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27
Real-time query scheduling for wireless sensor networks
- in Real-Time Systems Symposium
, 2007
"... Abstract — Recent years have seen the emergence of wireless cyber-physical systems that must support real-time queries of physical environments through wireless sensor networks. This paper proposes Real-Time Query Scheduling (RTQS), a novel approach to conflict-free transmission scheduling for real- ..."
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Cited by 26 (12 self)
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Abstract — Recent years have seen the emergence of wireless cyber-physical systems that must support real-time queries of physical environments through wireless sensor networks. This paper proposes Real-Time Query Scheduling (RTQS), a novel approach to conflict-free transmission scheduling for real-time queries in wireless sensor networks. First, we show that there is an inherent trade-off between latency and real-time capacity in query scheduling. We then present three new real-time schedulers. The non-preemptive query scheduler supports high real-time capacity but cannot provide low response times to high priority queries due to priority inversions. The preemptive query scheduler eliminates priority inversions at the cost of reduced capacity. The slack stealing query scheduler combines the benefits of the preemptive and non-preemptive schedulers to improve the capacity while meeting query deadlines. We provide schedulability analysis for each scheduler. The analysis and advantages of our approach are validated through NS2 simulations. Index Terms — Query scheduling, schedulability analysis, sensor networks
Near Optimal Rate Selection for Wireless Control Systems
"... Abstract—With the advent of industrial standards such as WirelessHART, process industries are now gravitating towards wireless control systems. Due to limited bandwidth in a wireless network shared by multiple control loops, it is critical to optimize the overall control performance. In this paper, ..."
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Cited by 22 (15 self)
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Abstract—With the advent of industrial standards such as WirelessHART, process industries are now gravitating towards wireless control systems. Due to limited bandwidth in a wireless network shared by multiple control loops, it is critical to optimize the overall control performance. In this paper, we address the scheduling-control co-design problem of determining the optimal sampling rates of feedback control loops sharing a WirelessHART network. The objective is to minimize the overall control cost while ensuring that all data flows meet their end-toend deadlines. The resulting constrained optimization based on existing delay bounds for WirelessHART networks is challenging since it is non-differentiable, non-linear, and not in closed-form. We propose four methods to solve this problem. First, we present a subgradient method for rate selection. Second, we propose a greedy heuristic that usually achieves low control cost while significantly reducing the execution time. Third, we propose a global constrained optimization algorithm using a simulated annealing (SA) based penalty method. Finally, we formulate rate selection as a differentiable convex optimization problem that provides a closed-form solution through a gradient descent method. This is based on a new delay bound that is convex and differentiable, and hence simplifies the optimization problem. We evaluate all methods through simulations based on topologies of a 74-node wireless sensor network testbed. Surprisingly, the subgradient method is disposed to incur the longest execution time as well as the highest control cost among all methods. SA and the greedy heuristic represent the opposite ends of the tradeoff between control cost and execution time, while the gradient descent method hits the balance between the two. I.
Priority Assignment for Real-Time Flows in WirelessHART Networks
"... Abstract—WirelessHART is a new wireless sensor-actuator network standard specifically developed for process industries. A key challenge faced by WirelessHART networks is to meet the stringent real-time communication requirements imposed by process monitoring and control applications. Fixed-priority ..."
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Cited by 10 (6 self)
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Abstract—WirelessHART is a new wireless sensor-actuator network standard specifically developed for process industries. A key challenge faced by WirelessHART networks is to meet the stringent real-time communication requirements imposed by process monitoring and control applications. Fixed-priority scheduling, a popular scheduling policy in real-time networks, has recently been shown to be an effective real-time transmission scheduling policy in WirelessHART networks. Priority assignment has a major impact on the schedulability of real-time flows in these networks. This paper investigates the open problem of priority assignment for periodic real-time flows for feedback control loops closed through a WirelessHART network. We first propose an optimal priority assignment algorithm based on local search for any given worst case delay analysis. We then propose an efficient heuristic search algorithm for priority assignment. We also identify special cases where the heuristic search is optimal. Simulations based on random networks and the real topology of a physical sensor network testbed showed that the heuristic search algorithm achieved near optimal performance in terms of schedulability, while significantly outperforming the traditional priority assignment policies for real-time systems. I.
Interference-Aware Real-Time Flow Scheduling for Wireless Sensor Networks
"... Abstract—With the emergence of wireless sensor networks, an enabling communication technology for distributed real-time systems, we face the critical challenge of meeting the end-to-end deadlines of real-time flows. This paper presents Real-time Flow Scheduling (RFS), a novel conflict-free real-time ..."
