LoRaWAN: from a radio link to a network

LoRaWAN (Long Range Wide Area Network) is a protocol built on top of LoRa for low-power, wide-area IoT networks. LoRa defines how the radio signal is modulated; LoRaWAN adds the network around it: gateways, a network server, device management and security. Where LoRa on its own is a point-to-point link, LoRaWAN lets thousands of devices send data to a platform through shared gateways.

Architecture

• End devices: sensors and PLCs with a LoRa radio that send small messages (uplinks) and may receive some (downlinks).
• Gateways: receive the messages from every device in range and forward them over IP (Ethernet, Wi-Fi or cellular) to the network server. They are in a star topology: devices talk to gateways, not to each other.
• Network server: removes duplicates, checks security and manages the network (for example, data rate adaptation).
• Application server: receives the decoded data of your devices and hands it to your platform (SCADA, database, dashboard) for example through MQTT or HTTP.

The network server can be a public community network such as The Things Network, a commercial operator, or your own private network (for example with the open source ChirpStack). For industrial installations, a private network is often preferred, because the data and the availability stay under your control.

Device classes

• Class A: the device opens two short receive windows only after sending. It is the lowest-power class and is supported by every device.
• Class B: adds receive windows at scheduled times, synchronised by a gateway beacon.
• Class C: the device listens almost all the time. It gets downlinks with low latency, but it needs mains power.

Security

LoRaWAN uses AES-128 encryption with two session keys: one authenticates the device against the network, and another encrypts the application data end to end, so the network operator cannot read it. A device joins the network either with OTAA (over-the-air activation, which generates new session keys at each join and is the recommended method) or with ABP (activation by personalisation, with fixed keys). Treat the device keys as credentials: do not publish them, and use a different set of keys for every device.

Limits to design around

• The maximum payload per message depends on the data rate and on the regional parameters, and can be as low as about 50 bytes at the longest range.
• Regional duty-cycle rules limit how often a device may transmit.
• LoRaWAN is not meant for real-time control: use it for monitoring and low-frequency commands.

Typical applications are smart city infrastructure, agriculture, environmental sensing, utility metering and asset tracking. See what Industrial Shields PLCs offer at www.industrialshields.com.