This paper explores an integrated sensing and communication (ISAC) system with backscattering RFID tags. In this setup, an access point employs communication beams to serve communication users while leveraging a sensing beam to interrogate RFID tags. Under the total transmit power constraint of the system, our objective is to design a joint sensing and communication beamforming codebook by considering the tag interrogation and communication requirements. To lay a foundation for the codebook design problem, we first study the beamforming design problem in a single-tag scenario and investigate two approaches: (i) a zero-forcing approach with optimized sensing/communication power allocation, for which a closed-form solution is derived under a dominant sensitivity condition, and (ii) a joint sensing and communication beamforming design obtained by transmit power minimization. Then, we investigate the codebook design problem in a multi-tag scenario. To resolve this, we propose a sector-based joint sensing and communication beamforming codebook that scans the region of interest. For each sector, semidefinite relaxation and generalized Benders decomposition are employed to handle the resulting optimization. The simulation results show that the proposed joint beamforming designs can effectively mitigate the mutual interference between sensing and communication functionalities, thus enhancing the interrogation range of the tags with minimized transmit power. Also, the efficacy of the proposed sector-based codebook design has been demonstrated in terms of interrogation success rate, offering a promising approach for the ISAC-backscattering systems.

翻译：本文研究了一种集成反向散射RFID标签的感知与通信一体化（ISAC）系统。在该系统中，接入点采用通信波束服务通信用户，同时利用感知波束查询RFID标签。在系统总发射功率约束下，我们旨在通过考虑标签查询与通信需求，设计联合感知与通信的波束赋形码本。为奠定码本设计问题的基础，我们首先研究单标签场景下的波束赋形设计问题，并探讨两种方法：(i) 采用优化感知/通信功率分配的迫零方法，在主导灵敏度条件下推导出闭式解；(ii) 通过发射功率最小化获得联合感知与通信的波束赋形设计。随后，我们研究多标签场景下的码本设计问题。为解决该问题，我们提出一种基于扇区的联合感知与通信波束赋形码本，用于扫描感兴趣区域。针对每个扇区，采用半定松弛与广义Benders分解处理相应的优化问题。仿真结果表明，所提出的联合波束赋形设计能有效抑制感知与通信功能间的相互干扰，从而以最小化发射功率扩展标签的查询范围。此外，基于扇区的码本设计在查询成功率方面的有效性已得到验证，为ISAC-反向散射系统提供了一种有前景的方法。