Restoring the patient’s occlusal function of broken teeth is a challenging task since tooth texture is very complex, a slight deviation may affect the patient’s chewing function and temporomandibular joint function. Therefore, how to efficiently repair the complete shape and real surface of the crown is a critical problem. Traditional technologies are hard to restore complete shape of the dental crown or lack inlay surface details, due to dataset limitations and complexity of missing parts. In this paper, we propose a multi-view crown restoration framework MVDC based on contrastive learning. Specifically, MVDC contains: 1) a multi-view generator with a specially designed loss measurement by using contrastive learning; 2) a multi-scale discriminator mechanism able to consider relation and consistency between teeth from different scales; 3) an occlusal groove extraction network to extract the occlusal details. We conducted extensive experiments on existing public datasets. The results showcase the superior performance of MVDC.

Traffic flow prediction provides valuable traffic information to transportation agencies and individuals in advance. Compared to next-step prediction, multi-step prediction provides users with traffic information for a longer time horizon, allowing users to have a more comprehensive understanding of traffic conditions. So far, various methods have been proposed for multi-step traffic flow prediction. However, most of them become sub-optimal in effectively detecting the spatio-temporal correlations of traffic data. Furthermore, as the number of prediction steps increases, the input data used to predict the flow of the next step tends to deviate further from the ground truth value. This deviation leads to a rapid decrease in prediction accuracy as the number of prediction steps increases. To address these issues, in this paper, we propose a deep spatio-temporal representation learning network named ST-RLNet for multi-step traffic flow prediction. The goal is to effectively generate the traffic data representation by better capturing the complex correlations of the data. In particular, we design a network called 3D-ConvLSTMNet to effectively extract short-term and long-term spatio-temporal data correlations for the next step prediction. To solve the performance degradation problem, we propose a feedback mechanism called PS-Feedback to dynamically reconstruct temporal correlation representations of input traffic flow for each round of next-step prediction. To evaluate the performance of the ST-RLNet, we conduct extensive experiments on two real-world datasets. Experimental results show that the ST-RLNet outperforms the state-of-the-art methods in both next-step and multi-step predictions, and exhibits consistent high performance under different traffic flows.

The increasing single-cell RNA sequencing (scRNA-seq) data enable researchers to explore cellular heterogeneity and gene expression profiles, offering a high-resolution view of the transcriptome at the single-cell level. However, the dropout events, which are often present in scRNA-seq data, remaining challenges for downstream analysis. Although a number of studies have been developed to recover single-cell expression profiles, their performance may be hindered due to not fully exploring the inherent relations between genes. To address the issue, we propose scDTL, a deep transfer learning based approach for scRNA-seq data imputation by harnessing the bulk RNA-sequencing information. We firstly employ a denoising autoencoder trained on bulk RNA-seq data as the initial imputation model, and then leverage a domain adaptation framework that transfers the knowledge learned by the bulk imputation model to scRNA-seq learning task. In addition, scDTL employs a parallel operation with a 1D U-Net denoising model to provide gene representations of varying granularity, capturing both coarse and fine features of the scRNA-seq data. Finally, we utilize a cross-channel attention mechanism to fuse the features learned from the transferred bulk imputation model and U-Net model. In the evaluation, we conduct extensive experiments to demonstrate that scDTL could outperform other state-of-the-art methods in the quantitative comparison and downstream analyses.

