Redesigning fronthaul for next-generation networks: beyond baseband samples and point-to-point links

The fronthaul is an indispensable enabler for 5G networks. However, the classical fronthauling method demands large bandwidth, low latency, and tight synchronization from the transport network, and only allows for point-to-point logical topology. This greatly limits the usage of fronthaul in many 5G scenarios. In this article, we introduce a new perspective to understand and design fronthaul for next-generation wireless access. We allow the renovated fronthaul to transport information other than time-domain I/Q samples and to support logical topologies beyond point-to-point links. In this way, different function splitting schemes can be incorporated into the radio access network to satisfy the bandwidth and latency requirements of ultradense networks, control/data decoupling architectures, and delay-sensitive communications. At the same time, massive cooperation and devicecentric networking could be effectively enabled with point-to-multipoint fronthaul transportation. We analyze three unique design requirements for the renovated fronthaul, including the ability to handle various payload traffic, support different logical topology, and provide differentiated latency guarantee. Following this analysis, we propose a reference architecture for designing the renovated fronthaul. The required functionalities are categorized into four logical layers and realized using novel technologies such as decoupled synchronization layer, packet switching, and session-based control. We also discuss some important future research issues.