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Automatic extraction of road from multisource remote sensing data has always been a challenging task. Factors such as shadow occlusion and multisource data alignment errors prevent current deep learning-based road extraction methods from acquiring road features with high complementarity, redundancy, and crossover. Unlike previous works that capture contexts by multiscale feature fusion, we propose a dual attention dilated-LinkNet (DAD-LinkNet) to adaptively integrate local road features with their global dependencies by joint using satellite image and floating vehicle trajectory data. First, a joint least-squares feature matching-based floating vehicle trajectory correction model is used to correct the floating vehicle trajectory; then a convolutional network model DAD-LinkNet based on a dual-attention mechanism is proposed, and road features are extracted from the channel domain and spatial domain of the target image in turn by constructing a dual-attention module in the dilated convolutional layer and adopting a cascade connection; a weighted hyperparameter loss function is used as the loss function of the model; finally, the road extraction is completed based on the proposed DAD-LinkNet model. Experiments on three datasets show that the proposed DAD-LinkNet model outperforms the state-of-the-art methods in terms of accuracy and connectivity.

Unlike standalone embedded devices, behaviors of a cyber-physical system (CPS) are highly dynamic. Many parameter values (e.g., those related to nature environment and third party black box functions) are unknown offline. Furthermore, distributed sub-CPSs may exchange data online. In this article, we first propose the concept of parametric hybrid automata (PHA) to describe such complex CPSs. As some PHA parameter values are unknown until runtime, conventional offline model checking is infeasible. Instead, we propose to carry out PHA model checking online, as a fault prediction mechanism. However, this usage is challenged by the high time cost of state reachability verification, which is the conventional focus of model checking. To address this challenge, we propose that the model checking shall focus on online scenario reachability validation instead. Furthermore, we propose a mechanism to compose/decompose scenarios. Our scenario reachability validation can exploit linear programming to achieve polynomial time cost. Evaluations on a state-of-the-art train control system show that our approach can cut online model checking time cost from over 1 h to within 200 ms.

In a reconfigurable battery pack, the connections among cells can be changed during operation to form different configurations. This can lead a battery, a passive two-terminal device, to a smart battery that can reconfigure itself according to the requirement to enhance operational performance. Several hardware architectures with different levels of complexities have been proposed. Some researchers have used existing hardware and demonstrated improved performance on the basis of novel optimization and scheduling algorithms. The possibility of software techniques to benefit the energy storage systems is exciting, and it is the perfect time for such methods as the need for high-performance and long-lasting batteries is on the rise. This novel field requires new understanding, principles, and evaluation metrics of proposed schemes. In this article, we systematically discuss and critically review the state of the art. This is the first effort to compare the existing hardware topologies in terms of flexibility and functionality. We provide a comprehensive review that encompasses all existing research works, starting from the details of the individual battery including modeling and properties as well as fixed-topology traditional battery packs. To stimulate further research in this area, we highlight key challenges and open problems in this domain.

In this paper, we present a deep hybrid model to detect abnormal flights. Deep hybrid models for anomaly detection use deep neural networks mainly autoencoder as feature extractors, the features learned within the hidden representations of autoencoder are then input to cluster algorithm to detect abnormal flights. The model can detect flight anomalies and associated risks without requiring predefined criteria or domain knowledge. In this paper, 2018 annual flight data of Daocheng Yading airport was taken as the experimental data which contains 981 flights. Our model performed well and 91 abnormal flights were detected.

This paper analyzes various UWB ranging methods such as SS-TWR and ADS-TWR. The Clock skew and antenna delay are two of the main sources of error.[1] Based on the analysis, this paper proposes a new chaotic particle swarm optimization algorithm for antenna delay, which uses the chaos particle swarm optimization algorithm based on the chaos optimization idea to search for the optimal antenna delay parameters, so as to obtain the antenna delay error of a smaller order of magnitude. Through experimental tests, the ranging error is effectively suppressed compared with the conventional method.

In this work, we aim to propose a reliable automatic highway on-ramp smart vehicle merging protocol that tolerates arbitrary wireless packet losses, and guarantees the widely adopted safety rule of Constant Time Headway (CTH) [1] . This is different from the existing literature, which assumes reliable communications infrastructure (e.g. [2] ) or focuses on safety rules other than the CTH (e.g. [3] ).

This paper presents an experimental study to compare the performance of model-free control strategies for pneumatic soft robots. Fabricated using soft materials, soft robots have gained much attention in academia and industry during recent years because of their inherent safety in human interaction. However, due to structural flexibility and compliance, mathematical models for these soft robots are nonlinear with an infinite degree of freedom &#x0028 DOF&#x0029 . Therefore, accurate position &#x0028 or orientation &#x0029 control and optimization of their dynamic response remains a challenging task. Most existing soft robots currently employed in industrial and rehabilitation applications use model-free control algorithms such as PID. However, to the best of our knowledge, there has been no systematic study on the comparative performance of model-free control algorithms and their ability to optimize dynamic response, i.e., reduce overshoot and settling time. In this paper, we present comparative performance of several variants of model-free PID-controllers based on extensive experimental results. Additionally, most of the existing work on model-free control in pneumatic soft-robotic literature use manually tuned parameters, which is a time-consuming, labor-intensive task. We present a heuristic-based coordinate descent algorithm to tune the controller parameter automatically. We presented results for both manual tuning and automatic tuning using the Ziegler–Nichols method and proposed algorithm, respectively. We then used experimental results to statistically demonstrate that the presented automatic tuning algorithm results in high accuracy. The experiment results show that for soft robots, the PID-controller essentially reduces to the PI controller. This behavior was observed in both manual and automatic tuning experiments; we also discussed a rationale for removing the derivative term.

