Bruce Lee-Inspired Fluid Antenna System: Six Research Topics and the Potentials for 6G

Abstract

While 5G is tasked to transform our lives for the better over the next 10 years, next-generation mobile communications, a.k.a. 6G, will undoubtedly demand even higher energy and spectral efficiencies capable of providing myriads of new services and experience to users everywhere they go. Although our technologies do evolve from one generation to the next, the root of the ambition in mobile communications has always been to ensure reliable performance from an uncertain, fluctuating medium. The previous generations have already seen numerous technologies such as advanced coding and signal processing, resource allocation, and most famously, multiple-input multiple-output to redeem some stability from the wireless medium. Inevitably, 6G will be built upon further disruptive technologies that enable another cycle of revolution. In this article, we examine one emerging technology, referred to as fluid antenna system that represents any software-controllable fluidic, conductive, or dielectric structure that can alter its shape and position to reconfigure the gain, radiation pattern, operating frequency, and other characteristics. Fluid antenna takes inspiration from Bruce Lee's Jeet Kune Do to innovate mobile communication systems design. In Bruce Lee's philosophy, one can imitate water to adapt combat style, whereas fluid antenna exploits the dynamic nature of fluids or switchable pixels to achieve ultimate flexibility for diversity and multiplexing benefits that have been unseen before in mobile devices, and the implication can be transformative. This article discusses the potential of fluid antenna systems for 6G, and in particular, we introduce six research topics in fluid antenna systems that if solved successfully could revolutionize mobile communications network design and optimization. This article intends to stimulate discussion that will help shape the development of 6G technologies.

Closed‐form expressions for spatial correlation parameters for performance analysis of fluid antenna systems

“…In ref. [8], this approach was referred to as fast fluid antenna multiple access (FAMA). We present our new results below when all users and channels are i.i.d.…”

Extra‐large MIMO enabling slow fluid antenna massive access for millimeter‐wave bands

“…In the s ‐FAMA system, each user selects the best port for maximizing the signal‐to‐interference plus noise ratio (SINR) so that $$$$\begin{equation} k_u^{s\text{-}{\rm FAMA}}=\arg \max _k\frac{\sigma _s^2{\left|g^{(u,u)}_k\right|}^2}{\sum _{\tilde{u}=1\atop \tilde{u}\ne u}^U\sigma _s^2{\left|g^{(\tilde{u},u)}_k\right|}^2+\sigma ^2_\eta }, \end{equation}$$$$in which $$\mathrm{E}[|{s}_{u}{|}^{2}]={\sigma}_{s}^{2}\;\forall u$$ and $$\sigma ^2_\eta$$ is the noise power. In other words, the port at each user changes only if the channels change, which is contrast to the more powerful but much less practical version, f ‐FAMA [4, 5].…”

“…One emerging technology that could fit the bill is fluid antenna [3]. Its potential impact on xG mobile communications was recently discussed in [4]. Of interest is the fluid antenna multiple access (FAMA) system where the fluid antenna at each user seeks to operate at the natural interference null on a symbol-by-symbol basis to allow spectrum sharing of many users [5].…”

“…in which E[|s u | 2 ] = σ 2 s ∀u and σ 2 η is the noise power. In other words, the port at each user changes only if the channels change, which is contrast to the more powerful but much less practical version, f -FAMA [4,5].…”

“…Figure 1 shows the multiplexing gain performance of an s-FAMA network with different number of users, U , and under different channel parameters, K and N p , according to the model in (4). The fluid antenna at each user is assumed to have N = 1000 ports and a size of W = 25.…”