Uplink Multiplexing of eMBB/URLLC Services Assisted by Reconfigurable Intelligent Surfaces

TL;DR

This work introduces a reconfigurable intelligent surface (RIS)–assisted uplink multiplexing scheme to support concurrent eMBB and URLLC services with no base-station coordination. It designs two RIS configurations based on eMBB CSI: an eMBB-oriented coherent beamformer $\boldsymbol{\psi}^{\mathrm{e}}$ that maximizes the eMBB effective channel $|\mathbf{g}_e^H \boldsymbol{\psi}^{\mathrm{e}}|^2$ (achieving high array gains up to $N^2$) and a URLLC-oriented configuration $\boldsymbol{\psi}^{\mathrm{u}}$ that mitigates interference during URLLC via either phasor-rotation or interference-nullning (IN) techniques. The scheme uses a three-phase frame (estimation, computing, payload transmission) and a URLLC preamble to detect traffic, enabling a switch to $\boldsymbol{\psi}^{\mathrm{u}}$ when URLLC traffic arrives. Outage analyses express instantaneous mutual information $I_e$ and $I_u$, yielding outage probabilities $P_e(r_e)$ and $P_u(r_u)$, and a latency term $D$ that accounts for preamble, switching, and payload transmission. Numerical results show that the proposed methods can outperform state-of-the-art preemptive puncturing by up to $4.9\times$ in URLLC outage, with performance improving as the RIS size increases, albeit with added estimation overhead; this approach enables balanced coexistence of heterogeneous uplink services under limited coordination.

Abstract

This letter proposes a scheme assisted by a reconfigurable intelligent surface (RIS) for efficient uplink traffic multiplexing between enhanced mobile broadband (eMBB) and ultra-reliable-low-latency communication (URLLC). The scheme determines two RIS configurations based only on the eMBB channel state information (CSI) available at the base station (BS). The first optimizes eMBB quality of service, while the second reduces eMBB interference in URLLC traffic by temporarily silencing the eMBB traffic. Numerical results demonstrate that this approach, relying solely on eMBB CSI and without BS coordination, can outperform the state-of-the-art preemptive puncturing by 4.9 times in terms of URLLC outage probability.

Figures (2)

• Figure 1: frame divided into estimation, computing, and payload transmission.
• Figure 2: outage probability and at the cell edge. When not otherwise specified, the transmit powers are $p_\text{e} = p_\text{u} = 23$ dBm, the has $N = 100$ elements, the traffic miss detection rate is $\epsilon_\text{m} = 0$, and the far-field distance is $\varrho_\text{f} = 4$ m. Also, in (e), $\xi$ is the fraction of mini-slots unaffected by the and the switching, as defined in \ref{['eq:mutual-information-embb']}.