IRS-Enabled Covert and Reliable Communications: How Many Reflection Elements are Required?

TL;DR

This paper investigates the minimum number of IRS reflection elements needed to ensure covert and reliable short-packet communications, deriving theoretical bounds and validating them through simulations.

Contribution

It provides a theoretical framework linking the number of IRS elements with covertness and reliability, addressing a key practical question in system design.

Findings

More IRS elements are needed for higher reliability under tighter covertness constraints.

The derived error probability expressions accurately predict system performance.

Asymptotic analysis offers guidelines for IRS design in high covertness regimes.

Abstract

Short-packet communications are applied to various scenarios where transmission covertness and reliability are crucial due to the open wireless medium and finite blocklength. Although intelligent reflection surface (IRS) has been widely utilized to enhance transmission covertness and reliability, the question of how many reflection elements at IRS are required remains unanswered, which is vital to system design and practical deployment. The inherent strong coupling exists between the transmission covertness and reliability by IRS, leading to the question of intractability. To address this issue, the detection error probability at the warder and its approximation are derived first to reveal the relation between covertness performance and the number of reflection elements. Besides, to evaluate the reliability performance of the system, the decoding error probability at the receiver is also derived. Subsequently, the asymptotic reliability performance in high covertness regimes is investigated, which provides theoretical predictions about the number of reflection elements at IRS required to achieve a decoding error probability close to 0 with given covertness requirements. Furthermore, Monte-Carlo simulations verify the accuracy of the derived results for detection (decoding) error probabilities and the validity of the theoretical predictions for reflection elements. Moreover, results show that more reflection elements are required to achieve high reliability with tighter covertness requirements, longer blocklength and higher transmission rates.