Hidden cameras have increasingly infiltrated hotel and Airbnb rooms, posing serious privacy risks. Detecting such cameras is challenging because they are visually inconspicuous and often embedded inside everyday objects. Even worse, existing handheld detectors are manual and also rely on single-angle illumination and hence suffer from high false-positive rates. We present SweepLED (pronounced "sweepled")1, a practical hidden camera detection system that operates on a commodity smartphone augmented with an unobtrusive LED-embedded case. SweepLED performs LED sweeping - a controlled sequence of multi-angle illumination - while the user simply holds the phone still by hand, enabling the camera to capture how reflections evolve under changing lighting. This reveals stable, lens-specific cues that distinguish hidden camera lenses from ordinary reflective objects, enabling robust detection with low user effort. We implement SweepLED using a compact hardware add-on and evaluate it in realistic environments containing 12 hidden-camera objects and 18 commonly reflective non-camera items. Our results demonstrate that SweepLED provides accurate and reliable hidden-camera detection using only unobtrusive smartphone-compatible hardware, achieving approximately 94% detection accuracy with a sweep time of under 5 s and a core component cost of less than USD $7.

Low-end earphones are widely spread due to their affordability, but their limited speaker hardware often leads to poor music playback quality. This raises a key question: Can we compensate for hardware limitations to enhance the listening experience without modifying the device? Existing EQ-based approaches attempt this, but they rely on frequency response curves (FRCs) measured under ideal conditions, which fail to capture real-world distortions such as harmonic and intermodulation effects.

Accurate swimming performance monitoring has traditionally relied on wearable sensors, which can disrupt natural technique and are impractical in competitive settings. In this paper, we present a fully vision-based system for automatic swimmer analysis using overhead drone footage, removing the need for any wearable device or underwater equipment. By fine-tuning pose estimation models for aerial aquatic conditions, our approach robustly extracts full-body swimmer skeletons even under challenging scenarios such as splashes and partial occlusions. From these poses, we classify swimming strokes, compute instantaneous speed, estimate lap times, and count individual strokes. Unlike existing methods, our system provides scalable, unobtrusive, and infrastructure-free tracking. Evaluated on real-world drone-captured swimming competition data, our method achieves a median speed estimation error below 4% (under 0.05 m/s), a median lap time error of just 0.03s, and stroke count errors typically under one stroke per lap.

In Affective computing, recognizing users' emotions accurately is the basis of affective human-computer interaction. Understanding users' interoception contributes to a better understanding of individually different emotional abilities, which is essential for achieving inter-individually accurate emotion estimation. However, existing interoception measurement methods, such as the heart rate discrimination task, have several limitations, including their dependence on a well-controlled laboratory environment and precision apparatus, making monitoring users' interoception challenging. This study aims to determine other forms of data that can explain users' interoceptive or similar states in their real-world lives and propose a novel hypothetical concept "cyberoception," a new sense (1) which has properties similar to interoception in terms of the correlation with other emotion-related abilities, and (2) which can be measured only by the sensors embedded inside commodity smartphone devices in users' daily lives. Results from a 10-day-long in-lab/in-the-wild hybrid experiment reveal a specific cyberoception type "Turn On" (users' subjective sensory perception about the frequency of turning-on behavior on their smartphones), significantly related to participants' emotional valence. We anticipate that cyberoception to serve as a fundamental building block for developing more "emotion-aware", user-friendly applications and services.

We present GradualReality, a novel interface enabling a Cross Reality experience that includes gradual interaction with physical objects in a virtual environment and supports both presence and usability. Daily Cross Reality interaction is challenging as the user’s physical object interaction state is continuously changing over time, causing their attention to frequently shift between the virtual and physical worlds. As such, presence in the virtual environment and seamless usability for interacting with physical objects should be maintained at a high level. To address this issue, we present an Interaction State-Aware Blending approach that (i) balances immersion and interaction capability and (ii) provides a fine-grained, gradual transition between virtual and physical worlds. The key idea includes categorizing the flow of physical object interaction into multiple states and designing novel blending methods that offer optimal presence and sufficient physical awareness at each state. We performed extensive user studies and interviews with a working prototype and demonstrated that GradualReality provides better Cross Reality experiences compared to baselines.

Human social interactions occur in group settings of varying sizes and locations, depending on the type of social activity. The ability to distinguish group formations based on their purposes transforms how group detection mechanisms function. Not only should such tools support the effective detection of serendipitous encounters, but they can derive categories of relation types among users. Determining who is involved, what activity is performed, and when and where the activity occurs are critical to understanding group processes in greater depth, including supporting goal-oriented applications (e.g., performance, productivity, and mental health) that require sensing social factors. In this work, we propose W4-Groups that captures the functional perspective of variability and repeatability when automatically constructing short-term and long-term groups via multiple data sources (e.g., WiFi and location check-in data). We design and implement W4-Groups to detect and extract all four group features who-what-when-where from the user's daily mobility patterns. We empirically evaluate the framework using two real-world WiFi datasets and a location check-in dataset, yielding an average of 92% overall accuracy, 96% precision, and 94% recall. Further, we supplement two case studies to demonstrate the application of W4-Groups for next-group activity prediction and analyzing changes in group behavior at a longitudinal scale, exemplifying short-term and long-term occurrences.

