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Opportunistic Spectrum Allocation for Interference Mitigation Amongst Coexisting Wireless Body Area Networks

Wireless Body Area Networks (WBANs) are seen as the enabling technology for developing new... (more)

Average Counting via Approximate Histograms

We propose a new algorithm for the classical averaging problem for distributed wireless sensors networks. This subject has been studied extensively and there are many clever algorithms in the literature. These algorithms are based on the idea of local exchange of information. They behave well in dense networks (e.g., in networks whose connections... (more)

Networking Wireless Energy in Embedded Networks

Wireless energy transfer has recently emerged as a promising alternative to realize the vision of perpetual embedded sensing. However, this technology transforms the notion of energy from merely a node’s local commodity to, similarly to data, a deployment-wide shareable resource. The challenges of managing a shareable energy resource are... (more)

Energy-Harvesting Wireless Sensor Networks (EH-WSNs): A Review

Wireless Sensor Networks (WSNs) are crucial in supporting continuous environmental monitoring, where sensor nodes are deployed and must remain... (more)

Harmonium: Ultra Wideband Pulse Generation with Bandstitched Recovery for Fast, Accurate, and Robust Indoor Localization

We introduce Harmonium, a novel ultra wideband (UWB) RF localization architecture that achieves decimeter-scale accuracy indoors. Harmonium strikes a balance between tag simplicity and processing complexity to provide fast and accurate indoor location estimates. Harmonium uses only commodity components and consists of a small, inexpensive,... (more)

Exploiting Electrical Grid for Accurate and Secure Clock Synchronization

Desynchronized clocks among network nodes in critical infrastructures can degrade system performance and even lead to safety incidents. Clock... (more)

Natural Timestamps in Powerline Electromagnetic Radiation

The continuous fluctuation of electric network frequency (ENF) presents a fingerprint indicative of time, which we call natural timestamp. This... (more)

Non-Bayesian Social Learning with Observation Reuse and Soft Switching

We propose a non-Bayesian social learning update rule for agents in a network, which minimizes the sum of the Kullback-Leibler divergence between the... (more)

Differentiating Clear Channel Assessment Using Transmit Power Variation

Clear Channel Assessment (CCA) is a core element of Wireless Sensor Network (WSN) Medium Access Control (MAC) protocols which is used on the... (more)

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About TOSN

TOSN publishes original research papers (approximately 30-40 printed pages each in ACM Transaction style) and tutorial and survey papers (approximately 30-50 printed pages each). We also accept short technical notes that focus on industrial technologies and practical experience.
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Forthcoming Articles
Optimal Rate Control for Energy Harvesting Systems with Random Data and Energy Arrivals

Due to the random and dynamic energy harvesting process, it is challenging to conduct optimal rate control in Energy Harvesting Communication Systems (EHCS). Existing works mainly focus on two cases: 1) The traffic load is infinite (as long as there is energy, there is data to transmit), where the objective is to optimize the rate control policy subject to the dynamic energy arrivals, thus maximizing the average system throughput; 2) The traffic load is finite, where the objective is to optimize the rate control policy, thus minimizing the time by which all the packets are delivered. In this work, we focus on the optimal rate control of EHCS from another important and practical perspective, where the data and energy arrivals are both random. Given any deadline of T, our goal is to maximize the total throughput in [0; T]. Specifically, two scenarios are considered: 1) Energy is ready before the transmission; 2) Energy arrives randomly during the transmission. In both scenarios, we assume that the data arrive randomly during the transmission. For the first scenario, we develop a novel Stepwise Searching Algorithm (SSA) based on the cumulative curve methodology, which is shown to achieve the optimal solution and the

DISH: DIstributed SHuffling against selective jamming attack in IEEE 802.15.4e TSCH networks

The MAC standard amendment IEEE 802.15.4e is designed to meet the requirements of industrial and critical applications. In particular, the Time Slotted Channel Hopping (TSCH) mode divides time into periodic, equally-sized, slotframes composed of transmission timeslots. Then, it combines time slotted access with multi-channel and channel hopping capabilities, providing large network capacity, high reliability and predictable latency, while ensuring energy efficiency. Since every network node considers the same timeslots at each sloframe and selects physical channels according to a periodic function, TSCH produces a steady channel utilization pattern. This can be exploited by a selective jammer to entirely thwart communications of a victim node, in a way which is stealthy, effective and extremely energy efficient. This paper shows how a selective jamming attack can be successfully performed even though TSCH uses the IEEE 802.15.4e security services. Furthermore, we propose DISH, a countermeasure which randomly permutes the timeslot and channel utilization patterns at every slotframe in a consistent and completely distributed way, without requiring any additional message exchange. We have implemented DISH for the Contiki OS and tested its effectiveness on TelosB sensor nodes. Quantitative analysis for different network configurations shows that DISH effectively contrasts selective jamming with negligible performance penalty.

