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Mobile Computing, IEEE Transactions on

Issue 12 • Date Dec. 2012

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Displaying Results 1 - 23 of 23
  • [Cover / Table of contents]

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

    Page(s): c2
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  • Opportunistic Retransmission in WLANs

    Page(s): 1953 - 1969
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2338 KB) |  | HTML iconHTML  

    This paper presents an efficient opportunistic retransmission protocol (PRO, Protocol for Retransmitting Opportunistically) to improve the performance of IEEE 802.11 WLANs. PRO is a link-layer protocol that allows overhearing nodes to function as relays that retransmit on behalf of a source after they learn about a failed transmission. Relays with better connectivity to the destination have a higher chance of delivering the packet than the source, thereby resulting in a more efficient use of the channel. PRO has four main features. First, channel reciprocity coupled with a runtime calibration process is used to estimate the instantaneous link quality to the destination. Second, a local qualification process filters out poor relays early. Third, a distributed relay selection algorithm chooses the best set of eligible relays among all qualified relays and prioritizes them. Finally, 802.11e Enhanced Distributed Channel Access (EDCA) is leveraged to make sure high-quality relays transmit with higher probability. PRO is designed to coexist with legacy 802.11 stations. Our extensive evaluation on both a controlled testbed and in the real world shows that PRO can improve throughput in diverse wireless environments. PRO helps the most when there is significant contention for the ether, under fading, and with user mobility. View full abstract»

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  • Position and Movement Detection of Wireless Sensor Network Devices Relative to a Landmark Graph

    Page(s): 1970 - 1982
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (967 KB) |  | HTML iconHTML  

    We present a novel probabilistic framework for reliable indoor positioning of mobile sensor network devices. Compared to existing approaches, ours adopts complex computations in exchange for high localization accuracy while needing low hardware investment and moderate set-up cost. To that end, we use full distributional information on signal measurements at a set of discrete locations, termed landmarks. Positioning of a mobile device is done relative to the resulting landmark graph and the device can be found near a landmark or in the area between two landmarks. Key elements of our approach include profiling the signal measurement distributions over the coverage area using a special interpolation technique; a two-tier statistical positioning scheme that improves efficiency by adding movement detection; and joint clusterhead placement optimization for both localization and movement detection. The proposed system is practical and has been implemented using standard wireless sensor network hardware. Experimentally, our system achieved an accuracy equivalent to less than 5 meters with 95 percent success probability and less than 3 meters with an 87 percent success probability. This performance is superior to well-known contemporary systems that use similar low-cost hardware. View full abstract»

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  • Received-Signal-Strength-Based Indoor Positioning Using Compressive Sensing

    Page(s): 1983 - 1993
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    The recent growing interest for indoor Location-Based Services (LBSs) has created a need for more accurate and real-time indoor positioning solutions. The sparse nature of location finding makes the theory of Compressive Sensing (CS) desirable for accurate indoor positioning using Received Signal Strength (RSS) from Wireless Local Area Network (WLAN) Access Points (APs). We propose an accurate RSS-based indoor positioning system using the theory of compressive sensing, which is a method to recover sparse signals from a small number of noisy measurements by solving an `1-minimization problem. Our location estimator consists of a coarse localizer, where the RSS is compared to a number of clusters to detect in which cluster the node is located, followed by a fine localization step, using the theory of compressive sensing, to further refine the location estimation. We have investigated different coarse localization schemes and AP selection approaches to increase the accuracy. We also show that the CS theory can be used to reconstruct the RSS radio map from measurements at only a small number of fingerprints, reducing the number of measurements significantly. We have implemented the proposed system on a WiFi-integrated mobile device and have evaluated the performance. Experimental results indicate that the proposed system leads to substantial improvement on localization accuracy and complexity over the widely used traditional fingerprinting methods. View full abstract»

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  • Distributed Fault-Tolerance for Event Detection Using Heterogeneous Wireless Sensor Networks