Object detection, while being an attractive interaction method for Augmented Reality (AR), is fundamentally error-prone due to the probabilistic nature of the underlying AI models, resulting in sub-optimal user experiences. In this paper, we explore the effect of three game design concepts, Ambiguity, Transparency, and Controllability, to provide better gameplay experiences in AR games that use error-prone object detection-based interaction modalities. First, we developed a base AR pet breeding game, called Bubbleu that uses object detection as a key interaction method. We then implemented three different variants, each according to the three concepts, to investigate the impact of each design concept on the overall user experience. Our user study results show that each design has its own strengths and can improve player experiences in different ways such as decreasing perceived errors (Ambiguity), explaining the system (Transparency), and enabling users to control the rate of uncertainties (Controllability).

Social identification: how much individuals psychologically associate themselves with a group has been posited as an essential construct to measure individual and group dynamics. Studies have shown that individuals who identify very differently from their workgroup provide critical cues to the lack of social support or work overloads. However, measuring identification is typically achieved through time-consuming and privacy-invasive surveys. We hypothesize that the extremities in-group norm affects individuals' behaviors, thus more likely to give rise to negative appraisals. As a more convenient and less-invasive technique, we propose a method to predict individuals who are increasingly different in identifying themselves with their working peers using mobility data passively sensed from the WiFi infrastructure. To test our hypothesis, we collected WiFi data of 62 college students over a whole semester. Students provided regular self-reports on their identification towards a workgroup as ground truth. We analyze the contrasts between groups' mobility patterns and build a classification model to determine students who identify very differently from their workgroup. The classifier achieves approximately 80% True Positive Rate (TPR), 73% True negative rate (TNR), and 78% Accuracy (ACC). Such a mechanism can help distinguish students who are more likely to struggle with negative workgroup appraisals and enable interventions to improve their overall team experience.

Material identification and target imaging play an important role in many applications. This paper introduces TagScan, a system that can identify the material type and image the horizontal cut of a target simultaneously with cheap commodity Radio-Frequency IDentification (RFID) devices. The key intuition is that different materials and/or target sizes cause different amounts of phase and RSS (Received Signal Strength) changes, when radio frequency (RF) signal penetrates through the target. Multiple challenges need to be addressed before we can turn the idea into a functional system, including (i) indoor environments exhibit rich multipath which breaks the linear relationship between the phase change and the propagation distance inside a target; (ii) without knowing either material type or target size, trying to obtain these two information simultaneously is challenging; and (iii) stitching pieces of the propagation distances inside a target for an image estimate is non-trivial. We propose solutions to all the challenges and evaluate the system's performance in three different environments. TagScan is able to achieve higher than 94 percent material identification accuracies for 10 liquids and differentiates even very similar objects such as Coke and Pepsi. TagScan can accurately estimate the horizontal cut images of more than one target behind a wall.

Fine-grained, unobtrusive monitoring of gym exercises can help users track their own exercise routines and also provide corrective feedback. We propose W8-Scope, a system that uses a simple magnetic-cum-accelerometer sensor, mounted on the weight stack of gym exercise machines, to infer various attributes of gym exercise behavior. More specifically, using multiple machine learning models, W8-Scope helps identify who is exercising, what exercise she is doing, how much weight she is lifting, and whether she is committing any common mistakes. Real world studies, conducted with 50 subjects performing 14 different exercises over 103 distinct sessions in two gyms, show that W8-Scope can achieve high accuracy-e.g., identify the weight used with an accuracy of 97.5%, detect commonplace mistakes with 96.7% accuracy and identify the user with 98.7% accuracy. Moreover, by adopting incremental learning techniques, W8- Scope can also accurately track these various facets of exercise over longitudinal periods, in spite of the inherent natural changes in a user's exercising behavior.

With mobile apps rapidly permeating all aspects of daily living with use by all segments of the population, it is crucial to support the evaluation of app usability for specific impaired users to improve app accessibility. In this work, we examine the effects of using our augmented virtuality impairment simulation system--Empath-D--to support experienced designer-developers to redesign a mockup of commonly used mobile application for cataract-impaired users, comparing this with existing tools that aid designing for accessibility. We show that the use of augmented virtuality for assessing usability supports enhanced usability challenge identification, finding more defects and doing so more accurately than with existing methods. Through our user interviews, we also show that augmented virtuality impairment simulation supports realistic interaction and evaluation to provide a concrete understanding over the usability challenges that impaired users face, and complements the existing guidelines-based approaches meant for general accessibility.

We present LpGL, an OpenGL API compatible Low-power Graphics Library for energy efficient AR headset applications. We first characterize the power consumption patterns of a state of the art AR headset, Magic Leap One, and empirically show that its internal GPU is the most impactful and controllable energy consumer. Based on the preliminary studies, we design LpGL so that it uses the device's gaze/head orientation information and geometry data to infer user perception information, intercepts application-level graphics API calls, and employs frame rate control, mesh simplification, and culling techniques to enhance energy efficiency of AR headsets without detriment of user experience. Results from a comprehen- sive set of controlled in-lab experiments and an IRB-approved user study with 25 participants show that LpGL reduces up to 22% of total energy usage while adding only 46 sec of latency per object with close to no loss in subjective user experience.

