## 7 Proposed Architecture for Cellular System Based on SDN, NFV, and C-RAN  
Building on the energy efficiency challenges identified in Sections 3-5 (SDN scalability, NFV performance overhead, C-RAN fronthaul limitations) and the convergence pitfalls mentioned in Section 6, we propose a conceptual integrated architecture, as shown in Figure 17.  
A comprehensive review of energy-efficient cellular networks utilizing SDN, NFV, and C-RAN technologies is presented as the primary focus of this article. The proposed architecture shown in Figure 17 demonstrates how these enabling technologies could be integrated into future cellular networks. This schematic representation is intended to serve as a conceptual foundation rather than an implemented solution, as the current work is focused on theoretical analysis and a survey of existing approaches. It is recognized that quantitative validation through simulations or field testing would be required to fully assess the proposed architecture's performance and energy efficiency benefits. These important practical evaluations have been planned as future work, with more details outlined in Section 8. Here is the functionality of each element of the proposed architecture presented in Figure 17:  
* **5G Core Control Plane With Virtualized Core Functions:** The core of the 5G and beyond cellular network can be fully virtualized since flexibility is more important for operators to support different use cases. Virtualization of the core will help to develop quicker solutions/applications, and the developed solutions can be deployed and tested faster. It could also pave the way for more innovative and flexible network services, as network operators would have more freedom to customize and optimize their networks based on a single, unified platform [97]. From an energy-efficiency perspective, virtualizing the 5G core delivers three significant benefits. First, hardware consolidation replaces dedicated appliances with virtualized functions, reducing power consumption by up to 40% through improved resource utilization [93]. Second, dynamic scaling enables core functions like UDM and AUSF to automatically adjust resources based on demand, eliminating energy waste during low-traffic periods. Third, by concentrating virtual resources in datacenters rather than in distributed hardware, operators achieve 35% savings in cooling costs through optimized thermal management [95]. * **SDN Controller:** The SDN controller oversees the entire network element and manages the resource allocation based on the demands. This is a central point that manages the data flow in the network through SDN principles, making the network programmable and more adaptable to varying traffic patterns and demands [97]. The SDN controller serves as the centralized intelligence for network-wide resource management, directly addressing the critical energy efficiency challenges identified in Section 6. By dynamically scaling resources to match real-time traffic patterns, it eliminates energy waste from over-provisioning, reducing idle power consumption compared to static architectures through optimal VNF placement [93]. The controller's global network view enables intelligent traffic routing that minimizes transmission hops, cutting routing energy while maintaining QoS requirements. * **Backhaul and Fronthaul Link:** Fiber optic cables and microwave links are two options for the backhaul connections that link the core network to the RAN architecture. Fiber optic cables are more energy efficient under heavy load conditions, while microwave links are better under low load conditions [48]. Fronthaul connects the BBUs in the C-RAN architecture to RRUs on cell towers, typically using high-bandwidth, low-latency connections such as fiber cables. * **Cloud vRAN:*
* The elements of C-RAN could also be virtualized to curtail the use of energy. The C-RAN elements are given below:
* BBU: Processes the baseband signal and is part of the C-RAN that can be centralized in a data center to serve multiple radio sites.