Can the Road To Flexible MIMO Be Paved by Tile-based Antenna Arrays?

As 5G+ (or "Beyond 5G") becomes more widespread, researchers are working to invent new radio antenna technology for faster, higher-capacity, and lower-latency communications. One of the key technologies employed to meet these goals is massive MIMO technology. MIMO incorporates multiple antennas at the transmitter and the receiver side of a wireless communication system.

 

The multi-tile schematic of a modular antenna array architecture. Image used courtesy of Nature

 

The problem with 5G+ technologies, however, is that they hinge on large antenna arrays that are costly and cumbersome to transport. Now, a team of researchers from Georgia Tech’s College of Engineering have created additively-manufactured, tile-based arrays of 5G+ "smart skins" that can be scaled to bring intelligence to any object or surface.

 How might such tile-based antenna arrays create large impacts in 5G MIMO systems? 

 

Massive MIMO for 5G

To understand this recent research, it may be useful to first discuss how massive MIMO functions.

Massive MIMO features a large number of receive antennas to achieve both spatial diversity and spatial multiplexing. Various reflected signals that have been attenuated by environmental conditions and obstacles arrive at the receive antennas with a relatively different version of the original signal. Thanks to spatial diversity, these signals at the receive antenna are mathematically computed together to improve the quality of the received signals.

 

Schematic of a massive multiple-input, multiple-output (MIMO) with beamforming technology. Image used courtesy of Chataut

 

 

Massive MIMO technology can be combined with beamforming technology, where the wireless signals are targeted to a direction that they are most useful instead of broadcasting to a wide area. By focusing the large antenna arrays on a specific section, less radiated power is consumed.

 

Design Considerations in Massive MIMO Systems

One of the main challenges to fabricate a massive MIMO architecture includes scaling antenna arrays for smaller designs. Thus, it is important to adopt millimeter-wave antennas with a smaller antenna element.

To do this, researchers from the University of California, Berkeley developed a technique to design the antenna arrays as a grid of identical modules. The modules, however, were linked to other devices in the system in a mesh network topology. This architecture enabled the designer to increase and decrease the array size by adding or removing the modules as deemed fit for a scalable network.

Another consideration to miniturizing MIMO architecture is channel models, which are built on plane wave propagation and may not support pencil-shaped beamforming originating from the MIMO arrays. Channel models based on spherical wave propagation may be an effective choice.

 

Tile-based, Phased-array MIMO System

To address these scalability challenges, Georgia Tech additively manufactured a number of small tile-like antenna arrays onto one flexible underlying layer. This structure allows researchers to affix the tile arrays to any number of objects or surfaces and bring electronically-steerable antenna networks to life on-demand.

 

Scalable tile arrays. Image used courtesy of Georgia Tech

 

Each of these tiles includes an antenna subarray and and a beamforming IC. This beamforming IC integrates eight antenna elements on a small-scale PCB substrate. When arranged together on an underlying layer or smart skin, the tiles are interconnected into large antennas arrays and massive MIMO. This modular tile method may enable companies to fabricate a large number of uniformly-sized tiles that can be easily replaced.

 

A close-up view of the massively scalable multi-tile antenna array. Image used courtesy of Nature

 

Designed to operate at millimeter-wave frequencies, the fabricated 2 × 2 tiles based 32-element MIMO antenna arrays exhibited +/− 30 beamsteering capability. According to the researchers, the tile array features no performance degradation when it is wrapped around a 3.5 cm radius curvature. What’s more, the architecture separates the RF feeding network and the antenna elements.

The researchers hope that this method may expand 5G+ applications and may even find use on unmanned aerial vehicles (UAVs) to bring broadband connectivity to low-coverage regions.