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IODetector: A generic service for indoor outdoor detection
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"... The location and context switching, especially the indoor/outdoor switching, provides essential and primitive information for upper layer mobile applications. In this paper, we present IODetector: a lightweight sensing service which runs on the mobile phone and detects the indoor/outdoor environment ..."
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The location and context switching, especially the indoor/outdoor switching, provides essential and primitive information for upper layer mobile applications. In this paper, we present IODetector: a lightweight sensing service which runs on the mobile phone and detects the indoor/outdoor environment in a fast, accurate, and efficient manner. Constrained by the energy budget, IODetector leverages primarily lightweight sensing resources including light sensors, magnetism sensors, celltower signals, etc. For universal applicability, IODetector assumes no prior knowledge (e.g., fingerprints) of the environment and uses only on-board sensors common to mainstream mobile phones. Being a generic and lightweight service component, IODetector greatly benefits many location-based and context-aware applications. We prototype the IODetector on Android mobile phones and evaluate the system comprehensively with data collected from 19 traces which include 84 different places during one month period, employing different phone models. We further perform a case study where we make use of IODetector to instantly infer the GPS availability and localization accuracy in different indoor/outdoor environments.
Energy-Harvesting Active Networked Tags (EnHANTs): Prototyping and Experimentation
"... This article focuses on a new type of wireless devices in the domain between RFIDs and sensor networksEnergy-Harvesting Active Networked Tags (EnHANTs). Future EnHANTs will be small, flexible, and selfpowered devices that can be attached to objects that are traditionally not networked (e.g., books, ..."
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This article focuses on a new type of wireless devices in the domain between RFIDs and sensor networksEnergy-Harvesting Active Networked Tags (EnHANTs). Future EnHANTs will be small, flexible, and selfpowered devices that can be attached to objects that are traditionally not networked (e.g., books, furniture, toys, produce, and clothing). Therefore, they will provide the infrastructure for various tracking applications and can serve as one of the enablers for the Internet of Things. We present the design considerations for the EnHANT prototypes, developed over the past 4 years. The prototypes harvest indoor light energy using custom organic solar cells, communicate and form multihop networks using ultra-low-power UltraWideband Impulse Radio (UWB-IR) transceivers, and dynamically adapt their communications and networking patterns to the energy harvesting and battery states. We describe a small-scale testbed that uniquely allows evaluating different algorithms with trace-based light energy inputs. Then, we experimentally evaluate the performance of different energy-harvesting adaptive policies with organic solar cells and UWB-IR transceivers. Finally, we discuss the lessons learned during the prototype and testbed design process.
Temperature-Assisted Clock Synchronization and Self-Calibration for Sensor Networks
"... Abstract—Synchronization is a pre-requisite for many sensor network applications. However, it remains challenging in sensor networks due to both the limited resources and the dynamic environments. In this paper, we propose a new two-phase clock synchronization scheme. The first one is the external c ..."
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Abstract—Synchronization is a pre-requisite for many sensor network applications. However, it remains challenging in sensor networks due to both the limited resources and the dynamic environments. In this paper, we propose a new two-phase clock synchronization scheme. The first one is the external clock synchronization phase, during which nodes update their clock by exchanging timestamp messages with the reference clock. Different from the conventional solutions, we propose to directly remove the clock skew during the external synchroniza-tion to achieve a higher synchronization accuracy and lower computational complexity. The second one is the clock self-calibration phase, as the accumulated clock skew will make the synchronized clock drift away again, we need to compensate the clock skew to maintain the clock synchronization accuracy. However, the compensation is non-trivial as the clock skew may not be constant due to the changing environment. Thus we propose the temperature-assisted clock self-calibration (TACSC) to dynamically compensate the clock skew according to the working temperature. Extensive simulation demonstrates that the proposed synchronization scheme can achieve a much lower root mean square error in the external synchronization phase. Furthermore, during the clock self-calibration phase, the TACSC scheme can improve the synchronization accuracy by more than one order of magnitude, which is verified by both simulation and testbed experimentation. Index Terms—Time synchronization, clock skew, wireless sen-sor networks. I.
IODetector: A Generic Service for Indoor/Outdoor Detection
"... The location and context switching, especially the indoor/outdoor switching, provides essential and primi-tive information for upper-layer mobile applications. In this article, we present IODetector: a lightweight sensing service that runs on the mobile phone and detects the indoor/outdoor environme ..."
