Maximising Battery Life for IoT Devices on LPWANS

Vanja Samuelsson, Founder of Qoitech


Modelling and understanding a device’s power consumption is a habitual problem for designers. A new tool could help

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IoT Connected Devices

It is generally agreed that the Internet of Things (IoT) has moved from the hype stage and is now about pragmatic adoption; a sentiment reflected by the fact that IoT has dropped from Gartner’s Hype Cycle for Emerging Technologies 2018 report, moving through its peak. It is now all about facilitating the interconnection of an estimated 30 billion to 50 billion devices by 2020.

There are several obvious technological barriers that continue to limit progress and two of the most significant are power consumption and (wireless) communications. The challenge is that not all wireless technologies available today are able to meet all of the IoT’s requirements, especially in terms of coverage and battery life. Low Power Wide Area Networks (LPWANs) have been called the backbone of the IoT, but they come in many shapes and sizes with differing trade-offs, making the life of an IoT device designer even more complex.

Evolution of LPWAN

LPWAN is a term for wireless wide area network technologies intended to connect low-power devices over long ranges. It is not a single technology, but a group of various low-power, wide area network technologies that take many shapes and forms. LPWANs can use licensed or unlicensed frequencies and include proprietary or open standard options. Created for machine-to-machine (M2M) and IoT networks, most were conceived to operate at a lower cost with greater power efficiency than traditional mobile networks. They are also able to support a greater number of connected devices over a larger area.

LPWAN roll out is a constantly changing situation, with both network standards and network deployments, licensed and unlicensed, still evolving. It is also a buyer’s market; there are several propositions ready that will enable organisations to leverage IoT and gain a competitive advantage.

An example of LPWAN evolution is the recent announcement from Leti, the research institute of CEA Tech. The field trials of its new LPWAN technology, LPWA-CB ­–­ that uses a waveform tailored for IoT applications ­– showed significant performance gains in coverage, data-rate flexibility and power consumption compared to leading technologies.

Leti’s approach is based on what it calls Turbo-FSK; a flexible approach to the physical layer. It also relies on channel bonding, which is the ability to aggregate non-contiguous communication channels to increase coverage and data rates. The field trials seem to confirm the benefits of Leti’s LPWAN approach in comparison to LoRa and NB-IoT, two leading technologies that enable wide-area communications at low cost and long battery life.

The challenge of power consumption

Many IoT devices are ‘deploy and forget’, meaning they need to run for extended periods on small batteries at low voltage levels and current consumption. To meet these requirements the LPWAN trade-off is between data rate, power consumption, and range. To achieve low power consumption you must compromise with lower data rate. But to really determine if you can achieve a long battery life, manufacturers need to characterise the current consumption of the device under active, idle, standby, and sleep modes. Device vendors also need to recreate typical operating conditions such as a remote software update, transmission repetition and the case where the device is unable to connect to the server, in order to really understand how much current is drawn in each scenario. That modelling and understanding of a device’s power consumption is a habitual problem for designers.

The expected battery life of IoT products depends on battery capacity and hardware setup, but also to a large extent on system behaviour. In order to verify expected battery life, testing must be carried out on a live system. Testing should be minimally invasive, and correctly capture and present how the system behaves during a representative time period.

The software solution

The solution is available for any developer, anywhere in the stack. Energy optimisation can now be applied at any point by hardware, firmware or app developers, using Otii. This is an energy consumption analysis tool for optimising devices under all conditions. It enables users to quickly understand the energy consumption of the products that they are working on, with the goal of making more sustainable and more energy efficient devices. The tool is easy to use, requires minimal setup, and lets developers measure and analyse energy usage at any stage of development.

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Figure 1: Qoitech Software Testing

It comprises a compact and portable source measurement unit, Otii Arc, and an easy to use, yet comprehensive desktop environment that can run on Ubuntu, Windows and macOS. The ability of the software to run on multiple platforms is a big advantage, it is also quick to install and provides a means for continuous measurement during the development process. The user interface allows for real time analysis; scroll, zoom and select parts of the current consumption while measuring. New recordings are easily added on top of the previous ones which makes it easy to track changes in the power consumption throughout development. For iterative tasks, automated testing can be performed by built-in scripting features. The Otii Arc itself acts as both the power supply to the IoT device and as a current and voltage measurement unit.

When considering the multiple communication networks that are on offer it is important to always keep well-informed of the relative power requirements as not all networks operate at the same low power levels; some are higher than others.