# Open RAN--Radio Access Network Evolution, Benefits and Market Trends
## 7 Conclusions--Challenges and Open Issues  
Open RAN may be treated as a wide list of features and use cases which have to be first specified and then implemented within multi-vendor networks to deliver expected value. Thus, unpredictability of how the process of real commercial deployment will look in next few years is recognized. Conversely, there are up-to-date market predications showing that Open RAN is going to bring measurable revenues in the global RAN market. According to report [73], total cumulative Open RAN revenues are projected to USD 10-15 B between 2020 and 2025 and Open RAN revenues get 10% percent of RAN market by 2025. Moreover, according to [74], Open RAN solutions are predicted to grow to USD 11.2 bn in 2026. However, most of the revenue is expected to go to incumbent vendors instead of new challengers and multi-vendor deployments. The authors of [75] predict that around 2027-2028, Open RAN will first time outrun the legacy RAN market as is perceived as quickly expanding. In [76], it is estimated that O-RAN market will attain overall (hardware, software, services) revenue of USD 21.371 B in 2028 by growing at a CAGR 83.1% (in the forecast period 2020-2028). Additionally, factors which may bring Open RAN closer to market success is the support of some countries in developing cutting-edge domestic technologies, positive impact of vertical market deployment, and new use cases. Developing of mature Open RAN solutions will take several years. According to the proposed use cases [77] and market expectations [46], future works will cover QoE, performance and energy efficiency aspects in first phase. Then, in the second phase, it is expected that Open RAN will support novel scenarios, namely, Radio Resource Allocation for Unmanned Aircraft Vehicle Applications, RAN Slice Service Level Agreement Assurance, Machine Learning and contend based radio resource optimization and mobility. To achieve the pointed out technical objectives and benefits, the recognized challenges and open issues need to be clarified and solved. First, it is not clear on the scale of future swapping legacy networks by Open RAN based solutions. Possible scenarios encompass alternative update legacy eNB/gNB to support O-RAN or new cells deploying next to those already run in field. It is not easy for greenfield suppliers to implement all advances features which are currently developed by brownfield vendors; thus, it is not sure that coverage or capacity of the cells will be kept in an easy way in case of swapping to Open RAN. Open RAN solutions are strongly 4G and 5G oriented--which may lead to keep at least to separate platforms to enable connections also with legacy networks (i.e., 2G, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Features Area** & **Theoretical Study** & **Lab/PoC** \\ \hline ML & [58; 60; 61; 65; 66; 69; 70] & [59; 62] \\ Energy-efficiency & [61] & [59] \\ RRM & [60; 65] & [59] \\ vRAN & [61] & [59] \\ Traffic steering & [60; 70] & \\ Throughput & [20; 60] & \\ Deployment & [22; 63; 67; 68; 72] & \\ Security & & [66] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Open RAN features area covered by research activity. 3G)--such deployment is not a desirable approach from operational, maintenance and cost reduction perspectives. Certainly, before introducing a new technology, mobile network operators need to test and verify it in labs and wide-scale trials. In case of a multi-vendor RAN stack, it is crucial to conduct interoperability tests based on adopted evaluation criteria and then run the process dedicated to integrating and maintaining networks, taking also into account risk ownership. As O-RAN allows to implement ML-assisted algorithms for radio resource management, another set of tests needs to be prepared to be confident that models are trained in a proper way and that selected KPI goals are achieved. In a multi-player environment, which is established by Open RAN, security concerns need to be evaluated and addressed. Finally, it should be said that there are high expectation towards Open RAN.