Wireless networks have been evolving at a frenetic pace to meet the ever increasing demands for higher capacity, lower latency, and massive number of connections. In the fifth generation (5G) radio access networks (RANS), millimeter-wave and higher band radio are instrumental in achieving such stringent requirements. The network deployment must go through significant densification to meet the extremely high demand of data traffic. This imposes a big challenge to the network architecture as well as to the design of fronthaul transport links in the network. Fronthaul is generally referred to as the connection link between baseband units and remote radio units. Fiber-based connections have been conventionally the mainstream technology for fronthaul. However, fiber-based fronthaul may not scale in a cost-effective way to meet dense and flexible deployment requirements. Wireless fronthaul could be a viable solution and an attractive alternative to fiber for such deployments. In this article, we first provide an overview of emerging fronthaul interfaces and requirements. We then highlight the enabling technologies and solutions that can be applied in wireless fronthaul to meet future fronthaul capacity and latency requirements in a robust manner. The discussed technologies include performing fronthaul compression, leveraging new higher band spectrum, optimizing high rank line-of-sight multiple-input multiple-output (LoS-MIMO) and applying forward-looking technologies like reconfigurable intelligent surfaces. Wireless fronthaul has the advantages of flexibility, scalability, and low cost compared to fiber-based fronthaul. However, it also raises challenges in reliably delivering the required key performance indicators. Simulation results of wireless fronthaul for a wide range of distances and point-to-multipoint deployment scenarios show that robust and reliable performance can be achieved using high rank LoS-MIMO at high millimeter-wave bands. The analysis of this article indicates that wireless fronthaul can be designed to meet the requirements and be an attractive option for future disaggregated RAN deployments.

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5G 和未来无线接入网络的无线前传：挑战和使能技术

无线网络一直在以疯狂的速度发展，以满足对更高容量、更低延迟和大量连接的不断增长的需求。在第五代 (5G) 无线接入网络 (RANS) 中，毫米波和更高频段的无线电有助于实现如此严格的要求。网络部署必须经过显着的密集化才能满足极高的数据流量需求。这对网络架构以及网络中前传传输链路的设计提出了很大的挑战。前传通常被称为基带单元和远程无线电单元之间的连接链路。基于光纤的连接通常是前传的主流技术。然而，基于光纤的前传可能无法以经济高效的方式扩展以满足密集和灵活的部署要求。对于此类部署，无线前传可能是一种可行的解决方案和有吸引力的光纤替代方案。在本文中，我们首先概述新兴的前传接口和要求。然后，我们重点介绍可应用于无线前传的支持技术和解决方案，以稳健的方式满足未来的前传容量和延迟要求。讨论的技术包括执行前传压缩、利用新的更高频段频谱、优化高等级视距多输入多输出 (LoS-MIMO) 以及应用可重构智能表面等前瞻性技术。无线前传具有灵活性、可扩展性、与基于光纤的前传相比，成本低。然而，它也对可靠地交付所需的关键绩效指标提出了挑战。针对各种距离和点对多点部署场景的无线前传仿真结果表明，在高毫米波段使用高秩 LoS-MIMO 可以实现稳健可靠的性能。本文的分析表明，可以设计无线前传来满足要求，并成为未来分散式 RAN 部署的一个有吸引力的选择。针对各种距离和点对多点部署场景的无线前传仿真结果表明，在高毫米波段使用高秩 LoS-MIMO 可以实现稳健可靠的性能。本文的分析表明，可以设计无线前传来满足要求，并成为未来分散式 RAN 部署的一个有吸引力的选择。针对各种距离和点对多点部署场景的无线前传仿真结果表明，在高毫米波段使用高秩 LoS-MIMO 可以实现稳健可靠的性能。本文的分析表明，可以设计无线前传来满足要求，并成为未来分散式 RAN 部署的一个有吸引力的选择。