer. This paper represents a first effort on network lifetime maximization that jointly considers the three layers. We first assume that link access probabilities are known and consider the joint optimal design of power control and routing. We show that the formulated optimization problem is convex and propose a distributed algorithm, JRPA, for the solution. We also discuss the convergence of JRPA. When the optimal link access probabilities are unknown, as in many practical networks, we generalize the problem formulation to encompass all the three layers of routing, power control, and link-layer random access. In this case, the problem cannot be converted into a convex optimization problem, but there exists a duality gap when the Lagrangian dual method is employed. We propose an efficient heuristic algorithm, JRPRA, to solve the general problem, and show through numerical experiments that it can significantly narrow the gap between the computed and optimal solutions. Moreover, even without a priori knowledge of the best link access probabilities predetermined for JRPA, JRPRA achieves extremely competitive performance with JRPA. Beyond the metric of network lifetime, we also discuss how to solve the problem of correlated data gathering under general utility functions. Numerical results are provided to show the convergence of the algorithms and their advantages over existing solutions. View full abstract»

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  • WiMAX/OFDMA Burst Scheduling Algorithm to Maximize Scheduled Data

    Page(s): 1692 - 1705
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    OFDMA resource allocation algorithms manage the distribution and assignment of shared OFDMA resources among the users serviced by the basestation. The OFDMA resource allocation algorithms determine which users to schedule, how to allocate subcarriers to them, and how to determine the appropriate power levels for each user on each subcarrier. In WiMAX, the downlink (DL) TDD OFDMA subframe structure is a rectangular area of N subchannels times K time slots. Users are assigned rectangular bursts in the downlink subframe. The size of burst, in terms of number of subchannels and number of time slots, varies based on the user's channel quality and data to be transmitted for the assigned user. In this paper, we study the problem of assigning users to bursts in WiMAX TDD OFDMA system with the objective of maximizing downlink system throughput for the Partially Used subcarrier (PUSC) subchannalization permutation mode. Our main contributions in this paper are: 1) we propose different methods to assign bursts to users, 2) we prove that our Best Channel burst assignment method achieves throughput within a constant factor of the optimal, 3) through extensive simulations with real system parameters, we study the performance of the Best Channel burst assignment method. To the best of our knowledge, we are the first to study the problem of DL Burst Assignment in the downlink OFDMA subframe for PUSC subchannalization permutation mode taking user's channel quality into consideration in the assignment process. View full abstract»

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  • Duopoly Competition in Dynamic Spectrum Leasing and Pricing

    Page(s): 1706 - 1719
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    This paper presents a comprehensive analytical study of two competitive secondary operators' investment (i.e., spectrum leasing) and pricing strategies, taking into account operators' heterogeneity in leasing costs and users' heterogeneity in transmission power and channel conditions. We model the interactions between operators and users as a three-stage dynamic game, where operators simultaneously make spectrum leasing decisions in Stage I, and pricing decisions in Stage II, and then users make purchase decisions in Stage III. Using backward induction, we are able to completely characterize the dynamic game's equilibria. We show that both operators' investment and pricing equilibrium decisions process interesting threshold properties. For example, when the two operators' leasing costs are close, both operators will lease positive spectrum. Otherwise, one operator will choose not to lease and the other operator becomes the monopolist. For pricing, a positive pure strategy equilibrium exists only when the total spectrum investment of both operators is less than a threshold. Moreover, two operators always choose the same equilibrium price despite their heterogeneity in leasing costs. Each user fairly achieves the same service quality in terms of signal-to-noise ratio (SNR) at the equilibrium, and the obtained predictable payoff is linear in its transmission power and channel gain. We also compare the duopoly equilibrium with the coordinated case where two operators cooperate to maximize their total profit. We show that the maximum loss of total profit due to operators' competition is no larger than 25 percent. The users, however, always benefit from operators' competition in terms of their payoffs. We show that most of these insights are robust in the general SNR regime. View full abstract»

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  • Using Partially Overlapping Channels to Improve Throughput in Wireless Mesh Networks

    Page(s): 1720 - 1733
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    Wireless mesh networks have attracted great interest in the research community recently. Much effort has been devoted to maximizing the network performance using limited channel resources in a multichannel multiradio wireless mesh network. It is believed that the limited spectrum resource can be fully exploited by utilizing partially overlapping channels in addition to nonoverlapping channels in 802.11b/g networks. However, there are only few studies of channel assignment algorithms for partially overlapping channels. In this paper, we first formulate the optimal channel assignment problem with the goal of maximizing the overall network throughput or maximizing the throughput of a multicast application. For both cases, we present a greedy algorithm for partially overlapping channel assignment, and then propose a novel genetic algorithm, which has the potential to obtain better solutions. Through evaluation, we demonstrate that the overall network throughput can be dramatically improved by properly utilizing the partially overlapping channels. The genetic algorithm outperforms the greedy algorithm in mitigating the network interference, and therefore leads to higher network throughput. In addition, the multicast throughput can also be dramatically improved by using our algorithms compared to previous work. View full abstract»

