Achievability of Fluid Antenna Multiple Access: A Han-Kobayashi's Comparison

Recently, fluid antenna system (FAS) has emerged as a potential candidate to deliver extra diversity and multiplexing gains. This new technology can also be adopted to mitigate interference namely, fluid antenna multiple access (FAMA). Unlike existing schemes, the key concept of FAMA is to communicate at a spatial moment where the interference is in deep fade. However, FAMA treats interference as noise and it remains unclear whether such a strategy is capacity-efficient. To address this question, we leverage insights from information theory and introduce a new Han-Kobayashi (HK)-FAMA scheme that considers rate splitting, power splitting and joint decoding, to be a capacity benchmark. Using this capacity benchmark, we then illustrate that FAMA (alone without HK) can be near to being optimal despite its simplicity. Besides, we employ a new performance metric based on the generalized degree-of-freedom (gdof) to explain the principle of FAMA.