Control Cyber-Physical Systems (CPSs) constitute a major category of CPS. In control CPSs, in addition to the well-studied noises within the physical subsystem, we are interested in evaluating the impact of cross-domain noise : the noise that comes from the physical subsystem, propagates through the cyber subsystem, and goes back to the physical subsystem. Impact of cross-domain noise is hard to evaluate when the cyber subsystem is a black box, which cannot be explicitly modeled. To address this challenge, this article focuses on the two-level control CPS, a widely adopted control CPS architecture, and proposes an emulation based evaluation methodology framework. The framework uses hybrid model reachability to quantify the cross-domain noise impact, and exploits Lyapunov stability theories to reduce the evaluation benchmark size. We validated the effectiveness and efficiency of our proposed framework on a representative control CPS testbed. Particularly, 24.1% of evaluation effort is saved using the proposed benchmark shrinking technology.

The charging and discharging procedure of a battery is a typical electrochemical process, which can be modeled as a dynamic system. State of charge (SoC) is a commonly used measure to quantify the charge stored in the battery in relation to its full capacity. Recent efforts of optimizing battery performance require more accurate SoC information. The noise in sensor readings makes the estimation even more challenging, especially in battery-operated systems where the supply voltage of the sensor keeps changing. Traditionally used methods of Coulomb counting and extended Kalman filter suffer from the accumulation of noise and common phenomenon of biased noise, respectively. The traditional approach of dealing with ever-increasing demand for accuracy is to develop more complicated and sophisticated solutions, which generally require special models. A key challenge in the adoption of such systems is the inherent requirement of specialized knowledge and hit-and-trial-based tuning. In this paper, we explore a new dimension from the perspective of a self-tuning algorithm, which can provide accurate SoC estimation without error accumulation by creating a negative feedback loop and enhancing its strength to penalize the estimation error. Specifically, we propose a novel method, which uses a battery model and a conservative filter with a strong feedback, which guarantees that worst-case amplification of noise is minimized. We capitalize on the battery model for data fusion of current and voltage signals for SoC estimation. To compute the best parameters, we formulate the linear matrix inequality conditions, which are optimally solved using open-source tools. This approach also features a low computational expense during estimation, which can be used in real-time applications. Thorough mathematical proofs, as well as detailed experimental results, are provided, which highlight the advantages of the proposed method over traditional techniques.

We propose a cyber-physical system of unmanned quadcopters to locate air pollution sources in a timely manner. The system consists of a physical part and a cyber part. The physical part includes unmanned quadcopters equipped with multiple sensors. The cyber part carries out control laws. We simplify the control laws by decoupling the quadcopters’ horizontal-plane motion control from vertical motion control. To control the quadcopter’s horizontal-plane motions, we propose a controller that combines pollutant dynamics with quadcopter physics. To control the quadcopter’s vertical motions, we adopt an anti-windup proportional-integral (PI) controller. We further extend the horizontal-plane control laws from a single quadcopter to multiple quadcopters. The multi-quadcopter control laws are distributed and convergent. We implement a prototype quadcopter and carry out experiments to verify the vertical control laws. We also carry out simulations to evaluate the horizontal-plane control laws. With quadcopter parameters set commensurate with our prototype implementation’s, our simulations show that the control laws can drive quadcopters to locate pollution source(s) in a timely way.

A weighted directed flight network in the Belt and Road Initiative(BRI) region was constructed in this paper, which takes the airports as nodes and the connection relations between airports as edges. Based on the complex network, the structural characteristics of the BRI flight network are statistically analyzed. At the same time, the Markov clustering algorithm was used to explore the clustering characteristics of national airports. The research results showed that: l The average degree of nodes in the flight network is 13.36, which means there are more than 13 airports directly connected with the one in average; The average distance among the BRI flight network is about 3.2, which means any two airports can be reached within more than 3 transfers in the regions of BRI; 2 The degree distribution of the nodes in the flight network presented a power-law distribution, BRI flight network is a kind of typical scale-free network which means vast majority of airports have a very small number of direct connections with other airports while the few remaining airports possess most direct links; 3 In this paper, we got 12 clusters in which the number of airports is more than 10 based on Markov clustering, airports in the Belt and Road Initiative show the characteristic of spatial clustering, that is, airports near to each other in space gather together. This paper aims to provide support for the development and decision-making of the Belt and Road Initiative aviation industry.

