When the radio signal propagates in the near-field (NF), the distance can be estimated by the curvature of the wavefront. This brings new opportunities for sensing and communication, but a computational burden as well. This paper first establishes a theoretical foundation for computationally efficient NF feature (i.e., angle-of-arrival (AOA) and distance) estimation.

An approach to characterising operator spectra using a ray-dynamical phase space, originating from treatments of quantum mechanics, is adapted to calculate degrees of freedom and channel capacities of wireless communication between surfaces. The method is grounded on propagation of correlation functions and exploits the outputs of Eulerian raytracing algorithms. It presents results using a signal-to-noise ratio expressed as a function of phase space coordinates, resolving it in terms of direction as well as position.