    Page(s): 1994 - 2007
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (698 KB) |  | HTML iconHTML  

    This paper presents a general fault-tolerant event detection scheme that allows nodes to detect erroneous local decisions by leveraging the local decisions reported by their neighbors. This detection scheme can handle cases where nodes have different accuracy levels. The derived fault-tolerant estimator is proven to be optimal under the maximum a posteriori (MAP) criterion. An equivalent weighted voting scheme is also derived. Further, two new error models are derived to take into account the neighbor distance and the geographical distributions of the two decision quorums. These models are particularly suitable for detection applications where the event under consideration is highly localized. The fault-tolerant estimator is simulated using a network of 1,024 nodes deployed randomly in a square region and assigned random probabilities of failure. Several estimation schemes that allow nodes to learn their error rates continuously are developed. These error rates are used in the distributed estimation schemes to assign appropriate weights to the nodes in the voting scheme. View full abstract»

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  • Dual Decomposition for Computational Optimization of Minimum-Power Shared Broadcast Tree in Wireless Networks

    Page(s): 2008 - 2019
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (710 KB) |  | HTML iconHTML  

    We consider the problem of constructing a shared broadcast tree (SBT) in wireless networks, such that the total power required for supporting broadcast initiated by all source nodes is minimal. In the well-studied minimum-energy broadcast (MEB) problem, the optimal tree varies by source. In contrast, SBT is source-independent, thus substantially reducing the overhead for information storage and processing. The SBT problem also differs from the range assignment problem (RAP), because the power for message forwarding in SBT, although being source-independent, depends on from which tree neighbor the message is received. We approach SBT from a computational optimization standpoint, and present a dual decomposition method applied to an optimization model that embeds multiple directed trees into a shared tree. For the dual decomposition method, some of the constraints in the model are preferably formulated implicitly. The dual decomposition scheme is coupled with a fast local search algorithm. We report computational results demonstrating the effectiveness of the proposed approach. In average, the performance gap to global optimality is less than three percent. View full abstract»

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  • Exploiting Spectrum Heterogeneity in Dynamic Spectrum Market

    Page(s): 2020 - 2032
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1475 KB) |  | HTML iconHTML  

    The dynamic spectrum market (DSM) is a key economic vehicle for realizing the opportunistic spectrum access that will mitigate the anticipated spectrum-scarcity problem. DSM allows legacy spectrum owners to lease their channels to unlicensed spectrum consumers (or secondary users) in order to increase their revenue and improve spectrum utilization. In DSM, determining the optimal spectrum leasing price is an important yet challenging problem that requires a comprehensive understanding of market participants' interests and interactions. In this paper, we study spectrum pricing competition in a duopoly DSM, where two wireless service providers (WSPs) lease spectrum access rights, and secondary users (SUs) purchase the spectrum use to maximize their utility. We identify two essential, but previously overlooked, properties of DSM: 1) heterogeneous spectrum resources at WSPs and 2) spectrum sharing among SUs. We demonstrate the impact of spectrum heterogeneity via an in-depth measurement study using a software-defined radio (SDR) testbed. We then study the impacts of spectrum heterogeneity on WSPs' optimal pricing and SUs' WSP selection strategies using a systematic three-step approach. First, we study how spectrum sharing among SUs subscribed to the same WSP affects the SUs' achievable utility. Then, we derive the SUs' optimal WSP selection strategy that maximizes their payoff, given the heterogeneous spectrum propagation characteristics and prices. We analyze how individual SU preferences affect market evolution and prove the market convergence to a mean-field limit, even though SUs make local decisions. Finally, given the market evolution, we formulate the WSPs' pricing strategies in a duopoly DSM as a noncooperative game and identify its Nash equilibrium points. We find that the equilibrium price and its uniqueness depend on the SUs' geographical density and spectrum propagation characteristics. Our analytical framework reveals the impact of spectrum heteroge- eity in a real-world DSM, and can be used as a guideline for the WSPs' pricing strategies. View full abstract»

