Fundamental Tradeoffs for ISAC Multiple Access in Finite-Blocklength Regime

2026-01-08

arXiv.org

AI Summary

This study investigates the fundamental trade-off between communication rate and sensing accuracy in uplink dual-functional integrated sensing and communication (ISAC) multiple-access systems under finite blocklength constraints. By constructing a geometric decomposition model for unbiased channel estimators, it reveals— for the first time—the intrinsic limitation imposed by inter-user cross-correlation within the codebook geometry on ISAC performance, and establishes a theoretical Pareto boundary between communication coding rate and sensing precision. The analysis integrates finite-blocklength information theory, Cramér–Rao bound techniques, and 3GPP-compliant system parameterization to derive both achievability and converse bounds. Numerical results demonstrate that blocklength, antenna array dimension, and sensing requirements significantly impact system performance, with the converse bound fundamentally constrained by Shannon capacity.

Technology Category

• Constraint Satisfaction and Optimization: Other Foundations of Constraint Satisfaction
• Multiagent Systems: Agent Communication
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

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• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics

Abstract

This paper investigates the fundamental communication--sensing tradeoffs of uplink dual-functional integrated sensing and communication (ISAC) multiple access under finite blocklength (FBL) constraints. Unlike conventional asymptotic analyses, we explicitly account for the limitations under FBL constraints imposed by short packets and low-latency transmission. By examining the unbiased channel state sensing estimator, we establish a geometric decomposition of the sensing error, indicating that it is jointly determined by the signal-to-noise ratio and the correlation structure of the information codebook. This insight reveals how cross-correlation among active users in the codebook geometry fundamentally constrains dual-functional ISAC performance. Consequently, we derive achievability and converse bounds that characterize the tradeoff between communication code rate and sensing accuracy in the FBL regime, with the converse further bounded by Shannon capacity. Moreover, by treating channel state sensing as a high-level sensing objective, a universal Cram\'er--Rao bound is derived to link channel estimation accuracy to practical sensing parameters. Examples of parameter sensing are also provided based on 3GPP standard. Numerical results validate the theoretical analysis and demonstrate the impact of blocklength, antenna dimensions, and sensing requirements.

Problem

• ISAC
• finite blocklength
• communication-sensing tradeoff
• multiple access
• channel state sensing

Innovation

• ISAC
• finite blocklength
• communication-sensing tradeoff
• codebook correlation
• Cramér–Rao bound