OFDM Enabled Over-the-Air Computation Systems with Two-Dimensional Fluid Antennas

TL;DR

This work introduces an OFDM-enabled over-the-air computation system enhanced by a two-dimensional fluid antenna system at the access point to exploit additional spatial degrees of freedom in frequency-selective channels. It develops a joint optimization framework that alternates between transmit precoder design, receive combiner computation, and fluid antenna position adjustment, employing majorization-minimization to handle the non-convex antenna-position problem. The proposed AO/MM-based algorithm achieves notable MSE reductions compared to fixed-position schemes and demonstrates that adaptive 2D antenna placement, coupled with OFDM AirComp, yields robustness to ISI and improves aggregation accuracy in multi-user settings. The results indicate practical benefits for dense IoT and edge intelligence scenarios where latency and accuracy are critical.

Abstract

Fluid antenna system (FAS) is able to exploit spatial degrees of freedom (DoFs) in wireless channels. In this letter, to exploit spatial DoFs in frequency-selective environments, we investigate an orthogonal frequency division multiplexing enabled over-the-air computation system, where the access point is equipped with a two-dimensional FAS to enhance performance. We solve the computation mean square error (MSE) minimization problem by transforming the original problem into transmit precoders optimization problem and antenna positions optimization along with receive combiners optimization problem. The latter is solved via a majorization-minimization approach combined with sequential optimization. Numerical results confirm that the proposed scheme achieves MSE reduction over the scheme with fixed position antennas.

Figures (2)

• Figure 1: MSE versus $P/\sigma^2$; comparison of different schemes, where $K = 5$, $N = 64$, and $M=4$.
• Figure 2: MSE versus $K$; comparison of different schemes, where $P/\sigma^2=10$ dB, $N = 64$, and $M=4$.