In this article, we consider an edge cache-assisted millimeter-wave cloud radio access network (C-RAN). Each remote radio head (RRH) in the C-RAN has a local cache, which can prefetch and store the files requested by the actuators. Multiple RRHs form a cluster to cooperatively serve the actuators, which acquire their required files either from the local caches or from the central processor via multicast fronthaul links. For such a scenario, we formulate a beamforming design problem to minimize the secure transmission delay under transmit power constraint of each RRH. Due to the difficulty of directly solving the formulated problem, we divide it into two independent ones: 1) minimizing the fronthaul transmission delay by jointly optimizing the transmit and receive beamforming and 2) minimizing the maximum access transmission delay by jointly designing cooperative beamforming among RRHs. An alternatively iterative algorithm is proposed to solve the first optimization problem. For the latter, we first design the analog beamforming based on the channel state information of the actuators. Then, with the aid of successive convex approximation and $S$ -procedure techniques, a semidefinite program (SDP) is formulated, and an iterative algorithm is proposed through SDP relaxation. Finally, the simulation results are provided to verify the performance of the proposed schemes.

中文翻译：

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边缘缓存辅助的安全低延迟毫米波传输

在本文中，我们考虑了边缘缓存辅助的毫米波云无线电访问网络（C-RAN）。C-RAN中的每个远程无线电头（RRH）都有一个本地缓存，该缓存可以预取并存储执行器请求的文件。多个RRH组成一个集群，以协作地为执行器提供服务，这些执行器通过多播前传链路从本地缓存或中央处理器获取所需的文件。对于这种情况，我们制定了波束成形设计问题，以在每个RRH的发射功率约束下将安全传输延迟最小化。由于直接解决公式化问题的难度，我们将其分为两个独立的问题：1）通过共同优化发送和接收波束成形来最小化前传传输延迟，以及2）通过共同设计RRH之间的协作波束成形来最小化最大接入传输延迟。提出了另一种迭代算法来解决第一个优化问题。对于后者，我们首先根据执行器的通道状态信息设计模拟波束成形。然后，借助逐次凸逼近和$ S $过程技术，制定了一个半定程序（SDP），并通过SDP松弛提出了一种迭代算法。最后，提供仿真结果以验证所提出方案的性能。我们首先根据执行器的通道状态信息设计模拟波束成形。然后，借助逐次凸逼近和$ S $过程技术，制定了一个半定程序（SDP），并通过SDP松弛提出了一种迭代算法。最后，提供仿真结果以验证所提出方案的性能。我们首先根据执行器的通道状态信息设计模拟波束成形。然后，借助逐次凸逼近和$ S $过程技术，制定了一个半定程序（SDP），并通过SDP松弛提出了一种迭代算法。最后，提供仿真结果以验证所提出方案的性能。