Electrocardiogram (ECG) signals offer rich information for analyzing and understanding the cardiac activity of a person. The continuous monitoring of ECG can help diagnose cardiac disorders, such as arrhythmia, effectively. While many wearable healthcare platforms offer continuous ECG monitoring, these devices are cumbersome in the fact that they need to be continuously attached to the human body, which causes uncomfortableness, and limits their usage when monitoring a person's ECG throughout the night as they sleep. In this work, we propose a fully non-intrusive sensing system for monitoring the ECG of a person while in bed. Specifically, we present Heartquake, a geophone-based sensing system for extracting ECG patterns using heartbeat vibrations that penetrate through the mattress. The cardiac activity-originated vibration patterns are captured on the geophone and sent to a server, where the data is filtered to remove external noise and passed on to a bidirectional long short term memory (Bi-LSTM) deep learning model for ECG waveform extraction. Our experimental results with 21study participants suggest that Heartquake can detect all five ECG peaks (e.g., P, Q, R, S, T) with an average error of as low as 16 msec when participants are stationary on the bed. With additional noise factors, this error shows an increase, but can be mitigated from model personalization to still be sufficient enough as a screening tool to detect urgent situations.

Much research argues that feeling overwhelmed by stress and for prolonged periods can lead to severe mental illness such as early onset depression and anxiety among many others. Recovering from severe stress to a normal state is much easier, in terms of the length of time and treatment required, compared to when more serious conditions have manifested [1]. Unfortunately, existing stress monitoring applications either require dedicated applications to be installed on the user's mobile device or use various mobile and wearable sensors [2, 4, 6, 7]; thus are not scalable to large number of users. Our goal is to provide a community-wide "safety net" that will automatically and non-intrusively detect individuals exhibiting signs of excessive stress without them installing any dedicated app. YouTube Demo Link https://youtu.be/LKQvIX4W6L0

Energy harvesting, from a diverse set of modes such as light or motion, has been viewed as the key to developing batteryless sensing devices. In this paper, we develop the nascent idea of harvesting RF energy from WiFi transmissions, applying it to power a prototype wearable device that captures and transmits accelerometer sensor data. Our solution, WiWear, has two key innovations: 1) beamforming WiFi transmissions to significantly boost the energy that a receiver can harvest ~23 meters away, and 2) smart zero-energy, triggering of inertial sensing, that allows intelligent duty-cycled operation of devices whose transient power consumption far exceeds what can be instantaneously harvested. We provide experimental validation, using both careful measurement studies as well as a controlled study with human participants, to show the viability of a custom-built WiWear-based wearable device, at least in office environments.

We present VitaMon, a mobile sensing system that can measure the inter-heartbeat interval (IBI) from the facial video captured by a commodity smartphone's front camera. The continuous IBI measurement is used to compute heart rate variability (HRV), one of the most important markers of the autonomic nervous system (ANS) regulation. The underlying idea of VitaMon is that video recording of human face contains multiple cardiovascular pulse signals with different phase shift. Our measurement on 10 participants shows the significant time delay (36.79 ms) between the pulse signals measured at the jaw region and forehead region. VitaMon leverages deep neural network models to extract both spatial and temporal information of the video to reconstruct a pulse waveform signal that is optimized for estimating IBI. We evaluated VitaMon with a dataset collected from 30 participants under various conditions involving different light intensity levels and motion artifacts. With the 15 fps video input (66.67 ms time resolution), VitaMon can measure IBI with an average error of 14.26 ms and 21.65 ms using personal and general model respectively. HRV features including geometry Poincare plot, time- and frequency-domain features extracted from the IBI measurement all have high correlation with the reference signal.

Stress and depression are a common affliction in all walks of life. When left unmanaged, stress can inhibit productivity or cause depression. Depression can occur independently of stress. There has been a sharp rise in mobile health initiatives to monitor stress and depression. However, these initiatives usually require users to install dedicated apps or multiple sensors, making such solutions hard to scale. Moreover, they emphasise sensing individual factors and overlook social interactions, which plays a significant role in influencing stress and depression while being a part of a social system. We present StressMon, a stress and depression detection system that leverages single-attribute location data, passively sensed from the WiFi infrastructure. Using the location data, it extracts a detailed set of movement, and physical group interaction pattern features without requiring explicit user actions or software installation on client devices. These features are used in two different machine learning models to detect stress and depression. To validate StressMon, we conducted three different longitudinal studies at a university with different groups of students, totalling up to 108 participants. Our evaluation demonstrated StressMon detecting severely stressed students with a 96.01% True Positive Rate (TPR), an 80.76% True Negative Rate (TNR), and a 0.97 area under the ROC curve (AUC) score (a score of 1 indicates a perfect binary classifier) using a 6-day prediction window. In addition, StressMon was able to detect depression at 91.21% TPR, 66.71% TNR, and 0.88 AUC using a 15-day window. We end by discussing how StressMon can expand CSCW research, especially in areas involving collaborative practices for mental health management.

In this paper, we present I4S, a system that identifies item interactions of customers in a retail store through sensor data fusion from smartwatches, smartphones and distributed BLE beacons. To identify these interactions, I4S builds a gesture-triggered pipeline that (a) detects the occurrence of "item picks", and (b) performs fine-grained localization of such pickup gestures. By analyzing data collected from 31 shoppers visiting a midsized stationary store, we show that we can identify person-independent picking gestures with a precision of over 88%, and identify the rack from where the pick occurred with 91%+ precision (for popular racks).