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The location and context switching, especially the indoor/outdoor switching, provides essential and primi-tive information for upper-layer mobile applications. In this article, we present IODetector: a lightweight sensing service that runs on the mobile phone and detects the indoor/outdoor environment in a fast, accu-rate, and efficient manner. Constrained by the energy budget, IODetector primarily leverages lightweight sensing resources, such as light sensors, magnetism sensors, and cell tower signals. For universal applica-bility, IODetector assumes no prior knowledge (e.g., fingerprints) of the environment and uses only on-board sensors common to mainstream mobile phones. Being a generic and lightweight service component, IODe-tector greatly benefits many location-based and context-aware applications. We prototype the IODetector on Android mobile phones and evaluate the system comprehensively with data collected from 34 traces that include 133 different places during a 6-week period, employing different phone models. We further perform a case study where we make use of IODetector to instantly infer the GPS availability and localization accuracy in different indoor/outdoor environments.
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"... Abstract—Device-free object tracking provides a promising solution for many localization and tracking systems to monitor non-cooperative objects, such as intruders, which do not carry any transceiver. However, existing device-free solutions mainly use special sensors or active RFID tags, which are m ..."
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Abstract—Device-free object tracking provides a promising solution for many localization and tracking systems to monitor non-cooperative objects, such as intruders, which do not carry any transceiver. However, existing device-free solutions mainly use special sensors or active RFID tags, which are much more expensive compared to passive tags. In this paper, we propose a novel motion detection and tracking method using passive RFID tags, named Twins. The method leverages a newly observed phenomenon called critical state caused by interference among passive tags. We contribute to both theory and practice of this phenomenon by presenting a new interference model that precisely explains it and using extensive experiments to validate it. We design a practical Twins based intrusion detection system and implement a real prototype by commercial off-the-shelf RFID reader and tags. Experimental results show that Twins is effective in detecting the moving object, with very low location errors of 0.75m in average (with a deployment spacing of
ShopMiner: Mining Customer Shopping Behavior in Physical Clothing Stores with COTS RFID Devices
"... Shopping behavior data are of great importance to under-stand the effectiveness of marketing and merchandising ef-forts. Online clothing stores are capable capturing customer shopping behavior by analyzing the click stream and cus-tomer shopping carts. Retailers with physical clothing s-tores, howev ..."
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Shopping behavior data are of great importance to under-stand the effectiveness of marketing and merchandising ef-forts. Online clothing stores are capable capturing customer shopping behavior by analyzing the click stream and cus-tomer shopping carts. Retailers with physical clothing s-tores, however, still lack effective methods to identify com-prehensive shopping behaviors. In this paper, we show that backscatter signals of passive RFID tags can be exploited to detect and record how customers browse stores, which items of clothes they pay attention to, and which items of clothes they usually match with. The intuition is that the phase readings of tags attached on desired items will demon-strate distinct yet stable patterns in the time-series when customers look at, pick up or turn over desired items. We design ShopMiner, a framework that harnesses these unique spatial-temporal correlations of time-series phase readings to detect comprehensive shopping behaviors. We have im-plemented a prototype of ShopMiner with a COTS RFID reader and four antennas, and tested its effectiveness in two typical indoor environments. Empirical studies from two-week shopping-like data show that ShopMiner could achieve high accuracy and efficiency in customer shopping behavior identification.
PhaseU: Real-time LOS Identification with WiFi
"... Abstract—WiFi technology has fostered numerous mobile computing applications, such as adaptive communication, fine-grained localization, gesture recognition, etc., which often achieve better performance or rely on the availability of Line-Of-Sight (LOS) signal propagation. Thus the awareness of LOS ..."
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Abstract—WiFi technology has fostered numerous mobile computing applications, such as adaptive communication, fine-grained localization, gesture recognition, etc., which often achieve better performance or rely on the availability of Line-Of-Sight (LOS) signal propagation. Thus the awareness of LOS and Non-Line-Of-Sight (NLOS) plays as a key enabler for them. Real-time LOS identification on commodity WiFi devices, however, is challenging due to limited bandwidth of WiFi and resulting coarse multipath resolution. In this work, we explore and exploit the phase feature of PHY layer information, harnessing both space diversity with antenna elements and frequency diversity with OFDM subcarriers. On this basis, we propose PhaseU, a real-time LOS identification scheme that works in both static and mobile scenarios on commodity WiFi infrastructure. Ex-perimental results in various indoor scenarios demonstrate that PhaseU consistently outperforms previous approaches, achiev-ing overall LOS and NLOS detection rates of 94.35 % and 94.19 % in static cases and both higher than 80 % in mobile contexts. Furthermore, PhaseU achieves real-time capability with millisecond-level delay for a connected AP and 1-second delay for unconnected APs, which is far beyond existing approaches. I.
FEMO: A Platform for Free-weight Exercise Monitoring
"... Regular free-weight exercise helps to strengthen the body’s natural movements and stabilize muscles that are importan-t to strength, balance, and posture of human beings. Prior works have exploited wearable sensors or RF signal changes (e.g., WiFi and Blue-tooth) for activity sensing, recognition an ..."
