The Tri-Hybrid MIMO Architecture

TL;DR

This work addresses scaling MIMO into cmWave bands ($6$ to $24$ GHz) with ultra-large arrays while controlling RF complexity and energy use. It introduces the tri-hybrid MIMO architecture that fuses digital beamforming, analog beamforming, and reconfigurable antennas (electromagnetic beamforming). The authors discuss architectural primitives, including the equivalent antenna dimensions and electromagnetic precoding, and propose modeling strategies based on circuit theory and full-wave EM to capture both reconfigurability and mutual coupling. They analyze spectral and energy efficiency tradeoffs and outline model-driven and data-driven configuration approaches, showing that tri-hybrid can achieve a favorable balance for large $N_{\mathsf{rf}}$ and aperture sizes. Together, these contributions lay a foundation for scalable, energy-efficient 6G MIMO systems that integrate advanced antenna technologies into the precoding framework.

Abstract

We present an evolution of multiple-input multiple-output (MIMO) wireless communications known as the tri-hybrid MIMO architecture. In this framework, the traditional operations of linear precoding at the transmitter are distributed across digital beamforming, analog beamforming, and reconfigurable antennas. Compared with the hybrid MIMO architecture, which combines digital and analog beamforming, the tri-hybrid approach introduces a third layer of electromagnetic beamforming through antenna reconfigurability. This added layer offers a pathway to scale MIMO spatial dimensions, important for 6G systems operating in centimeter-wave bands, where the tension between larger bandwidths and infrastructure reuse necessitates ultra-large antenna arrays. We introduce the key features of the tri-hybrid architecture by (i)~reviewing the benefits and challenges of communicating with reconfigurable antennas, (ii)~examining tradeoffs between spectral and energy efficiency enabled by reconfigurability, and (iii)~exploring configuration challenges across the three layers. Overall, the tri-hybrid MIMO architecture offers a new approach for integrating emerging antenna technologies in the MIMO precoding framework.

Figures (8)

• Figure 1: A general illustration of the tri-hybrid MIMO architecture. The antennas of the hybrid MIMO architecture are replaced by the new electromagnetic precoding layer that is created through the use of one or more reconfigurable antennas.
• Figure 2: The digital, hybrid, and tri-hybrid MIMO architectures at the transmitter.
• Figure 3: Power consumption for the digital, hybrid, and tri-hybrid architectures in the FR3 (upper-mid) band based on the parameters in RibeiroEtAlEnergyEfficiencyMmwaveMassive2018. Due to the negligible power consumption of each DMA element for beamforming and the reduced number of RF chains, the tri-hybrid architecture consumes far less power than the hybrid and digital transmitter architectures.
• Figure 4: Switched-pattern antenna
• Figure 5: Parasitic array