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  • Handover Incentives for Self-Interested WLANs with Overlapping Coverage

    Page(s): 2033 - 2046
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    We consider an environment where self-interested IEEE 802.11 Wireless Local Area Networks (WLANs) have overlapping coverage, and investigate the incentives that can trigger handovers between the WLANs. Our focus is on the incentives for supporting handovers due solely to the improved performance for all wireless networks. Such incentives arise due to a well-known property of 802.11 networks, where low rate users that send traffic significantly degrade the performance of high rate users that are associated with the same access point. A key difference of this paper compared to other works is that WLANs are self-interested, seeking to improve the performance of their own clients. We develop a comprehensive analytical model for accurately identifying and quantifying the handover gains. The model captures cases such as uplink and downlink traffic, wired link capacity constraints, and nonsaturated traffic conditions, and yields a practical handover decision policy. Simulations and experiments on a real testbed verify the accuracy of the model, and indicate that significant gains can be achieved through performance-induced handover incentives. View full abstract»

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  • Omnidirectional Mobile NLOS Identification and Localization via Multiple Cooperative Nodes

    Page(s): 2047 - 2059
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1316 KB) |  | HTML iconHTML  

    This paper presents an Omnidirectional mobile target-node (TN) localization technique in nonline-of-sight (NLOS) scenarios. Here, a TN cooperates with base-nodes (BNs) with antenna-arrays to allow them to find its position via time-of-arrival (TOA) and direction-of-arrival (DOA) measurements. When line-of-sight (LOS) channel is available, each BN localizes TNs in its coverage area with reasonable accuracy. However, when LOS channel is obstructed, considerable localization error is generated. To avoid NLOS error, a technique is proposed to identify if a TN is in the LOS of multiple BNs or not. The technique enables BNs to determine and localize their shared reflection points, and to localize NLOS TNs. The paper assumes single-bounce-reflection NLOS channel between BNs and TNs. In NLOS scenarios, when three or more reflection points are shared by a TN and multiple sets of BNs, the shared reflection points are localized via DOA fusion, and then the TN is localized via TOA fusion. The equations for NLOS identification, shared reflection points determination and localization and NLOS TN localization are theoretically derived. Simulations are conducted to evaluate the proposed technique in terms of the probability of false alarm and misdetection of NLOS identification and shared reflection points determination, and NLOS TN localization accuracy. View full abstract»

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  • A 6LoWPAN Sensor Node Mobility Scheme Based on Proxy Mobile IPv6

    Page(s): 2060 - 2072
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    In this paper, we focus on a scheme that supports mobility for IPv6 over Low power Wireless Personal Area Network (6LoWPAN) sensor nodes. We define a protocol for 6LoWPAN mobile sensor node, named 6LoMSN, based on Proxy Mobile IPv6 (PMIPv6). The conventional PMIPv6 standard supports only single-hop networks and cannot be applied to multihop-based 6LoWPAN. It does not support the mobility of 6LoMSNs and 6LoWPAN gateways, named 6LoGW, cannot detect the PAN attachment of the 6LoMSN. Therefore, we define the movement notification of a 6LoMSN in order to support its mobility in multihop-based 6LoWPAN environments. The attachment of 6LoMSNs reduces signaling costs over the wireless link by using router solicitation (RS) and router advertisement (RA) messages. Performance results show that our proposed scheme can minimize the total signaling costs and handoff latency. Additionally, we present the design and implementation of the 6LoMSN mobility based on PMIPv6 for a healthcare system. According to the experimental results, the 6LoMSN of the proposed PMIPv6-based 6LoWPAN can be expected to use more of the battery lifetime. We also verify that the 6LoMSN can maintain connectivity, even though it has the freedom of being able to move between PANs without a mobility protocol stack. View full abstract»

