부산대학교 도서관

Ultra-reliable and low-latency communications (URLLC) plays a critical role for the coming era of wireless industrial automation, which increases the flexibility without moderating the stringent requirements of latency and reliability. The task for URLLC is to deliver short packets from sensors to actuators via the central controller reliably and timely, during which large bandwidth is required for ensuring stringent quality-of-service (QoS) metrics. Due to the scarce spectrum resource shared by a large number of devices, and the dynamic channel changes over wireless links, it is challenging to achieve bandwidth-saving URLLC with one single method. Motivated by the observation that groups of devices working in close proximity to each other can form device-to-device (D2D) communications, this paper considers multi-connectivity (MC) together with other cross-layer methods including grant-free access, data replication, broadcasting, and processor-sharing server to minimize the total bandwidth under the QoS constraints of URLLC. With the cross-layer design, we fisrt derive the packet loss probability including the factors of collision due to the contention-based access scheme and decoding error due to the dynamic wireless channel, and hence the overall reliability of MC is provided. Then, we establish a framework to minimize the total bandwidth of MC, where the relationship of collision and packet loss probabilities, the monotonicity of collision and decoding error probabilities, and the relationship of the third type blocklength and size rule are proved to find the optimal resource allocation. Simulation results validate the analysis and show the performance gain by optimizing resource allocation with the considered cross-layer design.