Control-CPS software fault localization (SFL, aka bug localization) is of critical importance as bugs may cause major failures, even injuries/deaths. To locate the bugs in control-CPSs, SFL tools often demand many labeled ("correct"/"incorrect") source code execution traces as inputs. To label the correctness of these traces, we must judge the corresponding control-CPS physical trajectories' correctness. However, unlike discrete outputs, the boundaries between correct and incorrect physical trajectories are often vague. The mechanism (aka oracle) to judge the physical trajectories' correctness thus becomes a major challenge. So far, the ad hoc practice of ``human oracles'' is still widely used, whose qualities heavily depend on the human experts' expertise and availability. This paper proposes an oracle based on the well adopted autoregressive system identification (AR-SI). With proven success for controlling black-box physical systems, AR-SI is adapted by us to identify the buggy control-CPS as a black-box. We use this identification result as an oracle to judge the control-CPS's behaviors, and propose a methodology to prepare traces for control-CPS debugging. Comprehensive evaluations on classic control-CPSs with injected real-life and artificial bugs show that our proposed approach significantly outperforms the human oracle approach in SFL accuracy (recall) and latency, and in oracle false positive/negative rates. Our approach also helps discover a new real-life bug in a consumer-grade control-CPS.

Periodically online verification has been widely recognized as a practical and promising method to handle the non-deterministic and unpredictable behavior of dynamic CPS systems. However, it is a challenge to keep the online verification of CPS systems finishing quickly in time to give enough time for the running system to respond, if any error is detected. Nevertheless, the problems under verification for each cycle are highly similar to each other. Most of the differences are caused by run-time factors like changing of parameters’ values or the reorganization of active components in the system. Under this investigation, this paper presents an incremental verification technique for online verification of CPS systems. A method is given to distinguish the differences between the problem under verification and the previous verified problem. Then, by reusing the problem space of the previous verified problem as a warm-start base, the modified part can be introduced into the base, which can be solved incrementally and efficiently. A set of case studies on a real-case train control system is presented in this paper to demonstrate the performance of the incremental online verification technique.

Non-destructive measurement of hand vein is challenging but has potentialities in many applications. Because the hand veins are under skin, the 3D annotations of hand veins are hard to obtain, and the captured images also have much noise from the skins. The traditional binocular vision methods and supervised neural networks are hard to implement in such situation. In this paper, We propose a end-to-end self-supervised binocular network (SBMNet) to compute disparities by matching pixels between the left and right images without annotations. The Region Strategy and Perceptual Loss are adopted in the training phase to improve the accuracy and the robustness to the noise. We set up the hand vein measurement system and collect simulated and real hand vein data for evaluation. SBMNet has made a successful attempt on non-destructive hand vein measurement and also has impressive results on the public KITTI dataset.

In this article, we propose formation control of nonholonomic mobile robots avoiding obstacles in a distributed manner for cluttered environments. The introduction of a virtual robot restructures the formation control problem into a tracking control problem between the virtual reference robot and follower robots. A novel obstacle avoidance approach is proposed based upon the scaling of whole (partial) formation corresponding to a centralized (distributed) framework. For the distributed environment with limited communication, our approach utilized proportional-integral average consensus estimators, whereby information from each robot diffuses through the communication network. The theoretical contribution is to determine the time constant involved in the diffusion process, which can affect overall system performance. The asymptotic convergence of follower robots to the position and orientation of the reference robot is ensured using the Lyapunov function. The new technique is tested with complete, limited, and no information availability. Several simulation results are provided that demonstrate the formation control and obstacle avoidance for multirobots using the proposed scheme.

Multimedia streaming applications with stringent QoS requirements in 60 GHz mmWave wireless personal area networks (WPANs) demand high rate and low latency data transfer as well as little service disruption. In this paper, we consider the problem of robust relay placement in 60 GHz WPANs with directional antenna. Relays forward traffic from transmitter devices to receiver devices facilitating i ) the primary communication path for non-line-of-sight (NLOS) transceiver pairs, and ii ) secondary (backup) communication path for line-of-sight (LOS) or NLOS transceiver pairs. By incorporating a classic directional antenna model and characterizing the link contention, we formulate the robust minimum relay placement problem and the robust maximum utility relay placement problem with the objective to minimize the number of relays deployed and maximize the network utility, respectively. Efficient algorithms are developed to solve both problems and have been shown to incur less service disruption in presence of moving subjects that may block the LOS paths in the environment.

NAND flash memory is widely used in both hard real-time and soft real-time systems because of its unique properties, such as non-volatility, low power consumption, and fast access time. However, due to the variable garbage collection latency, the response time becomes unpredictable when multiple I/O requests are issued from the file system to flash media. In NAND flash memory storage systems, flash translation layer (FTL) is a typical software module to handle the I/O requests and manage NAND flash memory. Most of existing FTL schemes focus on improving average response time but worst-case response time remains an open problem. This paper proposes a real-time flash translation layer (RFTL) scheme to evenly distribute garbage collection time-cost, so as to guarantee a near optimum worst-case response time. This is achieved by using a new hybrid-level address mapping approach, which can provide guaranteed physical space to serve requests in any time period. Moreover, we propose a distributed garbage collection policy that enables RFTL to reclaim the space and serve the requests simultaneously. We conduct a set of experiments on a real hardware platform. Both the proposed scheme and other representative FTL schemes have been implemented in the hardware evaluation board. Experimental results show that our scheme improves worst-case response time by 41.51 percent and average response time by 88.85 percent.

