  The fronthaul (FH) is an indispensable enabler for 5G networks. However, the
classical fronthauling method demands for large bandwidth, low latency, and
tightly synchronized on the transport network, and only allows for
point-to-point logical topology. This greatly limits the usage of FH in many 5G
scenarios. In this paper, we introduce a new perspective to understand and
design FH for next-generation wireless access. We allow the renovated FH 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 scheme could be incorporated into the radio access network to satisfy
the bandwidth and latency requirements of ultra-dense networks, control/data
(C/D) decoupling architectures, and delay-sensitive communications. At the same
time, massive cooperation and device-centric networking could be effectively
enabled with point-to-multi-point FH transportation. We analyze three unique
design requirements for the renovated FH, 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 FH. 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.
