| 1. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Enhancing Feedback Control Scheduling Performance by On-line Quantification and Suppression of Measurement Disturbance
- 2005
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Ingår i: Proceedings of the 11th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769523021 ; , s. 2-11
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Konferensbidrag (refereegranskat)abstract
- In the control of continuous and physical systems, the controlled system is sampled sufficiently fast to capture the system dynamics. In general, this property cannot be applied to the control of computer systems as the measured variables are often computed over a data set, e.g., deadline miss ratio. In this paper we quantize the disturbance present in the measured variable as a function of the sampling period and we propose a measurement disturbance suppressive control structure. The experiments we have carried out show that a controller using the proposed control structure outperforms a traditional control structure with regard to performance reliability and adaptation.
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| 2. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Error-Driven QoS Management in Imprecise Real-Time Databases
- 2003
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Ingår i: Euromicro Conference on Real-Time Systems,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 63-
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Konferensbidrag (refereegranskat)abstract
- In applications such as web-applications, e-commerce, and engine control, the demand for real-time data services has increased. In these applications, requests have to be processed within their deadlines using fresh data. Since the workload of these systems cannot be precisely predicted, they can become overloaded and as a result, deadline and freshness violations may occur. To address this problem we propose a QoS-sensitive approach based on imprecise computation, applied on transactions and data objects. We propose two algorithms FCS-HEF and FCS-HEDF that give a robust and controlled behavior of RTDBs in terms of transaction and data preciseness, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms including FCS-EDF, which schedules the transactions using EDF.
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| 3. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Finite Horizon QoS Prediction of Reconfigurable Firm Real-Time Systems
- 2006
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Ingår i: IEEE International Conference on Embedded and Real-Time Computing Systems and Applications,2006. - Los Alamitos, California, USA : IEEE Computer Society. ; , s. 233-
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Konferensbidrag (refereegranskat)abstract
- Updating real-time system software is often needed in response to errors and added requirements to the software. Stopping a running application, updating the software, and then restarting the application is not suitable for systems with high availability requirements. On the other hand, dynamically updating a system may increase the execution time of the tasks, thus, degrading the performance of the system. Degradation is not acceptable for performance-critical real-time systems as there are strict requirements on the performance. In this paper we present an approach that enables dynamic reconfiguration of a real-time system, where the performance of the system during a reconfiguration satisfies a given worst-case performance specification. Evaluation shows that the presented method is efficient in guaranteeing the worst-case performance of dynamically reconfigurable firm real-time systems.
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| 4. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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QoD Adaptation for Achieving Lifetime Predictability of WSN Nodes Communicating over Satellite Links
- 2007
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Ingår i: International Conference on Networked Sensing Systems INSS,2007. - : IEEE. - 1424412315 ; , s. 19-26
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose an architecture consisting of a particular type of node, namely a communication server that collects and aggregates data, and establishes a link between the users and the sensor nodes through satellite communication. A key challenge with satisfying a lifetime requirement of the communication server is the unpredictability of the sensor data volume arriving at the communication server and the transmission power of the satellite terminal. To provide lifetime predictability we propose an approach that automatically adjusts the quality of the data such that the specified lifetime if achieved. We have shown through an extensive evaluation that the approach manages to provide an actual lifetime within 2% of the specified lifetime despite variations in workload and communication link quality.
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| 5. |
- Amirijoo, Mehdi, 1978-
(författare)
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QoS Control of Real-Time Data Services under Uncertain Workload
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Real-time systems comprise computers that must generate correct results in a timely manner. This involves a wide spectrum of computing systems found in our everyday life ranging from computers in rockets to our mobile phones. The criticality of producing timely results defines the different types of realtime systems. On one hand, we have the so-called hard real-time systems, where failing to meet deadlines may result in a catastrophe. In this thesis we are, however, concerned with firm and soft real-time systems, where missing deadlines is acceptable at the expense of degraded system performance. The usage of firm and soft real-time systems has increased rapidly during the last years, mainly due to the advent of applications in multimedia, telecommunication, and e-commerce. These systems are typically data-intensive, with the data normally spanning from low-level control data, typically acquired from sensors, to high-level management and business data. In contrast to hard real-time systems, the environments in which firm and soft real-time systems operate in are typically open and highly unpredictable. For example, the workload applied on a web server or base station in telecommunication systems varies according to the needs of the users, which is hard to foresee. In this thesis we are concerned with quality of service (QoS) management of data services for firm and soft real-time systems. The approaches and solutions presented aim at providing a general understanding of how the QoS can be guaranteed according to a given specification, even if the workload varies unpredictably. The QoS specification determines the desired QoS during normal system operation, and the worst-case system performance and convergence rate toward the desired setting in the face of transient overloads. Feedback control theory is used to control QoS since little is known about the workload applied on the system. Using feedback control the difference between the measured QoS and the desired QoS is formed and fed into a controller, which computes a change to the operation of the real-time system. Experimental evaluation shows that using feedback control is highly effective in managing QoS such that a given QoS specification is satisfied. This is a key step toward automatic management of intricate systems providing real-time data services.
