LoRa (long-range chirps)
A long-range, low-power data system that sends rising 'chirps'. Used for sensors and for mesh text messaging.
What does it sound like?
Rising 'whoop' chirps in short bursts.
Who uses it?
Sensor networks (LoRaWAN) and mesh messaging networks such as Meshtastic.
Where and when can I hear it?
902-928 MHz in the US, 868 MHz in Europe, 433 MHz in some places.
The science
LoRa uses chirp spread spectrum: each symbol is a tone that sweeps steadily across the channel, typically 125 kHz wide in LoRaWAN networks, and the data are carried by where in its sweep each chirp starts. A setting called the spreading factor, from 7 to 12, trades speed for reach: each step up halves the sweep rate and the data rate, so the same message takes longer on air. At spreading factor 7 on a 125 kHz channel the data rate is about 5.5 kilobits per second, while at spreading factor 12 a receiver can decode signals as weak as about -137 dBm.
Why use it?
Higher spreading factors give the receiver more processing gain, so tiny battery-powered devices can reach receivers kilometers away while transmitting only briefly. Signals sent at different spreading factors on the same channel at the same time do not interfere with one another, which networks use to manage congestion. The same kind of radios power Meshtastic, an open-source project that passes text messages from device to device where there is no cellular or Wi-Fi service.
Lore
Chirps were used in sonar and radar long before LoRa, and Semtech points out that bats and dolphins use the same effect to find prey. LoRa grew from Cycleo, a company founded in France in 2010 by Nicolas Sornin, Olivier Seller and Francois Sforza to add radios to gas, water and electricity meters; Semtech bought it in May 2012, and the LoRa Alliance formed in February 2015.
Easily confused with
- Wireless meter and sensor bursts (868/915 MHz): sensor bursts don't sweep in pitch