Localization is one of the fundamental tasks of Autonomous unmanned Vehicles (AuV) navigation systems [1]. In open space, Global Position System (GPS) can serve the localization need well. However, GPS is not always available in underwater environments due to high electromagnetic (EM) attenuation [2]. As a result, acoustic localization is more practical in the long range underwater context. Meanwhile, due to the wide availability of simple microphones and onboard clocks, Time of Arrival (ToA) based acoustic underwater localization algorithms is prevailing. Hence we shall focus on ToA based underwater acoustic localization.

Cyber-Physical Systems (CPS) integrate discrete-time computing and continuous-time physical-world entities, which are often wirelessly interlinked. The use of wireless safety-critical CPS requires safety guarantees despite communication faults. This paper focuses on one important set of such safety rules: Proper-Temporal-Embedding (PTE), where distributed CPS entities must enter/leave risky states according to properly nested temporal pattern and certain duration spacing. Our solution introduces hybrid automata to formally describe and analyze CPS design patterns. We propose a novel leasing based design pattern, along with closed-form configuration constraints, to guarantee PTE safety rules under arbitrary wireless communication faults. We propose a formal procedure to transform the design pattern hybrid automata into specific wireless CPS designs. This procedure can effectively isolate physical world parameters from affecting the PTE safety of the resultant specific designs. We conduct two wireless CPS case studies, one on medicine and the other on control, to show that the resulted system is safe against communication failures. We also compare our approach with a polling based approach. Both approaches support PTE under arbitrary communication failures. The polling approach performs better under severely adverse wireless medium conditions; while ours performs better under benign or moderately adverse wireless medium conditions.

A wireless electrocardiogram case study suggests that current CDMA2000 cellular technology has considerable potential in medical telemetry. Modifications to the network protocol stack ensure the highest data integrity and lowest service delay.

The charging power supply for batteries may be variable under many circumstances, e.g., when using solar panels or air-driven generators as the energy source. The mismatch between the voltages of the power supply and the battery may cause significant charging inefficiency. In this paper, we use reconfigurable batteries to solve this voltage mismatch problem. We develop algorithms to dynamically decide the battery connections, to both minimize the voltage mismatch and maintain SOC balancing among difference batteries. We build a hardware prototype to implement and validate our method and use simulation experiments to empirically evaluate its performance.

Wireless side monitoring employing distributed sniffers has been shown to complement wired side monitoring using Simple Network Management Protocol (SNMP) and base station logs, since it reveals detailed PHY and MAC behaviors, as well as timing information. Due to hardware limitations, wireless sniffers typically can only collect information on one channel at a time. Distributed algorithms are desirable to determine the optimal channel allocation of sniffer nodes to maximize the information collected. In this paper, we propose Gibbs sampler based algorithms for robust distributed monitoring of multi-channel wireless networks. Among several variants of the base Gibbs sampling approach, we find that most algorithms suffer from high sensitivity to parameter selection. In contrast, Gibbs sampling using a thermodynamic schedule is self-tuned and can adapt to different network configurations. Simulation studies show that the proposed algorithms can achieve faster convergence rate and have higher chance of reaching global optima than traditional Gibbs sampler algorithm.

ZigBee and other wireless technologies operating in the (2.4GHz) ISM band are being applied in Wireless Personal Area Networks (WPAN) for many medical applications. However, these low duty cycle, low power, and low data rate medical WPANs suffer from WiFi co-channel interferences. WiFi interference can lead to longer latency and higher packet losses in WPANs, which can be particularly harmful to safety-critical applications with stringent temporal requirements, such as ElectroCardioGraphy (ECG). This paper exploits the Clear Channel Assessment (CCA) mechanism in WiFi devices and proposes a novel policing framework, WiCop, that can effectively control the temporal white-spaces between WiFi transmissions. Such temporal white-spaces can be utilized for delivering low duty cycle WPAN traffic. We have implemented and validated WiCop on SORA, a software-defined radio platform. Experimental results show that with the assistance of the proposed WiCop policing schemes, the packet reception rate of a ZigBee-based WPAN can increase by up to 116% in the presence of a heavy WiFi interferer. A case study on the medical application of WPAN ECG monitoring demonstrates that WiCop can bound ECG signal distortion within 2% even under heavy WiFi interference. An analytical framework is devised to model the CCA behavior of WiFi interferers and the performance of WPANs under WiFi interference with or without WiCop protection. The analytical results are corroborated by experiments.

