Fluid Antenna Enabling Secret Communications

Recent researches have revealed that fluid antenna, a new position-switchable antenna technology, can make use of the spatial moments of deep fades of the interference signal occurred naturally due to multipath for multiple access. In this letter, this phenomenon is exploited in a physical layer security setup where a base station (BS) transmits an information-bearing signal to a legitimate user and an artificial noise (AN) signal to a potential eavesdropper while the user is equipped with a fluid antenna to overcome the AN signal. The proposed approach needs no effort from the base station (BS) to avoid the AN signal from harming the legitimate user. To enhance the secrecy rate, we study the power allocation of the information-bearing and AN signals if the channel state information (CSI) is available at the BS. Both perfect and imperfect CSI scenarios are investigated. Simulation results demonstrate that the proposed system, with a single fluid antenna with one radio-frequency (RF) chain at the user, achieves the secrecy rate that is comparable to the user utilizing maximal ratio combining (MRC) with many antennas instead, and is the only approach robust to CSI uncertainties of the eavesdropper, requiring no power allocation nor beamforming at the BS.

Automated summary

Recent research has discovered that the spatial moments of deep fades of interference signals caused by multipath can be exploited by a new position-switchable antenna technology called fluid antenna for multiple access. In this letter, the fluid antenna is used to overcome artificial noise (AN) signals, while a base station (BS) transmits an information-bearing signal to a legitimate user and an AN signal to a potential eavesdropper in a physical layer security setup. Power allocation of the information-bearing and AN signals is studied to enhance secrecy rate, considering perfect and imperfect channel state information (CSI) scenarios. Simulation results demonstrate that the proposed system achieves a comparable secrecy rate to that of maximal ratio combining (MRC) with many antennas, and is robust to CSI uncertainties of the eavesdropper, requiring no power allocation or beamforming at the BS.