4 research outputs found
Super-Wideband Massive MIMO
We present a unified model for connected antenna arrays with a massive (but
finite) number of tightly integrated (i.e., coupled) antennas in a compact
space within the context of massive multiple-input multiple-output (MIMO)
communication. We refer to this system as tightly-coupled massive MIMO. From an
information-theoretic perspective, scaling the design of tightly-coupled
massive MIMO systems in terms of the number of antennas, the operational
bandwidth, and form factor was not addressed in prior art and hence not clearly
understood. We investigate this open research problem using a physically
consistent modeling approach for far-field (FF) MIMO communication based on
multi-port circuit theory. In doing so, we turn mutual coupling (MC) from a foe
to a friend of MIMO systems design, thereby challenging a basic percept in
antenna systems engineering that promotes MC mitigation/compensation. We show
that tight MC widens the operational bandwidth of antenna arrays thereby
unleashing a missing MIMO gain that we coin "bandwidth gain". Furthermore, we
derive analytically the asymptotically optimum spacing-to-antenna-size ratio by
establishing a condition for tight coupling in the limit of large-size antenna
arrays with quasi-continuous apertures. We also optimize the antenna array size
while maximizing the achievable rate under fixed transmit power and
inter-element spacing. Then, we study the impact of MC on the achievable rate
of MIMO systems under light-of-sight (LoS) and Rayleigh fading channels. These
results reveal new insights into the design of tightly-coupled massive antenna
arrays as opposed to the widely-adopted "disconnected" designs that disregard
MC by putting faith in the half-wavelength spacing rule