In the IoT world there are many different technologies of wireless communication. Some of them are WiFi, Bluetooth, Z-Wave and ZigBee. One of the newest and most interesting wireless technologies is the LPWAN or Low Power Wide Area Network. LPWAN seems to be the means that will make the Internet of Everything possible. Sensors will be easily incorporated everywhere and they will able to send their data to servers that can process them. A battery is enough to keep such sensort running for years. LPWAN devices are long range transmitters so that no intermediate devices like routers are needed. Wireless LAN, Bluetooth or LTE are devices with high power consumption compared to LPWAN devices. Therefore they are not suitable for all kind of wireless communication.
In order to achieve this goal many consortia and producers developed new bidirectional radio communication standards that are concurrent to each other now fighting for dominance in the LPWAN market. Besides SigFox, NB-Fi and NWave there is currently the LoRaWAN (Long Range Wireless Area Network) that is showing strong traction. One reason for their success is that producing its hardware is quite cheap. Another reason is that the Netherlands and South Korea have already used this technology all over their countries.
The LoRaWAN receivers are sensitive enough to receive data from a sender 10km away. They use a specific modulation called CSS (Chirp Spread Spectrum). Due to one of the LoRaWAN chip producers, Semtech, this modulation helps devices to process data waves that are weaker than the noise level. The LoRaWAN specification is not published at the time of writing this post. In Europe LoRaWAN devices work in 433 MHz and 868 MHz, in the USA in 900 MHz and 915 MHz, the data transmission rate is about 50 kbit/s.
LoRaWAN end devices only communicate with gateways. Communication between LoRaWAN devices is not specified. The LoRaWAN gateways then transfer the data to a server. LoRaWAN end devices can also receive data. For power saving reasons they look for incoming data only in specific time windows. Here we differentiate between the classes A, B and C:
- Class A: The device sends a data packet to another device and waits for a predefined amount of time and then it looks whether data is there to be downloaded.
- Class B: The gateway devices sends beacons in specific time intervals that tell end devices when they should be ready to receive data.
- Class C: These end devices are connected to permanent power supply and can receive data permanently.
All LoRaWAN devices have a 64 bit long identifier – like the MAC address of a usual network device. A 32 bit long device address is used for communication that is assigned to the device during the activation procedure while being registered to the network. During this procedure the keys for AES encryption are exchanged as well.
There are LoRa modules on breakout boards and others that look like an XBee for existing Arduino shields. The French company Semtech seems to be the only producer of the chip and all other companies use these chips in their devices. The Chinese company HopeRF provides also chips (RFM69, RFM95, RFM96, RFM 97 and RFM98) that can transmit and receive data by LoRa standard.
You can get more on LoRaWAN on the Website of LoRa-Alliance.
In the meanwhile there is already a LoRa shield for Arduino that makes it very easy to use this new technology: