How Does CP Length Affect the Sensing Range for OFDM-ISAC?

2025-03-11

AI Summary

Conventional wisdom holds that the maximum radar sensing range in OFDM-based integrated sensing and communication (ISAC) systems is fundamentally limited by the cyclic prefix (CP) length to avoid inter-symbol interference (ISI) and inter-carrier interference (ICI). Method: This work theoretically demonstrates that random communication data inherently randomizes ISI/ICI, causing them to attenuate significantly after radar signal processing—effectively breaking the CP-imposed interference-free range limit. To further mitigate near-target masking and compensate for path-loss-induced SINR degradation at longer ranges, a sliding-window sensing scheme is proposed, iteratively detecting and canceling strong nearby targets. Contribution/Results: Analytical modeling and simulations confirm that effective sensing range substantially exceeds the CP-limited bound. The inherent interference randomization acts as a zero-overhead “mask,” requiring no additional signaling or resource allocation. This work redefines the fundamental design principle of CP in OFDM-ISAC systems and establishes a new paradigm for joint waveform optimization in integrated sensing and communication.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Security and Privacy: Large-scale security measurements

Abstract

Orthogonal frequency division multiplexing (OFDM), which has been the dominating waveform for contemporary wireless communications, is also regarded as a competitive candidate for future integrated sensing and communication (ISAC) systems. Existing works on OFDM-ISAC usually assume that the maximum sensing range should be limited by the cyclic prefix (CP) length since inter-symbol interference (ISI) and inter-carrier interference (ICI) should be avoided. However, in this paper, we provide rigorous analysis to reveal that the random data embedded in OFDM-ISAC signal can actually act as a free ``mask"for ISI, which makes ISI/ICI random and hence greatly attenuated after radar signal processing. The derived signal-to-interference-plus-noise ratio (SINR) in the range profile demonstrates that the maximum sensing range of OFDM-ISAC can greatly exceed the ISI-free distance that is limited by the CP length, which is validated by simulation results. To further mitigate power degradation for long-range targets, a novel sliding window sensing method is proposed, which iteratively detects and cancels short-range targets before shifting the detection window. The shifted detection window can effectively compensate the power degradation due to insufficient CP length for long-range targets. Such results provide valuable guidance for the CP length design in OFDM-ISAC systems.

Problem

• Impact of CP length on OFDM-ISAC sensing range
• Random data in OFDM-ISAC mitigates ISI/ICI interference
• Sliding window method enhances long-range target detection

Innovation

• Random data masks ISI in OFDM-ISAC signals
• Sliding window method mitigates power degradation
• Sensing range exceeds CP length limitations