Personalized patient representation learning (PPRL) is a critical element in clinical risk prediction. It aims to obtain a complete portrait of each patient based on Electronic Health Records (EHR). Although existing works have achieved remarkable progress in healthcare prediction, there are still three major issues. First, feature correlation is crucial for risk prediction, but it has not yet been fully exploited by existing works. Second, variation pattern of dynamic feature contains useful information about patient's physical status, but adaptive pattern recognition is still a challenge. Third, existing works usually adopt a two-stage embedding process to process each dimension of the EHR data. However, some useful low-level information for PPRL will be lost. To address these issues, in this paper, we propose a fine-grained PPRL architecture named FG RL- N et for clinical risk prediction based on EHR. Specifically, we propose a Medical Feature Correlation Detection Module (FCM) to effectively learn the feature correlations for each patient and a Temporal Variation Pattern Recognition Module (TVM) to effectively detect the variation patterns of each dynamic feature. Moreover, we design a Fine-Grained Representation Mechanism (FGRM) to preserve the low-level information (from both feature and visit dimensions) useful for risk prediction. In addition, in the stage of data preprocessing, We utilize generic medical classification knowledge to classify numerical dynamic data. We conduct the in-hospital mortality experiment and the decompensation experiment on a real-world dataset. The experiment results show that the FGRL-Net outperforms state-of-the-art approaches. The source code is provided in github https://github.com/JackyChio/FGRL-Net.

Predicting urban crowd patterns/flows is a challenging task due to complex spatial–temporal (ST) dependencies. In this article, we aim to examine and report the capability and effectiveness of the current most widely used graph convolutional networks (GCNs) on mobile data analysis in ST networks for crowd flow forecasting. Specifically, we propose a novel dual-stream framework leveraging multigraph with attentive ST networks (MG-ASTN) to simultaneously predict crowd in–out flow and origin–destination (OD) flow based on the trajectory data collected by on-board devices (e.g., GPS). MG-ASTN utilizes multi-GCNs encoding non-Euclidean correlations to explore pairwise relationships among regions. In addition, we further apply a cross-channel attention mechanism with 3-D temporal convolutional network to address the heterogeneity of ST features and capture more meaningful data representations for multitask learning. In the evaluation, we conduct experiments based on two real-world data sets and verify most well-known state-of-the-art methods for crowd flow prediction. The results demonstrate that MG-ASTN could outperform other solutions—in–out flow prediction with lowest RMSE and MAE, and OD flow prediction beyond others in most cases, thus it has great potential in modeling the complex correlations among regions in ST networks and enabling accurate prediction in urban computing.

Wi-Fi technology is becoming a promising enabler of device-free fitness tracking to provide reviews and recommendations for effective homely exercise. State-of-the-art Wi-Fi fitness assistants succeed in recognizing the simple meta-movements (e.g., Push-Up and Squat) with discrete and repeatable patterns. Unfortunately, these prior attempts can hardly scale to the combination movements of ever-growing interests in intensive fitness programs. Combination movements are composed of meta-movements that are mutually concatenated or inserted. They have a compound characteristic that inherits from the diversity of combination orders and continuity of meta-movements. The compound characteristic causes substantial training data collection costs and a challenge of combination decomposition that is a prerequisite for providing fine-grained fitness assessment. To this end, we proposeInFit, a Wi-Fi-based device-free fitness assistant system for combination movements. First, we design a novel data augmentation method, namelyStitching-based Virtual Sample Generation(SVSG), to reduce the training data collection costs by generating virtual combination movements. Second, a 2-stage combination movement recognition model is designed to learn temporal dependencies between movements and decompose combination movements. From its outputs, we can tell whether a combination movement is standard. Extensive experimental results show that InFit can achieve an average recognition accuracy of$94\%$. With zero training samples of combination movements, the average accuracy is$40\%$higher than the baselines. In addition, SVSG can provide a general enhancement on multiple competing schemes with similar sensing tasks.

Gesture recognition by using Inertial Measurement Unit (IMU) sensors plays an important role in various Internet of Things (IOT) applications, e.g., smart home, intelligent medical system and so on. Traditional technologies usually utilize machine learning algorithms to train different gestures during the offline phase, then recognize the gesture during the online phase. However, such technologies cannot recognize these gestures without prior training. Even for the same gesture, with different gesture amplitude may result in unsuccessful recognition. Also if we change the person to perform the same gesture, the algorithms fails. In order to overcome these drawbacks, we propose an approach, which will be able to track the human body motion in real-time and also recognize complicated gestures. It utilizes the accelerometer information and proposes comprehensive localization algorithms for each deployed sensor attached on the human body. Then, it takes the correlation and limitation among body parts into account to recognize the gesture. Our experiments results show that, the successful recognition rate of our algorithm is 100%. Furthermore, any part of the human body can be well tracked, the tracking accuracy can reach$0.06m$.

