Efficient URLLC with a Reconfigurable Intelligent Surface and Imperfect Device Tracking

TL;DR

This paper investigates how imperfections in device positioning affect the reliability of RIS-assisted URLLC, deriving bounds and optimizing power control to meet strict latency and reliability constraints.

Contribution

It introduces a method to analyze the impact of positioning errors on RIS-based URLLC and proposes a power control scheme ensuring reliability despite uncertainties.

Findings

Derived an upper bound on outage probability considering positioning errors.

Proposed a conservative power control method that guarantees URLLC constraints.

Achieved a tight bound with an optimality gap of 1.5 to 4.5 dB.

Abstract

The use of Reconfigurable Intelligent Surfaces (RIS) technology to extend coverage and allow for better control of the wireless environment has been proposed in several use cases, including Ultra-Reliable Low-Latency Communications (URLLC), communications. However, the extremely challenging latency constraint makes explicit channel estimation difficult, so positioning information is often used to configure the RIS and illuminate the receiver device. In this work, we analyze the effect of imperfections in the positioning information on the reliability, deriving an upper bound to the outage probability. We then use this bound to perform power control, efficiently finding the minimum power that respects the URLLC constraints under positioning uncertainty. The optimization is conservative, so that all points respect the URLLC constraints, and the bound is relatively tight, with an optimality gap between 1.5 and 4.5~dB.