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  • On the Throughput Capacity of Heterogeneous Wireless Networks

    Page(s): 2073 - 2086
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    A substantial body of the literature exists addressing the capacity of wireless networks. However, it is commonly assumed that all nodes in the network are identical. The issue of heterogeneity has not been embraced into the discussions. In this paper, we investigate the throughput capacity of heterogeneous wireless networks with general network settings. Specifically, we consider an extended network with n normal nodes and m = nb (0 ≤ b ≤ 1) more powerful helping nodes in a rectangular area with width s(n) and length n/s(n), where s(n) = nw and 0 ≤ w ≤ 1/2. We assume that there are n flows in the network. All the n normal nodes are sources while only randomly chosen nd (0 ≤ d ≤ 1) normal nodes are destinations. We further assume that the n normal nodes are uniformly and independently distributed, while the m helping nodes are either regularly placed or uniformly and independently distributed, resulting in two different kinds of networks called Regular Heterogeneous Wireless Networks and Random Heterogeneous Wireless Networks, respectively. We show that network capacity is determined by the shape of the network area, the number of destination nodes, the number of helping nodes, and the bandwidth of helping nodes. We also find that heterogeneous wireless networks can provide throughput higher in the order sense than traditional homogeneous wireless networks only under certain conditions. View full abstract»

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  • Efficient Distributed Algorithms for Dynamic Access to Shared Multiuser Channels in SINR-Constrained Wireless Networks

    Page(s): 2087 - 2097
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    In wireless networks, simultaneously active transmitters typically operate in separate communication channels to avoid mutual interference. This study focuses on the challenge of increasing the capacity of a wireless network by enabling multiple transmissions in each available channel. Active transmitters are assumed to maintain the receiver signal-to-noise-and-interference ratio (SINR) at a predetermined target value via power control to promote the quality of wireless connections. To this end, we propose distributed medium access algorithms that allow every transmitter-receiver pair to determine whether a target SINR is physically achievable through iterative power control in a given shared channel. The proposed algorithms are shown by theoretical analysis to be fast, accurate, and energy efficient. Numerical simulations demonstrate their ability to outperform related medium access schemes based on random access, carrier sensing, controlled power up, or invariant channel probing. Our major contribution consists of solving the open problem of accurate real-time computation of the spectral radius of an unknown network information matrix. This makes our framework applicable not only to testing target SINR achievability, but also to other aspects of wireless engineering such as energy efficiency, power control stability, and handover prioritization, in which knowledge of the spectral radius plays a key role. View full abstract»

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  • CapEst: A Measurement-Based Approach to Estimating Link Capacity in Wireless Networks

    Page(s): 2098 - 2108
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    Estimating link capacity in a wireless network is a complex task because the available capacity at a link is a function of not only the current arrival rate at that link, but also of the arrival rate at links which interfere with that link as well as of the nature of interference between these links. Models which accurately characterize this dependence are either too computationally complex to be useful or lack accuracy. Further, they have a high implementation overhead and make restrictive assumptions, which makes them inapplicable to real networks. In this paper, we propose CapEst, a general, simple yet accurate, measurement-based approach to estimating link capacity in a wireless network. To be computationally light, CapEst allows inaccuracy in estimation; however, using measurements, it can correct this inaccuracy in an iterative fashion and converge to the correct estimate. Our evaluation shows that CapEst always converged to within 5 percent of the correct value in less than 18 iterations. CapEst is model-independent; hence, it is applicable to any MAC/PHY layer and works with autorate adaptation. Moreover, it has a low implementation overhead, can be used with any application which requires an estimate of residual capacity on a wireless link and can be implemented completely at the network layer without any support from the underlying chipset. View full abstract»

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  • Temporal Correlation of Interference in Wireless Networks with Rayleigh Block Fading

