# Energy-Efficient On-Off Power Control of Femto-Cell Base Stations for Cooperative Cellular Networks
## 1 Introduction
### On-Off Power Control Schemes in MCS  
The most straightforward way to improve the EE of MCSs is to simply turn off base stations (BSs) whose operation is unnecessary in view of overall network performance [1; 13; 14; 15; 16; 17; 18; 19; 20]. Through the shutdown of BSs, electricity consumption can be reduced significantly because more than half of total electricity consumption in MCSs is caused by BSs. Consequently, on-off power control schemes for BS have been extensively studied in previous literature, especially in the context of GCNs [1; 3; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. The on-off power control schemes for BSs can be divided into two categories: which are statistical scheme and adaptive scheme. In the statistical scheme, the network operators manually decide which BSs to shutdown [1]. For example, BSs which are located in rural areas can be turned off during the nighttime because the amount of traffic load is likely to be low, such that users can be served without experiencing the degradation of quality of services (QoS) by a fewer number of BSs [1]. Generally, the statistical scheme is applied to macro BS (MBS), whose coverage is wide. On the other hand, in an adaptive scheme, BSs are flexibly turned off based on the real-time information, e.g., incurred traffic load on each BS [13; 14; 15; 19]. For example, certain BSs can be turned off for the period when the traffic load incurred at those BSs is sufficiently low [13; 14]. Unlike the statistical schemes, in the adaptive scheme, switched off BSs can also be turned on in real-time according to the environmental changes, e.g., sudden increase of traffic load. In general, the adaptive on-off power control scheme is applied to femto BSs (FBSs) whose transmission range is short [23; 24; 25; 26]. Note that due to its possibility to improve the performance of MCS, the FBS has been studied extensively in recent days, especially in the view of resource allocation [24; 25; 26]. In this paper, we focus on the adaptive on-off power control scheme for FBSs. Due to its importance, the adaptive on-off power control scheme has recently been the subject of extensive investigation [15; 16; 17; 18; 19; 20; 21; 22]. In [21], the on-off state of BS which operates based on the renewable generation, e.g., wind power, was optimized where the main objective is to minimize the on-grid power consumption. The coverage probability and EE of MBS were analyzed using the stochastic geometry in [15], which reveals that the strategic sleeping where MBS is turned off is based on the amount of traffic load, gives better performance compared with the random sleeping of MBS. The authors of [16; 17] considered the distance between the FBS and mobile station (MS) in the determination of which FBS to shut down, i.e., the operation of FBS which is far from MSs, is halted. Furthermore, in [18], the adaptive FBS switching-off scheme was considered for the indoor FBS in which the operation of redundant FBS is stopped by examining the achievable throughput. In addition, the switching-off of FBS was determined based on the results of subcarrier allocation such that FBS with a small number of allocated subcarriers, i.e., low traffic FBS, is turned off in [19]. Finally, the authors of [6] considered the on-off power control scheme for FBS in order to improve EE, where the FBS is turned on only when active MS is nearby. In most conventional on-off power control schemes for FBSs, the traffic load incurred on each FBS is generally used to determine which FBSs are to be halted [15; 18; 19]. Although the use of the incurred traffic load is reasonable in most of cases, it can be inappropriate when the cooperative transmission is used, in which multiple FBSs cooperate in data transmission to improve the performance, e.g., CoMP [27; 28; 29; 30; 31; 32].