Real-world deployments of WiFi-based indoor localization in large public venues are few and far between as most state-of-the-art solutions require either client or infrastructure-side changes. Hence, even though high location accuracy is possible with these solutions, they are not practical due to cost and/or client adoption reasons. Majority of the public venues use commercial controller-managed WLAN solutions, that neither allow client changes nor infrastructure changes. In fact, for such venues we have observed highly heterogeneous devices with very low adoption rates for client-side apps.

With app-based interaction increasingly permeating all aspects of daily living, it is essential to ensure that apps are designed to be inclusive and are usable by a wider audience such as the elderly, with various impairments (e.g., visual, audio and motor). We propose Empath-D, a system that fosters empathetic design, by allowing app designers, in-situ, to rapidly evaluate the usability of their apps, from the perspective of impaired users. To provide a truly authentic experience, Empath-D carefully orchestrates the interaction between a smartphone and a VR device, allowing the user to experience simulated impairments in a virtual world while interacting naturally with the app, using a real smartphone. By carefully orchestrating the VR-smartphone interaction, Empath-D tackles challenges such as preserving low-latency app interaction, accurate visualization of hand movement and low-overhead perturbation of I/O streams. Experimental results show that user interaction with Empath-D is comparable (both in accuracy and user perception) to real-world app usage, and that it can simulate impairment effects as effectively as a custom hardware simulator.

No abstract available.

We describe the design and implementation of a smartwatch-based, completely unobtrusive, food journaling system, where the smartwatch helps to intelligently capture useful images of food that an individual consumes throughout the day. The overall system, called Annapurna, is based on three key components: (a) a smartwatch-based gesture recognizer to identify eating gestures, (b) a smartwatch-based image capturer that obtains a small set of relevant and useful images with a low energy overhead, and (c) a server-based image filtering engine that removes irrelevant uploaded images, and then catalogs them through a portal. Our primary challenge is to make the system robust to the huge diversity in natural eating habits and food choices. We show how we address this by an appropriate coupling between a smartwatch's camera sensor and inertial sensor-based tracking of eating gestures, thereby helping to capture multiple likely-to-be-useful images with low energy overhead. Through a series of real-world, in-the-wild studies, we demonstrate the end-to-end working of Annapurna, which captures useful images in over 95% of all natural eating episodes.

Target imaging and material identification play an important role in many real-life applications. This paper introduces TagScan, a system that can identify the material type and image the horizontal cut of a target simultaneously with cheap commercial off the-shelf (COTS) RFID devices. The key intuition is that different materials and target sizes cause different amounts of phase and RSS (Received Signal Strength) changes when radio frequency (RF) signal penetrates through the target. Multiple challenges need to be addressed before we can turn the idea into a functional system including (i) indoor environments exhibit rich multipath which breaks the linear relationship between the phase change and the propagation distance inside a target; (ii) without knowing either material type or target size, trying to obtain these two information simultaneously is challenging; and (iii) stitching pieces of the propagation distances inside a target for an image estimate is non-trivial. We propose solutions to all the challenges and evaluate the system's performance in three different environments. TagScan is able to achieve higher than 94% material identification accuracies for 10 liquids and differentiate even very similar objects such as Coke and Pepsi. TagScan can accurately estimate the horizontal cut images of more than one target behind a wall.

No abstract available.

The rapid emergence of head-mounted devices such as the Microsoft Holo-lens enables a wide variety of continuous vision applications. Such applications often adopt deep-learning algorithms such as CNN and RNN to extract rich contextual information from the first-person-view video streams. Despite the high accuracy, use of deep learning algorithms in mobile devices raises critical challenges, i.e., high processing latency and power consumption. In this paper, we propose DeepMon, a mobile deep learning inference system to run a variety of deep learning inferences purely on a mobile device in a fast and energy-efficient manner. For this, we designed a suite of optimization techniques to efficiently offload convolutional layers to mobile GPUs and accelerate the processing; note that the convolutional layers are the common performance bottleneck of many deep learning models. Our experimental results show that DeepMon can classify an image over the VGG-VeryDeep-16 deep learning model in 644ms on Samsung Galaxy S7, taking an important step towards continuous vision without imposing any privacy concerns nor networking cost.

A central question in mobile computing is how do you test mobile applications, that depend on real context, in real environments with real users? User studies done in lab environments are frequently insufficient to understand the real-world interactions between user context, environmental factors, application behaviour, and performance results. I will introduce LiveLabs, a 5 year project that started at the Singapore Management University in early 2012. The goal of LiveLabs is to convert real environments, such as the entire Singapore Management University campus, a popular resort island, and a large convention centre, into living testbeds where we instrument both the environment and the cell phones of opted-in participants (drawn from the student population and members of the public). I will describe the broad LiveLabs vision and identify the key research challenges and opportunities. I will then talk about our current implementations at various venues and share the insights and lessons we have learned from them. In particular, I will highlight our current insights into indoor location tracking, dynamic group and queue detection, and energy aware context sensing for mobile phones. I will also share our current status and some of the non-obvious challenges that arise from deploying these systems in real environments. Finally, I will discuss how the global research community can use LiveLabs to test innovations in mobile sensing, analytics, applications, and interventions.

