Improving Reliability of Hybrid Bit-Semantic Communications for Cellular Networks

TL;DR

This work tackles reliability in hybrid BitCom-SemCom cellular networks by deriving closed‑form outage expressions for both pure and hybrid schemes and introducing a generalized outage metric that allows a controlled number of outage users. It develops a semantic‑utilization metric to align SemCom deployment with hardware and memory constraints, and provides closed‑form cell‑radius formulas (including for path loss exponent $a=2$) to meet target outage levels. The results show the hybrid BitCom-SemCom network can achieve lower outage and higher spectral efficiency than pure BitCom or SemCom, with the optimal radius depending on user QoS and resource budgets. Simulations validate the analytical expressions and offer design guidance for reliable, resource-aware hybrid networks in future cellular systems.

Abstract

Semantic communications (SemComs) have been considered as a promising solution to reduce the amount of transmitted information, thus paving the way for more energy-and spectrum-efficient wireless networks. Nevertheless, SemComs rely heavily on the utilization of deep neural networks (DNNs) at the transceivers, which limit the accuracy between the original and reconstructed data and are challenging to implement in practice due to increased architecture complexity. Thus, hybrid cellular networks that utilize both conventional bit communications (BitComs) and SemComs have been introduced to bridge the gap between required and existing infrastructure. To facilitate such networks, in this work, we investigate reliability by deriving closed-form expressions for the outage probability of the network. Additionally, we propose a generalized outage probability through which the cell radius that achieves a desired outage threshold for a specific range of users is calculated in closed form. Additionally, to consider the practical limitations caused by the specialized dedicated hardware and the increased memory and computational resources that are required to support SemCom, a semantic utilization metric is proposed. Based on this metric, we express the probability that a specific number of users select SemCom transmission and calculate the optimal cell radius for that number in closed form. Simulation results validate the derived analytical expressions and the characterized design properties of the cell radius found through the proposed metrics, providing useful insights.

Figures (7)

• Figure 1: Model of the hybrid BitCom-SemCom network cell of multiple users. The users inside the blue region have a received SNR for which SemCom utilization is used, as illustrated by the green arrows. Similarly, the users in the brown areas have a received SNR such that BitCom transmission is utilized by the BS, as indicated by the red arrows.
• Figure 3: Probability of at least one user being in outage for all types of networks and varying similarity threshold $M^{\mathrm{th}}$. For the BitCom and hybrid network, the $\mathrm{BER}$ value of the bit users is set to that of Table \ref{['table:tableParameters']} except for the capacity curves, where $\Gamma = 1$ and no error occurs for bit transmission.
• Figure 4: Probability of at least one user being in outage for all types of networks and varying outage rate threshold $R_{\mathrm{out}}$.
• Figure 5: Probability of $L_l=3$ or more users being in outage for increasing cell size and varying similarity and outage rate thresholds, when $a=2$, $\mathcal{P} = 1mW$. The continuous and dotted lines symbolize $L=10$ and $L=50$ users, respectively.
• Figure 6: Probability of $L_l = 2, L_l = 4$ or more users being in outage for increasing cell size and outage rate threshold $R_{\mathrm{out}}=0.12$, when $a=2$, $\mathcal{P} = 1mW$. The continuous and dotted lines symbolize $L=10$ and $L=50$ users, respectively.

Theorems & Definitions (4)

• Theorem 1
• Theorem 2
• Proposition 1
• Proposition 2