Special Issue "Age of Information: Concept, Metric and Tool for Network Control"

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Information Theory, Probability and Statistics".

Deadline for manuscript submissions: 23 February 2022.

Special Issue Editors

Prof. Dr. Anthony Ephremides
E-Mail Website
Guest Editor
ECE Department, University of Maryland, College Park, MD 20742, USA
Interests: information theory; communication theory; multi-user systems; communication networks; satellite systems; systems theory; stochastic systems; optimization; signal processing; wireless communications; age of information
Prof. Dr. Yin Sun
E-Mail Website
Guest Editor
Department of Electrical and Computer Engineering, Auburn University, Auburn, AL 36849-5201, USA
Interests: age of information; information freshness; wireless networks; remote estimation; machine learning

Special Issue Information

Dear Colleagues,

The concept of information freshness has developed over the last few years into an active and rapidly growing area of research. It has become known as the Age of Information (AoI). After its initial formal introduction, it became clear that it was very relevant (if not crucial) for numerous applications, ranging from autonomous vehicle systems, internet of things, real-time computing to database access, caching, and wireless communications. More importantly, the combination of transmission delay and sampling rate that are involved in the formulation of the AoI concept made it clear that there are far-reaching consequences in the relationship between signal processing, information theory, and control theory at a fundamental level. 

In this Special Issue, we aim at attracting contributions that span the full range of applications and theoretical foundations of the AoI concept, which, in fact, is also a performance metric and an analysis tool. Of special interest is the role of AoI in bridging different disciplines and the use of AoI in the analysis and optimization involved in important applications.

Prof. Anthony Ephremides
Prof. Yin Sun
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (7 papers)