CapNet: Exploiting Wireless Sensor Networks for Data Center Power Capping

As the scale and density of data centers continue to grow, cost-effective data center management (DCM) is becoming a significant challenge for enterprises hosting large scale online and cloud services. The servers need to be monitored, and the scale of operations mandates an automated management with high reliability and real-time performance. Existing wired networking solutions for DCM come with high cost. In this paper, we propose a wireless sensor network as a cost-effective networking solution for DCM while satisfying the reliability and latency performance requirements of DCM. We have developed CapNet, a real-time wireless sensor network for power capping, a time-critical DCM function for power management in a cluster of servers. CapNet employs an efficient event-driven protocol that triggers data collection only upon the detection of a potential power capping event. We deploy and evaluate CapNet in a data center. Using server power traces, our experimental results on a cluster of 480 servers inside the data center show that CapNet can meet the real-time requirements of power capping. CapNet demonstrates the feasibility and efficacy of wireless sensor networks for time-critical DCM applications.

Resource-efficient and Automated Image-based Indoor Localization

Image-based indoor localization has aroused much interest recently, because it requires no infrastructure support. Previous approaches on image-based localization, due to their computation and storage requirements, often process queries at server. This does not scale well, incurs round-trip delay, and requires constant network connectivity. Many also require users to manually confirm the shortlisted matched landmarks, which is inconvenient, slow, and prone to selection error. To overcome these limitations, we propose HAIL a highly automated (in terms of image selection or confirmation) image-based localization algorithm distributed in mobile devices. HAIL achieves resource efficiency (in terms of storage and processing) by keeping only those distinguishing visual features for each landmark, and employing a data structure to search for the features efficiently. It further utilizes the motion sensors and map constraint to enhance the localization accuracy without user operation. We have implemented HAIL on Android platform and conducted extensive experiments in a food plaza and a premium shopping mall. Our results show that it achieves much higher localization accuracy (reducing the localization error by more than 20%) and computation efficiency (by more than 40% in time) as compared with the state-of-the-art approaches.

Known and Unknown Facts of LoRa: Experiences from a Large Scale Measurement Study

LoRa is one of the LPWAN technologies designed for IoT has gained significant momentum amongst both industrial and research communities. Patented by Semtech, LoRa makes use of chirp spread spectrum modulation to deliver data. LoRa promises long battery life, far-reaching communication distances, and a high node density at the cost of data rate. In this paper we conduct a series of experiments to verify the claims made by Semtech on LoRa technology. Our results show that LoRa is capable of communicating over 10 km under line-of-sight environment however, under non-line-of-sight environments, LoRa performance is severely affected by obstructions such as buildings and vegetations. Moreover, the promised of prolonged battery life requires extreme tuning of parameters. Lastly, a LoRa gateway supports up to 6,000 nodes with PRR requirement of >70%. This study also explores the relationship between LoRa transmission parameters and proposes an algorithm to determine optimal settings in terms of coverage and power consumption under non-line-of-sight environment. It further investigates the impact of LoRaWAN on energy consumption and network capacity along with implementation of LoRa medium access mechanism and possible gains brought forth by implementing such a mechanism.

Privacy-Preserving Truth Discovery in Crowd Sensing Systems

The recent proliferation of human-carried mobile devices has given rise to the crowd sensing systems. However, the sensory data provided by individual participants are usually not reliable. To identify truthful values from the crowd sensing data, the topic of truth discovery, whose goal is to estimate user quality and infer truths through quality-aware data aggregation, has drawn significant attention. Though able to improve aggregation accuracy, existing truth discovery approaches fail to address the privacy concerns of individual users. In this paper, we propose a novel privacy-preserving truth discovery (PPTD) framework for crowd sensing systems, which can achieve the protection of not only users' sensory data but also their reliability scores derived by the truth discovery approaches. The key idea of the proposed framework is to perform weighted aggregation on users' encrypted data using homomorphic cryptosystem. In order to deal with large-scale data, we also propose to parallelize PPTD with MapReduce framework. Additionally, we design an incremental PPTD scheme for the scenarios where the crowd sensing data are collected in a streaming manner. Through extensive experiments on not only synthetic data but also real-world crowd sensing systems, we justify the guarantee of strong privacy and high accuracy of our proposed framework.

