http://www.computer.org/tmc 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 Sat, 18 May 2013 10:00:06 GMT http://csdl.computer.org/common/images/logos/tmc.gif List of recently published journal articles http://www.computer.org/tmc http://doi.ieeecomputersociety.org/10.1109/TMC.2013.51 Wireless data transmission consumes a significant part of the overall energy consumption of smartphones, due to the popularity of Internet applications. In this paper we investigate the energy consumption characteristics of data transmission over Wi-Fi, focusing on the effect of Internet flow characteristics and network environment. We present deterministic models that describe the energy consumption of Wi-Fi data transmission with traffic burstiness, network performance metrics like throughput and retransmission rate, and parameters of the power saving mechanisms in use. Our models are practical because their inputs are easily available on mobile platforms without modifying low-level software or hardware components. We demonstrate the practice of model-based energy profiling on Maemo, Symbian and Android phones, and evaluate the accuracy with physical power measurement of applications including file transfer, web browsing, video streaming and instant messaging. Our experimental results show that our models are of adequate accuracy for energy profiling and are easy to apply. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.51 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.47 This paper presents a novel framework that includes an inhomogeneous (time-variant) Hidden Markov Model (HMM) and learning from data concepts. The framework either recognizes or estimates user contextual inferences called 'user states' within the concept of Human Activity Recognition (HAR) for future context-aware applications. Context-aware applications require continuous data acquisition and interpretation from one or more sensor reading(s). Therefore, device battery lifetimes need to be extended due to the fact that constantly running built-in sensors deplete device batteries rapidly. In this sense, a framework is constructed to fulfill requirements needed by applications and to prolong device battery lifetimes. The ultimate goal of this paper is to present an accurate user state representation model, and to maximize power efficiency while the model operates. Most importantly, this research intends to create and clarify a generic framework to guide the development of future context-aware applications. Moreover, topics such as user profile adaptability and variant sensory sampling operations are examined. The proposed framework is validated by simulations and implemented in a HAR based application by the smartphone accelerometer. According to the results, the proposed framework shows an increase in power efficiency of 60% for an accuracy range from 75% up to 96%, depending on user profiles. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.47 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.43 Time synchronization is a fundamental service for Wireless Sensor Networks (WSNs). Although a number of message passing protocols can achieve satisfactory synchronization accuracy, they suffer poor scalability and high transmission overhead. An alternative approach is to utilize the global time references such as those induced by GPS and timekeeping radios. However, they require the hardware receiver to decode the out of band clock signal, which introduces extra cost and design complexity. This paper proposes a novel WSN time synchronization approach by exploiting the existing Wi-Fi infrastructure. Our approach leverages the fact that ZigBee sensors and Wi-Fi nodes often occupy the same or overlapping radio frequency bands in the 2.4 GHz unlicensed spectrum. As a result, a ZigBee node can detect and synchronize to the periodic beacons broadcasted by Wi-Fi access points (APs). A key advantage of our approach is that, due to the long communication range of Wi-Fi, a large number of ZigBee sensors can synchronize to the same beacons without any message exchange. We implement WizSync in TinyOS 2.1x and conduct extensive evaluation on a testbed consisting of 19 TelosB motes. Our results show that WizSync can achieve an average synchronization error of 0.12 milliseconds over a period of 10 days with radio power consumption of 50.9 microwatts/node. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.43 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.39 The performance of medium access control (MAC) depends on both spatial locations and traffic patterns of wireless agents. In contrast to conventional MAC policies, we propose a MAC solution that adapts to the prevailing spatial and temporal opportunities. The proposed solution is based on a decentralized partially observable Markov decision process (DEC-POMDP), which is able to handle wireless network dynamics described by a Markov model. A DEC-POMDP takes both sensor noise and partial observations into account, and yields MAC policies that are optimal for the network dynamics model. The DEC-POMDP MAC policies can be optimized for a freely chosen goal, such as maximal throughput or minimal latency, with the same algorithm. We make approximate optimization efficient by exploiting problem structure: the policies are optimized by a factored DEC-POMDP method, yielding highly compact state machine representations for MAC policies. Experiments show that our approach yields higher throughput and lower latency than CSMA/CA based comparison methods adapted to the current wireless network configuration. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.39 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.36 In a two-tier heterogeneous networking (HetNet) environment where femto access points (FAPs) with lower transmission power coexist with macro base stations (BSs) with higher transmission power, the FAPs may suffer significant performance degradation due to inter-tier interference. Introducing cognition into the FAPs through the spectrum sensing (or carrier sensing) capability helps them avoiding severe interference from the macro BSs and enhance their performance. In this paper, we use stochastic geometry to model and analyze performance of HetNets composed of macro BSs and cognitive FAPs in a multichannel environment. The proposed model explicitly accounts for the spatial distribution of the macro BSs, FAPs, and users in a Rayleigh fading environment. We quantify the performance gain in outage probability obtained by introducing cognition into the femto-tier, provide design guidelines, and show the existence of an optimal spectrum sensing threshold for the cognitive FAPs which depends on the HetNet parameters. We also show that looking into the overall performance of the HetNets is quite misleading in the scenarios where the majority of users are served by the macro BSs. Therefore, the performance of femto-tier needs to be explicitly accounted for and optimized. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.36 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.31 ZigBee and other wireless technologies operating in the 2.4GHz ISM band are being applied in WPAN for many medical applications. However, these low duty cycle, low power, and low data rate medical WPANs suffer from WiFi co-channel interferences. WiFi interference can lead to longer latency and higher packet losses in WPANs, which can be particularly harmful to safety-critical applications with stringent temporal requirements, such as ECG. This paper exploits the CCA mechanism in WiFi devices and proposes a novel policing framework, WiCop, that can effectively control the temporal white-spaces between WiFi transmissions. Such temporal white-spaces can be utilized for delivering low duty cycle WPAN traffic. We have implemented and validated WiCop on SORA SDR platform. Experimental results show that with the assistance of the proposed WiCop policing schemes, the PRR of a ZigBee-based WPAN can increase by up to 116% in the presence of a heavy WiFi interferer. A case study on the medical application of WPAN ECG monitoring demonstrates that WiCop can bound ECG signal distortion within 2% even under heavy WiFi interference. An analytical framework is devised to model the CCA behavior of WiFi interferers and the performance of WPANs under WiFi interference with or without WiCop protection. The analytical results are corroborated by experiments. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.31 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.24 Recent work has examined techniques to estimate the "best" modulation rate for data networks such as 802.11a/g. While accurate rate estimation yields better rate-selection decisions and increased throughput, those methods must still choose between a handful of modulation rates. Each modulation rate is effective in a range of actual signal-to-noise ratios (SNRs) but the limited number of practical rates means that transmitters are often forced to "step down" to a lower data rate despite having a higher SNR than the minimum required for that lower rate. In this paper we describe, evaluate and implement a practical multiuser communication scheme that exploits these discrete "steps" in modulation rates to transmit two packets in the time normally needed to transmit a single packet, increasing aggregate throughput precisely when it is most needed - when the network is busy and suffers from rate unfairness. Because the method transmits a group of packets simultaneously, we call this scheme Group Rate Transmission with Intertwined Symbols, or GRaTIS. In addition to up to 120% improvement in network throughput achieved by GRaTIS, the technique is backward compatible with 802.11 and doesn't require complex DSP algorithms as required by competing methods. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.24 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.22 Unattended Wireless Sensor Networks (UWSNs) are characterized by long periods of disconnected operation and fixed or irregular intervals between sink visits. The absence of an online trusted third party implies that existing WSN trust management schemes are not applicable to UWSNs. In this paper, we propose a trust management scheme for UWSNs to provide efficient and robust trust data storage and trust generation. For trust data storage, we employ a geographic hash table to identify storage nodes and to significantly decrease storage cost. We use subjective logic based consensus techniques to mitigate trust fluctuations caused by environmental factors. We exploit a set of trust similarity functions to detect trust outliers and to sustain trust pollution attacks. We demonstrate, through extensive analysis and simulations, that the proposed scheme is efficient, robust and scalable. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.22 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.16 In this paper, we give a global perspective of multicast capacity and delay analysis in Mobile Ad-hoc Networks (MANETs). Specifically, we consider four node mobility models: (1) two-dimensional i.i.d. mobility, (2) two-dimensional hybrid random walk, (3) one-dimensional i.i.d. mobility, and (4) one-dimensional hybrid random walk. Two mobility time-scales are included in this paper: (i) Fast mobility where node mobility is at the same time-scale as data transmissions; (ii) Slow mobility where node mobility is assumed to occur at a much slower time-scale than data transmissions. Given a delay constraint $D$, we first characterize the optimal multicast capacity for each of the eight types of mobility models, and then we develop a scheme that can achieve a capacity-delay tradeoff close to the upper bound up to a logarithmic factor. I http://doi.ieeecomputersociety.org/10.1109/TMC.2013.16 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.7 We propose two novel energy-aware routing algorithms for wireless ad hoc networks, called Reliable Minimum Energy Cost Routing (RMECR) and Reliable Minimum Energy Routing (RMER). RMECR addresses three important requirements of ad hoc networks: energy-efficiency, reliability, and prolonging network lifetime. It considers the energy consumption and the remaining battery energy of nodes as well as quality of links to find energy-efficient and reliable routes that increase the operational lifetime of the network. RMER, on the other hand, is an energy-efficient routing algorithm which finds routes minimizing the total energy required for end-to-end packet traversal. RMER and RMECR are proposed for networks in which either hop-by-hop or end-to-end retransmissions ensure reliability. Simulation studies show that RMECR is able to find energy-efficient and reliable routes similar to RMER, while also extending the operational lifetime of the network. This makes RMECR an elegant solution to increase energy-efficiency, reliability, and lifetime of wireless ad hoc networks. In the design of RMECR, we consider minute details such as energy consumed by processing elements of transceivers, limited number of retransmissions allowed per packet, packet sizes and, the impact of acknowledgment packets. This adds to the novelty of this work compared to the existing studies. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.7 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.13 Time synchronization plays a critical role in distributed network systems. In this paper, we investigate the time synchronization problem in the context of underwater sensor networks (UWSNs). Although many time synchronization protocols have been proposed for terrestrial wireless sensor networks, none of them can be directly applied to UWSNs. This is because most of these protocols do not consider long propagation delays and sensor node mobility, which are important attributes in UWSNs. In addition, UWSNs usually have high requirements in energy efficiency. To solve these new challenges, innovative time synchronization solutions are demanded. In this paper, we propose a pairwise, cross-layer, time synchronization scheme for mobile underwater sensor networks, called DA-Sync. The scheme proposes a frame work to estimate the doppler shift caused by mobility more precisely through accounting the impact of the skew. To refine the relative velocity estimation and consequently to enhance the synchronization accuracy, the Kalman filter is employed. Further, the clock skew and offset are calibrated by two runs of linear regression. Simulation results show that DA-Sync outperforms existing synchronization schemes in both accuracy and energy efficiency. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.13 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.8 Is it possible to migrate TCP/IP flows between different networks on modern mobile devices without infrastructure support or protocol changes? To answer this question, we make three research contributions. (i) We report a comprehensive characterization of IP traffic on 27 iPhone 3GS users for three months. (ii) Driven by these findings, we devise two simple, effective, and easily deployable system mechanisms to support seamless flow migration without network support, and extensively evaluate their effectiveness using our field collected traces of real-life usage. Wait-n-Migrate leverages the fact that most flows are short lived. It establishes new flows on newly available networks but allows pre-existing flows on the old network to terminate naturally. Resumption Agent takes advantage of the resumption functionality of modern protocols to securely resume flows without application intervention. Combined, they provide an unprecedented opportunity to immediately deploy policies that leverage multiple networks to improve the performance, efficiency, and connectivity of mobile devices. (iii) We report an iPhone based implementation of these system mechanisms and demonstrate their overhead to be negligible. Furthermore, we employ a sample switching policy, AutoSwitch, to demonstrate their performance. Through traces and field measurements, we show that AutoSwitch reduces user disruptions by an order of magnitude. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.8 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.257 We address the problem of identifying and isolating misbehaving nodes that refuse to forward packets in multi-hop ad hoc networks. We develop a comprehensive system called Audit-based Misbehavior Detection (AMD) that effectively and efficiently isolates both continuous and selective packet droppers. The AMD system integrates reputation management, trustworthy route discovery, and identification of misbehaving nodes based on behavioral audits. Compared to previous methods, AMD evaluates node behavior on a per-packet basis, without employing energy-expensive overhearing techniques or intensive acknowledgment schemes. Moreover, AMD can detect selective dropping attacks even if end-to-end traffic is encrypted and can be applied to multi-channel networks or networks consisting of nodes with directional antennas. We show via simulations that AMD successfully avoids misbehaving nodes, even when a large portion of the network refuses to forward packets. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.257 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.254 This paper considers random access protocols with multi-packet reception (MPR), which include both slotted-Aloha and slotted $\tau$-persistent CSMA protocols. For both protocols, each node makes a transmission attempt in a slot with a given probability. The goals of this paper are to derive the optimal transmission probability maximizing the system throughput for both protocols and to develop a simple random access protocol with MPR which achieves the system throughput close to the maximum value. To this end, we first obtain the optimal transmission probability of a node in slotted-Aloha protocol. The result provides a useful guideline to help us develop a simple distributed algorithm for estimating the number of active nodes. Then we obtain the optimal transmission probability in $\tau$-persistent CSMA protocol. An in-depth study on the relation between the optimal transmission probabilities in both protocols shows that under certain conditions the optimal transmission probability in slotted-Aloha protocol is a good approximation for $\tau$-persistent CSMA protocol. Based on this result, we propose a simple $\tau$-persistent CSMA protocol with MPR which dynamically adjusts the transmission probability $\tau$ depending on the estimated number of active nodes and thus can achieve the system throughput close to the maximum value. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.254 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.251 Wireless mesh networks in general, and WiFi mesh networks in particular, offer a cost-effective option to provide broadband connectivity in sparse regions. Effective support for real-time as well as high throughput applications requires a TDMA-based approach. However, multi-hop TDMA implementations in wireless have been few and far-between, and for good reasons. These present significant issues in terms of time synchronization, TDMA schedule dissemination, multi-channel support, routing integration, spatial reuse, etc. And achieving these efficiently, in the face of wireless channel losses presents a formidable challenge. In this work, we present an implementation of LiT MAC, a full-fledged multi-hop TDMA MAC, on commodity WiFi platforms. We undertake extensive evaluations using microbenchmarks as well as application level performance, using outdoor as well as indoor testbeds. We also present an integration of LiT MAC with various routing metrics, and a routing stability study of recently proposed routing metrics (ROMA, SLIQ). Our results show that we can achieve μs granularity time synchronization across several hops, and TDMA slot size as small as 2ms. These imply low control overheads. Experiments over several days, on our 9-node outdoor testbed shows that LiT MAC’s soft-state based approach is effective in robust operation even in the presence of significant external interference. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.251 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.238 This paper presents a fully functional and highly portable mini Unmanned Aerial Vehicle (UAV) system, HAWK, for conducting aerial localization. HAWK is a programmable mini helicopter - Draganflyer X6 - armed with a wireless sniffer - Nokia N900. We developed custom PI-Control laws to implement a robust waypoint algorithm for the mini helicopter to fly a planned route. A Moore space filling curve is designed as a flight route for HAWK to survey a specific area. A set of theorems were derived to calculate the minimum Moore curve level for sensing all targets in the area with minimum flight distance. With such a flight strategy, we can confine the location of a target of interest to a small hot area. We can recursively apply the Moore curve based flight route to the hot area for a fine-grained localization of a target of interest. We have conducted extensive experiments to validate the feasibility of HAWK and our theory. A demo of HAWK in autonomous fly is available at http://www.youtube.com/watch?v=ju86xnHbEq0. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.238 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.245 We study delay efficient data aggregation scheduling in wireless sensor networks subject to Signal to Interference-Plus-Noise Ratio (SINR) constraints. We construct a routing tree and propose two scheduling algorithms that can generate collision-free node schedules for data aggregation. We prove that the delay of each algorithm is upper-bounded by $O(R+\Delta)$ time-slots, where $R$ and $\Delta$ are the graph radius and the maximum node degree of a reduced communication graph for the original network respectively; the proposed algorithms are asymptotically optimum on delay for random wireless sensor networks. We evaluate the performances of the proposed algorithms on TOSSIM of TinyOS 2.0.2, the simulation results corroborate our theoretical analysis. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.245 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.242 The goal of 3GPP Long Term Evolution/System Architecture Evolution (LTE/SAE) is to move mobile cellular wireless technology into its fourth generation. One of the unique challenges of fourth-generation technology is how to close a security gap through which a single compromised or malicious device can jeopardize an entire mobile network because of the open nature of these networks. To meet this challenge, handover key management in the 3GPP LTE/SAE has been designed to revoke any compromised key(s) and as a consequence isolate corrupted network devices. This paper, however, identifies and details the vulnerability of this handover key management to what are called desynchronization attacks; such attacks jeopardize secure communication between users and mobile networks. Although periodic updates of the root key are an integral part of handover key management, our work here emphasizes how essential these updates are to minimizing the effect of desynchronization attacks that, as of now, cannot be effectively prevented. Our main contribution, however, is to explore how network operators can determine for themselves an optimal interval for updates that minimizes the signaling load they impose while protecting the security of user traffic. Our analytical and simulation studies demonstrate the impact of the key update interval on such performance criteria as network topology and user mobility. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.242 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.236 We study delay efficient data aggregation scheduling in wireless sensor networks subject to Signal to Interference-Plus-Noise Ratio (SINR) constraints. We construct a routing tree and propose two scheduling algorithms that can generate collision-free node schedules for data aggregation. We prove that the delay of each algorithm is upper-bounded by $O(R+\Delta)$ time-slots, where $R$ and $\Delta$ are the graph radius and the maximum node degree of a reduced communication graph for the original network respectively; the proposed algorithms are asymptotically optimum on delay for random wireless sensor networks. We evaluate the performances of the proposed algorithms on TOSSIM of TinyOS 2.0.2, the simulation results corroborate our theoretical analysis. