# Intelligent Dynamic Power Control with Cell Range Expansion for Small-Cells in 5G HetNets
## 3 Proposed Intelligent Dynamic Power Control with Cell Range Expansion  
In this section, we propose the intelligent DPC scheme with CRE to improve the performance of SUEs and CUEs for 5G HetNets. Figure 3 shows an example of the CRE operation in the proposed DCA scheme. In general, the RSRP of MUEs decreases gradually as the distance between MBSs and MUEs increases. Thus, it is necessary to offload MUEs with low RSRP from MBSs to SBSs using CRE to resolve the load and increase the performance of the remaining MUEs. The coverage of SBSs is virtually divided into inner and outer zones. Let \(\eta\) denote a given target bias to offload MUEs to SBSs. The area of the inner zone is the original coverage of SBSs, while the area of the outer zone is the boundary with RSRP + bias, i.e., extended coverage of SBSs, for CUEs. The proposed DPC scheme has two steps for CRE and DPC operations. In step 1, in the proposed DPC scheme, the MBS finds some MUEs to offload them to SBSs using CRE. Let \(\xi_{mn}^{MBS}\) and \(\xi_{mst}^{SBS}\) denote the RSRP between MBS \(m\) and MUE \(n\) and between SBS \(s\) of MBS \(m\) and MUE \(n\), respectively. Then, MBS \(m\) offloads MUE \(n\) to SBS \(s\) using CRE if the condition below is satisfied. \[\xi_{mn}^{MBS}<=\xi_{mst}^{SBS}+\eta. \tag{8}\]  
where \(\xi_{mn}^{MBS}=h_{mn}A(\theta)-10*log(12*N_{RB})\) and \(\xi_{mst}^{SBS}=h_{mst}-10*log(12*N_{RB})\). \(N_{RB}\) is the number of resource blocks in the channel bandwidth. Then, SBSs assign subchannels in different SGs for both SUEs and CUEs in the inner and outer zones. That is, SBSs assign subchannels in the same SG of MBSs in each site to their SUEs and CUEs in the inner zone while subchannels in different SGs are to their SUEs and CUEs in the outer zone. For example, in site 1, SBSs assign subchannels in SG A to SUEs and CUEs in the inner zone while subchannels in SG B and C to SUEs and CUEs in the outer zone. Thus, SBSs first calculate the SINRs of SUEs and CUEs using the same subchannels of MBSs and find some SUEs and CUEs that have SINRs less than a given threshold, \(\Gamma_{sth}\) to assign subchannels in other two SGs. In other words, SUEs and CUEs in the outer zone use different subchannels of MBSs to reduce interference between MBSs and SBSs. In step 2, SBSs dynamically allocate the appropriate transmission power for SUEs and CUEs. Figure 4 shows three different power control schemes, i.e., conventional (no power control), reduced equal power (REP) [35] and proposed DPC. In the conventional scheme, MBSs use no CRE and SBSs divide the total transmission power by the number of subchannels to fairly allocate for SUEs. In the REP scheme, SBSs allocate the transmission power statically and dynamically after CRE. That is, SBSs use a fixed transmission power obtained by \(\alpha P_{max}^{SBS}\) for SUEs and CUEs in the inner zone. \(p_{max}^{SBS}\) is the total transmission power of SBSs and \(\alpha\) is a parameter value to control the maximum transmission power for each subchannel. On the other hand, SBSs dynamically allocate the transmission power for subchannels over \(p_{max}^{SBS}\) using the reduced transmission power from subchannels in the outer zone. Finally, in the proposed DPC scheme, SBSs dynamically allocate the appropriate transmission power to SUEs and CUEs in both inner and outer zones after CRE. In order to find appropriate transmission power, SBSs repeat the operation of increasing or decreasing transmission power using \(\Gamma_{th}\) until \(\gamma_{mst}^{k}==\Gamma_{th}\). However, SBSs stop repeating to use the current transmission power for SUEs and CUEs if \(p_{max}^{SBS}==p^{SBS}\) or \(p^{SBS}\) is close to 0. The procedure of the proposed DPC scheme with CRE is described in Algorithm 1. Figure 3: An example of the CRE operation in 5G HetNets. ```
0:\(\forall m\in\mathbf{M},\forall n\in\mathbf{N},\forall t\in\mathbf{T},\forall k\in \mathbf{K}\)
1:// MBSs find some MUEs to offload them to SBSs.