Hybrid systems model checking is a great success in guaranteeing the safety of computerized control cyber-physical systems (CPS). However, when applying hybrid systems model checking to Medical Device Plug-and-Play (MDPnP) CPS, we encounter two challenges due to the complexity of human body: 1) there are no good offline differential equation-based models for many human body parameters; 2) the complexity of human body can result in many variables, complicating the system model. In an attempt to address the challenges, we propose to alter the traditional approach of offline hybrid systems model checking of time-unbounded (i.e., infinite horizon, a.k.a., long run) future behavior to online hybrid systems model checking of time-bounded (i.e., finite horizon, a.k.a., short run) future behavior. According to this proposal, online model checking runs as a real-time task to prevent faults. To meet the real-time requirements, certain design patterns must be followed, which brings up the codesign issue. We propose two sets of system codesign patterns for hard real time and soft real time, respectively. To evaluate our proposals, a case study on laser tracheotomy MDPnP is carried out. The study shows the necessity of online model checking. Furthermore, test results based on real-world human subject trace show the feasibility and effectiveness of our proposed codesign.

Most commercial network switches are designed to achieve good average throughput and delay needed for Internet traffic, whereas hard real-time applications demand a bounded delay. Our real-time switch combines clearance-time-optimal switching with clock-based scheduling on a crossbar switching fabric. We use real-time virtual machine tasks to serve both periodic and aperiodic traffic, which simplifies analysis and provides isolation from other system operations. We can then show that any feasible traffic will be switched in two clock periods. This delay bound is enabled by introducing one-shot traffic, which can be constructed at the cost of a fixed delay of one clock period. We carry out simulation to compare our switch with the popular iSLIP crossbar switch scheduler. Our switch has a larger schedulability region, a bounded lower end-to-end switching delay, and a shorter clearance time which is the time required to serve every packet in the system.

Recent progress in neural learning demonstrated that machines can do well in regularized tasks, e.g., the game of Go. However, artistic activities such as poem generation are still widely regarded as human’s special capability. In this paper, we demonstrate that a simple neural model can imitate human in some tasks of art generation. We particularly focus on traditional Chinese poetry, and show that machines can do as well as many contemporary poets and weakly pass the Feigenbaum Test, a variant of Turing test in professional domains.

With the emergence of many commercial-off-the-shelf (COTS) and/or open-source hardware and software, we can now build cheap Unmanned Aerial Vehicles (UAVs). This will enable a broad spectrum of potential UAV based mobile applications. In this work, we propose a simple open UAV platform: Ard-µ-copter. Ard-µ-copter is a quadcopter built upon the open source ArduPilot [1] infrastructure library and hardware. Comparing to the many existing commercial quadcopters platforms and open source quadcopter platforms, Ard-µ-copter platform is fully open source, simple (i.e. what the "µ" stands for), and with good documentations.

Recently there is a growing interest of incorporating cellular architecture (with wired base stations and last-hop wireless connections) into fieldbuses to support mobile real-time applications. A promising trend is that such cellular fieldbuses will go multichannel multiradio, due to the wide availability of cheap multichannel commercial-off-the-shelf (COTS) wireless nodes, and the rise of 4G and future cellular technologies. For multichannel multiradio cellular fieldbuses, per-flow real-time schedulability guarantee in the inter-cell level has not yet been well studied. Particularly, unlike 3G cellular networks, which use static FDMA/CDMA to isolate cells, the multichannel multiradio feature allows neighboring cells to use the same radio frequency channel at different time-slots, or the same time-slot at different radio frequency channels. How to carry out channel time-slot scheduling is therefore the focus of this paper. To address this issue, we propose a greedy scheduling algorithm, together with a polynomial time closed-form schedulability test. The relationship between the schedulability test result, greedy scheduling schedulability, and schedulability is explored. We prove the equivalence of the three for chained cellular fieldbus topology, a typical topology with broad applications. This also implies the optimality of greedy scheduling, and the sufficiency and necessity of the schedulability test in the context of chained topology. To demonstrate and validate these schedulability theories, we carry out a case study on a classic admission planning problem. The schedulability test not only serves as a planning constraint, but also guides us to propose an approximation algorithm to solve the NP-hard admission planning problem. Comparisons to exhaustive search corroborate the validity of our schedulability theories.

Wireless body area networks (WBAN) play a key role in the future of e-Health. In response, IEEE sets up working group 802.15.6 to standardize WBAN schemes. Of all existing standard proposals, the 2.4GHz proposal is the most mature and ready for mass production. However, as e-Health WBAN applications are often mission/life critical, people are concerned with the reliability (particularly, coexistence reliability) of this proposal. This study evaluates the 2.4GHz proposal under WiFi/Bluetooth interference in the context of medical multi-parameter monitoring. The authors conclude that WiFi poses a major threat to such application scenario, while Bluetooth does not.

