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On the Performance of Dual-Antenna Repeater Assisted Bi-Static MIMO ISAC

Anubhab Chowdhury, Erik G. Larsson

TL;DR

This work investigates a bi-static ISAC system aided by a dual-antenna repeater, addressing the joint problem of target detection and downlink data transmission. It develops a channel-agnostic modeling framework and a GLRT-based target detection scheme that accounts for repeater-induced echoes and interference, and proposes regularized precoding with target-centric or communication-centric sensing beamformers to balance sensing quality and downlink rates. The key contributions include a systematic signaling model, a tractable sensing/communication trade-off analysis, and numerical results demonstrating that placing repeaters in target hotspot areas can substantially improve detection probability while highlighting the associated downlink interference trade-offs. The findings have practical implications for deploying repeaters to enhance ISAC performance in realistic multi-user, MIMO scenarios, with future work pointing to channel estimation, time variation, and multi-repeater coordination.

Abstract

This paper presents a framework for target detection and downlink data transmission in a repeater-assisted bi-static integrated sensing and communication system. A repeater is an active scatterer that retransmits incoming signals with a complex gain almost instantaneously, thereby enhancing sensing performance by amplifying the echoes reflected by the targets. The same mechanism can also improve downlink communication by mitigating coverage holes. However, the repeater introduces noise and increases interference at the sensing receiver, while also amplifying the interference from target detection signals at the downlink users. The proposed framework accounts for these sensing-communication trade-offs and demonstrates the potential benefits achievable through a carefully designed precoder at the transmitting base station. In particular, our finding is that a higher value of probability of detection can be attained with considerably lower target radar-cross-section variance by deploying repeaters in the target hot-spot areas.

On the Performance of Dual-Antenna Repeater Assisted Bi-Static MIMO ISAC

TL;DR

This work investigates a bi-static ISAC system aided by a dual-antenna repeater, addressing the joint problem of target detection and downlink data transmission. It develops a channel-agnostic modeling framework and a GLRT-based target detection scheme that accounts for repeater-induced echoes and interference, and proposes regularized precoding with target-centric or communication-centric sensing beamformers to balance sensing quality and downlink rates. The key contributions include a systematic signaling model, a tractable sensing/communication trade-off analysis, and numerical results demonstrating that placing repeaters in target hotspot areas can substantially improve detection probability while highlighting the associated downlink interference trade-offs. The findings have practical implications for deploying repeaters to enhance ISAC performance in realistic multi-user, MIMO scenarios, with future work pointing to channel estimation, time variation, and multi-repeater coordination.

Abstract

This paper presents a framework for target detection and downlink data transmission in a repeater-assisted bi-static integrated sensing and communication system. A repeater is an active scatterer that retransmits incoming signals with a complex gain almost instantaneously, thereby enhancing sensing performance by amplifying the echoes reflected by the targets. The same mechanism can also improve downlink communication by mitigating coverage holes. However, the repeater introduces noise and increases interference at the sensing receiver, while also amplifying the interference from target detection signals at the downlink users. The proposed framework accounts for these sensing-communication trade-offs and demonstrates the potential benefits achievable through a carefully designed precoder at the transmitting base station. In particular, our finding is that a higher value of probability of detection can be attained with considerably lower target radar-cross-section variance by deploying repeaters in the target hot-spot areas.

Paper Structure

This paper contains 10 sections, 1 theorem, 21 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Signalling Scheme
  4. Sensing with repeater
  5. Downlink communication with repeater
  6. Estimation & Target Detection
  7. Downlink Analysis
  8. Numerical Results & Discussions
  9. Remarks and Open Questions
  10. Proof of Lemma \ref{['lem: GLRT_Repeater']}

Key Result

Lemma 1

Let $\pmb{\Sigma}_{{\mathsf{c}}}$ and $\pmb{\Sigma}_{{\mathsf{s}}}[\tau]$ denote the covariance of the clutter channel and the overall sensing noise $\dot{{\mathbf{ w}}}_{{\mathtt{ B}}}[\tau]$ (which are individually zero mean random vectors); and let $\mathcal{T}\triangleq \ln\mathcal{L}$ be the te where $\mathbf{t}_{\mathcal{H}_{1}}$, $\mathbf{t}_{\mathcal{H}_{0}}$, ${\mathbf{ Q}}_{\mathcal{H}_{

Figures (4)

  • Figure 1: System model: communication and sensing with a repeater, and its implications to both. Interference links are indicated by red arrows.
  • Figure 2: versus the target . Here, the repeater gains are measured with respect to the noise floor at the repeater. The threshold for is adjusted to maintain a of $0.01$.
  • Figure 3: of downlink per-user with different choices of precoders. Equal power allocation has been employed by the transmit .
  • Figure 4: Probability of detection with different repeater locations with respect to the target hotspot area. We assume the clutter variance to be $10$ dB below the noise floor and the is $0.01$.

Theorems & Definitions (4)

  • Remark 1
  • Lemma 1
  • proof
  • Remark 2