## 1 Introduction
Cellular networks are also adopting renewable energy sources such as solar and wind to power base stations. Along with these, attention is given to efficient resource allocation, load balancing, and intelligent network management based on traffic demand. In simple terms, the goal of green communication is to find a balance in delivering data while using the least amount of energy possible [9; 10; 11; 12; 13]. To mitigate these challenges, emerging paradigms, such as SDN, NFV, and C-RAN, offer evolutionary potential. These technologies enable dynamic resource management, hardware abstraction, and centralized processing, which are key enablers for energy-efficient networks. This paper aims to explore the potential of SDN, NFV, and C-RAN in creating a sustainable and green cellular network. These technologies hold the promise of transforming the traditional telecom network infrastructure into a more flexible, scalable, and energy-efficient one, thereby paving the way toward a green network. In addition, this paper serves as a comprehensive review of existing approaches and initiatives aimed at achieving energy efficiency in cellular networks. Figure 3 shows the block diagram of cellular architecture based on SDN, NFV, and C-RAN. In cellular communication, NFV can be utilized in mobile core networks for deploying telecommunication functions as virtual functions [14]. C-RAN can be used in the Baseband Unit (BBU) pool and Remote Radio Unit (RRU) network to lower the total cost of ownership and improve network performance. SDN can enhance the data plane, control plane, and application plane for handling data traffic, controlling network topology and defining requirements, respectively [15]. SDN decouples the control plane from the data plane and provides a centralized control that enables efficient network management and reduces the network's energy consumption [16]. On the other hand, NFV virtualizes network functions and runs them as software in data centers or clouds, leading to reduced network power consumption and deployment cost [17]. C-RAN, a cloud-based architecture for the radio access network, offers centralized processing, collaborative radio, and real-time cloud infrastructure, resulting in  
Figure 2: Overview of power consumption in cellular network [7]. The cellular RAN consumes 73% of total power, and the remaining 23% is consumed by the core network, data centers, and other components. enhanced spectral efficiency and energy efficiency. Detailed information about SDN, NFV, and C-RAN is presented in Sections 3, 4, and 5, respectively, in this paper. In this paper, the functionality and complexity of these technologies are delved into, and how they can be leveraged to create energy-efficient communication networks is discussed. The following key points are targeted:  
* A comprehensive review of existing initiatives and research efforts focused on reducing energy consumption in cellular networks. * The collective contribution of SDN, NFV, and C-RAN to reducing energy consumption in cellular networks. * Existing challenges and limitations in the convergence of these technologies for energy-efficient communication networks. * A cellular architecture is proposed based on SDN, NFV, and C-RAN to make the cellular network power efficient. This paper follows the following structure: Section 2 presents related work to make the cellular network energy efficient. Section 3 provides information about SDN and how it will help cellular networks. Section 4 elaborates on the NFV. Section 5 provides the information about C-RAN. Section 6 presents the SDN, NFV, and C-RAN convergence challenges and some possible solutions. Section 7 includes the proposed cellular architecture based on SDN, NFV, and C-RAN. Along with these, it provides information about supporting organizations. Section 8 concludes the paper with some future work.