Energy-Latency Tradeoff in Ultra-Reliable Low-Latency Communication with Retransmissions

TL;DR

This paper investigates the energy-latency tradeoff in URLLC systems using IR-HARQ, proposing an optimization algorithm that significantly reduces energy consumption while meeting latency constraints.

Contribution

It introduces a dynamic programming approach to optimize IR-HARQ parameters for energy efficiency under latency constraints in URLLC.

Findings

IR-HARQ achieves 25% energy savings over one-shot transmission.

The optimization balances retransmissions, blocklength, and power for energy efficiency.

The problem formulation accounts for finite blocklength and feedback delay.

Abstract

High-fidelity, real-time interactive applications are envisioned with the emergence of the Internet of Things (IoT) and tactile Internet by means of ultra-reliable low-latency communications (URLLC). Exploiting time diversity for fulfilling the URLLC requirements in an energy efficient manner is a challenging task due to the nontrivial interplay among packet size, retransmission rounds and delay, and transmit power. In this paper, we study the fundamental energy-latency tradeoff in URLLC systems employing incremental redundancy (IR) hybrid automatic repeat request (HARQ). We cast the average energy minimization problem with a finite blocklength (latency) constraint and feedback delay, which is non-convex. We propose a dynamic programming algorithm for energy efficient IR-HARQ optimization in terms of number of retransmissions, blocklength and power per round. Numerical results show that our IR-HARQ approach could provide around 25\% energy saving compared to one-shot transmission (no HARQ).