Selecting a radio system for the event of IoT units
Just in time for World IoT Day on April 9, 2021, ByteSnap Design, a UK-based specialist in the design and development of embedded systems, shared its findings and advice on choosing a wireless system for the development of IoT devices. World IoT Day gives us an opportunity to ponder IoT evolution, in its broader sense, is also a time to celebrate this rapidly evolving, emerging technology.
“Most IoT devices are wirelessly connected to the Internet. However, the IoT connectivity options are extensive as electronics designers are faced with a range of wireless systems, from Bluetooth Low Energy to ZigBee, ”explains Dunstan Power, Director at ByteSnap Design. “Each has its advantages and disadvantages, and we asked our experienced engineers to break down key considerations when choosing a wireless system for developing IoT devices.”
- Battery life – intermittent receivers are an option
IoT devices need to transfer data, although not always in large quantities. Long battery life is desirable for battery operated systems. The recipient of an IoT device is usually a major drain on the battery. As a result, radio systems should ideally be designed in such a way that the receiver for data transmission can be switched off and on at regular intervals.
Receiver performance issues make the use of Wi-Fi or GSM modems problematic for IoT systems that require months of operation or annual operation. Bluetooth Low Energy is one of the best standards for power consumption. Other options are the dust network and ZigBee in endpoint mode. It’s worth noting that newer Wi-Fi technologies in development have sporadic options where they will disconnect from the network and reconnect frequently.
2. Range – depending on the purpose
The range essentially depends on the connection budget of the radio. This is the combination of transmission power and reception sensitivity. Range is influenced by several factors, including the environment, and should be considered early on in a project.
LoRa is an example of an effective long-range, low-power radio solution that has broadcast hundreds of kilometers to weather balloons from the ground. The same LoRa radio on the ground can reach a few kilometers in a built environment. Within a building itself, this area drops off again. Designers should study the receiver sensitivity and transmit power, then tune the antennas to optimize for both. This will achieve the best range.
3. Size – may depend on the antenna size
Radios are small these days, with tiny chipsets, especially bluetooth chipsets. This is being driven by the development of small devices like smartwatches. In many cases, while the chips are small, the size of the antenna dwarfs the radio. A smartwatch only needs a small antenna as it usually only needs a short range to connect to the phone it is paired with. For a greater range, the device size must be increased to accommodate a larger antenna.
4. Unit cost – to adjust performance
Radio prices are falling as more are used in consumer devices. For example, Bluetooth Low Energy wireless silicon is available in bulk for little more than $ 1 per device.
The unit cost is a combination of silicon – provided the ratios are based on an IC with a built-in radio and are not discrete components. And typically, most large, low-power wireless ICs are under $ 5.
The antenna prices vary. The cheapest are PCB antennas. These are used in Bluetooth where the range is not important. While they are inexpensive, they take up space. Once a designer considers chip antennas or external antennas, the cost increases, but can be outweighed by better or repeatable performance.
5. Regulations and Compliance – at the beginning
Another important aspect at the beginning of a project is compliance. Developers need to determine in which countries the device will be sold. This affects the choice of radio, the compliance check and the resulting costs.
For the 2.4 GHz bands – like Bluetooth, ZigBee, and Wi-Fi – devices work worldwide, but these can be congested networks. It is important to check the assigned bands. There are often bands of equal value, but keep the following in mind:
- software will be different
- Circuits may need to be adjusted
- Tuning could be a problem.
Regulations don’t just affect frequency. They also affect the mark-to-space ratio of the data that can be output, so that the percentage utilization of the radio band in which a device is operated.
6th Development costs – depend on both performance and compliance requirements
An engineer designing an IoT device can choose between using a radio module or a chip-down approach. There is a trade-off between unit cost and development time. GSM modules are far from essential given the cost of certifying a radio. For Wi-Fi, modules are also generally used in devices whose volume is less than 100,000 pieces per year. In the case of radios with very low power consumption such as Bluetooth and Zigbee, the cost-benefit ratio is much less clear, as certification is easier due to the performance levels.
In addition to certification costs, the PCB and RF design around the chip also have an impact on development costs. Historically, wireless chips certainly required careful network balancing and a discrete design around the chip, which would require some effort and testing. Newer chips tend to have more of them in the device and there is less RF work to do.
7. Data rate – versus range and battery life?
The data rate requirement can vary widely – from a video application, which is typically a high data rate application, to a water meter that requires little daily data transfers, for example. The data rate can sometimes be weighed against range and battery life. It is tied to the bandwidth of the radio. The data rate is dependent on the operating band, both in terms of the applicable regulations (allocated bandwidth) and the physics of higher operating frequencies that enable a higher bandwidth.
GSM (LTE) radios and Wi-Fi are established options for high data rate IoT, while LoRa is a good option for short range, low data rate connections with low power consumption.
8. Interoperability – your own design or someone else’s profile?
If an IoT device needs to be compatible with other products, this can limit the choice of radio. The best examples of highly interoperable radios are Bluetooth and Wi-Fi. ZigBee also has many profiles that devices from different vendors can work with. By using interoperable technologies, software development costs can be saved.
9. Topology – star against network
Two classic topologies are star and network. An example of Star is the WLAN in a house, in which there is a central hub gateway to the Internet, with which several devices can establish a connection, but which must be within range of this central router.
Mesh networks transmit data in hops from device to device so that low-power radios can cover long distances. Using mesh means radios only need to transmit a short distance away, but a mesh network can become complex and therefore less consumer-friendly. “
This article was written and submitted by BySnap Design.