Heterogeneous Antenna Arrays for Multi-User MIMO: Addressing Limited Aperture Constraints

The contradiction between achievable sum rate enhancement and limited antenna aperture in base stations has prompted the exploration of the unconventional antenna architectures. We propose a novel heterogeneous antenna array architecture with uniform element spacing that leverages multiple elements with distinct directional patterns to reduce channel correlation and minimize mutual interference in multi-user environments. Unlike a regular array consisting of identical elements, this approach increases design flexibility while maintaining compatibility with digital beamforming techniques, without adding system costs. In such a framework, the joint configuration optimization problem is formulated by considering both the achievable sum rate and coverage performance of base stations, which is numerically solved to obtain a near-optimal array configuration within a prescribed optimality gap. Numerical results validate the superiority of the heterogeneous array over the regular array, with up to a 24.7% improvement in sum rate in high signal-to-noise ratios cases while maintaining the same coverage performance considering user scheduling. The same heterogeneous array (with fixed array topology) demonstrates performance gains across multiple channel environments as compared to the regular array. This environmental adaptability arises from the irregular element patterns, which spatially decorrelate channels by improving distinct angular resolvability for close-located users. These findings suggest that heterogeneous arrays offer a promising avenue for improving baseband communication with limited aperture constraints.