Many Cyber-Physical Systems (CPS) are highly nondeterministic. This often makes it impractical to model and predict the complete system behavior. To address this problem, we propose that instead of offline modeling and verification, many CPS systems should be modeled and verified online, and we shall focus on the system's time-bounded behavior in short-run future , which is more describable and predictable. Meanwhile, as the system model is generated/updated online, the verification has to be fast. It is meaningless to tell an online model is unsafe when it is already out-dated. To demonstrate the feasibility of our proposal, we study two cases of our ongoing projects, one on the modeling and verification of a train control system, and the other on a Medical Device Plug-and-Play (MDPnP) application. Both cases are about safety-critical CPS systems. Through these two cases, we exemplify how to build online models that describe the time-bounded short-run behavior of CPS systems; and we show that fast online modeling and verification is possible.

We present the Lightning Protocol, a hard real-time, fast, and lightweight protocol to elect the sensor closest to an impulsive sound source. This protocol can serve proximity-based localization or leader election for sensor collaboration. It utilizes the fact that electromagnetic waves propagate much faster than acoustic waves to efficiently reduce the number of contending sensors in the election. With simple RF bursts, most basic comparison operations, no need of clock synchronization, and a memory footprint as small as 5,330 bytes of ROM and 187 bytes of RAM, the protocol incurs O(1) transmissions, irrespective of the sensor density, and guarantees hard real-time (O(1)) localization time cost. Experiment results using UC Berkeley Motes in a common office environment demonstrate that the time delay for the Lightning Protocol is on the order of milliseconds. The simplicity of the protocol reduces memory cost, computation complexity, and programming difficulty, making it desirable for low-end wireless sensors.

Wireless LAN for industrial control (IC-WLAN) provides many benefits, such as mobility, low deployment cost, and ease of reconfiguration. However, the top concern is robustness of wireless communications. Wireless control loops must be maintained under persistent adverse channel conditions, such as noise, large-scale path loss, fading, and many electromagnetic interference sources in industrial environments. The conventional IEEE 802.11 WLANs, originally designed for high bandwidth instead of high robustness, are therefore inappropriate for IC-WLAN. A solution lies in the direct sequence spread spectrum (DSSS) technology: by deploying the largest possible processing gain (slowest bit rate) that fully exploits the low data rate feature of industrial control, much higher robustness can be achieved. We hereby propose using DSSS-CDMA to build IC-WLAN. We carry out fine-grained physical layer simulations and Monte Carlo comparisons. The results show that DSSS-CDMA IC-WLAN provides much higher robustness than IEEE 802.11/802.15.4 WLAN, so that reliable wireless industrial control loops become feasible. We also show that deploying larger processing gain is preferable, to deploying more intensive convolutional coding. The DSSS-CDMA IC-WLAN scheme also opens up a new problem space for interdisciplinary study, involving real-time scheduling, resource management, communication, networking, and control

How to allocate computing and communication resources in a way that maximizes the effectiveness of control and signal processing, has been an important area of research. The characteristic of a multi-hop Real-Time Wireless Sensor Network raises new challenges. First, the constraints are more complicated and a new solution method is needed. Second, a distributed solution is needed to achieve scalability. This article presents solutions to both of the new challenges. The first solution to the optimal rate allocation is a centralized solution that can handle the more general form of constraints as compared with prior research. The second solution is a distributed version for large sensor networks using a pricing scheme. It is capable of incremental adjustment when utility functions change. This article also presents a new sensor device/network backbone architecture---Real-time Independent CHannels (RICH), which can easily realize multi-hop real-time wireless sensor networking.

The last decade has witnessed the convergence of three giant worlds: electronics, computer science and telecommunications. The next decade should follow this convergence in most of our activities with the generalization of sensor networks. In particular with the progress in medicine, people live longer and the aging of population will push the development of wireless personal networks (WPAN) and wireless body area networks (WBAN), as more and more people will prefer not to go to hospital, should it be for convenience or for cost reasons. The recent advances in wireless technology have helped the development of wireless body area networks (WBAN), where a set of communicating devices gathered in/around a human body can communicate in a ad-hoc way. These devices are connected to sensors which monitor movements and vital body parameters. The WBAN have also been considered for sports and entertainment and thus, they are not only dedicated to medical and healthcare applications. The techniques involved are the latest emerging ones developed for general ad-hoc networks with a special attention to energy and reliability concerns due to the human lives that are involved.

Cyber-Physical Systems (CPS) integrate discrete-time computing and continuous-time physical-world entities, which are often wirelessly interlinked. The use of wireless safety critical CPS (control, healthcare etc.) requires safety guarantees despite communication faults. This paper focuses on one important set of such safety rules: Proper-Temporal-Embedding (PTE). Our solution introduces hybrid automata to formally describe and analyze CPS design patterns. We propose a novel lease based design pattern, along with closed-form configuration constraints, to guarantee PTE safety rules under arbitrary wireless communication faults. We propose a formal methodology to transform the design pattern hybrid automata into specific wireless CPS designs. This methodology can effectively isolate physical world parameters from affecting the PTE safety of the resultant specific designs. We conduct a case study on laser tracheotomy wireless CPS to show that the resulting system is safe and can withstand communication disruptions.

