Research professor at the University of Poitiers, Frédéric Launay has studied the energy consumption of IoT terminals in 4G and 5G and delivers several lessons.
JDN. The autonomy of connected objects is an essential subject for users, especially in cellular, a means of communication that consumes more energy. How to ensure that the battery lasts as long as possible?
Frederic Launay. Some players claim that the lifespan of their devices is ten years. In reality, it is impossible to guarantee autonomy, because it is conditioned by several parameters, depending on the use and implementation of the object:
- Latency: we must ask ourselves how urgent the data processing is. For example, if a forklift detects a man in its path, it cannot afford to wait two seconds before braking.
- The importance of information: is it serious if you lose a packet of data? If this is the case, it must be made reliable by retransmitting it or by having an acknowledgment. For example, the connected bins transmit their fill level every hour. If a packet is lost at a time, it doesn’t matter. On the other hand, in the case of a fire, the alarm must sound as soon as possible, an acknowledgment of the sending of data is necessary in this case.
- The range: if the transmitter is nearby, it will consume less than if it is 20 kilometers away. By doubling the distance, the consumption is multiplied at least by four. A solution to remedy this: the creation of mesh networks.
- The size of the data packet: the larger it is, the longer the transmission time will be, and therefore more energy consuming. It is therefore necessary to ask whether to transmit the whole packet or only a variation. For a temperature, is it necessary to transmit the temperature each time or only a temperature difference when it occurs? The use of theedge computing thus turns out to be relevant.
To estimate the autonomy of its object, it is therefore essential to study the uses that one wishes on a case-by-case basis.
Are there any mechanisms affecting the autonomy of connected objects?
“To estimate the autonomy of its object, it is essential to study the uses on a case-by-case basis”
If a device has to be interrogated from time to time, this assumes that it remains switched on to receive an information request message. To save energy, the simplest way is to use an object which only has to transmit information at fixed times. In this case, it suffices to configure it so that it sends its data at such interval of time. If it has to transmit every hour, there is no point in it being on in the meantime. This mechanism keeping the device in an unconnected state until it wakes up is called PSM, the power saving mode.
Another mechanism, wake-up radio (WuR), consists in adding to the terminal a radio receiver consuming little power and capable of recovering an interaction signal, when the terminal is to be contacted. Thus, instead of having an antenna permanently activated, only a low-power module works to intercept the call and wake up the object.
You have studied cell phones, do frequencies play a role in autonomy?
“If the connected object transmits its data every minute, instead of every ten minutes, there will be a factor of ten in terms of autonomy”
Lower frequencies have better ranges and better penetration. Thus, it is better to choose them. Transmissions on a free radio channel, such as on a network LoRaWAN, can suffer disturbances because different objects connect to it, since the free frequencies belong to everyone. To avoid these disruptions and the loss of messages, cellular operators offer dedicated frequencies that they buy at exorbitant prices, to which they add quality of service. They are therefore the ones who have control over the radio parameters, in particular over the frequency of information reading. Customers do not control PSM/eDRX on a carrier network without a commercial agreement – the problem may arise in roaming. If the connected object transmits its data every minute, instead of every ten minutes, there will be a factor of ten in terms of autonomy.
Apart from this contractual part, the advantage of cellular, in particular networks NB-IoT, is the possibility of roaming. The deployment of these NB-IoT networks is booming, operators hope to reach 20 billion objects worldwide connected to 4G/5G mobile networks by 2025.
Find more content on the subject on the site of the IoT Reflection Group.
Frédéric Launay is a lecturer at the LIAS laboratory (ENSIP Engineering School) and a teacher in the R&T department of the IUT of Poitiers. He teaches IP telephony, 4G mobile networks and 5Gthe IMS network and VoLTE.
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