W3W: Energy Management of Hybrid Energy Supplied Sensors for Internet of Things

The usage of hybrid energy supplied sensors in the Internet of Things has enabled longer lifetime of sensors and expanded scope of applications. These sensors can combine advantages of environmental energy harvesting techniques and wireless energy harvesting techniques. However, how to coordinate them is still a challenge and has not been studied extensively. In this paper, we present a system based on mobile crowd wireless charging to manage energy of hybrid energy supplied sensors. When environmental energy is insufficient, the system will utilize smart devices carried by mobile users as chargers to provide wireless energy. We construct and study a W3W problem in the system: \underline{w}hen to leverage mobile crowd wireless charging to support rechargeable sensors, \underline{w}here to perform wireless energy transfer, and \underline{w}hom to allocate and incentivize as chargers to maximize useful energy value over all sensors subject to a budget. In order to control the actual quality of wireless energy charging, we propose a design principle named task completion trustfulness. We consider offline and online conditions and design corresponding algorithms with incentive allocations. Extensive simulations are conducted to demonstrate the effectiveness of our algorithms, which also validates our theoretical results.

Introduction to the Special Issue on BuildSys'17

ECT: Exploiting Cross-Technology Transmission for Reducing Packet Delivery Delay in IoT Networks

Recent advances in cross-technology communication have significantly improved the spectrum efficiency in the same ISM band among heterogeneous wireless devices (e.g., WiFi and ZigBee). However, further performance improvement in the whole network is hampered because the cross-technology network layer is missing. As the first cross-technology network layer design, our work, named ECT, opens a promising direction for significantly reducing the packet delivery delay via collaborative and concurrent cross-technology communication between WiFi and ZigBee devices. Specifically, ECT can dynamically change the nodes priorities and reduce the delivery delay from high priority nodes under unreliable links. The key idea of ECT is to leverage the concurrent transmission of important data and raw data from ZigBee nodes to the WiFi AP. We extensively evaluate ECT under different network settings and results show that our ECTs packet delivery delay is more than 29 times lower than the current state-of-the-art solution.

Rulers on Our Arms: Waving to Measure Object Size through Contactless Sensing

This paper proposes a system, Aware, which turns our wearable or mobile device into a ruler. It can estimate the size of objects that are too tall to reach or too far to touch. Such a design will enable a rich set of applications which count on the size information of surrounding environments/objects. Aware purely utilizes the motion sensors on the device for object size measures. It can also integrate with the crowdsourcing feature for both performance improvement and result sharing. We propose a series of key techniques to address three major challenges in the Aware design: 1) user's angle of line-of-sights to the object is used in the size measure but motion sensors track only the angle of arm's waving, 2) motion sensors are noisy that require novel and effective data processing techniques, otherwise the errors could easily overwhelm the final result, and 3) in the crowdsourcing mode, Aware needs to identify vicinal objects of similar sizes and effectively fuse the measured sizes that correspond to the same object. We consolidate above designs and implement Aware on Android platforms. Extensive experiments with four users show that Aware can achieve accurate measurement performance for the objects of various sizes.

A General Framework for Spectrum Sensing Using Dedicated Spectrum Sensor Networks

Efficient spectrum sensing is essential for the success of Dynamic Spectrum Assignment (DSA) in Cognitive Radio Networks (CRNs). In conventional spectrum sensing schemes, secondary users (SUs) have to intelligently schedule their sensing and accessing cycles so that the spectrum opportunities are optimally exploited while the primary users are not harmed. In this paper, we propose a new sensing service model in which a dedicated spectrum sensor network (SSN) is adopted for the spectrum sensing tasks. We will describe the general framework for this SSN-enabled CRN and present the major challenges in such architecture. We will also study one of these challenges and formulate it as a boundary detection problem with notable and unknown erroneous inputs. A novel cooperative boundary detection scheme is designed which explores the recent advances in machine learning and computational geometry. We prove that our cooperative boundary detection can asymptotically approach the optimal solution. Real test-bed as well as simulation experiments show that compared with the traditional schemes, cooperative boundary detection can significantly reduce the spectrum sensing overhead and improve the effectiveness of DSA.

