Connecting your geographically dispersed IoT devices

The requirements of a simple ambient light sensor and light switch controller are very different to our home and office dependence on a Wi-Fi-based network. Also, the essential infrastructure needed for everything from lighting to traffic management is readily available within a city, although implementation costs are still considerable. However, consider a smart agricultural IoT deployment covering many square kilometres in the countryside. Connecting IoT devices to a suitable wireless network needs a different approach than how our smartphones, laptops, and home automation systems access the internet. As we'll see in the next section, low power wide area networks (LPWANs) offer a viable solution.

LPWANs uncovered

Unlike most Wi-Fi-connected devices, an IoT device typically needs to transfer minimal amounts of data. For example, a smart city light sensor transmits an ambient light reading every 10 minutes and responds to an instruction to turn the light on or off. The amount of data involved is no more than tens of bytes. LPWAN technologies offer low data bandwidths, and most use lower radio frequencies than WANs, which, combined with their low data rates, enables them to cover much larger distances. As most IoT devices, particularly those remotely deployed, rely on battery power, the amount of energy available for wireless communication is limited. The core advantage of an LPWAN for any such IoT device is that the amount of transmitter power required is minimal.

Each type of LPWAN has slightly different characteristics. For example, most operate in the unlicensed sub-GHz ISM frequency bands (industrial, scientific, and medical), and one uses the licensed cellular infrastructure. The attribute they all share is a device's battery life is measured in years. All but Wi-SUN use a star network topology.

Choosing an LPWAN

Let's briefly review some of the most popular LPWANs available today.

Wi-Fi HaLow: Promoted by the Wi-Fi Alliance and the only LPWAN to support the TCP/IP internet protocol, Wi-Fi HaLow uses the established WPA3 security method. This LPWAN uses the sub-GHz spectrum, quotes a range of better than 1 km, and a typical data rate of 150 kbps. With its Wi-Fi IEEE 802.11 parentage, higher density modulation techniques theoretically give maximum speeds of 86.7 Mbps. In reality, this would probably be outside the needs of a typical LPWAN requirement in terms of battery life.

Wi-SUN: The only LPWAN to offer a mesh topology, where deployed IoT devices can talk to each other, Wi-SUN offers a point-to-point range of up to 4km and data rates from 50kbps up to 300kbps. Wi-SUN also uses the sub-GHz unlicensed radio spectrum. Its mesh topology Wi-SUN FAN (field area network) approach provides a self-forming and self-healing capability so that devices can always find a route to the internet network. Link latency, the time for a measure to be sent and returned, is the lowest of all LPWANs, ideal for those applications that need it.

Sigfox: An early entrant on the LPWAN scene, Sigfox offers a region dependent data rate of 100bps or 600bps and quotes an urban range of 10km and a rural range of up to 40km. With a very low duty cycle across the network, Sigfox limits the number of messages transferred to 140 up and four down per day. Data packet size is perhaps the smallest of all LPWANs at 12 bytes, and security features occur during link sessions. The Sigfox LPWAN is owned exclusively by the Sigfox company, and private service provider networks are not possible.

LoRaWAN: LoRaWAN was also one of the earliest LPWANs available. It offers a maximum data rate of 27kbps and a quoted range of up to 15km in rural locations. Data security features include 128-bit AES features. Unlike Sigfox, there are no limits on the number of messages sent per day. There are several national and global LoRaWAN service provider networks serving both public and commercial customers.

NBIoT: This is the only LPWAN provided by cellular network operators using their licensed cellular infrastructure. Data rates of up to 127kbps are possible, and quoted range is typically less than 10 km, this relating to the maximum distance from a base station tower. NBIoT benefits from the cellular industry's 3GPP security features.

An LPWAN for every application

LPWANs provide low power, long-range wireless networking capabilities for resource constrained IoT devices. The data rates available are more than adequate for sensor-based edge nodes deployed in a broad range of IoT applications. With a device's battery life measured in years, LPWANs are helping accelerate IoT deployments.