# Narrowband Internet of Things (NB-IoT):
## 3 Narrowband-IoT Protocol Stack
### Media Access Control Layer
#### 3.2.4 Power and Energy Management  
The NB-IoT reduced complexity is intended to reduce the power consumption in different modes. PSM and eDRX are the implemented features dedicated to foster the long-lasting battery life.  
In [79], the authors presented the NB-IoT power measurement. Their measurements were set in such a way that NB-IoT transmission consumes 716 mW when at 23 dBm with a power efficiency of 37%. DL control and data signals consume 213 mW, idle-mode-eDRx and PSM consumes 21 mW and 13 mW, respectively. In general, according to their empirical measurements, it is shown that the power consumption is 10% lower than the 3 GPP estimates. During measurements, parameters such as time domain repetition, I-eDRx, and PSM were taken into consideration. To characterize each component in the proposed model, several test cases such as Tx power, UL, and DL data rates, I-eDRx, and PSM were used and all parameters except one at a time were fixed. Their results showed that the NB-IoT devices power consumption is independent of the subcarrier spacing. However, the total ON time of the devices is in many cases defining the overall battery life. As their remark, the data rates do not directly impact the power consumption, but it has a major direct impact because it defines the overall device ON time. If the transmitting interval is 1 h, the device achieves only 2.5 weeks of battery life. Increasing the duration to 24 h, the lifetime of the device increases to 12.8 years in PSM.  
In [80], the authors proposed a prediction-based energy-saving mechanism to reduce energy consumption by decreasing the number of scheduling request procedures. Their proposed scheme showed that it could reduce the NB-IoT active time from 5% to 16% for the medium and bad channel quality and achieve from 10% to 34% battery saving in different scenarios as compared to 3 GPP consumption simulation specifications in [43].  
In [81], the authors developed a semi-Markov chain with power saving mode, idle mode, random access, and transmission mode to study the energy requirement and delay performance for NB-IoT. It is noted that for massive synchronous connections, extra power is drained in random access and transmission states due to collisions. The paper further proposes an energy optimization model based on a priori method that takes into consideration the PSM duration as well as power consumption. The results demonstrate that for optimal energy and delay requirement, it is important to set the higher RACH transmission number to accommodate more delay on the UE. However, their optimization model did not consider the power consumption during the transition of different states, because when the UE is required to perform several sessions per day, it might go through several transitions that have a significant effect on power consumption. Furthermore, the mode does not include the small data transmission scheme during RRC connection as proposed in the updated standards. However, with the introduction of the new power class in NB-IoT Release 14, there is a need for practical experiments to evaluate the new coverage classes. With lower transmit power, the SNR detected at the base station becomes lower hence the device will need to perform more repetitions to enhance coverage.