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Mobile Computing, IEEE Transactions on

Issue 9 • Date Sept. 2013

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Displaying Results 1 - 16 of 16
  • Impact of the Connection Admission Process on the Direct Retry Load Balancing Algorithm in Cellular Networks

    Publication Year: 2013 , Page(s): 1681 - 1696
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB) |  | HTML iconHTML  

    We present an analytical framework for modeling a priority-based load balancing scheme in cellular networks based on a new algorithm called direct retry with truncated offloading channel resource pool (DRK). The model, developed for a baseline case of two cell network, differs in many respects from previous works on load balancing. Foremost, it incorporates the call admission process, through random access. In specific, the proposed model implements the Physical Random Access Channel used in 3GPP network standards. Furthermore, the proposed model allows the differentiation of users based on their priorities. The quantitative results illustrate that, for example, cellular network operators can control the manner in which traffic is offloaded between neighboring cells by simply adjusting the length of the random access phase. Our analysis also allows for the quantitative determination of the blocking probability individual users will experience given a specific length of random access phase. Furthermore, we observe that the improvement in blocking probability per shared channel for load balanced users using (DRK) is maximized at an intermediate number of shared channels, as opposed to the maximum number of these shared resources. This occurs because a balance is achieved between the number of users requesting connections and those that are already admitted to the network. We also present an extension of our analytical model to a multicell network (by means of an approximation) and an application of the proposed load balancing scheme in the context of opportunistic spectrum access. View full abstract»

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  • Decentralized Bargain: A Two-Tier Market for Efficient and Flexible Dynamic Spectrum Access

    Publication Year: 2013 , Page(s): 1697 - 1711
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1461 KB) |  | HTML iconHTML  

    Market mechanisms have been exploited as important means for spectrum acquisition and access in cognitive radio networks. In this paper, we propose a two-tier market for decentralized dynamic spectrum access. In the proposed Tier-1 market, spectrum is traded from a primary user (PU) to secondary users (SUs) in a relatively large time scale to reduce signaling overhead. Then, driven by dynamic traffic demands, SUs set up the Tier-2 market to redistribute channels among themselves in a small time scale. More specifically, we use a Nash bargain game to model the spectrum acquisition of SUs in the Tier-1 market and derive the equilibrium prices. We then employ a strategic bargain game to study the spectrum redistribution in the Tier-2 market, where SUs can exchange channels with low overhead through random matching, bilateral bargain, and the predetermined market equilibrium price. We investigate how various factors, such as the availability of channels and bargain partners, matching strategies, and traffic dynamics, affect the market relationships. This work provides new understanding on the spectrum market and valuable guidelines to primary and secondary network operators. View full abstract»

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  • Key Management for Multiple Multicast Groups in Wireless Networks

    Publication Year: 2013 , Page(s): 1712 - 1723
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2136 KB) |  | HTML iconHTML  

    With the emergence of diverse group-based services, multiple multicast groups are likely to coexist in a single network, and users may subscribe to multiple groups simultaneously. However, the existing group key management (GKM) schemes, aiming to secure communication within a single group, are not suitable in multiple multicast group environments because of inefficient use of keys, and much larger rekeying overheads. In this paper, we propose a new GKM scheme for multiple multicast groups, called the master-key-encryption-based multiple group key management (MKE-MGKM) scheme. The MKE-MGKM scheme exploits asymmetric keys, i.e., a master key and multiple slave keys, which are generated from the proposed master key encryption (MKE) algorithm and is used for efficient distribution of the group key. It alleviates the rekeying overhead by using the asymmetry of the master and slave keys, i.e., even if one of the slave keys is updated, the remaining ones can still be unchanged by modifying only the master key. Through numerical analysis and simulations, it is shown that the MKE-MGKM scheme can reduce the storage overhead of a key distribution center (KDC) by 75 percent and the storage overhead of a user by up to 85 percent, and 60 percent of the communication overhead at most, compared to the existing schemes. View full abstract»

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  • VeMAC: A TDMA-Based MAC Protocol for Reliable Broadcast in VANETs

    Publication Year: 2013 , Page(s): 1724 - 1736
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1214 KB) |  | HTML iconHTML  

    The need of a medium access control (MAC) protocol for an efficient broadcast service is of great importance to support the high-priority safety applications in vehicular ad hoc networks (VANETs). This paper introduces VeMAC, a novel multichannel TDMA MAC protocol proposed specifically for a VANET scenario. The VeMAC supports efficient one-hop and multihop broadcast services on the control channel by using implicit acknowledgments and eliminating the hidden terminal problem. The protocol reduces transmission collisions due to node mobility on the control channel by assigning disjoint sets of time slots to vehicles moving in opposite directions and to road side units. Analysis and simulation results in highway and city scenarios are presented to evaluate the performance of VeMAC and compare it with ADHOC MAC, an existing TDMA MAC protocol for VANETs. It is shown that, due to its ability to decrease the rate of transmission collisions, the VeMAC protocol can provide significantly higher throughput on the control channel than ADHOC MAC. View full abstract»

