Choosing Connectivity for an IoT Product

Start with five questions

There is no best radio, only the one that fits the product. These questions narrow it down quickly:

• Where will the device be? In a home or office with Wi-Fi, on a person near their phone, out in a field, or moving between places.
• What powers it? Mains power allows almost any radio. A small battery that must last for years rules out the power-hungry options.
• How much data, how often? A temperature reading every hour is tiny. Audio, images or frequent firmware updates are not.
• Who provides the network? The customer's Wi-Fi, the customer's phone, a mobile operator, or a network you or your customer runs.
• What does it cost per device per year? Some options add a data plan or network fee for every unit, for the life of the product.

Bluetooth Low Energy

Bluetooth Low Energy (LE) is the usual choice for wearables and personal devices that work with a phone. The Bluetooth SIG's technology overview says Bluetooth LE supports point-to-point, broadcast and mesh topologies, with data rates from 2 Mb/s down to 125 kb/s depending on the radio mode used (the slower Coded modes trade speed for range).

Range is a design choice rather than a fixed number. The SIG's range page puts the effective range "anywhere from more than a kilometer down to less than a meter", and explains that transmit power is "a design tradeoff between range and power consumption", alongside receiver sensitivity, antenna and obstacles.

The catch is that Bluetooth on its own does not reach the internet: the phone, or a hub, has to relay the data. That means a native or cross-platform app, which our guide on connecting a device to a mobile app covers in detail, including phone permissions and first-time setup.

Wi-Fi

Wi-Fi gives a device direct internet access in homes and offices without a phone in the middle, and handles larger amounts of data. It uses more power than Bluetooth LE, so it suits mains-powered or regularly charged devices. The step that most often goes wrong is setup: getting the device onto the customer's network, which is why many Wi-Fi products use Bluetooth for that step.

For low-power, longer-range use, the Wi-Fi Alliance describes Wi-Fi HaLow, introduced in 2017, which "operates in sub-1 GHz spectrum to deliver approximately 1 km range" for IoT sensors and wearables. It needs HaLow access points, so it is a choice for sites you equip, not for using a customer's existing home router.

Cellular: LTE-M and NB-IoT

Cellular IoT works anywhere the mobile network reaches, with no customer network or phone involved, which makes it the usual choice for trackers and equipment in the field. 3GPP, the body that writes mobile standards, completed NB-IoT in 2016 as part of Release 13, alongside eMTC (better known as LTE-M), as technologies operators can use for IoT. Check which of them the operators in your markets support before choosing a module.

Two costs to plan for: a SIM and data plan for every device, and the life of the network. GOV.UK says UK mobile network operators will switch off their 2G networks between 2029 and 2033 and that "All 2G-only devices need upgrading". Its connectivity timeline lists each operator's dates. A product designed today should not rely on 2G or 3G.

LoRaWAN

The LoRa Alliance describes LoRaWAN as a low-power, wide-area networking specification "designed to wirelessly connect battery operated 'things' to the internet". It "operates in unlicensed radio frequency bands", is known for long range ("up to 15 km in rural areas", by the Alliance's figure) and works through gateways that pass messages to a network server and then to your application.

LoRaWAN suits sensors that send small readings, such as meters, soil or parking sensors, over a wide area or deep indoors. It can run on a public network where one exists, or on your own gateways. It is not built for large or frequent data transfers, so features such as firmware updates need planning (the Alliance lists firmware updates over the air among its standard features).

Mesh: Thread and Zigbee

Mesh networks let devices pass messages for each other, so a building full of low-power devices can be covered through one hub or border router.

• Thread is based on the IEEE 802.15.4 radio and is an open IPv6-based protocol providing "device-to-device and device-to-cloud connections". Matter, the smart-home standard, runs over Thread and Wi-Fi, as our companion app guide explains.
• Zigbee, from the Connectivity Standards Alliance, describes its mesh as "self-organizing, self-healing" and "scalable to thousands of nodes", optimised for low power.

Both need a hub or border router to reach the internet. In homes, that is often a smart speaker or hub the customer already has; in commercial sites, it is part of the installation.

Certification and radio rules

Every radio brings paperwork, and it belongs in the plan and budget from the start.

• Legal radio rules. In the EU, the Radio Equipment Directive sets essential requirements for safety and health, electromagnetic compatibility and the efficient use of radio spectrum. In Great Britain, the Radio Equipment Regulations 2017 apply. Using a pre-certified radio module can reduce the testing, but the finished product is still yours to sign off. Our guide to radio and safety approvals covers FCC, CE and UKCA in more detail. Security rules for connected products are covered in our IoT security guide.
• Bluetooth. The Bluetooth SIG's qualification page says "All Bluetooth products must complete the Bluetooth Qualification Process on or before the date that you begin to sell or distribute the product", under your own company's membership: "Your supplier or other member companies cannot qualify your products on your behalf." A fee applies to the first product with a given design.
• Wi-Fi. Wi-Fi CERTIFIED is voluntary, but a company must be a Wi-Fi Alliance member to certify and use the logo.
• LoRaWAN. The LoRa Alliance certifies LoRaWAN end devices through authorised test labs, for interoperability with networks.
• Cellular. Ask each mobile operator you plan to use what device approval it requires before you commit to a module.

Combining two radios

Many products use two: Bluetooth for setup from the phone, then Wi-Fi or cellular for everyday data. Others add Bluetooth to a cellular tracker so an engineer can configure it on site. A second radio adds cost and testing, but it often makes setup far easier for customers. Whatever you choose, the device, the cloud platform and the app have to be designed together, and the radio decides how firmware updates reach the device.

Frequently asked questions

Which connectivity has the longest battery life?

It depends more on how often the device sends data and how much than on the radio name. Bluetooth LE, LoRaWAN, Thread and Zigbee are all designed for low power, and cellular IoT technologies such as NB-IoT and LTE-M were standardised for IoT devices. Wi-Fi generally suits devices that are mains powered or regularly charged.

Can a device use the customer's phone instead of its own internet connection?

Yes, with Bluetooth LE the phone app can relay data to the cloud. The device then only sends data while the phone is nearby with the app able to run, so it suits personal devices and wearables rather than equipment that must report around the clock.

Is 2G still safe to use for a new product in the UK?

No. GOV.UK says UK mobile network operators will switch off their 2G networks between 2029 and 2033 and that 2G-only devices need upgrading to 4G or 5G capable devices. Choose a technology with a long future in your markets.

Does a pre-certified radio module mean the product needs no certification?

No. A pre-certified module can reduce testing, but the finished product still has to meet the radio rules where it is sold, and Bluetooth products must complete the Bluetooth Qualification Process under your own company's membership.

Building a connected product? We build the firmware connectivity, the cloud backend and the mobile and web apps together, working alongside your hardware team or manufacturer. See our IoT development service and all our services, or email [email protected].