Balancing AoI and Rate for Mission-Critical and eMBB Coexistence with Puncturing, NOMA,and RSMA in Cellular Uplink

TL;DR

This work tackles the coexistence of mission-critical (MC) and eMBB services in a cellular uplink by evaluating three medium-access strategies: puncturing, NOMA, and RSMA. It develops a discrete-time Markov chain framework to derive closed-form expressions for MC average AoI and PAoI violation probabilities, along with the eMBB data rate, under each scheme. The study characterizes how the SNR gap between eMBB and MC users governs when NOMA or RSMA can approach puncturing's AoI performance while delivering higher eMBB rates, and it optimizes RSMA's power and rate-splitting parameters to maximize MC reliability. The results show that puncturing can yield the best MC freshness with lower eMBB rates, while NOMA/RSMA can achieve substantially higher eMBB rates with only modest AoI penalties in suitable regimes; an adaptive strategy switching among schemes based on channel conditions can thus balance timeliness and throughput in mixed-critical networks.

Abstract

Through the lens of average and peak age-of-information (AoI), this paper takes a fresh look into the uplink medium access solutions for mission-critical (MC) communication coexisting with enhanced mobile broadband (eMBB) service. Considering the stochastic packet arrivals from an MC user, we study three access schemes: orthogonal multiple access (OMA) with eMBB preemption (puncturing), non-orthogonal multiple access (NOMA), and rate-splitting multiple access (RSMA), the latter two both with concurrent eMBB transmissions. Puncturing is found to reduce both average AoI and peak AoI (PAoI) violation probability but at the expense of decreased eMBB user rates and increased signaling complexity. Conversely, NOMA and RSMA offer higher eMBB rates but may lead to MC packet loss and AoI degradation. The paper systematically investigates the conditions under which NOMA or RSMA can closely match the average AoI and PAoI violation performance of puncturing while maintaining data rate gains. Closed-form expressions for average AoI and PAoI violation probability are derived, and conditions on the eMBB and MC channel gain difference with respect to the base station are analyzed. Additionally, optimal power and rate splitting factors in RSMA are determined through an exhaustive search to minimize MC outage probability. Notably, our results indicate that with a small loss in the average AoI and PAoI violation probability the eMBB rate in NOMA and RSMA can be approximately five times higher than that achieved through puncturing.

Figures (9)

• Figure 1: System model of eMBB-MC coexistence: (a) Single-cell uplink transmission scenario of eMBB and MC users, (b) Time-frequency resource grid with prescheduled eMBB user and generic overlapping access scheme for a "generate-at-will" MC user, (c) Puncturing-based access, (d) NOMA-based access, and (e) RSMA-based access scheme.
• Figure 2: Two-user Gaussian multiple-access capacity region. $x_{m}$ and $x_{e}$ are the information symbols of MC and eMBB, respectively. $y$ is the received signal. $I(x_{e};y)$ is the mutual information between $x_{e}$ and $y$. $I(x_{e};y|x_{m})$ is the conditional mutual information between $x_{e}$ and $y$ given $x_{m}$tse2005fundamentalsmao2022rate.
• Figure 3: An example of the AoI evolution for the MC user.
• Figure 4: The DTMC model representing the AoI evolution of MC traffic.
• Figure 5: Illustration of optimizing the choice among puncturing, NOMA, or RSMA w.r.t. the thresholds $\Gamma_{\text{th}}^{*,\text{NOMA}}$ and $\Gamma_{\text{th}}^{*,\text{RSMA}}$.