# Power Efficient Random Access for Massive NB-IoT Connectivity
## 5 Performance Evaluations
Thus, in Figure 5a the average power consumption for the proposed PE-RAP is almost around 40% less than the existing RAP for a different number of configured repetitions in CE0. In Figure 5b, even when the probability of selection of CE0 is low, power saving is substantial. This is because in the proposed PE-RAP the device can quickly re-select a higher CE level while avoiding the sequential stepping up resulting in early success of RAP. On the other hand, in the existing RAP, the power levels are ramped sequentially until the device is able to succeed. Figure 6 shows the average power consumption for an existing RAP and a proposed PE-RAP for a varying number of configured repetitions in level CE1. Here also we consider three cases: (i) Probability of selection of CE1 is high such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.3,\ 0.5,\ 0.2\}\); (ii) CE1 manifests lower probability such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.3,\ 0.2,\ 0.5\}\); (iii) probability of selection of CE1 is average such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.33,\ 0.33,\ 0.34\}\). It can be observed from Figure 6 that the power consumption for the proposed PE-RAP is generally lower (almost half) than the existing RAP for different configurations of repetition values. Moreover, the proposed PE-RAP performs better for the higher configuration of repetition per attempt. Figure 5: Average power consumption over varying repetitions per attempt in CE0 (CE = coverage enhancement) for proposed PE-RAP and existing NB-IoT RAP. (**a**) Low value of \(q_{0}\); (**b**) High value of \(q_{0}\); (**c**) Average value of \(q_{0}\). Figure 7 shows the power consumption with the varying number of repetitions for level CE2. The number of repetitions in CE0 and CE1 are kept fixed (CE0 repetition 2 and CE1 repetition 4). Similar cases as in Figures 5 and 6 are considered, that is: (i) Probability of selection of CE2 is high such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.2,\ 0.3,\ 0.5\}\); (ii) CE2 manifests lower probability such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.5,\ 0.3,\ 0.2\}\); (iii) probability of selection of CE2 is average such that \(\{q_{0},\ q_{1},\ q_{2}\}=\{0.33,\ 0.33,\ 0.34\}\). Initially the power consumed by the device is very low due to a lower number of repetitions. Since number of repetitions and power levels are high for CE2, the high channel selection probability manifests high power consumption (Figure 7a). Lower selection probability of \(q_{2}\) means that the device selects CE0 and CE1 more often and thus the power consumption in Figure 7b is less than Figure 7a. The proposed PE-RAP performs better even in the highest CE level since the device has the flexibility to move from a higher CE level to a lower CE level for an RAP reattempt unlike the existing RAP resulting in the lower average power consumption. A few common observations from Figures 5-7: (i) As expected the power consumption increases as the number of repetitions increases for both the existing RAP and the proposed PE-RAP. (ii) As the number of repetitions increases the gap between the existing RAP and the PE-RAP increases. This is crucial since the fundamentals of the NB-IoT design are rooted in repetitions and the proposed PE-RAP manifests more power saving as the number of repetitions increases. Figure 6: Average power consumption over varying repetitions per attempt in CE1 for proposed PE-RAP and existing NB-IoT RAP. (**a**) Low value of \(q_{1}\); (**b**) High value of \(q_{1}\); (**c**) Average value of \(q_{1}\).