Technique For Real-time Systems Research Articles

Delay-dependent partial order reduction technique for real time systems

Almost all partial order reduction techniques proposed for time Petri nets (TPNs in short) are based on the notion of Partially Ordered Sets. The idea is to explore simultaneously, by relaxing some firing order constraints of persistent transitions (An enabled transition is persistent, if it cannot be disabled until its firing.), several equivalent sequences, while computing the convex hull of the abstract states reached by these equivalent sequences. However, unlike timed automata, in the TPN state space abstractions, the union of the abstract states reached by different interleavings of the same set of non conflicting transitions is not necessarily identical to their convex hull. Moreover, the convex hull over-approximation preserves neither the boundedness nor the reachability properties of the TPN. In this context, the main challenge is to establish sufficient conditions over transitions that ensure, in addition to their persistency, identity between the union and the convex hull of the abstract states reachable by their different interleavings. This paper shows how to weaken the sufficient conditions proposed in the literature, by taking into better account the structure, the marking, the static and the dynamic time parameters of the TPN.

Discrete feedback-based dynamic voltage scaling for safety critical real-time systems

Recently, the tradeoff between low energy consumption and high fault-tolerance has attracted a lot of attention as a key issue in the design of real-time systems. Dynamic Voltage Scaling (DVS) is commonly employed as one of the most effective low energy techniques for real-time systems. It has been observed that the use of feedback-based methods can improve the effectiveness of DVS-enabled systems. In this paper, we have investigated reducing the energy consumption of fault-tolerant hard real-time systems using the feedback control theory. Our proposed method makes the system capable of selecting the proper frequency and voltage settings in order to reduce the energy consumption, while guaranteeing hard real-time requirements in the presence of unpredictable workload fluctuations and faults. In the proposed method, the available slack-time is exploited by a feedback-based DVS at runtime to reduce the energy consumption. Furthermore, some slack-time is reserved for re-execution in case of faults. The simulation results show that compared with the traditional DVS method, our proposed method not only provides up to 59% energy saving, but also satisfies hard real-time constraints. Our proposed method is also effective in harnessing the static energy. The transition overheads are also taken into account in our simulation experiments.

A Laboratory Testbed for Embedded Fuzzy Control

<?Pub Dtl=""?> This paper presents a novel scheme called “Laboratory Testbed for Embedded Fuzzy Control of a Real Time Nonlinear System.” The idea is based upon the fact that project-based learning motivates students to learn actively and to use their engineering skills acquired in their previous years of study. It also fosters initiative and focuses students' attention on authentic real-world problems. At the same time, it enhances their learning. Students gain hands-on experience and improve their skills in product development, self-directed learning, teamwork, and project management. There has been a tremendous rise in the popularity of intelligent control techniques like fuzzy logic for use in industrial control applications in recent times. These techniques, which were primarily conceived for nonlinear control applications, are best implemented using embedded controllers, which can use their capabilities to the maximum. While courses in electrical and computer engineering cover several areas like digital and analog integrated circuits, microprocessors and control Systems, and process control, few of these integrate all these areas with focus on the application of intelligent techniques in real-time systems. Also, there is a growing need in industry for engineers who can perform software design and system integration for various applications in embedded control. This paper aims at developing such a practical task as one of the major projects in the eighth semester of the program offered by the Instrumentation and Control Engineering (ICE) Department of Netaji Subhas Institute of Technology (NSIT), Delhi University, India, to design a real-time embedded controller implementing an intelligent control technique, fuzzy logic, for control applications. These applications might, for example, be level control, flow control, or pressure control. The paper discusses an example of a real-time pressure control system for which a microcontroller-based fuzzy proportional-integral-derivative (PID) controller has been simulated and implemented with satisfactory results.

