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SAR/ISAR Imaging in 6G Network

Yanmo Hu, Shuowen Zhang, Ross Murch, Liang Liu

Abstract

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.

SAR/ISAR Imaging in 6G Network

Abstract

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.

Paper Structure

This paper contains 27 sections, 4 theorems, 54 equations, 6 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Motivations and Backgrounds
  3. Contributions
  4. System Model
  5. Signal Model for BI-SAR Imaging Mode
  6. Signal Model for BI-ISAR Imaging Mode
  7. A Unified Signal Model for BI-SAR and -ISAR Imaging
  8. Signal Model Simplification
  9. Bandwidth-Limited Approximation
  10. Far-Field Approximation
  11. Small-Angle Approximation for Scattering Function
  12. Signal Model Analysis
  13. Doppler Frequency
  14. Unambiguous Imaging Region
  15. Imaging Algorithm for BI Imaging Scheme
  16. ...and 12 more sections

Key Result

Proposition 1

(Doppler Frequency) The Doppler frequency of the scatterer is found to be sinusoidally modulated with respect to the azimuth angle. For a given azimuth angle $\Phi_k$, the Doppler frequency corresponding to a scatterer at position $\left(x, y\right)$ is expressed as $\blacktriangleleft$$\blacktriangleleft$

Figures (6)

  • Figure 1: System model of our considered imaging architecture. (a) BI-SAR imaging mode. (b) BI-ISAR imaging mode.
  • Figure 2: Experiment scenarios with (a) hardware, (b) a box with the size of $0.35\text{m} \times 0.41\text{m} \times 0.33\text{m}$ (along $x$, $y$, $z$ axes), and (c) four cylindrical targets located at $\left(7.5, 14.5\right)\text{cm}$, $\left(14.5, 9.5\right)\text{cm}$, $\left(-12, -11\right)\text{cm}$, and $\left(-5.5, -15\right)\text{cm}$.
  • Figure 3: Imaging results for the box target. (a) Result of the proposed IAA-DA algorithm. (b) Detection result of the reconstructed image. (c) Result of the SRDI algorithm 10475383. (d) Result of the FBP algorithm 3135465484121.
  • Figure 4: Imaging results for four cylindrical targets. (a) Result of the proposed IAA-DA algorithm. (b) Detection result of the reconstructed image. (c) Result of the SRDI algorithm 10475383. (d) Result of the FBP algorithm 3135465484121.
  • Figure 5: Results of the penetration imaging. (a) Scenario 1 with one cylindrical target within the box. (b) Result of the proposed IAA-DA algorithm for scenario 1. (c) Scenario 2 with two cylindrical target within the box. (d) Result of the proposed IAA-DA algorithm for scenario 2.
  • ...and 1 more figures

Theorems & Definitions (15)

  • Remark 1
  • Remark 2
  • Proposition 1
  • Proof 1
  • Proposition 2
  • Proof 2
  • Remark 3
  • Proposition 3
  • Proof 3
  • Remark 4
  • ...and 5 more