# An Energy-Efficient Coverage Algorithm for Macrocell--Small Cell Network Systems
## 5 Results and Discussions
### Effects of the Number of Users on the Various Performance Aspects  
The effect of the number of users on the outage ratios for the proposed algorithm, SBS-Cell-Enlarged, and SBS-Random, is shown in Figure 15. The outage ratios of all the three methods are equal to 0 when the traffic volume is low. This is due to the fact that each of them has a sufficient number of channels for providing service to users. As the traffic volume increases, the outage ratios of the three methods increase as well. Compared to the other two methods, the proposed algorithm is better able to delay or slow down the increase of the outage ratio. This is due to the fact that it can effectively resize or shut down SBSs depending on the traffic volume. Figure 15: Effect of the number of users on the outage ratios for the proposed algorithm, SBS-Cell-Enlarged, and SBS-Random. At the traffic volume of 390, the proposed algorithm has a relatively small outage ratio (about 0.4%). However, for SBS-Cell-Enlarged, the outage ratio is approximately 20%. This increase occurs since the cells of all SBSs are enlarged, and are therefore more likely to cover more users, but considering that the number of channels in a single SBS is limited, some users within coverage areas may not be able to access channels. As for SBS-Random, its outage ratio is significantly higher at approximately 40%. Since there are fewer available SBSs in the system, some users are prevented from using SBSs for transmission. Moreover, the number of channels that the MBS has is also limited. Thus, a higher outage ratio is observed. Next, when the traffic volume increases to 570, the proposed algorithm still exhibits the best performance among all three methods, due to its more effective resource allocation design. However, the outage ratio for SBS-Random is close to 52%, which means that the network is almost paralyzed. This is due to the fact that the SBSs and the MBS do not have enough channels to provide services. In addition, as expected, SBS-Cell-Enlarged also performs better than SBS-Random, due to the higher number of SBSs that the former allows. The effect of the number of users 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 16. Because it only activates the SBSs necessary for transmission, the proposed algorithm produces a lower total power consumption level than the other two methods. In particular, when the traffic volume is low (e.g., when the number of users is equal to 30), the proposed algorithm can reduce the power consumption by up to about 78% and 58%, as compared with the consumption levels for SBS-Cell-Enlarged and SBS-Random, respectively. Moreover, the results indicate that as the traffic volume increases, the curves for SBS-Cell-Enlarged and SBS-Random remain almost flat. This is due to the fact that all SBSs are constantly in the high power output state when using these two methods, and that only the MBS's transmission power will change, and its level is lower than the sum of the power levels in other parts; thus, a smaller degree of variation for each of the two curves is observed. Furthermore, when the traffic volume increases to about 150, the power consumption curves of the proposed algorithm and SBS-Random intersect, indicating that at this volume, the proposed algorithm is consuming as much power as SBS-Random. On the other hand, for traffic volumes lower than 150, the power consumption of SBS-Random is higher than that of the proposed algorithm. At the same time, according to our simulations, for traffic volumes lower than 150, the outage ratios of both the proposed algorithm and SBS-Random are equal to 0. Taken together, these findings mean that SBS-Random is wasting power relative to the proposed algorithm for traffic volumes lower than 150. For similar reasons, SBS-Cell-Enlarged causes excessive energy consumption at low traffic volumes.