Apr 2, 2023
LoRaWAN device classes – Understanding Network and Security for Far-Edge Computing
One of the primary design parameters for LoRaWAN devices is low power consumption. LoRaWAN devices don’t leverage any special battery technology. Some of them use simple AAA or AA batteries you can purchase at the supermarket. Rather, it’s because they try to spend as much time as possible doing as little as possible.
LoRaWAN device batteries are measured in terms of milliamp-hours (mAh), just the same as a power bank you might use to recharge your mobile phone. In the LoRaWAN specification, end devices/nodes can operate in three different modes: Class A, Class B, and Class C.
All end devices support Class A [14]. These spend most of their time in sleep mode. Because LoRaWAN is not a scheduled protocol, end devices can communicate any time there is a change in a sensor reading or when a local timer on the device goes off:
Figure 3.37 – Class A LoRaWAN temperature and humidity sensor
These devices can wake up and talk to the server at any random moment. After the device sends an uplink, it listens for a message from the network one and two seconds after the uplink (receive windows) before going back to sleep. Class A is the most energy efficient and results in the longest battery life. A 5,000mAh power bank for your phone could keep the average class A device running for 30 years 17.
17 Do not attempt this – it is likely such a power bank would self-discharge long before 30 years..
Examples of Class A devices include LoRaWAN-enabled pushbuttons that transmit alarm information in case of an emergency. There are such buttons on the market with a 600mAh capacity that can sustain 70,000 pushes of the button (and associated message transmission).
Class B devices are designed for use in applications where the device needs to transmit data more frequently, but still has relatively low power requirements. They are allowed to transmit data at regular intervals, and they listen for a response from the network after each transmission. This allows them to transmit data more frequently than Class A devices, and the part where they listen for a response ensures more reliability, but they still have a low power consumption:
Figure 3.38 – Class B LoRaWAN barometric pressure sensor
Devices in this class might include a smart meter that needs to reliably collect the kilowatt-hour utilization of a power circuit at regular intervals or an environmental sensor that needs to be sure it collects a windspeed sample at prescribed intervals for the dataset to be valid.
Class C devices are used in applications where the device needs to transmit data continuously. They are allowed to transmit data at any time and are always listening for a response from the network. They never go to sleep. This makes them the least power-efficient of the three classes:
Figure 3.39 – Class C LoRaWAN manhole sensor
An example might be a sensor in a manufacturing plant that ensures something dangerous remains within a specific temperature range. Another might be a device that’s used for real-time asset tracking, where we want to be actively alerted the moment something leaves the area it is supposed to be in.
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