Flow prediction attracts intensive research interests, since it can offer essential support to many crucial problems in public safety and smart city, e.g., epidemic spread prediction and medical resource allocation optimization. Among all the models in flow prediction, deep learning models (e.g., convolutional neural networks, recurrent neural networks, and graph neural networks) are popular and outperform other statistics and machine learning models, since they can learn intrinsic structures and extract features from spatial–temporal (ST) data. However, most of them set strict temporal periods in the prediction or separate the interaction between spatial and temporal correlations. Therefore, the prediction accuracy is affected. To overcome the difficulties, we propose a flow prediction network attentive spatial–temporal convolutional network (ASTCN), which can effectively handle large-scale flow data and learn complex features. In ASTCN, we leverage an attention mechanism to overcome the previous problem of strict temporal periods, and can effectively fuse ST data with multiple factors from different time-series sources. Furthermore, we propose a causal 3-D convolutional layer based on temporal convolutional networks (TCNs). It can simultaneously extract both spatial and temporal features to improve the prediction accuracy. We comprehensively conducted our experiments based on real-world data sets. Experimental results show that ASTCN outperforms the state-of-the-art methods by at least 3.78% in root mean square error. Therefore, ASTCN is a potential solution to other large-scale ST problems.

Inattentive driving is one of the high-risk factors that causes a large number of traffic accidents every year. In this article, we aim to detect driver inattention leveraging on large-scale vehicle trajectory data while at the same time explore how do these inattentive events affect driver behaviors and what following reactions they may cause, especially, for commercial vehicles. Specifically, the proposed system targets four most commonly occurring critical inattentive events, including smoking, phone call, turning back, and yawning. By applying a deep convolutional neural network (CNN) (Inception v3) with two data augmentation routines—Mixup and synthetic minority oversampling technique (Smote), we are able to balance the training data distribution and improve the generalization of the classification model. Then, based on the output derived from the inattention detection combining with point of interest (POI) and climate data, a long short-term memory (LSTM)-based model is deployed to predict driver upcoming abnormal operations on road (due to inattention) which may result in potential dangerous driving conditions, such as sudden acceleration/deceleration, aggressive left/right lane change, etc. To evaluate our proposed system, we collect more than 120000 real-world driving traces from over 200 drivers. The experimental results show that our model achieves a weight accuracy (WA) of 92.27% for inattentive driving detection and a WA of 91.67% for abnormal driving prediction, demonstrating its great potential of shaping good driving habits and promoting road safety.

Nowadays transceiver-free (also referred to as device-free) localization using Received Signal Strength (RSS) is a hot topic for researchers due to its widespread applicability. However, RSS is easily affected by the indoor environment, resulting in a dense deployment of reference nodes. Some hybrid systems have already been proposed to help RSS localization, but most of them require additional hardware support. In order to solve this problem, in this paper, we propose two algorithms, which leverage the Packet Received Rate (PRR) to help RSS localization without additional hardware support. Moreover, we take the environment noise information into consideration by utilizing the Signal-to-Noise Ratio (SNR) which is based on the RSS and Noise Floor (NF) information instead of pure RSS. Thus, we can alleviate the noise effect in the environment and make our system more sensitive to the target. Specifically, when reference nodes are sparsely deployed and RSS is very weak, PRR and SNR can help in performing localization more accurately. Our BEYOND RSS system is based on sparse wireless sensor networks, wherein the experimental results show that the average localization error of our approach outperforms the pure RSS based approach by about 15.19%.

