Reduced-Complexity Wideband Line-of-Sight MIMO Communication

An approach is proposed for line-of-sight multiple-input multiple-output communication at mmWave and sub-terahertz frequencies. This approach requires no precoding at the transmitter and only delay lines and additions at the receiver. As a result, it does not require multicarrier signaling, which entails a form of precoding, and yet it is suitable for wideband communication (in the sense of the bandwidth being large enough that the delay differences among transmit-receive antenna pairs cause frequency selectivity). Because of the unprecoded and potentially single-carrier nature of the transmission, and the simple structure of the associated receiver, the proposed approach is compatible with low-resolution analog-to-digital and digital-to-analog converters.

I. Introduction

The evolution of wireless access has been characterized by a persistent reduction in the transmission range and an unrelenting increase in bandwidth. As the range continues to decline, and we move to even higher frequencies in search of new spectrum, a tilting point is reached in that line-of-sight (LOS) propagation goes from hampering spatial multiplexing to being an instrument for it. Indeed, once the range and wavelength are both short enough, the array apertures suffice to resolve individual antennas at the other end of the link and the resulting multiple-input multiple-output (MIMO) channel acquires rank even in the absence of multipath components [1]–[23]. This is welcome news because short-range channels are predominantly LOS, hence the paradigm of LOS MIMO emerges as a very relevant one moving forward. At the same time, there are substantial differences with multipath-enabled MIMO at lower frequencies [24], chiefly that in LOS MIMO geometry becomes king [25].