# A Survey on Open Radio Access Networks: Challenges, Research Directions, and Open Source Approaches
## 8 Conclusions  
Open RAN is accelerating innovation and disrupting the cellular industry ecosystem. It aims to overcome the challenges faced by the cellular network industry through disaggregation and interoperability. Open RAN promises to bring a multivendor ecosystem, flexibility, cost efficiency, and performance improvement by leveraging state-of-the-art technologies and approaches. Many projects, activities, and standardization efforts have been created for Open RAN. However, there are many challenges in developing and implementing the Open RAN idea into reality.  
Figure 20: Logical resources of OSC Labs.  
We have presented a comprehensive overview of Open RAN and its importance, discussed its challenges and potential research directions, and addressed some of the challenges from an open-source perspective. We first summarized the evolution history of the RAN from traditional to vRAN. It helps identify the differences and development of the RAN technology. Then, we introduced the Open RAN movement and the technologies related to the Open RAN generation. After that, we discussed projects, activities, and standards related to Open RAN. It helps to elaborate on the current condition of Open RAN development. Next, we briefly explained the standardized Open RAN architecture from the O-RAN Alliance and its use cases. After that, we discuss challenges and future research directions for each O-RAN's standard architecture component. A number of broader issues relating to Open RAN and its future are also mentioned, including implementation and standardization, performance and cost improvement, security, and other open problems. Finally, we discuss how open source could potentially solve Open RAN challenges. Hopefully, this survey can be a useful starting reference for academia and industry to pursue further in-depth study on Open RAN.  
This research was funded by National Science and Technology Council, Taiwan, grant number 111-2221-E-011-069-MY3, 112-2218-E-011-004, and 112-2218-E-011-006; by Chunghwa Telecom, grant number NTUST-CHT-10353; and by Auray, grant number number NTUST-Auray-11226.  
Author [PERSON] was employed by the company Google, LLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.  
The following abbreviations are used in this manuscript:  
2G Second Generation  
3G Third Generation  
3 GPP 3 rd Generation Partnership Project  
4G Fourth Generation  
5G Fifth Generation  
5 GC 5G Core  
AI Artificial Intelligence  
API Application Program Interface  
BBU Baseband Unit  
BC Blockchain  
BS Base Station  
C-RAN Centralized/Cloud RAN  
CapEx Capital Expenditure  
CN Core Network  
COTS Commercial Off-The-Shelf  
CP Control Plane  
CPU Central Processing Unit  
CU Central Unit  
CUPS Control Plane and User Plane Splitting  
D-RAN Distributed RAN  
DL Downlink  
DU Distributed Unit  
E2E End-to-End  
eMBB enhanced Mobile Broadband  
eNB evolved Node B  
EPC Evolved Packet Core  
FG Focus Group  
FH Fronthaul  
FHI FH Interface  
FPGA Field-Programmable Gate Array