Given widely adopted vehicle tracking technologies, usage-based insurance has been a rising market over the past few years. With potential discounts from insurance companies, customers voluntarily install sensing devices in their vehicles for insurance companies, which are utilized to analyze their historical driving patterns to derive the risks of future driving. However, it is challenging to characterize and predict driving patterns, especially for new users with limited data. To address this issue, we propose and evaluate a system called MoCha to accurately characterize driving patterns for usage-based insurance. The key question we aim to explore with MoCha is whether we can fully explore long-term driving patterns of new users with only limited historical data of themselves by leveraging abundant data of other users and contextual information. To answer this question, we design (i) a multi-level driving pattern modeling component to capture the spatial-temporal dependency on both individual and group level, and (ii) a multi-task learning method to utilize underlying relations of driving metrics and predict multiple driving metrics simultaneously. We implement and evaluate MoCha with real-world on-board diagnostics data from a large insurance company with more than 340,000 vehicles. Further, we validate the usefulness of MoCha by predicting driving risks based on real-world claim data in a Chinese city, Shenzhen.

Strength training is becoming increasingly popular among all age groups, as it helps the participants increase muscle strength, improve body flexibility, reduce health risks, and reshape physical forms. However, strength training imposes strict regulations on gestures and requires professional instruction in real time for the sake of body-building efficiency and safety. For this purpose, in this article, we propose a novel low-cost system named iCoach, to provide real-time monitoring and coaching service for strength training participants. Specifically, we design and implement a smart fitness glove, which can be seamlessly equipped with a pervasive inertial unit. With this customized but low-cost device, we can recognize various training programs, detect nonstandard behaviors while exercising, and assess exercising qualities of a user. Our primary experimental results show that iCoach can recognize 15 sets of training programs, detect three common nonstandard behaviors, and assess the quality of training with high accuracy and reliability.

Profiling driver behaviors and designing appropriate pricing models are essential for auto insurance companies to gain profits and attract customers (drivers). The existing approaches either rely on static demographic information like age, or model only coarse-grained driving behaviors. They are therefore ineffective to yield accurate risk predictions over time for appropriate pricing, resulting in profit decline or even financial loss. Moreover, existing pricing strategies seldom take profit maximization into consideration, especially under the enterprise constraints. The recent growth of vehicle telematics data (vehicle sensing data) brings new opportunities to auto insurance industry, because of its sheer size and fine-grained mobility for profiling drivers. But, how to fuse these sparse, inconsistent and heterogeneous data is still not well addressed. To tackle these problems, we propose a unified PPP (Profile-Price-Profit) framework, working on the real-world large-scale vehicle telematics data and insurance data. PPP profiles drivers' fine-grained behaviors by considering various driving features from the trajectory perspective. Then, to predict drivers' risk probabilities, PPP leverages the group-level insight and categorizes drivers' different temporal risk change patterns into groups by ensemble learning. Next, the pricing model in PPP incorporates both the demographic analysis and the mobility factors of driving risk and mileage, to generate personalized insurance price for supporting flexible premium periods. Finally, the maximal profit problem proves to be NP-Complete. Then, an efficient heuristic-based dynamic programming is proposed. Extensive experimental results demonstrated that, PPP effectively predicts the driver's risk and outperforms the current company's pricing strategy (in industry) and the state-of-the-art approach. PPP also achieves near the maximal profit (difference by only 3%) for the company, and lowers the total price for the drivers.

Indoor localization technologies based on Radio Signal Strength (RSS) attract many researchers’ attentions, since RSS can be easily obtained by wireless devices without additional hardware. However, such technologies are apt to be affected by indoor environments and multipath phenomenon. Thus, the accuracy is very difficult to improve. In this paper, we put forward a method, which is able to leverage various other resources in localization. Besides the traditional RSS information, the environmental physical features, e.g., the light, temperature, and humidity information, are all utilized for localization. After building a comprehensive fingerprint map for the above information, we propose an algorithm to localize the target based on Naïve Bayesian. Experimental results show that the successful positioning accuracy can dramatically outperform traditional pure RSS‐based indoor localization method by about 39%. Our method has the potential to improve all the radio frequency (RF) based localization approaches.