Cloud platforms deploy data centers geographically distributed around the world and application providers select cloud infrastructures based on the requirements of their applications. While existing works mostly focus on the comparison on cloud services, we argue that proximity also plays a very important role when deciding in which cloud infrastructures to deploy the applications. In this paper, we design and evaluate the system, we call CSS, for automatic selection of cloud infrastructures. It not only considers the deployment cost, but also takes into account the location of cloud infrastructures, application clients and related applications, and the interaction among application components when selecting the cloud infrastructures. In order to address the scalability issue when the number of data centers and application components is large, we propose a stepwise application placement algorithm. Through experiments, we show that the algorithm is able to find a near-optimal placement policy within very short period of time.

To integrate the nowadays rapidly expanding distributed real-time systems, we need multi-hop real-time switched networks. A (if not "the") widely recognized/adopted real-time switch architecture is the TDMA crossbar real-time (TCRT) switch architecture. However, the original TCRT switch architecture assumes per-flow queueing. To support scalability, however, queue sharing (i.e. flow aggregation), must be allowed. With simple flow aggregation, flow burstiness can grow and infect, making schedulability and end-to-end delay bound analysis an open problem. To deal with this, we propose the real-time aggregate scheme. The scheme complies with the existing TCRT switch architecture, and deploys spatial-temporal isolation and over-provisioning to curb aggregate member flows' burstiness. This allows us to derive the closed-form end-to-end delay bound, and give the corresponding resource planning and admission control strategies. Simulations are carried out to show the effectiveness of the design.

Multimedia streaming applications with stringent QoS requirements in 60GHz mmWave wireless personal area networks (WPANs) demand high rate and low latency data transfer as well as low service disruption. In this paper, we consider the problem of robust relay placement in 60GHz WPANs. Relays forward traffic from transmitter devices to receiver devices facilitating i) the primary communication path for non-line-of-sight (NLOS) transceiver pairs, and ii) secondary (backup) communication path for line-of-sight (LOS) transceiver pairs. We formulate the robust minimum relay placement problem and the robust maximum utility relay placement problem with the objective to minimize the number of relays deployed and maximize the network utility, respectively. Efficient algorithms are developed to solve both problems and have been shown to incur less service disruption in presence of moving subjects that may block the LOS paths in the environment., Updated conference version, 10 pages, 5 figures

Hybrid systems model checking is a great success in guaranteeing the safety of computerized control cyber-physical systems (CPS). However, when applying hybrid systems model checking to Medical Device Plug-and-Play(MDPnP) CPS, we encounter two challenges due to the complexity of human body: i) there are no good offline differential equation based models for many human body parameters, ii) the complexity of human body can result in many variables, complicating the system model. In an attempt to address the challenges, we propose to alter the traditional approach of offline hybrid systems model checking of time-unbounded (i.e., long-run) future behavior to online hybrid systems model checking of time-bounded (i.e., short-run) future behavior. According to this proposal, online model checking runs as a real-time task to prevent faults. To meet the real-time requirements, certain design patterns must be followed, which brings up the co-design issue. We propose two sets of system co-design patterns for hard real-time and soft real-time respectively. To evaluate our proposals, a case study on laser tracheotomy MDPnP is carried out. The study shows the necessity of online model checking. Furthermore, test results based on real-world human subject trace show the feasibility and effectiveness of our proposed co-design.

The rapid scaling up of modern avionics is forcing its communication infrastructure to evolve from shared medium toward multi-hop switched real-time networks. This prompts the proposal of avionics full-duplex switched Ethernet (AFDX) standard. Since its publication, AFDX has been well-received, and is deployed or to-be-deployed in state-of-the-art aircrafts, such as Airbus A380/A400M/A350, Boeing 787, Bombardier CSeries etc. On the other hand, AFDX standard only specifies the behavior that an underlying switch must follow, but leaves the architecture design open. This creates an open market for switch vendors. Among the different candidate designs for this market, the TDMA crossbar real-time switch architecture stands out as it complies with and even simplifies many mainstream switch architectures, hence lays a smooth evolution path toward AFDX. In this paper, we focus on analyzing this switch design for AFDX networks. We first prove that TDMA crossbar real-time switch architecture complies with the AFDX specifications; and derive closed-form formulae on the corresponding AFDX networks' traffic characteristics and end-to-end real-time delay bound. Then we prove the resource planning problem in the corresponding AFDX networks is NP-Hard. To address this NP-Hard challenge, we re-model the problem. Based upon the re-modeling, we propose an approximation algorithm.

ZigBee and other wireless technologies operating in the (2.4GHz) ISM band are being applied in Wireless Body Area Networks (WBAN) for many medical applications. However, these low duty cycle, low power, and low data rate medical WBANs suffer from WiFi co-channel interferences. WiFi interference can lead to longer latency and higher packet losses in WBANs, which can be particularly harmful to safety-critical applications with stringent temporal requirements. Existing solutions to WiFi-WBAN coexistence either require modifications to WiFi or WBAN devices, or have limited applicability. In this paper, by exploiting the Clear Channel Assessment (CCA) mechanisms in WiFi devices, we propose a novel policing framework, WiCop, that can effectively control the temporal white-spaces between WiFi transmissions. Specifically, the WiCop Fake-PHY-Header policing strategy uses a fake WiFi PHY preamble-header broadcast to mute other WiFi interferers for the duration of WBAN active interval, while the WiCop DSSS-Nulling policing strategy uses repeated WiFi PHY preamble (with its spectrum side lobe nulled by a band-pass filter) to mute other WiFi interferers throughout the duration of WBAN active interval. The resulted WiFi temporal white-spaces can be utilized for delivering low duty cycle WBAN traffic. We have implemented and validated WiCop on SORA, a software defined radio platform. Experiments show that with the assistance of the proposed WiCop policing schemes, the packet reception rate of a ZigBee-based WBAN can increase by up to 43.8% in presence of a busy WiFi interferer.