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.236 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.206 Radio frequency (RF) sensing networks are a class of wireless sensor networks (WSNs) which use RF signals to accomplish tasks such as passive device-free localization and tracking. The algorithms used for these tasks usually require access to measurements of baseline received signal strength (RSS) on each link. However, it is often impossible to collect this calibration data (measurements collected during an offline calibration period when the region of interest is empty of targets). We propose adapting background subtraction methods from the field of computer vision to estimate baseline RSS values from measurements taken while the system is online and obstructions may be present. This is done by forming an analogy between the intensity of a background pixel in an image and the baseline RSS value of a WSN link and then translating the concepts of temporal similarity, spatial similarity and spatial ergodicity which underlie specific background subtraction algorithms to WSNs. Using experimental data, we show that these techniques are capable of estimating baseline RSS values with enough accuracy that RF tomographic tracking can be carried out in a variety of different environments without the need for a calibration period. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.206 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.232 The security of mobile devices such as cellular phones and smartphones has gained extensive attention due to their increasing usage in people's daily life. The problem is challenging as the computing environments of these devices have become more open and general-purpose while at the same time they have the constraints of performance and user experience. We propose and implement SEIP, a simple and efficient but yet effective solution for the integrity protection of real-world cellular phone platforms, which is motivated by the disadvantages of applying traditional integrity models on these performance and user experience constrained devices. The major security objective of SEIP is to protect trusted services and resources (e.g., those belonging to cellular service providers and device manufacturers) from third party code. We propose a set of simple integrity protection rules based upon open mobile operating system environments and application behaviors. Our approach significantly simplifies policy specifications while still achieves a high assurance of platform integrity. SEIP is deployed within a commercially available Linux-based smartphone and demonstrates that it can effectively prevent certain malware. The security policy of our implementation is less than 20kB, and a performance study shows that it is lightweight. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.232 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.223 In this paper, we investigate the Frequency Domain Packet Scheduling (FDPS) problem for 3GPP Long Term Evolution (LTE) UpLink (UL). Instead of studying a specific scheduling policy, we provide a unified approach to tackle this issue. First we formalize a general LTE UL FDPS problem which is suitable for various scheduling policies. Then we prove that the problem is MAX SNP-hard, which implies that approximation algorithms with constant approximation ratios are the best that we can hope for. Therefore we design two approximation algorithms, both of which have polynomial runtime. The first algorithm is based on a simple greedy method. The second one is based on the local ratio technique and it can approximately solve the LTE UL FDPS problem with a approximation ratio of 2. To further analyze the stability of the second 2-approximation algorithm, the general problem is specified to incorporate the queue length and channel quality information. We utilize the Lyapunov drift to prove it is stable for any ($/math$)-admissible LTE UL systems.The simulation results indicate good performance of the L-R scheduler. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.223 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.210 We present a new resource allocation scheme for cell-edge active users to achieve improved performance in terms of a higher system capacity and better quality-of-service (QoS) guarantee of the users, where we utilize the 2-dimensional resource allocation flexibility of orthogonal frequency division multiple access (OFDMA) networks. Here, the mobile stations (MSs) at the cell-edge can maintain parallel connections with more than one base station (BS) when it is in their coverage area. A MS, before handoff to a new BS, seeks to utilize additional resources from the other BSs if the BS through which its current session is egistered is not able to satisfy its requirements. The handoff procedure is termed as split handoff. In this study, first, we present the proposed shared resource allocation architecture and protocol functionalities in split handoff, and give a theoretical proof of concept of system capacity gain associated with the shared resource allocation approach. Then we provide a differentiated QoS provisioning approach that accounts for the MS speed, its channel quality, as well as the loads at different BSs. Via extensive simulations in Qualnet, the benefits of the proposed class-based split handoff approach is demonstrated. The results also indicate traffic load balancing property of the proposed scheme in heavy traffic conditions. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.210 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.208 Location privacy research has received wide attention in the past few years owing to the growing popularity of location-based applications, and the skepticism thereof on the collection of location information. A large section of this research is directed towards mechanisms based on location obfuscation enforced using cloaking regions. The primary motivation for this engagement comes from the relatively well researched area of database privacy. Researchers in this sibling domain have indicated multiple times that any notion of privacy is incomplete without explicit statements on the capabilities of an adversary. As a result, we have started to see some efforts to categorize the various forms of background knowledge that an adversary may possess in the context of location privacy. Along this line, we consider some preliminary forms of attacker knowledge, and explore what implication does a certain form of knowledge has on location privacy. Continuing on, we extend our insights to a form of adversarial knowledge related to the geographic uncertainty that the adversary has in correctly locating a user. We empirically demonstrate that the use of cloaking regions can adversely impact the preservation of privacy in the presence of such approximate location knowledge, and demonstrate how perturbation based mechanisms can instead provide a well-balanced trade-off between privacy and service accuracy. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.208 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.203 Mobile environments increasingly require distributed atomic transactions to support the growing diversity of financial, gaming, social networking and many other applications. The underlying mobile infrastructure is correspondingly evolving with increasingly diverse wired and wireless elements and also with increasing exposure to a variety of operational perturbations at the mobile elements and communication levels. Consequently, the challenge is not only in providing efficient non-blocking mobile commit (as a fundamental basis behind consistent mobile transactions) but to also provide efficient perturbation-resilient atomic commit in the heterogeneous mobile space. The contribution of this paper is in developing a perturbation-resilient mobile commit protocol that efficiently provides for and preserves strict atomicity for transactional applications. The protocol does not necessarily require access to the powerful communication/computation elements of the wired infrastructure during transaction execution. However, in case access to a wired network becomes possible, it then adapts to utilize this to (i) increase the resilience to network perturbations achieving higher commit rates, and (ii) reduce the wireless message overhead and the blocking of transaction participants leading to higher transactions throughput. In contrast, existing solutions are often tailored either for (a) infrastructure-based mobile environments, or (b) infrastructure-less ad-hoc networks. To our knowledge, there is no existing commit protocol that can adapt across diverse infrastructure communication modes. