MIMO Capacity Enhancement by Grating Walls: A Physics-Based Proof of Principle

Abstract

This paper investigates the passive enhancement of MIMO spectral efficiency through boundary engineering in a simplified two dimensional indoor proof of principle model. The propagation channel is constructed from the electromagnetic Green's function of a room with boundaries modeled as free space, drywall, perfect electric conductor (PEC), or binary gratings. Within this framework, grating coated walls enrich the non line of sight (NLoS) multipath field, reduce channel correlation, and enhance spatial multiplexing over a broad range of receiver locations. Comparisons with the drywall and PEC reference cases further reveal that the observed capacity enhancement arises not from diffraction alone, but from the combined effects of effective wall reflectivity, which confines and reradiates energy within the room, and diffraction induced angular redistribution, which enriches the channel eigenstructure.

Figures (12)

• Figure 1: Configuration of the proposed MIMO system: a two-dimensional empty room with engineered walls. The sketch is illustrative. In the ideal plane-wave grating picture, the reflected angles follow Eq. \ref{['eq:grating_b']}. In the actual finite-room problem, however, the wall is illuminated by a cylindrical wave and the observed scattering departs from that idealized prediction, as discussed later.
• Figure 2: Spatial distributions of the electric-field magnitude for the SISO case (top row) and the MIMO case (bottom row) in the two-dimensional room. (a) Free space SISO. (b) Drywall SISO. (c) Grating SISO. (d) PEC SISO. (e) Free space MIMO. (f) Drywall MIMO. (g) Grating MIMO. (h) PEC MIMO. The common parameters are $f=2.4$ GHz, $\ell_{\mathrm{room}}=w_{\mathrm{room}}=30\lambda$, $d_{\mathrm{TW}x}=5\lambda$, $d_{\mathrm{TW}y}=15\lambda$, $d_{\mathrm{T}}=d_{\mathrm{R}}=\lambda/2$, $\theta_{\mathrm{T}}=\theta_{\mathrm{R}}=0$, $p=2\lambda$ for the grating cases, $N_{\mathrm{T}}=N_{\mathrm{R}}=1$ for SISO and $N_{\mathrm{T}}=N_{\mathrm{R}}=6$ for MIMO. The line-current amplitude is $I_0=1$ A.
• Figure 3: Spatial distributions of the spectral efficiency for the SISO case (top row) and the MIMO case (bottom row) in the two-dimensional room. (a) Free space SISO. (b) Drywall SISO. (c) Grating SISO. (d) PEC SISO. (e) Free space MIMO. (f) Drywall MIMO. (g) Grating MIMO. (h) PEC MIMO. The common parameters are the same as in Fig. \ref{['fig:Efields_differ_walls']}. In addition, the total transmitted power and receiver noise power are set to $P_{\mathrm{T}}=1$ W and $P_{\mathrm{N}}=1\times10^{4}$ W, respectively, which correspond to a receiver SNR of $12$ dB in the free-space SISO case at $d_{\mathrm{TR}}=15\lambda$.
• Figure 4: Average capacity enhancement relative to free space for drywall, grating, and PEC boundaries. Values are extracted from the spatial capacity maps in Fig. \ref{['fig:Capacity_differ_walls']}.
• Figure 5: Spectral efficiency versus $d_\text{TR}$ along a specific propagation direction ($\theta_\text{TR}=\pi/4$), with the same configuration parameters as in Fig. \ref{['fig:Capacity_differ_walls']}. (a) SISO spectral efficiency in different walls. (b) MIMO spectral efficiency in different walls.