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Cited by 7 (3 self)
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Abstract—With the emergence of wireless sensor networks, an enabling communication technology for distributed real-time systems, we face the critical challenge of meeting the end-to-end deadlines of real-time flows. This paper presents Real-time Flow Scheduling (RFS), a novel conflict-free real-time transmission scheduling approach for periodic real-time flows in wireless sensor networks. In contrast to existing transmission scheduling algorithms that ignore interference between transmissions or prevent spatial reuse within the same channel, RFS supports spatial reuse through a novel interference-aware transmission scheduling. While recent work on conflict-free transmission scheduling focused on specialized communication patterns such as queries and converge cast, RFS is designed for peer-to-peer real-time flows with arbitrary inter-flow interference. Moreover, RFS has three salient that make it particularly suitable for real-time systems: First, RFS includes a real-time schedulability analysis that accounts for interference between real-time flows. Second, RFS improves reliability by incorporating retransmissions in a flexible scheduling scheme. Finally, RFS enhances scalability by dividing the network into neighborhoods and provides real-time performance for flows crossing multiple neighborhoods through a novel application of the Release Guard protocol. RFS was evaluated through simulations based on the traces collected from an indoor wireless sensor network testbed. Compared to a traditional TDMA protocol, RFS reduces flow latencies by up to 2.5 times, while improving the real-time capacity by as much as 3.9 times. I.
A Constructing Schedules for Time-Critical Data Delivery in Wireless Sensor Networks
"... Wireless sensor networks for industrial process monitoring and control require highly reliable and timely data delivery. To match performance requirements specialised schedule based medium access control (MAC) protocols are employed. In order to construct an efficient system it is necessary to find ..."
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Cited by 5 (0 self)
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Wireless sensor networks for industrial process monitoring and control require highly reliable and timely data delivery. To match performance requirements specialised schedule based medium access control (MAC) protocols are employed. In order to construct an efficient system it is necessary to find a schedule that can support the given application requirements in terms of data delivery latency and reliability. Furthermore, additional requirements such as transmission power may have to be taken into account when constructing the schedule. In this paper we show how such schedule can be constructed. We describe methods and tools to collect the data necessary as input for schedule calculation. Moreover, due to the high complexity of schedule calculation, we also introduce a heuristic. We evaluate the proposed methods in a real-world process automation and control application deployed in an oil refinery and further present a long-term experiment in an office environment. Additionally, we discuss a framework for schedule life-cycle management.
Analysis of EDF Scheduling for Wireless Sensor-Actuator Networks
"... Abstract—Industry is adopting Wireless Sensor-Actuator Net-works (WSANs) as the communication infrastructure for process control applications. To meet the stringent real-time performance requirements of control systems, there is a critical need for fast end-to-end delay analysis for real-time flows ..."
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Cited by 5 (5 self)
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Abstract—Industry is adopting Wireless Sensor-Actuator Net-works (WSANs) as the communication infrastructure for process control applications. To meet the stringent real-time performance requirements of control systems, there is a critical need for fast end-to-end delay analysis for real-time flows that can be used for online admission control. This paper presents a new end-to-end delay analysis for periodic flows whose transmissions are scheduled based on the Earliest Deadline First (EDF) policy. Our analysis comprises novel techniques to bound the communication delays caused by channel contention and transmission conflicts in a WSAN. Furthermore, we propose a technique to reduce the pessimism in admission control by iteratively tightening the delay bounds for flows with short deadlines. Experiments on a WSAN testbed and simulations demonstrate the effectiveness of our analysis for online admission control of real-time flows. I.
Accounting for Failures in Delay Analysis for WirelessHART Networks
"... Abstract—WirelessHART networks are gaining ground as a real-time communication infrastructure in industrial wireless control systems. Because wireless communication is often susceptible to transmission failures in industrial environments, it is essential to account for failures in the delay analysis ..."
