# Cell-Free Massive MIMO Power Consumption with Serial Front-Hauls
## 5 Conclusions  
This paper has highlighted that traditional power consumption models for distributed systems with dedicated front-haul links are not applicable when serial links are used, as they tend to overestimate power consumption. This overestimation occurs because, in the case of serial links, the front-haul power consumption does not increase linearly with the number of APs. Such inaccuracies can lead to erroneous energy efficiency analyses in massive MIMO systems and affect deployment design decisions. To address this issue, several adaptations have been proposed to ensure that the power consumption model is valid for serial front-hauls, hybrid serial/dedicated front-hauls, and fully dedicated front-hauls.  
This paper has highlighted that traditional power consumption models for distributed systems with dedicated links in the front-haul are not valid when serial links are considered because the consumption would be overestimated, since the front-haul power consumption does not increase linearly with the number of APs in this case. This overestimation could lead to erroneous energy efficiency analysis in massive MIMO systems and affect the final decisions on deployment designs. To overcome this inconvenience, some adaptations have been proposed to make the power consumption model valid for serial front-hauls, hybrid serial/dedicated front-hauls, and fully dedicated front-hauls.  
Figure 5: Total power consumption comparison versus the number of links used.  
Figure 6: Percentage of total power consumed in front-haul considering next generation APs versus the number of links used.  
The role played by the traffic-dependent and fixed front-haul power consumption with respect to the total front-haul power and the total power consumed by the system has been evaluated. According to the results, fixed front-haul power represents more than three-fifths of the total front-haul power. Additionally, if fully serial and fully dedicated front-haults are compared, the power consumed in front-haul with respect to the total power can vary considerably from one deployment to another. Finally, when considering next-generation APs and the power savings involved, the power consumed in front-haul becomes an even more significant part of the total power. These facts reinforce the need to use the power consumption model with the proposed modifications to make accurate power consumption estimations.  
In future works, the modeling of the fixed front-haul power as a function of the front-haul technology should be studied. To carry out this study, some manufacturing data will be required. In addition, sequential uplink processing implications over uplink power consumption should be analyzed.  
Conceptualization, D.P.-A., D.M.-S. and J.F.M.; methodology, D.P.-A., D.M.-S. and J.F.M.; software, D.P.-A. and D.M.-S.; validation, D.P.-A., [PERSON]-S. and J.F.M.; formal analysis, D.P.-A. and [PERSON]-S.; investigation, D.P.-A. and [PERSON]-S.; resources, D.P.-A., S.I, [PERSON]-S. and J.F.M.; data curation, D.P.-A. and [PERSON]-S.; writing--original draft preparation, D.P.-A. and D.M.-S.; writing--review and editing, D.P.-A., S.I, [PERSON]-S. and J.F.M.; visualization, D.P.-A., S.I, [PERSON]-S. and J.F.M.; supervision, [PERSON]-[PERSON] and J.F.M.; project administration, J.F.M.; funding acquisition, J.F.M. All authors have read and agreed to the published version of the manuscript.  
The work of [PERSON] was supported by the H2020 Marie Curie Program, with Project Grant No. 766231 WAVECOMBE-ITN-2017. The APC was funded by UPV research funds.  
Data sharing is not applicable.  
The authors declare no conflicts of interest.