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  • On the MDP-Based Cost Minimization for Video-on-Demand Services in a Heterogeneous Wireless Network with Multihomed Terminals

    Publication Year: 2013 , Page(s): 1737 - 1749
    Cited by:  Papers (1)
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (866 KB) |  | HTML iconHTML  

    In this paper, we deal with a cost minimization problem for a multihomed mobile terminal that downloads and plays a video-on-demand (VoD) stream. The cost consists of the user's dissatisfaction due to playback disruptions and communication cost for downloading the VoD stream. There are three components in our approach: parameter estimation, threshold adjustment, and threshold compensation. Since we do not assume any a priori knowledge about underlying random variables, necessary parameter values are estimated online. Using the resultant estimates, we formulate the problem as a Markov decision process (MDP) problem considering as if the random variables are exponentially distributed. To solve the MDP problem efficiently, we propose a threshold adjustment algorithm that exploits some structural properties of any optimal solution that are specific to our problem. Finally, to handle the cases where the random variables are not exponentially distributed, we propose a threshold compensation algorithm to compensate for the modeling error. Through extensive simulations, we compare the performance of our scheme with those of static threshold schemes. View full abstract»

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  • Routing-Toward-Primary-User Attack and Belief Propagation-Based Defense in Cognitive Radio Networks

    Publication Year: 2013 , Page(s): 1750 - 1760
    Cited by:  Papers (1)
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB) |  | HTML iconHTML  

    Cognitive radio (CR) networks have attracted many attentions recently, while the security issues are not fully studied yet. In this paper, we propose a new and powerful network layer attack, routing-toward-primary-user (RPU) attack in CR networks. In this attack, malicious nodes intentionally route a large amount of packets toward the primary users (PUs), aiming to cause interference to the PUs and to increase delay in the data transmission among the secondary users. In the RPU attack, it is difficult to detect the malicious nodes since the malicious nodes may claim that those nodes, to which they forward the packets, behave dishonestly and cause problems in the data transmission. To defend against this attack without introducing high complexity, we develop a defense strategy using belief propagation. First, an initial route is found from the source to the destination. Each node keeps a table recording the feedbacks from the other nodes on the route, exchanges feedback information and computes beliefs. Finally, the source node can detect the malicious nodes based on the final belief values. Simulation results show that the proposed defense strategy against the RPU attack is effective and efficient in terms of significant reduction in the delay and interference caused by the RPU attack. View full abstract»

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  • Estimating Performance of Mobile Services from Comparative Output-Input Analysis of End-to-End Throughput

    Publication Year: 2013 , Page(s): 1761 - 1773
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (547 KB) |  | HTML iconHTML  

    Mobile devices with ever-increasing functionality and the ubiquitous availability of wireless communication networks are driving forces behind innovative mobile applications enriching our daily life. One of the performance measures for a successful application deployment is the ability to support application-data flows by heterogeneous networks within certain delay boundaries. However, the quantitative impact of this measure is unknown and practically infeasible to determine at real time due to the mobile device resource constraints. We research practical methods for measurement-based performance evaluation of heterogeneous data communication networks that support mobile application-data flows. We apply the lightweight Comparative Output-Input Analysis (COIA) method estimating an additional delay based on an observation interval of interest (e.g., 1 second) induced on the flow. An additional delay is the amount of delay that exceeds nonavoidable, minimal end-to-end delay caused by the networks propagation, serialization, and transmission. We propose five COIA methods to estimate additional delay, and we validate their accuracy with measurements obtained from the existing healthcare and multimedia streaming applications. Despite their simplicity, our methods prove to be accurate in relation to an observation interval of interest, and robust under a variety of network conditions. The methods offer novel insights into application-data delays with regards to the performance of heterogeneous data communication networks. View full abstract»

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  • Dynamic Online-Calibrated Radio Maps for Indoor Positioning in Wireless Local Area Networks

    Publication Year: 2013 , Page(s): 1774 - 1787
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2424 KB) |  | HTML iconHTML  