Among various ranging techniques, Radio Signal Strength (RSS) based approaches attract intensive research interests because of its low cost and wide applicability. RSS-based ranging is prone to be affected by the multipath phenomenon which allows the radio signals to reach the destination through multiple propagation paths. To address this issue, previous works try to profile the environment and refer this profile during run-time. In a practical dynamic environment, however, the profile frequently changes and the painful retraining is needed. Ratherthan such static ways of profiling the environments, in this paper, we tryto accommodate the environmental dynamics automatically in real-time. The key observation is that given a pair of nodes, the RSS at different spectrum channels will be different. This difference carries the valuable phase information of the radio signals. By analyzing these RSS values, we are able to identify the amplitude of signals solely from the Line-of-Sight (LOS) path. This LOS amplitude is a simple function of the path length (the physical distance). We find that the analysis is a typical non-linear curvature fitting problem that has no general routing algorithms. We prove that, this problem format is ill-conditioned which has no stable and trustable solutions. To deal with this issue, we further explore the practical considerations for the problem and modify it to a greatly improved conditioning shape. We solve the problem by numerical iterations and implement these ideas in a real-time indoor tracking system called MuD. MuD employs only three TelosB nodes as anchors. The experiment results show that in a dynamic environment where five people move around, the averaged localization error is about 1 meter. Compared with the traditional RSS-based approaches in dynamic environments, the accuracy improves up to 10 times.

Traditional radio-based gesture recognition approaches usually require the target to carry a device (e.g., an EMG sensor or an accelerometer sensor). However, such requirement cannot be satisfied in many applications. For example, in smart home, users want to control the light on/off by hand gesture, without carrying any device. To overcome this draw-back, in this paper, we propose two algorithms able to recognize the target gesture (mainly the human hand gesture) without carrying any device, based on just Radio Signal Strength Indicator (RSSI). Our platform utilizes only 6 telosB sensor nodes and is with a very easy deployment. Experiment results show that the successful recognition radio can reach around 80% in our system.

Transceiver-free object localization is essential for emerging location-based service, e.g., the safe guard system and asset security. It can track indoor target without carrying any device and has attracted many research effort. Among these technologies, Radio Signal Strength (RSS) based approaches are very popular because of their low-cost and wide applicability. In such work, usually a large number of reference nodes have to be deployed. However, if in a very large area, many labor work to measure the positions of the reference nodes have to be performed, result in not practical in real scenario. In this paper, we propose Double Free, which can accurately track transceiver-free object without measuring the positions of the reference nodes. Users may randomly deploy nodes in a 2D area, e.g., the ceiling of the floor. Our Double Free contains two steps: reference node localization and target localization. The key to achieve the first step is to utilize the RSS difference in different channel to distinguish the Line-Of-Sight (LOS) signal from combined multiple paths' signal. Thus, the reference nodes can be accurately localized without additional hardware. In the second step, we propose two algorithms: Influential Link & Node (ILN) and MultiPath Distinguishing (MD). ILN is simple to implement, while MD can accurately model the additional signal caused by the target, then accurately localize the target. To implement this idea, 16 TelosB nodes are placed randomly in a 25×10m2laboratory. The experiment results show, the average localization error is only round 2 meters without requiring to measure the positions of reference nodes in advance. It shows enormous potential in those localization areas, where manual measurement is hard to perform, or hard labor work want to be saved.

Radio frequency (RF) based technologies play an important role in indoor localization, since Radio Signal Strength (RSS) can be easily measured by various wireless devices without additional cost. Among these, radio map based technologies (also referred as fingerprinting technologies) are attractive due to high accuracy and easy deployment. However, these technologies have not been extensively applied on real environment for two fatal limitations. First, it is hard to localize multiple objects. When the number of target objects is unknown, constructing a radio map of multiple objects is almost impossible. Second, environment changes will generate different multipath signals and severely disturb the RSS measurement, making laborious retraining inevitable. Motivated by these, in this paper, we propose a novel approach, called Line-of-sight radio map matching, which only reserves the LOS signal among nodes. It leverages frequency diversity to eliminate the multipath behavior, making RSS more reliable than before. We implement our system MODLoc based on TelosB sensor nodes and commercial 802.11 NICs with Channel State Information (CSI) as well. Through extensive experiments, it shows that the accuracy does not decrease when localizing multiple targets in a dynamic environment. Our work outperforms the traditional methods by about 60 percent. More importantly, no calibration is required in such environment. Furthermore, our approach presents attractive flexibility, making it more appropriate for general RF-based localization studies than just the radio map based localization.