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Cited by 3 (2 self)
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Abstract—WirelessHART networks are gaining ground as a real-time communication infrastructure in industrial wireless control systems. Because wireless communication is often susceptible to transmission failures in industrial environments, it is essential to account for failures in the delay analysis for realtime flows between sensors and actuators in process control. WirelessHART networks handle transmission failures through retransmissions using dedicated and shared time slots through different paths in the routing graphs. While these mechanisms for handling transmission failures are critical for process control requiring reliable communication, they introduce substantial challenges to worst-case end-to-end delay analysis for real-time flows. This paper presents the first worst-case end-to-end delay analysis for periodic real-time flows in a WirelessHART network that takes into account transmission failures. The delay bounds can be used to quickly assess the schedulability of real-time flows for industrial wireless control applications with stringent requirements on both high reliability and network latency. Simulations based on the topologies of a wireless sensor network testbed consisting of 69 TelosB motes indicate that our analysis provides safe upper bounds of the end-to-end delays of real-time flows at an acceptable level of pessimism. I.
Implementation and Experimentation of Industrial Wireless Sensor-Actuator Network Protocols
"... Abstract. Wireless sensor-actuator networks (WSANs) offer an appeal-ing communication technology for process automation applications. How-ever, such networks pose unique challenges due to their critical demands on reliability and real-time performance. While industrial WSANs have received attention ..."
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Cited by 3 (2 self)
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Abstract. Wireless sensor-actuator networks (WSANs) offer an appeal-ing communication technology for process automation applications. How-ever, such networks pose unique challenges due to their critical demands on reliability and real-time performance. While industrial WSANs have received attention in the research community, most published results to date focused on the theoretical aspects and were evaluated based on simulations. There is a critical need for experimental research on this important class of WSANs. We developed an experimental testbed by implementing several key network protocols of WirelessHART, an open standard for WSANs widely adopted in the process industries, including multi-channel TDMA with shared slots at the MAC layer and reliable graph routing supporting path redundancy. We then performed a com-parative study of the two alternative routing approaches adopted by WirelessHART, namely source routing and graph routing. Our study shows that graph routing leads to significant improvement over source routing in term of worst-case reliability, at the cost of longer latency and higher energy consumption. It is therefore important to employ graph routing algorithms specifically designed to optimize latency and energy efficiency. 1
Improving the response time analysis of global fixed-priority multiprocessor scheduling
- In The 20th International Conference on Embedded and Real-Time Computing Systems and Applications
, 2014
"... Abstract—In this paper we address the problem of schedulabil-ity analysis for a set of sporadic tasks with arbitrary deadlines running on a multiprocessor system with global fixed-priority preemptive scheduling. We prove the existence of a class of critical instants for releasing a task, one of whic ..."
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Cited by 3 (1 self)
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Abstract—In this paper we address the problem of schedulabil-ity analysis for a set of sporadic tasks with arbitrary deadlines running on a multiprocessor system with global fixed-priority preemptive scheduling. We prove the existence of a class of critical instants for releasing a task, one of which results in the worst-case response time of that task. Then, we propose a new analysis that improves over current state-of-the-art Response Time Analysis (RTA) by reducing its pessimism. We also observe that, in the case of unconstrained deadlines, the current RTA may underestimate the carry-in workload, and we propose a new formulation that corrects the problem. Finally, we evaluate the performance improvement of our new response time analysis method by empirical experiments with randomly generated task sets. Experimental results show that our new analysis method can successfully accept a consider-able amount of task sets that have to be treated as unschedulable by existing methods. I.
Three Aspects of Real-Time Multiprocessor Scheduling: Timeliness, Fault Tolerance, Mixed Criticality
, 2012
"... The design of real-time systems faces two important challenges: incorporating more functions/services on existing hardware to make the system more attractive to the mar-ket, and deploying existing software on multiprocessors (e.g., multicore) to utilize more processing power. Adding more services on ..."
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Cited by 1 (0 self)
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The design of real-time systems faces two important challenges: incorporating more functions/services on existing hardware to make the system more attractive to the mar-ket, and deploying existing software on multiprocessors (e.g., multicore) to utilize more processing power. Adding more services on the same hardware needs efficient resource utilization. In addition, satisfying the real-time constraints, while at the same time effi-ciently utilizing the multiprocessor platform, is a challenging problem. This thesis deals with global multiprocessor scheduling for real-time systems, that is, the fixed-priority scheduling of sporadic tasks, where each task is allowed to run on any processor. More specifically, this thesis considers three aspects of the design and analysis of global scheduling algorithms: timeliness, fault tolerance, and mixed criticality. Timeli-ness is about meeting the deadlines of the tasks; fault tolerance is about producing the correct output within the deadline even in the presence of faults; and mixed criticality is about facilitating the certification of systems when tasks having different criticality (or importance) are hosted on a common computing platform.