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  • Structural Analysis of User Association Patterns in University Campus Wireless LANs

    Page(s): 1734 - 1748
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    Wireless networks and personalized mobile devices are deeply integrated and embedded in our lives. Such wide adoptions of new technologies will impact user behavior and in turn will affect network performance. It is imperative to characterize the fundamental structure of wireless user behavior in order to model, manage, leverage and design efficient mobile networks. One major challenge in characterizing user behavior stems from the significant size and complexity of user behavioral data. Without summarization and dimension reduction, the sheer amount of data does not provide much useful information. The key contribution of the paper is a novel similarity metric based on a matrix representation of mobility preferences and its decomposition. This method provides an efficient way to reduce important spatiotemporal dynamics in user mobility into a few eigen-behavior vectors. This also facilitates nodes to exchange their mobility summaries and determine their mutual similarity locally. Without any assumption on the properties of user population, we use unsupervised learning (clustering) techniques to classify WLAN users. Such a user grouping scheme based on learned user behavior is crucial for applications relying on the usage context of each mobile device (e.g., participatory sensing, social-relationship-aware message forwarding). In this study, using our systematic TRACE approach, we analyze wireless users' behavioral patterns by extensively mining wireless network logs from two major university campuses to showcase its efficacy. While our findings partly validate intuitive repetitive behavioral trends and user grouping, it is surprising to find the qualitative commonalities and striking consistency of user behavior from the two universities. We discover multimodal user behavior for more than 60 percent of the users, and there are hundreds of distinct groups with unique behavioral patterns in both campuses. The sizes of the major groups follow a power-law distributio- . View full abstract»

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  • Spectrum: Lightweight Hybrid Address Autoconfiguration Protocol Based on Virtual Coordinates for 6LoWPAN

    Page(s): 1749 - 1762
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    Stateless address autoconfiguration protocols allow nodes to select addresses and validate the uniqueness of a selected address by duplicate address detection (DAD). The considerable cost of DAD results from the message complexity increase in multihop network topologies, such as wireless sensor networks. This paper proposes a lightweight, hybrid address autoconfiguration protocol, called Spectrum, that deploys IPv6-compatible addresses into 6LoWPAN networks in a distributed manner. Spectrum creates the virtual coordinate system on the network and deploys addresses based on the location of the nodes. The deployment policy based on the virtual locations of the nodes reduces the DAD cost in the initial configuration as well as the cost for additional configurations of newly arrived nodes. The authors implemented and tested the proposed scheme in a real environment. Simulations and experiments confirmed a reasonable message cost for both stateful and stateless autoconfigurations. View full abstract»

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  • PET: Probabilistic Estimating Tree for Large-Scale RFID Estimation

    Page(s): 1763 - 1774
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    Estimating the number of RFID tags in the region of interest is an important task in many RFID applications. In this paper, we propose a novel approach for efficiently estimating the approximate number of RFID tags. Compared with existing approaches, the proposed Probabilistic Estimating Tree (PET) protocol achieves O(loglogn) estimation efficiency, which remarkably reduces the estimation time while meeting the accuracy requirement. PET also largely reduces the computation and memory overhead at RFID tags. As a result, we are able to apply PET with passive RFID tags and provide scalable and inexpensive solutions for large-scale RFID systems. We validate the efficacy and effectiveness of PET through theoretical analysis as well as extensive simulations. Our results suggest that PET outperforms existing approaches in terms of estimation accuracy, efficiency, and overhead. View full abstract»

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  • A Comment on "MABS: Multicast Authentication Based on Batch Signature”

    Page(s): 1775 - 1776
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    Recently, Zhou et al. proposed a multicast authentication protocol named MABS which employs an efficient cryptographic primitive called batch verification to authenticate an arbitrary number of data packets simultaneously. Three implementations were presented: MABS-RSA, MABS-BLS, and MABS-DSA. In this comment, we are concerned with the last implementation, which is claimed to be much more efficient than the others. Our particular interest also lies in the fact that MABS-DSA was designed to thwart a known attack against its underlying batch DSA primitive and is claimed to be with increased security. After a careful revisit of the involved arithmetic, however, we find that the real issue lies in protocol correctness rather than security; the algorithm of MABS-DSA actually does not hold as one would expect. More specifically, even if each of the data packets was signed by an honest sender and securely delivered to the receiver, verification of the batch of signatures will still almost always fail. View full abstract»

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  • [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