Hybrid Beamforming Design for Bistatic Integrated Sensing and Communication Systems

TL;DR

This paper proposes hybrid beamforming algorithms for bistatic integrated sensing and communication systems in millimeter wave, balancing spectral efficiency and positioning accuracy with reduced hardware costs and half-duplex operation.

Contribution

It introduces two novel hybrid beamforming algorithms for bistatic ISAC systems, optimizing spectral efficiency under positioning error constraints, with one leveraging Riemannian trust-region and the other orthogonal matching pursuit.

Findings

Riemannian trust-region algorithm achieves better convergence and global optimality.

Orthogonal matching pursuit offers a computationally efficient alternative.

Numerical results validate the effectiveness of the proposed algorithms.

Abstract

Integrated sensing and communication (ISAC) in millimeter wave is a key enabler for next-generation networks, which leverages large bandwidth and extensive antenna arrays, benefiting both communication and sensing functionalities. The associated high costs can be mitigated by adopting a hybrid beamforming structure. However, the well-studied monostatic ISAC systems face challenges related to full-duplex operation. To address this issue, this paper focuses on a three-dimensional bistatic configuration that requires only half-duplex base stations. To intuitively evaluate the error bound of bistatic sensing using orthogonal frequency division multiplexing waveforms, we propose a positioning scheme that combines angle-of-arrival and time-of-arrival estimation, deriving the closed-form expression of the position error bound (PEB). Using this PEB, we develop two hybrid beamforming algorithms for joint waveform design, aimed at maximizing achievable spectral efficiency (SE) while ensuring a predefined PEB threshold. The first algorithm leverages a Riemannian trust-region approach, achieving superior performance in terms of global optima and convergence speed compared to conventional gradient-based methods, but with higher complexity. In contrast, the second algorithm, which employs orthogonal matching pursuit, offers a more computationally efficient solution, delivering reasonable SE while maintaining the PEB constraint. Numerical results are provided to validate the effectiveness of the proposed designs.