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OFDM Waveform Optimization for Bistatic Integrated Sensing and Communications

Ruolin Du, Zhiqiang Wei, Zai Yang, Ya-Feng Liu, Bingpeng Zhou, Derrick Wing Kwan Ng

TL;DR

This paper proposes a joint path coefficient and delay estimation (JPCDE) scheme, revealing that the achievable communication data rate (CDR) is determined by the number of communication subcarriers, whereas the delay sensing accuracy is governed by the index distribution of sensing subcarriers.

Abstract

This paper investigates the design of orthogonal frequency-division multiplexing (OFDM) waveforms for bistatic integrated sensing and communication (ISAC) systems. In the considered framework, an ISAC transmitter jointly optimizes subcarrier assignment and power allocation for a single OFDM waveform that simultaneously supports communication and sensing functionalities. Meanwhile, an ISAC receiver decodes information on communication subcarriers and estimates per-path propagation delays via exploiting pilot symbols on sensing subcarriers. We propose a joint path coefficient and delay estimation (JPCDE) scheme, revealing that the achievable communication data rate (CDR) is determined by the number of communication subcarriers, whereas the delay sensing accuracy is governed by the index distribution of sensing subcarriers. Building on this insight, we formulate an OFDM waveform optimization problem to maximize the CDR subject to sensing-accuracy and power-budget constraints. To solve this problem, we employ a quadratic transform and Lagrangian dual decomposition, which iteratively updates the subcarrier assignment and power allocation variables in closed-form. Our results reveal that a subcarrier is allocated for sensing if and only if its Fisher information gain exceeds the corresponding communication rate loss, while the power allocation for communication subcarriers exhibits a bounded water-filling structure. Simulation results demonstrate that the proposed frameworks substantially outperform existing baselines in both delay estimation accuracy and CDR.

OFDM Waveform Optimization for Bistatic Integrated Sensing and Communications

TL;DR

This paper proposes a joint path coefficient and delay estimation (JPCDE) scheme, revealing that the achievable communication data rate (CDR) is determined by the number of communication subcarriers, whereas the delay sensing accuracy is governed by the index distribution of sensing subcarriers.

Abstract

This paper investigates the design of orthogonal frequency-division multiplexing (OFDM) waveforms for bistatic integrated sensing and communication (ISAC) systems. In the considered framework, an ISAC transmitter jointly optimizes subcarrier assignment and power allocation for a single OFDM waveform that simultaneously supports communication and sensing functionalities. Meanwhile, an ISAC receiver decodes information on communication subcarriers and estimates per-path propagation delays via exploiting pilot symbols on sensing subcarriers. We propose a joint path coefficient and delay estimation (JPCDE) scheme, revealing that the achievable communication data rate (CDR) is determined by the number of communication subcarriers, whereas the delay sensing accuracy is governed by the index distribution of sensing subcarriers. Building on this insight, we formulate an OFDM waveform optimization problem to maximize the CDR subject to sensing-accuracy and power-budget constraints. To solve this problem, we employ a quadratic transform and Lagrangian dual decomposition, which iteratively updates the subcarrier assignment and power allocation variables in closed-form. Our results reveal that a subcarrier is allocated for sensing if and only if its Fisher information gain exceeds the corresponding communication rate loss, while the power allocation for communication subcarriers exhibits a bounded water-filling structure. Simulation results demonstrate that the proposed frameworks substantially outperform existing baselines in both delay estimation accuracy and CDR.
Paper Structure (11 sections, 20 equations, 4 figures)

This paper contains 11 sections, 20 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Bistatic OFDM-Based ISAC System Model
  3. OFDM Waveform Optimization based on JPCDE
  4. CRB Derivation
  5. Problem Formulation
  6. Solution Approach
  7. Update $\boldsymbol{P}^{(k)}$ and $y^{(k)}$ with fixed $\boldsymbol{u}^{(k)}$
  8. Update $\boldsymbol{u}^{(k+1)}$ with fixed $\boldsymbol{P}^{(k)}$ and $y^{(k)}$
  9. Update dual variables $\lambda^{(k+1)}$ and $\mu^{(k+1)}$
  10. Simulation Results
  11. Conclusion

Figures (4)

  • Figure 1: Bistatic OFDM-based ISAC system model.
  • Figure 2: Different sensing subcarrier assignment and power allocation strategies under an identical total power budget.
  • Figure 3: CDR versus the range error bound under different power budgets for the proposed JPCDE-based waveform optimization.
  • Figure 4: Sensing and communication performance versus $P_{\text{req}}$ of the proposed and baseline schemes, with range error bound set to $0.05~\text{m}$.