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Wireless Fronthaul for 5G and Future Radio Access Networks: Challenges and Enabling Technologies

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.