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 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 problems are formulated under two criteria: power consumption minimization and sum rate maximization. The downlink and uplink transmissions are tightly coupled due to both the desired target echo and the undesired interference received at the BS, making the problems challenging. To handle these issues in both cases, we first determine the optimal receive beamformers, which are derived in closed forms with respect to the BS transmit beamforming and the user transmit power, for radar target detection and uplink communications, respectively. Subsequently, we invoke these results to obtain equivalent optimization problems and propose efficient iterative algorithms to solve them by using the techniques of rank relaxation and successive convex approximation (SCA), where the adopted relaxation is proven to be tight. In addition, we consider a special case under the power minimization criterion and propose an alternative low complexity design. Numerical results demonstrate that the optimized FD communication-based ISAC brings tremendous improvements in terms of both power efficiency and spectral efficiency compared to the conventional ISAC with HD communication.
翻译:波束成形设计已广泛应用于具有全双工(FD)感知和半双工(HD)通信的集成感知和通信(ISAC)系统。为了实现更高的频谱效率,本文扩展了现有的ISAC波束成形设计,考虑到雷达和通信的FD能力。具体而言,我们考虑到一个ISAC系统,其中基站执行目标检测并与多个下行用户通信以及复用相同的时频资源的上行用户通信。我们在BS和用户端联合优化下行双功能发射信号以及上行接收波束形成器和用户的发送功率。问题基于两个准则制定:功耗最小化和和速率最大化。由于BS接收到的期望目标回波和不期望的干扰,下行和上行传输之间紧密耦合,使问题变得具有挑战性。为处理这些问题,我们首先确定了最佳接收波束形成器,分别针对雷达目标检测和上行通信,这些接收波束形成器与BS发射波束形成和用户发射功率有关,并在此基础上提出了等效优化问题并使用秩松弛和逐次凸松弛(SCA)技术提出了高效迭代算法来解决它们。采用的松弛被证明是紧的。此外,我们考虑了在功率最小化准则下的特殊情况,并提出了一种替代的低复杂度设计。数值结果表明,优化的FD通信ISAC相对于具有HD通信的传统ISAC在功率效率和频谱效率方面带来了巨大的改进。