Hierarchically Tunable 6DMA for Wireless Communication: Modeling and Optimization

This paper proposes a hierarchically tunable six-dimensional movable antenna (HT-6DMA) base station (BS) for wireless communication. The HT-6DMA BS consists of multiple arrays that can flexibly move on a spherical surface, with their three-dimensional (3D) positions and 3D rotations/orientations efficiently characterized in the global and their individual local coordinate systems (CSs), respectively. Compared with the existing 6DMA model, the proposed model is hierarchically tunable in the sense that each array’s position and rotation can be individually adjusted in a sequential manner with the other being fixed, thus greatly reducing their optimization complexity and improving the solution quality. We then consider an HT-6DMA BS serving multiple single-antenna users in the uplink communication. Specifically, we aim to maximize the average sum rate of the users in the long term by optimizing the positions and rotations of all 6DMA arrays at the BS. While the formulated problem is non-convex and challenging to solve, we propose efficient solutions to it by exploiting the hierarchical tunability of positions and rotations of 6DMA arrays in our proposed model. Numerical results show that the proposed HT-6DMA scheme can significantly outperform the traditional BS with fixed-position antennas (FPAs) as well as the existing 6DMA model and algorithm. It is also unveiled that most performance gains of the HT-6DMA come from the arrays’ global position adjustments, rather than their local rotation adjustments, which provides a useful guide for implementing 6DMA systems with practical performance-complexity trade-off consideration.