# Energy Consumption Analysis of LPWAN Technologies and Lifetime Estimation for IoT Application
## 4 Approach, LPWAN Communication Technology, and Energy Consumption Analysis
### LPWAN Communication Technology
#### 4.2.1 LoRaWAN  
LoRaWAN is an LPWAN communication technology designed to get long range, low cost, and low power star-of-stars topology [31]. LoRaWAN network constitutes of three basic elements: end-devices, gateway, and then a backhaul to the server as depicted in Figure 6. LoRaWAN provides security by incorporating end-to-end encryption using network and application key to maintain data integrity. End-device represents the sensors or actuators which uses LoRa physical layer to exchange message with the gateway [32]. Lora is a long range technology that uses the ISM band. This communication happens over the radio and further from the gateway to network server happens over IP based protocol stack. LoRa uses Chirp Spread Spectrum for low power and long-range  
Figure 4: Experiment setup for energy measurement using Keysight N6705B DC Power Analyzer. Figure 5: LPWAN modules used in the experiment for the energy analysis (**a**) LoRa/DASH7 module; (**b**) Sigfox module; (**c**) NB-IoT module. transmission. LoRa radio provides an option for different configurations to align the requirement of the application. These parameters are _frequency_ (region-based i.e., 863 MHz to 870 MHz in Europe); the _spreading factor_ (SF i.e., number of chips per symbol between 6 and 12); _coding rate_ (range between 1 to 4, where smaller rate has higher time on air); and the _bandwidth_ (125 kHz, 250 kHz, or 500 kHz). Total derived energy consumption depends upon the combination of these parameters. Considering different set of applications, the LoRaWAN specification [32] has defined three classes of end-devices (A,B,C). These classes have different energy consumption and process of operation. Three modes of device classes and their functionality are illustrated in Figure 7 and explained as below:  
* Class A: This is the most deployed class of end-device where the sensor can initiate uplink transmission as per the need and have to wait for two short downlink messages. This is the baseline class of device and most power efficient as compared to other class of devices. However, it uses a pure Aloha approach which results in considerable power loss. Most of the time this class of device sleeps to reduce energy consumption. * Class B: In this device class, periodic ping slots are initiated by the gateway as downlink messages. This helps in giving schedule slots to the end-device for sending the uplink messages. However, due to periodic beacon from the gateway and its data rate, there is more power loss. End-device periodically receives one of the beacons from network to align internal clock with the network. This beacon based timing reference can be used by the end-device as receive window. * Class C: This category of end-device consumes maximum power with almost continuous open receive windows. They offer lowest latency as it allows downlink transmission at any time. Figure 6: LoRaWAN network architecture. Figure 7: LoRaWAN device class. Mostly, this class of device is best suited for over the air firmware upgrade. Class C types of devices work same as Class A type, but they do not close the receive window until the next transmission. We did the energy measurement for Class A type of devices as they are currently the most deployed device for several applications. We configured the end-device with SF 9. Different SF configuration results into varying on air time [33] and results into distinct energy consumption. The uplink message from a device is captured through the power analyzer and shown in Figure 8. State depicted in the Figure 8 represents different process of operations in a LoRaWAN message transmission.