# An Energy-Efficient Coverage Algorithm for Macrocell--Small Cell Network Systems
## 5 Results and Discussions
### Effects of the Number of SBSs on the Various Performance Aspects  
Figure 18 shows the effect of the number of SBSs on the outage ratios of the proposed algorithm, SBS-Cell-Enlarged, and SBS-Random. The outage ratios of all the three methods are higher than 0.4 when the number of SBSs is small, indicating the paralyzed state of the entire network system regardless of the method applied. This is because the distribution of SBSs is sparse when the traffic volume is fixed, forcing most users to use the MBS for transmission. But when the bandwidth is limited, the MBS cannot provide channels to many users, which results in a growing outage ratio. Figure 18 also shows that, when the number of SBSs increases, the outage ratios of all the three methods decrease. However, the outage ratio of the proposed algorithm decreases faster when compared to the other two methods. More specifically, when the number of SBSs increases to about 160, the outage ratio of the proposed algorithm is close to 0. A continuous decrease in the outage ratio is also observed for SBS-Cell-Enlarged and SBS-Random. The cell enlargement of SBSs, which occurs when these two methods are used, can cover and provide services to users. However, due to the limited number of channels within one SBS, users may be unable to access any channels even though they are covered, and this causes outages. Due to the smaller number of SBSs as compared to SBS-Cell-Enlarged, SBS-Random does not allow some users to use SBSs for transmission. Also, the number of channels in the MBS is limited. Thus, the extent of the decrease in the outage ratio under SBS-Random is small. When the number of SBSs is equal to 190, the outage ratio of the proposed algorithm becomes 0, whereas the outage ratios of SBS-Cell-Enlarged and SBS-Random remain high. When the number of SBSs reaches 310, the outage ratio almost decreases to 0 under SBS-Cell-Enlarged, but remains high under SBS-Random. The effect of the number of SBSs on the total power consumption levels of transceivers at all the BSs for the proposed algorithm, SBS-Cell-Enlarged, and SBS-Random, is shown in Figure 19. When the number of SBSs is 40, the total power consumption levels of the three methods are similar. This is because, with 40 SBSs, distribution is considered sparse in relation to the entire network system being considered. The proposed algorithm only uses the SBSs that are needed, which makes it difficult to use these SBSs (i.e., the 40 SBSs) to provide service to users. Given that most users access services through the MBS, the total power consumption level of the MBS increases to its upper limit (i.e., 150 W). Moreover, it is known that the total power dissipated by each SBS is 5 W. Therefore, the total power consumption level of the proposed algorithm is only slightly lower than that of SBS-Cell-Enlarged. The difference in total power consumption is even smaller between SBS-Random and the proposed algorithm, indicating that SBS-Random and the proposed algorithm both use a similar number of SBSs. Figure 18: Effect of the number of SBSs on the outage ratios for the proposed algorithm, SBS-Cell-Enlarged, and SBS-Random. In addition, Figure 19 shows that, as the number of SBSs increases, the total power consumption levels of the three methods increase as well. Due to the smaller number of available SBSs, SBS-Random shows the lowest power consumption level among the three methods. Moreover, despite the same number of available SBSs for SBS-Cell-Enlarged and the proposed algorithm, the proposed algorithm can effectively control the switching and scaling of each SBS depending on user location and manage the power of each SBS, therefore ensuring the maximum utility of the SBSs being used; SBSs that are not needed are not used, which prevents unnecessary power dissipation. Therefore, as shown by the results, as the number of available SBSs gradually increases, so does the gap between the proposed algorithm and SBS-Cell-Enlarged. That is to say, the proposed algorithm saves significantly more power than SBS-Cell-Enlarged.