# A Survey on Open Radio Access Networks: Challenges, Research Directions, and Open Source Approaches
## 6 Challenges and Future Research Directions
### Open RAN Field Issues  
This subsection will discuss broader issues related to the Open RAN field. Overall, there are three challenges that MNOs may face regarding the Open RAN field, which are implementation and standardization problems, improving performance and cost, and securing Open RAN. This subsection will be closed by other open issues that may probably occur in an Open RAN architecture. Implementation and standardization problems are the first issues that we will discuss. Standardization is directly related to the O-RAN architecture because, as mentioned in previous sections, the O-RAN Alliance has made the most progress in developing the Open RAN framework compared to the other Open RAN projects. O-RAN Alliance has also provided detailed reference design specifications, complete with very clear documentation for each reference design. Even though O-RAN has provided such clear documentation, the alliance lacks robust, deployable, and well-documented software. Most of these O-RAN frameworks can not be used in real life, in actual networks [4]. It is caused by several reasons, such as the open source components proposed by O-RAN Alliance being incomplete, requiring additional integration, requiring further development for actual deployment, or containing components that lack robustness. The difficulty of keeping pace with recent architecture standards is also a challenge. The cellular network community feels pressured because they have to keep updating themselves to the specifications and technologies that have just recently been developed in new communication, networking, and programming standards [4]. The most widely known examples are the NR and the mmWave architecture, which were introduced as 5G enables by 3 GPP. Both of these architectures are currently being deployed in closed-source commercial networks. The current problem with these developments is that the RAN software libraries (OAI-RAN and srsRAN) still need to be fully developed to support NR because these developments require further coding and compatibility testing. The same thing goes for mmWave, where testing the mmWave architecture for 5G technology is still impossible because of complexity. This complexity is caused by the lack of accessible open hardware for the mmWave software to run, and it needs several beam management tests for the software to run properly. With the problems above, MNOs face dilemmas if they migrate their current RAN assets to Open RAN deployments. These decision points are summarized by [88]. The first question is whether MNOs should use the current Open RAN standard specifications, which still need to be completed, as we have mentioned, to open up the interfaces in vRAN or wait for the specifications to be more mature. The next question is whether MNOs should introduce Open RAN first in smaller networks before targeting macro RAN. While there is no simple answer and each operator will take different approaches, AT&T recommends that Open RAN implementation be introduced in incremental modules [44]. MNOs can launch Open RAN modules to their architecture bit by bit before changing the whole RAN architecture to Open RAN. Survey shows that small cells will be the initial focus of the vRAN deployment by MNOs [88]. Testing out in a localized network first before going to the main macro RAN would be a wise resolution [44; 88]. The other question related to keeping pace with the Open RAN standard is whether MNOs should migrate their RAN assets to disaggregated and virtualized options simultaneously [88]. The counterargument is that it is less risky to successfully disaggregate the BBU first before considering cloud deployment. While the benefits of using both disaggregation and virtualization concurrently are attractive, the survey shows that 25% of MNOs will implement them separately at first [88]. Through openness, Open RAN has unlocked the possibility of interoperability amongst different vendors. Although economically beneficial, this opportunity poses new emerging challenges.