Finite-Blocklength ISAC Multiple Access: A Source-Channel Coding Perspective
For designers of future massive IoT networks requiring short-packet ISAC, this paper provides the first tight finite-blocklength characterization of the rate-sensing tradeoff and demonstrates genuine integration gains.
This paper establishes the fundamental limits of integrated sensing and communication (ISAC) in the finite-blocklength multiple-access regime, proving that sensing-distortion constraints are equivalent to source-coding requirements. It derives tight achievability and converse bounds, showing that the energy cost of sensing fidelity grows nearly linearly in dB per decade of distortion tightening and is amplified by multiple-access load, with joint encoding outperforming orthogonal schemes.
Future networks must serve massive populations of devices that sense and communicate simultaneously under short-packet constraints, yet the fundamental limits of integrated sensing and communication (ISAC) in the finite-blocklength multiple-access regime remain largely undiscovered. This paper closes this gap from a source-channel coding perspective. We prove that satisfying a sensing-distortion constraint is information-theoretically equivalent to a source-coding requirement, which collapses sensing and communication into the joint recovery of a single effective payload within a coded multiple-access framework. Building on this equivalence, we derive a finite-blocklength achievability bound together with a Fano-sum many-user converse and a genie-aided single-user converse, yielding a tight characterization of the minimum energy per bit and the rate-sensing tradeoff. Numerical results reveal that the energy price of sensing fidelity grows almost linearly in dB per decade of distortion tightening and is significantly amplified by the multiple-access load, and that joint encoding of the effective payload strictly outperforms an optimized orthogonal two-phase scheme, demonstrating a genuine integration gain of ISAC at finite blocklength.