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Joint Optimization for Security and Reliability in Round-Trip Transmissions for URLLC services

Xinyan Le, Yao Zhu, Yulin Hu, Bin Han

TL;DR

This work addresses secure and reliable round-trip URLLC transmissions under finite blocklength by extending an LFP-based metric to bidirectional communications. It develops both an exact integer-programming benchmark and two efficient algorithms—BCD and MM with convex approximation—to jointly optimize redundant bits and blocklengths under latency and reliability constraints. The authors derive feasible-region bounds, prove partial convexity, and demonstrate near-optimal performance with significantly reduced computation, enabling practical round-trip secure URLLC designs. The results reveal a fundamental trade-off: increasing total blocklength improves reliability but increases redundancy, enhancing security at the cost of payload efficiency, with the proposed methods delivering scalable solutions for real-world URLLC scenarios.

Abstract

Physical layer security (PLS) is a potential solution for secure and reliable transmissions in future Ultra-Reliable and Low-Latency Communications (URLLC). This work jointly optimizes redundant bits and blocklength allocation in practical round-trip transmission scenarios. To minimize the leakage-failure probability, a metric that jointly characterizes security and reliability in PLS, we formulate an optimization problem for allocating both redundant bits and blocklength. By deriving the boundaries of the feasible set, we obtain the globally optimal solution for this integer optimization problem. To achieve more computationally efficient solutions, we propose a block coordinate descent (BCD) method that exploits the partial convexity of the objective function. Subsequently, we develop a majorization-minimization (MM) algorithm through convex approximation of the objective function, which further improves computational efficiency. Finally, we validate the performance of the three proposed approaches through simulations, demonstrating their practical applicability for future URLLC services.

Joint Optimization for Security and Reliability in Round-Trip Transmissions for URLLC services

TL;DR

This work addresses secure and reliable round-trip URLLC transmissions under finite blocklength by extending an LFP-based metric to bidirectional communications. It develops both an exact integer-programming benchmark and two efficient algorithms—BCD and MM with convex approximation—to jointly optimize redundant bits and blocklengths under latency and reliability constraints. The authors derive feasible-region bounds, prove partial convexity, and demonstrate near-optimal performance with significantly reduced computation, enabling practical round-trip secure URLLC designs. The results reveal a fundamental trade-off: increasing total blocklength improves reliability but increases redundancy, enhancing security at the cost of payload efficiency, with the proposed methods delivering scalable solutions for real-world URLLC scenarios.

Abstract

Physical layer security (PLS) is a potential solution for secure and reliable transmissions in future Ultra-Reliable and Low-Latency Communications (URLLC). This work jointly optimizes redundant bits and blocklength allocation in practical round-trip transmission scenarios. To minimize the leakage-failure probability, a metric that jointly characterizes security and reliability in PLS, we formulate an optimization problem for allocating both redundant bits and blocklength. By deriving the boundaries of the feasible set, we obtain the globally optimal solution for this integer optimization problem. To achieve more computationally efficient solutions, we propose a block coordinate descent (BCD) method that exploits the partial convexity of the objective function. Subsequently, we develop a majorization-minimization (MM) algorithm through convex approximation of the objective function, which further improves computational efficiency. Finally, we validate the performance of the three proposed approaches through simulations, demonstrating their practical applicability for future URLLC services.

Paper Structure

This paper contains 11 sections, 6 theorems, 25 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Preliminaries
  3. System Model
  4. Physical Layer Security in the FBL Regime
  5. Optimization and Analysis
  6. LFP Characterization and Problem Formulation
  7. Dimensionality Reduction
  8. Partial Convexity Analysis and Block Coordinate Descent
  9. Convex Approximation and Majorization-Minimization Algorithm
  10. Numerical Simulations
  11. Conclusion

Key Result

Lemma 1

Within the feasible set of (SP1), $\varepsilon_{be}$ and $\varepsilon_{ba}$ are decreasing in $m_2$ and increasing in $d_{r,2}$.

Figures (4)

  • Figure 1: Obtained LFP $\varepsilon^{(k)}_{\text{LF}}$ in each $k$-th iteration for solving (SP2) with iterative search and under forward variant SNR of Bob $\varepsilon_{ab} = \{1, 1.2\}$. Moreover, the globally optimal results $\varepsilon^*_{\text{LF}}$ obtained with (OP) via integer programming are also shown as a benchmark.
  • Figure 2: Minimized LFP $\varepsilon_{LF}$ against Bob’s SNR $\gamma_{ba}$ under various setups of Alice’s SNR $\gamma_{ab}$. The results obtained by solving (SP3), solving (OP), as well as with the assumption of the IBL are shown.
  • Figure 3: Minimized LFP $\varepsilon_{LF}$ against Bob’s SNR $\gamma_{ba}$ under various setups of Eve’s SNR $\gamma_{ae}$. The results obtained by solving (SP4), solving (OP), as well as with the assumption of the IBL are shown.
  • Figure 4: Minimized LFP $\varepsilon_{LF}$ and its corresponding redundant bits $d_{ri}$ against the available blocklength M under various setups of transmit power p.

Theorems & Definitions (12)

  • Lemma 1
  • proof
  • Corollary 1
  • proof
  • Lemma 2
  • proof
  • Corollary 2
  • proof
  • Lemma 3
  • proof
  • ...and 2 more