## 1 Introduction
In [19], the authors propose distributed activation/deactivation schemes, where a small cell BS is turned off if there is no serving UE and periodically awakes to detect the activity of UEs. In device-assisted-networking for cellular greening (DANCE) schemes, small cell BSs are activated or deactivated for varying traffic loads to optimize the number of activated/deactivated small cell BSs [20]. In [21], the authors proposed a joint BS on/off switching and user association algorithm for energy efficiency maximization. In [22], the on/off states of small cell BSs are controlled based on two uniform and non-uniform distributions of UEs. In [23; 24; 25], the authors analyze the energy efficiency of BSs in heterogeneous networks shared by multi-operators. In [23], the authors use distributed game theory to save power, where UEs of any mobile network operator are served by another mobile network operator and BSs of these UEs are turned off. In [24], the authors propose a cooperative BS switching off scheme, where BSs are turned off when its traffic load is low and UEs served by them can be covered by BSs operated by other mobile network operators. In [25], the authors propose pricing decision game and user association game, based on the relationship between roaming cost and user association. To further reduce the energy consumption of BSs, a new concept of control split plane and user plane or the separation of data and control was proposed [26; 27]. In heterogeneous network architecture with separated data and control, as shown in Figure 3, a macro cell BS (MBS) managesthe control signal and data traffic. On the other hand, small cell BS (SBS) manages only data traffic, since the control signal is provided by the MBS. The energy of SBSs can be saved significantly if there is little traffic within the coverage of SBSs, since they do not have to be awake to support the control signal, which is supported by a macro cell always and thus can be put into an inactive state to save power. A heterogeneous network can accommodate ever-increasing data traffic and can also reduce the energy consumption of BSs [28]. The performance of heterogeneous networks depends on the layout of SBSs when the density of data traffic is high or transmission power of a BS is low. Also, SBSs should awake in order to accommodate UEs from either macro cell or deactivated small cell and thus, energy consumption may increase [28; 29]. In cloud cooperated heterogeneous network architecture, an SBS has high transmission power in a direction towards a highly concentrated traffic area and thus, data transmission efficiency is improved [30]. Also, the cloud-radio access network (C-RAN) reduces unnecessary resource usage. In [31], technical challenges of BS on/off switching schemes are discussed in 5G systems, and the state of the art on BS on/off switching, technical challenges, and open problems are presented. In [32], dynamic traffic BS switching on/off scheme was proposed, in separated network architecture with coverage BS and traffic BSs. In [32], random sleeping scheme is considered. In [33], the authors proposed random and repulsive schemes in a separated network architecture. In random scheme, every BS is switched off with probability p. On the other hand, in repulsive scheme, small cell BSs with a smaller distance than R from a macro cell BS is switched off. Works on the optimization models and solution algorithms for the design and management of 5G networks have been carried out actively recently [34; 35; 36; 37; 38]. In [34], the authors design reusable functional block (RFB)-based 5G network architecture and consider the optimization problem of dynamically managing the RFBs by either maximizing user throughput or minimizing the number of used nodes subject to RFBs placement, 5G node capacity, user coverage and user data constraints.