How friendly are building materials as reflectors to indoor LOS MIMO communications?

The tremendous popularity of internet of things (IoT) applications and wireless devices have prompted a massive increase of indoor wireless traffic. To further explore the potential of indoor IoT wireless networks, creating constructive interactions between indoor wireless transmissions and the built environments becomes necessary. The electromagnetic (EM) wave propagation indoors would be affected by the EM and physical properties of the building material, e.g., its relative permittivity and thickness. In this paper, we construct a new multipath channel model by characterising wall reflection (WR) for an indoor line-of-sight (LOS) single-user multiple-input multiple-output (MIMO) system and derive its ergodic capacity in closed-form. Based on the analytical results, we define the wireless friendliness of a building material based on the spatially averaged indoor capacity and propose a scheme for evaluating the wireless friendliness of building materials. Monte Carlo simulations validate our analytical results and manifest the significant impact of the relative permittivity and thickness of a building material on indoor capacity, indicating that the wireless friendliness of building materials should be considered in the planning and optimisation of indoor wireless networks. The outcomes of this paper would enable appropriate selection of wall materials during building design, thus enhancing the capacity of indoor LOS MIMO communications.