In traditional radio-based localization methods, the target object has to carry a transmitter (e.g., active RFID), a receiver (e.g., 802.11 × detector), or a transceiver (e.g., sensor node). However, in some applications, such as safe guard systems, it is not possible to meet this precondition. In this paper, we propose a model of signal dynamics to allow the tracking of a transceiver-free object. Based on radio signal strength indicator (RSSI), which is readily available in wireless communication, three centralized tracking algorithms, and one distributed tracking algorithm are proposed to eliminate noise behaviors and improve accuracy. The midpoint and intersection algorithms can be applied to track a single object without calibration, while the best-cover algorithm has higher tracking accuracy but requires calibration. The probabilistic cover algorithm is based on distributed dynamic clustering. It can dramatically improve the localization accuracy when multiple objects are present. Our experimental test-bed is a grid sensor array based on MICA2 sensor nodes. The experimental results show that the localization accuracy for single object can reach about 0.8 m and for multiple objects is about 1 m.

Transceiver-free object tracking is to trace a moving object that does not carry any communication device in an environment with some monitoring nodes predeployed. Among all the tracking technologies, RF-based technology is an emerging research field facing many challenges. Although we proposed the original idea, until now there is no method achieving scalability without sacrificing latency and accuracy. In this paper, we put forward a real-time tracking system RASS, which can achieve this goal and is promising in the applications like the safeguard system. Our basic idea is to divide the tracking field into different areas, with adjacent areas using different communication channels. So, the interference among different areas can be prevented. For each area, three communicating nodes are deployed on the ceiling as a regular triangle to monitor this area. In each triangle area, we use a Support Vector Regression (SVR) model to locate the object. This model simulates the relationship between the signal dynamics caused by the object and the object position. It not only considers the ideal case of signal dynamics caused by the object, but also utilizes their irregular information. As a result, it can reach the tracking accuracy to around 1 m by just using three nodes in a triangle area with 4 m in each side. The experiments show that the tracking latency of the proposed RASS system is bounded by only about 0.26 m. Our system scales well to a large deployment field without sacrificing the latency and accuracy.

Radio Frequency (RF) based technologies play an important role in indoor localization, since Radio Signal Strength (RSS) is easily achieved by various wireless devices without additional cost. Among these, radio map based technologies (also referred as fingerprinting technologies) are attractive. They are able to accurately localize the targets without introducing many reference nodes. Therefore, their hardware cost is low. However, this technology has two fatal limitations. First, it is hard to localize multiple objects, since radio map has to collect all the RSS information when targets are at different possible positions. But due to the multipath phenomenon, different number of target nodes at different positions often generates different multipath signals. So when the target object number is unknown, constructing a radio map of multiple objects is almost impossible. Second, environment changes will generate different multipath signals and severely disturb the RSS measurement, making laborious retraining inevitable. In this paper, we propose a novel method, called Line-Of-Sight (LOS) map matching. It leverages frequency diversity of wireless nodes to eliminate the multipath behavior, making RSS more reliable than before. These reliable RSS signals are able to construct the radio map, which only reserves the LOS signal among nodes. We call it LOS radio map. The number of objects and environment changes will not affect the LOS signal between the targets and reference nodes. Such map is able to be constructed easily and require no training if reference nodes are carefully redeployed. Our basic idea is to utilize the frequency diversity of each wireless node to transmit data in different spectrum channel. Then it solves the optimization problem to get the LOS signal. Our experiments are based on TelosB sensor platform with three reference nodes. It shows that the accuracy will not decrease when localizing multiple targets in a dynamic environment. It outperforms the traditional methods by about60%. More importantly, no calibration is required in such environment. Furthermore, our approach presents attractive flexibility, making it more appropriate for general RF-based localization studies than just the radio map based localization.

