Issue No. 03 - March (2016 vol. 28)
Song Han , Department of Computer Science and Engineering, University of Connecticut, Storrs, CT
Kam-Yiu Lam , Department of Computer Science, City University of Hong Kong
Deji Chen , , Tongji University
Ming Xiong , , Google Inc
Jiantao Wang , Noah?s Ark Lab, Huawei Tech
Krithi Ramamritham , Department of Computer Science and Engineering, IIT Bombay
Aloysius K. Mok , Department of Computer Science, the University of Texas at Austin, Austin, TX
Maintaining the freshness of real-time data is one of the crucial design issues in cyber-physical systems (CPS). Past studies have focused on designing update algorithms to minimize the workload imposed by a fixed set of update tasks while ensuring the temporal validity of data. In this paper, we revisit this problem in
dynamic cyber-physical systems (DCPS) which may exhibit multi-modal behavior. Any solution to this problem must recognize that: (1) different update algorithms may be needed in different modes according to the workload in each mode, and (2) temporal validity of data must be maintained not only in each mode but also during the mode switch. To strike a balance between data freshness and system schedulability, we propose a utilization-based scheduling selection (UBSS) strategy. We first introduce two synchronous mode switch algorithms, named search-based switch (SBS) and adjustment-based switch (ABS) to search for the proper switch point online and execute all update tasks in the new mode synchronously. SBS checks for temporal validity at the beginning time slot of each idle period in the schedule, while ABS relaxes this restriction through schedule adjustment. To support immediate mode switch, we propose an asynchronous switch algorithm named instant switch (IS) to reduce the switch delay. IS schedules outstanding jobs from the old mode together with the jobs in the new mode using the least-available-laxity-first scheduling policy. Our experimental results demonstrate the effectiveness of these three algorithms. They also show that UBSS strategy can significantly outperform a single fixed update algorithm in terms of maintaining better data freshness while incurring only limited online switch overhead.
Switches, Real-time systems, Schedules, Algorithm design and analysis, Electronic mail, Protocols, Cyber-physical systems
S. Han et al., "Online Mode Switch Algorithms for Maintaining Data Freshness in Dynamic Cyber-Physical Systems," in IEEE Transactions on Knowledge & Data Engineering, vol. 28, no. 3, pp. 756-769, 2016.