Toward effective service composition for real-time SOA-based systems

Many application domains are increasingly leveraging service-oriented architecture (SOA) techniques to facilitate rapid system deployment. Many of these applications are time-critical and, hence, real-time assurance is an essential step in the service composition process. However, there are gaps in existing service composition techniques for real-time systems. First, admission control is an essential technique to assure the time bound for service execution, but most of the service composition techniques for real-time systems do not take admission control into account. A service may be selected for a workflow during the composition phase, but then during the grounding phase, the concrete service may not be able to admit the workload. Thus, the entire composition process may have to be repeated. Second, communication time is an important factor in real-time SOA, but most of the existing works do not consider how to obtain the communication latencies between services during the composition phase. It is clear that maintaining a full table of communication latencies for all pairs of services is infeasible. Obtaining communication latencies between candidate services during the composition phase can also be costly, since many candidate services may not be used for grounding. Thus, some mechanism is needed for estimating the communication latency for composite services. In this paper, we propose a three-phase composition approach to address the above issues. In this approach, we first use a highly efficient but moderately accurate algorithm to eliminate most of the candidate compositions based on estimated communication latencies and assured service response latency. Then, a more accurate timing prediction is performed on a small number of selected compositions in the second phase based on confirmed admission and actual communication latency. In the third phase, specific concrete services are selected for grounding, and admissions are actually performed. The approach is scalable and can effectively achieve service composition for satisfying real-time requirements. Experimental studies show that the three-phase approach does improve the effectiveness and time for service composition in SOA real-time systems. In order to support the new composition approach, it is necessary to effectively specify the needed information. In this paper, we also present the specification model for timing-related information and the extension of OWL-S to support this specification model.

Vector Doppler: spatial sampling analysis and presentation techniques for real time systems

The aim of the vector Doppler (VD) technique is the quantitative reconstruction of a velocity field independent of the ultrasonic probe axis to flow angle. In particular, vector Doppler is useful for studying vascular pathologies related to complex blood flow conditions. Clinical applications require a real-time operating mode and the capability to perform Doppler measurements over a defined volume. The combination of these two characteristics produces a real-time vector velocity map. In previous works we investigated the theory of pulsed-wave (PW) vector Doppler and developed an experimental system capable of producing off-line 3-D vector velocity maps. Afterward, for producing dynamic velocity vector maps, we realized a new 2-D vector Doppler system based on a modified commercial echograph. The measurement and presentation of a vector velocity field requires correct spatial sampling that must satisfy the Shannon criterion. In this work we tackle this problem, establishing a relationship between sampling steps and scanning system characteristics. Another problem posed by the vector Doppler technique is the data representation in realtime that should be easy to interpret for the physician. With this in mind we attempt a multimedia solution that uses both interpolated images and sound to represent the information of the measured vector velocity map. These presentation techniques are tested for real-time scanning on flow phantoms and preliminary measurements in vivo on a human carotid artery.

System-level power-aware design techniques in real-time systems

Power and energy consumption has recently become an important issue and consequently, power-aware techniques are being devised at all levels of system design; from the circuit and device level, to the architectural, compiler, operating system, and networking layers. In this paper, we concentrate on power-aware design techniques for real-time systems. While the main focus is on hard real-time, soft real-time systems are considered as well. We start with the motivation for focusing on these systems and provide a brief discussion on power and energy objectives. We then follow with a survey of current research on a layer-by-layer basis. We conclude with illustrative examples and open research challenges. This paper provides an overview of power-aware techniques for the real-time system engineer as well as an up-to-date reference list for the researcher.

Adding Hard Real-Time Tasks to Artificial Intelligence Environments

In this paper, we present a task model suitable for providing predictability to artificial intelligence tasks, that allows us to incorporate AI techniques in real-time systems guaranteeing their response time. Furthermore, we propose a Real-Time Artificial Intelligence System architecture based on the previous task model and on the blackboard model, which uses the feasibility theory for fixed priority scheduling in order to guarantee the minimum system quality required.

On Applying Imprecise Computation to Real-Time AI Systems

Imprecise computation is known as a technique for real-time systems where precise outputs are traded off for timely responses to system events. This paper discusses how the technique can be applied to a class of real-time Al systems designed for solving combinatorial problems and proposes an evaluation method for assessing if imprecise computation can satisfy both the timing and functional requirements of these systems.

SPECIFICATION OF REAL-TIME SYSTEMS

Inspite of numerous research advancements made in recent years in the area of formal techniques, specification of real-time systems is still proving to be a very challenging and difficult problem. In this context, this paper critically examines state-of-the-art specification techniques for real-time systems and analyzes the emerging trends.

The application of real-time design techniques to simulation

The paper discusses the application of the Ward and Mellor structured development techniques for real-time systems to the field of simulation. The tools and heuristics used by Ward and Mellor are extended to provide a useful approach to the design of real-time simulations. This is illustrated by the example of a real-time simulation of a manufacturing plant and process control system.