    Context-awareness and Location-Based-Services are of great importance in mobile computing environments. Although fingerprinting provides accurate indoor positioning in Wireless Local Area Networks (WLAN), difficulty of offline site surveys and the dynamic environment changes prevent it from being practically implemented and commercially adopted. This paper introduces a novel client/server-based system that dynamically estimates and continuously calibrates a fine radio map for indoor positioning without extra network hardware or prior knowledge about the area and without time-consuming offline surveys. A modified Bayesian regression algorithm is introduced to estimate a posterior signal strength probability distribution over all locations based on online observations from WLAN access points (AP) assuming Gaussian prior centered over a logarithmic pass loss mean. To continuously adapt to dynamic changes, Bayesian kernels parameters are continuously updated and optimized genetically based on recent APs observations. The radio map is further optimized by a fast features reduction algorithm to select the most informative APs. Additionally, the system provides reliable integrity monitor (accuracy measure). Two different experiments on IEEE 802.11 networks show that the dynamic radio map provides 2-3m accuracy, which is comparable to results of an up-to-date offline radio map. Also results show the consistency of estimated accuracy measure with actual positioning accuracy. View full abstract»

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  • Adaptive Channel Recommendation for Opportunistic Spectrum Access

    Publication Year: 2013 , Page(s): 1788 - 1800
    Cited by:  Papers (1)
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (882 KB) |  | HTML iconHTML  

    We propose a dynamic spectrum access scheme where secondary users cooperatively recommend "goodâ channels to each other and access accordingly. We formulate the problem as an average reward-based Markov decision process. We show the existence of the optimal stationary spectrum access policy and explore its structure properties in two asymptotic cases. Since the action space of the Markov decision process is continuous, it is difficult to find the optimal policy by simply discretizing the action space and use the policy iteration, value iteration, or Q-learning methods. Instead, we propose a new algorithm based on the model reference adaptive search method and prove its convergence to the optimal policy. Numerical results show that the proposed algorithms achieve up to 18 and 100 percent performance improvement than the static channel recommendation scheme in homogeneous and heterogeneous channel environments, respectively, and is more robust to channel dynamics. View full abstract»

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  • Fast and Accurate Cooperative Tracking in Wireless Networks

    Publication Year: 2013 , Page(s): 1801 - 1813
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    The utility of wireless networks for many applications is increased if the locations of the nodes in the network can be tracked based on the measurements between communicating nodes. Many applications, such as tracking fire fighters in large buildings, require the deployment of mobile ad hoc networks. Real-time tracking in such environments is a challenging task, particularly combined with restrictions on computational and communication resources in mobile devices. In this paper, we present a new algorithm using the Bayesian framework for cooperative tracking of nodes, which allows accurate tracking over large areas using only a small number of anchor nodes. The proposed algorithm requires lower computational and communication resources than existing algorithms. Simulation results show that the algorithm performs well with the tracking error being close to the posterior Cramer-Rao lower bound that we derive for cooperative tracking. Experimental results for a network deployed in an indoor office environment with external global position system-referenced anchor nodes are presented. A computationally simple indoor range error model for measurements at the 5.8-GHz ISM band that yields positioning accuracy close to that obtained when using the actual range error distribution is also presented. View full abstract»

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  • A New Approach to Fast Near-Optimal Channel Assignment in Cellular Mobile Networks

    Publication Year: 2013 , Page(s): 1814 - 1827
    Cited by:  Papers (2)
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1140 KB) |  | HTML iconHTML  

    This paper presents a novel method for solving channel assignment problems (CAPs) in hexagonal cellular networks with nonhomogeneous demands in a 2-band buffering system (where channel interference does not extend beyond two cells). The CAP with nonhomogeneous demand is first partitioned into a sequence of smaller subproblems, each of which has a homogeneous demand from a subset of the nodes of the original network. Solution to such a subproblem constitutes an assignment phase, where multiple homogeneous demands are assigned to the nodes corresponding to the subproblem, satisfying all the frequency separation constraints. The whole assignment process for the original network consists of a succession of multiple homogeneous assignments for all the subproblems. Based on this concept, we present a polynomial time approximation algorithm for solving the CAP for cellular networks having nonhomogeneous demands. Our proposed assignment algorithm, when executed on well-known benchmark instances, comes up with an assignment which is always within about 6 percent more than the optimal bandwidth, but requires a very small execution time (less than 5 millisecond on a HPxw8400 workstation). The proposed algorithm is very much suitable for real-life situations, where fast channel assignment is of primary importance, tolerating, however, a marginal deviation (6 percent) from the optimal bandwidth. View full abstract»

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  • Mobile Autonomous Router System for Dynamic (Re)formation of Wireless Relay Networks

    Publication Year: 2013 , Page(s): 1828 - 1841
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1017 KB) |  | HTML iconHTML  

    Multihop wireless relays can extend the area of network connectivity instantly and efficiently. However, due to the spatial dependence of wireless link-quality, the deployment of relay nodes requires extensive, expensive measurement, and management efforts. This paper presents a mobile autonomous router system, (MARS) through which a relay router autonomously seeks and adjusts the best "receptionâ position for itself and cooperatively forms a string-type relay network with other neighboring routers. Specifically, MARS 1) accurately characterizes spatial link-quality through a new measurement technique, 2) effectively probes/optimizes node positioning via a spatial probing algorithm, and 3) maintains error-tolerant position information via an inexpensive positioning algorithm. MARS has been prototyped with both a commodity mobile robot and a wireless router with IEEE 802.11 cards. Our experimental evaluation of both the MARS prototype and ns-2-based simulation show that MARS achieves an average of 95 percent accuracy in link-quality measurements, and reduces the measurement effort necessary for the optimization of a node's location by two-thirds, compared to exhaustive spatial probing. View full abstract»

