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IEEE Transactions on Mobile Computing http://www.computer.org The IEEE Transactions on Mobile Computing 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, (g) components, including devices, hardware, and software, (h) implementation issues, including interference, power, and software constraints of mobile devices, and (i) emerging technologies. en-us Mon, 3 Nov 2014 15:36:24 GMT http://csdl.computer.org/common/images/logos/tmc.gif IEEE Computer Society List of recently published journal articles http://www.computer.org/tmc PrePrint: Scheduling in Wireless Networks with Rayleigh-Fading Interference http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352278 We study approximation algorithms for optimization of wireless spectrum access with n communication requests when interference conditions are given by the Rayleigh-fading model. This model extends the deterministic interference model based on the signal-to-interference-plus-noise ratio (SINR) using stochastic propagation to address fading effects observed in reality. We consider worst-case approximation guarantees for the two standard problems of capacity maximization and latency minimization. Our main result is a generic reduction of Rayleigh fading to the deterministic non-fading model. It allows to apply existing algorithms for the non-fading model in the Rayleigh-fading scenario while losing only a factor of O(log n) in the approximation guarantee. This way, we obtain the first approximation guarantees for Rayleigh fading and, more fundamentally, show that non-trivial stochastic fading effects can be successfully handled using existing and future techniques for the non-fading model. We generalize these results in two ways. First, the same results apply for capacity maximization with variable data rates, when links obtain (non-binary) utility depending on the achieved SINR. Second, for binary utilities, we use a more detailed argument to obtain similar results even for distributed and game-theoretic approaches. Our analytical treatment is supported by simulations illustrating the performance of regret learning and, more generally, the relationship between both models. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352278 PrePrint: Privacy and Quality Preserving Multimedia Data Aggregation for Participatory Sensing Systems http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352253 With the popularity of mobile wireless devices equipped with various kinds of sensing abilities, a new service paradigm named participatory sensing has emerged to provide users with brand new life experience. However, the wide application of participatory sensing has its own challenges, among which privacy and multimedia data quality preservations are two critical problems. Unfortunately, none of the existing work has fully solved the problem of privacy and quality preserving participatory sensing with multimedia data. In this paper, we propose SLICER, which is the first k-anonymous privacy preserving scheme for participatory sensing with multimedia data. SLICER integrates a data coding technique and message transfer strategies, to achieve strong protection of participants’ privacy, while maintaining high data quality. Specifically, we study two kinds of data transfer strategies, namely transfer on meet up (TMU) and minimal cost transfer (MCT). For MCT, we propose two different but complimentary algorithms, including an approximation algorithm and a heuristic algorithm, subject to different strengths of the requirement. Furthermore, we have implemented SLICER and evaluated its performance using publicly released taxi traces. Our evaluation results show that SLICER achieves high data quality, with low computation and communication overhead. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352253 PrePrint: Temporal Starvation in CSMA Wireless Networks http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352256 It is well known that links in CSMA wireless networks are prone to starvation. Prior works focused almost exclusively on equilibrium starvation. Links in CSMA wireless networks are also susceptible to temporal starvation. Specifically, although some links have good equilibrium throughputs and do not suffer from equilibrium starvation, they can still have zero or little throughputs for extended periods from time to time. For real-time applications such as VoIP and video streaming, it is desirable to understand and characterize temporal starvation in CSMA wireless networks. To this end, we develop a “trap theory” to analyze temporal throughput fluctuations. The trap theory serves two functions. First, it allows us to derive new mathematical results that shed light on the transient behavior of CSMA networks. For example, we show that the duration of a trap, during which some links receive zero or little throughputs, is insensitive to the distributions of the transmission time (packet duration) and the backoff countdown time in the CSMA protocol given their respective means. This implies that the phenomenon of temporal starvation is fundamental and cannot be solved by simply manipulating the probability distributions of the backoff countdown time and transmission time alone. Second, with the trap theory, we can develop analytical tools for computing the “degrees of starvation” for CSMA networks to aid network design. For example, given a CSMA network, we can determine whether it suffers from starvation, and if so, which links will starve. Furthermore, the likelihood and durations of temporal starvation, if any, can also be computed. To further motivate the study of temporal starvation, we show that the existing remedies designed to solve equilibrium starvation may not work well as far as temporal starvation is considered. We believe that the ability to identify and characterize temporal starvation as established in this paper will serve as an important first step toward the design of effective remedies for it. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2352256 Issue: Sept. 2014 (Vol. 13 No.9) http://www.computer.org/csdl/trans/tm/2014/09/index.html IEEE Transactions on Mobile Computing http://www.computer.org/portal/site/tmc PrePrint: Performance Comparison of Routing Protocols for Cognitive Radio Networks http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346782 Cognitive radio networks (CRNs) have emerged as a promising solution to the ever-growing demand for additional spectrum resources and more efficient spectrum utilization. A large number of routing protocols for CRNs have been proposed recently, each based on different design goals, and evaluated in different scenarios, under different assumptions. However, little is known about the relative performance of all these protocols, let alone the tradeoffs among their different design goals. In this paper, we conduct the first detailed, empirical performance comparison of three representative routing protocols for CRNs, under the same realistic set of assumptions. Our extensive simulation study shows that the performance of routing protocols in CRNs is affected by a number of factors, in addition to PU activity, some of which have been largely ignored by the majority of previous works. We find that different protocols perform well under different scenarios, and investigate the causes of the observed performance. Furthermore, we present a generic software architecture for the experimental evaluation of CRN routing protocols on a testbed based on the USRP2 platform, and compare the performance of two protocols on a 6 node testbed. The testbed results confirm the findings of our simulation study. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346782 PrePrint: Parameter Estimation Method for Time-variant Target Object Using Randomly Deployed Sensors and its Application to Participatory Sensing http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347037 We propose a method for estimating the size, perimeter length, and location of a time-variant target object moving in a monitored area. This method uses only binary information from sensors of which locations are unknown, where the binary information includes whether each sensor has detected the target object or not. Analysis based on integral geometry provides the relationship between the number of sensors detecting the target object and the target object parameters to be estimated. Because this relationship is linear, a linear filter, such as the Kalman filter, is applicable to estimate parameters if we can assume that the dynamics of the parameters are linear. As a concrete example, the size, shape, and location of an active thunder area is estimated. The model discussed in this paper is applicable as a model of participatory sensing. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347037 PrePrint: Imitation-based Social Spectrum Sharing http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347052 Dynamic spectrum sharing is a promising technology for improving the spectrum utilization. In this paper, we study how secondary users can share the spectrum in a distributed fashion based on social imitations. The imitation-based mechanism leverages the social intelligence of the secondary user crowd and only requires a low computational power for each individual user. We introduce the information sharing graph to model the social information sharing relationship among the secondary users. We propose an imitative spectrum access mechanism on a general information sharing graph such that each secondary user first estimates its expected throughput based on local observations, and then imitates the channel selection of another neighboring user who achieves a higher throughput.We show that the imitative spectrum access mechanism converges to an imitation equilibrium, where no beneficial imitation can be further carried out on the time average. Numerical results show that the imitative spectrum access mechanism can achieve efficient spectrum utilization and meanwhile provide good fairness across secondary users. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347052 PrePrint: Distributed Channel Probing for Efficient Transmission Scheduling in Wireless Networks http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346757 It is energy-consuming and operationally cumbersome for all users to continuously estimate the channel quality before each transmission decision in opportunistic scheduling over wireless fading channels. This observation motivates us to understand whether and how opportunistic gains can still be achieved with significant reductions in channel probing requirements and without centralized coordination amongst the competing users. To that end, we first study a simple scenario that motivates us to consider the general setup and develop probing and transmission schemes that are amenable to distributed implementation. After characterizing the maximum achievable throughput region under the probing constraints, we provide an optimal probing algorithm. Noting the difficulties in the implementation of the centralized solution, we develop a novel Sequential Greedy Probing (SGP) algorithm, which is naturally well-suited for physical implementation and distributed operation. We show that the SGP algorithm is optimal in the important scenario of symmetric and independent ON-OFF fading channels. Then, we study a variant of the SGP algorithm in general fading channels to obtain its efficiency ratio as an explicit function of the channel statistics and rates, and note its tightness in the symmetric and independent ONOFF fading scenario. We further discuss the distributed implementation of these greedy solutions by using the Fast-CSMA technique. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346757 PrePrint: A Historical-Beacon-Aided Localization Algorithm for Mobile Sensor Networks http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346777 Range-free localization approaches are cost-effective for mobile sensor networks (because no additional hardware support is required). However, existing range-free localization approaches for mobile sensor networks suffer from either sparse anchor node problem or high communication cost. Due to economic considerations, mobile sensor networks typically have sparse anchor nodes which makes most range-free localization algorithms inaccurate. On the other hand, due to the power limitation of mobile sensor nodes (i.e., they are battery-operated) and high power consumption by communication, high communication cost will significantly reduce the network life time. For solving these two problems, in this paper, we use historical beacons (i.e., anchor nodes’ announcements delivered in previous time slots) and Received Signal Strength (RSS) to derive three constraints. By the aid of the three constraints, we introduce a low-communication-cost range-free localization algorithm (only one-hop beacon broadcasting is required). According to the theoretical analysis and simulation results, our three constraints can indeed improve the accuracy. Simulation results also show that our algorithm outperforms even in irregular-radio-signal environments. In addition, a hardware implementation running on sensor nodes, Octopus Xs, confirms theoretical analysis and simulation results. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2346777 PrePrint: An Adaptive Framework Coping with Dynamic Target Speed for Device-Free Passive Localization http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347303 The problem of device-free passive localization aims on locating moving objects which do not carry any localization devices. The rationale of this problem is based on the fact that a moving object can result in the changes of Received Signal Strength (RSS) of the wireless links. Existing studies on this problem usually do not consider the impact of dynamic target speed on device-free passive localization. However, the experiments show that the localization performance degrades substantially when an object is moving at dynamic speed. To meet this challenge, in this paper, we propose an adaptive device-free passive localization framework which has three components to detect target speed change and perform adaptive localization. This framework can be easily adapted for existing device-free localization methods which are based on the detection of signal strength changes. As demonstrated in the experiments, the proposed framework can lead to 50% and 30% improvement on median and maximum error respectively over the localization algorithms without considering dynamic moving speeds of the target. http://doi.ieeecomputersociety.org/10.1109/TMC.2014.2347303