Harnessing the Freedom of Non-Uniformity in Monostatic ISAC with Antenna Flexibility

TL;DR

This paper proposes a flexible non-uniform antenna array design for monostatic ISAC systems, optimizing antenna modes and beamforming to enhance communication rates with fewer active antennas.

Contribution

It introduces a joint optimization framework for antenna mode assignment and beamforming, demonstrating significant rate improvements over uniform arrays.

Findings

Non-uniform arrays outperform uniform baselines in sum-rate.

Fewer active antennas can match or exceed uniform array performance.

Geometry-aware design offers a compelling alternative to scaling arrays.

Abstract

This paper studies flexible non-uniform array design for monostatic integrated sensing and communication (ISAC) systems. An antenna pool is considered at the base station, where each candidate antenna can be dynamically assigned to transmit, receive, or inactive modes, such that a non-uniform effective array is jointly constructed with the ISAC precoding design. We formulate a sum communication rate maximization problem by jointly optimizing the ISAC beamforming schemes and antenna-mode assignment under sensing, power, and antenna mode constraints. We develop an alternating-optimization-based solution framework mainly with the aid of weighted minimum mean square error, continuous relaxation-based penalty, and successive convex approximation. Numerical results show that the proposed non-uniform array achieves higher sum-rates than the uniform-array baselines, with particularly large gains when the number of activated antennas is small. Moreover, the proposed non-uniform array can achieve, and in some cases exceed, the performance of uniform array baselines with substantially fewer activated antennas, highlighting geometry-aware non-uniform array design as a compelling alternative to brute-force antenna scaling-based array design.