Imaging is a crucial sensing function that finds wide applications in environmental reconstruction, autonomous driving, etc. However, the signal processing methods for existing radio imaging techniques, such as millimeter wave (mmWave) imaging, require high-resolution range estimation enabled by Gigahertz-level or even Terahertz-level bandwidth, and cannot be applied in 6G integrated sensing and communication (ISAC) network with Megahertz-level bandwidth. This paper proposes two novel high-resolution radio imaging schemes that can work on the 6G signals with limited bandwidth - bandwidth-independent synthetic aperture radar (BI-SAR), where the movable base station (BS) revolves along the static targets by 360 degrees; as well as bandwidth-independent inverse synthetic aperture radar (BI-ISAR), where the BS is static and the targets revolve along an axis by 360 degrees. Different from conventional SAR and ISAR counterparts that rely on range estimation, our proposed imaging schemes solely utilize Doppler information to perform imaging without any range information. The main technical challenge of our schemes lies in the anisotropic scattering functions over different directions, which hinder the coherent synthesis of the backscattered signals from all directions. We design an iterative adaptive approach-based Doppler association (IAA-DA) algorithm to tackle the above issue. Moreover, we also derive the imaging resolution to characterize the reconstruction quality. Real-world experiments are provided to show the feasibility and the effectiveness of our proposed 6G imaging schemes.

翻译：成像是一种关键的感知功能，广泛应用于环境重建、自动驾驶等领域。然而，现有无线电成像技术（如毫米波成像）的信号处理方法需要吉赫兹甚至太赫兹级带宽才能实现高分辨率距离估计，无法应用于具有兆赫兹级带宽的6G通感一体化（ISAC）网络。本文提出两种可在有限带宽的6G信号上实现高分辨率无线电成像的新方案：带宽独立合成孔径雷达（BI-SAR），其中可移动基站（BS）沿静态目标360度旋转；以及带宽独立逆合成孔径雷达（BI-ISAR），其中基站固定，目标沿某轴360度旋转。与传统依赖距离估计的SAR及ISAR方案不同，本文提出的成像方案仅利用多普勒信息进行成像，无需任何距离信息。方案面临的主要技术挑战在于不同方向上的各向异性散射函数会阻碍所有方向后向散射信号的相干合成。我们设计了基于迭代自适应方法的多普勒关联（IAA-DA）算法来解决该问题。此外，我们还推导了成像分辨率以表征重建质量。通过实际实验验证了所提6G成像方案的可行性与有效性。