In this paper, we present LiveLabs, a first-of-its-kind testbed that is deployed across a university campus, convention centre, and resort island and collects real-time attributes such as location, group context etc., from hundreds of opt-in participants. These venues, data, and participants are then made available for running rich human-centric behavioural experiments that could test new mobile sensing infrastructure, applications, analytics, or more social-science type hypotheses that influence and then observe actual user behaviour. We share case studies of how researchers from around the world have and are using LiveLabs, and our experiences and lessons learned from building, maintaining, and expanding Live-Labs over the last three years.

In this paper, we show that characterizing user behaviour from location or smartphone usage traces, without accounting for the interaction of individuals in physical-world groups, can lead to erroneous results. We conducted one of the largest studies in the UbiComp domain thus far, involving indoor location traces of more than 6,000 users, collected over a 4-month period at our university campus, and further studied fine-grained App usage of a subset of 156 Android users. We apply a state-of-the-art group detection algorithm to annotate such location traces with group vs. individual context, and then show that individuals vs. groups exhibit significant differences along three behavioural traits: (1) the mobility pattern, (2) the responsiveness to calls / SMSs and (3) application usage. We show that these significant differences are robust to underlying errors in the group detection technique and that the use of such group context leads to behavioural results that differ from those reported in prior popular work.

We present QueueVadis, a system that addresses the problem of estimating, in real-time, the properties of queues at commonplace urban locations, such as coffee shops, taxi stands and movie theaters. Abjuring the use of any queuing-specific infrastructure sensors, QueueVadis uses participatory mobile sensing to detect both (i) the individual-level queuing episodes for any arbitrarily-shaped queue (by a characteristic locomotive signature of short bursts of "shuffling forward" between periods of "standing") and (ii) the aggregate-level queue properties (such as expected wait or service times) via appropriate statistical aggregation of multi-person data. Moreover, for venues where multiple queues are too close to be separated via location estimates, QueueVadis also uses a novel disambiguation technique to separate users into multiple distinct queues. User studies, performed with 138 cumulative total users observed at 23 different real-world queues across Singapore and Japan, show that QueueVadis is able to (a) identify all individual queuing episodes, (b) predict service and wait times fairly accurately (with median estimation errors in the 10%--20% range), independent of the queue's shape, (c) separate users in multiple proximate queues with close to 80% accuracy and (d) provide reasonable estimates when the participation rate (the fraction of QueueVadis-equipped people in the queue) is modest.

Driven by the rapid market growth of sensors and beacons that offer Bluetooth Low Energy (BLE) based connectivity, this paper empirically investigates the performance characteristics of the BLE interface on multiple Android smartphones, and the consequent impact on a proposed BLE-based service: continuous indoor location. We first use extensive measurement studies with multiple Android devices to establish that the BLE interface on current smartphones is not as "low-energy" as nominally expected, and establish that continuous use of such a BLE interface is not feasible unless we choose a moderately large scan interval and a low duty cycle. We then explore the implications of such constraints, on the parameters of a smart phone's BLE stack, on the accuracy of a BLE-based indoor localization techniques. We show that while RF-based indoor location can be highly accurate (80% of estimates have errors less than or equal to 4 meters) for stationary users only if the density of beacons is high, the combination of (large scan interval, low duty cycle) causes the location error to degrade significantly for moving users. These results provide practical insights into the use cases and limitations for future BLE-based mobile services.

Mobile games, and especially multiplayer games are a very popular daily distraction for many users. We hypothesise that commuters travelling on public buses or trains would enjoy being able to play multiplayer games with their fellow commuters to alleviate the commute burden and boredom. We present quantitative data to show that the typical one-way commute time is fairly long (at least 25 minutes on average) as well as survey results indicating that commuters are willing to play multiplayer games with other random commuters. In this paper, we present GameOn, a system that allows commuters to participate in multiplayer games with each other using p2p networking techniques that reduces the need to use high latency and possibly expensive cellular data connections. We show how GameOn uses a cloud-based matchmaking server to eliminate the overheads of discovery as well as show why GameOn uses Wi-Fi Direct over Bluetooth as the p2p networking medium. We describe the various system components of GameOn and their implementation. Finally, we present numerous results collected by using GameOn, with three real games, on many different public trains and buses with up to four human players in each game play.

While mobile and wearable sensing can capture unique insights into fine-grained activities (such as gestures and limb-based actions) at an individual level, their energy overheads are still prohibitive enough to prevent them from being executed continuously. In this paper, we explore practical alternatives to addressing this challenge-by exploring how cheap infrastructure sensors or information sources (e.g., BLE beacons) can be harnessed with such mobile/wearable sensors to provide an effective solution that reduces energy consumption without sacrificing accuracy. The key idea is that many fine-grained activities that we desire to capture are specific to certain location, movement or background context: infrastructure sensors and information sources (e.g., BLE beacons) offer practical and cheap ways to identify such context. In this paper, we first explore how various infrastructure, mobile & wearable sensors can be used to identify fine-grained location/movement context (e.g., transiting through a door). We then show, using a couple of illustrative examples (specifically, the detection of `switch pressing' before exiting a room and the identification of `water drinking' after approaching a water cooler) to show that such background context can be predicted, with sufficient accuracy, with sufficient lead time to enable a `triggered' model for mobile/wearable sensing of such microscopic, transient gestures and activities. Moreover, such `triggered' sensing also helps to improve the accuracy of such microscopic gesture recognition, by reducing the set of candidate activity labels. Empirical experiments show that we are able to identify 82.2% of switch-pressing and 91.73% of water-drinking activities in a campus lab setting, with a significant reduction in active sensing time (up to 92.9% compared to continuous sensing).

