Increasing Terahertz MIMO Channel Capacity with Passive Reflectors

Communication at the terahertz band is a challenging yet exciting technology. It promises to deliver terabit/sec data rates for short distances but, due to its unique propagation characteristics, it suffers from significant impairments. To enable these high data rates, we need to use MIMO (Multiple Input Multiple Output) systems. However, given that natural reflected paths display enormous attenuation, we need to rely either on LoS (Line of Sight) MIMO or carefully placed reflectors to overcome environmental obstacles. We have observed that when using polished reflectors (e.g., metal plates), the channel behaves similarly to a LoS MIMO channel in that there is a decrease in capacity with distance and a periodicity. In this paper, we describe the construction of a novel reflector that maintains a steady capacity with distance. The reflector creates multiple independent paths between the transmit and receive antennas such that the eigenvalues of the channel matrix are non-trivial. This provides us with the capacity improvement. Our work is experimental and we focus on the frequency band around 410 GHz. We constructed a variety of reflectors and identified a design that improves capacity. We show that our reflector maintains a high capacity with increasing distance while a LoS path and a path constructed with a polished reflector show a decrease in capacity. We also used the same reflector at other frequencies and observed poorer behavior illustrating a dependence between wavelength and reflector design. Our results show that we can maintain high-capacity indoor channels by carefully designed reflectors.