# Energy Efficiency in Short and Wide-Area IoT Technologies--A Survey
## 4 Classification of Energy Efficiency Methods
### Energy Efficiency in LPWANs
#### 4.2.2 Cellular IoT (cIoT)
Coverage results showed that for SNR distributions overlap between good and bad locations, while RSRP distributions are more representative of different locations. It is also observed that energy consumption increases between the different Extended Coverage Levels (ECLs) a NB-IoT device can operate in, that is, ECL0, ECL1, and ECL2. In particular, the consumption increases while moving to ECL0 to ECL1 and ECL2, since in these latter, NB-IoT devices adopt a larger number of repetitions and maximum transmission power, in order to increase service reliability. Among several insights, it is observed that, in Connected mode, the energy consumption is depending on different factors, including (a) different devices (SARA-N211 module has a higher power consumption than the Quectel-BC95), (b) network operators (they might use different configurations and timers, and thus directly affect device operations and consumption), (c) device configurations (different RAI modes lead to different consumption) and (d) services (an increase in packet size causes an increase in energy consumption). In [157], the first NB-IoT diagnostic tool is presented and referred to as NB-Scope, able to support fine-grained collection of of power consumption and protocol message traces. NB-Scope can enable in-depth diagnoses of the NB-IoT network in terms of energy efficiency and, at the same time, is able to support heterogeneous NB-IoT modules while making minimal system modifications. NB-Scope has three key design aspects:  
* Layered Hardware Architecture, that partitions the hardware system into layers;* Software Abstraction, that introduces Application Program Interfaces (APIs) for letting developers and users access and control different NB-IoT modules;
* Trace Fusion of Power Consumption and Radio Access, that allows to collect and synchronize power consumption traces and radio access logs. In real-time benchmark mode, NB-Scope allows real-time interaction and analysis of the energy performance of NB-IoT modules. In field test mode, it allows the study of energy performance in real-world deployments of NB-IoT modules. The measurements presented in [157] were executed in more that 1200 locations, in two major cities in China and one city in USA; the focus of the analysis is on five NB-IoT applications--outdoor parking, indoor parking, smart door lock, smoke detection and smart water/electricity metering. Measurement results showed that indoor parking nodes consume about 2.7\(x\) more energy to transmit one packet when compared to water metering nodes. Moreover, the energy consumption of the nodes in the US is lower that the energy consumption in China, while using Quectel BC26 and BC66 NB-IoT modules respectively in China and the US. Furthermore, it is also showed that the energy consumption per packet increases after the device is more distant from the base station. The authors also study the impact of the Inactivity Period. It is configured in the base station and used to trigger a transition from Connected to Idle mode, if a device, during this period, does not have data exchange. One way to avoid energy wasting is to completely skip this period, resulting in a faster transit to Idle mode. The optimization proposed in [157] consists in reducing the timer to 5 s, which leads to an earlier release of the connection and to a 10% energy saving. **Data reduction techniques. ** Energy consumption can be also improved by reducing signaling and control transmissions, as well as optimizing the procedures for efficient data exchange. As discussed in [158], the NB-IoT standard introduces two procedures for the transmission of small amounts of data with reduced signaling, that is, Control Plane (CP) cIoT Evolved Packet System (EPS) optimization, and User Plane (UP) cIoT EPS optimization. On the one hand, CP optimization makes it possible to use the control plane of the cellular architecture, for forwarding data packets, after encapsulating them in Non Access Stratum (NAS) signaling messages directed to the MME.