In the public studying space, students sometimes hog seats. This behavior prevents others from access their needed seats, and requires man power to patrol and move stuffs from hogged seats to another place. In this paper, we present a capacitive sensor to check seat occupancy statuses in real-time (i.e. un-occupied, people occupying, and seat hogging). The device helps students to find available seats, and helps staffs to monitor seats usage remotely for better controlling over seat hogging problem without the need to patrol. Our experiment results show that the sensor can accurately detect seat occupancy. Moreover, it can clearly distinguish between human occupancy and seat hogging.

Recognizing user emotional states while running entertainment applications such as playing game or watching video is very important to understand and improve user experience. In this work, we designed a practical system using wearable physiological sensors including skin electrical conductivity and photoplethysmography (PPG) to recognize popular non-negative emotions that people experience when they watch videos or play games on their mobile devices. We demonstrates how our system recognizes emotional states in two phases: (1) classifying the levels of arousal (high or low) and valence (positive or neutral) at the accuracy of 94.74% and 78.95% respectively; (2) recognizing three non-negative emotions: excitement, contentment, amusement by mapping arousal and valence levels using Russel circumplex model of affect.

In this paper, we reduce the energy overheads of continuous mobile sensing for context-aware applications that are interested in collective context or events. We propose a cloud-based query management and optimization framework, called CloQue, which can support concurrent queries, executing over thousands of individual smartphones. CloQue exploits correlation across context of different users to reduce energy overheads via two key innovations: i) Dynamically reordering the order of predicate processing to preferentially select predicates with not just lower sensing cost and higher selectivity, but that maximally reduce the uncertainty about other context predicates, and ii) intelligently propagating the query evaluation results to dynamically update the uncertainty of other correlated, but yet-to-be evaluated, context predicates. An evaluation, using real cell phone traces from a real world dataset shows significant energy savings (between 30 to 50% compared with traditional short-circuit systems) with little loss in accuracy (5% at most).

A common problem in large urban cities is the huge number of retail options available. In response, a number of shopping assistance applications have been created for mobile phones. However, these applications mostly allow users to know where stores are or find promotions on specific items. What i

Detecting the group context of an individual (i.e., whether an individual is alone or part of a group) in crowded public spaces, such as shopping malls, is an important goal with many practical applications. However, in crowded indoor spaces, understanding the group-dependent movement behavior is a non-trivial problem as: (1) detecting groups is hard as the density ensures that at any location, a large number of people are moving together, (2) location tracking in many real-world venues is either absent or not very accurate, and (3) indoor mobility models that take into account group attributes (such as group size) are rare. In this paper, we first introduce GruMon, a platform for near real-time group monitoring in dense, public spaces, and then demonstrate how the movement & residency properties of individuals are significantly affected when they are in groups.

Real-time monitoring of groups and their rich contexts will be a key building block for futuristic, group-aware mobile services. In this paper, we propose GruMon, a fast and accurate group monitoring system for dense and complex urban spaces. GruMon meets the performance criteria of precise group detection at low latencies by overcoming two critical challenges of practical urban spaces, namely (a) the high density of crowds, and (b) the imprecise location information available indoors. Using a host of novel features extracted from commodity smartphone sensors, GruMon can detect over 80% of the groups, with 97% precision, using 10 minutes latency windows, even in venues with limited or no location information. Moreover, in venues where location information is available, GruMon improves the detection latency by up to 20% using semantic information and additional sensors to complement traditional spatio-temporal clustering approaches. We evaluated GruMon on data collected from 258 shopping episodes from 154 real participants, in two large shopping complexes in Korea and Singapore. We also tested GruMon on a large-scale dataset from an international airport (containing ≈37K+ unlabelled location traces per day) and a live deployment at our university, and showed both GruMon's potential performance at scale and various scalability challenges for real-world dense environment deployments.

In this paper, we present the design and implementation of Focus, a system for effectively and efficiently reducing power consumption of OLED displays on smartphones. These displays, while becoming exceedingly common still consume significant power. The key idea of Focus is that we use the notion of saliency to save display power by dimming portions of the applications that are less important to the user. We envision Focus being especially useful during low battery situations when usability is less important than power savings. We tested Focus using 15 applications running on a Samsung Galaxy S III and show that it saves, on average, between 23 to 34% of the OLED display power with little impact on task completion times. Finally, we present the results of a user study, involving 30 participants that shows that Focus, even with its dimming behaviour, is still quite usable.

