Shape Index Modulation for Fluid Antenna Systems

This paper proposes a novel shape index modulation (SIM) scheme for fluid antenna (FA) systems, termed as FA-SIM, exploiting the dynamic reconfigurability of FA shapes to introduce an additional index dimension for information encoding. By integrating SIM into FA systems, the proposed FA-SIM scheme enhances transmission efficiency and spectral utilization without increasing hardware complexity, offering improved flexibility and performance in next-generation wireless communications. Furthermore, we derive a closed-form expression for the upper bound on the average bit error probability (ABEP), providing theoretical insights into the system's error performance. Simulation results demonstrate that the proposed FA-SIM scheme achieves higher spectral efficiency (SE) than conventional fixed-position antenna systems while maintaining a cost-effective hardware implementation.