Movable Antenna Aided Orthogonal Channel Construction in Near-field LoS MIMO System

This paper proposes a novel movable antenna (MA) assisted orthogonal channel construction scheme for the near-field (NF) line-of-sight (LoS) multiple-input multiple-output (MIMO) system. Specifically, we consider a transmitter (Tx) equipped with a fixed-position uniform planar array (UPA) and a mobile receiver (Rx) equipped with a planar array consisting of MAs. We first introduce the concept of orthogonal modes (OMs), which represent the optimal positions of MAs for orthogonal channel construction. Under the NF spherical model, we show that these OMs can be effectively constructed using 2-D basis vectors. Moreover, we derive a sufficient and necessary condition for the basis vectors, enabling the straightforward determination of the OMs. To enhance system performance, we maximize the number of OMs within a predefined Rx region by rotating the Rx plane. The channel orthogonality is then maintained by dynamically moving the MAs to the OMs. We further propose an efficient analog beamforming scheme for spatial multiplexing. Simulation results validate that the proposed approach significantly improves NF LoS MIMO channel capacity.