  The fifth generation (5G) of cellular systems is introducing Ultra-Reliable
Low-Latency Communications (URLLC) services alongside more conventional
enhanced Mobile BroadBand (eMBB) traffic. Furthermore, the 5G cellular
architecture is evolving from a base station-centric deployment to a fog-like
set-up that accommodates a flexible functional split between cloud and edge. In
this paper, a novel solution is proposed that enables the non-orthogonal
coexistence of URLLC and eMBB services by processing URLLC traffic at the Edge
Nodes (ENs), while eMBB communications are handled centrally at a cloud
processor as in a Cloud-Radio Access Network (C-RAN) system. This solution
guarantees the low-latency requirements of the URLLC service by means of edge
processing, e.g., for vehicle-to-cellular use cases, as well as the high
spectral efficiency for eMBB traffic via centralized baseband processing. Both
uplink and downlink are analyzed by accounting for the heterogeneous
performance requirements of eMBB and URLLC traffic and by considering practical
aspects such as fading, lack of channel state information for URLLC
transmitters, rate adaptation for eMBB transmitters, finite fronthaul capacity,
and different coexistence strategies, such as puncturing.