Routing-Aware and Malicious Node Detection in a Concealed Data Aggregation for WSNs

A WSN needs to be not only energy efficient, but also secure. Various attacks may make data aggregation unsecure. We investigate the reliable and secure end-to-end data aggregation problem considering selective forwarding attacks and modification attacks in homogeneous WSNs, and propose two data aggregation approaches. Our approaches, namely, Sign-Share and Sham-Share, use secret sharing and signatures to allow aggregators to aggregate the data without understanding the contents of messages and the base station to verify the aggregated data and retrieve the raw data from the aggregated data. To best of our knowledge, this is the first lightweight en-routing malicious node detection in concealed data aggregation. We have performed extensive simulation to compare our approaches and the two state-of-the-art approaches PIP and RCDA-HOMO. The simulation results show both Sign-Share and Sham-Share consume reasonable amount of time in processing the data and aggregating the data. The simulation results show that our first approach achieved average network lifetime of 102.33\% over PIP, and average aggregation energy consumption of 74.93%. Also, it achieved average aggregations processing time and sensor's data processing time of 95.4%, 90.34% over PIP and 98.7%,92.07% over RCDA-HOMO respectively while it achieved average network delay of 71.95% over PIP

Network Management of Multi-Cluster RT-WiFi Networks

Applying wireless technologies in cyber-physical systems (CPS) has received significant attention in recent years. In our previous work, a high-speed and flexible real-time wireless protocol called RT-WiFi has been designed to support a wide range of CPSs. To serve the CPS applications with communication nodes geographically distributed over a large area, multi-cluster RT-WiFi networks with multiple access points (AP) need to be deployed. Although effective scheduling algorithms have been designed to schedule tasks in RT-WiFi networks with a single AP, uncoordinated packet transmissions from multi-cluster RT-WiFi networks may suffer from co-channel interferences that cause performance degradation. The multi-cluster RT-WiFi network management problem is to resolve the co-channel interference through channel assignment for clusters and phasing assignment for communication tasks. In this paper, we first derive a conjunctive normal form encoding of the problem, and design a TScheduler that searches feasible solutions through the SAT solver. A novel LRTree Scheduler is further designed to solve the problem in chain graphs while keeping the number of used channels small and the network management overhead low. A testbed of multi-cluster RTWiFi network is deployed to validate the design of the multi-cluster RT-WiFi network and evaluate the performance of the proposed scheduling algorithms.

A Framework for the Inference of Sensing Measurements based on Correlation

Network monitoring is an essential component of network operation and it is usually responsible for a significant overhead in large scale networks such as sensor and data center networks. In this paper, we show that measurement correlation can be successfully exploited to reduce the network monitoring overhead. In particular, we propose an online adaptive measurement technique with which a subset of nodes are dynamically chosen as monitors while the measurements of the remaining nodes are estimated using the computed correlations. We propose an estimation framework based on jointly Gaussian distributed random variables, and formulate an optimization problem to select the monitors under a total cost constraint. We show that the problem is NP-Hard and propose three efficient heuristics. We also develop statistical approaches that automatically switch between learning and estimation phases to take into account the variability occurring in real networks. Simulations carried out on real-world traces show that our approach outperforms previous solutions based on compressed sensing and it is able to reduce the monitoring overhead by 50% while incurring a low estimation error. Additionally, we show the efficacy of our approach for the specific application of sensor network based solar irradiance prediction of photovoltaics systems.

Memento: An Emotion Driven Lifelogging System with Wearables

Due to the increasing popularity of mobile devices, the usage of lifelogging has been dramatically expanded. People collect their daily memorial moments and share with friends, which has been an emerging lifestyle. We see great potential of lifelogging applications along with rapid growth of recent wearable market, where more sensors are introduced, i.e., electroencephalogram (EEG) sensors, that can further sense the user's mental activities, e.g., emotions. In this paper, we present the design and implementation of Memento, an emotion driven lifelogging system on wearables. Memento integrates EEG with smart glasses. Since memorable moments usually coincides with users' emotional changes, Memento leverages the knowledge from the brain-computer-interface domain to analyze the EEG signals to infer emotions and automatically launch lifelogging based on that. Towards building Memento on Commercial off-the-shelf wearable devices, we study EEG signals in mobility cases and propose a multiple sensor fusion based approach to estimate signal quality. We present a two-phase emotion recognition architecture, considering both the affordability and efficiency of wearable-class devices. We also discuss the optimization framework to select the suitable lifelogging method (video, audio or image) by analyzing the environment and system context. Finally our evaluation shows that Memento is responsive and user-friendly on wearables.

