Optimal Beamforming for Bistatic MIMO Sensing

TL;DR

This paper develops an optimization framework for beamforming in bistatic MIMO OFDM radar to minimize target localization error, revealing when single or multiple beams are optimal and analyzing transmit-receive configurations.

Contribution

It introduces a novel beamforming optimization approach for bistatic MIMO OFDM radar that accounts for prior target position knowledge and multiple subcarriers.

Findings

Single-beam per subcarrier is optimal under certain conditions.

Multiple beams are needed for optimality in some scenarios.

Optimal transmit-receive configurations depend on system parameters.

Abstract

This paper considers the beamforming optimization for sensing a point-like scatterer using a bistatic multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) radar, which could be part of a joint communication and sensing system. The goal is to minimize the Cram\'er-Rao bound on the target position's estimation error, where the radar already knows an approximate position that is taken into account in the optimization. The optimization considers multiple subcarriers, and permits beamforming with more than one beam per subcarrier. We discuss the properties of optimal beamforming solutions, including the case of a known channel gain. Numerical results show that beamforming with at most one beam per subcarrier is optimal for certain parameters, but for other parameters, optimal solutions need two beams on some subcarriers. In addition, the degree of freedom which end of the bistatic radar should transmit and receive in a bidirectional radar is considered.