Beamforming design has been widely investigated for integrated sensing and communication (ISAC) systems with full-duplex (FD) sensing and half-duplex (HD) communication. To achieve higher spectral efficiency, in this paper, we extend existing ISAC beamforming design by considering the FD capability for both radar and communication. Specifically, we consider an ISAC system, where the base station (BS) performs target detection and communicates with multiple downlink users and uplink users reusing the same time and frequency resources. We jointly optimize the downlink dual-functional transmit signal and the uplink receive beamformers at the BS and the transmit power at the uplink users. The problem is formulated to minimize the total transmit power of the system while guaranteeing the communication and sensing requirements. The downlink and uplink transmissions are tightly coupled, making the joint optimization challenging. To handle this issue, we first determine the receive beamformers in closed forms with respect to the BS transmit beamforming and the user transmit power and then suggest an iterative solution to the remaining problem. We demonstrate via numerical results that the optimized FD communication-based ISAC leads to power efficiency improvement compared to conventional ISAC with HD communication.

翻译：波束赋形设计已在具有全双工（FD）感知与半双工（HD）通信的集成感知与通信（ISAC）系统中得到广泛研究。为实现更高的频谱效率，本文通过同时考虑雷达与通信的全双工能力，扩展现有ISAC波束赋形设计。具体而言，我们研究了一个基站（BS）在相同时间和频率资源上进行目标检测并与多个下行用户及上行用户通信的ISAC系统。我们联合优化基站的下行双功能发射信号、上行接收波束赋形以及上行用户的发射功率。该问题被建模为在保证通信与感知需求的前提下最小化系统总发射功率。下行传输与上行传输紧密耦合，使得联合优化具有挑战性。为解决该问题，我们首先以基站发射波束赋形和用户发射功率的闭式形式确定接收波束赋形，随后针对剩余问题提出迭代求解方案。数值结果表明，与传统采用半双工通信的ISAC相比，基于优化全双工通信的ISAC可提升功率效率。