Hyeonjoong Cho

An Optimal Real-Time Scheduling Algorithm for Multiprocessors

We present an optimal real-time scheduling algorithm for multiprocessors

Heterogenous Quorum-Based Wake-Up Scheduling in Wireless Sensor Networks

one that satisfies all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. The algorithm called LLREF, is designed based on a novel abstraction for reasoning about task execution behavior on multiprocessors: the time and local execution time domain plane (or T-L plane). LLREF is based on the fluid scheduling model and the fairness notion, and uses the T-L plane to describe fluid schedules without using time quanta, unlike the optimal Pfair algorithm (which uses time quanta). We show that scheduling for multiprocessors can be viewed as repeatedly occurring T-L planes, and feasibly scheduling on a single T-L plane results in the optimal schedule. We analytically establish the optimality of LLREF. Further, we establish that the algorithm has bounded overhead, and this bound is independent of time quanta (unlike Pfair). Our simulation results validate our analysis on the algorithm overhead

Probability-Based Prediction and Sleep Scheduling for Energy-Efficient Target Tracking in Sensor Networks

We present heterogenous quorum-based asynchronous wake-up scheduling schemes for wireless sensor networks. The schemes can ensure that two nodes that adopt different quorum systems as their wake-up schedules can hear each other at least once in bounded time intervals. We propose two such schemes: cyclic quorum system pair (cqs-pair) and grid quorum system pair (gqs-pair). The cqs-pair which contains two cyclic quorum systems provides an optimal solution, in terms of energy saving ratio, for asynchronous wake-up scheduling. To quickly assemble a cqs-pair, we present a fast construction scheme which is based on the multiplier theorem and the (N,k,M, l)-difference pair defined by us. Regarding the gqs-pair, we prove that any two grid quorum systems will automatically form a gqs-pair. We further analyze the performance of both designs, in terms of average discovery delay, quorum ratio, and energy saving ratio. We show that our designs achieve better trade-off between the average discovery delay and quorum ratio (and thus energy consumption) for different cycle lengths. We implemented the proposed designs in a wireless sensor network platform of Telosb motes. Our implementation-based measurements further validate the analytically-established performance trade-off of our designs.

CQS-Pair: Cyclic Quorum System Pair for Wakeup Scheduling in Wireless Sensor Networks

A surveillance system, which tracks mobile targets, is one of the most important applications of wireless sensor networks. When nodes operate in a duty cycling mode, tracking performance can be improved if the target motion can be predicted and nodes along the trajectory can be proactively awakened. However, this will negatively influence the energy efficiency and constrain the benefits of duty cycling. In this paper, we present a Probability-based Prediction and Sleep Scheduling protocol (PPSS) to improve energy efficiency of proactive wake up. We start with designing a target prediction method based on both kinematics and probability. Based on the prediction results, PPSS then precisely selects the nodes to awaken and reduces their active time, so as to enhance energy efficiency with limited tracking performance loss. We evaluated the efficiency of PPSS with both simulation-based and implementation-based experiments. The experimental results show that compared to MCTA algorithm, PPSS improves energy efficiency by 25-45 percent (simulation based) and 16.9 percent (implementation based), only at the expense of an increase of 5-15 percent on the detection delay (simulation based) and 4.1 percent on the escape distance percentage (implementation based), respectively.

Energy efficient sleep scheduling based on moving directions in target tracking sensor network

Due to the heterogenous power-saving requirement in wireless sensor networks, we propose the Cyclic Quorum System Pair (CQS-Pair) which can guarantee that two asynchronous nodes adopt different cyclic quorum systems can hear each other at least once in bounded time intervals. To quickly assemble a CQS-Pair, we present a fast construction scheme, which is based on the Multiplier Theorem and the

T-L plane-based real-time scheduling for homogeneous multiprocessors

(N,k,M,\emph{l})

Scheduling distributable real-time threads in Tempus middleware

-difference pair defined by us. We show that via the CQS-Pair, two heterogenous nodes can achieve different power saving ratios while maintaining connectivity. The performance of a CQS-Pair is analyzed in terms of average delay and quorum ratio.

A text entry technique for wrist-worn watches with tiny touchscreens

This paper presents a target direction-based sleep scheduling algorithm (TDSS) for target tracking surveillance sensor networks. TDSS reduces the number of the proactively awakened sensor nodes and schedules their sleep pattern to enhance energy efficiency but suffer little performance loss. Both approaches are based on two probabilistic distribution models of target moving directions, normal distribution and linear distribution. We compare TDSS with the two models against the legacy circle-based proactively waking up scheme (Circle) and a working node reducing algorithm - MCTA. The evaluation result shows that TDSS achieves better energy efficiency but with less performance loss in terms of detection probability and detection delay.

A space-optimal wait-free real-time synchronization protocol

We consider optimal real-time scheduling of periodic tasks on multiprocessors-i.e., satisfying all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. We introduce a novel abstraction for reasoning about task execution behavior on multiprocessors, called T-L plane and present T-L plane-based real-time scheduling algorithms. We show that scheduling for multiprocessors can be viewed as scheduling on repeatedly occurring T-L planes, and feasibly scheduling on a single T-L plane results in an optimal schedule. Within a single T-L plane, we analytically show a sufficient condition to provide a feasible schedule. Based on these, we provide two examples of T-L plane-based real-time scheduling algorithms, including non-work-conserving and work-conserving approaches. Further, we establish that the algorithms have bounded overhead. Our simulation results validate our analysis of the algorithm overhead. In addition, we experimentally show that our approaches have a reduced number of task migrations among processors when compared with a previous algorithm.

Space-Optimal, Wait-Free Real-Time Synchronization

This paper presents the Tempus real-time middleware, which supports real-time CORBA 2.0s distributable threads (DTs) as an end-to-end programming abstraction for distributed real-time systems. DTs in Tempus can have time constraints, including time/utility functions (TUFs), can have resource constraints, including mutual exclusion, and can be scheduled according to utility accrual (UA) disciplines. Tempus propagates the scheduling parameters of DTs as they transit objects and hence perhaps node boundaries. Node-local instances of a UA scheduling algorithm use the propagated parameters to construct local schedules and resolve resource dependencies for local timeliness optimization, toward approximate, system-wide timeliness optimality. Tempus uses an application-level scheduling framework for node-local TUF/UA scheduling on real-time POSIX-compliant operating systems. Our experimental measurements demonstrate the effectiveness of the middleware in scheduling DTs.