Implementation of C-RAN Architecture with CU/DU Split on a Flexible SDR Testbed

Cloud Radio Access Network (C-RAN) is widely considered a significant part of fifth generation (5G) networks. This paper offers flexible Software Defined Radio (SDR) testbed for C-RAN researchers and developers to verify network function and evaluate system performance. In 5G C-RAN architecture, a Baseband Unit (BBU) of C-RAN is split into a Centralized Unit (CU) and a Distributed Unit (DU). As a consequence, a SDR testbed based on OpenAirInterface is built and extended to support the CU/DU split. In order to support communications between the CU and DU units, a succinct and effective interface protocol is designed. Specifically, the CU/DU control plane split at the RRC/RLC point is primarily addressed, so that User Equipment (UE) can complete attach UE and detach UE procedures through the decoupled CU and DU units. Besides, the CU/DU user plane split at the PDCP/RLC point is accomplished. Therefore, two independent units, CU and DU, can substitute for BBU. Finally, this paper evaluates the testbed using a real network setup, a commercial Evolved Packet Core (EPC), a remote radio head (RRU) and several commercial UEs. The results show that the testbed can successfully attach UE, detach UE and transmit data to commercial UEs over the air.