Abstract
In this paper, we propose a transmission mechanism
for fluid antennas (FAs) enabled multiple-input multiple-output
(MIMO) communication systems based on index modulation
(IM), named FA-IM, which incorporates the principle of IM into
FAs-assisted MIMO system to improve the spectral efficiency
(SE) without increasing the hardware complexity. In FA-IM, the
information bits are mapped not only to the modulation symbols,
but also the index of FA position patterns. Additionally, the
FA position pattern codebook is carefully designed to further
enhance the system performance by maximizing the effective
channel gains. Then, a low-complexity detector, referred to
efficient sparse Bayesian detector, is proposed by exploiting the
inherent sparsity of the transmitted FA-IM signal vectors. Finally,
a closed-form expression for the upper bound on the average bit
error probability (ABEP) is derived under the finite-path and
infinite-path channel condition. Simulation results show that the
proposed scheme is capable of improving the SE performance
compared to the existing FAs-assisted MIMO and the fixed
position antennas (FPAs)-assisted MIMO systems while obviating
any additional hardware costs. It has also been shown that
the proposed scheme outperforms the conventional FA-assisted
MIMO scheme in terms of error performance under the same
transmission rate.