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Research

Article
Scheduling to Minimize Age of Incorrect Information with Imperfect Channel State Information
Entropy 2021, 23(12), 1572; https://0-doi-org.brum.beds.ac.uk/10.3390/e23121572 - 25 Nov 2021
Viewed by 262
Abstract
In this paper, we study a slotted-time system where a base station needs to update multiple users at the same time. Due to the limited resources, only part of the users can be updated in each time slot. We consider the problem of [...] Read more.
In this paper, we study a slotted-time system where a base station needs to update multiple users at the same time. Due to the limited resources, only part of the users can be updated in each time slot. We consider the problem of minimizing the Age of Incorrect Information (AoII) when imperfect Channel State Information (CSI) is available. Leveraging the notion of the Markov Decision Process (MDP), we obtain the structural properties of the optimal policy. By introducing a relaxed version of the original problem, we develop the Whittle’s index policy under a simple condition. However, indexability is required to ensure the existence of Whittle’s index. To avoid indexability, we develop Indexed priority policy based on the optimal policy for the relaxed problem. Finally, numerical results are laid out to showcase the application of the derived structural properties and highlight the performance of the developed scheduling policies. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
Age of Information of Parallel Server Systems with Energy Harvesting
Entropy 2021, 23(11), 1549; https://0-doi-org.brum.beds.ac.uk/10.3390/e23111549 - 21 Nov 2021
Viewed by 229
Abstract
Motivated by current communication networks in which users can choose different transmission channels to operate and also by the recent growth of renewable energy sources, we study the average Age of Information of a status update system that is formed by two parallel [...] Read more.
Motivated by current communication networks in which users can choose different transmission channels to operate and also by the recent growth of renewable energy sources, we study the average Age of Information of a status update system that is formed by two parallel homogeneous servers and such that there is an energy source that feeds the system following a random process. An update, after getting service, is delivered to the monitor if there is energy in a battery. However, if the battery is empty, the status update is lost. We allow preemption of updates in service and we assume Poisson generation times of status updates and exponential service times. We show that the average Age of Information can be characterized by solving a system with eight linear equations. Then, we show that, when the arrival rate to both servers is large, the average Age of Information is one divided by the sum of the service rates of the servers. We also perform a numerical analysis to compare the performance of our model with that of a single server with energy harvesting and to study in detail the aforementioned convergence result. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
Age-Aware Utility Maximization in Relay-Assisted Wireless Powered Communication Networks
Entropy 2021, 23(9), 1177; https://0-doi-org.brum.beds.ac.uk/10.3390/e23091177 - 07 Sep 2021
Viewed by 477
Abstract
This article investigates a relay-assisted wireless powered communication network (WPCN), where the access point (AP) inspires the auxiliary nodes to participate together in charging the sensor, and then the sensor uses its harvested energy to send status update packets to the AP. An [...] Read more.
This article investigates a relay-assisted wireless powered communication network (WPCN), where the access point (AP) inspires the auxiliary nodes to participate together in charging the sensor, and then the sensor uses its harvested energy to send status update packets to the AP. An incentive mechanism is designed to overcome the selfishness of the auxiliary node. In order to further improve the system performance, we establish a Stackelberg game to model the efficient cooperation between the AP–sensor pair and auxiliary node. Specifically, we formulate two utility functions for the AP–sensor pair and the auxiliary node, and then formulate two maximization problems respectively. As the former problem is non-convex, we transform it into a convex problem by introducing an extra slack variable, and then by using the Lagrangian method, we obtain the optimal solution with closed-form expressions. Numerical experiments show that the larger the transmit power of the AP, the smaller the age of information (AoI) of the AP–sensor pair and the less the influence of the location of the auxiliary node on AoI. In addition, when the distance between the AP and the sensor node exceeds a certain threshold, employing the relay can achieve better AoI performance than non-relaying systems. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
A UoI-Optimal Policy for Timely Status Updates with Resource Constraint
Entropy 2021, 23(8), 1084; https://0-doi-org.brum.beds.ac.uk/10.3390/e23081084 - 20 Aug 2021
Viewed by 995
Abstract
Timely status updates are critical in remote control systems such as autonomous driving and the industrial Internet of Things, where timeliness requirements are usually context dependent. Accordingly, the Urgency of Information (UoI) has been proposed beyond the well-known Age of Information (AoI) by [...] Read more.
Timely status updates are critical in remote control systems such as autonomous driving and the industrial Internet of Things, where timeliness requirements are usually context dependent. Accordingly, the Urgency of Information (UoI) has been proposed beyond the well-known Age of Information (AoI) by further including context-aware weights which indicate whether the monitored process is in an emergency. However, the optimal updating and scheduling strategies in terms of UoI remain open. In this paper, we propose a UoI-optimal updating policy for timely status information with resource constraint. We first formulate the problem in a constrained Markov decision process and prove that the UoI-optimal policy has a threshold structure. When the context-aware weights are known, we propose a numerical method based on linear programming. When the weights are unknown, we further design a reinforcement learning (RL)-based scheduling policy. The simulation reveals that the threshold of the UoI-optimal policy increases as the resource constraint tightens. In addition, the UoI-optimal policy outperforms the AoI-optimal policy in terms of average squared estimation error, and the proposed RL-based updating policy achieves a near-optimal performance without the advanced knowledge of the system model. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
Relationship between Age and Value of Information for a Noisy Ornstein–Uhlenbeck Process
Entropy 2021, 23(8), 940; https://0-doi-org.brum.beds.ac.uk/10.3390/e23080940 - 23 Jul 2021
Viewed by 455
Abstract
The age of information (AoI) has been widely used to quantify the information freshness in real-time status update systems. As the AoI is independent of the inherent property of the source data and the context, we introduce a mutual information-based value of information [...] Read more.
The age of information (AoI) has been widely used to quantify the information freshness in real-time status update systems. As the AoI is independent of the inherent property of the source data and the context, we introduce a mutual information-based value of information (VoI) framework for hidden Markov models. In this paper, we investigate the VoI and its relationship to the AoI for a noisy Ornstein–Uhlenbeck (OU) process. We explore the effects of correlation and noise on their relationship, and find logarithmic, exponential and linear dependencies between the two in three different regimes. This gives the formal justification for the selection of non-linear AoI functions previously reported in other works. Moreover, we study the statistical properties of the VoI in the example of a queue model, deriving its distribution functions and moments. The lower and upper bounds of the average VoI are also analysed, which can be used for the design and optimisation of freshness-aware networks. Numerical results are presented and further show that, compared with the traditional linear age and some basic non-linear age functions, the proposed VoI framework is more general and suitable for various contexts. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
Channel Quality-Based Optimal Status Update for Information Freshness in Internet of Things
Entropy 2021, 23(7), 912; https://0-doi-org.brum.beds.ac.uk/10.3390/e23070912 - 18 Jul 2021
Cited by 1 | Viewed by 703
Abstract
This paper investigates the status updating policy for information freshness in Internet of things (IoT) systems, where the channel quality is fed back to the sensor at the beginning of each time slot. Based on the channel quality, we aim to strike a [...] Read more.
This paper investigates the status updating policy for information freshness in Internet of things (IoT) systems, where the channel quality is fed back to the sensor at the beginning of each time slot. Based on the channel quality, we aim to strike a balance between the information freshness and the update cost by minimizing the weighted sum of the age of information (AoI) and the energy consumption. The optimal status updating problem is formulated as a Markov decision process (MDP), and the structure of the optimal updating policy is investigated. We prove that, given the channel quality, the optimal policy is of a threshold type with respect to the AoI. In particular, the sensor remains idle when the AoI is smaller than the threshold, while the sensor transmits the update packet when the AoI is greater than the threshold. Moreover, the threshold is proven to be a non-increasing function of channel state. A numerical-based algorithm for efficiently computing the optimal thresholds is proposed for a special case where the channel is quantized into two states. Simulation results show that our proposed policy performs better than two baseline policies. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Article
Scheduling Strategy Design Framework for Cyber–Physical System with Non-Negligible Propagation Delay
Entropy 2021, 23(6), 714; https://0-doi-org.brum.beds.ac.uk/10.3390/e23060714 - 04 Jun 2021
Viewed by 796
Abstract
Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form [...] Read more.
Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies. Full article
(This article belongs to the Special Issue Age of Information: Concept, Metric and Tool for Network Control)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

  1. Sennur Ulukus (University of Maryland)
  2. Elif Uysal (Middle East Technical University)
  3. Nikolaos Pappas (Linköping University)
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