Advertisements are the de-facto currency of the Internet with many popular applications (e.g. Angry Birds) and online services (e.g., YouTube) relying on advertisement generated revenue. However, the current economic models and mechanisms for mobile advertising are fundamentally not sustainable and far from ideal. In particular, as we show, applications which use mobile advertising are capable of using significant amounts of a mobile users' critical resources without being controlled or held accountable. This paper seeks to redress this situation by enabling advertisement supported applications to become significantly more ``user-friendly''. To this end, we present the design and implementation of CAMEO, a new framework for mobile advertising that 1) employs intelligent and proactive retrieval of advertisements, using context prediction, to significantly reduce the bandwidth and energy overheads of advertising, and 2) provides a negotiation protocol and framework that empowers applications to subsidize their data traffic costs by ``bartering'' their advertisement rights for access bandwidth from mobile ISPs. Our evaluation, that uses real mobile advertising data collected from around the globe, demonstrates that CAMEO effectively reduces the resource consumption caused by mobile advertising.

This paper describes our experiences and observations with a localization system that continuously tracks the indoor location of a large number of consumer mobile devices. Unlike past work that focuses principally on the accuracy of the location tracking algorithm, we study the performance of the localization system in terms of key additional metrics: scalability and energy-efficiency, which can sometimes conflict with the desire for high accuracy. To ensure that our solution can handle both Android and iOS-based mobile devices (& other closed mobile platforms), we adapt the conventional client-side fingerprinting-based localization approaches to develop a novel and practical infrastructure-based location tracking strategy. We study the relative accuracy to the two approaches in two different types of indoor buildings. Our studies establish how the building and its occupancy characteristics affect the accuracy achievable by different algorithms, and provide insights into why scalable, energy efficient and accurate indoor location tracking remains a challenge in practice.

We describe how we studied, in-situ, the operational processes of three large high process maturity distributed software development companies and discovered three common problems they faced with respect to early stage project cost estimation. We found that project managers faced significant challenges to accurately estimate project costs because the standard metrics-based estimation tools they used (a) did not effectively incorporate diverse distributed project configurations and characteristics, (b) required comprehensive data that was not fully available for all starting projects, and (c) required significant domain experience to derive accurate estimates. To address these challenges, we collaborated with practitioners at the three firms and developed a new learning-oriented and semi-automated early-stage cost estimation solution that was specifically designed for globally distributed software projects. The key idea of our solution was to augment the existing metrics-driven estimation methods with a case repository that stratified past incidents related to project effort estimation issues from the historical project databases at the firms into several generalizable categories. This repository allowed project managers to quickly and effectively “benchmark” their new projects to all past projects across the firms, and thereby learn from them. We deployed our solution at each of our three research sites for real-world field-testing over a period of six months. Project managers of 219 new large globally distributed projects used both our method to estimate the cost of their projects as well as the established metrics-based estimation approaches they were used to. Our approach achieved significantly reduced estimation errors (of up to 60%). This resulted in more than 20% net cost savings, on average, per project - a massive total cost savings across all projects at the three firms!

As the current generation of mobile smartphones become more powerful, they are being used to perform more resource intensive tasks making battery lifetime a major bottle-neck. In this paper, we present a technique called dynamic AoV lookahead for reducing wireless interface power consumption upto 50% while playing a popular, yet resource intensive, mobile multiplayer games.

In this paper, we examined the impact of project-level configurational choices of globally distributed software teams on project productivity, quality, and profits. Our analysis used data from 362 projects of four different firms. These projects spanned a wide range of programming languages, application domain, process choices, and development sites spread over 15 countries and 5 continents. Our analysis revealed fundamental tradeoffs in choosing configurational choices that are optimized for productivity, quality, and/or profits. In particular, achieving higher levels of productivity and quality require diametrically opposed configurational choices. In addition, creating imbalances in the expertise and personnel distribution of project teams significantly helps increase profit margins. However, a profit-oriented imbalance could also significantly affect productivity and/or quality outcomes. Analyzing these complex tradeoffs, we provide actionable managerial insights that can help software firms and their clients choose configurations that achieve desired project outcomes in globally distributed software development.

In this paper, we show how tone mapping techniques can be used to dynamically increase the image brightness, thus allowing the LCD backlight levels to be reduced. This saves significant power as the majority of the LCD's display power is consumed by its backlight. The Gamma function (or equivalent) can be efficiently implemented in smartphones with minimal resource cost. We describe how we overcame the Gamma function's non-linear nature by using adaptive thresholds to apply different Gamma values to images with differing brightness levels. These adaptive thresholds allow us to save significant amounts of power while preserving the image quality. We implemented our solution on a laptop and two Android smartphones. Finally, we present measured analytical results for two different games (Quake III and Planeshift), and user study results (using Quake III and 60 participants) that shows that we can save up to 68% of the display power without significantly affecting the perceived gameplay quality.

The current generation of mobile smartphones are not just devices for voice communication. Instead, they are frequently used as mobile PC replacements that are used to edit documents, browse the web, check email, and play games. However, this functionality comes at the cost of battery lifetimes. Indeed, to maintain the slim form factor required for these phones (which impacts the amount of battery that can be put into the phone), it is quite common for the battery lifetimes of smartphones to be significantly shorter compared to previous generation of "dumber" phones.

