Be Water, My Antennas: Riding on Radio Wave Fluctuation in Nature for Spatial Multiplexing using Programmable Meta-Fluid Antenna

TL;DR

A novel meta-fluid antenna architecture that can freely surf on radio wave fluctuations with fine resolution in space to opportunistically avoid interference, eliminating the need for expensive signal processing is proposed.

Abstract

Interference and scattering, often deemed undesirable, are inevitable in wireless communications, especially when the current mobile networks and upcoming sixth generation (6G) have turned into ultra-dense networks. Current approaches relying on multiple-input multiple-output (MIMO) combined with artificial-intelligence-aided (AI) signal processing have drawbacks of being power-hungry and requiring wide bandwidth that raise scalability concerns. In this article, we take a radical approach and utilize the channel fading phenomenon to our advantage. Specifically, we propose a novel meta-fluid antenna architecture, referred to as the `fluid' antenna system (FAS), that can freely surf on radio wave fluctuations, like `fluid' figuratively speaking, with fine resolution in space to opportunistically avoid interference, eliminating the need for expensive signal processing. Our experimental results demonstrate that under rich scattering conditions, the proposed meta-fluidic architecture is able to exploit the natural ups and downs of radio waves in space for spatial multiplexing. These breakthrough results show that scattering can be desirable not harmful and interference can be dodged not suppressed, fundamentally changing our perception of fading and our understanding on how interference should be managed in wireless communications networks.

Figures (5)

• Figure 1: Illustration of the concept of FAS and FAMA. A downlink communication system is shown, where two distributed BSs are responsible for transmitting data to two mobile users in a typical rich-scattering environment (both outdoor and indoor). The figure in the middle also shows a user with a FAS mounted on her laptop, enabling the observation of the E-field distributions of the signals arriving from the two respective BSs. The figure on the right then illustrates the concept of FAMA. Specifically, this figure focuses on a particular horizontal dimension of the FAS and displays how the intensity of the radio signals changes along this dimension. It is clear that the radio signal intensity fluctuates, which gives rise to the opportunity for the FAS to avoid interference.
• Figure 2: The working principle of the proposed meta-fluid antenna. (a) This shows a schematic representation of the meta-fluid antenna architecture with $8\times15$ radiating elements and the simulated radiating pattern in the $yz$-plane if a given element is activated. (b) This figure shows the basic 3-dimensional (3D) structure of a meta-atom which consists of an upper element and a lower element. Each element is connected and controlled by 4 PIN diodes. (c) This figure illustrates the simulated E-field results against frequency focusing on one meta-atom if the upper element is in an 'ON' state but the lower element is in an 'OFF' state. The results show an approximate $13~{\rm dB}$ difference in their E-fields between the two elements. (d) The figures display the E-field distributions in the $xy$-plane in the three possible states for the meta-atom.
• Figure 3: The experimental setup of the FAMA system utilizing the meta-fluid antenna prototype Rx. (a) A photo shows the rich-scattering generators as the transmitter group and the meta-fluid antenna prototype in the chamber for measurement. Additionally, a red cable, which serves as the DC power cable for the FPGA, is also visible. The transmitter group and the receiver are separated by a distance of $0.5$ meters. (b) This photo shows the front view of the antenna prototype with two ports, one connecting to a $50\Omega$ load and another to the RF chain. The front side of the meta-fluid antenna is composed of $8$ rows and $15$ columns, totalling $120$ elements. Each element is controlled by $4$ PIN diodes, enabling toggling between the 'radiating' state and the 'non-radiating' state. (c) This photo shows the back view of the meta-fluid antenna attached to the integrated control board, which is seamlessly integrated with the antenna section through biasing vias. By reprogramming the FPGA, the radiating position of the meta-fluid antenna can be altered, allowing for dynamic control of the radiation pattern of the antenna.
• Figure 4: The SINR measurements at the meta-fluid antenna prototype in the frequency range 26 to 27 GHz in Case 9 of the transmitter group. (a) This figure shows the measured SINRs against the frequency in the situation where Tx1 is considered as the desired user and Tx2 and Tx3 are the interferers. Moreover, at $26.25~{\rm GHz}$, the SINR at the $(5,6)$-th position of the meta-fluid antenna is highlighted, which is the maximum SINR achievable by the meta-fluid antenna ($16.19~{\rm dB}$). (b) Similar results are provided for the situation where Tx2 is the desired user and Tx1 and Tx3 are interferers. In this case, the maximum SINR at $26.4~{\rm GHz}$ is highlighted, which corresponds to $10.90~{\rm dB}$ at the $(6,4)$-th position of the meta-fluid antenna. (c) Finally, the SINR results for the situation with Tx3 being the desired user and Tx1 and Tx2 being the interferers are shown. The $(5,9)$-th position at a frequency near $26.43~{\rm GHz}$ is highlighted, achieving an SINR of $17.89~{\rm dB}$.
• Figure 5: The SINR measurement data at the meta-fluid antenna in all the propagation situations (Case 1 to Case 10) at 26.5 GHz. (a) This figure focuses on the situation where Tx1 is the desired user in the calculation of SINR. The ranges of the SINR observable at the meta-fluid antenna are shown in all $10$ cases. In this situation, the average SINR over all the cases is also marked as $8.04~{\rm dB}$. (b) This figure provides similar SINR data but in the situation where Tx2 is considered as the desired user. In this situation, the average SINR achievable by the meta-fluid antenna is $7.74~{\rm dB}$. (c) This figure considers the situation treating Tx3 as the desired user and Tx1 and Tx2 as the interferers. In this case, the average SINR at the meta-fluid antenna is calculated to be $9.69~{\rm dB}$.