Among the various ranging techniques, Radio Signal Strength (RSS) based approaches attract intensive research interests because of its low cost and wide applicability. RSS-based ranging is apt to be affected by the multipath phenomenon which allows the radio signals to reach the destination through multiple propagation paths. To address this issue, previous works try to profile the environment and refer this profile in run-time. In practical dynamic environments, however, the profile frequently changes and the painful retraining is needed. Rather than such static ways of profiling the environments, in this paper, we try to accommodate the environmental dynamics automatically in real-time. The key observation is that given a pair of nodes, the RSS at different spectrum channels will be different. This difference carries the valuable phase information of the radio signals. By analyzing these RSS values, we are able to identify the amplitude of signals solely from the Line-of-Sight (LOS) path. This LOS amplitude is a simple function of the path length (the physical distance). We find that the analysis is a typical non-linear curvature fitting problem that has no general routing algorithms. We prove this problem format is ill-conditioned which has no stable and trustable solutions. To deal with this issue, we further explore the practical considerations for the problem and reform it to a greatly improved conditioning shape. We solve the problem by numerical iterations and implement these ideas in a real-time indoor tracking system called MuD. MuD employs only three TelosB nodes as anchors. The experiment results show that in a dynamic environment where five people move around, the averaged localization error is 1 meter. Compared with the traditional RSS-based approaches in dynamic environment, the accuracy improves up to 10 times.

RFID tag identification is a crucial problem in UHF RFID systems. Traditional tag identification algorithms can be classified into two categories, ALOHA-based and tree-based. Both of them are inefficient due to the incidental high coordination cost. In this paper, we bring CSMA into UHF RFID systems to enhance tag read rate by reducing coordination cost. However, it is not straightforward due to the simple hardware design of passive RFID tags, which is unable to sense the transmissions or collisions of other tags. To tackle this challenge, we propose receiver-based CSMA (RCSMA) in this paper. In RCSMA, the reader notifies the tags channel condition. According to different sensing results of reader's notifications, the tags take corresponding actions, e.g., random back off. RCSMA does not require special RFID tag hardware design. An absorbing Markov chain model is presented to analyze the performance of RCSMA and shown to be consistent with the simulation results. Compared with optimized ALOHA-based algorithms and optimized tree-based algorithms, RCSMA can enhance the tag read rate by 30-70 percent under different reader and tag data rates.

Energy efficiency is a critical criterion in wireless sensor networks (WSN). Given the energy consumption of a node, or even the whole network, is precisely measured. Great improvement can be expected in the WSN system optimization. In this paper, we propose a versatile nodal energy consumption monitoring schema, which precisely measures the energy consumption of each node at any moment. In addition, our schema can be integrated with existing test bed technologies to measure the energy consumption of the overall network. Results show that our method can fulfill various challenges in energy consumption measurement in wireless sensor network. We believe the design and implementation of this monitoring schema is an important move towards accurate and flexible energy efficiency analysis.

Transceiver-free object tracking is to trace a moving object without carrying any communication device in an environment where the environment is pre-deployed with some monitoring nodes. Among all the tracking technologies, RF-based technology is an emerging research field facing many challenges. Although we proposed the original idea, until now there is no method achieving scalability without sacrificing latency and accuracy. In this paper, we put forward a real-time tracking system RASS, which can achieve this goal and is promising in the applications like the safeguard system. Our basic idea is to divide the tracking field into different areas, with adjacent areas using different communication channels. So the interference among different areas can be prevented. For each area, three communicating nodes are deployed on the ceiling as a regular triangle to monitor this area. In each triangle area, we use a Support Vector Regression (SVR) model to locate the object. This model simulates the relationship between the signal dynamics caused by the object and the object position. It not only considers the ideal case of signal dynamics caused by the object, but also utilizes their irregular information. As a result it can reach the tracking accuracy to around 1m by just using three nodes in a triangle area with 4m in each side. The experiments show that the tracking latency of the proposed RASS system is bounded by only about 0.26s. Our system scales well to a large deployment field without sacrificing the latency and accuracy.

