“…where (i) P is the number of paths, (ii) ξ p ∼ CN 0, σ 2 p is the scattering amplitude of p-th path, such that P p=1 σ 2 p = 1, (iii) τ p is the propagation delay of the p-th path, (iv) a L (θ, ϕ) ∈ C L×1 is the steering vector of either Tx or Rx, function of Tx and Rx angles, respectively (φ t p , θ t p ) and (φ r p , θ r p ), and normalized such that a L (θ, ϕ) 2 F = L. As common for communication systems operating through back-scattering, the two-way channel to/from the STMM is characterized by a single dominant path, as for radar systems [29]. Multiple bounces can be considered, but their path loss is orders of magnitude higher, and thus are here neglected, considering P = 1 for both forward H i (t) and backward H o (t) channels.…”