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We consider the problem of resource provisioning for real-time cyber-physical applications in an open system environment where there does not exist a global resource scheduler that has complete knowledge of the real-time performance requirements of each individual application that shares the resources with the other applications. Regularity-based Resource Partition (RRP) model is an effective strategy to hierarchically partition and assign various resource slices among such applications. However, previous work on RRP model only discusses uniform resource environment, where resources are implicitly assumed to be synchronized and clocked at the same frequency. The challenge is that a task utilizing multiple resources may experience unexpected delays in non-uniform environments, where resources are clocked at different frequencies. This paper extends the RRP model to non-uniform multi-resource open system environments to tackle this problem. It first introduces a novel composite resource partition abstraction and then proposes algorithms to construct and reconfigure the composite resource partitions. Specifically, the Acyclic Regular Composite Resource Partition Scheduling (ARCRP-S) algorithm constructs regular composite resource partitions and the Acyclic Regular Composite Resource Partition Dynamic Reconfiguration (ARCRP-DR) algorithm reconfigures the composite resource partitions in the run time upon requests of partition configuration changes. Our experimental results show that compared with state-of-the-art methods, ARCRP-S can prevent unexpected resource supply shortfall and improve the schedulability up to 50%. On the other hand, ARCRP-DR can guarantee the resource supply during the reconfiguration with moderate computational overhead. [ABSTRACT FROM AUTHOR]

In this article, we consider symbolic model checking for event-driven real-time systems. We first propose a Synchronous Real-Time Event Logic (SREL) for capturing the formal semantics of synchronous, event-driven real-time […]

The adoption of real-time wireless technologies within the ever-growing field of networked industrial control systems is continuously gaining popularity. Widespread sensing and actuation devices based on high-throughput wireless standards allow for an increased system mobility and lower configuration and maintenance costs. The IEEE 802.11 standard, especially in its most recent amendments, pushes performance to a very high level, theoretically approaching those of the most common real-time Ethernet networks. Its nondeterministic communication behavior, however, makes 802.11 unsuitable for mission- and safety-critical applications with high-reliability requirements, at least in its standard form. In this paper, we present several major solutions that tackled this issue to achieve real-time and reliability guarantees in wireless networked control systems, capitalizing on the strong efforts devoted to the adoption of IEEE 802.11 physical layer (PHY) technologies. We first provide a deep analysis of the 802.11 protocols in order to propose guidelines toward smart parameter selection at the data-link layer (DLL). In addition, the design of effective rate selection algorithms is considered as a way of increasing both the timeliness and reliability of data delivery. A further systematic solution is represented by real-time (RT)-WiFi, a new time-division multiple-access (TDMA)-based highly configurable DLL protocol that enables high-speed hard real-time data exchange over 802.11 networks. An important goal of this paper is also to provide a thorough comparison among different discussed solutions, in order to put in evidence their advantages and disadvantages, possibly in relation with systems based on different underlying PHYs. We will finally highlight the open challenges and future directions in this active research field. [ABSTRACT FROM AUTHOR]

With the ever-growing interests in applying wireless technologies for networked embedded systems to serve as the communication fabric, many real-time wireless technologies have been recently developed to support time-critical sensing and control applications. We proposed in previous work the RT-WiFi protocol that provides real-time high-speed predictable data delivery and enables designs to meet time-critical industrial needs. However, without explicit reliability enforcement mechanisms, our previous RT-WiFi design is either subject to uncontrolled packet loss due to noise and other interferences or may suffer from inefficient communication channel usage. In this article, we explicitly consider interference from both Wi-Fi and non-Wi-Fi based interference sources and propose two sets of effective solutions for reliable data transmissions in RT-WiFi-based networked embedded systems. To improve reliability against general non-Wi-Fi based interference, based on rate adaptation and retransmission techniques, we present an optimal real-time rate adaption algorithm together with a communication link scheduler that has low network management overhead. A novel technique called overbooking is introduced to further improve the schedulability of the communication link scheduler while maintaining the required communication reliability. For Wi-Fi-based interference, we present mechanisms that utilize virtual carrier sensing to provide reliable data transmission while co-existing with regular Wi-Fi networks. We have implemented the proposed algorithms in the RT-WiFi network management framework and demonstrated the system performance with a series of experiments. [ABSTRACT FROM AUTHOR]

Unknown time delay poses a significant challenge to the design of networked motion control systems. Moreover, modeling uncertainties, mechanical disturbance, and sensor noise coexist with time delay in such systems, which makes the controller synthesis even more challenging. It has been proven effective to model the time delay as fictitious disturbance so that a disturbance observer (DOB) can be employed to cancel the negative effect of time delay. In this brief, a new double DOB (DDOB) design is proposed by adding one more DOB into the control system to handle actual external disturbance and enable satisfactory tracking performance. Design considerations of the baseline controller and the two DOBs are illustrated, and robust stability analysis is provided to handle modeling uncertainties. A real-time wireless communication protocol, RT-WiFi, is integrated with a DC motor to examine the performance of the proposed DDOB by simulations and experiments. [ABSTRACT FROM PUBLISHER]