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| 6. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Raising Motivation in Real-time Laboratories : The Soccer Scenario
- 2004
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Ingår i: Technical Symposium on Computer Science Education, SIGCSE,2004. - USA : Association for Computing Machinery (ACM). ; , s. 265-
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Konferensbidrag (refereegranskat)abstract
- Real-time systems is a topic that one cannot overlook in an engineer's education. However, teaching real-time systems in an undergraduate syllabus is a challenging experience due to conflicting constraints placed on such a course. In this paper we present a new setup for laboratories in the real-time systems course that successfully meets the constraints of mass education, stable environment management, short time span for the labs, and still enables deep involvement of students in the central topic of resource allocation with high motivation.
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| 7. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Specification and Management of QoS in Imprecise Real-Time Databases
- 2003
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Ingår i: International Database Engineering and Applications Symposium,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 192-
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Konferensbidrag (refereegranskat)abstract
- Real-time applications such as e-commerce, flight control, chemical and nuclear control, and telecommunication are becoming increasingly sophisticated in their data needs, resulting in greater demands for real-time data services. Since the workload of real-time databases RTDBs, providing real-time data services, cannot be precisely predicted, they can become overloaded and thereby cause temporal violations, resulting in a damage or even a catastrophe. Imprecise computation techniques address this problem and allow graceful degradation during overloads. In this paper, we present a framework consisting of a model for expressing QoS requirements in terms of data and transaction preciseness, an architecture based on feedback control scheduling, and a set of algorithms implementing different policies and behaviors. Our approach gives a robust and controlled behavior of RTDBs, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms, including FCS-EDF that schedules the transactions using EDF and feedback control.
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| 8. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Toward Adaptive Control of QoS-Importance Decoupled Real-Time Systems
- 2007
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Ingår i: IEEE International Workshop on Feedback Control Implementation and Design in Computing Systems and Networks,2007.
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Konferensbidrag (refereegranskat)abstract
- This paper deals with differentiated services in real-time systems. Tasks submitted to a real-time system are differentiated with respect to importance and QoS requirements. We use feedback control to enforce the requirements in QoS and ensure a hierarchical admission policy based on the importance of the tasks. The results show that the requirements are met during steady state when the workload is constant. The feedback control approach does not satisfactorily manage QoS when there is a sudden and significant workload change (transient state) due to the time-variant nature of the system. To address this, we present preliminary and promising results using adaptive control, and report on some challenges we are facing when applying the theory.
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| 9. |
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| 10. |
- Larsson, Erik, 1966-, et al.
(författare)
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What Impacts Course Evaluation?
- 2007
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Ingår i: 12th SIGCSE Conf. on Innovation and Technology in Computer Science Education,2007. - New York, NY, USA : ACM. - 9781595936103 ; , s. 333-333
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Konferensbidrag (refereegranskat)abstract
- Today most universities are using course evaluations. However, course evaluations are often discussed and questioned. This paper reports on a survey where we aim at finding out (1) if students have a preconceived notion of a course, (2) if course evaluation scores can be predicted early in a course, (3) if exam throughput impacts course evaluation, and (4) if web-based evaluation reflects the general opinion from students. The results from the study indicate that students do not let preconceived notion impact nor does exam throughput matter to course evaluation. Further, the final web-based results seem to correlate with opinion of students attending lectures. However, the evaluation grades tend to be defined early in the course; hence first impression lasts.
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