For the C-RAN concept to be widely deployable for future 5G networks, the cost of the optical fibre fronthaul needs to be reduced. The use of Ethernet in the fronthaul, instead of a technology dedicated to digitised radio, opens the possibilities for sharing the optical infrastructure with a fixed access network, and the use of the same technology in a wide variety of shorthaul networks (e.g. in server rooms of local area networks, data centres), if a low-cost transport profile can be defined. Then, assuming the desired bit-rates can be delivered, there is the question of whether a frame-/packet-based transport technology can meet the required latency and synchronisation specifications. In iCIRRUS the approach to this problem will be two-pronged: we will examine transport profiles and C-RAN architecture requirements which minimise deleterious effects, while also investigating techniques which can mitigate against impairments due to mobility, delay and frequency offsets.
Fronthaul is perhaps the most widely discussed flavour of C-RAN in the industry at present. The underlying requirement here is to transport digitized air interface signals between the baseband unit (BBU) and Remote Radio Head (RRH) over an extremely low latency and high bandwidth transport layer. For Midhaul, the challenge is to analyse a more forgiving, yet still challenging partition of the BBU with synchronization and control aspects placed in the central location and the air interface component of the base station maintained at the remote site. Backhaul refers to the transport of all mobile traffic over IP tunnels as is standard practice for LTE models.
The revolutionary C-RAN architecture proposed must meet and/or exceed current customer quality of experience (QoE) expectations. Such QoEs are contingent on both S1/core and RAN loading, and iCIRRUS will target measuring handset QoE at levels that meet/exceed throughput and delay for CPRI- based systems. Thus end-user performance measurement and micro-probing of the fronthaul/midhaul and backhaul for jitter, latency and loss, will be implemented for metric collection. Then, such metrics from the Ethernet C-RAN can feed the SON engine to adapt the network and optimize performance.