On Highly Spaced Antennas for Locally Distributed MIMO

The persistent increase in frequency leads to a growing demand for efficient antenna arrays with large apertures capable of generating pencil beams. New technologies have been proposed to meet these requests, e.g., holographic multiple-input multiple-output (MIMO) and distributed MIMO. However, these solutions might have practical limitations, such as the channel state information acquisition for holographic MIMO, or have prohibitive deployment costs for distributed MIMO. This paper proposes using a fully digital array with few highly spaced antennas (beyond the conventional spacing), namely locally distributed MIMO (LDMIMO). The results demonstrate the benefit of the proposed solution. In particular, the advantage over holographic MIMO is remarkable. With LDMIMO, achieving the same spatial selectivity of holographic MIMO with 40x fewer elements is possible. The same gain is reached during the beam-sweeping procedure for the initial access, where LDMIMO allows a 40x faster operation compared to holographic MIMO.