Wireless connectivity is becoming more prevalent in our lives. As Wi-Fi continues to evolve, it is now commonplace to wirelessly stream megabytes of data over a WAN (wide area network) at home or at work. So what about streetlights as part of a smart city? The ambient light sensors and light switch controllers on streetlights have different needs than those of Wi-Fi-based networks at home or in the office. Critical infrastructure such as streetlights and traffic control systems must be available all the time in a city and are expensive to implement. What about smart agricultural IoTs that span square kilometers in rural areas? Connecting these IoT devices to a suitable wireless network requires a different approach than connecting smartphones, laptops, and home automation systems to the Internet. A useful solution in these cases is a low-power wide area network (LPWAN).


■ LPWAN (Low Power Wide Area Network)

Unlike most Wi-Fi connected devices, IoT devices typically transmit only a small amount of data. For example, a smart city streetlight sensor transmits a light reading every 10 minutes and then executes a command to turn the streetlight on or off. The amount of data transmitted is no more than a few tens of bytes. LPWAN technologies have lower data bandwidths and most use lower radio frequencies than WANs. Therefore, they can cover much longer distances at lower data rates. In addition, most IoT devices are battery-powered, which limits the amount of energy available for wireless communication. This is especially true for IoT devices deployed in remote locations. The biggest advantage of LPWANs for such IoT devices is the extremely low transmitter power required.

Each LPWAN technology is slightly different. Most LPWAN technologies operate in unlicensed sub-GHz ISM (industrial, scientific, and medical) frequency bands, while some use licensed cellular infrastructure. What all technologies have in common is that they extend the battery life of devices to several years. Additionally, except for Wi-SUN, all of them use a star network topology.

■ Which LPWAN technology to choose?

Now, let’s take a look at some of the representative LPWAN technologies used today.

Wi-Fi HaLow: A technology promoted by the Wi-Fi Alliance and the only LPWAN that supports the TCP/IP Internet protocol, it uses the existing established WPA3 security technique. It uses sub-GHz bands, has a possible range of more than 1 kilometer, and has a data rate of 150 kbps. It is based on Wi-Fi IEEE 802.11 and uses high-density modulation techniques, theoretically enabling a maximum speed of 86.7 Mbps. However, this is far beyond the needs of typical LPWANs when considering battery life.

Wi-SUN: The only LPWAN that supports mesh topology (so IoT devices can talk to each other), with a point-to-point range of up to 4 kilometers and data rates of 50kbps to 300kbps. Wi-SUN also uses the sub-GHz unlicensed radio spectrum. The Wi-SUN FAN (field area network) mesh topology provides self-forming and self-healing capabilities, so devices can always find a path to the Internet network. It has the lowest link latency of all LPWAN technologies, making it suitable for latency-critical applications.

Sigfox: An early LPWAN technology, it offers data rates of 100bps or 600bps depending on the area, and ranges from 10km in urban areas to 40km in rural areas. Sigfox has an extremely low duty cycle throughout the network, limiting the number of messages per day to 140 upstream and 4 downstream. The data packet size is 12 bytes, the smallest of all LPWANs, and uses security features during link sessions. Sigfox LPWAN is a proprietary technology owned by a company called Sigfox, and private service provider networks cannot use it.

LoRaWAN: LoRaWAN is also one of the early LPWAN technologies. The data rate is up to 27kbps, and the distance can be up to 15km in rural areas. It includes 128-bit AES as a data security feature. Unlike Sigfox, there is no limit to the number of messages that can be transmitted per day. There are multiple LoRaWAN service provider networks operating worldwide for public and commercial use.

NBIoT: The only LPWAN technology that cellular network operators offer using their own cellular infrastructure. Data rates up to 127kbps are possible, and the possible range is less than 10km. This range is based on the maximum distance from the base station tower. NBIoT uses the cellular industry's 3GPP security features.

■ Utilizing LPWAN in various applications

LPWANs enable low-power wireless networking over long distances for resource-constrained IoT devices. They provide data rates that are more than sufficient for sensor-based edge nodes in a variety of IoT applications. LPWANs are accelerating IoT deployments in a variety of areas by enabling battery life of devices for several years.