# Accounting for Energy Cost When Designing Energy-Efficient Wireless Access Networks
## 3 Results and Discussion
### Results: Strategy 3 Microcell BSs Networks  
Figure 15 shows the results for the strategy _microcell BSs networks_. The introduction of the configurations composed by microcell base stations only provides some benefits in terms of cost reduction (Figure 14(a)): their usage provides a total cost reduction of more than 31%, with respect to the reference scenario (Table 2). The difference in terms of necessary energy cost between the case with 187 microcell base stations and the one with only 126 microcell base stations is negligible (less than 1%). Consequently, the total power consumption is similar, as well (Figure 14(b)), to the number of active base stations (Figure 14(c)). In the reference scenario, the number of active base stations is lower, but the presence of macrocell base stations contributes significantly to the total power consumption. The average user coverage is larger  
Figure 14: Take action according to the energy price: effects of threshold variation on the total energy cost (**a**) and the user coverage (**b**). Figure 15: Results obtained with microcell BS configurations. when the base stations are spaced by 40 m (187 microcell base stations usage): 99.81% in this case, while approximately 97% in the reference scenario and when the distance between the base stations is 50 m. This is because in the configuration with 187 microcell base stations, more redundancy is introduced, and therefore, a higher number of users can be served. When the deactivation of base stations is possible, in case of an energy shortage, the increase of the minimum percentage of covered users implies the increase of the total outgo. This is caused by the higher quantity of required power (Figure 15b) due to the higher number of active base stations (Figure 15c) necessary to provide the required user coverage. In fact, it is possible to achieve more than a 38% reduction of total outgo, when at least 95% of users are always covered, and up to 47.32% when the minimum user coverage required is 90%, in the scenario with microcell base stations spaced by 40 m. In case 126 microcell base stations are used, more than a 34% and an approximately 43% cost reduction are obtained, when the minimum user coverage is 95% and 90%, respectively. The user coverage is reduced, but not compromised, since it is always larger than 92.5% (Figure 15d). Only Microcell BSs: Deactivation of Some BSs (Time Window Effects)  
Simulations are performed changing the time window value in _Only Microcell BSs: Deactivation of some BSs_. This varies from 1-10 h. Figure 16 shows that the total outgo decreases for increasing durations of this parameter, at the expense of the user coverage reduction (Figure 17). This is due to the fact that with the growth of the time window, microcell base stations are deactivated more in advance so that more energy is saved. Consequently, a smaller quantity of electricity needs to be bought, but a lower percentage of users can be served. With the time window equal to four, when 90% of users are always served, the total outgo is reduced by 42.01% (50-m BS spacing), with respect to the reference scenario, and by 45.88% in the case  
Figure 16: _Only Microcell BSs: Deactivation of some BSs_. Effects of the time window on the total outgo. Figure 17: _Only Microcell BSs: Deactivation of some BSs_. Effects of the time window on the user coverage. of 40 m between two base stations. This causes a user coverage drop of 4.22% and 3.2%, respectively. Nevertheless, the user coverage is acceptable since it is always greater than 92.92%. In case the percentage of served customers needs to be at least 95%, then more than 38.14% of the total outgo is saved, with 187 microcell base stations (40 m spacing) and more than 34% with 126 microcell base stations (50-m spacing), decreasing the coverage of the users compared to the reference scenario by less than 1%.