Sensing-Induced Embodied Communication in the Near Field

Abstract

Integrated sensing and communication is turning the cellular infrastructure into an active observer of the physical world. When such infrastructure interacts with embodied agents capable of deliberately changing their states and surroundings, the physical world itself can become a communication medium. This paper studies the fundamental communication limits of this sensing-induced embodied communication paradigm in the near field. We consider an agent that maps messages to the positions of a controllable scatterer within a bounded three-dimensional (3D) region, while a base station decodes the selected position from multi-snapshot monostatic sensing echoes. Near-field spherical wavefronts resolve both angle and range, expanding the embodied-symbol space from a 2D plane to a 3D volume. This gain, however, comes with a position-dependent and anisotropic reliability geometry. We characterize this geometry through the pairwise Bhattacharyya distance and derive a local ellipsoidal representation of the resulting 3D confusability regions, whose principal axes quantify directional sensing resolution. The ellipsoid further degenerates into the 2D transverse ellipse in the far-field limit, unifying the two regimes. We then formulate the finite-snapshot $ε$-capacity and translate reliable codebook design into a 3D packing problem. A face-centered cubic construction provides an achievable rate, while a geometric converse yields a complementary upper bound. Numerical results validate the proposed geometry and demonstrate the capacity gain of near-field volumetric packing over far-field planar packing. These results establish a unified geometric and information-theoretic framework for communication through deliberately configured physical states.