Traditional RF-based indoor positioning approaches use only Radio Signal Strength Indicator (RSSI) to locate the target object. But RSSI suffers significantly from the multi-path phenomenon and other environmental factors. Hence, the localization accuracy drops dramatically in a large tracking field. To solve this problem, this paper introduces one more resource, the dynamic of RSSI, which is the variance of signal strength caused by the target object and is more robust to environment changes. By combining these two resources, we are able to greatly improve the accuracy and scalability of current RF-based approaches. We call such hybrid approach COCKTAIL. It employs both the technologies of active RFID and Wireless Sensor Networks (WSNs). Sensors use the dynamic of RSSI to figure out a cluster of reference tags as candidates. The final target location is estimated by using the RSSI relationships between the target tag and candidate reference tags. Experiments show that COCKTAIL can reach a remarkable high degree of localization accuracy to 0:45m, which outperforms significantly to most of the pure RF-based localization approaches.

Sensing coverage is essential for most applications in wireless networks. In traditional coverage problem study, the disk coverage model has been widely applied because of its simplicity. Though notable recent works point out that the disk model has many critical limitations when applied in practice, few successful works have been conducted to comprehensively study the issue. Motivated by this, in this paper we propose a new coverage model called T-R model. T-R model is derived from a real application of transceiver-free object detection. Compared with the traditional disk model, T-R model is able to describe many new coverage features such as the probabilistic coverage, the link-centric coverage units and the correlations between multiple coverage units. These new capabilities make T-R model a better abstraction of individual sensors. To evaluate the performance of T-R model, we conduct comprehensive empirical studies based on a test-bed of 30 telosB nodes. Experimental results show that the TR model can adequately describe the sensing behavior in the transceiver-free object detection applications. The average error between the model and the reality is only 8%. Moreover, T-R model presents attractive flexibility, making it more appropriate for general coverage problem studies than the transceiver-free object detection.

RF-based transceiver-free object tracking, originally proposed by the authors, allows real-time tracking of a moving object, where the object does not have to be equipped with an RF transceiver. Our previous algorithm, the best cover algorithm, suffers from a drawback, i.e., it does not work well when there are multiple objects in the tracking area. In this paper, we propose a localization model of distance, transmission power and the signal dynamics caused by the objects. The signal dynamics are derived from the measured radio signal strength indication (RSSI). Using this new model, we propose the ldquoprobabilistic cover algorithmrdquo which is based on distributed dynamic clustering thus it can dramatically improve the localization accuracy when multiple objects are present. Moreover, the probabilistic cover algorithm can reduce the tracking latency in the system. We argue that the small overhead of the proposed algorithm makes it scalable for large deployment. Experimental results show that in addition to its ability to identify multiple objects, the tracking accuracy is improved at a rate of 10% to 20%.

In traditional radio-based localization methods, the target object has to carry a transmitter (e.g., active RFID), a receiver (e.g., 802.11x detector), or a transceiver (e.g., sensor node). However, in some applications, such as safe guard systems, it is not possible to meet this precondition. In this paper, we propose a model of signal dynamics to allow tracking of transceiver-free objects. Based on radio signal strength indicator (RSSI), which is readily available in wireless communication, three tracking algorithms are proposed to eliminate noise behaviors and improve accuracy. The midpoint and intersection algorithms can be applied to track a single object without calibration, while the best-cover algorithm has potential to track multiple objects but requires calibration. Our experimental test-bed is a grid sensor array based on MICA2 sensor nodes. The experimental results show that the best side length between sensor nodes in the grid is 2 meters and the best-cover algorithm can reach localization accuracy to 0.99 m