Optimal Sampling and Scheduling for Timely Status Updates in Multi-Source Networks

• Published in: IEEE transactions on information theory Vol. 67; no. 6; pp. 4019 - 4034
• Main Authors: Bedewy, Ahmed M., Sun, Yin, Kompella, Sastry, Shroff, Ness B.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Age; Age of Information; age-penalty; Complexity; Complexity theory; data freshness; Data integrity; Delays; Freshness; information updates; Iterative algorithms; Measurement; multi-source; Optimal scheduling; Optimization; Penalty function; Sampling; Scheduling; Wireless sensor networks
• ISSN: 0018-9448; 1557-9654
• DOI: 10.1109/TIT.2021.3060387

We consider a joint sampling and scheduling problem for optimizing data freshness in multi-source systems. Data freshness is measured by a non-decreasing penalty function of age of information , where all sources have the same age-penalty function. Sources take turns to generate update packets, and forward them to their destinations one-by-one through a shared channel with random delay. There is a scheduler, that chooses the update order of the sources, and a sampler, that determines when a source should generate a new packet in its turn. We aim to find the optimal scheduler-sampler pairs that minimize the total-average age-penalty at delivery times (Ta-APD) and the total-average age-penalty (Ta-AP). We prove that the Maximum Age First (MAF) scheduler and the zero-wait sampler are jointly optimal for minimizing the Ta-APD. Meanwhile, the MAF scheduler and a relative value iteration with reduced complexity (RVI-RC) sampler are jointly optimal for minimizing the Ta-AP. The RVI-RC sampler is based on a relative value iteration algorithm whose complexity is reduced by exploiting a threshold property in the optimal sampler. Finally, a low-complexity threshold-type sampler is devised via an approximate analysis of Bellman's equation. This threshold-type sampler reduces to a simple water-filling sampler for a linear age-penalty function.