Aiming to achieve ubiquitous global connectivity and target detection on the same platform with improved spectral/energy efficiency and reduced onboard hardware cost, low Earth orbit (LEO) satellite systems capable of simultaneously performing communications and radar have attracted significant attention. Designing such a joint system should address not only the challenges of integrating two functions but also the unique propagation characteristics of the satellites. To overcome severe echo signal path loss due to the high altitude of the satellite, we put forth a bistatic integrated sensing and communication (ISAC) framework with a radar receiver separated from the satellite. For robust and effective interference management, we employ rate-splitting multiple access (RSMA), which splits and encodes users messages into private and common streams. We optimize the dual-functional precoders to maximize the minimum rate among all users while satisfying the Cramer-Rao bound (CRB) constraints. Given the challenge of acquiring instantaneous channel state information (iCSI) for LEO satellites, we exploit the geometrical and statistical characteristics of the satellite channel. To develop an efficient optimization algorithm, semidefinite relaxation (SDR), sequential rank-1 constraint relaxation (SROCR), and successive convex approximation (SCA) are utilized. Numerical results show that the proposed framework efficiently performs both communication and radar, demonstrating superior interference control capabilities. Furthermore, it is validated that the common stream plays three vital roles: i) beamforming towards the radar target, ii) interference management between communications and radar, and iii) interference management among communication users.

翻译：为实现全球泛在连接与目标探测在同一平台上的集成，并提升频谱/能量效率、降低星载硬件成本，能够同时执行通信与雷达功能的低轨（LEO）卫星系统已引起广泛关注。设计此类联合系统不仅需应对功能融合的挑战，还需考虑卫星特有的传播特性。为克服卫星高轨道导致的严重回波信号路径损耗，本文提出一种双基地集成感知与通信（ISAC）框架，其雷达接收机与卫星分离。为实现鲁棒高效的干扰管理，我们采用速率分割多址接入（RSMA）技术，将用户消息拆分为私有流与公共流并进行编码。我们通过优化双功能预编码器，在满足克拉美-罗界（CRB）约束条件下最大化所有用户中的最低速率。针对低轨卫星瞬时信道状态信息（iCSI）获取困难的问题，本文利用卫星信道的几何与统计特性。为构建高效优化算法，我们采用半定松弛（SDR）、序列秩一约束松弛（SROCR）及逐次凸逼近（SCA）方法。数值结果表明，所提框架能高效协同执行通信与雷达功能，展现出卓越的干扰控制能力。此外，研究验证了公共流发挥的三重关键作用：i）向雷达目标进行波束成形；ii）管理通信与雷达间的干扰；iii）协调通信用户间的干扰。