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  • Adaptive Wireless Channel Probing for Shared Key Generation Based on PID Controller

    Publication Year: 2013 , Page(s): 1842 - 1852
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (871 KB) |  | HTML iconHTML  

    Generating a shared key between two parties from the wireless channel is an increasingly interesting topic. The process of obtaining information from the wireless channel is called channel probing. Previous key generation schemes probe the channel at a preset and constant rate without any consideration of channel variation or probing efficiency. To satisfy the usersâ requirements for key generation rate (KGR) and to use the wireless channel efficiently, we propose an adaptive channel probing scheme based on the proportional-integral-derivative controller, which is used to tune the probing rate. Moreover, we use the Lempel-Ziv complexity to estimate the entropy rate of channel statistics (received signal strength), which is considered as an indicator of probing efficiency. The experimental results show that the controller can dynamically tune the probing rate and, meanwhile, to achieve a user desired KGR. It stabilizes the KGR at the desired value with error below 1 bit/s. Besides, channel probing process is efficient under different user velocities, motion types, and sites. View full abstract»

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  • Networking Low-Power Energy Harvesting Devices: Measurements and Algorithms

    Publication Year: 2013 , Page(s): 1853 - 1865
    Cited by:  Papers (6)
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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1902 KB) |  | HTML iconHTML  

    Recent advances in energy harvesting materials and ultra-low-power communications will soon enable the realization of networks composed of energy harvesting devices. These devices will operate using very low ambient energy, such as energy harvested from indoor lights. We focus on characterizing the light energy availability in indoor environments and on developing energy allocation algorithms for energy harvesting devices. First, we present results of our long-term indoor radiant energy measurements, which provide important inputs required for algorithm and system design (e.g., determining the required battery sizes). Then, we focus on algorithm development, which requires nontraditional approaches, since energy harvesting shifts the nature of energy-aware protocols from minimizing energy expenditure to optimizing it. Moreover, in many cases, different energy storage types (rechargeable battery and a capacitor) require different algorithms. We develop algorithms for calculating time fair energy allocation in systems with deterministic energy inputs, as well as in systems where energy inputs are stochastic. View full abstract»

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  • Bicriteria Optimization in Multihop Wireless Networks: Characterizing the Throughput-Energy Envelope

    Publication Year: 2013 , Page(s): 1866 - 1878
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1295 KB) |  | HTML iconHTML  

    Network throughput and energy consumption are two important performance metrics for a multihop wireless network. Current state-of-the-art research is limited to either maximizing throughput under some energy constraint or minimizing energy consumption while satisfying some throughput requirement. Although many of these prior efforts were able to offer some optimal solutions, there is still a critical need to have a systematic study on how to optimize both objectives simultaneously. In this paper, we take a multicriteria optimization approach to offer a systematic study on the relationship between the two performance objectives. To focus on throughput and energy performance, we simplify link layer scheduling by employing orthogonal channels among the links. We show that the solution to the multicriteria optimization problem characterizes the envelope of the entire throughput-energy region, i.e., the so-called optimal throughput-energy curve. We prove some important properties of the optimal throughput-energy curve. For case study, we consider both linear and nonlinear throughput functions. For the linear case, we characterize the optimal throughput-energy curve precisely through parametric analysis, while for the nonlinear case, we use a piecewise linear approximation to approximate the optimal throughput-energy curve with arbitrary accuracy. Our results offer important insights on exploiting the tradeoff between the two performance metrics. View full abstract»

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  • Maximizing Transmission Opportunities in Wireless Multihop Networks

    Publication Year: 2013 , Page(s): 1879 - 1892
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2107 KB) |  | HTML iconHTML  

    Being readily available in most of 802.11 radios, multirate capability appears to be useful as WiFi networks are getting more prevalent and crowded. More specifically, it would be helpful in high-density scenarios because internode distance is short enough to employ high data rates. However, communication at high data rates mandates a large number of hops for a given node pair in a multihop network and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called multihop transmission opportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively to minimize the MAC-layer overhead between hops. This seemingly collision-prone nonstop forwarding is proved to be safe via analysis and USRP/GNU Radio-based experiment in this paper. The idea of MTOP is in clear contrast to the conventional opportunistic transmission mechanism, known as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity in a single-hop WLAN. We conducted an extensive simulation study via OPNET, demonstrating the performance advantage of MTOP under a wide range of network scenarios. 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