The degrees of freedom (DoFs) attained in monostatic integrated sensing and communications (ISAC) are analyzed. Specifically, monostatic sensing aims for extracting target-orientation information from the line of sight (LoS) channel between the transmitter and the target, since the Non-LoS (NLoS) paths only contain clutter or interference. By contrast, in wireless communications, typically, both the LoS and NLoS paths are exploited for achieving diversity or multiplexing gains. Hence, we shed light on the NLoS exploitation vs. reduction tradeoffs in a monostatic ISAC scenario. In particular, we optimize the transmit power of each signal path to maximize the communication rate, while guaranteeing the sensing performance for the target. The non-convex problem formulated is firstly solved in closed form for a single-NLoS-link scenario, then we harness the popular successive convex approximation (SCA) method for a general multiple-NLoS-link scenario. Our simulation results characterize the fundamental performance tradeoffs between sensing and communication, demonstrating that the available DoFs in the ISAC channel should be efficiently exploited in a way that is distinctly different from that of communication-only scenarios.

翻译：分析了单静态综合遥感和通信(ISAC)所达到的自由度(DoFs),具体地说,单静态遥感的目的是从发射机和目标之间的视线(LOS)通道中提取定向信息,因为非LOS(NLOS)路径只包含杂乱或干扰。相比之下,在无线通信中,一般情况下,LOS和NLOS路径都被用于实现多样性或多重联动收益。因此,我们阐明了NLOS开发与减少单一ISAC情景中的平衡。特别是,我们优化了每种信号路径的传输能力,以尽量扩大通信率,同时保证目标的感知性能。为单一NLOS-链接情景而开发的非电解问题首先以封闭形式解决,然后我们利用流行的convex近似法(SCA)实现多样性或多重联动效果。我们模拟的结果说明了感测与通信之间的基本性能偏差,表明ISAC频道中现有的DoF应当以不同于通信情景的有效方式加以利用。