Integrating sensing functionalities is envisioned as a distinguishing feature of next-generation mobile networks, which has given rise to the development of a novel enabling technology -- \emph{Integrated Sensing and Communication (ISAC)}. Portraying the theoretical performance bounds of ISAC systems is fundamentally important to understand how sensing and communication functionalities interact (e.g., competitively or cooperatively) in terms of resource utilization, while revealing insights and guidelines for the development of effective physical-layer techniques. In this paper, we characterize the fundamental performance tradeoff between the detection probability for target monitoring and the user's achievable rate in ISAC systems. To this end, we first discuss the achievable rate of the user under sensing-free and sensing-interfered communication scenarios. Furthermore, we derive closed-form expressions for the probability of false alarm (PFA) and the successful probability of detection (PD) for monitoring the target of interest, where we consider both communication-assisted and communication-interfered sensing scenarios. In addition, the effects of the unknown channel coefficient are also taken into account in our theoretical analysis. Based on our analytical results, we then carry out a comprehensive assessment of the performance tradeoff between sensing and communication functionalities. Specifically, we formulate a power allocation problem to minimize the transmit power at the base station (BS) under the constraints of ensuring a required PD for perception as well as the communication user's quality of service requirement in terms of achievable rate. Finally, simulation results corroborate the accuracy of our theoretical analysis and the effectiveness of the proposed power allocation solutions.

翻译：将感知功能集成被视为下一代移动网络的显著特征，由此催生了一种新兴使能技术——集成感知与通信（ISAC）。刻画ISAC系统的理论性能边界对于理解感知与通信功能在资源利用方面如何相互作用（如竞争或协作），同时为开发有效物理层技术提供见解和指导原则具有重要意义。本文刻画了ISAC系统中目标监测检测概率与用户可达速率之间的基础性能权衡。为此，我们首先讨论了无感知干扰和有感知干扰通信场景下用户的可达速率。此外，我们推导了感兴趣目标监测的虚警概率（PFA）和成功检测概率（PD）的闭式表达式，其中考虑了通信辅助感知和通信干扰感知两种场景。同时，理论分析中还考虑了未知信道系数的影响。基于分析结果，我们对感知与通信功能之间的性能权衡进行了全面评估。具体而言，我们构建了一个功率分配问题，在确保感知所需的PD以及通信用户服务质量（即可达速率）要求的约束下，最小化基站（BS）的发射功率。最后，仿真结果验证了理论分析的准确性以及所提功率分配方案的有效性。