Extending Battery System Operation via Adaptive Reconfiguration

Large-scale battery packs are commonly used in applications such as electric vehicles (EVs) and smart grids. Traditionally, to provide stable voltage to the loads, voltage regulators are used to convert battery packs output voltage to those of the loads required levels, causing power loss especially when the difference between the supplied and required voltages is large or when the load is light. In this paper, we address this issue via a reconfiguration framework for the battery system. By abstracting the battery system as a cell graph, we develop an adaptive reconfiguration algorithm to identify the desired system configurations based on real-time load requirements. Our design is evaluated via both prototype-based experiments, EV driving trace-based emulations, and large-scale simulations. The results demonstrate an extended system operation time of up to 5x especially when facing severe cell imbalance.

Radiation Constrained Fair Charging for Wireless Power Transfer

Recently wireless power transfer technology (WPT) attracts considerable attention and becomes a promis- ing technology to prolong the lifetime of wireless sensor networks (WSNs) by providing perpetual energy to sensors. However, electromagnetic radiation (EMR) incurred by WPT is largely overlooked by most existing literatures. In this paper, we first propose and study the radiation constrained fair charging problem for WP- T, i.e., maximizing the minimum utility of sensors by adjusting the power of wireless chargers with no EMR intensity at any location in the field exceeding a given threshold Rt. To address this problem, we first adopt an area discretization method to transform it from nonlinear to linear. Then, we propose four algorithms to deal with the reformulated problem, i.e., 1/3 and 1/4 Approximation Algorithms, Primal-Dual algorithm and area division algorithm. In particular, the area division algorithm is not only fully distributed but also provably achieves an approximation ratio of (1  ?). Further, we conduct extensive simulations and build a field testbed to verify our theoretical findings. Our simulation results show that the approximation ratios of the proposed algorithms hold; the Primal-Dual and area division algorithms have comparable performance of the optimal results and outperform baseline algorithms obviously.

LaPS: LiDAR-assisted Placement of Wireless Sensor Networks in Forests

The deployment of a wireless sensor network (WSN) is crucial to its reliability and performance. Yet, node placement is typically determined in-field via effort-demanding trial-and-error procedures, because existing approaches over-simplify the radio environment; this especially holds for forests, the focus of this paper, where trees greatly affect communication. We present LaPS, an approach exploiting remote sensing to identify the best node placement automatically and prior to deployment. Airborne Light Detection and Ranging (LiDAR) data acquired for the target forest are automatically processed to estimate its properties (e.g., tree position and diameter) that, once incorporated into a specialized path loss model, enable per-link estimates of the radio signal attenuation induced by trees. Finally, a genetic algorithm explores placement options by evolving towards a (sub-)optimal solution while satisfying the user's spatial and network requirements, whose formulation is very flexible and broadly applicable. Our experiments, focused on a real forest, confirm that LaPS yields topologies of significantly higher quality w.r.t. approaches using a regular placement or a standard path loss model. Further, the ability to quickly explore the impact that changes in user requirements have on topology is invaluable to improve the operation of WSNs and reduce the effort of their in-field deployment.

FIRST: A Framework for Optimizing Information Quality in Mobile Crowdsensing Systems

Mobile crowdsensing allows data collection at a scale and rate that was once impossible. One of the biggest challenges in mobile crowdsensing is to accurately classify between reliable and unreliable sensing reports. To this end, we propose a novel Framework for optimizing Information Reliability in Smartphone-based participaTory sensing (FIRST), that leverages the collective action of mobile trusted participants (MTPs) to securely assess the reliability of sensing reports. FIRST models and solves the challenging problem of determining before deployment the minimum number of MTPs to be used in order to achieve desired classification accuracy. We extensively validate FIRST with real-world mobility traces and through an implementation in iOS and Android of a system leveraging human participants. Experimental results demonstrate that FIRST is effective in optimizing information reliability by reducing the impact of three security attacks (i.e., corruption, on/off, and collusion), while outperforming prior work by achieving on the average a classification accuracy of almost 80% in the considered scenarios. We conclude the paper by discussing our ongoing research efforts in cooperation with the U.S. Department of Geological Survey (USGS) to develop a smartphone-based system to test the performance of FIRST as part of the USGS National Map Corps project.

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