publications

2021

1. PAPER

   Age of Information Minimization with Power and Distortion Constraints in Multiple Access Channels

   B, Gagan G,  S, Jayanth, and Bhat, Rajshekhar V

   IEEE Wiopt Oct 2021

   Abs

   Emerging fifth generation and beyond networks are expected to deliver accurate information as fresh as possible. In this work, we consider a wireless fading multiple access channel, where M users communicate to a base station (BS) in a time-slotted system. Each user can sample an information packet in any slot of interest, compress it to a finite number of bits and then transmit the compressed packet to the BS. The compression and transmission result in distortion and power consumption, respectively. Using the age of information (AoI) metric for quantifying freshness of information, we consider minimization of a long-term weighted average AoI across the users, subject to average power and distortion constraints at each user, for obtaining the number of bits to be transmitted by a user in a given slot. We cast the problem as a constrained Markov decision process (CMDP) and solve it via Lagrange relaxation. We show that a threshold-type policy is optimal for the relaxed problem. We also propose a convex optimization problem to obtain a suboptimal but simpler stationary randomized policy, whose minimum achievable average AoI is within twice that of the optimal policy. Via numerical simulations, we illustrate the threshold structure of the CMDP based solution and study variation of the average AoIs achieved by the proposed policies when the bounds on the average power and distortion constraints are varied.

2022

1. PAPER

   Age of Processed Information Minimization over Fading Multiple Access Channels

   S, Jayanth, and Bhat, Rajshekhar V

   2022 IEEE International Conference on Communications (ICC): Wireless Communications Symposium (IEEE ICC’22 - WC Symposium) May 2022

   Abs

   In many real-time applications, timely accessibility to actionable insights, usually obtained by processing raw status updates, is an important requirement. In this paper, we consider users equipped with sensors and actuators. The sensors of a user generate status updates which need to be processed for driving the actuators of the user. The processing task of a user can be carried out locally or it can be offloaded to an edge server, located at a common base station (BS). The users access the BS via a fading multiple access channel using a non-orthogonal multiple access technique. To measure the timeliness of processed information, we adopt a metric called age of processed information (AoPI), defined as the time elapsed since the generation of last successfully processed packet available at the user. In this setting, we formulate a problem for minimizing a long-term average AoPI across the users, when the users are subjected to average power constraints. The BS has to decide when a user should generate a status update and whether it should be processed locally or at the edge server. We cast the problem as a constrained Markov decision process (CMDP) and obtain the optimal policy via Lagrange relaxation. We derive several structural properties of the policy. We also obtain a simpler but suboptimal policy via Lyapunov optimization and bound its performance. Using numerical simulations, we demonstrate the threshold structure of CMDP based solution and study behavior of the average AoPI under different policies when problem parameters are varied.