In this paper, we describe the design, analysis, implementation, and operational deployment of a real-time trip information system that provides passengers with the expected fare and trip duration of the taxi ride they are planning to take. This system was built in cooperation with a taxi operator that operates more than 15,000 taxis in Singapore. We first describe the overall system design and then explain the efficient algorithms used to achieve our predictions based on up to 21 months of historical data consisting of approximately 250 million paid taxi trips. We then describe various optimisations (involving region sizes, amount of history, and data mining techniques) and accuracy analysis (involving routes and weather) we performed to increase both the runtime performance and prediction accuracy. Our large scale evaluation demonstrates that our system is (a) accurate --- with the mean fare error under 1 Singapore dollar (~ 0.76 US$) and the mean duration error under three minutes, and (b) capable of real-time performance, processing thousands to millions of queries per second. Finally, we describe the lessons learned during the process of deploying this system into a production environment.

In this paper, we study the decision making process involved in the five year lifecycle of a Bluetooth software product produced by a large, multi-national test and measurement firm. In this environment, customer change requests either have to be added as a standard feature in the product, or developed as a special customized version of the product. We first discuss the influential factors, such as evolving standards, market share, installed-base, and complexity, which collectively determined how the firm responded to product change requests. We then develop a predictive decision model to test the collective impact of these factors on determining whether to standardize or customize a customer's change request. Finally, we develop and test a customization cost estimation model, for use by software product teams, which specifically accounts for factors unique to the customization stage of a product lifecycle.

We present the results of a three year field study of the software development process choices made by project teams at two leading offshore vendors. In particular, we focus on the performance implications of project teams that chose to augment structured, plan-driven processes to implement the CMM level-5 key process areas (KPAs) with agile methods. Our analysis of 112 software projects reveals that the decision to augment the firm-recommended, plan-driven approach with improvised, agile methods was significantly affected by the extent of client knowledge and involvement, the newness of technology, and the project size. Furthermore this decision had a significant and mostly positive impact on project performance indicators such as reuse, rework, defect density, and productivity.

In this paper, we present the design and evaluation of a near-field communication-based mobile p2p payment application, called mFerio, that is designed to replace cash-based transactions. We first identify design criteria that payment systems should satisfy and then explain how mFerio, relative to those criteria, improves on the limitations of cash-based systems. We next describe mFerio's implementation and user interface design, focusing on the balance between usability and security. Finally, we present the results of a two-phase user study, involving a total of 104 people, that shows that mFerio has low cognitive load and is also fast, accurate, and easy to use - even outperforming cash in terms of speed and cognitive load in common payment situations.

Cyber foraging is the transient and opportunistic use of compute servers bymobile devices. The short market life of such devices makes rapid modification of applications for remote execution an important problem. We describe a solution that combines a "little language" for cyber foraging with an adaptive runtime system. We report results from a user study showing that even novice developers are able to successfully modify large, unfamiliar applications in just a few hours. We also show that the quality of novice-modified and expert-modified applications are comparable in most cases.

Software firms are increasingly distributing their software development effort across multiple locations. In this paper we present the results of a two year field study that investigated the effects of dispersion on the productivity and quality of distributed software development. We first develop a model of distributed software development. We then use the model, along with our empirically observed data, to understand the consequences of dispersion on software project performance. Our analysis reveals that, even in high process maturity environments, a) dispersion significantly reduces development productivity and has effects on conformance quality, and b) these negative effects of dispersion can be significantly mitigated through deployment of structured software engineering processes.

Remote execution can transform the puniest mobile device into a computing giant able to run resource-intensive applications such as natural language translation, speech recognition, face recognition, and augmented reality. However, easily partitioning these applications for remote execution while retaining application-specific information has proven to be a difficult challenge. In this paper, we show that automated dynamic repartitioning of mobile applications can be reconciled with the need to exploit application-specific knowledge. We show that the useful knowledge about an application relevant to remote execution can be captured in a compact declarative form called tactics. Tactics capture the full range of meaningful partitions of an application and are very small relative to code size. We present the design of a tactics-based remote execution system, Chroma, that performs comparably to a runtime system that makes perfect partitioning decisions. Furthermore, we show that Chroma can automatically use extra resources in an over-provisioned environment to improve application performance.

Wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. We present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both SACK and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled.

This paper examines the attributes of TCP tunnels which are TCP circuits that carry IP packets and benefit from the congestion control mechanism of TCP/IP. The deployment of TCP tunnels reduces the many flows situation on the Internet to that of a few flows. TCP tunnels eliminate unnecessary packet loss in the core routers of the congested backbones which waste precious bandwidth leading to congestion collapse due to unresponsive UDP flows. We also highlight that the use of TCP tunnels can, in principle, help prevent certain forms of congestion collapse described by Floyd & Fall (see IEEE/ACM Transactions on Networking, vol.7, no.4, p.458-72, 1999). Using a testbed often Intel PCs running the Linux operating system and traffic generators simulating user applications, we explore: the benefits which TCP tunnels confer upon its payload of user IP traffic; the impact on the congestion within network backbones, and the protection that tunnels offer with respect to the various competing classes of traffic in terms of bandwidth allocation and reduced retransmissions. The deployment of TCP tunnels on the Internet and the issues involved are also discussed and we conclude that with the RFC2309 recommendation of using random early drop (RED) as the default packet-drop policy in Internet routers, coupled with the implementation of a pure tunnel environment on backbone networks makes the deployment of TCP tunnels a feasible endeavour worthy of further investigation.