Maintaining the freshness of real-time data is one of the crucial design issues in cyber-physical systems (CPS). Past studies have focused on designing update algorithms to minimize the workload imposed by a fixed set of update tasks while ensuring the temporal validity of data. In this paper, we revisit this problem in dynamic cyber-physical systems (DCPS) which may exhibit multi-modal behavior. Any solution to this problem must recognize that: (1) different update algorithms may be needed in different modes according to the workload in each mode, and (2) temporal validity of data must be maintained not only in each mode but also during the mode switch. To strike a balance between data freshness and system schedulability, we propose a utilization-based scheduling selection (UBSS) strategy. We first introduce two synchronous mode switch algorithms, named search-based switch (SBS) and adjustment-based switch (ABS) to search for the proper switch point online and execute all update tasks in the new mode synchronously. SBS checks for temporal validity at the beginning time slot of each idle period in the schedule, while ABS relaxes this restriction through schedule adjustment. To support immediate mode switch, we propose an asynchronous switch algorithm named instant switch (IS) to reduce the switch delay. IS schedules outstanding jobs from the old mode together with the jobs in the new mode using the least-available-laxity-first scheduling policy. Our experimental results demonstrate the effectiveness of these three algorithms. They also show that UBSS strategy can significantly outperform a single fixed update algorithm in terms of maintaining better data freshness while incurring only limited online switch overhead. [ABSTRACT FROM PUBLISHER]

Although the deferrable scheduling algorithm for fixed priority transactions ( DS-FP) has been shown to provide a better performance compared with the More-Less (ML) method, there is still a lack of any comprehensive studies on the necessary and sufficient conditions for the schedulability of DS-FP. In this paper, we first analyze the necessary and sufficient schedulability conditions for DS-FP, and then propose a schedulability test algorithm for DS-FP by exploiting the fact that there always exists a repeating pattern in a DS-FP schedule. To resolve the limitation of fixed priority scheduling in DS-FP, we then extend the deferrable scheduling to a dynamic priority scheduling algorithm called DS-EDF by applying the earliest deadline first (EDF) policy to schedule update jobs. We also propose a schedulability test for DS-EDF and compare its performance with DS-FP and ML through extensive simulation experiments. The results show that the schedulability tests are effective. Although the schedulability of DS-EDF is lower than DS-FP and the repeating patterns in DS-EDF schedules are longer than those in DS-FP due to the use of dynamic priority scheduling, the performance of DS-EDF is better than both DS-FP and ML in terms of CPU utilization and impact on lower priority application transactions. [ABSTRACT FROM PUBLISHER]

Localization in wireless sensor networks is an important functionality that is required for tracking personnel and assets in industrial environments, especially for emergency response. Current commercial localization systems such as GPS suffer from the limitations of either high cost or low availability in many situations (e.g., indoor environments that exclude direct line-of-sight signal reception). The development of industrial wireless sensor networks such as WirelessHART provides an alternative. In this article, we present the design and implementation of ColLoc: a collaborative location and tracking system on WirelessHART as an industrially viable solution. This solution is built upon several technological advances. First, ColLoc adds the roaming functionality to WirelessHART and thus provides a means for keeping mobile WirelessHART devices connected to the network. Second, ColLoc employs a collaborative framework to integrate different types of distance measurements into the location estimation algorithm by weighing them according to their precision levels. ColLoc adopts several novel techniques to improve distance estimation accuracy and decreases the RSSI presurvey cost. These techniques include introducing distance error range constraints to the measurements, judiciously selecting the initial point in location estimation and online updating the signal propagationmodels in the anchor nodes, integrating Extended Kalman Filter (EKF) with trilateration to track moving objects. Our implementation of ColLoc can be applied to any WirelessHART-conforming network because no modification is needed on the WirelessHART field devices. We have implemented a complete ColLoc system to validate both the design and the effectiveness of our localization algorithm. Our experiments show that the mobile device never drops out of the WirelessHART network while moving around; with the help of even one dependable anchor, using RSSI can yield at least 75% of distance errors below 5 meters, which is quite acceptable for many typical industrial automation applications. [ABSTRACT FROM AUTHOR]

Maintaining sensor data validity while exercising timely control is crucial in real-time sensing and control systems. The goal of scheduling algorithms deployed in such systems is to maintain the validity of real-time sensor data so as to maximize the schedulability of update transactions with minimum update workload so that control actions occur on time. In this paper, we first propose a dynamic scheduling algorithm, called Deferrable Scheduling with Least Actual Laxity First (DS-LALF). DS-LALF is designed by extending the deferrable scheduling algorithm, DS-FP which is designed for fixed priority systems. We develop a schedulability test algorithm for DS-LALF based on pattern analysis and a pattern search algorithm to find the shortest and earliest pattern in the schedule. Then, based on DS-LALF, a co-scheduling algorithm called Co-LALF--to schedule update transactions and control transactions in a real-time sensing and control system together--is developed 1) to meet the deadlines of all the control transactions and 2) to maximize the quality of data (QoD) utilized by the control transactions. Co-LALF schedules the jobs in the ascending order of their actual laxities and defers the release times of update jobs as long as the corresponding sensor data are maintained within the required quality. Experimental results show that DS-LALF incurs lower update workload compared with DS-FP and ML, and its schedulability is close to DS-FP but is much better than ML and DS-EDF. The experimental results also show that Co-LALF is effective in improving the overall performance by ensuring better QoD for the real-time data while meeting the deadline constraints of all the control transactions. [ABSTRACT FROM AUTHOR]