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Regular free-weight exercise helps to strengthen the body’s natural movements and stabilize muscles that are importan-t to strength, balance, and posture of human beings. Prior works have exploited wearable sensors or RF signal changes (e.g., WiFi and Blue-tooth) for activity sensing, recognition and counting etc.. However, none of them have incorporate three key factors necessary for a practical free-weight exer-cise monitoring system: recognizing free-weight activities on site, assessing their qualities, and providing useful feedbacks to the bodybuilder promptly. Our FEMO system responds to these demands, providing an integrated free-weight ex-ercise monitoring service that incorporates all the essential functionalities mentioned above. FEMO achieves this by attaching passive RFID tags on the dumbbells and lever-aging the Doppler shift profile of the reflected backscatter signals for on-site free-weight activity recognition and as-sessment. The rationale behind FEMO is 1): since each free-weight activity owns unique arm motions, the corre-sponding Doppler shift profile should be distinguishable to each other and serves as a reliable signature for each ac-tivity. 2): the Doppler profile of each activity has a strong spatial-temporal correlation that implicitly reflects the qual-ity of each performed activity. We implement FEMO with COTS RFID devices and conduct a two-week experimen-t. The preliminary result from 15 volunteers demonstrates that FEMO can be applied to a variety of free-weight activ-ities and users, and provide valuable feedbacks for activity alignment.
1FLIGHT: Clock Calibration and Context Recognition using Fluorescent Lighting
"... Abstract—In this paper, we propose a novel clock calibration approach called FLIGHT, which leverages the fact that the fluorescent light intensity changes with a stable period that equals half of the alternating current’s. By tuning to the light emitted from indoor fluorescent lamps, FLIGHT can inte ..."
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Abstract—In this paper, we propose a novel clock calibration approach called FLIGHT, which leverages the fact that the fluorescent light intensity changes with a stable period that equals half of the alternating current’s. By tuning to the light emitted from indoor fluorescent lamps, FLIGHT can intelligently extract the light period information and achieve network wide time calibration by referring to such a common time reference. The light period can be also viewed as an indoor context indicator. As sampling the light sensor consumes substantially less energy, FLIGHT provides us a lightweight clock calibration and time synchronization solution. In addition, FLIGHT suits various mobility-enabled scenarios and it can work well even when the network is temporarily disconnected. We address a series of practical challenges and implement FLIGHT in TelosB motes. We conduct comprehensive experiments using a 12-node test-bed in both static and mobile environments. Over one-week measurement suggests that compared with existing technologies, FLIGHT can achieve tightly synchronized time with low energy consumption. We further leverage the periodical pattern and upgrade FLIGHT to recognize the ambient indoor/outdoor context, based on which the on/off states of a variety of location-based services can be controlled automatically for mobile devices. Index Terms—Clock calibration, time synchronization, energy efficiency, fluorescent lighting, context recognition. 1
ToneTrack: Leveraging Frequency-Agile Radios for Time-Based Indoor Wireless Localization
"... Indoor localization of mobile devices and tags has received much attention recently, with encouraging fine-grained localization re-sults available with enough line-of-sight coverage and hardware infrastructure. Some of the most promising techniques analyze the time-of-arrival of incoming signals, bu ..."
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Indoor localization of mobile devices and tags has received much attention recently, with encouraging fine-grained localization re-sults available with enough line-of-sight coverage and hardware infrastructure. Some of the most promising techniques analyze the time-of-arrival of incoming signals, but the limited bandwidth available to most wireless transmissions fundamentally constrains their resolution. Frequency-agile wireless networks utilize band-widths of varying sizes and locations in a wireless band to effi-ciently share the wireless medium between users. ToneTrack is an indoor location system that achieves sub-meter accuracy with min-imal hardware and antennas, by leveraging frequency-agile wire-less networks to increase the effective bandwidth. Our novel signal combination algorithm combines time-of-arrival data from differ-ent transmissions as a mobile device hops across different chan-nels, approaching time resolutions previously not possible with a single narrowband channel. ToneTrack’s novel channel combina-tion and spectrum identification algorithms together with the tri-angle inequality scheme yield superior results even in non-line-of-sight scenarios with one to two walls separating client and APs and also in the case where the direct path from mobile client to an AP is completely blocked. We implement ToneTrack on the WARP hardware radio platform and use six of them served as APs to lo-calize Wi-Fi clients in an indoor testbed over one floor of an office building. Experimental results show that ToneTrack can achieve a median 90 cm accuracy when 20 MHz bandwidth APs overhear three packets from adjacent channels.