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.203 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.190 Radio Frequency (RF) tomography is the method of tracking targets using received signal-strength (RSS) measurements for RF transmissions between multiple sensor nodes. When the targets are near the line-of-sight path between two nodes, they are more likely to cause substantial attenuation or amplification of the RF signal. In this paper, we develop a measurement model for multi-target tracking using (RF) tomography in indoor environments and apply it successfully for tracking up to three targets. We compare several multi-target tracking algorithms and examine performance in the two scenarios when the number of targets is (i) known and constant; and (ii) unknown and time-varying. We demonstrate successful tracking for experimental data collected from sensor networks deployed in three different indoor environments posing different tracking challenges. For the case of a fixed number of targets, the best algorithm achieves a root mean squared error tracking accuracy of approximately 0.3m for a single target, 0.7m for two targets and 0.8m for three targets. Tracking using our proposed model is more accurate than tracking using previously proposed observation models; more importantly the model does not require the same degree of training. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.190 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.192 In this paper we present SpiderRadio, a software defined cognitive radio prototype for dynamic spectrum access networking. The medium access control (MAC) layer of SpiderRadio is implemented in software on top of commodity IEEE 802.11a/b/g hardware. However, the proposed architecture and implementation are applicable to other spectrum bands as well. We also present a dynamic spectrum sensing methodology for primary incumbent detection. The proposed method is based on observing the PHY errors, received signal strength and statistical model building. For coordination among radio nodes, synchronization and fast channel switching, we present new communication protocols, design extended management frame structure and modify the hardware abstraction layer. Several fundamental trade-offs (e.g., complexity vs. network performance) to be considered during a dynamic spectrum access radio network prototype implementation are also discussed in detail. To demonstrate the practical capabilities of the proposed SpiderRadio prototype, we also present various testbed experimental measurement results. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.192 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.186 Epidemic attack is a severe security problem in network-coding enabled wireless mesh networks (WMNs). Malicious nodes can easily launch such form of attack to create an epidemic spreading of polluted packets and deplete network resources The contribution of this work is to address such security problem. We allow the presence of "smart'' attackers, i.e., they can pretend to be legitimate nodes to probabilistically transmit valid packets to reduce the chance of being detected. We also address the case when attackers cooperatively inject polluted packets so the batch verification performed by the detector will not match most of the time. We employ the time-based checksum and batch verification to determine whether there are polluted packets, then propose a set of fully "distributed'' and "randomized'' detection algorithms so each legitimate node can identify malicious nodes within its neighbors and purge them for future communication. We provide formal analysis to quantify various measures of the algorithms, e.g., probability of false positive and probability of false negative, as well as the probability distribution of time needed to identify all malicious nodes. We provide a game-theoretic analysis to show the interaction and the convergence property of the detection process. Finally, simulation and system prototyping are carried out to show the efficiency of the detection algorithm. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.186 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.137 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, aiming to cause interference to the primary users 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 (BP). Firstly, 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. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.137 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.155 In this paper, we study the sum-rate maximization algorithms for downlink and uplink orthogonal frequency division multiple access (OFDMA) systems under proportional-rate constraint (PRC) and minimum-rate constraint. We develop a low-complexity weighted channel signal-to-noise ratio (w-SNR)-based ranking scheme for user selection on each subchannel in OFDMA combined with waterfilling (WF) power allocation. Both offline and online optimization algorithms are developed to optimize the SNR weight vector to maximize the sum rate while satisfying several constraints, such as PRC. The offline weight optimization technique relies on the analytical throughput results developed in this paper, and the online weight adaptation method tracks the user rates and meets the PRC using a sub-gradient search. Furthermore, we introduce a novel SNR operating region test to enhance the multiuser diversity gain and the sum rate. The proposed schemes have a low complexity which is linear to the numbers of users and subchannels. Simulation results verify the accuracy of the developed analytical rate and fairness formulas, and show that the proposed w-SNR schemes can achieve higher sum rates than several benchmark schemes which provide the PRC with either short-term or long-term fairness. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.155 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.173 Today, professional documents, created in applications such as PowerPoint and Word, can be shared using ubiquitous mobile terminals connected to the Internet. GoogleDocs and EasyMeet are good examples of such collaborative Web applications dedicated to professional documents. The static adaptation of professional documents has been studied extensively. Dynamic adaptation can be very useful and practical for interactive multimedia applications, because it allows the delivery of highly customized content to the end-user without the need to generate and store multiple transcoded versions. In this paper, we propose a dynamic framework that enables us to estimate transcoding parameters on the fly in order to generate near-optimal adapted content for each user. The framework is compared to current dynamic methods as well as to static adaptation solutions. We show that the proposed framework provides a better trade-off between quality and storage compared to other static and dynamic approaches. To quantify the quality of the adapted content, we introduce a measure of the quality of the experience based on its visual quality of the adapted content, as well as on the impact of its total delivery time. The framework has been tested on (but is not limited to) OpenOffice Impress presentations. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.173 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.171 Development of dynamic spectrum access and allocation techniques recently have made feasible the vision of cognitive radio systems. However, a fundamental question arises: Why would licensed primary users of a spectrum band allow secondary users to share the band and degrade performance for them? And how can we design incentive schemes to enable spectrum sharing using cooperative communication schemes? We consider a principal-agent framework, and propose a contracts-based approach. First, a single primary and a single secondary transmitter-receiver pair with a Gaussian interference channel between them are considered. The two users may contract to cooperate in doing successive-interference cancellation. Under full information, we give equilibrium contracts for various channel conditions. These equilibrium contracts yield Pareto-optimal rate allocations when physically possible. We then allow for time-sharing and observe that in equilibrium contracts there is no actual time-sharing. We show that the designed contracts can be made robust to deviation by either user post-contract. We also show how these can be extended to multiple secondary users. We show that under hidden information, when the primary user has a dominant role, neither user has an incentive to lie about their direct channel coefficients, or manipulate the cross channel measurements, and Pareto-optimal outcomes are achieved at equilibrium. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.171 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.140 Successive interference cancellation (SIC) is an effective way of multipacket reception to combat interference in wireless networks. We focus on link scheduling in wireless networks with SIC, and propose a layered protocol model and a layered physical model to characterize the impact of SIC. In both the interference models, we show that several existing scheduling schemes achieve the same order of approximation ratios, independent of whether or not SIC is available. Moreover, the capacity order in a network with SIC is the same as that without SIC. We then examine the impact of SIC from first principles. In both chain and cell topologies, SIC does improve the throughput with a gain between 20% and 100%. However, unless SIC is properly characterized, any scheduling scheme cannot effectively utilize the new transmission opportunities. The results indicate the challenge of designing an SIC-aware scheduling scheme, and suggest that the approximation ratio is insufficient to measure the scheduling performance when SIC is available. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.140 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.131 Co-channel links in a Wireless LAN are separated across orthogonal time slots to avoid interference. With increasing density of links, time-sharing the channel leads to severe capacity problems. In this paper, we identify a specific class of interference scenarios called asymmetric interference scenarios where the nature of interference is different at the receivers of the concurrent signals. We show that, with appropriate handling, asymmetric interference allows each receiver to decode its intended reception successfully. We represent the signal combination at the receiver as a function fc and propose a solution called Symbiotic Coding (SC) such that fc(E1(d1, d2),E2(d1, d2)) is equal to E1(d1, d2), where d1 and d2 are the intended and interfering data symbol sequences and E1 is the encoder at sender 1 and E2 at sender 2 respectively. SC thus enables successful simultaneous co-channel transmissions even if they result in a collision. The performance of SC scales with the number of interfering links achieving median throughput improvements of 30% and 86% over time sharing with two and three interfering links respectively. We address fundamental challenges in realizing SC including synchronization, coding algorithms, extensions to different modulations. We also implement SC on software defined radios and demonstrate its practical achievability. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.131 http://doi.ieeecomputersociety.org/10.1109/TMC.2012.128 In this paper, a unified analytical framework is established to study the stability, throughput and delay performance of homogeneous buffered IEEE 802.11 networks with Distributed Coordination Function (DCF). Two steady-state operating points are characterized using the limiting probability of successful transmission of Head-of-Line (HOL) packets p given that the network is in unsaturated or saturated conditions. The analysis shows that a buffered IEEE 802.11 DCF network operates at the desired stable point p=pL if it is unsaturated. pL does not vary with backoff parameters, and a stable throughput can be always achieved at pL. If the network becomes saturated, in contrast, it operates at the undesired stable point p=pA, and a stable throughput can be achieved at pA if and only if the backoff parameters are properly selected. The stable regions of the backoff factor q and the initial backoff window size W are derived, and it is shown that the stable regions are significantly enlarged with the request-to-send/clear-to-send (RTS/CTS) mechanism, indicating that networks in the RTS/CTS mode are much more robust. Nevertheless, the delay analysis further reveals that lower access delay is incurred in the basic access mode for unsaturated networks. If the network becomes saturated, the delay performance deteriorates regardless of which mode is chosen. http://doi.ieeecomputersociety.org/10.1109/TMC.2012.128 http://opac.ieeecomputersociety.org/opac?year=2013&volume=12&issue=07&acronym=tmc IEEE Transactions on Mobile Computing http://www.computer.org/portal/site/tmc/ http://doi.ieeecomputersociety.org/10.1109/TMC.2013.53 A novel method for a mobile phone centric observation of a user’s facing direction is presented. To estimate this direction, our proposed technique exploits the acceleration pattern that can be measured by a smartphone as the user is walking. For an accurate analysis of the acceleration pattern, the proposed approach benefits from a new trigonometric interpolation scheme. Our algorithm is independent of the initial orientation of the device and is adaptable to various wearing positions on a user’s body, which gives the user a larger degree of freedom. A detailed description of the algorithm, which has been customized for a trouser pocket is presented. In addition, complementary hints for adaptation of the algorithm to other wearing positions along with an example of chest pocket position are provided. We have evaluated a prototype implementation of our algorithm on a smartphone, through several field experiments. It has been observed that our algorithm outperforms the conventional GPS and PCA-based techniques in terms of accuracy, reliability and energy consumption. The results also show that our approach has been able to handle the sudden variations of the user’s direction. We have further incorporated our algorithm into a dead-reckoning application as an example of its real-world utility http://doi.ieeecomputersociety.org/10.1109/TMC.2013.53 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.52 When a spread-spectrum receiver in a network discovers that it is processing a jamming signal transmitted by a compromised node, its first response is to attempt to identify the compromised node. In this paper, an adaptive array is used to find the direction to the jamming source despite the presence of interference signals transmitted by both legitimate network nodes and external sources. Unlike other direction-finding algorithms, the desired-signal classification (DESIC) algorithm requires no information or special assumptions about the interference signals to effectively cancel them and find the desired direction. Simulation experiments show that the DESIC algorithm provides an excellent performance in many scenarios, even when the received signals cannot be resolved by the widely used MUSIC algorithm. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.52 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.49 In this paper, the problem of throughput optimization in decentralized wireless networks with spatial randomness under queue stability and packet loss constraints is investigated. Two key performance measures are analyzed, namely the effective link throughput and the network spatial throughput. Specifically, the combination of medium access probability, coding rate, and maximum number of retransmissions that maximize each throughput metric is analytically derived for a class of Poisson networks, in which packets arrive at the transmitters following a geometrical distribution. Necessary conditions so that the effective link throughput and the network spatial throughput are stably achievable under bounded packet loss are determined, as well as upper bounds for both cases by solving the unconstrained optimization problem. Our results show in which system configuration stable achievable throughputs can be obtained as a function of the network density and the arrival rate. They also evince conditions for which the per-link throughput-maximizing operating points coincide or not with the aggregate network throughput-maximizing operating regime. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.49 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.48 The paper considers a hybrid wireless sensor network with static and mobile sensors, where each static sensor can detect only one attribute of event while a mobile sensor can analyze multiple attributes of events. Static sensors monitor the environment and report where events appear. Mobile sensors then move to these event locations to conduct more in-depth analysis. A critical issue is how to schedule the traveling paths of mobile sensors so as to extend their lifetime. We formulate this issue as a multi-round multi-attribute sensor dispatch problem and prove it to be NP-complete. Then, we develop a two-phase dispatch heuristic that adopts the concepts of Pareto optimality and spanning-tree construction. Our heuristic allows arbitrary numbers of mobile sensors and event locations and tries to reduce and balance the energy consumption of mobile sensors in each round. Through simulations, we verify the effectiveness of our heuristic. The paper contributes in defining a new sensor dispatch problem and developing an energy-efficient solution to the problem. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.48 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.45 Vehicular ad hoc networks (VANETs) are an emerging wireless network technology used to improve road safety. Commercial services will play an important role in drawing customers to VANETs. Therefore, service-oriented vehicular networks offer an effective and promising approach. To meet the diverse requirements of different users, fine-grained access control is inevitable. This paper aims to address security, privacy and billing issues in service- oriented vehicular networks. Taking advantage of a portable electronic currency, the proposed scheme mitigates the long authentication delay of centralized AAA architecture. A variant attribute-based encryption ensures fine-grained access control and secure billing. Only vehicles possessing the proper service attributes and valid electronic currency are authorized to access the requested service file. The security properties of entity authentication, session key agreement, privacy, fraud electronic currency prevention, double-spending prevention, and nonrepudiated billing are achieved. Extensive analysis and simulations demonstrate that our scheme is a viable candidate to replace a centralized AAA architecture with a decentralized method for better scalability in service-oriented vehicular networks. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.45 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.42 For real-time applications running over handheld mobile terminals (MT) in heterogeneous environments, efficient vertical handover (VH) algorithms are required in maintaining a seamless connectivity and an acceptable level of quality. While received signal strength based methods have dominated this class of algorithms, we propose a thorough system analysis framework and perform rigorous analysis for packet-loss based algorithms for an interworking environment comprising the cellular network and the Wireless Local Area Network (WLAN). The basic VH algorithm analyzed here is based on the moving average of the packet loss rate and we employed both a simple packet loss and Gilbert packet loss pattern. Modifications to the analytical framework have been made by employing block-wise packet loss patterns in order to keep the computational burden within practical limits. Performance trends of call drop probabilities and WLAN usage efficiency are shown with varying system and handover thresholds, and analytical results are compared to that obtained from Monte Carlo simulations. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.42 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.41 The increased demand for wireless connectivity emphasizes the necessity of efficient wireless communication as resources such as the available spectrum and energy reserves become limiting factors for network proliferation. Recent advancements in softwaredefined radio enable high flexibility of the physical layer allowing fine grained transmission adjustments. Although communication efficiency can greatly benefit from physical layer flexibility, modern wireless protocols can neither handle these new opportunities nor allocate resources according to the overlying application needs. In this work we develop WhiteRate, a method for physical layer parameter adaptation that efficiently utilizes available energy and spectrum resources, while maintaining the desired quality of communication. Our solution adjusts the modulation and coding scheme, and channel width to achieve a communication profile that matches application requirements. We implement WhiteRate in GNUradio and evaluate it in both indoor and outdoor environments. We demonstrate improvements on two important fronts: spectrum utilization and energy efficiency. Moreover, we show that by using WhiteRate, both benefits can be achieved simultaneously. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.41 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.37 While the static indoor geo-location of mobile terminals (MT) has been extensively studied in the last decade, the prediction of the trajectory of a MT still is the major problem for designing mobile location systems (TSs). It is important to augment mobile geo-location architectures with a prediction dimension to deal with distortions caused by obstacles, and ultimately produce a more accurate positioning system. Different prediction approaches have been proposed in the literature, the most common is based on prediction filters such as linear predictors, Kalman filters, and particle filters. In this paper, we take the prediction one step further by using digital fractional integration (DFI) to predict the actual trajectory of MTs. We evaluate the performance of our proposed DFI prediction in two indoor trajectory scenarios inspired from typical users mobility patterns in typical indoor conditions. To illustrate the efficiency of the proposed method in particularly noisy environments, we consider two other MT trajectory scenarios, namely spiral and sinusoidal trajectories. Experimental results show a significant performance improvement over most common predictors in the relevant literature, particularly in noisy cases. Extensive study of short-archive principle using 5, 10, and 25 previous estimated positions, showed the benefit of using DFI operator with only the most recent locations of a MT. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.37 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.35 New communication technologies integrated into modern vehicles offer an opportunity for better assistance to people injured in traffic accidents. Recent studies show how communication capabilities should be supported by artificial intelligence systems capable of automating many of the decisions to be taken by emergency services, thereby adapting the rescue resources to the severity of the accident and reducing assistance time. To improve the overall rescue process, a fast and accurate estimation of the severity of the accident represent a key point to help the emergency services to better estimate the required resources. This paper proposes a novel intelligent system which is able to automatically detect road accidents, notify them through vehicular networks, and estimate their severity based on the concept of data mining and knowledge inference. Results show that a complete Knowledge Discovery in Databases (KDD) process, with an adequate selection of relevant features, allows generating estimation models able to predict the severity of new accidents. We develop a prototype of our system based on off-the-shelf devices, and validate it at the Applus+ IDIADA Automotive Research Corporation facilities, showing that our system can notably reduce the time needed to alert and deploy the emergency services after an accident takes place. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.35 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.30 Data collection is a common operation of Wireless Sensor Networks (WSNs), of which the performance can be measured by its achievable network capacity. Most existing works studying the network capacity issues are based on the unpractical model called deterministic network model. In this paper, a more reasonable model, probabilistic network model, is considered. For snapshot data collection, we propose a novel Cell-based Path Scheduling (CPS) algorithm which achieves the capacity of &#x03a9(\frac{1}{5\ω\ln n}\cdot W)$ in the sense of the worst case and the order-optimal capacity in the sense of expectation, where n is the number of sensor nodes, ω is a constant, and W is the data transmission rate. For continuous data collection, we propose a Zone-based Pipeline Scheduling (ZPS) algorithm. ZPS significantly speeds up a continuous data collection process by forming a data transmission pipeline, and achieves a capacity gain of $\frac{N \sqrt{n}}{\sqrt{\log n} \ln n}$ or $\frac{n}{\log n \ln n}$ times better than the optimal capacity of the snapshot data collection scenario in order in the sense of the worst case, where N is the number of snapshots in a continuous data collection task. The simulation results also validate that the proposed algorithms significantly improve network capacity compared with the existing works. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.30 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.27 The surge in vehicular network research has led, over the last few years, to the proposal of countless network solutions specifically designed for vehicular environments. A vast majority of such solutions has been evaluated by means of simulation, since experimental and analytical approaches are often impractical and intractable, respectively. The reliability of the simulative evaluation is thus paramount to the performance analysis of vehicular networks, and the first distinctive feature that has to be properly accounted for is the mobility of vehicles, i.e., network nodes. Notwithstanding the improvements that vehicular mobility modeling has undergone over the last decade, no vehicular mobility dataset is publicly available today that captures both the macroscopic and microscopic dynamics of road traffic over a large urban region. In this paper, we present a realistic synthetic dataset, covering 24 hours of car traffic in a 400-km2 region around the city of Köln, in Germany. We describe the generation process and outline how the dataset improves the traces currently employed for the simulative evaluation of vehicular networks. We also show the potential impact that such a comprehensive mobility dataset has on the network protocol performance analysis, demonstrating how incomplete representa- tions of vehicular mobility may result in over-optimistic network connectivity and protocol performance. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.27 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.28 We consider the detection of activities from non-cooperating individuals with features obtained on the Radio Frequency channel. Since environmental changes impact the transmission channel between devices, the detection of this alteration can be used to classify environmental situations. We identify relevant features to detect activities of non-actively transmitting subjects. In particular, we distinguish with high accuracy an empty environment or a walking, lying, crawling or standing person, in case-studies of an active, device-free activity recognition system with software defined radios. We distinguish between two cases in which the transmitter is either under the control of the system or ambient. For activity detection the application of one-stage and two-stage classifiers is considered. Apart from the discrimination of the above activities, we can show that a detected activity can also be localised simultaneously within an area of less than 1 meter radius. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.28 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.25 The performance of Delay-Tolerant Networks (DTNs) is governed by the interplay of diverse factors such as bundle fragmentation, scheduling, and buffer spacing. However, a comprehensive study of DTN routing performance taking into account such realistic limitations seldom performed in the literature. In this paper, we look at Queueing Petri Nets (QPNs) as a candidate framework for modeling the performance of DTN routing, taking into account all the realistic factors impacting performance. We envisage a three-fold validation scheme to assert the veracity of our model, via comparison of results obtained from simulations of the QPN vis-a-vis those obtained from direct simulation of the underlying DTN and experimental results obtained from a testbed of Android devices that employ a mobility emulation scheme. We also solve the QPN, by deriving the underlying reachability graph and constructing an equivalent stochastic jump process. We identify the stochastic process to be a Semi-Markov Process (SMP) and hence arrive at a closed form expression for the end-to-end delivery latency by computing the hitting time of the SMP. We find that the model accurately captures the behavior of a DTN in numerous realistic scenarios, showing the efficacy of QPNs as a suitable analytical framework for evaluating DTNs. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.25 http://doi.ieeecomputersociety.org/10.1109/TMC.2013.23 Passive monitoring utilizing distributed wireless sniffers is an effective technique to monitor activities in wireless infrastructure networks for fault diagnosis, resource management and critical path analysis. In this paper, we introduce a quality of monitoring (QoM) metric defined by the expected number of active users monitored, and investigate the problem of maximizing QoM by judiciously assigning sniffers to channels based on the knowledge of user activities in a multi-channel wireless network. Two types of capture models are considered. The user-centric model assumes frame-level capturing capability of sniffers such that the activities of different users can be distinguished while the sniffer-centric model only utilizes the binary channel information (active or not) at a sniffer. For the user-centric model, we show that the implied optimization problem is NP-hard, but a constant approximation ratio can be attained via polynomial complexity algorithms. For the sniffer-centric model, we devise stochastic inference schemes to transform the problem into the user-centric domain, where we are able to apply our polynomial approximation algorithms. The effectiveness of our proposed schemes and algorithms is further evaluated using both synthetic data as well as real-world traces from an operational WLAN. http://doi.ieeecomputersociety.org/10.1109/TMC.2013.23