Fluid Antenna Systems for 6G Wireless Communications: Implementation, System Optimisation and Theoretical Analysis

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The forecast by International Telecommunication Union (ITU) predicts that by 2030, the overall mobile data traffic will reach 5 zettabytes (ZB) per month. Multiple-input multiple-output (MIMO) is the most celebrated mobile technology that provides the needed upgrade from 2G to 3G, from 3G to 4G and most recently from 4G to 5G in the form of massive MIMO. In 5G, the number of antennas at the base station (BS) has been increased to 64 to cope with the rising demands. However, the number of antennas at a mobile handset (referred to as user equipment (UE) in the standards) remains small (<=4). This is due to the limited space at the UE, as the common practice is to deploy multiple antennas only if they are sufficiently apart (>=half of the wavelength) to have sufficient diversity of signals at different antennas for ensuring performance gains.It makes us wonder if it is possible to utilise the spatial diversity in a small space of UE more effectively. What if an antenna can be formless, shapeless like water? This is what this project is all about - to design novel antenna systems, coined fluid antennas, that can provide the ultimate reconfigurability and agility for signal and information processing. It is worth pointing out that seawater, albeit much less conductive than metal, has already been demonstrated a radiation efficiency of 70% by Mitsubishi Electric, and fluid antennas using conductive fluids or liquid metals for different reconfigurabilities have been actively researched in recent years.Despite the interest for fluid antennas in the antenna community, it was not until the original work by the investigators when the characteristics of fluid antenna was exploited for the optimisation of wireless communications systems. In the pioneering work, it was revealed that an agile fluid antenna system could, for the first time, realise:(*) Fading-free communications: one fluid antenna could achieve the same diversity as a massive number of fixed antennas.(*) Interference-free communications: spatial multiplexing for multiuser communications can be obtained by skimming through the fading envelopes observed in the space of the fluid antenna, by tuning to the most favourable position (or port) where the interference is in a deep fade, without the need for complex coordination and signal processing.Motivated by the great potential, this project identifies several fundamental challenges of fluid antenna systems, including, design and implementation, signal processing and optimisation, and fundamental network performance analysis, and aims to overcome these challenges in the realisation of the fluid antenna empowered mobile communications technologies by researching on four fronts: (1) Design and implementation of a pump-less, droplet fluid antenna - this addresses the implementation challenges of the fluid antenna system.(2) Information-theoretic network performance analysis in general channel models, representing the 5G/6G bands - this addresses the performance analysis of the communication networks using fluid antennas in the 5G and potential 6G bands.(3) Port selection and opportunistic fluid antenna multiple access (FAMA) - this tackles the network management and resource allocation of mobile communication networks using fluid antennas.(4) Fluid MIMO - this investigates the design and optimisation of MIMO using fluid antennas and multi-droplet fluid MIMO systems.The research directions have never been explored and will play a key role in revolutionising mobile communications. This project has received strong support from BT, Toshiba TRL and VIAVI Solutions who will advise on testbed implementations and ensure industrial relevance of the project.