    Page(s): 2109 - 2120
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    The temporal correlation of interference is a key performance factor of several technologies and protocols for wireless communications. A comprehensive understanding of interference correlation is especially important in the design of diversity schemes, whose performance can severely degrade in case of highly correlated interference. Taking into account three sources of correlation-node locations, channel, and traffic-and using common modeling assumptions-random homogeneous node positions, Rayleigh block fading, and slotted ALOHA traffic-we derive closed-form expressions and calculation rules for the correlation coefficient of the overall interference power received at a certain point in space. Plots give an intuitive understanding as to how model parameters influence the interference correlation. View full abstract»

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  • Sum Rate Increase via Variable Interference Protection

    Page(s): 2121 - 2132
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (661 KB) |  | HTML iconHTML  

    The sum rate of spectrum-sharing in decentralized and self-organizing wireless networks is investigated in this paper. Such networks pose the following two fundamental challenges: 1) cochannel interference and 2) the hidden node problem. For a slotted shared wireless medium, where resources are partitioned into time-frequency slots, time-multiplexed receiver initiated busy burst (BB) transmissions solve these problems by establishing an exclusion region around an active receiver by means of receiver feedback. The size of this exclusion region is controlled by an interference threshold that determines whether a user is allowed to transmit on a specific time-frequency resource unit. We propose a novel approach for setting the interference thresholds based on a heuristic derived for a two-link network. First, for two-links, the optimum threshold value is derived that maximizes the sum rate. Second, for multiple links, the new heuristic threshold that only relies on locally available information is derived. It is demonstrated via simulations that heuristic thresholding achieves superior sum rate compared to a fixed system-wide threshold. To complement simulation results, an analytical approach is developed to approximate the probability density function (pdf) of the sum of the interferers in BB setting with fixed threshold with a cumulant-based shifted log normal fitting method. View full abstract»

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  • The X Loss: Band-Mix Selection for Opportunistic Spectrum Accessing with Uncertain Spectrum Supply from Primary Service Providers

    Page(s): 2133 - 2144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB) |  | HTML iconHTML  

    In a cognitive radio network, primary service providers (PSPs) set prices for the vacant licensed bands and sell/lease them for pecuniary gains while the secondary service provider (SSP) can buy/rent the bands and support opportunistic spectrum accessing (OSA). However, due to the unpredictable activities of primary services, the SSP may suffer the monetary risk or failure to meet the traffic demands from the secondary users (SUs). It is challenging for the SSP to measure the risk for OSA, to choose the bands to use, and to split the traffic on the band-mix, when there are multiple vacant bands from PSPs. In this paper, we first introduce the X loss, an intuitive measurement for the risk for OSA. Although the X loss is attractively simple, it underestimates the potential risk for OSA and is mathematically not subadditive, which makes it difficult to support the band-mix selection for traffic splitting. To overcome this problem, we propose a more suitable risk measurement, which is subadditive and consistent with the SSP's perception of the risk. Based on the proposed risk metric, we formulate the band-mix selection problem as an optimization problem and solve it by linear programming. View full abstract»

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  • Regarding the Pagination of the October 2012 and November 2012 Issues of the IEEE Transactions on Mobile Computing

    Page(s): 2145
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    The IEEE Computer Society regrets that the pages listed for the October 2012 and November 2012 issues of the IEEE Transactions on Mobile Computing were incorrectly labeled and do not follow sequentially from earlier issues of the journal. Although the October 2012 issue replicates the pagination of the September 2012 issue, these pages are considered final as published and will be officially retained. Any citations for papers published in these issues should therefore cite the pages as they are listed on the individual papers and on the Table of Contents. The pagination of this issue, December 2012, has been restored to the correct page numbers. Our sincere apologies for any confusion. View full abstract»

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  • IEEE open access publishing [advertisement]

    Page(s): 2146
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    Page(s): 2147
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  • OnlinePlus Publicaiton Model

    Page(s): 2148
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  • [Inside back cover]

    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