Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions

TL;DR

This paper reviews the emerging field of holographic MIMO (HMIMO) communications, discussing its theoretical basis, enabling technologies, and future research directions for next-generation wireless systems.

Contribution

It provides a comprehensive overview of HMIMO, highlighting its physical principles, technological advancements, and potential to revolutionize wireless communication systems beyond existing MIMO technologies.

Findings

HMIMO utilizes ultra-thin, large surfaces with reconfigurable antennas or metamaterials.

HMIMO can manipulate electromagnetic waves with high precision and efficiency.

The field is in early stages, with fundamental limits and technical challenges yet to be fully understood.

Abstract

Future wireless systems are envisioned to create an endogenously holography-capable, intelligent, and programmable radio propagation environment, that will offer unprecedented capabilities for high spectral and energy efficiency, low latency, and massive connectivity. A potential and promising technology for supporting the expected extreme requirements of the sixth-generation (6G) communication systems is the concept of the holographic multiple-input multiple-output (HMIMO), which will actualize holographic radios with reasonable power consumption and fabrication cost. The HMIMO is facilitated by ultra-thin, extremely large, and nearly continuous surfaces that incorporate reconfigurable and sub-wavelength-spaced antennas and/or metamaterials. Such surfaces comprising dense electromagnetic (EM) excited elements are capable of recording and manipulating impinging fields with utmost flexibility and precision, as well as with reduced cost and power consumption, thereby shaping arbitrary-intended EM waves with high energy efficiency. The powerful EM processing capability of HMIMO opens up the possibility of wireless communications of holographic imaging level, paving the way for signal processing techniques realized in the EM-domain, possibly in conjunction with their digital-domain counterparts. However, in spite of the significant potential, the studies on HMIMO communications are still at an initial stage, its fundamental limits remain to be unveiled, and a certain number of critical technical challenges need to be addressed. In this survey, we present a comprehensive overview of the latest advances in the HMIMO communications paradigm, with a special focus on their physical aspects, their theoretical foundations, as well as the enabling technologies for HMIMO systems. We also compare the HMIMO with existing multi-antenna technologies, especially the massive MIMO, present various...