On Optimal Movable Antennas in Integrated Sensing and Communications

This paper investigates the optimization of movable antenna (MA) arrays for integrated sensing and communications (ICAS) in downlink multiple-input single-output (MISO) systems. We propose an idealized beamsteering model that enables flexible configuration of antenna positions to enhance the signal-to-noise ratio (SNR) for both communication and radar sensing tasks. The study begins with analytical solutions for optimal antenna spacing in simplified scenarios involving one or two users and a radar target, demonstrating the advantages of controlled antenna aliasing and separate beamforming. For more complex scenarios with multiple users and targets, we propose a suboptimal yet efficient two-stage heuristic combining antenna distance optimization with weighted MMSE beamforming and power allocation. The results show that movable antennas can significantly enlarge the achievable SNR region and improve capacity, especially in cases with conflicting beamforming objectives. Numerical simulations validate the proposed methods and highlight the potential of MA technology for future 6 G integrated sensing and communication systems.