The ever-increasing demand for intelligent, automated, and connected mobility solutions pushes for the development of an innovative sixth Generation (6G) of cellular networks. A radical transformation on the physical layer of vehicular communications is planned, with a paradigm shift towards beam-based millimeter Waves or sub-Terahertz communications, which require precise beam pointing for guaranteeing the communication link, especially in high mobility. A key design aspect is a fast and proactive Initial Access (IA) algorithm to select the optimal beam to be used. In this work, we investigate alternative IA techniques to fasten the current fifth-generation (5G) standard, targeting an efficient 6G design. First, we discuss cooperative position-based schemes that rely on the position information. Then, motivated by the intuition of a non-uniform distribution of the communication directions due to road topology constraints, we design two Probabilistic Codebook (PCB) techniques of prioritized beams. In the first one, the PCBs are built leveraging past collected traffic information, while in the second one, we use the Hough Transform over the digital map to extract dominant road directions. We also show that the information coming from the angular probability distribution allows designing non-uniform codebook quantization, reducing the degradation of the performances compared to uniform one. Numerical simulation on realistic scenarios shows that PCBs-based beam selection outperforms the 5G standard in terms of the number of IA trials, with a performance comparable to position-based methods, without requiring the signaling of sensitive information.

中文翻译：

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为 6G V2X 网络加快 5G NR Sidelink 的初始接入

对智能、自动化和互联移动解决方案不断增长的需求推动了创新的第六代 (6G) 蜂窝网络的发展。计划对车载通信的物理层进行彻底的变革，向基于波束的毫米波或亚太赫兹通信的范式转变，这需要精确的波束指向以保证通信链路，特别是在高移动性的情况下。一个关键的设计方面是快速主动的初始访问 (IA) 算法，用于选择要使用的最佳波束。在这项工作中，我们研究了替代 IA 技术以加强当前的第五代 (5G) 标准，以实现高效的 6G 设计。首先，我们讨论依赖于位置信息的基于位置的协作方案。然后，由于道路拓扑约束导致通信方向的非均匀分布的直觉，我们设计了两种优先波束的概率码本（PCB）技术。在第一个中，PCB 是利用过去收集的交通信息构建的，而在第二个中，我们使用数字地图上的霍夫变换来提取主要道路方向。我们还表明，来自角概率分布的信息允许设计非均匀码本量化，与均匀码本量化相比，减少了性能下降。实际场景的数值模拟表明，基于 PCB 的波束选择在 IA 试验次数方面优于 5G 标准，性能可与基于位置的方法相媲美，且无需发送敏感信息。