Wan Yeon Lee

Optimal Scheduling for Real-Time Parallel Tasks*This work was supported by the Research Grant from Hallym University, Korea and the ITRC program of the Korea Ministry of Information & Communications under grant IITA-2005-(C1090-0502-0020).

We propose an optimal algorithm for the real-time scheduling of parallel tasks on multiprocessors, where the tasks have the properties of flexible preemption, linear speedup, bounded parallelism, and arbitrary deadline. The proposed algorithm is optimal in the sense that it always finds out a feasible schedule if one exists. Furthermore, the algorithm delivers the best schedule consuming the fewest processors among feasible schedules. In this letter, we prove the optimality of the proposed algorithm. Also, we show that the time complexity of the algorithm is O(M2 · N2) in the worst case, where M and N are the number of tasks and the number of processors, respectively.

Hierarchical Real-Time Scheduling Framework for Imprecise Computations

Hierarchical scheduling frameworks provide ways for composing large and complex real-time systems from independent sub-systems. In this paper, we consider the imprecise reward-based periodic task model in a compositional scheduling framework. Thus, we introduce the imprecise periodic resource model to characterize the imprecise resource allocations, and the interface model to abstract the imprecise real-time requirements of the component. The schedulability analysis of mandatory parts is analyzed to meet the minimum requirement of tasks. In addition, we provide a scheduling algorithm for guaranteeing a certain amount of reward, which makes it feasible to compose multiple imprecise components efficiently.

Energy-efficient scheduling of a real-time task on DVFS-enabled multi-cores

We propose an energy-efficient scheduling of a long-lived real-time video task running on DVFS-enabled multi-core platforms. The proposed scheme reduces the energy consumption by executing the task in parallel on an appropriate number of cores with the other cores powered off, and assigning as lower frequency as possible while meeting the deadline. Evaluation shows that the scheme saves a significant energy consumed when executing the task on a single core, up to 67%.

Compositional real-time scheduling framework for periodic reward-based task model

As the size and complexity of embedded software systems increase, compositional real-time scheduling framework is widely accepted as means to build large and complex systems. A compositional real-time scheduling framework proposes to decompose a system into independent subsystems and provides ways to assemble them into a flexible hierarchical real-time scheduling system while guaranteeing the internal real-time requirements of each subsystem. In this paper, we consider the imprecise reward-based periodic task model in compositional scheduling framework. Thus, we introduce the imprecise periodic resource model to characterize the imprecise resource allocations provided by the system to a single component, and the interface model to abstract the imprecise real-time requirements of the component. The schedulability of mandatory parts is also analyzed to meet the minimum requirement of tasks. Finally, we provide a scheduling algorithm to guarantee a certain amount of reward, which makes it feasible to efficiently compose multiple imprecise components.

Maximum-Utility Scheduling of Operation Modes With Probabilistic Task Execution Times Under Energy Constraints

We propose a novel scheduling scheme that determines the instant operation modes of multiple tasks. The tasks have probabilistic execution times and are executed on discrete operation modes providing different utilities with different energy consumptions. We first design an optimal offline scheduling scheme that stochastically maximizes the cumulative utility of the tasks under energy constraints, at the cost of heavy computational overhead. Next, the optimal offline scheme is modified to an approximate online scheduling scheme. The online scheme has little runtime overhead and yields almost the maximum utility, with an energy budget that is given at runtime. The difference between the maximum utility and the output utility of the online scheme is bounded by a controllable input value. Extensive evaluation shows that the output utility of the online scheme approaches the maximum utility in most cases, and is much higher than that of existing methods by up to 50% of the largest utility difference among available operation modes.

Real-Time Data Stream Management System for Large Volume of RFID Events

A data stream management system (DSMS) for the real-time processing of a large volume of RFID events is proposed herein. It allows the real-time scheduling of groups of operators, the components of a query, to process user queries of various kinds within the time limit. It also creates user-level threads consisting of operators, and the DSMS scheduler schedules the threads of a query, depending on the priority. A prototype of the proposed system was built, and the scheduling of a large volume of RFID events was shown through experiments.

Dynamic Two-Tier Cell Structure for Bandwidth Reservation of Handoffs in Cellular Networks

To satisfy both the bandwidth efficiency of low-speed mobile hosts (MHs) and seamless handoff of high-speed MHs in cellular networks, this paper proposes a reservation scheme which exploits a dynamic two-tier cell structure and the handoff probability. The dynamic two-tier cell structure determines the reservation and non-reservation zones according to the speed of MHs. The handoff probability is calculated using the moving speed and the direction of MHs.

Integrity verification of the ordered data structures in manipulated video content

Video content stored in Video Event Data Recorders (VEDRs) are used as important evidence when certain events such as vehicle collisions occur. However, with sophisticated video editing software, assailants can easily manipulate video records to their advantage without leaving visible clues. Therefore, the integrity of video content recorded through VEDRs cannot be guaranteed, and the number of related forensic issues increases. Existing video integrity detection methods use the statistical properties of the pixels within each frame of the video. However, these methods require ample time, because they check frames individually. Moreover, the frame can easily be replaced and forged using the appropriate public software. To solve this problem, we propose an integrity checking mechanism using the structure of ordered fields in a video file, because existing video editing software does not allow users to access or modify field structures. In addition, because our proposed method involves checking the header information of video content only once, much less detection time is required compared with existing methods that examine the entire frames. We store an ordered file structure of video content as a signature in the database using a customized automated tool. The signature appears according to the video editing software. Then, the suspected video content is compared to a set of signatures. If the file structure matches with a signature, we recognize a manipulated video file by its corresponding editing software. We tested five types of video editing software that cover 99% of the video editing software market share. Furthermore, we arranged 305,981 saving options for all five video editing suites. As a result, we obtained 100% detection accuracy using stored signatures, without false positives, in a collection of 305,981 video files. The principle of this method can be applied to other video formats.

ICLS : Intelligent Cricket-based Location Tracking System Using Sensor Fusion

The key issues in ubiquitous sensor networks for context awareness is location-tracking. The main goal of location-tracking is to find the position of a moving object. In this paper, we describes the design and implementation of ICLS (Intelligent Cricket-based Location System). Especially, a more accurate location-tracking system using a sensor fusing mechanism is proposed herein. The benefits of sensor fusion are that it can obtain more accurate, complete, or dependable results. ICLS employs an ltrasonic sensor for ranging by time-of-flight measurements and uses a magnetic sensor to detect obstacles. To yield a more accurate navigation, a novel pass finding algorithm is also proposed in this paper. The results of the experiment that was conducted in this study show that a mobile robot moves towards a destination with a high degree of accuracy.

Energy-Aware Error Correction for QoS-Provisioning Real-Time Communications in Wireless Networks

A key issue in QoS-provisioning real-time wireless communications is to provide the QoS requirement with low energy consumption. In this paper, we propose an energy-efficient error correction scheme for real-time communications with QoS requirements in wireless networks. The QoS requirement of a message stream is modeled with (m, k) constraint, implying that at least m messages should be sent to a receiver during any window of k periods. The proposed scheme adaptively selects an error correcting code in an energy-efficient manner so that it maximizes the number of QoS provisionings per unit energy consumption.