# Cell-Free Massive MIMO Power Consumption with Serial Front-Hauls
## 4 Power Consumption Comparison
### Considering Conventional APs  
In the first study, traditional values of power consumption in APs are considered. Specifically, in the computation of (3), the values for AP fixed power (\(P_{m}^{\text{AP, fix}}\)), AP fixed power RF chain (\(P_{m}^{\text{AP, chain}}\)), and AP maximum transmit power (\(P_{m}^{\text{PR}}\)) are assumed to be 8 W, 0.2 W, and 0.1 W respectively, as in [12].  
Figure 3 shows the traffic-dependent front-haul power, the fixed front-haul power, the total front-haul power, and the total power versus the number of used serial links (\(N\)) using the modified power consumption model. In the graph, the power consumption values associated with fully serial front-haul are allocated at the leftmost point of the curves when \(N=1\). At the same time, values associated with fully dedicated front-haul configurations are placed at the rightmost point. Intermediate values correspond to hybrid serial/dedicated front-haul configurations. As can be inferred, the rightmost point is equivalent to applying the original power consumption model for the deployment of 100 APs. In other words, the rightmost point should be taken as a reference for comparison.  
As can be noticed, there is an increasing power consumption trend with respect to using more links to connect the same number of APs. The traffic-dependent and fixed front-haul powers represent 63.24% and 36.76% of the total front-haul power, respectively,  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Value** \\ \hline Power amplifier efficiency (\(\alpha_{m}^{\text{AP}}\)) & 0.39 \\ AP maximum transmit power (\(P_{m}^{\text{tx}}\)) & 0.1 W \\ Number of RF chains (\(L_{\Lambda}\)) & 1 \\ Coherence interval length (\(\tau_{c}\)) & 200 samples \\ Training phase length (\(\tau_{\text{p}}\)) & 20 samples \\ Spectral efficiency in downlink (\(S_{\text{dl}}\)) & 86 Mbits/s/Hz \\ Bandwidth (\(B\)) & 20 MHz \\ Traffic-dependent power consumption & 0.25 W/Gbps \\ coefficient (\(\chi_{m}^{\text{FH}},\chi_{n}^{\text{FH}}\)) & \\ Fixed front-haul power per link & 5 W \\ in conventional systems (\(P_{m}^{\text{FH, fix}}\)) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Power consumption modeling parameters [9; 12; 25].  
Figure 3: Power consumption versus the number of links used.  
independently of the number of front-haul links used. However, let us compare the power consumed in front-haul with respect to total power. We see that the former has a variable impact on the latter, depending on how serialized the deployment is. This impact is quantitatively shown in Figure 4.  
The results represented in these figures can be directly derived from the presented equations. Their main purpose is to illustrate, considering traditional power consumption values in APs, that power consumption is overestimated when the traditional power consumption model is applied to serial front-haul deployments. As shown in the graph, the percentage of total power consumed in front-haul goes from 1.59% for fully serial front-haul to 61.73% for fully dedicated front-haul. Using the original model would lead to overestimating the impact of front-haul power on the total power if serial or hybrid serial/dedicated links were used. In cases similar to this one, our adaptations are vital for more accurate results.