C-RAN stands for Cloud- Radio Access Network (RAN) or sometimes Centralized-RAN. It is a new deployment paradigm of the RAN that tries to reduce operational costsassociated with having the complex software part of the LTE eNodeB (the radio cell) deployed at remote locations. Instead in C-RAN the Base-Band Unit (BBU), which is the software part of the LTE eNodeB is deployed in some accessible location (i.e. Central office or Cloud), whereas Remote Radio Heads or Units (RRH or RRU) with the antennas are kept at the remote locations.
The idea behind C-RAN is that by having the BBU centralized there will be less reason for infrastructure operators to have to access the remote locations where the RRH are deployed and costs for maintenance of the radio infrastructure overall reduces. It also permits a more controlled and NFV/SDN friendly network. Moreover, centralization of traditionally dispersed RAN elements’ logic might bring additional advantages.
Between RRH and BBU elements a new interface appears – “front-haul”. The front-haul is not yet standardized because there is significant research ongoing on how to separate the eNodeB into RRH/BBU and several split have been proposed . The split is considered somewhere on the eNodeB protocol stack, and the selection of the layer is critical because it determines the requirements for the front-haul interface. The most conventional split, used in current networks, refers to a well-known Radio over Fiber (RoF) concept with transferring so called IQ data over fiber. Such a fronthaul interface commonly based on the CPRI or OBSAI protocol impose stringent latency and delay requirements that few technologies e.g. dark fiber, can support and which drastically reduces the distance allowed between RRUs and BBU. All of that makes the C-RAN technology applicable only to limited number of locations and expensive to deploy, thus many organizations (e.g. NGMN, Small Cell Forum) are proposing alternative splits in the PHY, MAC or higher layers that permit using Ethernet based technologies for the front-haul.
OpenEPC includes an eNodeB emulator which supports all eNodeB protocols but the LTE Physical layer. Instead the OpenEPC eNodeB emulator uses Ethernet and DHCP extended to emulate LTE radio attachments and generates all the standard signaling towards the core network. This emulator allows OpenEPC customers to interact with an LTE network without the need of purchasing an eNodeB or owning a spectrum license.
Since end of 2014 CND has been developing an eNodeB prototype that uses also the LTE PHY from a third party and a easy-extendable MAC layer of CND. The interface with the 3rd party respects the SmallCell Forum Functional API (FAPI). Since the 3rd party hardware and the OpenEPC eNodeB prototype are deployed separated this is already a C-RAN implementation. Since mid 2015 CND is participating in the 5G-CrossHaul project and contributing its C-RAN expertise to create new front-haul/back-hauling solutions.
But CND did not stop here and it developed further the concept to create a separate RRU/BBU components with a split just on top the MAC layer. The RRH can integrate with a 3rd party hardware using FAPI or use the lower layer emulators permitting to experiment with C-RAN without any LTE radio interfaces. The BBU supports as of today CND own proprietary front-haul interface over Ethernet but others will be implemented in the feature.
CND’s OpenEPC C-RAN optional package is available for test-bed customers that want to experiment with C-RAN concepts and want to understand better and innovate the RAN towards 5G. The roadmap includes deployment in containers and dynamic selection of C-RAN mode (BBU co-located with RRHs or split) as well as lowering the split to the MAC layer. OpenEPC C-RAN is going to be an incredible enhancement for companies and organization researching with the likes of SoDeRA and other LTE PHY boards.
If you want to see OpenEPC C-RAN eNodeB it will be demonstrated as part of the 5G-CrossHaul project at EUCNC 2016 in Athens.
(Radio physical layer is emulated over Ethernet or using 3rd Party SDR board)