## 8 Conclusions  
In this paper, a comprehensive survey of energy-efficient cellular networks was presented, focusing on the transformative potential of SDN, NFV, and C-RAN to reduce power consumption and enable sustainable 5G and beyond networks. Through a systematic analysis of the existing literature, key trends, challenges, and solutions in green telecommunications were identified. A conceptual architecture that integrates SDN, NFV, and C-RAN was discussed, demonstrating the potential of these technologies to significantly improve energy efficiency. However, the primary contribution of this work is considered to be the thorough review of state-of-the-art approaches rather than the detailed implementation of a specific architecture. In Table 1, prior works are categorized based on their contributions to hardware efficiency, renewable energy integration, and emerging paradigms. This structured classification provides valuable insights into existing research efforts, highlighting areas where further advancements are needed. The convergence of SDN, NFV, and C-RAN has been identified as a promising pathway to achieving energy savings of approximately 40 to 50% through dynamic resource allocation, hardware consolidation, and centralized processing. Nevertheless, several critical challenges remain, including issues related to interoperability in multi-vendor SDN/NFV environments and the absence of standardized frameworks to ensure scalability. It is recommended that future research focuses on the following areas:  
* Quantitative validation: Simulations or testbed implementations should be conducted to evaluate the real-world energy efficiency of the proposed architectures under diverse traffic conditions. * AI-driven optimization: Machine-learning techniques should be employed to enhance SDN/NFV orchestration, enabling more intelligent resource management. * Standardization efforts: Interoperability gaps, particularly in Open RAN and hybrid cloud-edge deployments, should be addressed to facilitate seamless integration. * 6G integration: The convergence with emerging technologies, such as terahertz communication and quantum networking, should be explored to further advance sustainability goals. By addressing these challenges, the transition from theoretical frameworks to practical implementations can be facilitated, ensuring that green networking principles become embedded in future cellular infrastructure. This review is intended to serve as a foundational reference for researchers and practitioners aiming to develop energy-efficient cellular networks, thereby promoting the adoption of sustainable practices within the telecom industry. Conceptualization, R.S., L.M.P.L., E.O.Z., M.S.B., C.K. and L.D. ; methodology, R.S., L.M.P.L., E.O.Z., M.S.B., C.K. and L.D. ; formal analysis, R.S., L.M.P.L. and E.O.Z. ; investigation, R.S., L.M.P.L., E.O.Z. and C.K. ; resources, M.S.B., L.D., and C.K. ; data curation, R.S., M.S.B., L.M.P.L. and C.K. ; writing--original draft preparation, R.S., L.M.P.L., E.O.Z., M.S.B. and C.K. ; writing--review and editing, R.S., L.M.P.L., E.O.Z., M.S.B., and C.K. ; visualization, R.S. ; supervision, M.S.B., C.K. and L.D. ; project administration, M.S.B., L.D. and C.K. ; funding acquisition, M.S.B., L.D. and C.K. All authors have read and agreed to the published version of the manuscript. Funding:This research is conducted under the umbrella of the \"Innovative solutions for next generation of Green COMmunications infrastructures (GreenCOM)\" project, funded by Innovations-fonden. For further details, please visit the project website [[https://greencom.dtu.dk/](https://greencom.dtu.dk/)]([https://greencom.dtu.dk/](https://greencom.dtu.dk/)), accessed on 2 April 2025. **Acknowledgments:** The authors would also like to express their gratitude towards the Digital & Sustainable Innovation team of FORCE Technology (DSI), Horsholm, Denmark for their indispensable contributions to this work. **Conflicts of Interest:** Author [PERSON] was employed by the company TDC (Denmark).