A statistical model for the MIMO channel with rough reflection surfaces in the THz band

Based on the reflection properties of rough surfaces, we propose a statistical multiple-input multiple-output (MIMO) antenna system in the terahertz (THz) band for nanocommunications. Firstly, our analysis of scattering from a rough surface indicates that the reflection from a single surface can be a cluster of rays. Secondly, a new MIMO model for THz communications is proposed. In this model, the number of multipaths is highly dependent on the roughness of the reflecting surfaces. When the surface is ideally smooth, the MIMO channel is sparse and as a result, the capacity is sub-linear with the MIMO scale. On the other hand, when the surface is rough, more degrees of freedom are provided by the scattered rays. Finally, channel capacities with different surface roughness are numerically calculated and compared between different MIMO scales. The results show that in contrast to the GHz range, large scale THz multiple antennas may not provide as much multiplexing gain. Therefore, it is necessary to determine the antenna scale according to the actual propagation environment.