ISAC权衡悬崖：波形不确定性与有限块长下的基本极限
The ISAC Tradeoff Cliff: Fundamental Limits under Waveform Uncertainty and Finite Blocklength
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中文总结 AI 辅助
本文针对ISAC系统，在有限块长解码不确定性下，推导感知性能的费舍尔信息与CRB，揭示通信可靠性边界即感知信息边界，刻画“权衡悬崖”转变，并给出临界速率表达式，为系统设计提供可靠性余量指导。
中文摘要 AI 辅助
集成感知与通信（ISAC）利用共享波形实现通信与感知功能的联合设计，但其性能关键取决于感知接收机处可获得的发射信号的准确性。在实际系统中，该信号通过有限块长解码获得。本文开发了一个分析框架，用于量化相关解码不确定性对感知性能的影响。我们通过等效噪声公式对解码误差进行建模，该公式捕捉了其对感知接收机的二阶效应，并推导了相应的费舍尔信息量和克拉美-罗界（CRB）。由此得到的表征揭示了一个由通信速率和解码可靠性控制的基本感知-通信权衡。这表明，经典的有限块长可靠性结果对ISAC系统产生了根本性的新见解：当解码后的通信波形以数据辅助方式被重用为感知参考时，通信可靠性边界同时也充当感知信息边界。我们识别并刻画了感知性能中的急剧转变——称为“权衡悬崖”——该转变源于有限块长可靠性效应。随着通信速率接近容量，这一转变将接近理想感知性能的区域与估计误差过大的区域分隔开来。此外，我们提供了该转变发生时的临界速率的显式表达式，表明其依赖于块长、信道色散和目标错误概率。在AWGN和块衰落信道下的蒙特卡洛模拟验证了理论分析并确认了观察到的趋势。研究结果为以适当可靠性余量运行ISAC系统以避免严重感知退化提供了设计见解。
英文摘要
Integrated Sensing and Communication (ISAC) enables the joint design of communication and sensing functionalities using a shared waveform, but its performance critically depends on the accuracy of the transmitted signal available at the sensing receiver. In practical systems, this signal is obtained by finite blocklength decoding . This paper develops an analytical framework for quantifying the impact of the associated decoding uncertainty on sensing performance. We model decoding errors via an equivalent noise formulation that captures their second-order effect on the sensing receiver, and derive the corresponding Fisher Information and Cramér--Rao Bound (CRB). The resultant characterization reveals a fundamental sensing--communication tradeoff governed by the communication rate and decoding reliability. This shows that the classical finite blocklength reliability results in a fundamentally new insight concerning ISAC systems: when the decoded communication waveforms are reused as sensing references in a data-aided fashion, the communication reliability boundary also acts as a sensing-information bound. {We identify and characterize a sharp transition in sensing performance -- referred to as the Tradeoff Cliff -- arising from finite blocklength reliability effects.} This transition separates the regimes of near-ideal sensing performance from those of excessive estimation error as the communication rate approaches capacity. Furthermore, we provide an explicit expression for the critical rate at which this transition occurs, showing its dependence on blocklength, channel dispersion, and target error probability. Monte Carlo simulations under both AWGN and block fading channels validate the theoretical analysis and confirm the trend observed. The results provide design insights for operating ISAC systems with an appropriate reliability margin to avoid severe sensing degradation.
发表机构
- Indian Institute of Technology Hyderabad（印度理工学院海得拉巴分校）
- University of Southampton（南安普顿大学）
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