# Intelligent Dynamic Power Control with Cell Range Expansion for Small-Cells in 5G HetNets
## 1 Introduction  
Recently, the fifth generation (5G) wireless cellular technology has been developed to increase the speed and reliability of the rapidly increasing mobile data traffic from various smart devices such as smartphones, tablet PCs, and Internet of Things (IoT) devices [1; 2; 3; 4; 5]. In addition, 5G networks adopt a heterogeneous network (HetNet) architecture where different types of small-cells, i.e., microcells, picocells, and femtocells are overlapped with the conventional macrocells [6; 7; 8]. The small cell is a cost-effective radio base station with low transmission power to improve the system capacity and extend the coverage. 5G networks also consider an ultra-dense network (UDN) architecture where a large number of small cells with a short coverage range are densely deployed on the coverage of macrocells [9; 10]. However, in HetNets, macro base stations (MBSs) serve most smart devices in their coverage since the transmission power of MBSs is higher than that of small-cell base stations (SBSs). It means that SBSs have enough subchannels to assign each small-cell user equipment (SUE) but MBSs lack subchannels to assign for each MUE when SBSs reuse the limited frequency bands of MBSs [11]. Thus, in order to solve the load balancing problem, the third generation partnership project (3 GPP) standardized cell range expansion (CRE) technology to extend the coverage of SBSs by adding a bias to the reference signal receive power (RSRP) and then a fraction of MUEs located close to SBSs are offloaded to SBSs, i.e., some MUEs become CRE user equipments (CUEs) [12; 13; 14; 15; 16]. Further, in HetNets, MBSs and SBSs have strong interference with each other [17; 18; 19; 20; 21; 22; 23; 24; 25; 26] and CUEs have more serious interference from both MBSs and neighboring SBSs than SUEs. Therefore, it is necessary to study interference management schemes with consideration of CRE for 5G HetNets. Research has investigated interference management schemes using static and dynamic power control for MBSs and SBSs in HetNets with time division duplex (TDD) and frequency division duplex (FDD) [27; 28; 29; 30; 31; 32; 33; 34; 35; 36]. In [27; 28; 29; 30; 31], authors proposed power control schemes using almost blank subframe (ABS) to dynamically or statically configure frames with empty or low transmission power to reduce interference to CUEs. In [32], authors proposed a static power control scheme that allocates the same transmission power for all subchannels of SBSs according to the CRE bias and thus it is difficult to allocate the appropriate transmission power to both CUEs and SUEs even though the power control algorithm is simple. In [33], the authors proposed a dynamic power control (DPC) scheme to dynamically allocate different transmission power of every subchannel for CUEs only and thus it has a system performance higher than other schemes with static power control. In [34; 35], authors proposed DPC schemes in which MBSs assign different groups of subchannels to MUEs and CUEs and allocate the appropriate transmission power for CUEs. In [36], authors proposed DPC schemes in which MBSs and SBSs assign the same group of subchannels to MUEs and CUEs and then SBSs allocate the appropriate transmission power for CUEs. Most of the previous work only considered the performance of CUEs using the power control of either MBSs or SBSs after CRE but did not consider the performance of SUEs served by the SBSs. Table 1 summarizes the methods used in existing studies. In [37; 38; 39], as a broader concept than CRE, authors introduced user association schemes in which MUEs or SUEs establish connections to MBSs and SBSs for various purposes, i.e., spectrum efficiency, energy efficiency, quality of service (QoS) provision and fairness, using RSSI, power control, and bias. In this paper, we propose a novel intelligent DPC scheme with CRE to improve the performance of both SUEs and CUEs in the downlink (DL) 5G HetNets.