We all know that an important feature of Low Power Wide Area Network (LPWAN) is its ultra-low power consumption. Most LPWAN technologies claim they can sustain a battery life of more than 10 years – making them the preferred connection type for battery-powered IoT sensor networks.
How does LPWAN achieve such long battery life?
star topology
Due to long physical distances, LPWAN can be deployed in a star topology while still effectively covering a large geographical area. As mentioned in the previous article, a single-hop star topology saves orders of magnitude more energy than a mesh topology for short-range wireless networks.
Asynchronous communication
Most low-power wide-area networks operating in unlicensed spectrum use lightweight media access control (MAC) protocols for asynchronous communications. For example, the commonly used ALOHA random access protocol. In an ALOHA system, nodes access the channel and send messages at any time without signaling to the base station to request permission or sensing the current transmissions of other nodes for coordination.
The main advantage of this random access protocol is that it does not require complex control overhead. This greatly reduces power consumption and simplifies transceiver design. The downside is that asynchronous communication can significantly hinder scalability. This is because data transmission between nodes is uncoordinated, increasing the chance of packet collisions and data loss.
sleep mode
LPWAN end nodes are programmed to be active only when they need to transmit messages. Outside of this time, the transceiver shuts down and enters deep sleep mode, consuming very little power. Assuming that a node only needs to send few messages a day (uplink), the power consumption is very low.
In two-way communication, the end node must be awake to listen for downlink messages sent from the base station. A listening schedule can then be set up so that nodes only wake up at predefined times to receive downlink messages. Alternatively, nodes and base stations can be coordinated so that downlink messages are sent shortly after the uplink arrives. This helps reduce the time a node needs to be “on” to receive data.
Do different LPWAN technologies have the same battery life?
The answer is definitely no. In fact, power consumption and resulting battery life can vary significantly not only between different LPWAN technologies, but even between different deployment models of the same technology. Let’s look at the two main factors below.
First, “broadcast” radio time—the primary indicator of power consumption during transmission—varies significantly between different LPWAN systems. To be clear, transmission is the most energy-intensive activity of an end node. Broadcast time is the total time it takes for a message to propagate from a node to the base station. Under other conditions being equal, the shorter the broadcast time, the lower the power consumption. If the same message is sent 3 times for redundancy, its total broadcast time and power consumption will be tripled.
Secondly, not all LPWANs employ a combination of all 3 above methods. For example, to improve quality of service, cellular LPWANs employ synchronization protocols whereby end nodes must signal to the base station to request permission to send messages (i.e., a handshake). In addition to imposing higher energy consumption requirements due to excessive overhead, this process also makes the power consumption and overall battery life of each transmission unpredictable, because it is difficult to predict how many handshakes need to be performed before the message is allowed to be sent. .
Endorsed by ETSI, Telegram Segmentation introduces a unique transmission method that minimizes broadcast time while addressing the trade-off between quality of service and power consumption.
Finally, 10 or even 20 years is actually a very long time when it comes to battery life, but there are a number of factors that need to be fully considered in order to achieve this. Apart from general conditions such as message frequency and the type of battery used (preferably one with a low self-discharge rate), at the end of the day, choosing the right LPWAN technology does matter. nbiot module
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