LoRa and LoRaWAN

What the two terms stand for, what LoRaWAN is made for and how a network is built.

Two layers

LoRa (from "Long Range") is the radio technique. It uses chirp spread spectrum modulation (CSS): every symbol is a tone that sweeps across the whole channel. This lets a receiver decode signals that lie below the noise level. The technique comes from the French company Cycleo, which Semtech acquired in 2012. Semtech still makes most LoRa radio chips today.

A LoRa packet starts with regular chirps (the preamble). In the data, each chirp starts at a different frequency: that starting point carries the information.

LoRaWAN is the network protocol on top. It defines how devices join, how messages are encrypted and counted, and how the network controls the transmission settings. The specification is open and maintained by the LoRa Alliance. Versions 1.0.x (mainly 1.0.3 and 1.0.4) and 1.1 are in use. The frequencies for each world region are set in a separate document, the "Regional Parameters".

In short: LoRa is the radio link, LoRaWAN the network.

What LoRaWAN is made for

Small amounts of data: typically 10 to 50 bytes per message.
Sending rarely: minutes to hours between two messages.
Long range: a few kilometres in a city, much more in the countryside and with line of sight.
Battery operation: devices sleep almost all the time and often run for several years.
Not suited to voice, images, real-time control or frequent replies to the device.

How a network is built

A device is not tied to a gateway: every gateway in range receives its packet. The network server removes the duplicates.

Part	Task
End device (node)	Sensor, tracker or field tester. Sends uplinks, occasionally receives downlinks.
Gateway	Receives everything it hears on 8 or more channels at once and passes it unchanged to the network server. A gateway cannot read the payload.
Network server (LNS)	Checks the messages, removes duplicates (when several gateways hear the same packet), picks the gateway for the reply and controls the data rate.
Join server	Manages the keys used when devices join.
Application server / integration	Decrypts the payload and hands it to the application by webhook, MQTT or similar.

This is why a field tester often shows several gateways for the same message.

Uplink and downlink

Uplink: device → network. The usual case.
Downlink: network → device. Only possible shortly after an uplink. While a gateway transmits, it cannot receive on any channel. Downlinks are therefore scarce.

Device classes

Class A: after every uplink two short receive windows open. Only then can the network reply.

Class	Behaviour	Typical use
A	After every uplink two short receive windows open (RX1 after 1 s, RX2 one second later; on TTN RX1 after 5 s). Otherwise the device sleeps.	Almost all sensors, field testers too
B	Additional receive windows at fixed times, synchronised by beacons from the gateways.	Rare
C	Listens almost all the time. High power consumption.	Mains-powered devices, e.g. actuators