Movable-Antenna Array Enhanced Beamforming: Achieving Full Array Gain with Null Steering

TL;DR

This paper introduces a novel movable antenna array beamforming method that optimizes antenna positions and weights to achieve full array gain and null steering, surpassing fixed-position array limitations.

Contribution

It proposes a joint optimization of antenna positions and weights for movable antenna arrays, enabling full gain and null steering with closed-form solutions.

Findings

Achieves full array gain over desired directions.

Enables null steering over multiple undesired directions.

Outperforms conventional fixed-position array beamforming.

Abstract

Conventional beamforming with fixed-position antenna (FPA) arrays has a fundamental trade-off between maximizing the signal power (array gain) over a desired direction and simultaneously minimizing the interference power over undesired directions. To overcome this limitation, this letter investigates the movable antenna (MA) array enhanced beamforming by exploiting the new degree of freedom (DoF) via antenna position optimization, in addition to the design of antenna weights. We show that by jointly optimizing the antenna positions vector (APV) and antenna weights vector (AWV) of a linear MA array, the full array gain can be achieved over the desired direction while null steering can be realized over all undesired directions, under certain numbers of MAs and null-steering directions. The optimal solutions for AWV and APV are derived in closed form, which reveal that the optimal AWV for MA arrays requires only the signal phase adjustment with a fixed amplitude. Numerical results validate our analytical solutions for MA array beamforming and show their superior performance to the conventional beamforming techniques with FPA arrays.