Power is a problem for IoT developers – and communication links are one of the most power hungry elements of a typical system. Whilst sensors and other peripherals can be powered down for long periods of time, communications, particularly receivers, often need to be kept in listening mode for transmissions.
The current situation
Low energy systems allow batteries and hence the devices to last longer, avoiding the cost and inconvenience of replacing either the devices or their batteries. A great solution is to power the system from energy in the environment, such as solar power. As it stands now most of the existing systems are complex, hard to configure, have been designed for specific purposes and most importantly require some knowledge of electronic design experience to configure. Another important issue is the overall integrity and reliability of the designed IoT system. Using cheap and non-standard components may bring the cost down at the expense of the overall reliability.
The communications link
A significant power user in an IoT device is the communications link. Especially in mobile applications with long range requirements, high power consumption becomes one of the limiting factors. IoT systems can be organised in many different ways, two examples are given here.
In Figure 1 a separate communications link is used for each device to be controlled. The communication with the internet and the cloud are through a common central processor. Users can interact with the system by communicating directly with the cloud or through the central processor. Although this configuration is very flexible its cost is high. A more practical approach is shown in Figure 2 where the devices to be controlled are all connected to a common processor which then communicates with the internet and the cloud as required.
Several communications technologies such as 802.11x Wi-Fi, Bluetooth, ZigBee, Thread, Cellular, NFC, Low Power Radio (LPR) are currently in use by the designers, each having its own advantages and disadvantages.
Although 802.11x Wi-Fi may seem to be the natural choice for communication, it has the disadvantages that the power consumption is high, it is costly, and its operation may require the existence of a Wi-Fi router which may not be available at the place of implementation. The configuration of some of the other communication technologies such as the Bluetooth, ZigBee, and Thread are complex and their useful ranges are limited.
In addition, these devices operate in the 2.4GHz band which is prone to electromagnetic noise from mobile phones, microwaves and so on.
Low power radio
A better alternative can be lower power radio (LPR) modules, which can offer low power consumption and are affordable. Some of the most important requirements of a communications link for connecting IoT devices are: wide supply voltage, low power consumption, ultra-low standby current, long range, conformance to an international standard, which is probably one of the most desirable requirements as it proves that the device is reliable and of high standard. For safety critical applications, Category 1 (EN300220) receiving capability is needed.
Narrowband LPR receivers and transmitters can successfully operate over very long ranges. For example, the Radiometrix M48 can be used to create a point to point wireless communication link with a range of up to 3km. No electronic design knowledge is needed to set up the link: plug one end into a PC via the USB port and the other into the device or sensor using the RS232, RS485 or USB port and you are up and running.
The link is also delay free – communication is instant and very reliable which is great for clock synchronisation and also for noisy environments. Data rates are comparatively low – 4800bit/s – 19.2kbit/s is typical, but this is plenty for short bursts of sensor data.
Often LPR modules support multiple bands enabling global use, and can hop between different channels to avoid interference.
Power saving for transmitters is usually done by setting the device in standby mode and only waking it up during data transmission. Another way of extending battery life, for short links, is backing off transmission power in line with the required range.
A wide supply-voltage (3.1-9Vdc) means that the device will continue to work even from a nearly exhausted battery or a solar panel in comparatively unfavourable conditions.
Power management for receivers can be more challenging, as often they need to be kept ‘always-on’ to listen for messages.
Appropriately designed narrow-band receivers can consume less than 1mA, allowing “always-on” functionality in energy-limited solar or battery-operated equipment without excessively draining the power source and limiting operation.
LPR modules do need a gateway to connect to the internet, for example to send and receive data from a cloud.
It is also important that a secure protocol is specified and used in bare RF based communications. However, given their ease of set up, lower power consumption and long range LPR modules are certainly worth considering when designing an IoT communications link
Professor Dr Dogan Ibrahim is a senior researcher at the Near East University Faculty of Engineering Department of Computer Information Systems in Nicosia.