Effective Diversity and Coding Gain over Fluid Antenna Channels

In this work, fluid antenna channels are investigated from the diversity and coding gain perspectives. From the dominant eigenvalues of the channel correlation matrix, the maximum diversity of the channel is estimated based on the Jakes’ correlation model. Two examples of Reed-Solomon-coded QAM constellations are then proposed that achieve the diversity limits of the channel. In addition, transmit port selection is analyzed, and finally two code constructions that achieve the diversity-security tradeoff of fluid compound channels are proposed. Results show that, for a fixed array width, diversity (and coding gain) quickly saturates with the increasing number of antennas where the performance is dictated by the number of dominant eigenvalues. Also, in absence of CSI at the transmitter side, the best option is to transmit over all ports rather than selecting a subset of ports by minimizing their correlation.