The rapid scaling up of Networked Control Systems (NCS) is forcing traditional single-hop shared medium industrial fieldbuses (a.k.a. fieldbuses) to evolve toward multi-hop switched fieldbuses. Such evolution faces many challenges. The first is the re-design of switch architecture. To meet the real-time nature of NCS traffic, and to lay a smooth evolution path for switch manufacturers, it is widely agreed that a (if not the) promising switch architecture is an input queueing crossbar architecture running TDMA scheduling. The second challenge is real-time multicast. NCS applications usually involve complex distributed multiple-input-multiple-output interactions, which by their nature necessitate real-time multicast. In shared medium fieldbuses, real-time multicast is straightforward as data sent to the medium is heard by all nodes. On multi-hop switched fieldbuses, however, real-time multicast becomes non-trivial. In this paper, we prove real-time multicast on multi-hop switched fieldbuses is NP-Hard. What is more, real-time multicast on multi-hop switched fieldbuses is fundamentally different from Internet multicast, due to real-time requirement and the homogeneous input queueing crossbar switch architecture. Particularly, switch external links' capacities are no longer mutually independent. Such drastic change of assumptions warrants developing new routing algorithms, and a heuristic algorithm is hereby proposed.

The report of the President's Council of Advisors on Science and Technology (PCAST) has placed CPS on the top of the priority list for federal research investment [6]. This article first reviews some of the challenges and promises of CPS, followed by an articulation of some specific challenges and promises that are more closely related to the sensor networks, ubiquitous and trustworthy computing conference.

Fault tolerance is an important aspect in real-time computing. In real-time control systems, tasks could be faulty due to various reasons. Faulty tasks may compromise the performance and safety of the whole system and even cause disastrous consequences. In this paper, we describe On-demand real-time guard (ORTEGA), a new software fault tolerance architecture for real-time control systems. ORTEGA has high fault coverage and reliability. Compared with existing real-time fault tolerance architectures, such as Simplex, ORTEGA allows more efficient resource utilizations and enhances flexibility. These advantages are achieved through the on-demand detection and recovery of faulty tasks. ORTEGA is applicable to most industrial control applications where both efficient resource usage and high fault coverage are desired.

The convergence of computers and the physical world is the theme for next generation networking research. This trend calls for real-time network infrastructure, which requires a high-speed real-time WAN to serve as its backbone. However, commercially available high-speed WAN switches (routers) are designed for best-effort Internet traffic. A real-time switch design for the aforementioned networks is missing. We propose a real-time switch design using a crossbar switching fabric. The proposed switch can be implemented by making minimal modification, or even simplification, to the widely implemented iSLIP crossbar switch scheduler. Our real-time switch serves periodic and aperiodic traffic with real-time virtual machine tasks, which simplifies analysis, provides isolation, and facilitates future hierarchical scheduling and flow aggregation. Taking advantage of the fact that most industrial real-time network flows rarely change, our switch is better adapted to providing high bandwidths and low latencies.

The convergence of computer and physical world calls for next generation Wide Area Network (WAN) infrastructures for hard real-time and embedded applications. Such networks need virtual topologies to achieve scalability, configurability, and flexibility. Virtual topologies are made of virtual links, for which, the state-of-the-art building tool is Guaranteed Rate server based aggregates (GR- aggregates). However, common-practice weight assignment scheme couples GR-aggregate End-to-End (E2E) delay bound with aggregate's data throughput inverse proportionally. This is undesirable for many hard real-time embedded sensing/actuating applications, whose traffic has small data throughput but requires short E2E delay. We propose Guaranteed Delay server based aggregates (GD-aggregates), which allow assigning weights according to priorities instead of data throughput. This decouples E2E delay guarantee from data throughput, hence meets the needs of hard realtime embedded applications. In addition, GD-aggregates can be analyzed with simple closed form formulae, and can be easily planned with optimization tools.

We address two necessary issues needed for developing safe and reliable MD PnP systems: robust wireless networking and automated checking for component interoperability and reliability. First, the robustness of a wireless network can be improved by the use of DSSS-CDMA, which tradeoff throughput to achieve higher reliability and persistence of connections as needed. Second, automated checking of components interoperability and reliability can be partially addressed by the use of the integrated framework for assumptions and dependencies (IFAD) by specifying a machine-checkable encoding of component information, checking interface assumptions, and finding how various environmental changes can impact the system.